WORLD FORUM ON SMART MATERIALS AND SMART STRUCTURES TECHNOLOGY
BALKEMA – Proceedings and Monographs in Engineering, Water and Earth Sciences
PROCEEDINGS OF THE WORLD FORUM ON SMART MATERIALS AND SMART STRUCTURES TECHNOLOGY (SMSST’07), CHONGQING & NANJING, CHINA, 22–27 MAY, 2007
World Forum on Smart Materials and Smart Structures Technology Edited by B.F. Spencer, Jr. University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
M. Tomizuka University of California, Berkeley, California, USA
C.B. Yun Korea Advanced Institute of Science and Technology, Daejeon, Korea
W.M. Chen Chongqing University, Chongqing, China
R.W. Chen Nanjing University of Aeronautics and Astronautics, Nanjing, China
LONDON / LEIDEN / NEW YORK / PHILADELPHIA / SINGAPORE
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Table of Contents
Preface
XXV
Keynote Lectures Intelligent structures and systems: Dream, reality, and future S.L. Huang
3
Structural health monitoring with smart NDE technology S.S. Lee, I.B. Kwon & D.J. Yoon
17
Fiber optic nerve systems for materials and structures that can feel pain K. Hotate
21
Ionic polymer-metal composite: an emerging smart material K.J. Kim, R. Tiwari, I.-S. Park, D. Kim, D. Pugal, S.J. Kim, K. Jung, S.-M. Kim, W. Yim & J. Lee
31
Long-term health monitoring of post-tensioning box girder bridges M. Wang
41
Smart structures technology in education Y. Zhang
49
Bilateral teleoperation in physical support for human K. Ohnishi
55
Research of smart materials and structures at NUAA J.H. Qiu
63
Localization of damage in structural systems: Algorithms and issues A new theorem on damage localization and its implementation D. Bernal
75
Damage detection and localization using time domain residuals C.-P Fritzen, P. Kraemer & K.J. Xing
76
Wave propagation-based damage detection and localization S. Hurlebaus
77
Damage localization with modeling errors and uncertainties J.Y. Ching & Y.-C. Chen
78
Issues in Kalman filter-based damage evaluation without excitation information A. Haldar, R. Martinez-Flores & H. Katkhuda
79
Application-driven infrastructure monitoring in Japan A new research project on development of a practical monitoring system of urban infrastructure toward mitigation of disaster and accidents Y. Fujino & Y. Mizuno
V
83
Synchronized sensing for structural health monitoring using smart sensors T. Nagayama, B.F. Spencer, Jr. & Y. Fujino
84
Distributed inversion algorithm for sensor networks M. Abe & Y. Fujino
85
Long-term remote monitoring of a cable stayed bridge and seasonal fluctuation of modal parameters Y. Miyamori, H. Kimura, T. Oshima & T. Ayame
86
Localization and time synchronization of sensor network for infrastructure monitoring K. Oguni
88
Quick earthquake damage detection method for bridge structures J. Sakai, H. Kobayashi & S. Unjoh
89
Smart structural systems technologies Project COVICOCEPAD under smart structural systems technologies of program Eurocores R.C. Barros
93
The SMorph (Smart Aircraft Morphing Technologies) collaborative research project J.E. Cooper, A. Suleman & S. Ricci
94
SCMeRe – shape control of membrane reflectors G. Rodrigues, A. Preumont, R. Bouzidi, S. Pellegrino & Y. Stockman
95
Micro-measurement and monitoring system for aging underground infrastructure (Underground M3) K. Soga & P.J. Bennett
96
ESF S3T Eurocores project MAFESMA: Tools for modeling, design and control of smart structural systems based on shape memory alloys P. Sittner & J. VanHumbeeck
97
Civil infrastructure monitoring and assessment (1) Real-time monitoring system and stiffness identification of a long-span cable-stayed bridge with neural networks G. Chen & W. Wang
101
Validation of a wireless traffic vibration monitoring system for the Voigt Bridge K.J. Loh, J.P. Lynch, Y. Wang, K.H. Law, M. Fraser & A. Elgamal
102
Application of chaos theory analysis to smart structure techniques for highway infrastructure S. Jin & R.A. Livingston
104
Monitoring the jacket platform structures in China Bohai Sea Z. Duan, J.P. Ou, Z. Zhou, H. Li, X. Zhao & D. Zhou
106
Smart control systems-based on MR fluids (1) Autonomous-decentralized semiactive control scheme for buildings utilizing MR damper-based variable slip-force level damper Y. Nitta & A. Nishitani Semi-active base isolation system for buildings using MR dampers S.F. Ali, A. Ramaswamy & A.K. Agarwal Design and application of MR damper-based control system with electromagnetic induction part for structural control S.J. Moon, Y.C. Huh, H.J. Jung, K.M. Choi & H.J. Lee
VI
109 110
111
Feasibility of smart passive system-based on MR dampers for civil engineering applications H.J. Jung, K.M. Choi, H.J. Lee & S.W. Cho
112
Intelligent control system for automotive suspension-based on Magneto-rheological technology W.M. Chen, X.M. Dong, M. Yu, C.R. Liao, H.H. Zhang & S.L. Huang
113
Localization of damage in structural systems: Algorithms Modal strain energy index for damage detection of a three-dimensional frame structure S.Q. Wang, X.X. Bao & H.J. Li
117
A combined damage detection method-based on modal strain energy and frequencies H. Guo & Z. Li
119
The study on damage state simulation for validating damage identification and safety evaluation algorithms Y.C. Yang, F.Y. Yang, Y.G. Wang & M. Zhang
120
Statistical damage detection-based on strain mode shapes L. Gongbiao
121
Element level structural damage detection with unknown excitation Y. Lei, J.Y. Lei & Y. Song
122
Multi-scale sensing for structural health monitoring S.H. Sim & B.F. Spencer, Jr.
123
Electroactive sensors and actuators (1) On the dynamic behavior of piezoelectric sensors bonded to elastic media G.L. Huang & X.D. Wang
127
Strain in concrete columns of different strengths, monitored by cement-based strain sensor H. Xiao, L. Hui & O. Jin-ping
128
Vibration reduction of HDD disk-spindle system using piezoelectric shunt damping S.C. Lim, Y.M. Han & S.B. Choi
130
Shear excitation in piezoelectric ultrasonic motors M. Schönecker
131
Smart structural systems and materials Dynamic analysis of a biology-inspired miniature directional microphone Z. Chen, A. Lacher & M. Yu
135
Magneto-mechanical coupling of smart composites with chain-structured magnetostrictive particles H.M. Yin & L.Z. Sun
136
Natural frequency of beams with embedded piezoelectric sensors and actuators C.N. Della & D. Shu
137
Effects of polarization orientation on the effective electromechanical properties of 1–3 piezoelectric composites C.N. Della & D. Shu Hybrid damage monitoring in PSC girder bridges using acceleration-impedance signatures J.T. Kim, W.B. Na, J.H. Park, D.S. Hong & H.S. Do Probabilistic distribution of displacement response of frictionally, damped structures under earthquake loads S.-H. Lee, K.-J. Youn, K.-W. Min & J.-H. Park
VII
139 140
141
Civil infrastructure monitoring and assessment (2) Long-term structural health monitoring of the 2006 Torino’s Olympic pedestrian cabled-stayed bridge L.M. Giacosa, A. De Stefano, P. Civera & F. Ansari
145
New methods for structural condition assessment of highway and airports L.M. Sun
146
Qinghai-Tibet railway subgrade temperature monitoring system-based on FBG sensors B. Sun, J. Dai & W. Zhang
147
On structural safety assessment of bridges by EWMA control chart and reliability analysis A.Z. Liang, W.M. Chen, Y. Zhu, Y. Fu & B.J. Cao
148
Application of wireless monitoring system for the ambient vibration study of the Wuyuan steel arch bridge Y. Lei, W.A. Shen, Y. Song & J.P. Lynch
149
Magnetorheological fluids and dampers (1) Analytical study on MR fluid shock absorber with annular channel employing biviscous constitutive relationship C.R. Liao, H.H. Zhang, M. Yu, W.M. Chen & S.L. Huang
153
Geometric design of a circular plate MR clutch J.M. He, J. Huang & L.J. Fu
154
Research on cylindrical Magnetorheological fluids clutch Y. Yang, H. Li, J. Huang & B.-S. Kang
155
Smart sensing for structural health monitoring (S3HM) A. Deraemaeker, G. De Roeck, E. Reynders, K. Worden, G. Manson, J. Kullaa, V. Lämsä & W. Ostachowicz
156
Structural health monitoring Damage monitoring and life predication from nondestructive evaluation to structural health monitoring G.Y. Tian, J. Wilson, B. Zhang & H. Wang Structural health monitoring of aircraft components with the impedance method K.J. Xing & C.-P. Fritzen
159 160
Structural health monitoring on damage evolution of 6 story reinforced building through shaking table test K. Morita & T. Matsumori
161
Study on measuring error caused by movement of benchmark for auto total station in health monitoring X.-H. Lei, W.M Chen, P. Zhang, R.-B. Yue & X.-C. Xiong
162
Ultra-wideband communication for wireless sensor networks in structural health monitoring Y. Li, Z. Tian & J. Tan
163
Piezoelectric composite sensors (1) Study on abrasion resistance, chloride permeability and microstructure of concrete containing nanoparticles C. Lan, R. Wang, J. Yuan, H. Xiao & H. Li
VIII
167
A study on self-sensing properties of carbon fibre sheet as structural materials in civil engineering W. Zhou, H. Li & J.P. Ou
168
Effects of cure temperature on magnetostrictive properties of polymer-bonded Terfenol-D composite X.C. Guan, X.F. Dong & J.P. Ou
169
Numerical analysis on the cymbal and half cymbal membranes for piezoelectric synthetic jet actuator H.S. Qian, B.F. Wang, Y. Zhou & L. Xun
171
Innovative sensing systems: Fiber sensors (1) Fiber optic sensors application on the SHM of a pedestrian cable-stayed bridge in Italy L.M. Giacosa, A. De Stefano & F. Ansari
175
Analysis on a novel reflective intensity modulated fiber optic temperature sensor J. Dai, W. Zhang, B. Sun & Y. Du
176
A novel all-fiber surface roughness sensor-based on laser scattering H. Huang, U.S. Tata & A. Majumdar
178
Optimized design of configuration parameter for a novel Fiber Ring Laser Gyroscope M. Zhang, S. Chen & L. Fu
179
SHM of civil structures Recent progress of bridge structural health monitoring research in Chongqing University Y. Zhu, W.M. Chen, Y. Fu & S.L. Huang
183
A study on structural health monitoring scheme of cables and ties of Cai-yuanba Bridge Z. Huang, P. Yang & G. Liu
184
Multisensor and automated measurement of bridge deck condition D. Huston, J. Cui, D. Burns, N. Gucunski, A. Maher & F. Jalinoos
185
A study on joint of steel and concrete box girder of Shi-banpo Bridge in Chongqing P. Yang, Z.Y. Xie & G. Liu
186
Appropriateness of shear-building models for ASCE SHM benchmark structure M. Zhang, H.J. Li & S.-L.J. Hu
187
Innovative sensing systems (1) Design of MOEMS gyroscope Y. Zhao & S. Chen
191
Optimum strain gauges distribution for loading identification following fuzzy pattern recognition and hybrid genetic algorithm G. Li & W.L. Qu
192
Quantification of orthotropic characteristic of OPCM sensor Y. Luo, Z. Li, H. Liu & J. Liang
193
Wireless fiber optic acoustic sensors for crack monitoring I.B. Kwon, C.-Y. Kim, S. Ung, D.-C. Seo, D.-J. Yoon & S.S. Lee
195
Recent advances in structural damage and fault detection in the US Structural damage detection using eigenstructure assignment method and LMIs technique B. Chen & S. Nagarajaiah
IX
199
Structural health monitoring of a reinforced concrete frame using piezoceramic-based smart aggregates G. Song, H. Gu, C. Olmi, A. Laskar & Y.-L. Mo
200
Experience in introducing smart structures technology into civil engineering curriculum Y. Zhang
202
Structural health monitoring with higher harmonics S. Hurlebaus
203
Trust-region optimization-based model updating with subset selection and damage functions for SHM W. Song, S.J. Dyke, G. Yun & T. Harmon Adaptive damage tracking of structure with unknown excitations: Experimental verification H. Huang, J.N. Yang & L. Zhou
204 206
Model updating for civil applications On the computation of zeros in systems identified from output signals D. Bernal & O.F. Tigli
209
Model updating and damage detection of damped systems using incomplete complex modes S.-L.J. Hu, F.S. Liu & H.J. Li
210
Non-linear identification of MDOF systems with hysteresis from seismic response data R. Ceravolo, G.V. Demarie & S. Erlicher
211
Identification of crack locations and extents by Bayesian model class selection H.F. Lam, C.T. Ng & L.S. Katafygiotis
213
Probabilistic condition monitoring of smart structural elements D. Zonta & M. Pozzi
215
Finite element model updating of a truss model using incomplete modal data Y.X. Zhang, S.H. Sim & B.F. Spencer, Jr
216
Life-cycle performance assessment-based on structural health monitoring State identification by soft computing techniques during service conditions S. Arangio, F. Bontempi, F. Giuliano & G. Pieri
219
Insurance derivatives for buildings to reduce the damage due to large earthquakes A. Mita & H. Tamura
220
Condition assessment of buildings using acceleration data for life cycle predictions Y. Qian & A. Mita
221
Safety evaluation of infrastructures-based on long-term measured data of structural health monitoring systems H. Li & J.P. Ou
222
Novel technologies and methods of SHM for decision making Improvement of health monitoring system for environment with noise H. Furuta & H. Hattori
X
227
Estimation of probability density function of long-term strain measurement for reliability assessment Y.Q. Ni, X.G. Hua, K.W. Chen & J.M. Ko
228
Issues in using video images for structural health monitoring R. Zaurin & F.N. Catbas
229
FBG-based distributed sensing system for bridge health monitoring R.J. Sun, Z. Sun & L.M. Sun
230
Smart materials and intelligent systems Bio-inspired structural monitoring system architecture R.A. Shoureshi & L. Faravelli
233
Processing of fiber optic dynamic strain records for structural monitoring A. Del Grosso, F. Lanata, A. Torre & L. Denegri
234
Experimental applications of a case-based reasoning method for structural damage assessment L.E. Mujica, J. Rodellar & J. Vehí
235
Fiber optic sensing technologies for smart materials and structures D. Inaudi & A. Del Grosso
236
Seismic analysis of retrofitted historical masonries using passive control systems C.A. Syrmakezis
237
Optimal experimental design for structural health monitoring applications H.F. Lam, C. Papadimitriou & E. Ntotsios
238
Data-driven approaches and structural informatics for next generation smart structures (1) Image-based spatial-temporal information retrieval for vibration measurement Y.F. Ji & C.C. Chang
241
A data processing and analysis system for the instrumented suspension Jiangyin Bridge H.F. Zhou, Y.Q. Ni & J.M. Ko
242
Adaptive quadratic sum squares error with unknown inputs for damage identification of structures J.N. Yang & H. Huang
243
Initialization of multilayer feedforward neural networks to approximate nonlinear functions in engineering mechanics applications J.-S. Pei & E.C. Mai
244
Structural damage and fault detection (1) Flexibility-based local damage detection algorithm for structural joints and its decentralized implementation with wireless sensor units A. Masuda, S. Kobashi & F.-G. Yuan Identification of damages in the vertical links of a CFST arch bridge model S.J. Wang, H.C. Xie, Z.Q. Gong, B.F. Spencer, Jr. & R.K. Giles
247 248
Smart control systems-based on MR fluids (2) Research on running attitude control of full vehicle with Magnetorheological suspensions and road test R. Li, W.M. Chen, M. Yu, X.M. Dong, C.R. Liao & H.H. Zhang
XI
251
Design approaches of mitigating cable vibration using MR dampers on the cable-stayed bridges X.Y. Wang, Z.Q. Chen, Y.Q. Ni & J.M. Ko Modeling of passive magnetorheological fluid dampers coupled with stay cables in cable-stayed bridges M. Liu, H. Li & J.P. Ou
252
253
System identification Experimental study of tuned mass damper in reducing floor vertical vibration due to machinery M.L. Chang, C.C. Lin, J.M. Ueng & K.H. Hsieh A new method to detect natural frequency of bridge-based on connected pipes system W.M. Chen, X.-H. Lei, G.-P, Liu & P. Zhang
257
258
Cable force identification by global optimization using coupled local minimizers W.Y. Liao, Y.Q. Ni & J.M. Ko
259
Inverse analysis for identification of a truss structure with incomplete vibration strain B. Xu
260
Identification of the inter-story stiffness of shear type structures using the extended Kalman filer H. Liu, M. Wang, Y. Zheng & X. Zhou
261
Analysis and assessment of structural systems Wind pressure distribution rules for complicated roof structures with holed surface J. Teng, M.Y. Qin, Y.H. Zhu & W. Lu
265
Serviceability conditions in the design of suspension bridges F. Bontempi & F. Giuliano
266
A web-based assessment system of slope stability Q. Zhou, H. Yuan & Y. Tao
267
Study on measurement system of tilting train-based on math platform X.M. Wang, W.B. Ni, F. Li & J.H. Lin
268
Real-time substructure testing with equivalent force control method and its application to smart damping G. Xu & B. Wu
269
Motion and vibration control structures (1) Designing the tuned mass dampers for towers of suspension bridges F. Casciati & F. Giuliano
273
Semi-active vibration isolation system with stiffness on-off control Y. Liu, H. Matsuhisa & H. Utsuno
274
Data-driven approaches and structural informatics for next generation smart structures (2) Information-driven wireless sensing and control for civil structures Y. Wang, J.P. Lynch & K.H. Law
277
Structural health monitoring using smart sensors T. Nagayama, B.F. Spencer, Jr. & J.A. Rice
278
XII
Interactive sensor data retrieval and management method for integrated structural health monitoring system J. Li & Y. Zhang An intelligent framework for knowledge discovery from a large amount of data in SHM N. Yabuki Parallel data processing architectures for identification of structural modal properties using dense wireless sensor networks A.T. Zimmerman, R.A. Swartz, D.A. Saftner, J.P. Lynch, M. Shiraishi & M. Setareh
279 280
281
Structural damage and fault detection (2) Damage detection for crane girder subjected to moving load K.J. Shin, C.W. Jung, H.W. Seo & W.J. Kim
285
Structural damage detection using static strain data S.A. Jang, S.-H. Sim & B.F. Spencer, Jr.
286
Predicting of damages in concrete structure using PZT and motor oscillator I.-S. Kim, D.-E. Lee, H. Kim, D. Kim & W. Kim
287
Damage detection in offshore jacket structures using incomplete modal data J. Wang, H. Li & S.-L.J. Hu
288
Magnetorheological fluids and dampers (2) Investigation of attitude harmony control of full car for Magnetorheological semi-active suspension X.M. Dong, M. Yu, Z. Li, C. Liao, W.M. Chen, H. Zhang & S.L. Huang
291
Design analysis of a Magnetorheological damper J. Huang, L.Q. Liao & C.H. Lin
292
Analysis of effect of different connecting ways upon the dynamic response time of MR damper X. Huang, M. Yu, L. Mao, C. Liao & W.M. Chen
293
Design and characterization on inner bypass Magneto-rheological damper with magnetic bias H. Zhang, C. Liao, W.M. Chen & M. Yu
294
System identification and damage detection Structure damage detection method-based on modal strain energy F.Y. Yang, Y.C. Yang & M. Zhang
299
Information acquisition method-based on space similarity structure J. Teng, W. Lu, H.J. Liu & Y.H. Zhu
300
Finite element modal updating of Shibanpo Bridge using experiment test results G. Liu, P. Yang & Z. Huang
301
Evaluation of the concrete strength using IE and SASW methods D.S. Kim, S.W. Jin & E.S. Bang
302
Comparison of modal identification of output-only systems with simultaneous and non simultaneous monitoring T. Kuroiwa & H. Iemura Experimental and theoretical identification of an Italian pedestrian cable-stayed bridge L.M. Giacosa, L. Gioanola, A. De Stefano & P. Civera
XIII
303 304
Innovative actuators Research on the structures and geometric parameters of synthetic jet actuator Y. Zhou, B.F. Wang, L. Zhang, H.S. Qian & X. Wang Research on the variable voltage variable frequency inverter-based on DSP for piezoelectric micro-jet actuator L. Xun, B.F. Wang & H.S. Qian Performance characteristics of a piezoelectric-driven dispenser for semiconductor package Q.H. Nguyen, B.Y. Yun & S.B. Choi
307
308 309
Motion and vibration control structures (2) A design of automatic controller for seismic protection system of towers T. Rengaraja & P. Devadas Manoharan
313
Vibration control of pipe line applying SMA energy absorb support Y. Du & H. Li
314
Enhancing the performance capabilities of seismically isolated buildings using multi-stage friction pendulum sliding bearings T.A. Morgan & S.A. Mahin Active optimal control of SSI system-based on the finite element model of SSI system F.X. Wang & J.P. Ou Hybrid vibration suppression of multiple vibration modes of flexible structures using piezoelectric elements and analog circuit K. Yamada, H. Matsuhisa & H. Utsuno
315 316
317
Innovative sensing systems (2) Sensor-integrated biofeedback smart system for measuring human biological expressions Y. Lin & H. Cai
321
Study on Spectrometer induced periodic fluctuant error in EFPI strain sensing system X. Gan, Y. Zhu, H. Mei, P. Zhang & W.M. Chen
322
Effect of photochemical oxidization on stability and SO2 sensing performance of porous silicon X.-M. Li, X. Xiang & L.-C. Wang
323
Analysis and design of SMA damper Y. Yang, H. Li, J. Huang & B.-S. Kang
324
Wireless thermometer-based on quartz tuning fork resonators J. Xu, B.You, J. Cui & X. Li
326
Transformative application of smart sensor technology in health monitoring Non-contact ultrasonic rail flaw detection S. Coccia, I. Bartoli, P. Rizzo, F. Lanza di Scalea, M. Fateh & T.-L. Yang
329
Recent developments in theoretical and experimental investigations with ultrasonic sensors T. Kundu, S. Banerjee, S. Das & C.M. Dao
330
Effects of environmental temperature fluctuations on vibration properties of concrete bridge structures M.P. Singh & H. Nandan
331
XIV
Structural damage identification using curvature flexibilities M.P. Singh & S. Bisht
332
Innovative sensors and actuators A dynamic strain measurement system using fiber grating sensors and its application in structural health monitoring C.S. Shin, B.L. Chen & C.C. Chiang
335
Distributed optical fiber sensors for deflection measurement of structure C.Y. Wang, H.L. Wang & M.H. Chen
336
Piezoelectric type real-time scouring monitoring sensor at the foundation of bridge pier C.Y. Wang, M.H. Chen, H.L. Wang & W.K. Fan
337
Tunable vibration absorber incorporating piezoelectric-magnetostrictive sensoriactuator S.W. Or, C.Y. Lo, H.L.W. Chan & P.K. Choy
338
A tailor-made MR damper for bridge cable vibration control: Experiment and modeling Z.H. Chen, Y.Q. Ni, S.W. Or & K.H. Lam
340
Nano-scale materials for civil infrastructures Multifunctionality and smart structures-based on cement filled with nano-materials H. Li, H. Xiao, M. Zhang, B. Han & J.P. Ou
343
Carbon nanotube film sensor S. Nagarajaiah, Z. Li, P. Dharap & E.V. Barrera
345
Nanostructured cement-based materials D.D.L. Chung & S. Wen
346
In-situ materials monitoring Rebar corrosion monitoring using novel embedded filament mini-sensors A. Holst, K. Hariri, H. Budelmann & S. Bruder
349
Using tip-based fiber optic pH probes for the early detection of degradation in civil infrastructure N. Puran, G. Khalil & M. Ghandehari
350
Moisture sensing in porous media S. Zheng, P. Spellane, A. Sidelev & M. Ghandehari
352
A model-free method for structural damage identification-based on dynamic strain sensing of distributed fiber optic sensors Z. Wu & S. Li
353
Educating next-generation engineers on smart structures technology Student society for research on intelligent structural systems at SNU J.K. Kim
357
Hysteresis-based structural damage detection using multi-resolution sensor data Y. Zhang, J. Li & Y. Chae
358
Impact of mechatronics and smart structures on engineering education V. Giurgiutiu & L. Yu
359
Connected control method experiment as an international benchmark in smart structures education R.E. Christenson, L.E. Loebach, T. Watanabe & K. Seto
360
XV
Teleoperation and teleparticipation of instructional shake tables using the NEES cyberinfrastructure S.J. Dyke, Z. Jiang, R.E. Christenson, X. Gao & S. Courter
361
Course material development for a graduate course on structural health monitoring H. Huang
362
Signal processing for SHM Bridge scour surveillance using guide electromagnetic wave technology X.B. Yu & X. Yu
365
Research of deteriorated data restoring in nonlinear system S. Hu, W.M. Chen, Y. Fu & Z. Liang
366
Development of a signal processing tool to remove vehicle induced vibration signals from recorded seismic data for the vibration-based SHM M. Wang, Y. Zheng & H. Liu
367
Smart materials and structural systems Multi-scale modeling for electro-mechanical coupling of ferroelectrics Y. He, J. Fan, Z. Xu & Y. Wang
371
Smart ties for the retrofit of arches and vaults M. Dolce & D. Cardone
372
Seismic performance of cellular-solid shear walls L. Chen & P. Tsopelas
373
Assessment of adhesive bond strength in laminated safety glass S. Huo & H. Reis
374
Smart structural systems Development of fragility relationships for smart structures E. Taylor, W. Barnawi & S.J. Dyke
377
Self-centering building system composed of rocking structural members T. Azuhata, T. Ishihara & M. Midorikawa
378
Development of the smart maintenance and management system for the soil slope structures S.R. Lee & Y.K. Kim
379
Experimental investigation on hysteretic characteristics of a transmission tower with friction-type reinforcing members J.-H. Park, B.-W. Moon, S.-K. Lee & K.-W. Min
380
Motion and vibration control (1) Active vibration control using hybrid mount featured by electromagnetic actuator and piezostack actuator V.Q. Nguyen, Y.S. Paeng, J.Y. Yook, Y.M. Han, S.B. Choi & S.J. Moon
385
Control performance evaluation of ER suspension system under road test K.G. Sung, Y.M. Han, J.W. Sohn, S.B. Choi, Y.S. Lee & M.S. Han
386
Experimental study on semiactive modal neuro-control scheme H.J. Lee, K.M. Choi, I.W. Lee & S.J. Lee
388
The application of nonlinear energy sinks controller in a full car semi-active suspension system with MR dampers L. Zheng, Y.N. Li, A. Baz & A. Elsabbagh
XVI
390
A new arching PZT actuator and its application in vibration control of smart structures W. Wang & Z. Yang
391
Research of process controls parameter optimal selection-based on improved genetic algorithm G.F. Yan, X.H. Huang & F. Tan
392
Bio-inspired structures and materials (1) Flapping performance of a flapper actuated by the compressed LIPCA Q.V. Nguyen, H.C. Park & N.S. Goo
395
Dry adhesive structures designed to reduce the effective stiffness Y.-S. Cho, D.-H. Jung, H. Han, J.-H. Kim, W.-D. Kim & H.O. Kang
396
Damage detection and control of structures The acousto-ultrasonic approach: Several industry applications H. Reis & A. Vary
401
A magnetostrictive sensor for structural health monitoring in a non-ferromagnetic plate Y. Yang, L. Zhou & F.-G. Yuan
402
Vibration and aeroelastic control of composite structures using PZT actuators M. Kameyama & H. Fukunaga
403
Structural health monitoring for composite airframe of next generation space vehicles J.-B. Ihn & J. Huang
404
New sensor technology for civil engineering structures (1) Magnetic-field-driven micromachine applying multi-functional Fe-Pd ribbon T. Okazaki & Y. Furuya Hydrothermal synthesis of Kx Na1 –xNbO3 powders for fabrication of lead-free piezoelectric ceramics K.J. Zhu, J.H. Qiu, Z.L. Meng, K. Kajiyoshi, K. Yanagisawa & N. Li
407
408
External force and displacement estimation for self-sensing control of a piezoelectric actuator A. Badel, J.H. Qiu & T. Nakano
409
Eddy current monitoring toward advanced plant maintenance T. Takagi, H. Endo & T. Uchimoto
411
Morphing structures and systems Adaptive aeroelastic structures for improved aircraft performance J.E. Cooper, V. Hodigere-Siddaramaiah, G.A. Vio, S. Miller & G. Dimitriadis
415
Dynamic shape control of thin-walled structures M. Krommer & H. Irschik
416
Real-time control performance of a model-reference adaptive structural control system S.Y. Chu & S.C. Lo
417
Bio-inspired structures and materials (2) Numerical analysis for the non-matting condition of dry adhesive pillar-array structures H. Han, Y.-S. Cho & W.-D. Kim
XVII
421
Water strider’s (Aquarius paludum) (Heteroptera: Gerridae) stroke force on the water P.J. Perez Goodwyn, J. Wang, Z. Wang, A. Ji, Z. Dai & J. Fujisaki Self-healing wire and cable insulation D. Huston, D. Burns, D. Hurley & B. Tolmie
422 423
Localization of damage in structural systems: Algorithms Compressional wave-based damage identification by migration technique in concrete beam Y. Luo, Z. Li, Z. Wang & G. Zhao Application of adaptive HHGA–RBF neural network to damage monitoring for composite structures Z.-Q. Li & S.-J. Zheng
427
429
On the Hilbert-Huang transform and its application to system identification X. Fang, Y. Lu & J. Tang
430
Hierarchical PSD damage detection methods for smart sensor networks R.K. Giles & B.F. Spencer
431
New sensor technology for civil engineering structures (2) Predicting concrete compression strength using PZT C.J. Cho, D.-E. Lee, C.-M. Suk & W. Kim
435
Basis and application of GMR sensors for reinforced concrete elements J.S. Popovics, G. Gallo, P.L. Chapman & M. Shelton
436
A forensic study of the collision of a cargo ship with the Vincent Thomas Bridge H-B, Yun, R.D. Nayeri, S.F. Masri, F. Tasbihgoo, M. Wahbeh & R. Wolfe
437
Electroactive sensors and actuators (2) Fabrication and performance of functionally graded piezoelectric bending actuators J.H. Qiu & K.J. Zhu
441
Nonlinear dynamics of acoustic compressors A. El-Sabbagh & A. Baz
442
Guided wave piezoelectric wafer active sensor arrays for damage detection L. Yu & V. Giurgiutiu
443
Strain sensing with a piezoelectric biopolymer H. Richter, F.G. Torres & J. Sanchez
444
Motion and vibration control (2) SOGFCMAC Fuzzy artificial neural network for active vibration control of flexible plate L. Deng, R.W. Chen & Z. Hou
447
Adaptive neural network structure-based on sensitivity analysis X.-H. Yu
448
Optimal design method for sensors/actuators placement in the active vibration control of a 2D flexible plate F. Han, R.W. Chen & Q. Liu
XVIII
449
Research on controller of active probe of AFM for micro-manipulation L. Hao, W.M. Chen, J. Zhang & N. Xi Modeling, identification and control of mechatronic systems equipped with smart actuators: research advances in Spain N. Luo, M. Zapateiro, J. Rodellar & F. Ikhouane
450
452
Innovative sensing systems (3) Influences of thermoelectric parameters on property of gas sensor H. Huang, W.L. Luan, S.J. Mao & S.T. Tu
455
A blocked beacon discovering scheme for sensor localization C. Wan & A. Mita
456
Development of a PVDF-based rubber-tread deformation sensing system for understanding wheel/ground interactions J. Yi & H. Liang
457
Design of intelligent flow auto-monitoring system-based on GPRS wireless network X. Tian, R.W. Chen & T. Lei
459
Development of integrated wireless sensor powered by MsM energy harvester S. Liu, L. Wang & F.G. Yuan
461
Paradigms and technologies related to the engineering and management of intelligent infrastructures and constructed systems (1) Current status and future issues on bridge management H. Furuta, M. Kayano & E. Watanabe A new maintenance and management methodology of smart infrastructures due to performance-based design A. Kawamoto, W. Shiraki, K. Yasuda, N. Ito, M. Dogaki & E.A. Aktan The frontiers of smart monitoring technology N. Miyamoto, T. Okamoto, S. Sumitro & H. Matsuda
465
467 469
Concepts and issues of structural health monitoring for structural reliability and decision making F.N. Catbas & D.M. Frangopol
470
Model updating in hybrid simulation Finite element model updating for roof space truss structure of Shenzhen Citizen Center W.L. Qu, J. Wang & H. Liu
473
Research on a smart external prestressed bridge with position-adjustable saddles J. Wu, Z. Wu & X. Liang
474
Stochastic modal parameters identification by frequency-domain spectrum-driven methods D. Dan, L.M. Sun & Z. Min
475
Structural damage and fault detection (3) Successive zooming genetic algorithm in structural damage detection of truss bridge H.W. Kwon, W.J. Kim & Y.D. Kwon
XIX
479
Damage detection of spatial truss structure by using wavelet analysis D. Tan, W.L. Qu & S. Li
480
Damage detection in beam-like structures using deflections obtained by modal flexibility matrices K.Y. Koo, C.B. Yun, J.J. Lee, D.S. Hong & J.T. Kim
481
Application of empirical mode decomposition for structural damage detection: Experimental investigation J. Chen & G.-Y. Zhao
482
Civil infrastructure monitoring and assessment (3) Do online identification on Donghai Bridge anywhere, anytime, and anyway D. Dan, L.M. Sun & Y. Wang
485
Shake table experimental verification for a structural damage identification technique L. Zhou, S. Wu & J.N. Yang
487
Damage assessment of concrete structures by drilling tests C. Kondo & A. Mita
488
Electroactive sensors and actuators (3) Suppression of the snap-through behaviors of composite shell structures using piezoelectric actuator S.-H. Oh, J.-H. Roh, I. Lee & J.-H. Han Profile and placement optimization for piezoelectric shunt damping system K. Li, Z. Yang, H. Sun & L. Zhang Experimental study on placement optimization of transducers of piezoelectric shunt damping system for plate vibration H. Sun, Z. Yang, K. Li & L. Zhang
491 492
493
Motion and vibration control of structures The energy dissipation performance of displacement dependent semi-active hydraulic damper W.P. Sung, M.H. Shih & S.-P. Hsu
497
Linear control design for regeneratively-actuated structures with energy storage subsystems J.T. Scruggs
498
Intelligent hybrid control for braking-induced longitudinal vibration response of floating-type railway cable-stayed bridge W.L. Qu, J. Liu, J.W. Tu, Q. Zhou & S. Qin
499
Innovative sensing systems: Fiber sensors (2) Analysis on strain transfer of fiber optic Fabry-Perot sensors-based on FEM method W. Zhang, J. Dai, B. Sun & Y. Du Experiment on dynamic response of fiber optic Fabry-Perot sensors and its application in structural health monitoring W. Zhang, J. Dai, B. Sun & Y. Du
XX
503
504
Sensitivity enhancement of long-gage FBG sensors for small macro-strain measurements S. Li & Z. Wu An effective method of temperature compensation about long-period fiber grating with strain characteristic Y. Wang, D.K. Liang & B. Zhou
505
506
Paradigms and technologies related to the engineering and management of intelligent infrastructures and constructed systems (2) Korean experiences with smart bridges H.M. Koh, H.S. Lee, W. Park & J.F. Choo
509
Developments and experiments in biomimetic robots Effect of artificial caudal fin on performance of a biomimetic fish robot actuated by piezoelectric actuators S. Heo, T. Wiguna, H.C. Park & N.S. Goo
513
Experimental investigation on a biomimetic flapping wing with macro-fiber composites D.-K. Kim, J.-H. Han & K.-J. Kwon
515
Model identification and control of a fish-like robot W.L. Chan, T. Kang & Y.J. Lee
517
Motion and vibration control (3) Investigation of an optimal motion pattern for a robotic fish C. Han, S. Lee & J. Park Analysis and testing of shape memory alloy-driven biorobotic fish fins with multi propulsion modes Y.-H. Zhang, Y. Song & J. Yang
521
522
A building with semi-active base isolation using sliding mode control I. Nagashima, Y. Shinozaki, R. Maseki, J. Toyama, K. Yoshida, Y. Kitagawa, Y. Sanui & H. Komatsu
523
Semi-active vibration isolation using MR damper for a building-like structure H. Nishimura, H. Aratake, J. Nakasone, N. Inoue, Y. Nakmura, M. Watakabe, H. Ryujin, Y. Ito, M. Kanagawas & M. Nagaya
525
Gain-scheduled control of smart structures with dynamic characteristic variation I. Kajiwara & R. Tsuchiya
527
Novel method to utilize piezoelectric film as multi-mode displacement sensor and its application to active vibration control S. Kobayashi, M. Nishikiori, T. Watanabe & K. Seto
529
Smart systems and mechatronics All-terrain vehicle robot with controllable auxiliary mass M. Yokoyama & R. Adachi Multi-objective optimal control of semi-active suspension system with MR dampers M.G. Luo, L. Zheng, Y.N. Li & A. Baz
XXI
533
534
Virtual reality simulation of a full car active suspension system with nonlinear energy sink controller J. Smoker, A. Baz & L. Zheng Oscillations of piezoelectric microscale resonators B. Balachandran
535 536
Magnetorheological fluids and dampers (3) Dynamic performance and control of ER damper in vehicle L. Zheng, Y.N. Li, M.G. Luo & J. Shao
539
Optimal design of MR damper and dynamic characteristics L. Zheng, Y.N. Li, J.S. Wei, S.S. Li & R.G. Li
540
Effects of water on the rheological properties of oil-based MR fluids H.B. Cheng, X.H. Wang, J.M. Wang, J. Zhang, W.Y. Zhao, W.L. Qu, Q.J. Zhang & W.X. Gao
541
Stable oil-based MR fluids with core-shell composite particles H.B. Cheng, J. Zhang, S. Xu, W.Y. Zhao, J.W. Tu, W.L. Qu, Q.J. Zhang & W.X. Gao
542
Study on the shear behavior of MREs-based on chain-like model M. Yu, X. Yan, L. Mao & H. Wen
543
Data-analysis methods Modeling of magnetorheological fluid damper with force lag considerations X.C. Guan, C.F. Bian, P.F. Guo & J.P. Ou
547
Enhancement of the spatiotemporal resolution of pulse-echo methods by digital filtering Q.F. Li, L.H. Shi, D.K. Liang & G. Li
549
A new temperature compensation method for flow measurement employing FLNN Z. Hou, R.W. Chen & Y. Meng
550
Research on signal separation of self-sensing piezoelectric actuator Q. Liu, R.W. Chen & B. Gu
551
Smart control systems-based on MR fluids (3) Structural reliability analysis-based on support vector machine M.N. Noori, Y. Cao, F.G. Yuan, T. Yokoi & A. Masuda
555
Study on a Magnetorheological fluid bladder spring for isolation system X.Z. Zhang, W.H. Li & X.Y. Wang
556
Fuzzy vibration control of intelligent structures with MR dampers Y.Q. Guo, S.M. Fei & Z.D. Xu
557
Study on multi-field coupled model for Magnetorheological fluids in microchannel Y. Su, Y. Zhang, J. Yue & B. He
558
Applications of smart materials Adaptive tuned dynamic vibration absorbers working with MR elastomers W.H. Li, X.Z. Zhang, B. Liu & X.Y. Wang Theoretical and experimental investigation into dynamic characteristics of a rotor supported on a disk-type Magnetorheological fluid damper C. Zhu
XXII
561
562
Technologies and methods of SHM An analytical and experimental study of TLCD for structural vibration control A.Y.P. Wang, Y.H. Chen & B.C.L. Lee
565
Application of smart 3-D laser scanner in structural health monitoring S. Sumitro, H. Matsuda, Y. Itoh & S. Nishimura
566
Magnetorheological fluids and dampers (4) US-China joint task force on integrated structural health monitoring S.D. Glaser, H. Li, M.L. Wang & J.P. Ou An experimental study into dynamic behavior of a magnetorheological fluid squeeze film damper – overhung flexible rotor C. Zhu
571
572
Dynamic performance of Magneto-rheological dampers subject to impact load L. Zhang, J. Wang & L. Qian
573
Effect of fluted flow channel on magnetic field in magneto-Rheological damper Y. Li, J. Wang & H. Hu
574
Piezoelectric composite sensors (2) A two-way controllable Magnetorheological (MR) fluid damper G. Aydar, X. Wang, F. Gordaninejad & C. Evrensel
577
Preparation and characterization of novel aqueous MR fluids-based on core-shell composite particles H.B. Cheng, J.M. Wang, J. Zhang, W.Y. Zhao, W.X. Gao, W.L. Qu & Q.J. Zhang
578
Mechanical and stress-sensitive properties of multi-walled carbon nanotubes reinforced cement matrix composites J.L. Luo & Z.D. Duan
579
Interactions between N coating fibers in fiber piezoelectric composites B.H. Yang & C.F. Gao
580
A higher order theory for piezoelectric plate J. Jiang & D. Li
581
Innovative sensors and actuators: shape memory alloys Prediction of electrical properties of carbon nanotube/polymer composites N. Hu, Z. Masuda & H. Fukunaga
585
Earthquake response modification of bridges using superelastic shape memory alloys J.E. Padgett & R. DesRoches
586
Applications of shape memory alloys in control of buildings under seismic loads R. DesRoches & J. McCormick
587
Natural frequency analysis of a composite laminated plate with embedded shape memory alloy wires under thermal activation Q. Liu, J.T. Ren & Y.Q. Guo Shape memory alloy devices for monumental cultural heritage retrofitting S. Casciati
XXIII
588 590
Study on self-adaptive trigger mechanism of composite tubes J.-J. Gong, X.-W. Wang & X.-F. Wang
591
“Stretchable silicon” wired sensor networks for smart materials K. Huang, R. Dinyari, J.Y. Kim, P. Peumans, J. Feng, G. Lanzara & F.K. Chang
592
Author index
593
XXIV
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Preface
Smart Materials and Smart Structures are destined to be an important part of the technological revolution that is transforming engineering practice and changing the human interface and experience with the natural and built environment. To provide an opportunity for scientists and engineers, professionals, and government agents to come together and engage in interdisciplinary discussions on the future of smart technologies, Chongqing University, Nanjing University of Aeronautics and Astronautics, and Hong Kong Polytechnic University jointly hosted The World Forum on Smart Materials and Smart Structures Technology (SMSST’07) – the first global event of its kind. Held on May 22–27, 2007 in Chongqing and Nanjing, China, the Forum was a worldwide event that highlighted the major advancements in multifunctional materials and material systems, smart sensors and signal processing technology, smart actuators and mechatronics, wireless sensing, energy harvesting, system and structural control, structural health monitoring, self-adaptive and self-diagnosing structures, autonomous intelligent structures and systems, and smart aerospace systems. Participants came from many countries on all continents to present their work in 5 keynote and 79 parallel sessions over the course of the Forum. The financial support of the Forum’s principal sponsors, the US National Science Foundation (NSF), the National Natural Science Foundation of China (NSFC), the Asian Office of Aerospace Research and Development of Air Force Office of Scientific Research (AFOSR), the Asia-Pacific Network of Centers for Research in Smart Structures Technology (ANCRiSST), the International Association for Smart Materials and StructuresChina, the International Association for Structural Control and Monitoring-Japan, the International Association for Structural Control and Monitoring-USA, and the International Technology Center Pacific, is gratefully acknowledged. Additional acknowledgement is given to the Forum’s co-sponsors: the Korea Science and Engineering Foundation, the Architectural Institute of Korea, the China Instrument and Control Society, the China Instrument and Control Society – Structural Vibration Control Branch, the China Civil Engineering Society – Bridge and Structural Engineering Branch, the China Civil Engineering Society – Smart Material and Structure Systems Branch, the Chongqing Science Technology Committee, the Chongqing Association for Science and Technology, the Earthquake Engineering Society of Korea, the Jiangsu Science Technology Committee, the Korean Society of Civil Engineers, and the Korean Society of Steel Construction. The leadership and guidance of Professor Huang Shanglian of Chongqing University, Professor and President Ou Jinping of Dalian University of Technology, and Professor and former President of Nanjing University of Aeronautics and Astronautics Hu Haiyan were critical to the success of the Forum. The inexhaustible work of Ryan Kent Giles and Honghui Zhang in preparing for the Forum and of Shin Ae Jang, Jennifer Rice, and SungHan Sim in collecting and editing the manuscripts for publication is also appreciated. Finally, primary credit for the success of the Forum belongs to the authors whose excellent presentations and papers made this valuable volume possible. May 2007 The Editors: B.F. Spencer, Jr. M. Tomizuka C.B. Yun W.M. Chen R.W. Chen
XXV
Keynote Lectures
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Intelligent structures and systems: Dream, reality, and future Shang-Lian Huang Key Laboratory for Optoelectronic Technology & System, Education Ministry of China Chongqing University, Chongqing, China
ABSTRACT: During the past two decades, some of safe, comfortable and effective engineering structures were achieved in the fields of smart structures and systems, but the reality is that we have not yet realized the goal of any real intelligent structures and systems. The future work is still very tough. This paper gives a review of recent progresses in this field. In the first part, the human-faced threats are simply introduced. The second part mainly gives the bionic concept of intelligent structures and systems and its definition. In the third part, we focus on the realistic state of arts, as examples of the applications for smart structures and systems, the bridge structural health monitoring systems, and vehicle adaptive suspension systems based on the MR damper, which have been developed by Chongqing University, are detailed shown and explained, some of the monitoring and control results are given. In the end, the near further research items and the future perspective of intelligent structures and systems are presented. Keywords: Intelligent or Smart Structures and Systems; Health Monitoring; Remote Group Structural Health Monitoring System; Adaptive Structure; Vehicle Suspension Systems; Fiber Optic Strain Sensor; Laser; Image Deflectometer; MR Actuator; Human Simulated Intelligent Control.
1
INTRODUCTION
Yangtze River, Gaojiahuayuan Bridge across Jialing River and Xiangjiapo Crossroads Bridge are developed. The vehicle adaptive suspension systems based on MR damper and HISC strategy are also studied (Liao Changrong 2001, Yu miao 2003, Dong Xiaomin 2006). But now, any real human-like intelligent structures and systems have not been made, there are still many researches and developments must be done. This paper will give our viewpoint related dream, reality, and future of intelligent structures and systems.
In 1989, as an initiator, a proposal to the State Council of Science and Technology of China and National Natural Science Fundation of China to make an initiative project in the fields of Smart Structures and Systems in China was submitted. Since then, under the support of different funds, Center for Smart Structures and Systems of Chongqing University (CSSCQU) has been engaged in research and development of this field (Huang Shanglian, 1990). Up to now, a lot of smart sensors based on optoelectronic principles have been studied deeply, (Liang Dawei 1991, Tu Yaqing 1992, Luo Fei 1993, Huang Shanglian 1993, Zhou Jian 1994, Jiang Yi 1994, Chen Weimin 1995, Tang Feng 1996, Zhao Tingchao 1996, Gu Yuan 1997, etc) and some of them have been successfully applied to smart structures and systems, such as fiber optic FP strain sensor (Feng Jun 2000, Wang Nin 2001, Chen Weimin 2002, Shun Jiyong 2002), laser deflectometer (Yong Zhu 2000, Liu Liandong 2002), optoelectronic deflectometer and self-calibrating imaging system (Zhang Jie 2004, Dong Hui 2004, Chen Weimin 2005). Especially, the bridge structural health monitoring systems, such as Dafosi Bridge across Yangtze River (Yong Zhu 2003, Fu Yumei 2004), and the remote group structural health monitoring system for three bridges at Chongqing, including Masangxi Bridge across
2
HUMAN-FACED THREATS
We, human, are facing many threats in our daily life. (1) Natural disasters: earthquakes, hurricane, rainstorm, thunderbolt, flooding, landslides. (2) Structural degradation: material aging and corrosion, environmental changes, structural deterioration. (3) Man-made disturbances: jerry construction, design mistakes, corruption and degeneration, breaking laws and principles. Natural disasters are difficult to forecast accurately, structural degradation can not be avoided, man-made disturbances are impossible to prevent effectively, can people really do anything about them? Could we
3
Figure 1. Chongqing Dafosi Bridge across the Yangtze River.
These structures and systems, I think, which could be named smart, but not intelligent structures and systems. For smart structures and systems, there are mainly four key technologies:
only conservatively design overweight, higher energy consumption, and lower performance structures? 3
DREAM
Facing so many threats, we have a dream for safer, comfortable, and efficient engineering structures for a long time. Human expects future engineering structures should sense and respond to internal structural state and external environmental changes at optimum conditions on time, so that they should have:
(1) Sensors and signal processing: optical Fibers, Laser, Image, MEMS, PZT/PVDF, and other smart sensing and signal processing technology. (2) Actuators: SMA, PZT, ER/MR Fluids, Electrostrictive and Magnetostrictive Devices, etc. (3) Control Algorithms: LMS, Fussy, Artificial Neural Network, Human Simulated Intelligent Controls, etc. (4) Structural Integration: Nonlinear mathematical and physical modeling, interface coupling characteristics, optimization of system integration, structural damage assessment etc.
(1) a neural systems, which can sense or forecast hidden troubles for global deformation, local strain/stress and other parameters which influence the structural performances. (2) a muscular systems that can adapt to changing the shape, strength, stiffness, damping, and vibration patterns of the structures. (3) a survival and healing ability, which can protect themselves under disaster occurrence and survive continuously. (4) a ‘brain’ that can rapidly process sudden events, and adjust and control adaptively, making the whole structure and system always under optimized state.
4.1
4.1.1
Chongqing Dafosi Bridge across Yangtze River Constructed in August 2001, Dafosi Bridge is a cablestayed bridge across Yangtze River in Chongqing China. Its main span is 450 m and the two side spans is 198 m (Fig. 1). The deck in main span is a composite structure made of steel box girders and C60 pre-cast reinforced concrete, while the side span is composed of pre-stressed concrete beam. The Bridge has been monitoring by many sensors (Fu Yumei 2002, Yong Zhu 2003, Huang Shanglian 2004). The schematic of the Health Monitoring System is shown in Fig. 2, and it consists of three parts: Local Control and Data Processing, Measurement System and Remote Management and Analysis. In order to monitoring this bridge, we have arranged six monitoring items: strain/stress of main girder, temperature field of main girder, displacement of girder, and displacement of towers, dynamic characteristic of the girder,
Such systems, which have above-mentioned characteristics, are called ‘Intelligent Structures and Systems’. 4
Structural health monitoring
Here, some of the bridge structural health monitoring systems, which have been developed by Chongqing University, as examples of applications for the smart structures and systems will be given.
REALITY
Are current advances in science and technology good enough to realize intelligent structures and systems? At least to say, up to now, scientists and engineers have not yet made any real human-like intelligent structures and systems; they only have added a few intelligent functions and life characteristics in some structures. Sensory systems, muscular systems, and motor control systems are far away from real biological structures .But they have been already applied to the structural health monitoring of some engineering structures, and a few prototypes with adaptive structures have been demonstrated in recent years.
4
Figure 2. Schematic of the health monitoring system.
Figure 3. (a) Embedded EFPI strain sensor (b) installation picture (c) Portable EFPI strain gauge.
Figure 4. Girder deflection sensors.
output (Wang Lin 2001). Girder Deflection Sensors are given in Fig. 4 (Hu Weijun 2003, Zhang Peng 2002, Zhang Ju 2003, Zhang Jie 2004), and the displacement of girder can induce water level changes in common pipe. The opto-electronic sensors installed on the end of the pipe sense these changes, transfer
cable tension and vibration. For each item, there are corresponding sensors. In all, more than one hundreds sensors were embedded in or installed on the bridge. Fig. 3 (a) and Fig. 3 (b) show the Embedded EFPI Strain Sensor, Fig. 3(c) shows Portable EFPI strain gauge which can measure the EFPI Strain Sensor
5
to digital signal, with deflection range 200, 400, 600 mm, accuracy 0.1 mm (Yang Jianchun 2006). We also have developed another deflection sensor, named Laser Deflectometer (Dong Hui 2004, Chen Weimin 2005), shown in Fig. 5. Laser is installed in measured structure, the assembled photo receiver is fixed in immovable position, can gain precise laser facula position through digital signal processing for the camera output. With the same method, the structural
deformation can be given by gaining the laser facula change. The temperature change of bridge is shown in Fig. 6. The results of No. 9 and No. 11 EFPI strain sensor are expressed in Fig. 7. Fig. 8 shows the deflection monitoring results about three months.
4.2 Chongqing Masangxi Bridge across Yangtze River Chongqing Masangxi Bridge across Yangtze River is shown in Fig. 9. Sensor systems include: 48 fiber optic FP sensors, 4 laser deflectometers, 18 self-calibrating imaging systems, 28 temperature sensors, 4 humidity sensors, 4 accelerators. Here, the two- dimension Laser Deflectometer (shown in Fig. 10), which is combination of the Laser Deflectometer and Imaging Deflectometer, has been developed, it can measure the
Figure 5. Laser deflectometer.
Figure 6. Temperature change of bridge.
Figure 7. Result of No. 9 and No. 11 EFPI Strain Sensor embedded in Section 20.
6
Figure 8. Deflection monitoring results.
4.2.2 Xiangjiapo Crossroads Bridge Xiangjiapo Crossroads Bridge (shown in Fig. 16) is a bridge with high flexible pier, and it has also been monitored (He Yongqi 2004). The tiltmeter is installed on the Bridge top for monitoring the pier displacements. 4.3
Remote group structural health monitoring system
The schematic of the Remote Group Structural Health Monitoring System (RGSHMS) for three bridges, Xiangjiapo, Masangxi, and Gaojiahuayuan Bridge is shown in Fig. 17 (Luo Haisong 2006, Tong Yanqun 2006). The system consists of local information acquisition and transmission system, information processing and safety evaluation system. The acquired sensor’s information through remote transmission network is transmitted to Group Monitoring Center; here, information processing, safety assessment, and warning up can be automatically achieved. Fig. 18 shows the remote group monitoring center. Fig. 19 gives the output of EFPI strain sensors installed on Masangxi Bridge Fig. 20 shows the output of EFPI strain sensors installed on Gaojiahuayuan Bridge. Fig. 21 shows the output of displacement sensors installed on Xiangjiapo Crossroads Bridge.
Figure 9. Chongqing Masangxi Bridge across the Yangtze River.
displacement between two non-intervisible points. The 2D self-calibrating imaging deflectometer (in Fig. 11) has been put forward. Using two-cursor targets, the adjusted and installed errors can be avoided, so that the precise deflection value (Xia Ze 2004) can be calculated. The installation pictures are shown in Fig. 12. The Fig. 13 shows the temperature and strain measurement results; the inverse cross-correlation between temperature and strain changes (Dong Hui 2004) is clearly shown. The Fig. 14 shows the temperature and deflection in middle of span, with cross-correlation. 4.2.1 Chongqing Gaojiahuayuan Bridge across Jialing River Gaojiahuayuan Bridge across the Jialing River (shown in Fig. 15) has been monitored (Fu Yumei 2006). Sensor systems include: 24 fiber Optic FP sensors, 12 Self-calibrating imaging systems, 16 Temperature sensors, 2 Humidity sensors.
4.4
Safety assessment
After acquiring the sensor’s information, we need adopt Safety Assessment Algorithm to estimate the structures safety.The structural safety can be estimated by monitoring the change tendency of bridge typical parameters.
7
Figure 10. Two-dimension laser deflectometer.
Figure 11. 2D Self-calibrating imaging deflectometer.
Figure 12. (a) 2D laser defelctometer (b) 2D self-calibrating imaging (c) monitoring by accelerator.
Figure 13. Temperature and strain measurement results.
8
Figure 14. Temperature and deflection in middle of span. InfInformation Processing Safety Evaluation
Group Monitoring Center
Information Acquisition and Transmission
Remote transmission Network
Xiangjiapo
Masangxi
Gaojiahuayuan
Figure 17. Schematic of RGSHMS. Figure 15. Gaojiahuayuan Bridge across the Jialing River.
Figure 18. Remote group monitoring center.
Changrong 2001), as second example of applications for smart structures and systems. Full car dynamics model has been analyzed (Fig. 23) (Yu Miao 2003). Closed Loop Control of Smart Structure Systems has also been developed (Yu Miao 2006, Dong Xiaomin 2006).
Figure 16. Xiangjiapo Crossroads Bridge.
There are three Safety Assessment Algorithms we have adopted (Zhou Jianting 2005, Liang Zhongbao 2006):
4.6 The development of Human Simulated Intelligent Control (HSIC)
(1) Safety Assessment Based on Exponentially Weighted MovingAverage Control Chart (EWMA) (2) Safety Assessment Based on Relative Guideline (3) Safety Assessment Based on Information Fusion.
1979, Prof. Zhou Qijian of Chongqing University proposed the control theory;1983, the control theory was firstly published on international journal (Zhou Qijian 1987, Dong Xiaomin 2006); in recent years, with combination of schema theory in cognitive science, the HSIC based on schema theory has come into being. Some breakthroughs have been achieved, including
4.5 Adaptive structures Here, we introduce an Adaptive Suspension based on Magneto-rheological Damper. The System has been developed by Chongqing University (Fig. 22, Liao
9
Figure 19. Output of EFPI strain sensors installed on Masangxi Bridge.
Figure 20. Output of EFPI strain sensors installed on Gaojiahuayuan Bridge.
Figure 21. Output of displacement sensors installed on Xiangjiapo Crossroads Bridge.
characteristic identification and memory based on characteristic model, the multimode control and multi-controller structure based on characteristic identification. Fig. 24 shown the hierarchical structure of
HSIC, including parameter adjust schema and motor intelligent schemas of running control. The application of HSIC in MR suspension is given in Fig. 25.
10
Figure 22. MR fluid shock absorber for mini-bus suspension.
Figure 23. (a)Virtual car (b)Seven DOF model of full car.
Figure 24. The hierarchical structure of HSIC.
11
Figure 25. The application of HSIC in MR suspension.
(2)
(3)
(4)
Figure 26. (a) Control system for Chang’an minibus (b) Control system for Mazda sedan.
The control systems have been applied in Chang’an minibus and Mazda sedan, shown in Fig. 26. Results of power spectral density of heave acceleration at driver’s seat at 80 km/h on B class road, and one at driver’s seat at 30 km/h on D class road are expressed in Fig. 27 and Fig. 28 (Dong Xiaomin 2006). We can see different control algorithms have different control results. It is undoubted that the HSIC algorithm has better results.
5
(5)
FUTURE RESEARCH NEEDS
What should we do in the near future?
(6)
(1) Sensing Technology: Fiber optical, laser, image, piezoelectric, piezomagnetic, passive wireless, MEMS sensors, which
12
suitable to be permanently embedded in or installed on structures; and other novel smart sensors for measuring strain/stress, acceleration, velocity, displacement, deformation, deflection, crack and other structural parameters; distributed, quasi-distributed, multiplexing, demultiplexing, sensor networks, multi-sensor data fusion techniques. Signal Processing and Transmission: Signal modulation, demodulation, coding and decoding, weak signal extracting from strong noise, fiber optic and wireless remote monitoring, remote monitoring system using internet, methods for managing and examining high volume of data collected from day to day. Actuator Technology: Different types of smart actuators for passive, active, semi-active, and hybrid control, such as SMA, piezoelectric stacks, ER/MR fluid dampers or actuators, etc; full-scale actuators, especially for application to civil infrastructure systems, appropriate dynamic models of actuators must be studied. Control Algorithms and Devices: Algorithms and devices for passive, active, semiactive, and hybrid control of nonlinear systems, with emphasis on energy-effective approaches and hardware for handling strong inputs, especially, the intelligent control methodology and intelligent controllers have priority been investigated. System Integration The embedded sensors and actuators, the longterm behavior and the interfacial strength between them and host structures, will influence the mechanical properties and /or performance of the structures. To get a trustable safety assessment of the structures, the reliability of sensors and the health monitoring systems should be carefully studied and strongly improved. Damage Identification: Sensors are typically point-located or cover some small area within structure, whereas damage may be occurred at some distance away from any
Figure 27. Power spectral density of heave acceleration at driver’s seat at 80 km/h on B class road.
Figure 28. Power spectral density of heave acceleration at driver’s seat at 30 km/h on D class road.
case, etc. Space Structures: satellite, space station, reusable launch vehicle, etc. Land/marine structures: automobile, express train, submarine, ship, etc. (8) Non-Technological Issues: Sociological Concern: The worker should be trained to handle embedded or installed sensors and transmission network. The owner or operator should be properly educated to maintain and use smart systems. There should be enough propaganda to let people know the importance of smart structures and systems.
sensors. The information must be combined and extrapolated in some manner to detect any damage. Structural safety assessment should be based on history data and changing tendency of monitored structures. Novel identification algorithms are critically needed to relate the sensor measurements to physical conditions of the structure in term of damages or defects. The relationship between damages or defects and measurable physical quantities of the structure with damage must be deeply studied (7) Applications in Structural Health Monitoring and Adaptive structures: Civil infrastructures: bridge, highway, building, power plant, airport runway, etc. Aircraft and Missile Structures: helicopter, airplane, engine, motor
Political Concern: establishment of the national or international standard for smart structure and systems, especially for structural health monitoring. Legislation
13
Tu Yaqing; Huang Shanglian. Neural Network Processing of Fiber optic Sensing Signals. Piezoelectrics & Acoustooptics. 1992, (06) Luo Fei; Huang Shanglian. Measurement of spatial distribution of mode coupling in high-birefringent fiber by interferometry. Acta Optica Sinica. 1993 (11) Huang Shanglian. Smart Structures-An Impending Revolution in Engineering. Piezoelectrics & Acoustooptics, 1993 (01) Zhou Jian; Huang Shanglian. Optical fiber sensor for solidify composite material. Journal of Transcluction Technology. 1994, (03) Jiang Yi; Huang Shanglian. Large 3-D Measuring Technique Based on Fourier Transform Profilometry. OPTICS AND PRECISION ENGINEERING. 1994, (06) Huang Minshuang; Chen Weimin; Huang Shanglian. The Theoretical Analysis of Distributed Optic Fiber Strain Sensor Based on Brillouin Scatter. OPTO-ELECTRONIC ENGINEERING. 1995, (04) Chen Wei-Min; Jiang Yi; Huang ShangLian. Strain Sensing Technique Based on Fiber Bragg Grating. OPTICAL COMMUNICATION TECHNOLOGY. 1995, (03) Tang Feng; Hang Shanglian; Pei Liujin .Technology for Integrating Optical Fiber Sensor in Smart Structure. JOURNAL OF TRANSDUCER TECHNOLOGY. 1996, (01) Zhao Tingchao; Huang Shanglian; Chen Weimin;Tang Jun; Fu Yong. Phase Noise due to Modulating in Fiber Optic Gyroscope. PIEZOELECTRICS & ACOUSTOOPTICS. 1996, (06) GuYuan; PanYingjun; Huang Shanglian. Measuring Method of Pressure-induced Birefringence in Single-mode Fiber Based on the Detecting Technology of State of Polarization. ACTA PHOTONICA SINICA. 1997, (08) Huang Shanglian; Tao Baoqi. Shen Yapeng. Intelligent Structure Systems: Dream, Reality and Future. CHINA MECHANICAL ENGINEERING, 2000 (Z1) Feng Jun; Zhu Yong; Li Xianyu; Shi Rong; Chen Weimin; Huang Shanglian. Experiment Study on Shrink Strain Monitoring of Concrete with Fiber Optic F-P Strain Senor. ACTA PHOTONICA SINICA. 2000, (10) Wang Nin; Zhu Yong; Chen Weimin; Huang Shanglian. Real-time Data Acquisition and Process System of Fiber Strain Instrument Based on Multithread. Measurement & Control Technology, 2001, (11) Chen Weimin; Zhu Yong; XQ Chen; Huang Shanglian. Embedded probe of fiber strain sensor for concrete. Chinese Patent Bureau, ZL 012 56921.6, Beijing, 2002. Wang Nin; Zhu Yong; Chen Weimin; et al, Application of Fiber Optic F-P Strain Sensor in the test of elastic modulus of Concrete. China Civil Engineering Journal, Vol. 36(6), 45 ∼ 50, 2003. Chen Weimin; ZhuYong; Feng Jun; Huang Shanglian. Experiment Study on Fiber Optic F-P Strain Senor System. CHINA CIVIL ENGINEERING JOURNAL. 2002 (04) Sun JiYong; Chen Weimin; Zhu Yong; Huang Shanglian. Influence of Optical Source Spectrum on Optical Fiber F-P Strain Sensor Influence of Optical Source Spectrum on Optical Fiber F-P Strain Sensor. Acta Optica Sinica, 2002, (05) Wang Nin; Zhu Yong; Chen Weimin; Huang Shanglian Study of Improved Algorithm About Influences of the Wavelength Quantization Error on the Accuracy of Fiber Optic
for structural health monitoring on large civil infrastructures should put orders of the day.
6
FUTURE
In the future, whether we could make human-like intelligent structures by means of engineering methods? In the beginning of the 21st century, it is expected that smart structures and systems will find widespread applications in the fields of the structural health monitoring, vibration control, noise suppression, and adaptive control surfaces, etc; the aeronautics, airspace, automobiles, trains, and the civil infrastructures, robots industry etc., will be improved from the development of smart structures and systems. In the future, because of revolution in the areas of life, materials, information, and engineering the intelligent function and life characteristics in engineering structures not only in macroscopic scale, but also in microscopic scale would be achieved. It is expected that the real human simulated intelligent structures and systems would be realized. This will make the harm of natural disasters, structural degradation, and man-made disturbance to be mitigated, even avoided. People will be able to live in safer and more comfortable environments. The engineering structures will be more effective, energy saving, and lightweight. The long-term dream of human being would come reality. We believe that such a day would come someday.
ACKNOWLEDGEMENT I would like to thank Ministry of Education of the People’s Republic of China, Ministry of Science and Technology of the People’s Republic of China, Ministry of Science and Technology of Chongqing for their imbursements, and our cooperation associations for their useful help. I would also like to thank my colleagues, Prof. W.M. Chen, Prof. Y.M Wen, Prof. D.H.Wan, Prof.Y.Zhu, and Prof. M.yu, and Dr.Y.M.Fu, Dr. C.R.Liao, Dr P. Zhang, Dr. Z.B. Liang, Dr. X.M Dong, Dr. H.H. Zhang, Dr. X.H. Lei, Dr. J.Zhang, and other postgraduates, for their contributions in the R&D of smart structures and systems in Chongqing University. REFERENCES Huang Shanglian; Liang Dawei; Luo Fei.The Present and Future of Distributed Fiber Optic Sensors. Opto-electronic Engineering, 1990, (3) Liang Dawei; Huang Shanglian. Research Status and Development of Distributed Optical-Fiber Temperature Sensor. Journal of Applied Optics, 1991, (02)
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F-P Strain Sensing System. Piezoelectrics & Acoustooptics, 2002, (03) Zhu Yong; Fu Yumei; Liu Liandong; et al.. High Dynamic Multi-channel Laser Deflectometer for Bridge, Workshop on research and monitoring of long span bridges. Hong Kong, April. 2000. Liu Liandong; Zhu Yong; Chen Weimin. Research on laser deflecto-meter and displacement measurement system. Laser Journal, 2001, (06) Liu Liandong; Zhu Yong; Fu Yu-mei; Zhang Peng; Chen Wei-min; Huang Shanglian; Research on a Kind of Laser Deflection Meter System. China Instrmentation, 2001, (03) Zhang Jie; Zhu Yong; Tan Jin; Chen Weimin. A New Photoelectric Liquid Level Sensor Based on Joint-hoses. Chinese Journal of Scientific Instrument, 2004, (S2) Yang Jianchun; Chen Weimin. Application of connected pipe optoelectronic liquid level sensor in bridge deflection monitoring. Transducer and Microsystem Technology, 2006 (08) Fu Yumei; Zhu Yong; Chen Weimin; Yu Miao; Huang Shanglian; Study on Remote State Monitoring System and Application on Bridges. Journal of Foreign Highway, 2002 (02) ZhuYong; FuYumei; Chen Weimin; Huang Shanglian; Health monitoring system for Dafosi Cable-stayed Bridge, Vol. 5057, SPIE, 2003. Fu Yumei; Zhu Yong; Chen Weimin; Huang Shanglian. Study on Remote State Automatic Monitoring System, and Application on Bridges. CHINA CIVIL ENGINEERINGJOURNAL. 2003, (02) Huang Shanglian; Chen Wei-min; Rao Yunjiang; Zhu Yong; Fu Yumei; Fiber Optic Strain Sensors and Their Applications in Structural Health Monitoring. Measurement & Control Technology, 2004, (05) ZhuYong; FuYumei; Chen Weimin; Huang Shanglian. Health Monitoring System for Dafosi Cable-stayed Bridge.Vol. 5057, SPIE, 2003 Zhang Ju. Development on Local Monitoring Software for DaFoSi Yangtse River Bridge and Its Application. Master Dissertation in Chongqing University. 2003 Zhang Peng. Study and Implementation of Long Span Cablesupported Bridge Deflection Measurement System Based on DSP. Master Dissertation in Chongqing University, 2002 Hu Weijun. The Research on Deflection Measuring System of Chongqing DaFoSi Bridge of Changjiang River with Opto-electronic Level System in Connected Pipes. Master Dissertation in Chongqing University, 2003 Wang Lin; Zhu Yong; Feng Jun; Chen Weimin; Huang Shanglian. Theory Analysis of Influences of the quantization error of wavelength on the accuracy of Fiber-Optic F-P strain sensing system. Sensor Technique Transaction. 2001(4) Zhang Jie; Zhu Yong; Tan Jin; Chen Weimin. A New Liquid Sensor of Opto-electric Deflectometer Based on Joint-pipe. 2004 Optics Conference. Hangzhou
Yang Jianchun; Chen Weimin. Connected Pipe Optoelectronic Deflection Measurement System and the Application in Dakota Yangtze River Bridge. Journal of Optoelectronics·Laser, 2006, (03) Dong Hui; Chen Wei-min; Fu Yumei; Xia Zhe. Method of laser & imaging deflection measurement. Journal of Transducer Technology, 2004 (10) Dong Hui; Chen Wei-min; Fu Yu-mei; Xia Zhe. Study on stability of laser & imaging deflection measurement system. Laser Journal, 2004, (05) Chen Weimin; Lu Jin; Xia Ze; Zhu Yong . Department. Analysis on the Photometric Characteristics of Imaging Deflection Measuring System for Bridge. Acta Photonica Sinica, 2005, (01) Xia Ze. Large Span Bridge Deflection Measurement with Self-calibration Imaging. Master Dissertation in Chongqing University, 2004 Dong Hui. Deflection Remote Monitoring System of Mashangxi Changjiang Bridge. Master Dissertation in Chongqing University, 2004 Lu Haisong. Study on Multi-points Measuring Technology for Fiber Fabry-Perot Strain Sensing. Master Dissertation in Chongqing University. 2006 Tong Yanqun. Software Design & Development of Data Acquisition and Processing in Cluster Center of Bridge. Master Dissertation in Chongqing University, 2006 Fu Yumei. Study on Key Technology of Data Acquisition and Processing in Bridge Health Monitoring System, Post Doctor Dissertation in Chongqing University. 2006 He Yongqi. Research and Development of the Field Monitoring System for the Displacement of the Top of Pier for the High-pier Bridge. Master Dissertation in Chongqing University, 2004 Zhou Jianting. A Study on Reliability Theory Based Safety Evaluation for Bridge Remote Monitoring Systems. Doctor Dissertation in Chongqing University. 2005 Liao Zhongbao. Structural safety assessment of brdige by monitoring information Statistic analysis. Doctor Dissertation in Chongqing University, 2006 Liao Changrong. Study on Magnetorheological Fluid Damper for Automobile Suspension System. Doctor Dissertation in Chongqing University, 2001 Yu Miao. Study on Control System of Automobile Magnetorheological Semi-active Suspension. Doctor Dissertation in Chongqing University, 2003 Yu Miao Human Simulated Intelligent Control for Vehicle Suspension Based on Magneto-rheological Technology. Post Doctor Dissertation in Chongqing University, 2006 Dong Xiaomin.Human Simulated Intelligent Control of Automobile Magnetorheological Semi-active Suspension. Doctor Dissertation in Chongqing University, 2006 ZHOU Qijian;. Intelligent Control and Its Perspective. Information and Control. 1987, (02)
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structural health monitoring with smart NDE technology Seung-Seok Lee, Il-Bum Kwon & Dong-Jin Yoon Safety Metrology Group, Korea Research Institute of Standards and Science, South Korea
ABSTRACT: Smart NDE (Nondestructive Evaluation) technology deals with advanced sensing technology having small size, real time operation, and non-contact measurement rising the conventional NDE technology such as ultrasonic test, acoustic emission, visual test etc. This technology can also apply on structural health monitoring. Safety metrology group of KRISS is working on NDE technology during about 25 years. In this presentation, we are going to briefly introduce our works about smart NDE technology for structural health monitoring. At first, we explain some sensing technology based on ultrasonic test implemented by advanced MEMS based transducer and phased array EMAT(electromagnetic acoustic transducer). Also, laser based ultrasonic test is included. Secondly, we move to watch on some works of smart active layer technology to detect acoustic emission signals of structural damages. Lastly, we carry on fiber optic sensor technology, which measure some distributed displacement and temperature on the surface of a building. Keywords: 1
Smart NDE technology, ultrasonic test, acoustic emission, fiber optic sensors
INTRODUCTION
condition. Various ultrasonic transducers are showing in figure 1. We have developed also one more ultrasonic technology, so called as, laser-based ultrasonics, which use a high power pulsed laser to generate ultrasonic waves in materials. This laser based ultrasonic technology is shown in figure 2. If pulsed laser reached on the surface of a sample, then the ultrasonic waves shall be generated. At that time, some ultrasonic receiver can catch the signals. In our works, we have developed a fiber optic sagnac interferometric ultrasonic receiver to detect the signals.
Recently, nondestructive evaluation technology has developed small size, non-contact, real time operating sensors to apply to diagnose industrial plants or public infrastructures effectively. This movement is called as smart NDE technology. Structural health monitoring technology is also dealing with advanced sensor technology to sense structural health status. So, these two research fields are to be met at the same needs of advanced sensor technology. Safety Metrology Group has worked on developing nondestructive evaluation technology such as ultrasonic sensing, acoustic emission, electromagnetic sensing, visual inspection during 25 years in Korea. Our research group has much experience on developing sensing technology on defect detection of various structures, such as pipe line, power plant etc. Therefore, in this presentation, we will briefly introduce our works on smart NDE technology (advanced NDE sensing technology), such as ultrasonic transducers, acoustic emission sensing, and fiber optic sensors. 2 2.1
2.2 Acoustic emission sensing technology Acoustic Emission (AE) is the elastic energy that is released by a material when it undergoes deformation or fracture. In figure 3, we can see a SAL(smart active layer) to identify some defect location. An actuator makes elastic waves and AE sensors, no. 1, no.2, no.3, and no.4 catch the signals. After all, these signals are processed to get the defect information. A model bridge, which has a SAL sensor under the bottom surface of the bridge, is prepared to show the operation of SAL sensor shown in figure 4. Embedded AE sensors can give the location information of AE source in figure 5. We are now developing a new acoustic sensor based on biologically inspired ear. An ear of human body operates with tiny sound sensitive hair cell. So, we make similar hair cell like beams with piezo-ceramic materials shown in figure 6. This sensor can sense the
SMART NDE TECHNOLOGY Ultrasonic sensing technology
Ultrasonic sensing is a usual technique to inspect some defect detection in NDE field. However, we are developing new ultrasonic transducer to sense ultrasonic signal at many points in small area under non-contact
17
Figure 2. Laser based ultrasonic technology.
Figure 3. Smart active layer (SAL) sensor.
Figure 1. Various ultrasonic transducers. Figure 4. Model bridge for acoustic emission detection.
frequency bandwidths of acoustic signals wider than that of conventional AE sensors.
2.4 Fiber optic sensor technology 2.3
Structural testing technology
We are also going to develop some fiber optic sensor technology for applying structural health monitoring. In figure 8, a fiber optic OTDR (optical time domain reflectometry) sensor shows its operational schematics. When a pulsed light is launched in an optical fiber, this light can reflect at some mirrors locating in the
In order to simulate real structural behavior, our group has structural testing equipments, such as 100 ton, 50 ton, 10 ton actuators with universal multiaxial hydraulic controller. In figure 7, wind blade is tested by some whiffle trees on the blade.
18
Figure 5. Source location by SAL sensor.
Figure 8. Fiber optic OTDR sensor.
Figure 6. Biologically inspired AE sensor.
Figure 7. Wind blade structural test.
fiber. If the light is leaked between two mirrors, then the second signal is decreased. So, we can sense the external physical parameter, which changes the light leakage between two mirrors. Another fiber optic sensor is a distributed sensor using Brillouin scattering of an optical fiber shown in figure 9. The pulsed pumping light is launched at one end of an optical fiber, when the CW probe light is also traveled from another end of the fiber. If Brillouin frequency, which is the material property of the optical fiber, is same as the difference between the frequency of the pulsed light and that of the probe light, then the back scattering light is amplified by transferring the light power from pulsed light to probe light.
Figure 9. Fiber optic BOTDA sensor.
We can analyze the scattering signal to know Brillouin frequency. This value of Brillouin frequency can give the external effects such as strain and temperature because this frequency is proportional to the external physical parameters. In order to confirm this sensor’s feasibility, we install the optical fiber on our research building to monitor the distributed temperature on the
19
Figure 11. Organization of KRISS (Korea Research Institute of Standards and Science).
– Standardization of Integrity Measurement Technologies for Industrial Facilities and Structures : Development of Fitness-For-Service (FFS) assessment technologies for safe and effective maintenance of industrial facilities/structures, Development of standard procedures in RiskBased-Inspection (RBI) for establishing FitnessFor-Service assessment standards. – Development of future-oriented measurement technologies for the safer life: Standard measurement techniques in mechanical properties of thin layer in metal and ceramic, Precise measurement techniques of small quantities of the particles using ultrasonic wave, Development of new technologies for the man-made disaster prevention
Figure 10. Measurement of distributed temperature.
surface of the building as shown in figure 9. Also, the measured distributed temperature is showing in figure 10.
3
INTRODUCTION OF SAFETY METROLOGY GROUP AT KRISS
We would like to introduce our group, Safety Metrology Group at KRISS (Korea Research Institute of Standards and Science). KRISS is a national metrology institute establishing the national measurement standards of global confidence. This institute has three research division; division of physical metrology, division of metrology for quality life, and division of advanced technology. Our safety metrology group is included in division of metrology for quality life. We make every effort for the better quality of life through the development and dissemination of future-oriented safety measurement technologies as well as the establishment and maintenance of national standards in field of the safety metrology related to various applications including infrastructures, industries, power plants and vehicles.
4
SUMMARY
We briefly introduced our works about smart NDE technology for structural health monitoring. We explained what smart NDE sensing technology included, as like ultrasonic sensing technology, acoustic emission sensing technology, and fiber optic sensor technology. We introduced our institute being mainly responsible for establishing measurement standards and science in Korea. Our group also was presented as a research group of developing some measurement technology for structural diagnosis and monitoring. Therefore, we hope to work together with civil structural research groups internationally to accomplish real application of smart NDE sensing technology.
– Development of Standards MeasurementTechnologies in Safety Fields : Establishment of measurement traceability in fields of nondestructive evaluation, Development of standard system for evaluating the mechanical properties of metals, Development and dissemination of certified reference materials
20
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Fiber optic nerve systems for materials and structures that can feel pain K. Hotate The University of Tokyo, Tokyo, Japan
ABSTRACT: In the field of fiber sensor technologies, recently, distributed and multiplexed sensing schemes have been studied and developed. In the systems, a long length fiber acts a “nerve” for feeling strain and/or temperature distribution along the fiber. Performances of the artificial nerve systems have markedly improved within the last couple of years, in spatial resolution and measurement speed. By embedding the “fiber-optic nerve system” in aircraft wings, bridges and tall buildings, these materials and structures can sense damage to prevent disasters. Keywords:
1
Fiber optic sensors, distributed sensing, fiber-optic nerve systems.
INTRODUCTION
been studied and developed [1-3]. Besides simple configurations, in which the fiber acts only as a data transmission line, sophisticated configurations have also been developed, in which the fiber is used as a device to create unique sensing mechanisms. (See Figure 1).
The research field of fiber sensors was established in the early 1970s, on the basis of the same devices and photonic principles as fiber communication technology. In this field, various types of sensors have
Figure 1. Classification of fiber sensor technologies. (a) Sensors with a fiber as an information transmission line, (b) sensors with a fiber as a sensing element, and (c) schemes for multiplexed and distributed sensing.
21
Recent research in this field has been concentrated on distributed and multiplexed sensing schemes, which provide us with “fiber optic nerve systems” for making materials and structures to feel their “pain” [4–8]. Fiber Bragg gratings act as strain or temperature sensors, and wavelength division multiplexing (WDM) technologies have been used as sensor multiplexing schemes. Brillouin and Raman scattering in the fiber provide us with strain and temperature sensing mechanisms, respectively. By combining fiber sensors with optical time domain reflectometry (OTDR) schemes, distributed strain and temperature sensing systems have been developed. In our group, we have proposed and developed a scheme for distributed sensing, which is not based on OTDR, but on the synthesis of the interference characteristics of continuous lightwaves [6–8]. A spatial resolution of 1.6 mm and sampling speed of 60 Hz has already been realized, which are 500 times finer and 10,000 times faster than those of the OTDR schemes, respectively. These fiber optic nerve systems will be able to create novel health monitoring functions for materials and structures. Aircraft wings, spacecraft fuel tanks, bridges and tall buildings will be able to sense damage with these schemes and thereby prevent disasters.
Nerve System for Smart Materials
Buildings
?!? Optical Fiber
?!??
Optical Fiber
Nerve System for Smart Structures Optical Fiber Bridge, Tunnel, Dam, Highway, Levee, .......
?!? Km range Sub m resol.
Figure 2. Structures and materials that can feel pain with fiber optic nerve systems.
and 104 times faster than those of the time-domain technologies, respectively [6–8]. Recently, the spatial resolution has been more improved to be 1.6 mm. In the sections below, we discuss the principle of the correlation-domain technique, and show its applications to fiber optic nerve systems.
3 2
Se curity and Safety System
~ 100 m range Sub cm resol.
FIBER OPTIC NERVE SYSTEMS
BRILLOUIN OPTICAL CORRELATION DOMAIN ANALYSIS
3.1 Principle and functions
Recently, distributed and multiplexed fiber optic sensors, which is shown in Fig. 1(c), have been particularly studied and developed [6-11]. Optical fiber itself acts as a sensor for strain and pressure, and so on, through its optical properties, such as scattering and propagation mode coupling [9]. By additionally applying a way of analyzing these properties distributed along the fiber, the fiber provides us with a nerve function for the materials and structures in which the fiber is embedded. The fiber nerve can sense damage occurring in the materials and structures. Materials and structures having this self-diagnosis function are called “smart materials” and “smart structures”, as schematically illustrated in Fig. 2. Time-domain techniques, such as OTDR, have been studied for use as a distributed sensing scheme [9]. However, they have shown difficulties in realizing satisfactory performances, such as achieving a high spatial resolution and a high sampling rate. To overcome these difficulties, we have proposed optical correlation domain techniques using continuous light waves [2, 3, 6–8]. By applying the correlation domain technique, for example, to a fiber-Brillouin distributed strain-sensing scheme, we have demonstrated a 1 cm spatial resolution and a 57 Hz sampling rate, which are 100 times
Distributed strain sensing based on Brillouin scattering in an optical fiber is a promising technique [9, 10] for use in a fiber optic nerve system. Brillouin scattering has a frequency of about 11 GHz downshifted from the input lightwave. The frequency shift is changed by longitudinal strain applied to the fiber. The techniques developed so far, however, have a spatial resolution limit of about 1 meter [9, 10,12–14]. The optical spectrum width of the lightwave for generating Brillouin scattering must be narrower than that of the Brillouin gain spectrum (BGS). Since the typical BGS width is 30 MHz, the practical limit of the spatial resolution in pulse-based systems is 1 m [9, 10]. Additionally, the pulse-based systems require the measurement time of several minutes, because the backscattered power in a single pulse is quite small [9, 10]. To improve the resolution and the sampling rate, we have proposed and developed a technique called Brillouin optical correlation domain analysis (BOCDA) [7, 8, 15–18]. It is based on the control of the correlation between the pump and probe continuous light waves, which excite a stimulated Brillouin scattering (SBS). Figure 3 shows the basic system for the BOCDA [7, 8]. One output of the coupler, serving as the pump, is chopped by an electrooptic modulator (EOM) with a radio frequency, and launched into the fiber under test.
22
Figure 3. Brillouin optical correlation domain analysis (BOCDA) system [7, 8]. (a) System configuration, and (b) position-selective excitation of stimulated Brillouin scattering.
Figure 4. Detection of concrete cracks with sub-mm width by embedding a distributed fiber strain sensor using the BOCDA system [21]. (a) Concrete specimen, and (b) distributed strain profiles measured along the fiber with crack width d. (experimented with Shimizu Corp.).
The other output is modulated by another EOM with a microwave frequency, so that sidebands are generated around an incident lightwave frequency [10]. The first lower sideband, serving as the probe, propagates against the pump in the fiber and reaches the detector. The point of our system is that the pump and the probe are identically frequency-modulated at the laser diode (LD). As a result, SBS occurs exclusively at the correlation peak position, where the two lightwaves are highly correlated, as shown in Fig. 3(b). We can shift the correlation peak along the fiber by simply changing the FM frequency. The increase in the probe power due to the Brillouin gain is detected by a lock-in amplifier. We obtain the BGS by varying the LD modulation frequency. Thus, the BGS distribution is obtained. We have demonstrated the measurement of the strain distribution along the surface of a pipe of only 15 cm diameter with the spatial resolution of 1 cm [18]. This system uses a continuous light wave, thus, the measurement speed is faster than that of pulse-based techniques. BGS measurement with a 57 Hz sampling rate has already been realized [19, 20]. This technique also has a random access function to any position along the fiber.
Distributed strain profiles were measured along the concrete specimen using the BOCDA system with a 2 cm spatial resolution, as the concrete specimen was progressively loaded. The BGS was measured at 1 cm intervals along the concrete specimen. The strain profiles along the concrete specimen are shown, corresponding to the crack widths, in Fig. 4(b) [21]. Even a small crack less than 0.1 mm can be recognized through the distributed strain measurements. Figure 5(a) shows a photograph of a 2-storey building model used in dynamic strain measurements [22]. A Kobe earthquake-type waveform was applied, and the dynamic strain response, measured at the two positions shown in Fig. 5(a), are shown in Figs. 5(b) and 5(c) [22]. Here, we can see that the instantaneous peak strain greatly exceeds the yielding strain, which means that the structure has been significantly damaged. Using the BOCDA system, both the distributed strain information with cm-order spatial resolution and the dynamic response of the structure can be obtained. These data enable us to analyze, in detail, the damage caused in the structure.
3.2 Examples of application of BOCDA technique 3.3 Performance improvement of BOCDA technique
Figure 4(a) shows an experimental setup for concrete crack detection with an embedded fiber, using the BOCDA system [21]. The 20 cm concrete sample, which was made by two-stage casting to intentionally induce a weak plane at the center, was loaded to generate a crack.
Figure 6 shows a BOCDA system which has recently been developed. This system includes newly proposed schemes to improve the system performances. In Fig. 6, a polarization diversity scheme is introduced [23, 24]. The state of polarization (SOP) of the
23
Figure 5. Dynamic and multiple-point strain measurement of building model [22]. (a) Building model having two storeys, and (b) and (c) strain-time waveforms measured at two positions when an earthquake waveform was applied to the model. (experimented with Kajima Corp.)
Figure 6. BOCDA system with schemes to improve the performance [23–27].
24
Figure 7. Brillouin gain spectrum measured by the BOCDA system without (a) and with (b) the polarization diversity scheme [24].
Figure 8. The comparison of the data in the case of the single and the double lock-in detections [25]. (a) The BGS graphs corresponding to the SMF (upper) and the DSF (lower) sections of the FUT. (b) Measured Brillouin peak frequencies around the DSF section of the FUT in the single (dashed line) and the double (solid line) lock-in systems.
filter is used to obtain selectively the prove component that has the information on the applied strain. When the amplitude of the LD frequency modulation becomes wide to improve the spatial resolution, however, the spectrum of the probe is overlapped with those of the reflected components of the probe and the carrier. To avoid the problem, the new scheme is introduced [25]. Figure 8 shows the noise reduction in the Brillouin spectrum, which is realized by the scheme [25]. Besides the Brillouin spectrum at the correlation position, spectrum component corresponding to the non-correlated portion along the fiber is also generated. Then, the total spectrum obtained in the BOCDA system has a shape shown in Fig. 9 [26, 27]. When strain applied at the measurement position,
lightwave is changed along the fiber, so efficiency to generate the stimulated Brillouin scattering is also changed along the fiber. To avoid the data fluctuation due to the SOP change, the SOP of the pump wave is altered between the two orthogonal SOP’s in time domain by using a polarization switch, as shown in Fig. 6 [24]. The two system output, which are corresponding to the two orthogonal SOP, are averaged to obtain a stabilized Brillouin spectrum. Figure 7(b) shows the stabilized Brillouin spectrum obtained with the diversity scheme [24]. For the lock-in detection, we have also introduced a new scheme, in which the modulation is applied both on the pump and the prove lightwave, as shown in Fig. 6 [25]. In the basic system shown in Fig. 3, an optical
25
Figure 9. (a) Schematic of a Brillouin optical correlation domain analysis (BOCDA) system. Measured Brillouin gain spectrum (BGS) is the sum of local BGS’s (LBGS). (b) Variation of the BGS in response to the applied strain to the sensing (correlation peak) position. Note that the maximum measurable strain is limited by the peak of the background noise and that the measurable strain limit is decreased in longer measurement range [26, 27].
Figure 10. (a) Optical spectrum without (gray) and with (black) the optimized IM. (b) Structure of a fiber under test composed of several sections of SMF and DSF. The overall length is about 1,010 m [27].
the Lorentzian-shaped signal caused at the position slips down along the slope of the mountain-shaped non-correlated spectrum component. When the height of the signal peak becomes lower than that of the mountain-shaped spectrum component, the strain can not be measured. We have found that the problem can be solved by using an intensity modulation onto the input lightwave [26, 27]. Figure 10(a) shows the averaged lightwave spectrum synthesized both with the frequency and the intensity modulation.The shape of the spectrum shown in Fig. 10(a) is almost ideal, which is proved in simulations [27]. Figure 10(b) shows a sample fiber used in the experiment to verify the function of the intensity modulation. Even the ratio of total length of the fiber to the spatial resolution become large, the Lorentzianshaped signal spectrum can be clearly detected by the
Figure 11. Results of a distributed measurement with 1-km range. (a) BOCDA signal with (black) and without (gray) the IM at a 30-cm DSF section (∼505.5 m). (b) BOCDA signal with (black) and without (gray) the IM at a SMF section. (c) Distribution of Brillouin frequency shift around the DSF sections. The measurement step was 10 cm [27].
intensity modulation scheme, as shown in Fig. 11(a) and (b) [27]. In Fig. 11(c), strain applied portion along the 1,000 m fiber is clearly recognized with 30 cm spatial resolution [27]. We have tried to improve the spatial resolution to be mm order by applying the intensity modulation scheme and the beat lock-in scheme [28]. As shown in Fig. 12,
26
to generate the correlation peaks, and a phase delay at the point shifting from the probe to the pump makes it possible to sweep the peak position [29]. We have estimated and compensated the RF transfer function of the LD and the driver circuit for the rectangular modulation of the LD, and have successfully synthesized the waveform to generate the ideal rectangular frequency modulation. This method is called the time-division pump-probe generation scheme. Figure 13(a) additionally has another scheme. The measurement range of the basic BOCDA system is restricted to be about 10 m, because of the periodic nature of the correlation peaks [15, 16]. Then, we have additionally developed a new method, in which a relatively wide pulse is used to select only one correlation peak [30], which we call the “temporal gating scheme”. Figure 13(a) has both the time-division pump-prove generation scheme and the temporal gating scheme [31]. By the system, 8 cm spatial resolution with a 250 m measurement range has been realized as shown in Fig. 13(b) [31].
Figure 12. Structures of the fibers under test (upper) and the measurement results (lower) in (a) FUT-1 and (b) FUT-2 composed of several spliced sections of different fibers [28].
4
The visibility of the interference pattern changes as a function of the differential time delay between the two waves. The visibility as a function of the time delay is called the optical coherence function. In general, the function is determined by the optical spectral characteristics of the light source. We have shown that the function can be arbitrarily synthesized by modulating both the frequency of the laser source and the phase in one arm of the interferometer [2,6]. This is called “synthesis of optical coherence function” scheme (SOCF). In the SOCF system, one of the most useful synthesized functions is that with periodical deltafunction-like peaks. This function is synthesized by stepwise optical frequency modulation that has a constant period and an identical frequency increment [2,6].An easier way to synthesize the coherence peak is to modulate the light source frequency by a sinusoidal waveform. The BOCDA is an example of an application of the SOCF. Additionally, we have proposed and developed various distributed sensing systems with the SOCF scheme. Applying the SOCF technique to polarization mode coupling in a high-birefringence optical fiber, a distributed fiber-optic lateral-force sensing can be realized [32–36]. The basic setup is shown in Fig. 14 [36]. A continuous lightwave from a LD is linearly polarized, and excites one polarization mode of the PM fiber. When stress is applied to the PM fiber, the orthogonal polarization mode is induced at that point. The
Figure 13. Simplified BOCDA system with time-division pump-probe generation scheme and temporal gating scheme [30]. (a) System configuration, and (b) distributed strain sensing.
the Brillouin frequency shift at the DSF fiber of several millimeter can be clearly measured with the spatial resolution of 1.6 mm [28].
3.4
DISTRIBUTED LATERAL FORCE SENSING
Simplified BOCDA system
Figure 13(a) shows the configuration of a simplified BOCDA system, in which we use the direct frequency modulation of the LD to generate the pump and probe light waves in time domain [29]. We modulate the emission frequency of the LD with a waveform which is summation of the rectangular wave component and the sinusoidal wave component. The rectangular wave component generates the pump and probe lightwaves alternatively. The frequency difference between the two is linearly swept by simply changing the modulation amplitude, so that the BGS profile is obtained. The sinusoidal wave component modulates the pump and probe synchronously
27
two polarization modes are separated by the polarization beam splitter, and interfere with each other on the detectors. The orthogonal polarization mode has a time delay linearly dependent on the position of the stress-applied point, because of the speed difference between the two polarization modes. By synthesizing and scanning the coherence peak, the distribution of the mode coupling coefficient can be directly obtained.The lateral force distribution measured by this configuration is shown in Fig. 14(b). The resolution is improved by using lasers with wider tenability [33]. We adopted a superstructure grating distributed Bragg reflector laser diode (SSG-DBR LD) [37], and obtained 20 cm spatial resolution, as shown in Fig. 14(b). 5
MULTIPLEXED FIBER BRAGG GRATING SENSORS WITH THE SAME BRAGG WAVELENGTH
Fiber Bragg grating (FBG) multiplexed strain sensing has been widely studied [11]. FBGs have a periodical reflective index change in the core of the fiber, which causes wavelength-selective reflection. The reflected wavelength, called the Bragg wavelength, is given by its period [11].Therefore, longitudinal strain applied to the FBG cause a change in the Bragg wavelength. For multiplexing the FBGs, different Bragg wavelengths are assigned to each FBG.
Figure 14. Distributed fiber-optic lateral force sensing by the synthesis of optical coherence function technique [33]. (a) System configuration with a polarization-maintaining fiber as a sensor head, and (b) lateral force distribution measured with 20 cm spatial resolution.
Figure 15. Setup for multipoint strain measurement by fiber Bragg gratings with the same Bragg wavelength using the synthesis of optical coherence function technique [45].
28
scattering. Compared with time-domain techniques, spatial resolution and the measurement speed have been much improved, and cm- or mm-order spatial resolution and 60 Hz sampling rate have already been demonstrated. Fiber optic nerve systems are expected to be part of a new technology to realize materials and structures that can sense damage, which will enhance the safety and security of society in the 21st Century.
ACKNOWLEDGEMENTS Figure 16. Simultaneous and dynamic measurement of FBG spectrum with random access function [45].
These studies have been carried out under the support of a “Grant-in-Aid for Specially Promoted Research” (2001–2003), a “Grant-in-Aid for Creative Scientific Research” (2004–2008), and the “21st Century COE Program,” (2004–2007) all from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
However, this wavelength division multiplexing scheme has a drawback. We need different kinds of FBGs. The number of FBGs multiplexed is limited to be about 10, because of the finite bandwidth of the source for the WDM measurement. Several schemes have been proposed, in which the same Bragg wavelength FBGs can be multiplexed [3840]. However, these require calculation of the obtained data. Thus, real-time monitoring of the dynamic strain cannot be realized. We have proposed a scheme, in which FBGs with the same Bragg wavelength can also be multiplexed using the SOCF scheme. This system can achieve a high-speed measurement [41–44]. Figure 15 shows the setup. The location of the coherence peak, synthesized by a simple sinusoidal frequency modulation, is tuned so that one FBG is selected, and the center frequency f0 of the LD is swept to measure the FBG reflection spectrum. By the above scheme, dynamic strain measurement has been demonstrated using a random access function to the FBGs, as shown in Fig. 16 [45]. The sampling speed is improved to be 10 kHz.
6
REFERENCES 1. “Optical Fiber Sensor” eds. J. Dakin, and B. Culshaw, (Artech House, Boston, 1997) vol. IV. 2. K. Hotate: Optical Fiber Technology, 3 (1997) 356. 3. K. Hotate: in Sensors Update, eds., H. Balets, W. Goepelard and J. Hesse, (Wiley-VCH, Weinheim, 2000) vol. IV, chap. 8, p. 131. 4. Proc. 16th Intern. Conf. on Optical Fiber Sensors, Nara, Oct. 2003. 5. Proc. 17th Intern. Conf. on Optical Fiber Sensors, Bruges, May 2005. 6. K. Hotate: IOP Meas. Sci. and Technol. 13 (2002) 1746. 7. K. Hotate and Z. He: J. Lightwave Technology, 24 (2006) 2541. 8. K. Hotate: Jpn. J. Applied Physics, 45 (2006) 6616. 9. T. Horiguchi, A. Rogers, W. C. Michie, G. Stewart, and B. Culshaw: in Optical Fiber Sensors, eds. J.Dakin and B.Culshaw, (Artech House, 1997) vol. IV, chap. 14, p. 309. 10. L. Thévenaz: in Trends in Optical Non-Destructive Testing and Inspection, eds. P. Rastogi and D. Inaudi, (Elsevier, 2000) Chap. 29, p. 447. 11. A.D. Kersey: in Optical Fiber Sensors, eds. J. Dakin and B. Culshaw, (Artech House, Boston, 1997) vol. IV, chap. 15, p. 369. 12. X. Bao, D. J. Webb and D. A. Jackson: Opt. Lett. 18 (1993) 1561. 13. M. Niklas, L. Thevenaz, and P. Robert: Opt. Lett. 21 (1996) 758. 14. M.N. Alahbabi, Y.T. Cho, and T.P. Newson: J. Opt. Soc. Am. B 22 (2005) 1321. 15. K. Hotate and T. Hasegawa: IEICE Trans. on Electron. Vol.E83, (2000) 405.
CONCLUSIONS
Distributed and multiplexed fiber optic sensing is a recent topic in the field of fiber sensor technologies. Multipoint and dynamic-strain sensing with FBGs has been studied and well developed. Time domain technologies with a pulsed lightwave have also been developed for the fully distributed measurement of strain or temperature, based on the properties of Brillouin scattering in the fiber. Without using any mechanical moving parts or calculation, a distributed sensing function can be provided by the optical-correlation-domain technique using a continuous light wave. We have, for example, developed a system for measuring the strain distribution along an optical fiber based on Brillouin
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16. K. Hotate and M. Tanaka: IEICE Trans. on Electron. E84-C, (2001) 1823. 17. K. Hotate and M. Tanaka: IEEE Photon. Technol. Lett. 14, (2002) 179. 18. M. Tanaka and K. Hotate: IEEE Photonics Technol. Lett. 14, (2002) 675. 19. S.S.L. Ong and K. Hotate: Proc. CLEO/Pacific Rim 2003, Shanghai, Dec. 2003. 20. K. Hotate and S.S.L. Ong: IEEE Photonics Technol. Lett. 15 (2003) 272. 21. S.S.L. Ong, H. Kumagai, H. Iwaki and K. Hotate: 16th Int. Conf. Optical Fiber Sensors, Nara, Oct. 2003, p.462. 22. S.S.L. Ong, M. Imai,Y. Sako,Y. Miyamoto, S. Miura and K. Hotate, 16th Intern. Conf. on Optical Fiber Sensors, Nara, Oct. 2003, 458. 23. K. Hotate and K. Abe, 17th Intern. Conf. Optical Fiber Sensors, Bruges, May 2005, p.591. 24. K. Hotate, K. Abe and K.-Y. Song: Photonics Technology Letters, 18 (2006) 2653. 25. K.-Y. Song and K. Hotate: IEEE Photonics Technology Letters, 18 (2006) 499. 26. K.-Y. Song, Z. He and K. Hotate: Optics Express, 14 (2006) 4256 27. K.-Y. Song, Z. He and K. Hotate: J. Lightwave Technology, 25 (2007) 1238. 28. K.-Y. Song, Z. He and K. Hotate: Optics Letters, 31, (2006) 2526. 29. K. Hotate and T. Yamauchi, Jpn. J. Appl. Phys., 44, (2005) L1030. 30. M. Kannou, S.Adachi and K. Hotate: Proc. 16th Int. Conf. Optical Fiber Sensors, Nara, Oct. 2003, p. 454.
31. K. Hotate and H. Arai: Proc. 17th Int. Conf. Optical Fiber Sensors, Bruges, May 2005, p.184. 32. T. Saida and K. Hotate: IEEE Photonics Technol. Lett. 9 (1997) 484. 33. Z.-Y. He and K. Hotate: J. Lightwave Technol. 20 (2002) 1715. 34. K. Hotate and K. Makino: Proc. SPIE Photonics East, Rhode Island, 5272 Oct. 2003, p.157. 35. K. Hotate, X. Song and Z.-Y. He: IEEE Photonics Technol. Lett. 13 (2001) 233. 36. K. Hotate, A. Kuramoto and Z. He: IEEE Photonics Technol. Lett. 16 (2004) 578. 37. H. Ishii, H. Tanobe, Y. Tohmori, Y. Kondo, and Y. Yoshikuni: IEEE J. Quantum Electronics 32 (1996) 433. 38. L.C.G. Valente, A. M. B. Braga, A. S. Ribeiro, R. D. Regazzi, W. Ecke, C. Chojetzki, R. Willsch: IEEE Sens. J. 3 (2003) 31. 39. M.G. Shlyagin, S.V. Miridonov, and V. V. Spirin, Proc. SPIE 4578, 2002, p.8. 40. B. A. Childers, T. L. Brown, J. P. Moore, and K. H. Wood: Proc. SPIE 4578, (2002) 19. 41. K. Hotate, M. Enyama, S. Yamashita and Y. Nasu: Meas. Sci. and Technol. 15 (2004) 148. 42. M. Enyama, Z. He and K. Hotate: Meas. Sci. and Technol. 16 (2005) 977. 43. M. Enyama and K. Hotate: Proc. SPIE 5589, Philadelphia, Oct. 2004, p. 144. 44. Z. He, T. Hayashi and K. Hotate: Proc. SPIE 6004, Boston, Oct. 2005, p. 65. 45. Z. He,T. Hayashi and K. Hotate: Proc. 18th Int. Conf. Optical Fiber Sensors, Cuncun, Oct. 2006.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Ionic polymer-metal composite: an emerging smart material K. J. Kim, R. Tiwari, I.-S. Park, D. Kim1 , D. Pugal2 , S. J. Kim3 , K. Jung & S.-M. Kim Active Materials and Processing Laboratory, Mechanical Engineering Department, University of Nevada-Reno, Reno, NV, U.S.A. 1 currnetly at FormFactor, Livermore, CA, U.S.A. 2 (also) IMS Lab, Institute of Technology, Tartu University, Estonia 3 currently at School of Mechanical and Aerospace Engineering, Seoul National University, Seoul, S. Korea
W. Yim & J. Lee Mechanical Engineering Department, University of Nevada-Las Vegas, NV, U.S.A.
ABSTRACT: Ionic Polymer Metal Composite (IPMC) is an emerging smart material capable of soft sensing and actuation. This paper summarizes our recent (Kim and Kim, 2006, 2007a, b; Kim et al., 2007, Kim et al., in press; Pugal et al., in prep.; Park et al., 2007; Park & Kim, 2007; Park et al., in press; Yim et al., 2007) and on-going research activities regarding IPMC sensors and actuators. Keywords:
1
Ionic Polymer-Metal Composite(s), Sensors, Actuators
INTRODUCTION
the system. This leads into the observation that the material is quite attractive by showing inclination for possible transduction as well as actuation (Akle & Leo, 2004; Asaka & Oguro, 2000; Bao et al., 2002; BarCohen, 2004; Farinholt and Leo, 2004; Kim et al., 2006; Kim and Tadokoro, 2007; Nemat-Nasser and Li, 2000; Nemat-Nasser and Zamani, 2006; Newbury and Leo, 2003; Paquette et al., 2003; 2004; 2005a; b; Punning, 2007; Shahinpoor and Kim, 2000; 2001; Shahinpoor 2003, Shahinpoor et al., 2007). The sensing capabilities of IPMCs have been studied. Various modeling schemes have been considered based upon different theoretical formulations. IPMC sensor applications include dynamic sensing, quasi-static sensing, pressure sensing, velocity sensor, and chemical or electrochemical sensing. The IPMC operation mechanism is somewhat complex and not fully understood; however recent progress has been made leading to the belief that IPMC ionic transducer/sensors will be capable for use in advanced sensing applications.
Ionic Polymer-Metal Composites (IPMCs) are a unique polymer transducer that, when subjected to an imposed bending stress, exhibits a measurable charge across the chemically and/or physically placed effective electrodes of the electro-active polymer (Kim et al., 2006). IPMCs are also known as bending actuators capable of large bending motion when subjected to a low applied electric field (∼10 kV/m) across the metalized or conductive surface (Fig. 1). The first discovery of IPMC actuator was in 1992 by Oguro and his co-workers (Oguro et al., 1992). Also, the sensing applications of IPMCs were first presented in 1992 (Sadeghipour et al., 1992). The voltage found across the IPMC under an imposed bending stress is one to two orders of magnitude smaller than the voltage required to replicate the bending motion input into
2
IPMC ACTUATOR/SENSOR
2.1 Basic structure of IPMC and actuator/sensor operating principles
Figure 1. A typical IPMC placed under an applied AC voltage step function input of 3.0 volts (adopted from Paquette et al., 2004).
IPMC is made of thin ionic polymer layer and metal electrodes. Figure 2 exemplifies one such strip of
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Figure 4. Schematic of water soaked IPMC without electric field (left) and bending of water soaked IPMC when electric field is applied to them (right).
region will shrink. This volume redistribution leads to the bending deformation of IPMCs. Although the above description about the IPMC’s actuation mechanism is presently well adopted within the IPMC community (de Gennes et al., 2000), more study to fully understand the actuation mechanism may be needed. IPMC is also capable of sensing due to the internal motion of ions. Applied mechanical bending causes cation density to increase on compressed side, and to decrease on the stretched side (Kothera, 2002; Punning, 2007). In order to restore ion balance inside the polymeric membrane, cations migrate from higher to lower density region, producing charge. IPMC as sensor may be employed for the purpose of harvesting uncarpeted, wasted mechanical energy, in the form of vibration (Sodano et al., 2004). Numerous source of mechanical vibration may be taken into consideration like automobiles, health monitoring systems, ships, process instrumentations and aircrafts. The captured mechanical energy can be converted into useful electrical energy and stored for future use.
Figure 2. An IPMC strip made from Nafion™ -117 and platinum metal electrode.
2.2 Self-oscillating IPMC Figure 3. An SEM image of IPMC cross section showing distinct layers.
Herein, we present a unique feature of IPMCs, self-oscillation. The self-oscillatory feature of IPMC allows one to develop desired properties for numerous future engineering applications including selfoscillating propulsor-blades for small underwater vehicles, self regulating drug delivery systems, artificial organs such as heart, biosensors, etc. Under certain circumstances, a series of electrochemical reactions, oxidation of small organic molecules on a Pt electrode are of interest. The potential and current is believed to be influenced by the surface reactions. For example, (HCHO), the anodic oxidation of HCHO (formaldehyde) on a Pt surface is accompanied by the appearance of intermediate species, i.e., CO and OH. Therefore, the overall reaction, which involves the reaction of PtOH with the intermediate Pt-CO and the conversion of Pt-OH to Pt oxides, can lead to the occurrence of complex voltammetric responses. It should be pointed out that HCHO is dissociated on the electrode surface at lower anodic
IPMC made from Nafion™ -117 (Dupont® ) and platinum electrode. Figure 3 illustrates the magnified image of the strip obtained using scanning electrode microscope (a cross-sectional view for the thickness direction). The Nafion™ variants consist of fluorocarbon polymer backbones, sulfonate ionomers as ionic groups, and cations (counter ions). By applying an electrical field to IPMCs electroplated by metal or the conducting medium, one causes cations to move toward the cathode carrying with water (=solvent) molecules as shown in Figure 4. Thus, on both electrode sides, it takes the volume differential. That is, the cathodeside will be rich in water molecules, while the anode side will exhaust the water (=solvent) molecules. In a cation-rich region, the polymer backbones will expand to maintain the regional volume and the opposite
32
Figure 6. An equivalent circuit model of IPMC (revised from Kim and Kim, 2007a).
allows for the material to be modeled using an equivalent RC circuit (Fig. 6) to describe the charging/discharging behavior associated with the IPMC. Then, we can include two resistors and two capacitors, which primarily account for the effective electrodes on the surface of the IPMC. There will also be a resistor placed between the two RC circuits to account for material between the electrodes and the resistance mainly due to ion migration through the polymer matrix. The capacitance, C1 and C2 , could be set equal to each other by assuming that the IPMC electrode surfaces are prepared identically throughout the manufacturing process. The value of R1 and R2 could be also set equal to each other for the same reason and will remain constant, along with the value for the resistor across the middle, Re , throughout. Then, charge equation can be written as equation (3).
Figure 5. Potential oscillations of an IPMC (1M HCOOH) under various applied constant currents.
potential via. successive dehydrogenation processes. At a higher anodic potential than that of dehydrogenation potential, water oxidation takes place and shows explosive nature of interactions during the intermediate formation. Also, a similar situation for HCOOH (Fig. 5) displays the potential oscillation under various constant currents. Pt is particularly vulnerable to this poisoning effect. These simultaneous adsorption and desorption phenomena result in the oscillatory potential. 2.3
Modeling perspectives
A study by de Gennes and his coworkers was the first to present the standard Onsager formulation on the underlining principle of IPMC actuation/sensing phenomena using linear irreversible thermodynamics (de Gennes et al., 2000). When static conditions are imposed, a simple description of mechanoelectric effect is possible based upon two forms of transport: ion transport (with a current density, J , normal to the material) and solvent transport (with a flux, M , we can assume that this term is solvent flux). The conjugate and the pressure forces include the electric field, E, gradient, −∇p. The resulting equation has the concise form of,
Assuming that the relation between applied charge, Q, and local stress, σ, of IPMC is pseudo-linear, the following equation can be expressed as,
where c1 is an experimentally obtained modeling parameter. Another way to handle IPMC is to directly solve the Nernst-Planck equation which describes diffusion/convection in presence of electric field and charges and migration of the particles (Pugal et al., in prep.). The general form of the equation is
where κ and K are the membrane conductance and the Darcy permeability, respectively. A cross coefficient is usually L12 = L21 = L, experimentally measured to be of the order of 10−8 (m/s)/(V/m). The simplicity of the above equations provides a compact view of underlining principles of both actuation and sensing of IPMC but is applicable for only static conditions with small deflections. IPMC is both inherently resistive and capacitive (Paquette et al., 2003; Kim and Kim, 2007a). This
∂C + ∇ · (−D∇C − zµFC∇φ) = −u · ∇C, ∂t
(5)
where C is concentration, D diffusion constant, F Faraday constant, u velocity, z charge number, electric potential, and µ mobility of species, which is found by using known relation µ = D/(RT ). There T is absolute temperature and R universal gas constant. As anions are fixed, they maintain constant charge density throughout the polymer. After a voltage is applied
33
Figure 7. Finite element modeling of IPMC with n elements (revised from Yim et al., 2007).
to the electrodes of an IPMC, all free cations will start migrating towards cathode, causing current in the outer electric circuit. Because of the fact that ions cannot move beyond the boundary of the polymer, charges start to accumulate, resulting in increase of the electric field, which cancels out the applied one. The process could be described by Gauss’ Law: = −φ = F · ρc , ∇ ·E ε
Figure 8. Relative capacitance vs. inner electrode thickness and the particle gap (Pt particle diameter of 50 nm, revised from Kim et al., in press).
of IPMCs as actuators and sensors. Herein, we emphasize the capacitive effect of electrodes. Our electrode model (Kim et al., in press) assumes the electrode is composed of particles and the voids between the particles. The model is created to understand the tendency and the influence of the parameters (electrode thickness, particle size, particle gap, etc.) on the electrical properties of IPMC’s. Two metal particles (electrodes) and the void (dielectric) are considered as capacitors. The inner electrode, where the metal particles are insulated by Nafion™ , can build capacitors. However, the upper electrode, where the metal particles are electrically connected, cannot form a capacitor. The capacitors arranged in the thickness direction have a series of connections, and those arranged in the width and length directions have parallel connections because the electric field is vertical to the electrode surface. The capacitance is not the capacitance of the whole IPMC but the regional capacitance around a single electrode. Our study revealed that the IPMC would have 103 orders of magnitude smaller capacitance if there is no inner electrode. Thus, if we manufacture IPMCs without inner penetration, the charge transport, Q(t), will be limited and actuation will not be in effect. Figure 8 shows that the relative capacitance, Ct /Ct−1 , decreases when the inner electrode thickness increases. The capacitors’capacitance has smaller series connections than one capacitor. Therefore, widely distributed capacitors have a smaller capacitance. A close gap between particles creates high capacitance. Although the number of the capacitors with series connections is increased when the particles are densely distributed and have the same thickness, the gap between the electrodes decreases. The number of capacitors having parallel connections increases exponentially. The capacitance increases when the particle gap is closed. From these findings, it can be concluded that the capacitance of the inner electrode
(6)
where ρc is charge density, ε is absolute dielectric constant and E is the strength of the electric field. The charge density variable is related to charge concentration: ρc = zC + zanion Canion .
(7)
The second term in Equation (7) is constant at every point of the polymer. The coupling between Equations (5) and (6) is strong, i.e. no weak constraints have been used. Absolute dielectric constant ε could be explicitly written as ε = ε0 εr , where is dielectric constant in vacuum and equals 8.85 × 10−12 F/m. A steady state of the cations forms when electric field created by distribution of cations cancels out the applied electric field, i.e. the strength of the electric field inside the polymer is approximately zero. It is interesting to note that there are fluctuations in charge distribution only in really thin boundary layers, leading to the conclusion that there is no charge imbalance inside the polymer. Often times, segmented uses of IPMC are useful for engineering applications. One effective way to handle the dynamics of segmented IPMC strip is to use the finite element approach. We can assume that the number of segments, n, is the same as the number of elements used in the model as shown in Figure 7. Hence, there are n + 1 nodes with the nodes of an element i being node i and i + 1. The displacement of an arbitrary point P in Figure 7 can be expressed in terms of nodal displacements and slopes. Detailing modeling sequences and results can be found elsewhere (Yim et al., 2007). Recently, we started to model the electrode which we believe playing a critical role to the performance
34
Figure 10. Storage modulus results of Nafion™ and various IPMC types with temperature scanning range from room temperature to 250◦ C at 1 Hz in a tensile mode (adopted from Park et al., 2007).
Figure 9. Magnetization curves for Ni-doped IPMCs (revised from Park et al., 2007).
is increased when the inner electrode thickness is minimal and the density is high. 2.4
The results of storage modulus as a function of temperature in a tensile mode are shown in Figure 10. The first transition peaks demonstrate the Tg , which represents a major transition for polymers as physical properties change drastically. The Tg (s) of Nafion™ and Pt, Au, Pd, IL-Pt IPMCs are 112.5, 121.4, 157.7, 118.9, and 70.1◦ C, respectively. Au IPMC shows the highest Tg among the various types of IPMCs as high mechanical properties. Not only does Au IPMC have a high Tg , but other types of IPMCs show the same Tg value as their mechanical values. IL-Pt IPMC, showing the lowest mechanical value, has very low Tg , 70.1◦ C due primarily to the existence of an ionic liquid in the polymer matrix.
Magnetically responsive IPMCs
In our recent study (Park & Kim, 2007), we attempted to investigate the responsive characteristics of IPMCs that are electroded with magnetically-responsive materials, such as Ni.The properties of such IPMCs are responsive to multi-fields – not only electrical but also magnetic fields. Such Multi-Field Responsive (MFR) IPMCs are expected to have attractive features including active damping, the replacement of precious metal (Au, Pt, etc), and the possibility of responding to multiple driving forces – both electrically and magnetically, respectively. In order to make IPMCs be responsive to magnetic fields, transition metals such as Ni, Fe, and Co are initially considered as electrode materials. Generally, transition metals go through a simple oxidation-reoxidation reaction, possess electron storage ability, and produce a magnetic field. Ni was doped on the NafionTM film. Although an inexpensive material, Fe may be of interest, Ni was chosen because it is more stable than Fe in an oxidized state. 2.5
2.6 Electrochemical properties of IPMCs Although the electrochemical phenomena on the electrode surface of IPMCs is one of the important factors (Kim and Kim, 2006) when interpreting the fundamental actuation mechanism of IPMCs, presently the electrochemistry of IPMCs is not well studied. The electrochemical reactions observed during IPMC bending may result in performance degradation with the relaxation of IPMCs and unnecessary over-potentials for operation. We performed a study of the electrochemical properties of IPMCs. Useful techniques include Voltammetry, AC impedance, and capacitance measurements. The Nyquist plots of the Pt IPMC indicated the similarity of the impedance values of the Nafion™ and the supporting electrolytes regardless of applying potential. The impedance values of electrodes increased with the applications of voltages between 0 and 1.2V vs. SCE, and decreased above 1.3V vs. SCE. The capacitance value shown corresponds to the value of the interface capacitance at each potential, when the interface is a pure capacitor.
Mechanical properties of IPMCs
Precious metals are the most well known for electroding metals for IPMC manufacturing. In our recent study (Park et al., 2007), we compared the various electrode type IPMCs (Pt, Au, and Pd) and Pt electroded ionic liquid (IL-Pt) IPMC, to view their mechanical characteristics using a dynamic mechanical analysis (DMA). The measured stiffness depends on its modulus of elasticity, which in turn relies on the choice of geometry and mode of strain using Young’s modulus. Temperature scanning of DMA makes it possible to conveniently measure the accuracy of Tg .
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Figure 11. A typical capacitance of an IPMC: Mott-Schottky experiment of Pt IPMC in 0.5 M H2 SO4 solution at the frequency of 150 Hz (revised from Kim & Kim, 2006).
Figure 13. Charged battery voltage profiles.
Figure 14. Three segments IPMC actuator.
3.2 Microwave driven IPMCs
Figure 12. Experimental set-up of energy harvesting in the bending mode.
3 3.1
Despite recent progress of power electronics, still a major shortcoming in dealing with IPMC is the lack of technologies that can be controlled with a stable power supply source under unstructured environments. Currently, we are working on a microwave-based intelligence wireless link. This remote wireless link can be a breakthrough: the effective remote motion control adapts to a variety of unstructured environmental conditions based on the microwave. It has been observed by many researchers that wiring the power line to a respective electrode surface is challenging, especially in a micro-scale actuation as shown in Figure 14. There are many actuator applications where tethered operation is prohibited, and a battery weight can be a major obstacle for actual implementation of the systems. Figure 15 shows the fundamental concept of the microwave driven IPMC actuators.
ONGOING STUDIES Energy harvesting IPMCs
Experimental set-up for energy harvesting is shown in Figure 12. Shaker is vibrated at 10 Hz frequency using sine wave. This frequency of vibration is distinguishable from the resonance frequency of IPMC samples. One end of the sample is clamped while the other end is pinned to the shaker shaft to have a better control on the sample motion. Under dynamic excitation, IPMC produces a sinusoidal waveform. In order to store the sensor voltage on a battery, the signal is converted to DC using a full bridge rectifier circuit. The rectified signal is used for charging a capacitor followed by a battery placed in parallel to the capacitor (Sodano et al., 2004). The voltage stored on the 30 mAh rechargeable NiMH battery. Two IPMC layers of 3 cm × 1 cm dimension were attached to each other using 5% recast Nafion™ and silver conductive paste. The result of the experiment is shown in Figure 13.
3.3 IPMCs as Deformation sensors Another way to employment IPMC sensors is to measure the changes of surface resistance. Although this is quite challenging since the complex nature of IPMCs,
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Figure 15. A block diagram of microwave wireless power transmission.
Figure 17. The surface resistance change outputs.
Figure 18. The concept of IPMC paints.
is new and can be carried out by spraying IPMCmaking constituents directly onto the surface of a structure. The advantage of this type of IPMC sensor is that it can be sprayed directly onto any complex structures and cured at an ambient temperature. Similar to piezoelectric paints, it is a thick-film technology. Unlike piezoelectric materials, the IPMC paints do not need poling and/or other processes to make IPMC materials active. The technique that we are currently adopted is to utilize liquid Nafion™ . The drying induced the recast film to be obtained but is mechanically poor (cracked and brittle) and is also easily dissolved in polar solvents, including water and alcohol. A number of answers to this problem have been thought. Typically, the processes include additive solvents to obtain good insoluble recast Nafion™ films (Kim & Shahinpoor, 2003).
Figure 16. A measurement setup of the surface resistance change of an IPMC.
we are currently constructing an experimental concept representing the sensing principles for an IPMC and supporting data are provided in Figures 16 and 17, respectively. Using this method, we will be able to measure the surface resistance changes of IPMC under deformation. The underlying concept is based on the surface resistance being altered and consequently measurable. In our experiment, we have placed the IPMC in a configuration as seen in Figure 16 using a resistive circuit with a differential amplifier. The changes in surface resistance under different mechanical loadings were clearly measurable as seen in Figure 17. 3.4
4
CONCLUDING REMARKS
The paper presented a brief summary of our recent and on-going research activities in connection with IPMC sensors and actuators. Active research areas of interest to our group are to use IPMC as energy harvesting material, to develop microwave driven untethered actuators, to adequately measure the changes of surface resistance for deformation-sensor applications, and to develop large surface applicable IPMC paints.
IPMC paints
Another on-going research activity is to develop IPMC paints. The concept of making “IPMC paints” (Fig. 17)
37
ACKNOWLEDGEMENTS
Kim, K. J., Paquette, J., Leo, D. J. & Farinholt, K. M. 2006. Ionic polymer-metal composite for sensory applications. Encyclopedia of Sensors, 5: 97–116, American Scientific Publishers. Kim, S. J., Kim, S. M., Kim, K. J. & Kim, Y. H. in press. An electrode model for ionic polymer-metal composites. Smart Materials and Structures. Kim, K. J. & Tadokoro, S. 2007. Electroactive Polymers for Robotic Application: Artificial Muscles and Sensors, Springer, London. Kothera, C. S. 2002, Micro-manipulation and bandwidth characterization of ionic polymer actuators. Masters Thesis, Virginia Tech., Blacksburg, VA. Nemat-Nasser and Li, J.Y. 2000. Electromechanical response of ionic polymer-metal composites. Journal of Applied Physics 87 (7): 3321–3331. Nemat-Nasser, S. & Zamani, S. 2006. Effect of solvents on the chemical and physical properties of ionic polymermetal composites, Journal of Applied Physics 99: 1–17. Newbury, K. & Leo, D. J. 2003. Linear electromechanical model of ionic polymer transducers – Part I: Model development. Journal of Intelligent Material Systems and Structures. 14(6): 333–342. Oguro, K., Kawami, Y. & Takenaka, H. 1992. Bending of an ionconducting polymer film-electrode composite by an electric stimulus at low voltage. Journal of Micromachine Society 5: 27–30. Paquette, J., Kim, K. J., Nam, J.-D. & Tak, Y. S. 2003. An equivalent circuit model for ionic polymer-metal composites and their performance improvement by a clay-based polymer nano-composite technique. Journal of Intelligent Materials Systems and Structures (JIMSS) 14: 633–642. Paquette, J. W. & Kim, K. J. 2004. Ionomeric electroactive polymer artificial muscle for naval applications, IEEE Journal of Oceanic Engineering 29: 729–737. Paquette, J. W., Kim, K. J. & Kim, D. 2005a. Low temperature characteristics of ionic polymer-metal composite actuators. Sensors and Actuators A 118: 135–143. Paquette, J. W., Kim, K. J., Kim, D. & Yim, W. 2005b. The behavior of ionic polymer-metal composites in a multilayer configuration. Smart Materials and Structures 14: 881–888. Pugal, D., Kim, K. J., Punning, Kasemägi, H., Kruusmaa, M., & Aabloo, A., in prep., A self-oscillating ionic polymermetal composite bending actuator. Journal of Applied Physics. Park, I.-S., Kim, S. M. & Kim, K. J. 2007. Mechanical and thermal behavior of ionic polymer-metal composites: effects of electrode metals. Smart Materials and Structures 16: 1090–1097. Park, I.-S. & Kim, K. J. 2007. Multi-fields responsive ionic polymer-metal composite. Sensors and Actuators: A, 135: 220–228. Park, I.-S., Jung, K., Kim, D. & Kim, K. J., in press. State of understanding of ionic polymer-metal composites as electroactive actuators and sensors. The MRS Bulletin. Punning, A. 2007. Electromechanical characterization of ionic polymer-metal composite sensing actuators. PhD dissertation, Tartu University, Estonia. Sadeghipour, K., Salomon, R. & Neogi, S. 1992. Development of a novel electrochemically active membrane and “smart” material based vibration sensor/damper. Smart Materials and Structures, 1: 172–179.
The authors thank financial support from U.S. National Science Foundation (IIS-0328274/75; IIS0713075/83), U.S. Office of Naval Research (N0001404-1-0673), and Nevada System of Higher Education (NSHE). Also, KJK expresses his thanks to Dr. C. Liu (National Science Foundation), Prof. M. Tomizuka (UC Berkeley), Prof. B. Spencer (University of Illinois at Urbana-Champaign), and Prof. F. Gordaninejad (University of Nevada, Reno) for their encouragement. In addition, KJK would like to extend his special thanks to many dedicated IPMC researchers including Prof. A. Aabloo (Tartu University), Dr. K. Asaka (AIST), Dr.Y. Bar-Cohen (NASA/JPL), Prof. D. Leo (Virginia Tech), Prof. S. Nemat-Nasser (UCSD), Dr. K. Oguro (Osaka National Research Institute), Prof. M. Shahinpoor (U of Maine), Prof. X. Tan (Michigan State University), and Mr. J. Paquette (Northrop Grumann). Their dedicated work toward IPMCs is invaluable.
REFERENCES Akle, B. & Leo, D. J. 2004. Electromechanical transduction in multilayer ionic transducers. Smart Materials and Structures 13: 1081–1089. Asaka, K. & Oguro, K. 2000. Bending of polyelectrolyte membrane platinum composites by electric stimuli. Part II. Response kinetics. Journal of Electroanalytical Chemistry 480: 186–198. Bao, X., Bar-Cohen, Y. & Lih, S. 2002. Measurements and macro models of ionomeric polymer-metal composites (IPMC). Proc. SPIE EAPAD Conference 4695: 286–293. Bar-Cohen, 2004. Electroactive Polymer (EAP) Actuators as Artificial Muscles. SPIE Press, Bellingham, Washington. de Gennes, P., Okumura, K., Shahinpoor, M. & Kim, K. J. 2000. Mechanoelectric effects in ionic gels. Europhysics Letters 50(4): 513–518. Farinholt, K. & Leo, D. J. 2004. Modeling of electromechanical charge sensing in ionic polymer transducers. Mechanics of Materials 36: 421–433. Kim, D. & Kim, K. J. 2006. Experimental investigation on electrochemical properties of ionic polymer-metal composite, Journal of Intelligent Materials Systems and Structures (JIMSS) 17: 449–454. Kim, D. & Kim, K. J. 2007a. A theoretical and experiment study for self-oscillatory ionic polymer-metal composite actuators, Smart Materials and Structures 16: 1789–1795. Kim, D. & Kim, K. J. 2007b. Ionic polymer-metal composite actuators exhibiting self-oscillation. Sensors and Actuators A 137: 129–133. Kim, D., Kim, K. J., Tak, Y., Pugal D. & Park, I.-S. 2007. A self-oscillating electroactive polymer. Applied Physics Letter, 90: 184104(1–3). Kim, K. J. & Shahinpoor, M. 2002. Development of three dimensional ionic polymer-metal composites as artificial muscles. Polymer 43(3): 797–802.
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Shahinpoor, M. & Kim, K. J. 2000. The effect of surface-electrode resistance on the performance of ionic polymer–metal composite (IPMC) artificial muscles. Smart Materials and Structures. 9: 543–551. Shahinpoor, M. & Kim, K. J. 2001. Ionic polymer–metal composites—I. Fundamentals. Smart Materials Structures. 10: 819–833. Shahinpoor, M. 2003. Mechanoelectrical phenomena in ionic polymers. Mathematics and Mechanics of Solids 8: 281–288.
Shahinpoor, M., Kim, K. J. & Mojarrad, M. 2007. Artificial Muscles: Applications of Advanced Polymeric NanoComposites Taylor and Francis-CRC, New York. Sodano, H. A., Inman, D. J. & Park, G. 2004, A review of power harvesting from vibration using piezoelectric materials.The Shock andVibration Digest 36(3): 197–205. Yim, W., Lee, J. & Kim, K. J. 2007. An artificial muscle actuator for biomimetic underwater propulsors, Bioinspiration & Biomimetics, 2: S31–S41.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Long-term health monitoring of post-tensioning box girder bridges Ming L. Wang University of Illinois- Chicago, Chicago, USA
ABSTRACT: A number of efforts had been sought to instrument bridges for the purpose of structural monitoring and assessment. The outcome of these efforts, as gauged by advances in the understanding of the definition of structural damage and their role in sensor selection as well as in the design of cost and data-effective monitoring systems, has itself been difficult to assess. The authors’ experience with the design, calibration, and operation of a monitoring system for the Kishwaukee Bridge in Illinois has provided several lessons that bear upon these concerns. The systems have performed well in providing a continuous, low-cost monitoring platform for bridge engineers with immediate relevant information. Keywords:
1
Bridge health monitoring system, crack opening displacement (COD), bootstrap method.
INTRODUCTION
of measuring ambient vibration data provided by a photographic seismograph that was attached to the bridge. Wind, moving water, traffic, or people working on the bridges caused the recorded vibrations. Studies of wind-induced vibration on the Golden Gate Bridge are summarized by Vincent (1958). Vincent discussed the development of a mechanical accelerometer specifically for this bridge and obtained measurements to verify that structural modifications to the bridge would prevent objectionable torsion vibrations. With the development of design theories and construction techniques for long-span bridges, a lot of large bridges were built during the last fifty years. For the safety of these giants, some long-term bridge monitoring systems were developed and installed. The typical examples are Commodore Barry Bridge Monitoring System (USA), Jindao Grand Bridge Monitoring System (Korea), Akashi Kaikyo Bridge Monitoring System (Japan), Alamillo Bridge Monitoring System (Spain), Hummer Bridge Monitoring System (UK), and Zhanjiang Bay Bridge Monitoring System (China), etc. In all of the long-term monitoring systems, the most extensively instrumented one is the Wind and Structural Health Monitoring System (WASHMS) for Tsingma Bridge in Hong Kong, which sensory system consists of approximately 350 sensors and their relevant interfacing units, including the latest GPS system. However, the current long-term bridge monitoring systems lack the specific techniques to provide reliable diagnosis information of bridge condition. Most of these monitoring systems can only collect data from the sensor network and perform some simple
Bridges play an essential part of a highway network. They are open to traffic, resistant to natural disaster, and undaunted by millions of loading cycles per year. However, this fortitude is quite expensive to maintain and do occasionally fail (DeWolf et al. 1989). The fact that many bridges are carrying greater average loads than predicted during their design has significantly increased the need to monitor bridge performance over the past few years. To effectively manage bridges today, there is a great need to monitor the real-time conditions of bridges, and the deterioration rates of their components, so that efficient and pro-active measures can be taken (Carder 1937, Catbas et al. 2000, Cheung et al. 1997, Ashkenazi 1997). By using the latest stateof-the-art technologies, it is possible to utilize health monitoring systems on highway bridges to determine their behavior and condition, and promote a response to maintenance and inspection needs (DeWolf et al. 2002). Bridge health monitoring systems have historically been implemented for the purpose of understanding bridge behavior under various loads and environmental effects (Bampton et al. 1986, Barr 1987, Brownjohn 1994, Lau 1997, Leitch 1987, Macdonald 1997). One of the earliest documented bridge monitoring exercises was conducted on the Golden Gate and Bay Bridges in San Francisco to learn about the dynamic behavior and possible consequences of earthquakes by Carder (1937). Carder’s study was applied to the probability analysis of damage caused by resonance during seismic excitation. The experimental procedure consisted
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Figure 1. Shear cracks on the webs of Kishwaukee Bridge.
data processing. The work of analysis and assessment has to be done manually by human specialists with the help of different independent analysis tools. For a real-time monitoring system, such as WASHMS, the huge amount of data daily collected with a high sampling rate (e.g., 100Hz) will overwhelm the computers of those bridge engineers and make the evaluation difficult and inefficient. This paper will provide a supplement to the current research on bridge health monitoring and improve the understanding of bridge behavior.
2 2.1
Figure 2. Static diagnosis load test on the southbound Kishwaukee Bridge.
A long-term monitoring program is therefore imperative for structural surveillance of Kishwaukee Bridge to provide continuous health records for the bridge management department (Lloyd et al. 2004). Since the major problem of Kishwaukee Bridge is shear cracks on the webs, a specifically designed structural health monitoring system was installed on the Kishwaukee Southbound Bridge in 2003 (Lloyd et al. 2004). This system monitors and records the strain, crack opening displacement, and acceleration of the bridge, as well as the temperature outside and inside the bridge girder. Using shear strain measured through a rosette of three crack opening displacements across cracks, its corresponding shear resistance capacity can be predicted. Thus, the operation and management for this bridge is transformed into a more objective and quantitative process. This process provides for optimal integration of experimental, analytical, and informational system components (Lloyd et al. 2004). In addition, the outcome of the process provides valuable information for current evaluation of structural integrity, durability, and reliability (Lloyd 2003). Using this information, composed from the sensory system, data acquisition system, and health assessment system, the bridge owner and maintenance authorities can make rational decisions in assigning the budgets for both maintenance and repair.
KISHWAUKEE BRIDGE MONITORING Backgrounds
Kishwaukee River Bridge (Rockford, IL) is a posttensioned precast segmental concrete box–girder bridge opened to traffic in 1980. The bridge has five spans with lengths of 170 ft + 3 × 250 ft + 170 ft (51.8 m + 3 × 76.2 m + 51.8 m). As the firstgeneration of segmental structures, the Kishwaukee Bridge engineers chose the design of a single shearkey joint usually located close to the center of gravity of the cross section. These joints are quite vulnerable especially during polymerization of the glue. Problem arose during and after the completion of the bridge. The epoxy applied between segments was not hardened properly in some joints. The epoxy was unable to carry fully the shear stress and was instead acting as a lubricant that caused reduction of shear resistance capacity. Therefore a substantial part of the shear force was concentrated at the shear keys (Wang 2001). As shown in Figure 1, the inclined cracks went through only for the length of one segment but not continuously to the next segment. Many steel pins were inserted to the webs between segments to stop the propagation of shear cracks. It proves to be effective and successful slowing done the progress of cracking. However, there is a need to know current shear carrying capacity as well as the extent of propagation of cracks.
2.2
Static load test
In order to determine actual health status of Kishwaukee Southbound Bridge and set up the baseline for the following long-term health monitoring, we did two static load tests in 2000. The bridge was tested for service loading conditions. The weight of the trucks was comparable with a weight of the design truck defined
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Figure 3. LVDT sensors installed on the inner surface of the web. Figure 4. Arrangement of half-scale experiment.
in AASHTO LRFD Bridge Design Specifications. The design weight of the truck (72 kips) was amplified by a dynamic factor of δ = 1.320. Four different positions of the trucks were proposed on the bridge, as shown in Figure 2. Visual inspection of the shear cracks determined the most damaged webs in the bridge. Web SB2-N4E was chosen for in-situ measurement of deformation due to shear forces. Three linear variable displacement transducers (LVDT) were installed at the interior surface of the web, close to the neutral axis, as shown in Figure 3. Measured displacements were used for estimation of the web’s shear stiffness. The load stage using trucks located in position #2 (second load) was selected for assessment, because neither transverse bending moments nor vertical axial stresses accompanied the imposed load in the web of segment SB2-N4. Shear forces generated by trucks located in position #3 (second load) were used for calculation of the steel stress increment in reinforcement. Average shear strain and shear stiffness of the cracked web:
similar to the design value, while the tangent shear modulus has been reduced about 50–55% by shear cracks. Therefore the change of bridge shear stiffness has little influence on its flexural stiffness. Dynamic tests and FEM simulation also corroborate the negligible effect of shear stiffness on flexural stiffness. 2.3 Half-scale experiment of concrete girder In order to determine the shear carrying capacity of Kishwaukee Bridge, a half-scale I-beam model was cast in the Lab. The following parameters are measured in this experiment: deflection of the end of cantilever; flange strains; web strains; reinforcement strains; prestressing force; elongation of the strands. Figure 4 presents the arrangement of the half-scale experiment. The three half-scale I-beam segments were put between the anchoring block and the dispersal segment. The friction between the joints of three segments was reduced to a certain degree to simulate the unhardened epoxy problem on the southbound Kishwaukee Bridge. The prestressing reinforcement was low relaxation strands with a high yielding point of 1800 MPa. The upper prestressing force N1 was applied with eight 3-strand tendons on the top flange while four 4-strand tendons were used to apply the lower prestressing force N2 on the bottom flange.The shear forceV was applied with a hydraulic jack. The propagation of shear cracks on the I-beam webs is shown in Figure 5. According to the visual inspection records, the type and inclination of these shear cracks are similar to the actual cracks on the Kishwaukee Bridge. It indicates the experiment successfully simulated the actual damage condition of Kishwaukee Bridge.The relationship of shear stress and shear strain is shown in Figure 6. After the linear elastic phase, the concrete cracked and the steel reinforcement carried much of the shear force itself, which is evident from the graph.About the yielding point of shear reinforcement, the reduced tangent shear modulus was roughly 5300 MPa. According to the analysis of the static load test,
To determine the global flexural stiffness of the bridge, strain gauges were installed at the webs of segments located next to the closures. Measured concrete strains were used for calculation of curvature in Eq. 3 and evaluation of the modulus by Eq. 4:
The assessed value of modulus was still in the range from 35,000 MPa to 40,000 MPa. This value is very
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Figure 5. Propagation of shear cracks on the i-beam.
Figure 6. Relationship of shear stress and shear strain.
the current tangent shear modulus is approximately 6740 MPa at the worst location (SB2-N4) of the southbound Kishwaukee Bridge. This means the shear steels are still in the safe region of stress-strain curve. However, more strict regulations should be encouraged so that no overweight truck passes over the bridge which might induce further damage. 2.4
Figure 7. Pre-processing and post-processing of acceleration and frequencies.
while the local damage can be captured by sensors such as strain gages, linear variable displacement transducer (LVDT), etc. The raw acceleration data are collected and preprocessed to obtain the natural frequencies in a sensor substation. Then the acceleration and frequency data are transferred into the database server via the internet in real time, as shown in Figure 7(a). After that, the application server will analyze the data to get the hourly bootstrap mean and its confidence intervals, as shown in Figure 7(b). Based on the five dynamic tests from 1999–2000, the global dynamic characteristics of the bridge are obtained from the acceleration data with the related temperature values. Those structural parameters are setup as the baseline of global health assessment. Temperature has a significant influence on the natural frequencies of a structure. Hence it is important to derive the relationship between temperature and natural frequencies, i.e., how much the frequency will change due to the variation of 1◦ C. To a certain degree, this relationship can represent the change of the bridge bending stiffness due to the temperature variation. Figure 8 provides the temperature-related regression curves and parameters of the first three modes from year 1999 to year 2004. As shown in the figure,
Real-time global and local health evaluation
Kishwaukee bridge monitoring system has been collecting and processing data and generating evaluation and health reports for five years. The system can analyze the frequency distribution, crack opening displacement, shear strain in the web, and traffic information in real time for the Kishwaukee Bridge. Automated warning/alarm system is in effect to warn against any further local structural damage on the bridge, system problems, sensor dysfunction, and data errors. After establishing the baseline of bridge health, a long-term monitoring system can be used to provide the continuous health information of a bridge. For concrete bridges, cracks, especially the shear cracks act as the main role of local damages. And the global health information of a bridge can be represented with the bridge stiffness. Both global and local conditions of bridges need be evaluated in order to determine their in-service behavior and justify rehabilitation and repair plans. The global health information can be provided by dynamic measurement,
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Figure 9. Pre-processing and post-processing of crack opening displacement.
and confidence intervals. The result is shown in Figure 9(b). In order to find out whether the shear cracks propagated during year 2004, it is necessary to analyze the relationship between temperature and crack opening displacements, i.e., to find how much the crack opening displacement will change due to a variation of 1◦ C. Based on the data of these two years, the analysis result of crack opening displacements is given in Figure 10 according to their locations. In three years, the crack opening displacements due to temperature show some difference between the west web and the east web. As shown in the graph, on the west web, the crack opening displacement increased at the rate of about 1 micrometer per year. But on the east web of SB2-N4, the corresponding parameters are almost the same as before. The difference between the west web and the east web is possibly due to the heavier traffic on the west side of the bridge. This result conforms to the visual inspection of Illinois Department of Transportation. According to the analysis on crack opening displacement, we can evaluate the average shear strain of the cracking webs. Based on the global and local measurements, the rule-based expert system gives the shear carrying capacity of the bridge with ductile mode of failure. Figure 11 presents the shear stress-shear strain curve of the cracked web at Segment SB2-N4. As shown in the graph, the monthly maximum shear strain is over the baseline of the static load test in 2000. However, this value is still far below the yielding point. It indicates that the most damaged segment (SB2-N4) is still working in the nonlinear-elastic zone.
Figure 8. Relationship between temperature and first three modes.
the changes of the first two modes due to the variation of 1◦ C during 2004 are almost the same as the baseline (1999–2000). However, the analysis about mode 3 during year 2004 shows a little increase in the frequency change due to the unit temperature variation. According to the theory of dynamic analysis, the changes of higher modes usually reflect the development of local damages. In order to verify the result of global health assessment and inspect the state of local damage, it is necessary to carry out the specific local health evaluation. The raw data of crack opening displacement (COD) are preprocessed in sensor substation and transferred into the database server via the internet, as shown in Figure 9(a). Then based on the hourly record of crack opening displacements, the application server will analyze those data to obtain their bootstrap distribution
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Figure 12. Stress monitoring of post tensioning cables.
Figure 13. Calibration and installation monitoring system.
are jointed using epoxy resin and post-tensioned with external tendons in each span as shown in Figure 12. The construction of this viaduct by utilizing pre-cast segments with large post-tensioning forces is a challenge due to rare experience for such a construction type. Therefore, a full-scale model test was carried out to verify the safety performance of the anchorage blocks and deviators (Sumitro 2002). Besides verifying the safety of the each part, the frictional effect between the deviator and the post-tensioned tendon was also measured. The verification test was conducted by measuring the tendon forces at either side of the deviator. Then the friction coefficient was calculated from the different stresses of the post-tensioned tendon located between these symmetrical adjacent sides of deviator. The most commonly used method to measure the post-tensioning tendon stress is by attaching strain gages to the strands that form the tendons. However, this method is not applicable in this case since the epoxy-coated strands are used for external tendons. Therefore, elasto-magnetic (EM) sensor technology (Sumitro et al. 2002 & 2004, Wang et al. 2005) was adopted. Verification test and calibration were conducted as shown in Figure 13 to verify changes in magnetic properties with respect to stress and temperature changes. As verified by the field measurements, besides obtaining conclusive friction coefficient of the new polyethylene covering sheath material, the stress loss due to set-loss at fixation stage, relaxation, creep and shrinkage, and elastic deformation effects were clearly observed as shown in Figure 14. Pre-stress losses in a life-cycle time of external PC bridge are significantly affected by concrete creep, concrete shrinkage
Figure 10. Relationship between crack opening displacement and temperature.
Figure 11. Main interface page.
3 3.1
OTHER APPLICATIONS Cable force monitoring during construction
Kamikazue viaduct is a double box girder PC bridge. This bridge consists of 1040 segments in a span of 17 continuous box-girders, and has a length of 630 m by 16 m in width. The bridge was erected by span-byspan method using movable false-work. The segments
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diagnosis in the monitoring system. All the realtime raw data shall be pre-processed in the bridge to increase the speed of data transmission, save the capacity of database, and improve the efficiency of health assessment. Automatic measurements should not be considered to be the be-all and end-all of bridge health monitoring. Its place is firmly entrenched in assisting engineers to conveniently carry out the damage detection, analysis, and evaluation of bridges. Figure 14. Long-term monitoring result by EM sensor at span P2-P3.
ACKNOWLEDGMENTS and steel tendon relaxation. It was confirmed in previous laboratory tests that EM sensory technology can measure the actual stress at PC tendon and relaxation. This bridge test was conducted to verify the capability and reliability of EM sensory technology for long-term structural health monitoring on external tendon PC bridge using pre-fabricated sensors and site-fabricated sensors. To better resemble a real application on an existing bridge, stresses measured by site-fabricated sensors at span P2-P3 within 240 days from May 2002 to January 2003 were used and is illustrated in Figure 14. The long-term pre-stress losses were observed in a period between primary pre-stressing within span P2-P3 and secondary prestressing in the adjacent spans. Pre-stress losses were clearly observed, which was caused by elastic deformation from secondary pre-stressing. The average prestress losses in the period between primary prestressing and secondary prestressing (180 days) is 41.2 N/mm2 and 43.1 N/mm2 for tendons 2E1 and 2E6, respectively. These values are in good agreement with the designed pre-stress losses, i.e. 20.0 N/mm2 prestress losses for concrete elastic deformation and 20.0 N/mm2 pre-stress losses for concrete creep and shrinkage.
4
The authors gratefully acknowledge the initiation and continuous support in funding from the Illinois Department of Transportation, US National Science Foundation and Smart Structure Inc. Additional assistance from at Keisoku Research Consultant, Co. in Japan, Dr. Sumitoro of Smart Structures, Dr. Dr. M. Chandoga and Dr. J. Halvoník at Slovak University of Technology in Bratislava is greatly appreciated. This paper is the integration of two papers presented in the same workshop. REFERENCES DeWolf, J., T. Descoteaux, J. Kou, R. Lauzon, D. Mazurek, and R. Paproski. “Expert Systems for Bridge Monitoring.” Computing in Civil Engineering: Proceedings of the Sixth Conference, p. 203–210, American Society of Civil Engineers, Atlanta, GA, 1989. DeWolf, J., R.G. Lauzon,Y. Fu, andT.F. Lengyel, “Long-Term Monitoring of Bridges in Connecticut for Performance Evaluation of Structures.” Performance of Structures: From Research to Design, 2002 Structures Congress, p. 195–196, American Society of Civil Engineers, Denver Colorado, 2002. Carder DS, Observed vibrations of bridges. Bulletin, Seismological Society of America, vol. 27, 267–303, 1937. Catbas FN, Grimmelsman KA, Aktan AE, Structural identification of the Commodore Barry Bridge. Proceedings of SPIE vol. 3995, 84–97, 2000. Cheung M. S., Tadros G. S., Brown J., Dilger W. H., Ghali A., Lau D. T., Field monitoring and research on performance of the Confederation Bridge. Canadian Journal of Civil Engineering Vol. 24, 951–962, 1997. Ashkenazi V., Roberts G. W., Experimental monitoring of the Humber Bridge using GPS. Civil Engineering, Proc ICE 120 177–182, 1997. Bampton M. C. C., Ramsdell J. V., Graves R. E., Strope L. A., Deer Isle-Sedgwick suspension bridge. wind and motion analysis, Report FHWA/RD-86/183, 1986. Barr I. G., Waldron P., Evans H. R., Instrumentation of glued segmental box girder bridges. Monitoring of Large Structures and Assessment of their Safety. IABSE Colloquium Bergamo, 1987. Brownjohn J. M. W., Bocciolone M, Curami A, Falco M, Zasso A, Humber Bridge full-scale measurement campaigns 1990–1991. JWEIA 52 185–218, 1994.
CONCLUSION
A real-time bridge monitoring system includes a realtime data acquisition, a real-time data analysis, and a health reporting system. It should provide the current health status of the bridge in real-time. It should be able to determine the current strength and resistant capacity of a structure. The key point is to use the minimum number of sensors to collect, process, and analyze the real-time dynamic and static data from the most critical positions of the bridge. A large-scale real-time monitoring system can generate huge amount of data every day. The excessive information will overwhelm and decrease the productivity of the bridge engineers if there is no any integrated program of data preprocessing and health
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Lau CK, Wong KY, Design, construction and monitoring of three key cable-supported bridges in Hong Kong. Proc 4th International Kerensky Conference on Structures in the new millennium, Hong Kong, 105–115, 1997. Leitch J, Long A E, Thompson A, Sloan T D, Monitoring the behaviour of a major box-girder bridge. Structural Assessment Based on Full and Large-Scale Testing, BRE Garston 212–219, Butterworths, 1987. Macdonald JHG, Dagless EL, Thomas BT, Taylor CA, Dynamic measurements of the Second Severn Crossing. Proc, ICE, Transport, 123, no. 4, 241–248, 1997. Miyata T, Yamada H, Katsuchi H, Kitagawi, 2002, Fullscale measurement of Akashi-Kaikyo Bridge during typhoon, JWEIA 90, 1517–1527. Vincent, G. S. (1958) “Golden Gate Bridge Vibration Study,” ASCE Journal of the Structural Division, 84(ST6). Wang M. L., etc., “Health Assessment of the Kishwaukee River Bridge.” Technical Report to IDOT, University of Illinois, April, 2001. Lloyd, G., M. L. Wang, and X. Wang, “Thermo-mechanical Analysis of Long-term Global and Local Deformation Measurements of the Kishwaukee Bridge Using the Bootstrap.” Earthquake Engineering and Engineering Vibration, Vol. 3, No. 1, p. 107–115, June, 2004. Lloyd, G., M. L. Wang, and X. Wang, “Thermo-mechanical Analysis of the Kishwaukee Bridge from global and local deformation measurements.” Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems, Shih-Chi Liu, Vol. 5391, p. 618–623, SPIE, San Diego, 2004. Lloyd, G., M. L. Wang, and X. Wang, “Components of a Real-time Monitoring System for a Segmental Pre-cast Concrete Box Girder Bridge”, Structural Materials Technology (SMT): NDE/NDT for Highways and Bridges 2004, Buffalo, NY, 2004. Lloyd, G., M. L. Wang, X. Wang, and J. Love, “Recommendations for Intelligent Bridge Monitoring
Systems: Architecture and Temperature-Compensated Bootstrap Analysis.” Smart Structures and Materials 2003: Smart Systems and Nondestructive Evaluation for Civil Infrastructures, Shih-Chi Liu, Vol. 5057, p. 247–258, SPIE, San Diego, 2003. Lloyd, G., M. L. Wang, X. Wang, and J. Halvonik, “Bootstrap Analysis of Long-Term Global and Local Deformation Measurements of the Kishwaukee Bridge.” The 4th International Workshop on Structure Health Monitoring, Fu-Kuo Chang, p. 163–171, Stanford University, Stanford, 2003. Wang X., M. L. Wang, Y. Zhao, H. Chen, and L. L. Zhou, “Smart Health Monitoring System for a Prestressed Concrete Bridge.” Smart Structures and Materials 2004: Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems, Shih-Chi Liu, Vol. 5391, p. 597–608, SPIE, San Diego, 2004. Wang, X. and M. L. Wang, “Smart Health Monitoring System of a Prestressed Box Girder Bridge.” HK Proceedings of ICANCEER 2002, the Hong Kong Polytechnic University, Hong Kong, 2002. S. Sumitro, A. Jarosevic, and M.L. Wang, “Elasto-Magnetic Sensor Utilization on Steel Cable Stress Measurement.” The First fib Congress, Concrete Structures in the 21th Century, Osaka, 13–19 October 2002, Session 15, pp.79– 86, 2002. S. Sumitro, T. Okamoto, S. Kurokwa, K. Shimano, K. Hida, and M.L. Wang, “Concrete Structure Health Monitoring System by Utilizing Actual-Stress-Measurement-Based”, Proc. Of Concrete under Severe Conditions: Environment and Loading, CONSEC’04, Seoul, pp.1639–1646, 2004. Guodun Wang, Ming L. Wang, Yang Zhao, Yong Chen, Bingnan Sun, “Application of EM Stress Sensors in Large Steel Cables”, Smart Structures and Materials 2005: Smart Structures and Integrated Systems. Edited by Flatau, Alison B. Proceedings of the SPIE, Volume 5765, pp. 395–406, 2005.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Smart structures technology in education Y. Zhang Department of Civil & Environmental Engineering, Lehigh University, Bethlehem„ Pennsylvania, USA
ABSTRACT: This paper summarizes recent education activities in smart structures technology. One of the motivations for these education activities is to prepare the next-generation engineers with the cutting-edge technology, for which they may see broad application in their professional practice. The scope of smart structures education is first introduced. The result of a recent international survey of students in US, China, Korea, and Japan on smart structures technology development is next described. The survey result discloses some important information about students’ understanding of and their interests in smart structures technology development and application. Lastly, this paper also describes the achievements made by engineering education professionals as presented in a special education session of SMSST07 Conference. Keywords:
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Curriculum Development, Education, Engineering, Sensor, Smart Structures.
INTRODUCTION
Major factors behind the accelerating interest in these areas are the exponential growth in sensor technologies, materials, wireless communication, MEMS, structural health monitoring, structural control and information technology, resulting in novel smart sensors with wireless communication, structural control devices, and robust and efficient data analysis and interpretation system. With the benefits in sight, smart structures technology is seeing quick movement into engineering field. For example, civil infrastructures of the future will be integrated with sensors and control devices through information networks to enhance their performance at a reduced life-cycle cost. From an educational perspective, it is desirable to prepare the future engineers of the society for the cutting-edge technologies in smart structures technology, for which they may see broad application in their profession. This paper summarizes some of the recent education activities including the writer’s experience in incorporating smart structures technologies into engineering curriculum.
Smart structures technology, an integrated engineering field comprising sensor technology, structural control, structural health monitoring, information processing and innovative structural system design with adaptive functions might revolutionize the design, construction and maintenance of civil engineering structures. In the past few years, rapid progress has been made in the areas of smart structures technology, receiving increased attention from researchers and practitioners for the potentially high impact on the design, maintenance and retrofit of civil engineering structures including steel structures. Smart structural systems – equipping structures with an integrated system of networked sensors, information processing unit, controllers and actuating devices that allow them to respond “adaptively” to environmental changes, will be constructed to be self-sensing and monitoring, capable of self-diagnosis with intelligence, of self-healing and repair, and of adaptive response to minimize damage due to various classes of disturbances. Smart materials can be used for the various technological aspects of the smart structural system. The key features of a smart structural system include: • • • • • •
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High performance at reduced life-cycle cost Self-diagnosis with intelligence Self-healing and repair Robust (fault tolerant, fail-safe) Adaptive response to various classes of disturbances Information based maintenance for reduced service interruption
INTERNATIONAL SURVEY ON SMART STRUCTURES TECHNOLOGY DEVELOPMENT AND EDUCATON
In early May of 2007, a survey on smart structures technology development and education was conducted among a total of 54 students by email. Among the 54 students surveyed, 16, 13, 18, and 7 were from USA, China, Korea, and Japan, respectively. The US students
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were from a group of student delegations that were planning to attend the World Forum on Smart Materials and Smart Structures Technology (SMSST07) conference held in China from May 22 to 27, 2007. The survey data is given in Appendix II. It is seen that most of the students (almost 80%) taking the survey had a background in civil engineering. Most of the students (80%) agreed that “Smart Structures Technology” is of importance to engineering education and about 61% of the students agreed that incorporating a “smart structures technology” course into undergraduate curriculum is very important. It is also interesting to note that in question 5 of the survey – “if you were given an handson opportunity to take a course in “smart structures technology,” which sensor below would interest you most?”, 50% of the students choose wireless sensor network and 18.5% choose fiber optic sensor. It is also interested to note that about 74% of the students think that lab sessions or hands-on experiments is important to the success of conveying knowledge to students in a “smart structures technology” course. Lastly, when asked about whether there will a strong job market in the field of smart structures technology in ten years, about 65% of the students had a positive view. The following summarizes the survey result (The number in the bracket indicates the number of participants in the corresponding country. Indicated in the bracket are per cent of students checking the box).
(4)
(5)
(6)
(7)
(1) What is your major field of study or research? [79.6%] Civil Engrg. [3.7% ] Mechanical Engrg. & Mechanics [7.4% ] Aerospace Engrg. [9.3% ] Others (e.g., Electrical Engrg., Computer Science, Materials Science & Engrg.) (2) Do you agree this definition of smart structural system: “an engineering structural system integrated with networked sensors, information processing hardware and software, controllers and actuating devices that synergistically would allow the system to respond “adaptively” to changes due to internal and external causes” [ ] (on a numeric scale 1–5, 1 = disagree, 3 = neutral, 5 = strongly agree) 1 (0%) 2 (3.7%) 3 (16.7%) 4 (44.4%) 5 (33.3%) No response (1.9%) (3) Which topic in “Smart Structures Technology” interests you most (choose one only) [16.7%] Sensor technology [24.1%] Structural control method for hazard mitigation and performance enhancement [27.8%] Structural system identification and structural health monitoring (including data mining/pattern recognition, data fusion, and reliability based decision making)
(8)
(9)
(10)
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[9.3%] Smart materials and their application in sensing and energy dissipation devices [18.5%] All of the above [3.7%] Others (Nanotechnology) Do you agree that “Smart Structures Technology” is of importance to engineering education? [ ] (on a numeric scale 1–5, 1 = disagree, 3 = neutral, 5 = strongly agree) 1 (0%) 2 (1.9%) 3 (18.5%) 4 (27.8%) 5 (51.9%) If you were given an hands-on opportunity to take a course in “smart structures technology,” which sensor below would interest you most? (choose one only) [9.3%] GPS sensor [50.0% ] Wireless sensor network [18.5%] Fiber optic sensor [16.7%] photogrammetry sensor (using video camera to measure 3-d dynamic displacement of a structure) [5.6%] other How do you think the role of lab sessions or hands-on experiments to the success of conveying knowledge to students in a “smart structures technology” course (choose one only)? [ ] (on a numeric scale 1–5, 1 = disagree, 3 = neutral, 5 = strongly agree) 1 (0%) 2 (1.9%) 3 (22.2%) 4 (20.4%) 5 (53.7%) No response (1.9%) If you were given an opportunity to do an experimental term project as part of the “smart structures technology” course, what topic would you select for term project? [18.5%] making a sensor using smart material (e.g., piezoelectric or magnetostrictive materials) [29.6%] structural control (e.g., a tuned or active mass damper) [35.2%] building and validating vibration based structural health monitoring method for scaled structure [16.7%] developing and validating a local damage detection method (e.g., ultrasonic surface wave based method) How do you rate the importance of the role of “Smart materials” in “smart structures technology”? [ ] (on a numeric scale 1–5, with 1 = not important, 3 = neutral, 5 = very important) 1 (1.9%) 2 (3.7%) 3 (16.7%) 4 (33.3%) 5 (42.6%) No response (1.9%) Do you agree that incorporating a “smart structures technology” course into undergraduate curriculum is very important (e.g., to broaden their view and career)? [ ] (on a numeric scale 1–5, with 1 = disagree, 3 = neutral, 5 = strongly agree) 1 (3.7%) 2 (14.8%) 3 (20.4%) 4 (29.6%) 5 (31.5%) Do you agree that there will a strong job market in the field of smart structures technology in ten years? [ ] (on a numeric scale 1–5, with
1 = disagree, 3 = neutral (unsure), 5 = strongly agree) 1 (5.6%) 2(5.6%) 3 (24.1%) 4 (27.8%) 5 (37.0%)
interesting to note that in the survey results (Zhang & Lu 2008) about 41% of the students strongly agree that the smart structures technology might become useful in the future. It is also noted that in both survey #1 (given in the first class) and survey #2 (given in the last class), a large percentage (about 40%) of the students thought that “Smart materials and their application in sensing and energy dissipation devices” is the topic that interests them most in this course. In survey #2 which was conducted in the last class, a significant number of students in the class indicated that “smart structures technology” is of importance to civil engineering and introducing this subject into civil engineering curriculum is useful to undergraduate students. From this survey, it is also found that students were happy with the time distribution (1:1.5) between the lecture and lab session for this course. Since the long-term education objective of instructions is to develop in students the right blend of technical knowledge, scientific tools, and communication skills, hands-on experiments which combine theory and technology applications form an important link in effective conveyance of knowledge. To facilitate the education in smart structures technology, smart structures technology test-bed consisting of prototype “smart” structure with a lab scale and various sensors and structural control devices should be utilized (Zhang 2008). To show students how sensors work in a real-world smart structural system, the lab-scale prototype “smart” structure needs to be designed with the goal that the final system as an outcome of integrating many different components and sensors will simulate a real-word prototype bridge monitoring and control system in a manageable and well-controlled laboratory environment. It is believed that in this way students will better understand the optimal application and limitations of each sensor type in a real-world context.
It is seen that the survey data reveals the need for introducing smart structures technology to engineering curriculum, which is important to ensuring the continued development of innovative structural systems for the world’s future.
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PROMOTING EDUCATION IN SMART STRUCTURES
To ensure the continual progress and success of smart structures technology, and its broad impacts on the society, educators and professionals worldwide need to make active efforts in promoting the education in smart structures technology. Most of general public including today’s engineering students are unaware of the remarkable properties of smart structures technology. It is thus an important task for us to make people aware of the significant benefit from incorporating smart structures technology and doing this will help us with the following achievements: •
Gain strong support from industry, property owner, policy maker, and funding agencies is essential to the health development of smart structures technology • Attract more people from different fields to do multidisciplinary research in smart structures technology • Train next-generation engineers with smart structures technology that will see broad application in their professional practice It is also noted that education in smart structures is not only limited to curriculum development. Broadly speaking, education efforts should be made to include the following groups:
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• • •
students (curriculum development), engineers (short course and workshop), policy makers and property owners (outreach activities), • industry (technology transfer) • ourselves (professional conferences and journal publications)
EDUCATION SESSION IN SMSST’07
The introduction of smart structures technology during a student’s career is promising to the continued development of innovative structural systems for the world’s future. In the World Forum on Smart Materials and Smart Structures Technology (SMSST07) conference which was held in Chongqing & Nanjing, China from May 22 to 27, 2007, an invited session titled “Educating next-generation engineers on smart structures technology” was organized, which provides a forum for educators and researchers in the integrated engineering field of smart structures technology to exchange and share experience in curriculum development in this area.A total of six papers were presented in this session, which reflect the unique views and experiences of presenters in educating students about new
Additionally, it is recognized by the writer that the education materials can be most effectively conveyed to students and general public if hands-on demonstration or experiments on the various technologies are arranged in conjunction with education session. In the writer’s class titled “Smart Structures Technology” given in the Spring’06 semester, two surveys was conducted among the 17 students (11 are undergraduate students in civil engineering) enrolled in the class. It is
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course content of “Smart Structural System” is comprised of five major topics: experimental structural dynamics, structural control, smart materials, sensor technology, structural health monitoring in accordance with the above discussions. Structural health monitoring algorithms which are generally incorporated in the data processing unit and are an indispensable part of any viable smart structural system is of practical importance and thus is covered as a major part of this course. Through this course, students will gain an appreciation of the state-of-the-art smart structures technology and study in detail some of the most important theories and hardware to implement smart structural systems that contain built-in control, sensory, and diagnostic elements. Since this one-semester course covers very broad topics, the knowledge level for this course is set as introductory. Otherwise, students, especially undergraduate students, could quickly be overwhelmed with too much information and end up with a frustrated student who is trying to “survive” this course. The ultimate goal is to have a stream of classes that would allow a student with an interest in the smart structures area to take advanced courses that would provide the knowledge and hands-on experiences that they need and desire. Base on the survey data, an experiment-based learning approach is emphasized. One of the requirements for this course is a term project, in which students will have an opportunity to design and experimentally verify a technique with potential application to smart structures. Through such an integrative project, students will be able to gain hands-on experience in designing and evaluating the performance of an integrated smart structural system in a real world context. In the Spring’06 semester, students chose to build a Japanese pagoda which was instrumented with MEMS accelerometers and was also tested with base isolators under earthquakes simulated by a shake table test. One of the goals of this term project is to reinforce the students’ understanding of what they learned in this course such as sensor technology, structural control, structural health monitoring, and vibration testing. Giurgiutiu and Yu (2007) presented a paper that is focused on tackling the impact that Mechatronics and Smart Structures disciplines have on the engineering education. Mechatronics is an emerging engineering area that will likely alter the fundamental nature of engineering education, since the disciplines of electrical and mechanical engineering merge together into seamless continuum. Mechatronics integrates the classical fields of mechanical engineering, electrical engineering, computer engineering, and information technology to establish basic principles for a contemporary engineering design methodology. In addition to overview of mechatronics and curriculum development, the talk by Giurgiutiu and YU also described a mechatronics course MECH367 that is designed
technologies. The six papers presented in this special education session are: •
•
•
•
•
•
“Student society for research on intelligent structural systems at SNU” by Professor Kim, Seoul National University, South Korea “Experience in introducing smart structures technology into civil engineering curriculum” by Professor Zhang, Lehigh University, USA “Impact of Mechatronics and Smart Structures on Engineering Education” by Professor Giurgiutiu, University of South Carolina, USA “Connected Control Method Experiment as an International Benchmark in Smart Structures Education” by Professor Christenson, University of Connecticut, USA “Teleoperation and Teleparticipation of Instructional Shake Tables Using the NEES Cyberinfrastructure” by Professor Dyke, Washington University, USA “Course material development for a graduate course on structural health monitoring” by Professor Huang, Univ of Texas, USA
Kim (2007) reported the results of this new experiment at Seoul National University as well as propose ways to start a global network of undergraduate student societies. Traditional structural engineering is merging with information technology, sensor technology and control technology. Research at the graduate level is very active in this new field. In order to accelerate this process and to keep pace with development in other industries, structural engineering needs to attract very talented students to this new field (Kim 2007). One of the many possible strategies will be to encourage undergraduate students by exposing them to these new technologies early on. Seoul National University has been offering a course named Structural Information Engineering at the undergraduate level since 2004. At the beginning it was intended to emphasize experiments but soon it evolved into an introductory course for intelligent structural systems. The students were provided with opportunities to become acquainted with sensor technologies, control theory, remote monitoring, and even robotics. In addition to the course, the university decided in fall 2006 to help students organize an undergraduate student society for research on intelligent structural systems. The society’s members will engage in the research and study of intelligent structures and systems (Kim 2007). They will share information, knowledge and experience with each other and make them available to their fellow students and future students. As part of the curriculum development plan for smart structures technology, a course titled “Smart Structural Systems” was taught in the Spring’06 semester in the Department of Civil & Environmental Engineering at Lehigh University (Zhang 2007). The
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technology transfer, and professionals through workshops, special sessions in professional conferences and publication in journal publications. To ensure the continual progress and success of smart structures technology, and its broad impacts on the society, educators and professionals worldwide need to make active efforts in promoting the education in smart structures technology. To effectively convey the technology to students and practicing engineers, hands-on experiments are very useful tools. The result of a recent international student survey revealed the need for introducing smart structures technology to engineering curriculum, which is important to ensuring the continued development of innovative structural systems for the world’s future. Special sessions on smart structures education such as the invited session titled “Educating next-generation engineers on smart structures technology” will provide important forum for educators and researchers in the integrated engineering field of smart structures technology to exchange and share experience in curriculum development in this area.
for non-EE undergraduates at University of South Carolina. Structural control is one realization of smart structure technology that has been shown to have great promise in reducing unwanted structural vibrations resulting from dynamic loads. The talk given by Christenson et al. (2007) discussed the usefulness of the coupled building experiment for teaching students structural dynamics, control and the connected-control method. Specifically it will highlight how coupled building experiments at Nihon University in Japan have been utilized as an international learning experience undergraduate US researchers over the past five summers. The cyberinfrastructure of NSF-sponsored Network for Earthquake Engineering Simulation (NEES) can be tailored to provide teleoperation and teleparticipation of bench-scale instructional shake tables to help educate future civil engineers. The paper by Dyke et al. (2007) discussed the establishment of a collaboratory of bench-scale instructional shake table deployment sites that provide for real-time online laboratory experiments leveraging the unique capabilities of the NEES initiative to offer laboratory experiences previously unavailable to undergraduate students. Their paper also described initial laboratory exercises developed to educate students in the fundamentals of earthquake engineering (e.g. structural engineering, structural dynamics) as well as introducing them to emerging technology and multidisciplinary tools which promise to revolutionize civil engineering. Research on Structural Health Monitoring (SHM) is highly multi-disciplinary, requiring the researchers to have a broad knowledge on subjects traditionally falling under the category of aerospace/structural/ mechanical engineering, materials science, electrical engineering, computer science, etc. The paper by Huang (2007) presents the course materials developed for a new graduate course on SHM. The course materials can be grouped into five course modules, fundamentals of SHM, vibration-based damage detection, strain-based damage detection, life prediction, and structural health reasoning. Special emphasis is given to optical fiber sensors and acoustic techniques for damage detection. Computer simulations are heavily utilized to help student visualizing how the measurement parameters change as damages are developed in the structures. 5
ACKNOWLEDGEMENT The research work described in this paper was partially supported by the National Science Foundation under Grant No. CMS-0546963 (program directors: Dr. S.C. Liu and Dr. Elizabeth VanderPutten). Encouragement from Dr. Bill Spencer and Dr. Masayoshi Tomizuka to purse smart structures education is also appreciated. The authors are also grateful to the Pennsylvania Infrastructure Technology Alliance and Lehigh University for providing additional financial support for this research. However, the findings, opinions and conclusions expressed in this paper are solely those of the writers and do not necessarily reflect the views of the sponsors. REFERENCES Christenson, R., Loebach, L., Seto, K. & Watanabe, T. 2007. Connected Control Method Experiment as an International Benchmark in Smart Structures Education. Proc. World Forum on Smart Materials and Smart Structures Technology (SMSST’07), Chongqing & Nanjing, China, May 22–27, 2007. Dyke, S., Jiang, Z. & Christenson, R. 2007. Teleoperation and Teleparticipation of Instructional Shake Tables. Proc. World Forum on Smart Materials and Smart Structures Technology (SMSST’07), Chongqing & Nanjing, China, May 22–27, 2007. Giurgiutiu, V. & Yu, L. 2007. Impact of Mechatronics and Smart Structures on Engineering Education. Proc. World Forum on Smart Materials and Smart Structures Technology (SMSST’07), Chongqing & Nanjing, China, May 22–27, 2007.
CONCLUSION
This paper describes recent education efforts in smart structures technology. In addition to curriculum development, education efforts also include outreach activities to students, engineers (short course and workshop), policy makers and industry through
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Huang, H. 2007. Course material development for a graduate course on structural health monitoring. Proc. World Forum on Smart Materials and Smart Structures Technology (SMSST’07), Chongqing & Nanjing, China, May 22–27, 2007. Kim, J. 2007. Student society for research on intelligent structural systems at SNU. Proc. World Forum on Smart Materials and Smart Structures Technology (SMSST’07), Chongqing & Nanjing, China, May 22–27, 2007.
Zhang, Y. 2007. Experience in introducing smart structures technology into civil engineering curriculum by Professor Zhang, Proc. World Forum on Smart Materials and Smart Structures Technology (SMSST’07), Chongqing & Nanjing, China, May 22–27, 2007. Zhang, Y. & Lu, L.W. 2008. Introducing Smart Structures Technology into Civil Engineering Curriculum: Education Development at Lehigh University. ASCE Journal of Professional Issues in Engineering Education & Practices, in press (to appear in January 2008 issue).
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Bilateral teleoperation in physical support for human Kouhei Ohnishi Keio University, Japan
ABSTRACT: Robots and intelligent machines in future should be autonomous in open situation to realize physical support for human. Since they intend to adapt themselves to unstructured environment, more complicated behaviors are needed. Controlled touching motion is one of the most important actions for the purpose. Haptics for real-world will treat such issues. Teleoperation with haptic realization will be a future target. Touching motion is inherently bilateral, since an action is always accompanied by a reaction. That means the artificial realization of touching needs very fast controller to keep the time-delay as small as possible. Not only time delay but also frequency range of force signal is important for vivid sensation. The acceleration controller brings wide-band controller which satisfies above requirements. The bilateral control with high transparency realizes the haptic database. By using bilateral preservation of action and reaction, it is possible to realize the individual’s skill acquisition, skill training, skill transfer to the robots, haptic broadcasting, and so on. Furthermore, in order to support for human activities in remote environment, bilateral teleoperation over Internet is also one of the important issues. The paper shows that the acceleration-based bilateral teleoperation with a disturbance observer has robustness against even the communication delay.
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INTRODUCTION
Robots and intelligent machines in future should support human physically. Additionally, the physical support by them must be based on individual’s “action” and “sensation”. For such a physical support, it is necessary to realize “action-based” recognition in the real environment rather than “model-based” recognition. They should communicate the environmental information in harmony with the individual’s “sensation” to him. These relationship among human, robots, and the real environment is able to be represented as Figure 1. Robots and intelligent machines should act as an interface between a human and an environment as Figure 2. From this point of view, real-world haptics will be one of the key-technologies for the realization of physical support for human based on human’s action and sensation. This is because that haptic sensation is important for human activities as well as auditory sensation and visual sensation. Directional property of human sensation is shown in Figure 3. Auditory and visual sensations are unilateral information whereas haptic information (touching sensation) is bilateral information of action and reaction. To obtain and transmit the haptic information, a bilateral control is necessary. A bilateral teleoperation
Figure 1. Relationship among human, robot, and real environment.
Figure 2. Human activity with device.
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machines to adapt themselves to the unstructured environment. Moreover, the bilateral control with high transparency realizes the haptic database. It is able to preserve not only the environmental information but also the individual’s action as a personal history. This will achieve the personal database based on haptic information. The bilateral preservation may realize the individual’s skill acquisition, skill training, skill transfer to the robots, haptic broadcasting, and so on. Additionally, in order to expand the bilateral teleoperation to remote support for human activities, bilateral teleoperation over Internet is also one of the important issues. However, the communication delay must be a serious problem for the purpose. Then, acceleration control based bilateral teleoperation with a disturbance observer has robustness against even the communication delay. From the point of view, this paper introduces some ideas to deal with these important issues for realization of bilateral teleoperation in physical support for human. This paper is organized as follows. The following section discusses bilateral “action-based” recognition of the environment and the spatial mode transformation by DFT matrices. In section 3, abstraction method of human action as haptic database is described. Section 4 shows the teleoperation with time delay. At the last section, some concluded remarks are described.
Figure 3. Directional property of human sensation.
2 Figure 4. Sensory substitution by physical agent.
BILATERAL RECOGNITION OF REAL ENVIRONMENT
2.1 Environmental recognition system is composed of a master system and a slave system as Figure 4. A human operator manipulates a master system, and a slave system contacts with the real environment through bilateral control. In bilateral teleoperation, “transparency” is one of the important indices. There are two kinds of transparency; time-domain transparency and spatial transparency. A bilateral teleoperation that has high timedomain transparency transmits wideband force feedback. To attain wideband force feedback, a bilateral teleoperation based on acceleration control is necessary. On the contrary, a bilateral teleoperation with high spatial transparency is able to extract the spatial information of the real environment at many contact points. This extraction of the environmental spatial information is called quarry of environmental “modes”. To obtain high spatial transparency, a bilateral teleoperation must extract a lot of environmental modes. Then, through the bilateral teleoperation with high “transparency”, a human operator is able to feel vivid haptic information from the real environment. This is also important for robots and intelligent
The section introduces the environmental recognition. The environmental recognition is classified as follows. •
Unilateral recognition for motion planning – model-based – feed forward – soft real-time system • Bilateral recognition for real-time action – action-based – feedback – hard real-time system Touching motion is inherently bilateral, since an action is always accompanied by a reaction. That means the artificial realization of touching needs very fast feedback controller to keep the time-delay as small as possible. 2.2
Discrete fourier transform
In this section, recognition of environment in contact motion is described. The environment may have infinite modes. On the contrary, a robot has finite number
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Figure 5. Shape of end-effectors.
Figure 7. Environmental recognition (face-to-face contact).
Figure 6. Parallellink manipulator.
The inverse discrete Fourier transformation (IDFT) is shown in (8)
of degree-of-freedom (DOF) for its motion. It is necessary for motion controller to obtain information from the environment at least to the extents of DOF [1]. Figure 5 shows various shapes inscribed in a circle of planar end-effectors. In this paper, discrete Fourier transform (DFT) matrices are introduced [2] to decompose the environmental information. Here, G, g, W and N are the transformed value, initial value, a rotator, and an arbitrary number, respectively. The definition of the DFT is described as follows,
In (8), FN∗ is a complex conjugate matrix of FN . 2.3 An example of real environmental recognition In this subsection, an example of real environmental recognition is shown. The experiment is done using a parallel-link manipulator shown in Figure 6. The robot has a planar end-effector with 3 supporting points. The end-effector contacts the unknown environment. The environmental modes are extracted based on the DFT. As a result, the environmental profile is abstracted as the environmental modes. Figures 7 and 8 show the experimental results in the case of face-to-face and face-to-point contact, respectively. In each figure, we define the graphs (c) and (d) as surface profile. The end of arm A, B and C were given sinusoidal wave as command value of z direction, and each command is out of phase by
The DFT is expressed as the following matrix F N
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Figure 8. Environmental contact).
recognition
(face-to-point
Figure 10. Robust bilateral control system.
ability of spatial transparency depends on its DOF or number of sensing points. 3.2 Bilateral control for haptic database In bilateral control, the goal of force for artificial realization of the “law of action and reaction” between the master system and slave system is represented as (9);
On the other hand, the goal of position for tracking of the master system and slave system each other is represented as (10); Figure 9. Transparency teleoperation.
as
an
index
of
bilateral
In bilateral control, the coinstantaneous achievements of force control and position control are required. However, force control and position control are not able to be realized at the same time in one real axis. In this paper, in order to attain the robustness in the system, (9) and (10) are transformed into the acceleration dimension [3];
2π/3. This active motion of the end-effector is called “groping motion”. Then, the environmental surface profile provided the information about contact condition, position and slope of unknown environment and so on. 3
BILATERAL HAPTIC DATABASE
3.1 Transparency in bilateral teleoperation Transparency is an important index for construction of haptic database. There are two kinds of transparency; temporal and spatial transparencies. In other words, a bilateral control system has its own characteristics as time filter and space filter. Figure 9 represents the relationship among human, robots, and environment from the point of view of the transparency.Transmission of environmental information to human is depends on the bilateral teleoperation system’s ability of transparency. Higher time transparency transmits wide frequency bandwidth of information. On the contrary, higher spatial transparency transmits much environmental information corresponding to modes. However, the physical agent’s
Acceleration control is the best solution to achieve a robust motion control [4]–[8]. The block diagram of the robust bilateral control system is shown in Figure 10. As a result, high reproducibility and high operationality are achieved in acceleration based controller. A parallel multi-DOF haptic system with flexible actuators [9] has been developed as Figure 11. This kind of haptic multi-DOF system may achieve the physical support for the motion of human’s hand. In the future, if preservation technology of human motion is realized through this kind of haptic system, it would also be a key technology for human skill acquisition [10].
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Figure 13. Example of bilateral teleoperation system with time delay.
Figure 11. Haptic telehand system.
Figure 14. Concept of network disturbance (ND).
networks must deal with time delay problem. Time delay in control systems deteriorates the performance and possibly destabilizes the system. Furthermore time delay over internet is usually time-varying. The timevarying behavior also affects the performance and the stability of the system. In this section, time delay compensation method in bilateral teleoperation systems based on the concept of network disturbance (ND) and communication disturbance observer (CDOB) is presented [13]. Firstly, the concept of ND is introduced using a simple example of bilateral teleoperation system. Then, time delay compensation method by CDOB is described. The validity of the proposed method is verified by results of bilateral teleoperation experiment over Internet between Japan and Slovenia.
Figure 12. Applications of Bilateral Haptic Database.
3.3 Applications of bilateral haptic database A development of bilateral haptic database may also be an important challenge for realization of human support. Through the bilateral control with high transparency, not only environmental information [11], but also the individual’s motion or skill as a personal history [12] is able to be preserved into the bilateral haptic database. Then, it may achieve a lot of kinds of physical support for human activities, such as the haptic e-learning, the individual’s skill acquisition, the skill training, the skill transfer to the robots, the haptic broadcasting, and so on. Figure 12 shows the example to the application of bilateral haptic database. Real-world haptics like a bilateral teleoperation is a newborn technology, and it has a huge potential for development. Thus, a wide variety of researches are prospective. 4
4.1 Concept of network disturbance (ND) Figure 13 shows a simple example of bilateral teleoperation system with time delay. The feedback signal to master side sXe−Ts (T = T1 + T2 ) is delayed by time delay on communication line. The time delay elements affect both the performance and the stability of the system. Here, Figure 14 is an equivalent transformation of Figure 13. In Figure 14, although feedback signal to master side is delayed, there is no time delay element
BILATERAL TELEOPERATION OVER INTERNET
This section presents bilateral teleoperation over Internet. Generally, teleoperation over long-distance
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Figure 15. Schematic diagram of time delay compensation.
Figure 17. Manipulator in Slovenia.
Figure 16. Manipulator in Japan.
on communication line. Instead of time delay, there exists ND described as follows;
In fact, it can be regarded that the feedback signal is delayed by not time delay but ND. This is the concept of ND.
Figure 18. One way delay time.
experiment over Internet between Japan and Slovenia was conducted. In this section, the experimental setup is firstly introduced. Then experimental results over internet demonstrate the validity of the proposed method.
4.2 Time delay compensation ND is estimated by CDOB and the estimated ND is utilized for time delay compensation. Figure 15 illustrates a schematic diagram of time delay compensation based on the concept of ND and CDOB. Since feedback signal to master side is not delayed any more, it turns out that time delay compensation is achieved. Furthermore, the time delay compensation method has a distinctive characteristic for bilateral teleoperation over Internet. The method does not need delay time model (most of predictive methods like Smith predictor need delay time model). Therefore it can be applied to the case of time-varying delay. 4.3
4.3.1 Experimental setup Manipulators of both master side (Japan) and slave side (Slovenia) are shown in Figures 16 and 17, respectively. Both manipulators are 1 DOF (degree-offreedom) rotary manipulators. Bilateral information transmission of control signals was executed using TCP/IP protocol. The measured one way delay time on communication line was as shown in Figure 18. Figure 18 shows that time delay was constantly timevarying.
Experiment
4.3.2 Experimental results Figure 19 shows a position response. The dashed circles in the figure mean that slave manipulator has
For the verification of the validity of proposed time delay compensation method, bilateral teleoperation
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•
Action-based recognition is possible by the DFT for environment. It is immediately fed back to upperlevel in order that human and/or robot is more adaptive to environment. • Vivid tactile and/or force sensation is possible in the haptic telehand robot. Experimental robot realizes wide frequency response for good force reproducibility. • The information of environment in real-world haptics is real-time. Time delay is compensated by communication delay observer even if it includes jitter.
REFERENCES Figure 19. Position response.
[1] S. Katsura, K. Ohnishi: “Quarry of Modal Information from Environment for Advanced Motion Control,” IEEJ Transactions on Industry Applications, Vol. 126-D, No. 4, pp. 372–378, April, 2006. [2] R. Kubo, K. Ohnishi: “An Extraction Method of Environmental Surface Profile Using Planar End-Effectors,” Proceedings of the 9th IEEE International Workshop on Advanced Motion Control, AMC’06ISTANBUL, Vol. 1, pp. 368–373, March, 2006. [3] S. Katsura,Y. Matsumoto, K. Ohnishi: “Realization of “Law of Action and Reaction” by Multilateral Control,” IEEE Transactions on Industrial Electronics, Vol. 52, No. 5, pp. 1196–1205, October, 2005. [4] K. Ohnishi, M. Shibata, T. Murakami: “Motion Control for Advanced Mechatronics,” IEEE/ASME Transactions on Mechatronics, Vol. 1, No. 1, pp. 56–67, March, 1996. [5] A. Sabanovic: “Sliding Modes in Power Electronics and Motion Control Systems,” Proceedings of the 29th IEEE Annual Conference of the IEEE Industrial Electronics Society, IECON’03-ROANOKE, pp.997–1002, November, 2003. [6] A. Sabanovic, S. Khan, C. Onal: “Hybrid Motion Controller – SMC Point of View,” Proceedings of the IEEE International Symposium on Industrial Electronics, ISIE’05DUBROVNIK, pp. 1483– 1488, June, 2005. [7] M. Tomizuka: “Sensors in the Engineering of Modern Mechatronic Systems,” Proceedings of the 3rd IFAC Symposium on Mechatronic Systems, MECHATRONICS’04SYDNEY, pp. 19–24, September, 2004. [8] M. Tomizuka: “Intelligent Power Assist Systems: Mechatronic Systems Auto-Adaptive to Varying Human Characteristics and Environmental Conditions,” Proceedings of the 2006 IEEE International Conference on Mechatronics and Automation, pp. nil19–nil20, June, 2006.
Figure 20. Force response.
contact to the environment. It turns out that the system was not destabilized by time delay and accurate position tracking was achieved. Besides, force response is shown in Figure 20. Figure 20 demonstrates that contact force from the environment was successfully transmitted bilaterally. These experimental results illustrate that the proposed time delay compensation method sufficiently compensated time delay effect even in the case of time-varying delay.
5
CONCLUDED REMARKS
•
Real-world haptics will realize human support engineering. • Human, robot and environment have unilateral and bilateral relation corresponding model-based and action-based recognition respectively. The relation is evaluated by using both space filter and frequency characteristics.
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[9] K. Tsuji, Y. Soeda, H. Nagatomi, M. Kitajima, Y. Morikawa, S. Ozawa, T. Furukawa, Y. Kawai, K. Ohnishi: “Free Allocation of Actuator against End-Effector by Using Flexible Actuator,” Proceedings of the 9th IEEE International Workshop on Advanced Motion Control, AMC’06ISTANBUL, pp. 329–333, March, 2006. [10] S. Katsura, T. Suzuyama, K. Ohishi, K. Ohnishi: “Motion Acquisition and Reproduction of Human Hand by Interaction Mode Control,” Proceedings of the IEEE International Symposium on Industrial Electronics, ISIE ’06 MONTREAL, Vol. 4, pp. 3136–3141, July, 2006. [11] T. Shimono, S. Katsura, K. Ohnishi: “Abstraction and Reproduction of Force Sensation from Real
Environment by Bilateral Control,” IEEE Transactions on Industrial Electronics, Vol. 54, No. 2, pp. 907–918, April, 2007. [12] T. Shimono, S. Katsura, K. Ohnishi: “A Realization of Haptic Skill Database by Bilateral Motion Control,” Proceedings of the 32nd Annual Conference of the IEEE Industrial Electronics Society, IECON’06 PARIS, pp. 5252–5257, November, 2006. [13] K. Natori, T. Tsuji, K. Ohnishi, A. Hace, K. Jezernik: “Robust Bilateral Control with Internet Communication,” Proceedings of the 30th Annual Conference of the IEEE Industrial Electronics Society, IECON’04 BUSAN, Vol.3, pp. 2321–2326, November, 2004.
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World Forum on Smart Materials and Smart Structures Technology – Spencer Jr (ed) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Research of smart materials and structures at NUAA Jinhao Qiu The Aeronautical Key Laboratory for Smart Materials & Structures, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, China
ABSTRACT: The research activities of the Aeronautic Science Key Lab for Smart Materials and Structures, Nanjing University of Aeronautics and Astronautics are introduced. The research fields include structural health monitoring, structural vibration reduction and noise suppression, adaptive wing and smart rotor, sensor and actuation technology, functional materials and devices, and system integration and measurement technology. Three fields of research are introduced in detail. The first field is the structural health monitoring (SHM). Research subjects includes hybrid structural health monitoring using FBG sensors and piezoelectric sensors, wireless sensor network, multi-agent based distributed SHM technology, and braided composites with embedded optic fibers. The second field introduced is development of high-performance piezoelectric materials using a hybrid sintering process consisting of microwave heating and hot-press. This approach is applied to the fabrication of PZT and PNN-PZT materials and their properties were improved significantly. The third field introduced is the development of high-performance piezoelectric devices, including functionally graded piezoelectric actuators and piezoelectric fibers. The functionally graded piezoelectric actuators are fabricated by gradually changing the piezoelectric and dielectric properties of the materials in the thickness direction of the actuator.
1
INTRODUCTION
At present, the Laboratory has 7 professors, 3 associate professors, 1 engineer, about 30 Ph.D. students and more than 80 master students. The Lab has more than 2500 m2 of space and has received 8 million RMB fund for purchase of new experimental equipment and apparatus for the 5-year period from 2006 to 2010. The average yearly research fund from the government and industry is more than two million RMB. The researchers in the key lab have undertaken more than 30 important projects in recent years, including two key projects funded by the National Natural Science Foundation. They have also received one national invention award, one national excellent teaching award and twelve provincial and ministerial awards for their innovative and excellent research. Over four hundreds technical papers have been published. Academic relationships have been established with corresponding labs in China, USA, Germany, Japan, France and India for exchanges and collaborations. In the next three chapters, three research fields of the laboratory are introduced. The first field is the structural health monitoring (SHM). Research subjects includes hybrid structural health monitoring using FBG sensors and piezoelectric sensors, wireless sensor network, multi-agent based distributed SHM technology, and braided composites with embedded optic fibers. The second field introduced is development of high-performance piezoelectric
The Aeronautical Science Key Laboratory for Smart Materials & Structures at Nanjing University of Aeronautics and Astronautics (NUAA) is the only ministerial-level key laboratory in China at present, which is specialized in smart materials and structures. In 1991, a multidisciplinary research team was organized at NUAA to carry out research in the new field of smart materials and structures. With the development of the team, a key laboratory was established by the former Aviation Industry Corporation of China (AVIC) in 1997 to further promote research in this important field. After ten years of development, the key lab has further extended its research fields, which include structural health monitoring, structural vibration reduction and noise suppression, adaptive wing and smart rotor, sensor and actuation technology, functional materials and devices, and system integration and measurement technology. Important resources and advanced experimental facilities in the Key Lab include testing system for optical fibers, damage detection systems such as C-scan and acoustic emission systems for composite materials, MTS tensiontorsion testing machine, structural dynamic analysis system (LMS), data acquisition system, ferroelectric analyzer (TF-2000), testing system for adaptive wing models, and testing system for smart rotors, etc.
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method are realized. Adopting the hybrid monitoring system, the strain field and the temperature field are monitored. The strain distribution was obtained when the wing box is under torsion and bending load. Adopting the hybrid monitoring system, based on PZT sensor array and active wave technique, combined with advanced signal processing method such as time reversal, damage diagnosis is realized. Based of the PZT sensor network, to realize multiple test channels for lamb wave monitoring, any of the PZT sensors can be assigned to act as the actuator or receiver by the computer to excite or sense the lamb wave signal. The damage monitoring process is controlled by an integrated sensor array scanning and damage diagnostic system including hardware and diagnostic software. 2.2 Wireless sensor network for SHM Though the wing box demonstration research is successful, some problems are presented. The key problem is for the big structure, the number of sensors is big and sensor information is tremendous. It is a great challenge for the central computer to sample and process all these data in an acceptable speed. Another problem is when density sensors are adopted, the wires to connect them increase, causing the weight of the whole monitoring system increasing greatly. This is not allowable in lots of application areas, especially in the aircraft. Hence to reduce the weight of the sensor networks, to coordinate and manage the density sensor networks, to fuse the information from different kinds of sensors to take advantage of different estimation methods to make a reliable estimation of the whole structure in an acceptable speed is still a challenge. The distributed structural health monitoring technology for large-scale engineering structures based on smart sensor and multi-agent technology is discussed. By adopting wireless smart sensor with embedded microprocessors, portion of signal processing and computation can be done locally and simultaneously [3]. The amount of information needs to be transmitted over the network will be reduced greatly and the system speed will be improved. Besides, if the smart sensor adopts the wireless communication links, information can be communicated in a wireless way which will reduce the weight of the sensor network, thus facilitate densely distributed sensing. Our research is to develop wireless sensor node suitable for SHM requirements: small size, low power, integrated for SHM. Fig. 2 shows the wireless sensor node developed in the Laboratory. When the encapsulation for SHM is considered, the wireless sensors are easily connected with PZT and strain gauge. To monitor the different kinds of damage in the structure efficiently, the robust wireless sensor network protocol need to be researched.
Figure 1. Health monitoring of a wing box.
materials using a hybrid sintering process consisting of microwave heating and hot-press. This approach is applied to the fabrication of PZT and PNN-PZT materials and their properties were improved significantly. The third field introduced is the development of high-performance functionally graded piezoelectric actuators. The functionally graded piezoelectric actuators are fabricated by gradually changing the piezoelectric and dielectric properties of the materials in the thickness direction of the actuator.
2 2.1
STRUCTURAL HEALTH MONITORING Health monitoring of a Wing box
A hybrid wing box health monitoring system as shown in Fig. 1(a) was developed based on hybrid piezoelectric sensor array and Bragg grating sensor array [1, 2]. Wing box is an important part of the aircraft structure. The wing box is made of carbon fiber composite material. The PZT sensors and the optic fiber sensors are arranged on the skin. To make it easy to arrange the sensor array and ensure the arrangement process of each element to be the same, the smart layers are manufactured. The arrangement of the sensor array distribution is shown in Fig. 1(b). A PZT-Fiber integration health monitoring system is developed. Piezoelectric sensor array based active lamb wave diagnostic method and Bragg grating based structural strain monitoring
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Figure 4. Braided composite with optical fiber.
study to evaluate the efficiency of the proposed MAS based SHM system design and the advantages of the MAS based SHM system. Comparing to past system, many advantages can be obtained. The system can deal with geographically distributed networks, fuse different kinds of sensor data and give an efficient evaluation result of the large structure using uncomplicated logic; through collaboration, the structure damage can be identified automatically; useless data can be automatically discarded; using the agent learning ability, the sensor performance shifting and the influence from environment parameters can be eliminated.
Figure 2. Health monitoring network using wireless sensors.
2.4 Braided composite with optical fiber 3-D braided composite technology has stimulated a great deal of interest in the world at large [5]. Impacts from hail, debris, tools, etc. can delaminate conventionally-laminated composites because of the relatively weak resin interface between laminae. The through-the-thickness or interlacing reinforcement in braided composites has the potential to reduce or even eliminate delamination and thus reduce or eliminate strength degradation due to accidental damage. In addition, braided composites will potentially cost less than traditional laminated composites that are fabricated with unidirectional tape, because a 3-D, fully integrated structure can be directly fabricated into various structural shapes by adopting 3-D braiding technology, which does not require fiber cloth tailoring and layering.A reliable understanding of the properties of 3-D braided composites is of primary importance for the successful utilization of these materials. A new method was proposed to study the mechanical performance of braided composite materials using embedded fiber optic sensors, as shown in Fig. 4. Experimental research is performed to devise the methods of incorporating the optical fiber into a 3D braided composite structure. To validate the ability
Figure 3. Multi-agent system for SHM.
2.3
Multi-agent system
The multi-agent system (MAS) as shown in Fig. 3 was developed to coordinate the distributed, diverse, heterogeneous wireless sensor information for large structures [4]. Multi-agent system is viewed as a crucial technology not only for effectively exploiting the increasing availability of diverse, heterogeneous and distributed information sources, but also as a framework for building large, complex and robust distributed information processing systems which exploit the efficiencies of organized behavior. Multi-agent system based SHM system architecture is designed. A MAS based composite SHM system is studied as a case
65
of the optic fiber to withstand the manufacturing process, the optical performance of the optic fiber is first studied before and after incorporation into the 3-D braided composites, and also after the entire manufacturing process of the 3-D braided composites. Also the method is used to monitor the molding process, such as Rein Transfer Molding (RTM) process. Using the braided fiber sensor, the mechanical performance of the material and mechanism of the damage failure were studied. Experiments were conducted to measure interval strain under loading condition of tension and bending in the 3-D carbon fiber braided composite specimens, both locally and globally. Experimental results show that multiple fiber optic sensors can be braided into the 3-D braided composites to determine its mechanical properties, providing a more accurate measurement method and leading to a better understanding of these materials. 3
Wave- guide Cooling water Gas inlet
Viewing port
Sample
Die
Platinum thermocouple
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700
Figure 5. Schematic diagram of microwave and hot-press hybrid sintering apparatus.
furnace and the hydraulic press subsystem can deliver the maximum force of 49 kN. The die used in the hot-press accessory was made from alumina. Alumina lagging is also placed around the die to avoid heat dissipation. The preliminarily formed samples were covered with zirconia powders to prevent them from sticking to the alumina die.
MICROWAVE AND HOT-PRESS HYBRID SINTERING PROCESS
In order to improve the performance of PZT actuators, several processes including a hybrid sintering process and a hydrothermal process for synthesizing powders, were developed. The hybrid sintering process, which is the combination of 28 GHz microwave sintering and hot-press, was applied to the sintering of PZT actuators with the optimal sintering conditions [6, 7]. Due the rapid and uniform heating of the samples in microwave sintering process, the sintering time was reduced to about 1/8 of the time needed for the traditional technology. On the other hand, shorter sintering time results in less evaporation of Pb in the sintering process. The density of sintered samples was higher than 99% of the theoretical density due to high pressure of hot-press. The measurement results showed that the electromechanical coupling factor was increased significantly and the piezoelectric constants could be improved by nearly 40% with the hybrid process. In this chapter, the hybrid sintering and its application are introduced. 3.1
f641 f591
Alumina rod
3.2 Preparation of sintering specimens The PZT specimens used in the study were made from PZT powder C82 developed by Fuji Ceramics Corporation. These powders was compacted into specimens of two different shapes with cold press under 200 MPa, one of which is a disk with the diameter of 17 mm and thickness of 15 mm and the other is a plate of 55 mm long, 35 mm wide and 20 mm thick. The binder of the specimens was burned out at 700◦ C for five hours. The specimens in disk shape were prepared for the measurement of piezoelectric properties and observation of microstructure, and those in plate shape were used for vibration test. The specimens were sintered with both the hybrid sintering process and the conventional sintering process for the comparison of performances. In conventional sintering process, the surface temperature of the specimens is higher than internal temperature, since they are heated from the outside. However in the case of microwave sintering, the internal temperature is higher than surface temperature, since they are uniformly heated theoretically and the surface temperature becomes lower due to heat dissipation. In the hybrid sintering process, a number of specimens were stacked vertically and sintered together. The temperature of the specimens was measured with a platinum thermo- couple, the measurement error of which was less than 5◦ C. In order to measure the internal temperature, a hole of 5 mm in diameter and 1.5 mm in depth was made on the bottom specimen of the stack and the end of the thermo-couple was inserted into the hole. The measured temperature was used in the feedback control of the output power
Principle of microwave sintering process
The hybrid sintering apparatus of microwave and hotpress used for the sintering of the PZT ceramics is schematically illustrated in Fig. 5. The applicator of the microwave sintering furnace is connected to the 28 GHz gyrotron, the power of which is 10 kW, capable of heating specimens up to 2000◦ C. The typical dimensions of the applicator are 600 mm in diameter and 900 mm in length, which allows a volume of 300 mm (diameter) by 300 mm (height) in the applicator to offer spatially uniform distribution of wave field. On the other hand, the hot-press accessory is mounted in applicator of the microwave sintering
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Figure 6. Temperature and pressure schedules of hybrid sintering process.
of the microwave generator to ensure the temperature of the specimens in agreement with the scheduled temperature of the sintering process. The temperature scheduling of microwave sintering process and the pressure scheduling of hot-press are shown in Fig. 6. In the hybrid sintering process, the temperature of specimens was raised from the room temperature to the sintering temperature at the rate of 6000◦ C/hour, maintained for 30 minutes and then cooled at the same rate as that of the heating phase. The whole cycle of the hybrid sintering process should have taken about two hours. However, the temperature of specimens decreases much more slowly than the scheduled rate due to the lack of forced cooling and the actual sintering process took about 7 hours. Sintering temperatures between 1100◦ C and 1250◦ C were tried at the step of 50◦ C in the experiment. The pressure of hot-press was raised to the predetermined value (20 MPa or 40 MPa) when the temperature of the PZT specimens was maintained at the maximum sintering temperature. 3.3
Figure 7. The SEM photographs of microstructure of hybrid and conventional sintered specimens.
bath with a DC filed of 2 kV/mm and oil temperature of 170◦ C for 30 minutes, and then cooled down to 50◦ C in the field. The dielectric constants of the polarized specimens were measured at the frequency of 1 kHz. The electromechanical coupling factors kp and k31 and the frequency constant Np were determined by the resonant-antiresonant frequency method with a HP4194A impedance analyzer. The elastic compliance E coefficient S11 , piezoelectric constant d31 , and the frequency constant Np are calculated from the following formulas:
Evaluation of properties
The surfaces of the specimens sintered with the hybrid sintering process were polished in a polishing machine and the thickness was reduced to 1 mm from the original thickness of 1.3 mm. The density and porosity of the specimens were measured with the Archimedes technique using water. The phase structure of the specimens was established by X-ray diffraction (XRD) using CuKα. Furthermore the sintered specimens were mirror-polished and chemically etched in 30% HNO3 solution added with several drops of HF. The microstructure of etched surface of the specimens was observed under scanning electron microscope (SEM), and the grain size was measured with linear intercept method. The specimens for the measurement of kp were disks of 15 mm in diameter and 1 mm in thickness, while the specimens for the measurement of k31 were plates of 12 mm long and 3 mm wide cut from the disks. After sputtered with gold electrodes on both surfaces, specimens were polarized in a silicon oil
where fs is the resonance frequency, is length of specimens, d is diameter of specimens, and ε0 is dielectric constant in a vacuum. The same measurements were also performed for specimens of the same shape fabricated with conventional sintering process. The measurement results are used in the comparison to show the improvement of performances due to the new sintering process. The dependence of the grain size of the specimens on the sintering temperature was also investigated. The SEM microstructures are shown in Fig. 7 (a) and (b) for specimens of the hybrid sintering process and in Fig. 7 (c) and (d) for specimens of the conventional sintering process. It can obviously seen that the average
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Figure 8. Density and grain size.
Figure 9. Electromechanical coupling factor.
grain size of specimens of the hybrid sintering process, which is about 4 µm for the sintering temperature of 1250◦ C, is larger that that of the specimens of conventional sintering process. It can also be seen from Fig. 7 (a) and (b) that the average grain size increases with the sintering temperature. For the conventional sintering process, only porous specimens can be obtained at 1150◦ C as shown in Fig. 7 (c), but pores were significantly reduced when sintered at 1250◦ C, as shown Fig. 7 (d). For the hybrid sintering process, specimens with few pores can be obtained even at 1150◦ C as shown in Fig. 7 (a). Fig. 8 illustrates the dependence of the density and grain size of the specimens on the sintering temperature of the hybrid sintering process and the conventional process. The theoretical density of the material is 7.75 g/cm3 . The density of the specimens fabricated with hybrid sintering process was larger than that of conventionally sintered specimens when the sintering temperature was above 1100◦ C. For the conventionally sintered specimens, the density increases with sintering temperature below 1250◦ C but decreases slightly over 1250◦ C while the grain size increases with sintering temperature in the whole considered temperature range. For the specimens of hybrid sintering process, no strong correlation was observed between the density and grain size. Figs. 9 and 10 show the electromechanical coupling factor kp and the piezoelectric constant d31 as functions of the sintering temperature. The d31 and kp of the specimens of the same sintering process exhibit very similar tendency of variation. Moreover, The d31 and
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Figure 10. Piezoelectric constants.
kp of the hybrid-sintered specimens are much larger than those of the conventionally sintered specimens. The maximum value of kp of hybrid-sintered specimen, achieved at the sintering temperature of 1250◦ C, is approximately 75%, and the maximum value of d31
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of the same specimen, achieved at the same sintering temperature, is about 360 × 10−12 m/V, nearly 40% larger than 260 × 10−12 m/V, the d31 of conventionally fabricated specimens. If the curves of d31 and kp are compared with those of grain size in Figure 2.4, it can be concluded that the increase of both d31 and kp is attributed to the increase of grain size in the specimens. In the conventional sintering, the percentage of pore usually increases with increasing grain size so that the piezoelectric constant d31 and coupling factor kp decrease. However, the grain size was increased without increasing pores in hybrid sintering process due to the rapid and internal heating. 4
Figure 11. Mechanism of bending deflection.
FUNCTIONALLY GRADED PIEZOELECTRIC ACTUATORS
Pb(Ni1/ Pb( 1/3Nb2/ 2/3)O3
The conventional bimorph actuators are manufactured by bonding two piezoelectric elements to a metal shim layer. Due to discontinuity of material properties, stress concentration, which is the cause of delamination and cracks, is generated at the interfaces between the PZT layers and the shim layer. In order to improve the reliability of PZT bending actuators, a new type of functionally graded (FG) PZT bending actuator was designed and fabricated. The material compositions with different dielectric and piezoelectric constants were selected from the PNN-PZ-PT (Pb(Nb1/3 Ni2/3 )O3 − PbZrO3 − PbTiO3 ) family and used as the four layers in the new FG PZT actuator [8,9,10]. The piezoelectric constant and dielectric constant were graded oppositely in the thickness direction. Stress distribution of the FG PZT actuator under external voltage was analyzed using FEM and the simulation results showed the stress discontinuity in the new actuator is smaller than that of traditional bimorph actuator. Durability test was performed with the fabricated FG PZT actuators and conventional bimorph actuator and the results showed that the durability of the FG PZT actuators is much higher than that of bimorph actuator. 4.1
B
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Figure 12. PNN-PZ-PT family.
but large dielectric constant (material-L) is required. The large dielectric constant can reduce the voltage loss in the low-performance piezoelectric material. As shown in Fig. 11, bending deformation is generated in the actuator with the same mechanism as that of unimorph actuator when a voltage is applied to a two-layer actuator of the two materials. However, large stress discontinuity is also induced in the interface of the two materials. In order to increase the generated deformation, the difference of the material properties of the two layers should be as large as possible. On the other hand, the larger the difference of material properties is, the larger the stress discontinuity is. In order to reduce the stress discontinuity the material properties should be graded smoothly in the thickness direction. But smooth distribution of material properties raises difficulties in the practical fabrication. Hence, a four-layer structure was used in the FG actuator.The material compositions of the four layers were chosen from the PNN-PZ-PT family.
Material compositions and thickness of layers
The authors proposed a new type of functionally graded piezoelectric actuator and illustrated that the stress discontinuity could be significantly reduced in the FG piezoelectric actuator using FEM analysis in the former study. As the task of this research project, the FG piezoelectric actuator was designed and fabricated. To obtain large bending deflection, the combination of a high-performance piezoelectric material with large piezoelectric constants but small dielectric constant (material-H) and a low-performance piezoelectric material with small piezoelectric constants
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Table 1. A B C D
Laser sensor Thermal couple KEYENCE LC2440
Pb(Ni1/3 Nb2/3 )0.5 (Ti0.7 Zr0.3 )0.5 O3 Pb(Ni1/3 Nb2/3 )0.7 (Ti0.7 Zr0.3 )0.3 O3 Pb(Ni1/3 Nb2/3 )0.65 (Ti0.7 Zr0.3 )0.35 O3 Pb(Ni1/3 Nb2/3 )0.6 (Ti0.7 Zr0.3 )0.4 O3
Multi Meter
Material properties. E s11
Power source
d31 (10−12 m/V)
(10−12 m2 /N)
kp (%)
ε/ε0
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Figure 13. Experimental setup for durability test. 1.4
The piezoelectric constants, dielectric constant and coupling factor of 40 compositions in PNN-PZ-PT family shown in Fig. 12 were measured, and four of them were chosen as the materials of the four layers in the FG actuator. The compositions of the four materials are shown in Table 1 and their properties are shown in Table 2. Material A has the largest d31 but smallest ε while material B has the smallest d31 but largest ε. The four materials were laminated in the order of A-D-C-B. 4.2
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Figure 14. Frequency response (Applied signal: white noise; Voltage: 50Vp-p for bi-morph and 100Vp-p for FGM).
applied to the FG actuator is 100 volts and that applied to the bimorph actuator is 50 volts. From the frequency response, the natural frequencies of the FG actuator and bimorph actuators were estimated to be 360 Hz and 335 Hz, respectively. It can further be seen that the structural damping factor of the bimorph actuator is much higher than that of the FG actuator. In order to estimate the damping ratio of the actuators, their free vibration responses were measured and the results are shown in Fig. 15. The estimated damping ratio of the FG actuator is 0.016 while that of the bimorph actuator is 0.086 for the first mode. The high damping ratio of bimorph actuator can be attributed to the material damping of bonding layers as discussed in the later section.
Measurement of performance
Since the internal stress distribution is very difficult to measure, durability was used to evaluate the performance of the actuators. Empirically, improvement of stress distribution and mechanical strength at the interface of layers will suppress the fatigue of the actuator and consequently improve the durability of the actuator. In the durability test, the vibration of a cantilever actuator was excited by a voltage at various frequencies. The size of the FG bending actuators is 42 × 8 × 0.9 mm. As shown in Fig. 13, the displacement of vibration at the free end was measured with a laser displacement sensor (KEYENCE, LC-2440) and the temperature of the actuator was measured near the clamped end by a thermo-couple. The variation of amplitude and temperature with time was recorded by a data acquisition system based on LabView. In order to investigate the influence of vibration amplitude, the test was performed at various frequencies. 4.3
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Table 2.
A B C D
Material compositions.
4.4 Durability at low frequency The FG piezoelectric actuators and bimorph actuator were driven at 20 Hz and 100 Hz, much lower than the resonance frequency. In order to generate bending vibrations of the same amplitude in the actuators, the voltages applied to the FG actuator and the bimorph actuator are set to 500 volts and 80 volts (peak-topeak), respectively. Figure 16 shows the results of durability test at 20 Hz. There is neither obvious temperature rise, nor amplitude drop during the test period
Frequency characteristics and damping ratio
A random signal (white noise) was applied to the actuators for the measure of the frequency response of the FG actuator and the bimorph actuator. The results are shown Fig. 14. The peak-to-peak value of voltage
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4.5 Durability at resonant frequency Durability test was also performed at the respective resonant frequencies of the FG actuators and the bimorph actuators. The peak-to-peak amplitude of the voltage applied to the FG actuator was set to 40 volts while that applied to bimorph actuator was set to 14 volts. The variation of vibration amplitude and actuator temperature was shown in Fig. 17. In spite of lower voltage, the amplitude of vibration is larger than that of former section due to resonance. The amplitude of FG actuator remained constant during the test period of 240 minutes (about 5 × 106 cycles) and the temperature rise was less than 10◦ C. However, the temperature of bimorph actuators rose to about 110◦ C and the amplitude almost dropped to 0 in less than 2 minutes. Even though the amplitude remained at very lower level thereafter, the temperature remained at 110◦ C. The bimorph actuator broke down due to delamination in 25 minutes (about 5 × 105 cycles) after the start of test. Two bimorph actuators and two FG actuators were tested. The average lifetime of the two tested bimorph actuators was 24 minutes, but both the FG actuators did not fail in the test period of 240 minutes. The decrease of vibration amplitude of the bimorph actuators may be attributed to the depolarization of piezoelectric material and the change of vibration characteristics of the actuators. The Curie temperature of the piezoelectric material used in the bimorph
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Figure 17. Results of durability test at resonance. Temperature (°C)
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Figure 16. Results of durability test at 20 Hz.
at this frequency. The bimorph actuator broke down due to cracks in 138 hours (about 107 cycles), while the FG actuators did not break down after 300 hours (2.16 × 107 cycles) of test. The average lifetime of the three bimorph actuators tested was 146 hours, while the lifetime of all the three FG actuators was longer than 300 hours. The amplitude of vibration of both the FG actuators and the bimorph actuators was about 280 µm, a little smaller than the simulation result of about 350 µm. The experimental results also showed that much higher voltage is required for FG actuator to generate the same amount of displacement as conventional bimorph actuators. One of the reasons is that the effective thickness of the FG actuator is much larger than that of the bimorph actuator.
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actuator is 138◦ C but it was found in the experiment that the output strain of the material decreased significantly due to depolarization when the temperature exceeded 60◦ C. Since the tolerable temperature of the bonding material is 120◦ C, the decrease of stiffness of the bonding material due to the temperature rise may also change the resonance frequency of the actuator and thus cause the drop of vibration amplitude though further confirmation is necessary. Delamination of the bimorph actuator can be attributed to the deterioration of the bonding material due to temperature rise, the structural weakness and stress concentration in the bonding interface frequency characteristics and damping ratio.
based on smart wireless sensor and multi-agent technology, Smart Materials and Structures,15(1):1-8–2006. ShenfangYuan,Yingdi Xu and Ge Peng(2004), New developments in structural health monitoring based on diagnostic Lamb wave, Journal of Material Science & Technology, 20(5):490–496. Jian Wu, Shenfang Yuan, A wireless sensor network node designed for exploring structural health monitoring applications, Smart Materials and Structures,16:1898-1906– 2007. Shenfang Yuan, Fahard Ansari, Xiaohui Liu and Yang Zhao(2005), Optic fiber-based dynamic pressure sensor for WIM system, Sensors and Actuators, Sensors and Actuators A: Physical, 120(1): 53–58. Hirofumi Takahashi, Kazuaki Kato, Jinhao Qiu and Junji Tani, Property of Lead Zirconate Titanate Actuator Manufactured with Microwave Sintering Process, Japan Journal of Applied Physics, Vol.40, No.2 (2001), pp.724–727. Hirofumi Takahashi, Kazuaki Kato, Jinhao Qiu and Junji Tani, Fabrication of high-performance PZT actuators using microwave and hot-press hybrid sintering process, Japan Journal of Applied Physics, Vol.40, No. 7 (2001), pp.4611–4614. Junji Tani, Jinhao Qiu and Teppei Morita, High Functionally Graded Piezoelectric Actuators, Trans. of Materials Research Society of Japan, Vol.26 (2001), 283–286. Jinhao Qiu, Junji Tani, Teppei Morita and Hirofumi Takahashi, High Durability of Functionally Graded Piezoelectric Bending Actuators, Proc. Of DETC ’01, ASME, Pittsburgh, Pennsylvania, Sep. 2001, Paper No.: DETC2001/VIB-21493. Jinhao Qiu, Junji Tani, D.J. Warkentin and Takuichro Soga, Stress Analysis of RAINBOW Actuators and Relief of Stress by Gradation of Material Composition, Journal of The Japan Society of Applied Electromagnetics and Mechanics (in Japanese), Vol.7, No.2 (1999), pp.185–192.
SUMMARY The research activities of the Aeronautic Science Key Lab for Smart Materials and Structures, Nanjing University of Aeronautics and Astronautics are introduced. The research fields include structural health monitoring, structural vibration reduction and noise suppression, adaptive wing and smart rotor, sensor and actuation technology, functional materials and devices, and system integration and measurement technology. Three research fields, including structural health monitoring, development of high-performance piezoelectric materials, and development of high-performance actuator devices, have been introduced in detail. REFERENCES Shenfang Yuan, Structural health monitoring and damage control, National Defense Press, 2007. Shenfang Yuan , Xiaosong Lai, Xia Zhao, Xin Xu and Liang Zhang, Distributed structural health monitoring system
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Localization of damage in structural systems: Algorithms and issues
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A new theorem on damage localization and its implementation D. Bernal Northeastern University, Center for Digital Signal Processing, Boston MA
1
INTRODUCTION
the transfer matrix for the q coordinates and ν is arbitrary. Stated otherwise, the vectors that span the null space of the change in the transfer matrix are Laplace transforms of loads that induce zero stress in the damaged region.
This paper discusses a new theorem that maps changes in transfer matrices (G) to the spatial position of stiffness related damage. Implementation of the Dynamic Damage Locating Vector (DDLV) theorem in the time domain is computationally taxing as it involves: (1) processing the data to compute transfer matrices for the reference and the potentially damaged states (2) computation of the null space of G along a discretized Bromwich contour (3) selection of a specific vector from the null space at each s-location (if multidimensional) (4) numerical Laplace inversion of the s-functions and, finally (5) computation of the stress field history for the signals in step four. The numerical burden is drastically reduced, however, by focusing not on the time history of the stress field but on its Laplace transform. In this way information on the location of damage is obtained from each point in the s-plane where G is evaluated.
3 • • • • • •
DDLV LOCALIZATION ALGORITHM IN S-PLANE Select a point s in the complex plane. ˜ subtract to Compute the transfer matrices G and Gget G. Compute the null space of G – if multidimensional select and arbitrary vector, . Apply to the model and obtain the complex displacement and associated stress fields. The damaged elements are those where both the real and the imaginary part of the stress field is zero. Robustness (in the noisy case) can be promoted by aggregating results from several s-locations.
2 THE DDLV THEOREM 4 Consider a finite dimensional representation of a linear viscously damped structure in two states: one where the stiffness matrix is K and the other (K + K), where K derives exclusively from reductions in some of the stiffness parameters. Designate the collection of elements that contribute to K as constituting the physical domain D and assume that f(t) is a time history of loads acting at a set of coordinates q with σ(t) being the associated stress field over D . The DDLV theorem states that if f is such that σ ≡ 0 then L(f) = Null(G) ν where G is the change in
OBSERVATIONS
The DDLV theorem provides rigorous decoupling of localization from severity and applies to arbitrary skeletal systems. It is shown that G is guaranteed to be rank deficient throughout the s-plane when the rank of the change in the stiffness matrix resulting from damage is less than the number of sensors. In the practical situation where the transfer matrices are modally truncated robustness is promoted by performing the evaluation at s-locations that are near the identified poles.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Damage detection and localization using time domain residuals C.-P. Fritzen, P. Kraemer & K.J. Xing Institut of Mechanics and Control Engineering-Mechatronics, University of Siegen, Germany
1
EXTENDED ABSTRACT
reference model is used in conjunction with the current experimental data of the monitored structure. If there is an inconsistency between the “undamaged” model and the data the generated residuals change their statistical properties. This effect can be used for damage diagnosis. Typical tools for residual generation are Kalman Filters or discrete time series models. The localization technique used here work on the basis of local sensing areas in the higher frequency range. The methodology is demonstrated by a practical example (AIRBUS A320 fuselage). The purpose is to localize a damaged stringer using piezo-electric elements as actuators and sensors.
Structures equipped with an integrated sensor, actuator network and computational abilities to process the measured information can be considered as intelligent structures able to perform a self-diagnosis. Most of the methods have in common that measurements from the current state are used and extracted features are compared to those of the healthy state. This paper focuses on a class of methods that generate and evaluate time domain residuals. These methods use a model representing the undamaged state. The model can be derived either from mechanical principles or can be identified from experimental data. This
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Wave propagation-based damage detection and localization S. Hurlebaus Zachry Department of Civil Engineering, Texas A&M University, College Station, TX, USA
monitoring have to be processed automatically and continuously. Two basic approaches exist in damage detection which make use of elastic waves: global and local techniques. The global technique – sometimes called mechanical vibrometry – is based on determining the eigenfrequencies, eigenmodes and damping characteristics of the structure under consideration. These characteristics are directly dependent upon a component’s material and geometrical properties. For example, a crack will change the stiffness and the damping properties of a specimen (the crack changes the component’s physical characteristics) which results in a change of the eigenfrequencies and the damping coefficients. The local approach is based on the propagation of elastic waves – the velocity (in addition to other wave attributes) of these elastic waves are directly dependent upon the component’s material and geometrical properties. Furthermore, local techniques use the reflection, refraction, and mode conversion properties at interfaces and boundaries of cracks for damage detection. This paper focuses on wave propagation based damage detection and localization techniques. First, a “smart layer” is described. The smart layer consists of a matrix of piezoelectric polymers. This smart layer can be used for monitoring thickness changes and delaminations in composite materials. Secondly, a laser-based method for detecting and localizing of discontinuities in panels is discussed. Finally, an autonomous technique for monitoring of overhead transmission lines based on guided waves is presented.
This paper presents damage localization methodologies using local or wave propagation based techniques. First, a “smart layer” for damage detection and localization is described. The smart layer consists of a matrix of piezoelectric elements which are driven in the pulse-echo mode. This smart layer can be used for monitoring thickness changes and delaminations in composite materials. Secondly, a laser-based method for detecting and localizing of discontinuities in panels is discussed. Specifically, Lamb waves in thin plates are generated and detected using laser ultrasonics. The location and relative size of the discontinuity is determined via a signal processing procedure involving a time-frequency-representation and a special correlation applied in the group velocity-frequency domain. Finally, an autonomous technique for monitoring of overhead transmission lines based on guided waves is presented. Structural health monitoring (SHM) is an extension and further development of nondestructive evaluation (NDE) for structures during operation. While there exists a number of different methods for nondestructive evaluation such as X-rays, microwaves, thermography, elastic waves, spectroscopy, the methods used for structural health monitoring are limited by their requirement to be capable of monitoring in-service structures. Most structural health monitoring techniques use elastic waves as the means for interrogation. However, the difference between nondestructive evaluation and SHM based on elastic waves is in the interpretation of the results. While the signals can be interpreted by human involvement in nondestructive evaluation, the signals in structural health
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Damage localization with modeling errors and uncertainties J.Y. Ching & Yi-Chu Chen National Taiwan University of Science and Technology, Taipei, Taiwan, China
1
INTRODUCTION
known through prior system identification. Damages are simulated by reducing the stiffnesses of certain stories. The actual damage pattern and the stiffnesses of all floors are taken as unknown after the simulated damage. Three damage cases are considered: (a) second-story stiffness is damaged; (b) first-story and third-story stiffnesses are damaged; (c) first-, second-, and third-story stiffnesses are damaged. Four measurement scenarios are considered: (a) two sensors at the ground floor and roof; (b) three sensors at the ground floor, 2nd floor, and roof; (c) four sensors at ground, 1st, 3rd floors and roof; (d) six sensors at all floors. Given the vibration data obtained after the simulated damage, 32 different models are chosen to localize and quantify the damage. The only difference between various models is in their assumed damage patterns. For each model, its evidence is estimated by TMCMC; also, the samples of the unknown stiffnesses at the last stage can be used to estimate the mean values of the stiffnesses. The criterion of damage localization is simple: the assumed damage pattern of the model with the largest evidence gives the predicted damage locations. Once the damage locations are found, the estimated stiffnesses at the damage locations directly quantify the damage severity.The analysis results show that TMCMC is successful in both identifying damage locations and quantifying damage severities.
Damage localization techniques are as powerful tools for structural health monitoring based on measured responses of instrumented civil engineering systems. If the assumed model is inappropriate, the damage detection and localization may fail miserably. The model selection issue is called the first level of uncertainties. There is another level of uncertainties: even if an appropriate model has been found, it is impossible to eliminate the uncertainties in the unknown stiffness parameters by using the response data. Those two levels of uncertainties are critical for damage localization and quantification. Previously, a two-step approach is taken to resolve the two-level problem (Papadimitriou 2004). In this paper, a unified method of resolving the two-level problem is proposed. This method is called the transitional Markov chain Monte Carlo (TMCMC) approach (Ching and Chen 2007). With a single run of the approach, not only the unknown parameters can be estimated (which resolve the second-level of uncertainties) but the evidence of the chosen model can also be found (which resolve the first-level of uncertainties). 2 TWO LEVELS OF UNCERTAINTIES Let M be the assumed model for the target system, θ be the uncertain model parameters and D be the measured data. Given the chosen candidate models {M (i) : i = 1, . . . , Nclass }, the solution to the first level of uncertainties is to calculate the evidences { f (D|M (i) ) : i = 1, . . . , Nclass }, which quantify the relative plausibilities of the candidate models. Suppose M is the assumed model for the target system. The solution to the second level of uncertainties is to find the posterior PDF of θ conditioned on M and D. 3
REFERENCES Ching, J. and Chen, Y.-C. 2007. Transitional Markov chain Monte Carlo method for Bayesian model updating, model class selection and model averaging. To appear in ASCE Journal of Engineering Mechanics. Papadimitriou, C. 2004. Bayesian Inference Applied to Structural Model Updating and Damage Detection. 9th ASCE Joint Specialty Conference on Probabilistic Mechanics and Structural Reliability.
EXAMPLE
We consider a 5-DOF linear structure as an example. Before damage, the actual stiffnesses are assumed to be
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Issues in Kalman filter-based damage evaluation without excitation information A. Haldar & R. Martinez-Flores University of Arizona, Tucson, U.S.A.
H. Katkhuda Hashemite University, Zarqa, Jordan
1
INTRODUCTION
generated noise-free and noise-contaminated (artificially added) response information and with limited laboratory experiments.
An objective nondestructive inspection-based defect evaluation procedure is urgently needed to assess health of structures in normal operating condition or just after natural (earthquakes, high winds, etc.) or man-made (blasting, explosion, etc.) events. Detection of defects that alter the dynamic response behavior of structures can be used for this purpose. To locate defects at the local element level, a finite elementbased system identification (SI) approach will be ideal. Changes in the stiffness properties of elements can be used to locate the defect spot(s). To increase its implementation potential, the procedure should be able to locate defective element(s) using minimum information. To address minimum information required to identify a system, its three components, i.e., (i) input excitation information, (ii) output response information, and (iii) the system to be identified, need further study. Outside the highly controlled laboratory environment, the measurement of excitation information is always error-prone. Just after a natural and made-made event, the information the input excitation is expected to be unavailable. It would be very desirable if a system can be identified without using excitation information. Numerous finite elements are required to represent a realistic structure and thus the required dynamic degrees of freedom (DDOFs) are expected to be very large. The simultaneous collection of response information at a large numbers of DDOFs may not be practical in most cases. Also, measured response information is expected to be noise-contaminated. Thus, the application potential of the nondestructive defect evaluation procedure will be significantly improved if the structure can be identified with only limited noisecontaminated response information and without the excitation information. The research team at the University of Arizona proposed a two-stage SI-based procedure for this purpose. They verified the method using extensive computer
2
BASIC CONCEPT
Kalman filter-based SI approach is used if the response information is limited and noise-contaminated. To implement the concept, the excitation information and the initial state vector must be available. To meet the objectives of the study, the necessary information can be generated using a two-stage approach. Stage 1 – Based on the available response information, a sub-structure(s) can be considered. It will then be identified using the Modified Iterative Least Square with Unknown Input (MILS-UI) method. The identified elements properties can be used to generate the initial state vector. The MILS-UI method will also generate the excitation information. Stage 2 – Using the information from Stage 1, the whole structure can be identified. This will be denoted hereafter as the GILS-EKF-UI approach. 3
IMPLEMENTATION ISSUES
Some implementation issues need further study. Issues related to the location, size, and the numbers of substructure, the minimum and type of response information required to identify large structural systems, and the location of the defect spot(s) with respect to the node point(s) where response information is available, etc. are specifically addressed in this paper. This paper is based on work partly supported by University of Arizona Foundation under a small grant program. Any opinions, findings, conclusions, or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the sponsor.
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Application-driven infrastructure monitoring in Japan
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A new research project on development of a practical monitoring system of urban infrastructure toward mitigation of disaster and accidents Y. Fujino & Y. Mizuno The University of Tokyo, Tokyo, Japan CREST, Japan Science and Technology Agency, Japan
1
INTRODUCTION
system and they are critical element in order to activate urban lives. These now raise the question of what would be the nervous system. A human feels pains and send messages to the brain, which reacts properly to other organs. Infrastructure lacks the nervous system at this moment.
In recent years, natural disasters and accidents associated with urban infrastructures such as transportation systems and civil structures have been increased and their reduction is considered to be one of the societal important issues in Japan. Monitoring/sensing is believed to be a key modern technology toward safety and security of urban infrastructure. Japan Science and Technology Agency started a new focused research proposal-based program entitled by Integrated Advanced Sensing (Director: Kiyoshi ITAO) as a part of Core Research for Evolutionary Science and Technology (CREST) in 2005. 2
4
In general, a risk surrounding us is a very complicated problem including a large number of sub-elements. In the following, we define “risk”, “hazard”, and “vulnerability”. The hazard is an external event affecting our infrastructure and the vulnerability is an internal fragility of our infrastructure. The risk is expressed as a product of the hazard and the fragility.
URBAN SPACE AND ITS RISK
Although the services of the public utilities are improved as urban population grows, it is also clear that urban arrears are vulnerable. The issues of urban space and life are summarized five “S” words: speed; safe; security; sustainability; and service. Nonetheless these are the requirements for pleasant daily lives, these needs to be maintained whenever and recovered instantly when disasters take place. 3
SENSING FOR RISK QUANTIFICATION AND VISUALIZATION
risk = hazard × vulnerability 5
(1)
SUMMARY
This paper describes the outline of a new project (Principal Investigator Yozo FUJINO 2006–2012) that started in 2006. The project consists of four subprojects; 1) development of a measurement system of 6-degree displacements for multiple points using free optical laser, 2) high resolution optical fiber sensing system, 3) new hazard (rain and wind) line sensing system using leaky coaxial (LCX) cable, 4) semi-active sensing system of civil structures such as buildings and bridges, 5) development of sensing network and data processing system for infrastructure monitoring. The system developed will be installed in the buildings of the main campus of the University of Tokyo and in the high speed train viaducts.
URBAN INFRASTRUCTURE AND NEEDS FOR SENSING
The variety of infrastructure facilities exists. Some are built to shelter us from harsh environments and climate, such as houses and residential buildings. The others form networks and grids such as transportation and utilities. In analogy to a human body, buildings and dams for flood control are considered as frames. Transportation and utilities correspond to the circulation
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Synchronized sensing for structural health monitoring using smart sensors T. Nagayama University of Tokyo, Tokyo, Japan
B.F. Spencer, Jr. University of Illinois at Urbana-Champaign, Urbana, IL, USA
Y. Fujino University of Tokyo, Tokyo, Japan
of acquired data cannot be assumed to be as good as that of a traditional wired system. The noise level of low-power MEMS-type sensors is oftentimes higher than that of conventional sensors. The precise control of sample timing is difficult to achieve on smart sensors with limited resources. For intense analyses of dynamic structural behavior, reliable data quality is imperative. Smart sensors with reliable dynamic measurement capabilities are needed. Many smart sensors have been developed to address the challenges of full-scale implementation; this project examines the Imote2 developed by Intel. The Imote2 is a new smart sensor platform developed by Intel for data intensive applications. The main board of the Imote2 incorporates a low-power X-scale processor and a radio. The processor speed may be scaled based on the application demands, thereby improving its power usage efficiency. One of the important characteristics of the Imote2 that separates it from previously developed wireless sensing nodes is the amount of data it can store. The Imote2 has 256 KB of integrated SRAM, 32 MB of external SDRAM, and 32 MB of Strataflash memory. The latter is particularly important for storing the large amount of data required for real-time, dynamic structural monitoring. Intel has created a basic sensor board to interface with the Imote2. Their basic sensor board can measure 3-axes of acceleration, light, temperature, and relative humidity. All of the sensors on this board are digital, thus it requires no analog to digital converter. Smart sensors such as the Imote2 have the potential to enable structural health monitoring using numerous measurement data points. However, the quality of data from smart sensors can be degraded if sampling is not appropriately performed. Issues effecting synchronized sensing have been explained. A resamplingbased approach has been proposed that addressed these issues. The performance of the resampling-based approach has been experimentally verified using the Imote2.
Our lives rely heavily on the pervasive civil infrastructure in which industrialized nations have made huge investments. To properly manage civil infrastructure, its condition and serviceability need to be assessed. Measurement and proper data processing are expected to give a reasonable assessment of the structure’s condition. Then, the serviceability can be improved based on that assessment. The physical state of a structural system is among the factors that determine its serviceability. Sensing physical quantities in detail offers the potential to better estimate structural conditions. Engineers, owners, and users can make better decisions based on the processed information. Structural condition assessment is not always straightforward. Such is the case in the Structural Health Monitoring (SHM) of buildings, bridges, and towers. These structures are large and consist of many members that make structural condition assessment difficult and prohibitively expensive. One approach in SHM to alleviate this difficulty is based on vibration measurement. Because buildings, bridges, and towers are large and complex, information from a few sensors is inadequate to accurately assess the structural condition. To fully comprehend dynamic behavior, densely distributed sensors need to monitor the structural motion at a sampling frequency sufficiently high to capture salient dynamic characteristics. To meet the need of implementing a densely distributed network, smart sensors have been developed recently. A smart sensor ideally has five essential features: (1) on-board microprocessor, (2) sensing capability, (3) wireless communication, (4) battery powered, and (5) low cost. Among these features, flexible communication and information processing capabilities are what differentiate a smart sensor from a standard sensor. Although smart sensors have been used for SHM research and demonstration, acquired data has not been intensively analyzed to reveal structural characteristics. In a smart sensor system, the quality
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Distributed inversion algorithm for sensor networks M. Abe BMC Corporation, Chiba, Japan
Y. Fujino The University of Tokyo, Tokyo, Japan
1
INTRODUCTION
information can be collected by multi-hop communication or through prescribed network gateways. The sensor network is assumed to be located at the region apart from the source events with a constant distance. This configuration could be interpreted as the simplified model of fire detection by temperature sensors distributed on the ceiling or damage detection of underground structures from surface deflection measurement. A distributed algorithm is constructed to estimate source distribution using information of neighboring sensor node and iterative computing. Although the algorithm is distributed, information of farther nodes is also indirectly and approximately reflected in cascade manner.
Application of sensor networks for monitoring of civil infrastructures is attracting wide interest from research community. Densely measured data have been found extremely useful to capture structural performance and sensor network technology is expected to be one of the key technologies to bring innovation in structural health monitoring. Each sensor node in the sensor networks has not only sensing but also processing and communication capabilities, which are expected to provide intelligence and reliability in sensing. Because of the scale of the infrastructure systems, the number of sensors would be enormous in actual implementation, and certain distributed computing would naturally be required for process and manage such huge network. In this paper, a distributed computing algorithm for sensor networks to solve a class of inverse problems is proposed, which utilizes processing and communication capabilities.
2
3
CONCLUSIONS
The major findings are as follows: – The developed distributed computing is shown to have the capability to trace overall tendency of distribution even with limited number of iterations. – Distributed computing, in comparison to centralized method, is observed to have higher reliability, so that the local measurement error does not propagate and remains local. – Convergence, stability and accuracy of the proposed method are numerically studied. Determination of these parameters is critical for design of sensor networks for distributed environment. – The proposed method is also extended to twodimensional problems, and the similar characteristics of the one-dimensional cases are observed.
DEVELOPMENT OF ALGORITHM
The problem considered here is the inversion of location, intensity and distribution of source event from measurement of sensor networks by distributed computing. To focus on the characteristics of distributed computing, simplified models are employed for both sensor networks and physical phenomena. The objective physical phenomenon is assumed to decay with distance and measurement at the sensor node is determined by integration of these source effects over the entire region of source distribution. Each sensor node is assumed to consist of the sensing unit to measure physical quantity, the processor for limited capability of data analysis and data storage, and the wireless communication unit to communicate with neighboring nodes. When all information is required or at the emergency, each nodal
Although the current study is focused on fundamental and theoretical studies, advantages of distributed computing for sensor networks are clearly demonstrated. Further theoretical studies on accuracy and reliability, and research on implementation at realistic and general configurations would be required to improve applicability of the method.
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Long-term remote monitoring of a cable stayed bridge and seasonal fluctuation of modal parameters Y. Miyamori, H. Kimura & T. Oshima Kitami Institute of Technology, Kitami, Hokkaido, Japan
T. Ayame Engaru Town Office, Engaru, Hokkaido, Japan
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INTRODUCTION
The authors have continued remote vibration monitoring of a cable stayed bridge in Hokkaido, Japan. More than 1,200 samples of ambient vibration have been collected in 2 years. The Natural Excitation Technique (NExT) and the Eigensystem Realization Algorithm (ERA) are applied to ambient vibration data for detecting little changes of modal parameters. From these results, the relationship between modal parameters and environmental effects of intact structure is examined in this study to understand basic structural response. And its results will be utilized further study of health monitoring for real bridges.
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Figure 1. Temperature vs. natural frequency of the 2nd mode.
identified in lower modes. And they fluctuate with one-year period. Figure 1 shows identified natural frequency of the 2nd mode versus temperature of bottom of the pylon at the time. There is negative correlation between temperature and natural frequency. From natural vibration analyses of numerical bridge model, it is considered that natural frequencies of cable stayed bridge decrease at higher temperature because structural members have axial compressive force by thermal stress and stiffness of the member decreases apparently. In cold season this mechanism functions inversely.
OBSERVED BRIDGE AND DATA PROCESSING METHOD
Satsunai Seiryu Bridge is located in Hokkaido, Japan. The main span of the bridge is 132 m and total length of bridge is 230 m. 9 accelerometers, 2 thermometers and other sensors are installed in the bridge. From November 2004, ambient vibration data for SHM have been recorded twice in a day at 2:00 am and 2:00 pm. To October 2006, 667 and 648 samples had been recorded respectively. Sampled data are transmitted to a data storage server in laboratory via ISDN from signal conditioning unit at the bridge site. NExT and ERA are applied to obtain modal parameters. Numerical simulation model is also composed to examine a factor of fluctuation of modal parameters.
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4
CONCLUSION
In this study long-term remote vibration monitoring of a cable stayed bridge have benn performed in 2 years. And more than 1,200 samples of ambient vibration have been recorded. Modal parameters of the bridge are identified by using NExT and ERA. ERA gives number of modes in each sample including numerical modes. However structural modes appear continuously in long-term monitoring.
MODAL PARAMETERS OF THE BRIDGE
From results of ERA to long-term monitoring data, natural frequencies of the bridge are continuously
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Natural frequencies of the bridge fluctuate seasonally. Natural frequencies increase in cold season and decrease in warm season. Natural vibration analyses with thermal load indicate thermal stress decrease its stiffness apparently for
increasing temperature and opposite mechanism acts for decreasing temperature. Detailed investigation will be performed for quantitative explanation.
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Localization and time synchronization of sensor network for infrastructure monitoring Kenji Oguni Earthquake Research Institute, The University of Tokyo, Bunkyo, Tokyo, Japan
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INTRODUCTION
In this paper, localization achieved by clustering the neighboring set of nodes with Delaunay polygons is presented. Using the observed relative distance between sensor nodes as input data, relative positions of nodes are determined by properly connecting local Delaunay clusters. This is opposite from Delaunay tessellation of a space for given arrangement of points. In this sense, this localization algorithm is called inverse Delaunay algorithm. In the inverse Delaunay algorithm, the following characteristic of Delaunay polygon is used. Delaunay polygons on 2 are triangles with no point in their circumscribed circle This characteristic is fully utilized in constructing local clusters and for enhancement of the robustness of local clusters (i.e., toughness of the local clusters against measurement error).
This paper presents a hierarchical sensor network system for robust localization and time synchronization. This system consists of parent nodes with a low priced L1 GPS receiver and child nodes equipped with an acoustic ranging device. Relative positions between child nodes are estimated based on acoustic ranging through the inverse Delaunay algorithm. This algorithm localizes all the nodes simultaneously, thus, the accumulation of the error in the localization is suppressed. Relatively localized child sensor nodes are given global coordinates with the help of GPS on parent nodes. The parent node consists of a low priced L1 GPS receiver and wireless LAN. Noise tolerant acoustic ranging algorithm that employs digital signal processing techniques is implemented in the child node. Experiments show that this ranging algorithm gives average range estimation error below 10 cm. In addition to the capability of localization, ability for time synchronization is implemented. This system consists of three types of nodes, i.e., (i) a time node which broadcasts time stamp, (ii) sensing nodes which get data from on-board sensors and (iii) a sink node. Every data from sensor node is synchronized by using broadcasted time stamps as reference.
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3 TIME SYNCHRONIZATION BASED ON BROADCAST TIME STAMP Among many approaches (Elson et al. 2001) for time synchronization of wireless sensor network, we implement a method with broadcast time stamp in Mica2. The major reasons to employ broadcast time stamp are: (i) time synchronization based on broadcast time stamp is suitable for devices with limited power for computation and communication, and (ii) sensing of mechanical behavior of civil infrastructure has relatively relaxed requirement for accuracy (e.g., 100 us – 5 ms) in time domain.
INVERSE DELAUNAY ALGORITHM FOR RELATIVE LOCALIZATION
Each and every sensor node in the randomly distributed sensor network is localized by using internode distance as input data set. Since the inter-node distance is measured by inaccurate acoustic ranging devices, accumulative localization using small number of reference nodes may result in erroneous localization or even failure in localization itself. To suppress the accumulation of error and to enhance the robustness, localization should be based on local clusters (Moore et al. 2004).
REFERENCES Moore, D., Leonard, J., Rus, D. and Teller, S. 2004. Robust Distributed Network Localization with Noisy Range Measurements. Proceedings of the Second ACM SenSys. Elson, J., Girod, L. and Estrin, D. 2001 Time Synchronization for Wireless Sensor Networks, Proceedings of the 2001 International Parallel and Distributed Processing Symposium (IPDPS) San Francisco, California, USA, April.
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Quick earthquake damage detection method for bridge structures J. Sakai Public Works Research Institute, Tsukuba, Japan
H. Kobayashi Hanshin Expressway Company Limited, Osaka, Japan
S. Unjoh Public Works Research Institute, Tsukuba, Japan
1
INTRODUCTION
When an extreme earthquake occurs, it is essential to detect the severe structural damage that affect the structural safety immediately after the big event. Currently, detection/evaluation of such damage is done by visual inspection of experts, which is time-consuming process. For detecting and evaluating the seismic damage quickly without experts’ inspections, the authors have been conducting a research project to develop a damage detection method using intelligent sensors. This paper introduces the damage detection system proposed and demonstrates the efficiency of the proposed method based on the results of a series of shaking table tests.
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DAMAGE DETECTION SYSTEM AND PROPOSED METHOD Figure 1. Proposed system.
Figure 1 shows a damage detection system proposed in this research project. This system enables road administrators to gather information on the damage and safety of structures in a running patrol car during an emergency patrol after an extreme earthquake. Idealizing a bridge column as a SDOF system, and assuming elastoplastic skeleton curve of forcedisplacement relation, the maximum response ductility µ, which is an index of the degree of damage, can be given as
where T0 and Td are the natural period of the system before and after damage.
Figure 2. Response of specimens and change of natural period.
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acceleration and the change of natural period that was computed by Fast Fourier Transform (FFT) of the response acceleration. Due to the seismic damage, the natural period elongates. Figure 3 demonstrates the accuracy of the estimated response ductility by the proposed method. The estimated ductility provides a good agreement with the actual ductility, and thus, the method has ability to provide information about the structural damage. 4
CONCLUSIONS
A quick damage detection system using intelligent sensors is proposed, and the efficiency of a method estimating the seismic damage is demonstrated. The method has ability to estimate the degree of damage.
Figure 3. Efficiency of method.
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EFFICIENCY OF PROPOSED METHOD
The efficiency of the proposed method is evaluated based on the results of a series of shaking table tests. Figure 2 demonstrates the time histories of response
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Smart structural systems technologies
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Project COVICOCEPAD under smart structural systems technologies of program Eurocores R.C. Barros Faculdade de Engenharia da Universidade do Porto (FEUP), Porto, Portugal
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GENERAL DESCRIPTION
liquid dampers and tuned liquid column dampers, for which the damping forces resisting the actions result from: viscous interactions between liquid and rigid container, hydrodynamic head loss between opposite container walls or from passing orifices, and internal viscosity of liquid. To evaluate the behavior of a semi-active device in a structural system, a term (with two parts) is included (Guerreiro et al. 2007) in the equation of dynamic equilibrium, that reflects the force generated in the seismic protection device: one part displacement dependent; other part velocity dependent. Dissipation cycles are compared for passive and semi-active devices, to ascertain differences of behavior. Some results of an experimental campaign conducted by COVICOCEPAD partners, on coupling liquid damping devices with rigid structural models, are outlined (Corbi & Orefice 2005). Experimental results indicate potential effectiveness of using liquid dampers for the specific cases studied.
Tall or long-span civil engineering (CE) structures should be designed to enable better performance under dynamic and transient loads, through the use of damping systems (passive, active and semi-active) to reduce structural accelerations, velocities and displacements. The Collaborative Research Project (CRP) COVICOCEPAD – an acronym for Comparison of Vibration Control in Civil Engineering using Passive and Active Dampers (Barros 2005) – submitted to and approved by the European Science Foundation (ESF) Eurocores Program with PESC (Program in Physical and Engineering Sciences) entitled Smart Structural Systems Technologies (S3T), addresses cumulatively the following areas (and sub-areas) of research within the S3T call: Modeling of Structures (as dynamic systems, with in-service degradation, with damper devices as integrated structural elements, using modern techniques of shape displacement-velocity-acceleration control and minimization); Sensors and Actuators (by optimization of emerging technologies for structural applications); Systems (by advanced modeling of control systems); Analysis and Decision Making (by structural performance evaluation and damage assessment). The performance of selected structures will be assessed and some parametric studies are envisioned, that are expected to contribute to the mitigation of earthquake and vibration hazards in structural engineering through vibration control (Barros 2005). 2
REFERENCES Barros, R.C. 2003. Some Developments on Vibration Control for Tank Shells and Pipelines. In A. Baratta and O. Corbi (eds), Intelligent Structures: An Overview on the Ongoing European Research, pp. 187–201. Napoli, Italy: Fridericiana Editrice Universitaria. Barros, R.C. 2005. Comparison of Vibration Control in Civil Engineering using Passive and Active Dampers (COVICOCEPAD). Collaborative Research Program of the European Science Foundation: Eurocores Program Smart Structural Systems Technologies, pp. 1–65, Strasbourg: France. Corbi, O. & Orefice, R. 2005. Dissipation of Dynamic Vibrations of Rigid Blocks by Liquid Sloshing Motion. In G. Augusti, G.I. Schueller, M. Ciampoli (eds), Structural Safety and Reliability. Rotterdam: Millpress. Guerreiro, L., Barros, R.C. & Bairrao, R. 2007. Algorithms for Semi-Active Devices Control, In M. Papadrakakis et al. (eds.), ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering; Rethymno, Crete, 13–16 June 2007. Greece: (in-press).
BACKGROUND AND RECENT DEVELOPMENTS WITHIN COVICOCEPAD
R&D developed in the recent past by the partners of this CRP, constitutes a strong reason and motivation for the application of COVICOCEPAD to the emerging possibilities of the field of intelligent structures with control devices. Recent experience associated with the sloshing response of tanks seismically excited (Barros 2003) will be used to develop mathematical models of tuned
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The SMorph (Smart Aircraft Morphing Technologies) collaborative research project J.E. Cooper School of Mechanical, Aerospace and Civil Engineering, University of Manchester, UK.
A. Suleman IDMEX, Instituto Superior Técnico, Lisboa, Portugal.
S. Ricci Department of Aerospace Engineering – Politecnico di Milano, Milano, Italy.
the smart technologies to be implemented effectively, via studies into their optimal use and application. These methodologies will also be compared as part of the overall project. The CRP will provide an effective means to enable mathematical models, test hardware and experimental test data to be exchanged between the partners. The aims of the SMORPH CRP are:
Since the start of manned flight, Aeroelasticity has often been considered as a “necessary evil”, causing potentially catastrophic problems such as divergence, aileron reversal and flutter. Traditional aircraft design is based upon the premise that all aeroelastic effects are undesirable, and therefore aircraft structures are built to be stiff and heavy in order to avoid them. Conventional aircraft designs are unable to alter their structural shape in flight. Consequently, the structure has to be designed either to have the optimal aerodynamic shape at a single point in the flight envelope. The last few years have seen an increasing interest in the development of aircraft structures that allow aeroelastic deflections to be used in a beneficial manner. Such an approach is termed “morphing” and can be defined as a capability to provide superior and/or new vehicle system performance by tailoring the vehicle’s state to adapt the environment and multi-variable mission. These improvements are general, and can be related to different disciplines, including the use of smart structures, embedded actuators and mechanisms to adapt the shape of the wing in flight. This paper describes the work that is planned in the recently started ESF S3T SMorph Collaborative Research Project including an overview of some of the prototype demonstrators. The SMorph project consists of three partners: the University of Manchester (UMAN), Instituto Superior Técnico (IST), Lisboa and the Department of Aerospace Engineering, Politecnico di Milano (PoliMi). The rationale is to develop novel structural concepts and implementations of morphing aeroelastic. The partners will all develop novel means to allow
To develop several new concepts for morphing aeroelastic structures To develop modelling technologies for morphing aeroelastic structures To develop methodologies to determine the best means of implementing morphing technologies for aerospace structures for optimal performance To design, manufacture and test wind tunnel and RPV models that include morphing aeroelastic concepts from all of the partners To evaluate and validate the morphing concepts developed in this CRP To evaluate and validate the implementation and optimisation technologies developed in this CRP and to use them as the design methodology for some of the test models. The CRP consists of four tasks divided between the partners: Novel Morphing Technologies. Modelling Methodologies for Smart Morphing Technologies. Design and Optimisation Techniques for Smart Morphing Technologies. Experimental Validation.
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SCMeRe – shape control of membrane reflectors G. Rodrigues & A. Preumont Active Structures Laboratory – Université Libre de Bruxelles, Belgium
R. Bouzidi Research Institute of Civil Engineering and Mechanics – Université de Nantes, France
S. Pellegrino Deployable Structures Laboratory – University of Cambridge,UK
Y. Stockman Centre Spatial de Liège, Belgium
large space reflectors possible.To achieve this, the consortium consists of four groups with complementary expertises, respectively in active control of piezoelectric structures (Active Structures Laboratory – Université Libre de Bruxelles), deployable space structures and membrane wrinkling (Deployable Structures Laboratory – University of Cambridge), optics and reflector metrology (Centre Spatial de Liège) and numerical methods for highly nonlinear structures (Research Institute of Civil Engineering and Mechanics, University of Nantes). Research activities have initiated with a review of earth-borne adaptive optics and followed the setting of an experimental adaptive optics bench and the development of a simulator of an adaptive optics system.
Large space telescopes are constrained by system mass and space available in stowed configuration. With the use of Gossamer structures, made of membranes or thin shells of reflecting material ultra large, lightweight telescopes can be envisioned with an areal mass several orders of magnitude less than current monolithic passive mirrors (Hubble), and also much lighter than segmented ones (JWST). In its most daring concept, a flimsy membrane mirror is station kept and its shape is adjusted by software to compensate for manufacturing errors and external disturbances; the secondary mirror of the telescope is placed on an independent spacecraft which is also station kept and contains further control devices to compensate for the residual error. This project addresses some of the scientific and technological challenges to make
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Micro-measurement and monitoring system for aging underground infrastructure (Underground M3) K. Soga & P.J. Bennett University of Cambridge, Department of Engineering, Cambridge, UK
One of the greatest challenges facing civil engineers in the 21st century is the stewardship of ageing infrastructure. Nowhere is this more apparent than in the networks of tunnels and pipelines that lie beneath the major cities around the world. Much of this underground infrastructure was constructed more than half a century ago and there is widespread evidence of deterioration of this old infrastructure. This European Science Foundation funded project comprises an integrated research program to evaluate and develop a prototype wireless sensor network system called the “Underground M3 system” for condition assessment and monitoring of ageing underground infrastructure. The main aim of the research is to develop a system that uses a tiered approach to monitor the degree and rate of deterioration. It is proposed that the system comprises of (1) Tier 1: Microdetection using advances in computer vision (Figure 1) and (2) Tier 2: Micro-monitoring and communication using advances in micro electro mechanical systems (Figure 2) and wireless communication. These potentially low-cost technologies will be able to reduce costs associated with end-of-life structures, which is essential to the viability of their rehabilitation, repair and reuse. The paper presents an overview of the project entitled “Micro-Measurement and Monitoring System for Ageing Underground Infrastructure (Underground M3)” funded by the EUROCORES Smart Structural Systems Technologies (S3T) Programme of the European Science Foundation. It is a three year
project, which started in October 2006. The participating institutions are (i) University of Cambridge, (ii) Czech Technical University in Prague, (iii) Consiglio Nazionale delle Ricerche (CNR), and (iv) Universidad Politecnica de Catalunya. One of the main features of the project is the participation of underground railway owners and maintenance operators. The associate partners of the project are (i) Tubelines, UK, (ii) Metronet Alliance, UK, (iii) Barcelona Metro, Spain, (iv) Madrid Metro, Spain, (v) Prague Metro, Czech Rep., (vi) Soldata, France, and (vii) Katholieke Universiteit Leuven, Belgium. The monitoring system developed for this project will be installed and tested at three metro systems in Europe; Prague Metro, London Underground and Barcelona Metro. The challenges of this project are to validate the capability of recently developed computer vision techniques in underground environments and to demonstrate how large numbers of small, low-cost sensors can be deployed and integrated into large-scale engineering systems in order to improve performance and extend the lifetime while continuously evaluating and managing uncertainties and risks.
Figure 2. Tier 2 Micro-monitoring using MEMS strain sensors.
Figure 1. Tier 1 Micro-detection using Computer Visions.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
ESF S3T Eurocores project MAFESMA: Tools for modeling, design and control of smart structural systems based on shape memory alloys P. Sittner Institute of Physics ASCR, v.v.i., Prague, Na Slovance, Czech Republic
Jan Van Humbeeck MTM-KULeuven, Leuven, Belgium
In this presentation, research work performed in frame of a recently started European collaboration project MAFESMA is briefly introduced. This project attempts to bridge the fast growing gap between quickly extending material knowledge of shape memory alloys (SMA) on one side and the design, development and control of SMA actuated smart structures on the other side. The research work focuses SMA material characterization and development, thermomechanical experiments mapping the functional behaviors of SMAs, development of mechanics models and their numerical implementation into finite element codes and development of control algorithms for actuator applications. The work carried out within the project is introduced by presenting and briefly discussing selected examples of recent results of mutual collaborations among the MAFESMA partners.
Figure 1. Logo of the S3T EUROCORES project MAFESMA suggesting interplay between the functional behaviors, modelling and engineering applications of SMAs.
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Civil infrastructure monitoring and assessment (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Real-time monitoring system and stiffness identification of a long-span cable-stayed bridge with neural networks G. Chen and W. Wang Center for Infrastructure Engineering Studies (CIES), University of Missouri-Rolla, Missouri, USA
In this study, seismic responses are directly used to identify the stiffness of the Bill Emerson Cable-stayed Bridge. An emphasis is placed on how training data sets affect the accuracy of a neural network. A new damage indicator that is independent of earthquake randomness is proposed in this study. Due to its criticality and proximity to the New Madrid Seismic Zone, Missouri, USA, the cablestayed bridge was monitored in real time for both structural and soil responses. The structure consists of three cable stayed spans and an Illinois approach. The seismic instrumentation system consists of a total of 84 accelerometers, Q330 digitizers, and Baler units for data concentrator and mass storage, Figure 1, two data collection hubs were established at two towers, each communicating with the central station through wireless transmissions with their antennas installed on top of the towers. A 3-D finite element model of the cable-stayed bridge was developed using SAP2000 structural analysis software. The model was validated by comparing its first 10 natural frequencies with those from measured data induced by the May 1, 2005 earthquake, which occurred about 180 km from the bridge with Richter’s Magnitude 4.1. The calculated frequencies
agree with their respective measured values with a maximum error of less than 6.1%. The “as-built” or healthy condition of the existing structure is referred to as an “as-built” structure. The structure with a typical scenario of damage will be referred to as a “damaged” structure. A neural network strategy is introduced and schematically shown in Figure 2 for system identification of the bridge. The strategy involves two neural networks. The first one, emulator neural network (ENN), will be trained for the “as-built” bridge to accurately predict its response time histories at time step K+1 based on the measured responses at time step K. The second network shown in Figure 2, parameter evaluator neural network (PENN), will be trained for the “damaged” bridge to relate the prediction error by the well-trained ENN or Response Weighted RootMean-Square difference to the change of structural parameters. The proposed strategy can predict the stiffness of damaged structure accurately. The proposed neural network based technique can not only detect each damage scenario successfully, but also identify the location of changes correctly. Indeed, the maximum identification error for the stiffness ratios is less than 5% for 324 damage indices of 81 damage scenarios when noise is not present. It is also observed that the accuracy of the identified stiffness ratio seems independent of the level of damage in columns.
Emulator Neural Network (ENN)
Measured Response at Step K
Predicted Response at Step K+1
Measured Response at Step K+1 Bridge Parameters
Figure 1. Seismic instrumentation system: hardware.
Figure 2. A identification.
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RW-RMS Difference
Parameter Evaluator Neural Network (PENN)
neural
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Validation of a wireless traffic vibration monitoring system for the Voigt Bridge K.J. Loh & J. P. Lynch Department of Civil & Environmental Engineering, University of Michigan, Ann Arbor, MI, USA
Y. Wang & K.H. Law Department of Civil & Environmental Engineering, Stanford University, Stanford, CA, USA
M. Fraser & A. Elgamal Department of Structural Engineering, University of California at San Diego, La Jolla, CA, USA
A prototype wireless sensing system consisting of 20 sensor nodes is instrumented on the Voigt Bridge (La Jolla, CA) to demonstrate and compare its embedded computational performance against a tethered monitoring system permanently installed by Prof. Elgamal and his research group at UCSD. An innovative feature of their monitoring system is that it includes a high-resolution video camera that can track vehicle traffic in real-time. While processing of acceleration time histories by the wireless sensors can be used to roughly approximate bridge traffic conditions, this study leverages the high-resolution video data of the tethered monitoring system to provide quantitative information on bridge loading. This paper begins by describing the wireless sensor hardware and software design followed by a description of signal conditioning circuitry that is used to amplify (up to 20 times) and filter raw sensor data. Here, a high-pass RC filter (cutoff frequency of 0.02 Hz) and a low-pass fourth order Bessel filter (cutoff frequency of 25 Hz) are combined to formulate a band-pass filter. Then, preliminary time history response data obtained from ambient traffic monitoring is compared with those collected by the cabled system to validate wireless sensor performance. Embedded data processing is employed by each wireless sensor to calculate Fourier response spectra corresponding to the bridge response. Upon comparing the FFT results computed onboard each sensing unit to those measured and computed offline by the cabled system, the response correlates well with little to no discrepancies. In addition, using the FFT results, operational deflection shapes (ODS) for the first four modes of vibration of the bridge are presented. Here, the ODSs are calculated by the wireless
Figure 1. Four operational deflection shapes identified by wireless monitoring system.
monitoring system using different input loads (i.e. modal hammer, cars, and truck). The ODSs obtained suggest the bridge is primarily dominated by flexural and torsional bending modes.
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While it is advantageous to validate the wireless sensing system against a pre-installed permanent tethered SHM system, another advantage of installing wireless sensors on the Voigt Bridge is that a highresolution video camera is also installed to monitor bridge traffic continuously. By correlating recorded acceleration time histories measured by the wireless system to the video data, the influence of traffic on the bridge response can be directly linked.
Figure 2. Recorded acceleration time histories (wired and wireless) at four sensor locations as a delivery truck transverses the bridge. Video frames corresponding to three times of loading are presented while showing the truck location at each instant.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Application of chaos theory analysis to smart structure techniques for highway infrastructure Shuang Jin NDE Center, TFRHC/FHWA, Wiss, Janney, Elstner Associate, Inc. Georgetown Pike, McLean, VA, USA
Richard A. Livingston Office of Infrastructure R&D, Turner-Fairbank Highway Research Center, FHWA, USA, Georgetown Pike, McLean, VA, USA
ABSTRACT: Chaos theory concerns systems with dynamic behavior that is neither purely deterministic nor strictly random. It has several possible applications to smart structures in the highway infrastructures. These include: long-term structural health monitoring, detection of hazardous loading conditions, sensor network optimization, and control of chaotic vibrations. This paper presents recent research at the Turner Fairbank Highway Research Center of the Federal Highway Administration in these applications. Keywords:
Chaos theory, bridges, smart structures, nonlinear vibration, structural health monitoring.
This has included advances in nonlinear 3-dimensional finite element modeling and stochastic modeling of the ambient traffic loads in order to produce largescale, high-fidelity computer simulations of bridge dynamics. These extensive computer simulations have enabled the detailed investigation of loading and structural conditions that give rise to various chaotic patterns structural response. They also can be used to evaluate the sensitivity of chaos parameters for detecting damage with structural health monitoring (SHM) systems. In order to perform these simulations more efficiently, a parallel processor workstation with 32 dual-core processors was recently acquired, which reduced the computation time by a factor of 6 to 14 depending on the size of the model. Another area of research concerns the development of improved algorithms for the analysis of nonlinear structural response data for possible chaotic behavior. These include the introduction of a fractal interpolation technique to enhance the Maximum Entropy method for estimating the most unbiased probability density function of the data. Also, the polynomial chaoses method for approximating chaotic trajectories was extended to use non-Gaussian random variables. These algorithm developments enabled more effective extraction of nonlinear system invariants from the observed structural response time series.
A third research area concerned the implementation of these algorithms in user-friendly Windows-based software, CTBR, to automate the chaos theory analysis of response data series. The software will simplify the work of highway engineers in the analysis of structural health monitoring data from smart highway infrastructure system. The rapid evaluation of the chaos parameters can be used to effectively summarize the condition of the highway structures from large monitoring data sets from existing monitoring systems. Alternatively, it can be used to guide the improved design of sensor networks for new structural health monitoring systems. The presentation demonstrates the application of these useful chaos theory analysis tools to several examples of different types of highway bridge structures including the AASHTO generic steel girder bridge, the Commodore Barry cantilever Bridge, the recent new bascule drawbridge span of the new Woodrow Wilson Bridge and the Bill Emerson cablestayed bridge. For each of these bridges, the simulations predicted chaotic behavior. In the specific case of the Bill Emerson Bridge for which both numerical simulations and actual monitoring data were available, a comparison of the chaos parameters showed very close agreement between the former and the latter.
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This illustrates the effectiveness of using chaos parameters, i.e., Lyapunov exponents, to define a baseline condition index for long-term structural health monitoring of highway bridges. This research has also confirmed that bridges of different structural designs and construction materials can all exhibit complex
nonlinear or chaotic behavior which by cannot be revealed by conventional linear dynamics analysis. Therefore chaos theory analysis can be critical in the successful implementation of smart techniques for the highway infrastructure.
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Monitoring the jacket platform structures in China Bohai Sea Zhongdong Duan, Jinping Ou, Zhi Zhou, Hongwei Li, Xuefeng Zhao & Daocheng Zhou Harbin Institute of Technology
1
INTRODUCTION
Offshore structure for the major purpose of oil and gas exploitation is one of the critical infrastructures worthy of monitoring. China Bohai Sea is the major region where China offshore oil and gas exploration and exploitation activities concentrate since its start in 1970’s. Monitoring of offshore platform structures in China Bohai Sea has been more than fifteen years. The development of monitoring systems for offshore platform structures in China Bohai Sea since 1990’s is introduced with an emphasis on the recent on-line monitoring system using advanced sensors. 2
MONITORING OF ICE LOADING AND VIBRATIONS OF OFFSHORE PLATFORM STRUCTURES
Moving ice has been a great threat to the offshore platform structures in Bohai Sea. The first monitoring system was established in a platform in JZ20-2 oil field in Bohai sea by China National Offshore Oil Corporation (CNOOC) in early 1990’s. From over a thousand ice force histories, the spectrum densities of ice loads when ice floes assume different failure patterns were estimated. Based on the monitored environmental loads, Xiao and Ou, etc., developed a method to alert the safety margin of the structures by comparing the instantly calculated structural overall response. 3
SMART SENSORS AND INTEGRATED SHM SYSTEM FOR CB32A PLATFORM STRUCTURE
Some advanced sensors and their integrated SHM system for monitoring CB32A offshore jacket platform structures is presented. Fiber Bragg Optic Sensors for strains, Polyvinylidene Fluoride (PVDF) sensors for
cracks and fatigue life gauge for accumulative fatigue damage are adopted for monitoring structural local responses. The characteristics of these sensors, the encapsulation techniques, and placement of sensors in this structure are introduced. The integration of load monitoring subsystem and data management and process program into a SHM system for CB32A platform structure is discussed. 4
PROCESSING AND ANALYSIS OF MONITORING DATA
Assessment and processing of the monitored data are in initial stage, and preliminary results of data verification are presented. The Principal Component Analysis and Statistical Process Control is applied to detect the any changes in the structure. This method can effectively eliminate the influence of environmental factors on the change in structural modal parameters. A software based on this method is developed. The program was developed in Matlab language. Based the monitored data from real offshore platform structure, the system safety evaluation of the structure based on the base shear force and the monitoring index based the ultimate base shear capacity is conducted. 5
CONCLUSIONS
Two generations of monitoring technologies and systems for steel fixed jacket platform structures in China Bohai sea are introduced. Several methods are developed and integrated into the monitoring systems to either alert changes in structural properties or make safety evaluation based on the monitored data. Critical issues to advance the monitoring technology to become an acceptable and standard practice of offshore oil and gas industry are summarized.
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Smart control systems based on MR fluids (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Autonomous-decentralized semiactive control scheme for buildings utilizing MR damper-based variable slip-force level damper Y. Nitta Department of Architecture, Ashikaga Institute of Technology, Tochigi, Japan
A. Nishitani Department of Architecture, Waseda University, Tokyo, Japan
1
INTRODUCTION
This paper proposes a semiactive structural control scheme utilizing variable slip-force level dampers. The slip-force level dampers fall into the category of variable friction type of dampers. An uncontrolled friction damper with the constant slip-force level does not dissipate energy until reaching the slip-force level and then forming a hysteretic loop. If the slip-force levels are controllable, the damper would effectively work out from small to large levels of seismic excitations. This is the basic concept of semiactive control for variable slip-force level dampers. The control effectiveness of these dampers greatly depends on how to determine the slip-force level. In this paper, the slip-force level is controlled based on only the measurement of the local response information, by taking into account the relationship between the supply electric voltage and slip-force level. The proposed control scheme does not need to centralize the response information of the structure with one central computer, and can calculate the slip-force level of each damper by its own decentralized microprocessor. In this paper, MR damper, in which the magnitude of slip-force level can be controlled, is utilized to realize the concept of variable slip-force level dampers. The effectiveness of this scheme is demonstrated by conducting numerical simulations.
2 AUTONOMOUS-DECENTRALIZED SEMIACTIVE CONTROL ALGORITHM Utilizing acceleration response information, this paper proposes an autonomous-decentralized semiactive control strategy employing MR dampers. From the structural control point of view, as already mentioned, the crucial question is how to set MR damper slip-force level appropriately. In the algorithm
employed in this paper, the magnitude of slip-force, fy, i , in the damper installed in the ith story is altered every half cycle so as to be proportional to the peak inertia force in the following manner:
where, [ • ]EX : measured peak value for every half cycle; mi : mass of ith story; µ: certain constant value x¨ a, i : absolute acceleration of ith story, and φi : ith element of first mode vector. 3
CONCLUSION
This paper has presented a new autonomousdecentralized semiactive control scheme utilizing MR dampers. The proposed scheme is expected to work effectively from the case of small seismic excitation to the case of sever seismic excitation. In the proposed autonomous-decentralized system, there are a number of distributed control devices, each of which can be controlled by its own decentralized microprocessor only based on the local response information such as absolute accelerations and the sign of the damper force. The proposed scheme controls the magnitude of the damper slip-force level based upon the local absolute acceleration data and the modal parameters of first mode, taking into ac count the relationship between the supply electric voltage and slip-force level. The effectiveness of this algorithm has been presented by the conducting the computer simulations. The proposed autonomous-decentralized control could decrease the peak displacement and base shear without increasing peak absolute accelerations and inter-drifts. The proposed algorithm has around the same control effect as the centralized semiactive control.
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Semi-active base isolation system for buildings using MR dampers Sk. Faruque Ali & Ananth Ramaswamy Department of Civil Engineering, Indian Institute of Science, Bangalore, India
Anil K. Agarwal Deptartment of Civil Engineering, City College of the City University of New York, NY, USA
1
2
INTRODUCTION
The protection of a structure, its material content and the human occupants, against damage induced by large environmental loads, e.g., earthquake, strong wind and waves etc., is, without doubt, a worldwide priority. The extent of protection may range from safe and reliable operation, comfort to human occupants, to structural survival. Inelastic deformation based design method have become a thing of the past and focus is now on structural control. Base– isolation is one of the most widely applied structural protection technique against seismic events. Various researchers have studied the potential of base isolation under far–field and near–field earthquakes. Studies reveled that base isolation strategy perform poor under near source excitation. Optimal control algorithms need an exact mathematical model for an actual structure to minimize its vibration. Today, structures are built more slender and flexible and contain many complex features. Therefore, obtaining a reduced order model becomes erroneous and control mechanism based on it never becomes optimal. Fuzzy logic based control neither needs accurate mathematical model nor depends on a reduced order model. Therefore, FLC provides better and reliable control mechanism. In this work we combine the niceties of semiactive control technique (using magnetorheological dampers) with the base isolation mechanism to provide a hybrid control mechanism. A genetic algorithm (GA) based adaptive fuzzy logic control (FLC) technique (GAFLC) has been proposed to monitor the voltage requirement of the damper. The adaptive FLC modifies its rule base, input–output membership function shape, spread, input scaling variables based on the acceleration and velocity feedback.
CONTROLLER DESIGN
A hybrid mechanism consisting of base isolation and the GAFLC driven semi–active (MR) damper. For analytical studies simple BoucWen hysteretic model of the MR damper has been taken. The nonlinear force– voltage relation is mapped using GAFLC. The advantages of fuzzy control include simplicity and intrinsic robustness since it is not affected by the plant model selection. FLC input–output relation in the first mode of vibration of the structure, is exploited to design the adaptive rule base keeping the symmetry in the rule base intact. To achieve the symmetry in rule base, a geometric approach is taken which reduces the required chromosome length and thereby the search space is reduced. This reduces the computational overhead of the optimization scheme. Present FLC has two inputs, relative velocity and acceleration at the point of the action of the damper and one output, control voltage, v(t) 2 [0, 1], which is then passed to the MR damper. In this geometric approach the consequent space is overlayed upon the ‘premise coordinate system’ and is in effect partitioned into non–overlapping small regions (in our case 5), where each region represents a consequent fuzzy set (details in full paper). The adaptive rule base has been created using only two variables CA and CS representing the angle of inclination of consequent line and spread of the consequent spaces. This method not only allows us to keep the symmetry but also decreases the computation on the optimization process. A 3D base isolated building has been taken where MR dampers, attached at the base provide the hybrid mechanism. Simple genetic algorithm has been used to minimize a multiobjective cost function. The results obtained show the efficiency of the proposed method over base isolated system acting alone.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Design and application of MR damper-based control system with electromagnetic induction part for structural control S.J. Moon & Y.C. Huh e-Engineering Research Center, KIMM, Daejeon, Korea
H.J. Jung, K.M. Choi & H.J. Lee Department of Civil and Environmental Engineering, KAIST, Daejeon, Korea
1
INTRODUCTION
Many studies on magnetorheological fluid (MR) dampers have been recently carried out as a kind of semi-active vibration control device (Zhang et al., 2006). In this paper, the suboptimal design procedure for MR dampers is derived from considerations on optimization problem and magnetic analysis. Figure 1. Manufactured Electro-Magnetic Induction Part r.
2
4
DESIGN PROCEDURE
In the first design step, the damping force and velocity of the MR damper to be designed are determined through numerical simulation. Also, principal dimensions including piston diameters, pole length and gap size are decided by introducing constrained nonlinear optimization problem. The objective of the optimization problem is to maximize the dynamic range with design damping force. In the second design step, the shape of the piston head is selected based on magnetic analysis and sensitivity analysis. Finally, the coils of the magnetic components are designed to interface properly with power supplies. According to the proposed design procedure, a four-stage MR damper has been finally manufactured.
3 TESTING AND EVALUATION The MR damper designed and manufactured by the authors has been tested with harmonic dynamic displacements applied by a servo-hydraulic testing system. In the total damping force of the MR damper, the uncontrollable force is about 2 kN or more and controllable force approximately 8 kN or less. The goal in this study is to design an MR damper for having the controllable force of 7 kN at design velocity. The experimental data shows that the designed MR damper based on above-mentioned design procedures have attained our end.
INTEGRATED DESIGN OF MR DAMPER AND EMI PART
The smart passive control system that consists of an MR damper and an electromagnetic induction (EMI) device was recently developed. To obtain the optimal performance of the smart passive system, the integrated design of an MR damper and an EMI part should be carried out. The integrated design of the smart passive system is preliminary investigated. 5
CONCLUSIONS
In this paper, the design procedure for MR dampers has been sub-optimally derived. Principal dimensions have been decided by introducing optimization problem. The shape of the piston head have been selected based on magnetic analysis and design sensitivity analysis. A 4-stage MR damper has been finally produced. The design procedure has been confirmed through some testing with a hydraulic testing machine. In addition, the integrated design method of an MR damper-based control system with an EMI part is preliminary investigated. REFERENCES H. H. Zhang, C. R. Liao, W. M. Chen, and S. L. Luang, “A Magnetic Design Method of MR Fluid Dampers and FEM Analysis on Magnetic Saturation,” Journal of Intelligent Material Systems and Structures, Vol. 17, 2006, pp. 813– 818.
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Feasibility of smart passive system-based on MR dampers for civil engineering applications H.J. Jung, K.M. Choi & H.J. Lee Korea Advanced Institute of Science and Technology, Daejeon, Korea
S.W. Cho Samsung SDS, Seoul, Korea
1
INTRODUCTION
The smart passive control system based on MR dampers was proposed to solve the problems of the conventional MR damper-based smart control systems by Cho et al. (2005). This paper investigates the feasibility of the system for civil engineering applications. The experimental tests on the large-scale smart passive system are carried out using a shaking table. 2
Figure 2. Feasibility test setup.
SMART PASSIVE SYSTEM
16
The smart passive control system consists of an MR damper and an electromagnetic induction (EMI) device as shown in figure 1. An EMI device changes the kinetic energy of the reciprocation motion of an MR damper to the electric energy according to the Faraday’s law of electromagnetic induction, and then the electric energy is used to change the damping characteristics of an MR damper by forming magnetic field in the damper. Thus, the smart passive system does not need sensors, controllers, and external power source. 3
w/ MR damper (1 Hz) w/ MR damper (1.5 Hz)
Power (W)
12
8
4
0 0
5
10
15
20
25
Base amplitude (mm)
Figure 3. Generated power vs. base amplitude.
FEASIBILITY TEST RESULTS
The preliminary feasibility test of the smart passive system consisting of 10 kN MR damper and largescale EMI device has been carried out using a shaking table as shown in figure 2. Figure 3 shows the results of the electric power generated from the EMI part.
4
CONCLUSIONS
The feasibility of the recently developed smart passive system has been experimentally investigated. The experimental results show that the EMI part could generate the enough power to change the damping characteristics of the MR damper. Therefore, the smart passive system can be considered as one of the promising control strategies for full-scale civil engineering structures. REFERENCES
Figure 1. Schematic model of the smart passive system.
Cho S W, Jung H J and Lee I W (2005) Smart passive system based on magnetorheological damper Smart Materials and Structures 14 707–714.
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Intelligent control system for automotive suspension-based on Magneto-rheological technology W.M. Chen, X.M. Dong, M. Yu, C.R. Liao, H.H. Zhang & S.L. Huang Department of Opto-Electronic Engineering, Chongqing University, Chongqing, China
Starting in the 1990’s, a number of investigators have explored the possibility of using MR fluids devices for semi-active vibration mitigation, especially the smart suspensions for automobiles based on the combination features of passive and active control devices. As an initiative introducer of the smart materials application in China, Center for Intelligent Structure (CIS), Chongqing University, which interferes into the intelligent structures and systems and civil structures health monitoring fields, has expanded comprehensive study on MR semi-active suspensions for automobiles. The research on intelligent control system for automotive suspension in CIS, Chongqing University involves the actuator, sensing and control technology. The actuator technology involves the panorama of fundamental design theory and design modes, sealing technical study and accumulator compensation, MR actuator manufacturing, testing and modeling, durability test and dynamic response analysis, etc. The sensing and control technology of MR semi-active suspensions are tightly related. The sensors distribution is significant for the control effect appraisal, it is a problem related to vehicle engineering. MR semiactive control research of suspensions in CIS involves
the vehicle dynamics modeling, control strategy development, control electronics implementation, road test and appraisal. Based on the vehicles investigated, specific dynamics model is built to simulate the ride comfort and steering stability, which are the primary targets to compromise for vibration suppression. Control strategy development is the key process of control implementation, many strategies proposed by scholars gained good effect of vibration mitigation. Sky-hook control, fuzzy control etc. have been realized in specific object, and initiated wavelet frequency domain control strategy, the comparison of control effect under different controls is performed. A novel intelligent control theory of human-simulation intelligent control (HSIC) scheme is formulated and implemented to attenuate unwanted vibrations such as pitch angle acceleration. Electronics implementation is based on the DSP technology, which is suitable for the digital signal processing. After the integration onto vehicles of the MR damper and control electronics, the road test is carried out on a mini-bus and a passenger car respectively. The results show that good vibration suppression effect is achieved, especially in rough roads, simultaneously, the steering stability is improved.
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Localization of damage in structural systems: Algorithms
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Modal strain energy index for damage detection of a three-dimensional frame structure S.Q. Wang, X.X. Bao & H.J. Li Department of Offshore Engineering, Ocean University of China, Qingdao, China
Because of disadvantages for traditional inspection method such as visual inspection, localized supersonic detection, etc. vibration based global damage detection method are becoming promising. Several damage detection methods have been proposed for predicting damage location and severity (Sohn et al. 2003). The purpose here is to investigate the damage localization for damaged diagonal braces, horizontal beams and vertical columns under different modes and different partial DoFs with modal strain energy (MSE) index. A three-dimensional five-story frame
structure is adopted (Fig.1). Nine damage cases were investigated (Tab.1) with 10% loss of the elastic modulus of the appropriate members of the frame structure. The following conclusions can be drawn. (1) MSE index can localize damaged diagonal member(s) correctly using the first bending mode in x and y directions, with XY DoFs of.each mode. (2) One should use the first bending mode in x and y directions, with XYZ DoFs of each mode, to localize damaged vertical member. (3) One requires the first two bending modes in x and y directions, with XYZ DoFs of each mode, to localize the damaged horizontal member(s). (4) For localizing damaged brace and column, if the first bending modes in x and y directions, with XYZ DoFs of each mode, are used, both the damaged diagonal brace and the damaged column can be correctly localized.
Table 1.
Damage cases of the structure. Natural frequencies/Hz
Damage Cases location
1st mode 1st mode 2nd mode 2nd mode in x-dir in y-dir in x-dir in y-dir
Unda 1 2 3 4 5 6
22.813 22.788 22.813 22.801 22.812 22.813 22.787
36.194 36.194 36.093 36.151 36.194 36.192 36.092
83.992 83.987 83.963 83.814 83.926 83.974 83.958
109.95 109.94 109.94 109.77 109.94 109.91 109.94
22.775
36.150
83.809
109.76
22.787
36.192
83.969
109.90
22.800
36.149
83.795
109.73
7 8 9
Figure 1. Sketch of the three-dimensional five-story frame structure.
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– x-brace 43 y-brace 48 Column 19 x-beam 23 y-beam 22 x-brace 43 y-brace 48 x-brace 43 Column 19 y-beam 22 x-brace 43 y-beam 22 Column 19
(5) For detecting damaged brace and beam, the first two bending modes in x and y directions, with XYZ DoFs of each mode, are required for correct diagnosis. (6) For detecting damaged column and beam, one can only localized the vertical column with XYZ DoFs of each mode.
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(7) The diagonal brace is the easiest structural member for damage localization and the horizontal beam is the most difficult one while the vertical column is among between.
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A combined damage detection method based on modal strain energy and frequencies Huiyong Guo & Zhengliang Li School of civil Engineering, Chongqing University, Chongqing, P.R. China
ABSTRACT Damage detection by mode strain energy has been widely discussed in recent literature and used in practical applications. In general, the modal strain energy methods for damage detection are often effective to identify single damage sites. The methods are, however, unstable for the identification of multiple damage locations. Meanwhile, the incompleteness of measured modes also greatly affects the result of damage localization. In order to obtain more accurate and special inference, it is desired to develop a new method to improve reliability. Here, a combined damage detection (CDD) method is presented to solve the problem. The method uses information fusion technique, which can improve the reliability and stability for the identification of multiple damage locations. First, a modal strain energy dissipation ratio method (MSEDRM) is introduced, which use the modal strain energy to detect damage. For the modal strain energy dissipation ratio method, Structural damage was described as the process of energy dissipation. And the damage coefficient will be acquired by using the method. The relative higher damage coefficient value means that the assumed damage is closely correlated to the true damage state, and the element is more probable damage element. Then, the frequency change damage detection method (FCDDM) is presented and analyzed, which use frequencies to identify damage. The frequency method uses the Moore-Penrose generalized inverse matrix to calculate the damage coefficient. Similarly, the predicted damage location is indicated by the high value. In order to achieve improved accuracies and more specific inferences than those could be achieved by the MSEDRM method and the FCDDM method, a
combined damage detection method is presented. The combined damage detection method utilizes modal strain energy and frequencies to localize multiple structural damage sites. The method uses the information fusion technique to integrate information. We consider an information system consisting of two information sources, modal strain energy and frequencies. And NE elements or objects will be identified (The NE elements can be expressed as A1 , A2 , · · · ANE ). Modal strain energy is regarded as information sources S1 , and the local decision m1 can be obtained by using the MSEDRM method. (The acquired values will be converted into probability values, i.e. each of the damage coefficient values is divided by the sum of all values.). Similarly, the changes of natural frequencies are regarded as information sources S2 , and the local decision m2 can be obtained by using the FCDDM method (Similarly, the acquired values will be converted into probability values.). Thus, the basic identification results are obtained. Then, the acquired local decision m1 and m2 are sent to a fusion center. In the fusion center we can use the evidence combination theory to integrate information. Through the method, we can obtain more accurate results. A truss structure is analyzed as a numerical example to illustrate the performance of the proposed method. Taking into account the results of the numerical investigations of the multiple damage identification, the following conclusion can be drawn: (1) the MSEDRM method and The FCDDM method are difficult to successfully identify damage sites when there are multiple damages in the structure. Nevertheless, they can point out the potential damage locations for following fusion. (2) The proposed CDD method can perfectly identify damage sites, and the identification results of the CDD method are better than those of both the MSEDRM method and The FCDDM method.
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The study on damage state simulation for validating damage identification and safety evaluation algorithms Y.C. Yang Engineering College, Ocean University of China, Qingdao, China
F.Y. Yang Engineering College, Ocean University of China, Qingdao, China Offshore Oil Engineering (Qingdao) Co., Ltd, China
Y.G. Wang & M. Zhang Engineering College, Ocean University of China, Qingdao, China
ABSTRACT Shape Memory Polymer (SMP), a kind of smart materials which can memorize its former shape, has the general characters of plastics and rubbers and its obvious advantage is that the elastic modulus reduces with the temperature increase, which is named as shape memory effect (SME). The paper analyzes the damage simulation in numerical simulation and model test. At the same time, simple evaluation is given to the present method of damage state simulation. Then the paper discusses the memory mechanism and introduces mechanical test to study SMP’s shape memory mechanism as LgE − T . A new thinking is put forward
to make the stiffness-controlled specimen according to the deficiency of present simulation methods, which could not simulate the damage process. Therefore mechanical test is carried out to study the relationship between stiffness of SMP and temperature, stiffnesscontrollable model member is made and used in the test of damage state simulation under the condition of heated wind to control its temperature so as to change its stiffness. The validating test proves that the stiffness-controlled specimen can simulate the damage process of accumulation and has the potential of validating the damage identification and structural safety evaluation algorithms.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Statistical damage detection-based on strain mode shapes Li Gongbiao Hubei Key Laboratory of Roadway Bridge & Structural Engineering, Wuhan University of Technology, Wuhan, Hubei, China.
In this study, the strain mode shapes (SMS) of spatial frame structures are derived. Using the theory of perturbation matrix of SMS, the changes in SMS before and after damage events can be expressed by the reduction of elements stiffness. Using conditional probability density function (PDF) derived from sets of measured modal information determined at different times, a probabilistic damage approach is thus developed. The detailed steps are explained as following 1. For spatial frame structures, the strains of all elements can be obtained by the displacements of all nodes owing to axial stress is predominant, and the relationship can be expresses by a transition matrix. So the SMS of a spatial frame structure can be obtained by the mode shapes directly. Combined with the first rank perturbation matrix, changes in mode shapes are in a linear manner with changes in stiffness matrices of elements as following
where x0i = the ith strain mode shape before damage; λ0i = the ith eigenvalue (square value of the ith natural frequency of the structure) before damage; xi1 = the change of the ith strain mode shape; K ε1 = the change of the global strain mode stiffness matrix; Kεi = the ith element stiffness contribution to the global strain mode stiffness matrix; ci = the coefficient defining a fractional reduction of the ith elemental stiffness; Nm = the rank of modal parameters; Nc = the number of potential damaged elements. 2. Considering the uncertainty in model construction and modal parameters testing, a Bayesian statistical method is employed here. A Bayesian statistical method employing SMS is followed to obtain the posterior probability density function (PDF) of the parameters. The most probable values and standard deviations of the parameters are determined through maximizing the PDF. 3. As there are many elements in a real structure and it is impossible to allocate a reduction coefficient to
every element, all elements must be divided into groups and every group is allocated an equivalent coefficient. A similarity degree is defined for elements classification as following
where xi and xj are two vectors; · is the Euclidean norm; ε is a little constant which employed to avoid zero value denominator. By selecting the elements with high similar degrees of strain perturbation vectors into a group, all elements are classified. 4. A two steps damage detection approach is proposed here. On the first step, a substructure approach is followed in which the whole structure is divided into a set of groups and every group is allocated an uncertain parameter. By maximizing the updated PDF, the optimal parameters are determined, and then the potential damaged elements are selected. On the second step, an element stiffness reduction parameter of every potential damaged element is taken as an index for damage. Then the damage is detected through the Bayesian probabilistic framework such as on the first step. At last, the performance of the proposed approach has been demonstrated through a numerical example. White noise with root mean square (RMS) equal to 5%, 10% or 15% of the RMS of the measured mode shapes is added to simulate the measurement noise. Different classes of modal data are employed. Simulation results show that the substructure approach is efficient and valid to detect the range of potential damaged elements. And with the first three rank strain mode shapes employed in the two steps method, all damages are located correctly and the detected damage degree can be expressed with a probability form. Considering the existence of noise contamination and the large amount of structural elements, the proposed approach is promising in the real application of damage detection.
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Element level structural damage detection with unknown excitation Y. Lei, J.Y. Lei & Y. Song Department of Civil Engineering, Xiamen University, Xiamen, China
1
INTRODUCTION
Recently, some time domain SI methodologies including traditional least-squares estimation, extended Kalman filter and quadratic sum squares error method have been proposed for the identification of the dynamic properties of structural elements. However, these approaches require that information about structural displacement and velocity responses are available or they are obtained through integration of measured acceleration responses. Velocity and displacement responses are usually obtained by integrating measured acceleration responses, which result in errors. The displacement responses obtained through double integrations often involve significant drifts because of the noise contamination on the measured acceleration responses. Moreover, for many civil structures it is impractical to measure displacement, velocity and acceleration responses at all dynamic DDOFs due to the high cost of deploying a dense array of sensors in large civil structures. In practice, only a limited number of accelerometers are usually installed in structures to measure acceleration responses at some DDOF of the structures. In the proposed algorithm, only limited numbers of acceleration measurements of structures are utilized. Structure state vectors are treated as implicit functions of structural dynamic parameters and excitations. The
unknown structural dynamic parameters and excitation inputs are identified by an algorithm based on recursive least squares estimation with unknown excitations (RLSE-UI). Structural damage at element level is detected by the degrading of stiffness of damaged structural elements. Numerical simulation results of a three-story plan shear building with proportional damping and a one-story plane steel frame structure with Rayleigh damping demonstrate that the proposed algorithm can identify structural element stiffness parameters and detect structural damage at element level with good accuracy. Table 1. Story stiffness parameters (ki : MN/m) of the three story building. Story No.
Undamaged (Analy.)
Undamaged (Ident.)
damaged (Analy.)
damaged (Ident.)
1 2 3
300.0 240.0 200.0
303.2 237.5 199.4
300.0 240.0 180.0
307.1 237.7 179.1
Figure 2. One story steel frame.
Table 2.
Stiffness ki (MN/m) of the one-story frame.
Element No.
Undamaged (Analy.)
Undamaged (Ident.)
damaged (Analy.)
damaged (Ident.)
12.312 4.925 12.312
12.24 5.04 12.26
12.312 4.925 9.85
12.38 5.02 10.15
Figure 1. Three-story shear building.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Multi-scale sensing for structural health monitoring S.H. Sim Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, USA
B.F. Spencer, Jr. Nathan M. and Anne M. Newmark Endowed Chair of Civil Engineering, University of Illinois at Urbana-Champaign, Urbana, USA
With realization of potential of structural health monitoring (SHM) as an effective tool to monitor civil infrastructures has come extensive research, producing a wide variety of SHM techniques. One of the main approaches in SHM is to use measured vibration data to determine structural damage. Most of the vibrationbased approaches have employed global measurements, limiting their ability to localize damage. Multi-scale sensing using a heterogeneous mix of measured data at various scales has the potential to provide for more accurate characterization of the state of a structure. To date, little effort has been devoted to the development of multi-scale sensing strategies for damage detection. Studer and Peters (2004) presented a damage identification system for composite structures using strain, integrated strain, and strain gradients measured from optical fiber sensors. Law et al. (2005) used a wavelet-based approach to combine acceleration and strain responses to obtain better damage detection results than using the two measurements separately. Based on these results, Kijewski-Correa et al. (2006) developed a decentralized SHM strategy that uses measured strain and acceleration and can be implemented on a wireless sensor network. While these results are promising, further effort is needed to develop effective multi-scale damage detection strategies that can be applied to a broad class of structures. The flexibility-based damage locating vector (DLV) method proposed by Bernal (2002) is a promising damage detection approach for SHM. Damage detection methods based on the flexibility matrix have been shown to be effective (Gao et al. 2007). Gao (2005) developed a distributed computing strategy based on the DLV method that can be implemented on a dense array of sensor such as will be needed to effectively monitor large civil infrastructure. Nagayama and Spencer (2007) realized this distributed computing strategy on a network of smart using Intel’s Imote2. The DLV method has been shown to be quite versatile and effective.
Figure 1. 53 DOF planar truss model.
This paper presents a damage detection approach employing multi-scale sensing that builds off of the work of Bernal (2002), Gao (2005), and Nagayama and Spencer (2007). In particular, the stochastic DLV method (Bernal 2006) is extended to utilize strain and acceleration in combination. Numerical simulations are presented to verify the efficacy of the proposed method. Numerical simulations are conducted to verify the efficacy of the proposed extension to the stochastic DLV method using multi-scale data. Consider the 53 degree-of-freedom (DOF) planar truss model shown in Figure 1. Damage is simulated by a 40% stiffness reduction in element 9. The vertical and horizontal accelerations are measured at nodes 2∼4 and 16∼18 and the strain is measured at elements 3∼11. The excitation is a band-limited white noise input force applied in the vertical direction at node 6. The proposed multi-scale data damage detection strategy outperformed the stochastic DLV method using only a single type of data in the numerical simulation studies. In particular, the limitation of the strain-only case that the strain in the damaged element needs to be measured for damage detection to be successful was resolved with the aid of acceleration. This result shows the proposed multi-scale damage detection strategy is promising for SHM. Experimental verification of the proposed approach is currently underway. The authors gratefully acknowledge the support of this research by the National Science Foundation, under grant CMS 0301140 and 0600433 (Dr. S. C. Liu, program manager).
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Electroactive sensors and actuators (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
On the dynamic behavior of piezoelectric sensors bonded to elastic media G.L. Huang Department of Systems Engineering, University of Arkansas at Little Rock, Little Rock, AR, USA
X.D. Wang Department of Mechanical Engineering, University of Alberta, Canada
ABSTRACT: Surface-bonded piezoelectric sensors can be used to monitor the mechanical behavior of structures for damage detection. This article provides a comprehensive theoretical study of the dynamic coupling between a surface piezoelectric sensor and an elastic half-plane. Attention is focused on the transformation of mechanical deformation into electric signals under dynamic loads. The effect of the longitudinal stiffness of the sensor is included in the developed sensor model. The problem is then formulated by using Fourier transform and solving the resulting integral equations in terms of the interfacial stress. The accuracy of the developed sensor model is evaluated by comparing with results from the finite element analysis. Numerical simulation is conducted to study the relation between the sensor response and the deformation of the host medium under static and dynamic loads. The results indicate the significant effects of the geometry of the sensor, the material mismatch of the system, and the loading frequency upon the sensor response.
1
INTRODUCTION
Since newly developed piezoelectric materials exhibit strong electromechanical coupling, using networks of piezoelectric sensors/actuators in the design of the so-called smart structures has attracted significant attention from the industrial and research communities (Bar-Cohen, 2000). The results indicate that the piezoelectric elements will change the mode shapes and natural frequencies of the beam.The dynamic coupling between piezoelectric sensors and the host structure has also been observed through numerical studies using the finite element method (FEM) (Varadan et al., 1997, Sirohi and Chopra, 2000). The objective of the present study is to provide a comprehensive theoretical study of the static and dynamic mechanoelectrical behavior of piezoelectric sensors surface-bonded to an elastic half-plane under high frequency in-plane mechanical loads. Numerical simulation is conducted to show the effects of the geometry, the material combination, and the loading frequency upon the behavior of sensors. The analytical solutions are given for special static cases. 2
SENSOR MODEL AND RESULTS
The current study will be focused on the case where high-frequency mechanical loads are applied, which result in elastic waves in the host structure with their typical wavelength being comparable to the length of
the sensor. In this case, the inertia effect of the sensor must be considered. The equation of motion of the sensor in the longitudinal direction can be expressed as
Based on the sensor model, the effects of different sensor parameters and loading frequencies upon the mechanical and electric response of the sensor show the necessity to account for the interaction between the sensor and the host medium due to the material mismatch, especially for relatively high loading frequencies. The very stiff sensors or very high wave numbers should be avoided to ensure reliable sensing. It should be mentioned that for a specific loading frequency a lower wave number can be achieved by using a shorter sensor. REFERENCES Bar-Cohen,Y. 2000. “Emerging NDE Technologies and Challenges at the Beginning of the 3rd Millennium – Part I,” Material Evaluation, 58(1):17–30. Sirohi, J. and Chopra, I. 2000. “Fundamental understanding of Piezoelectric Strain Sensors,” Journal of Intelligent Materials Systems and Structures, 11:246–257. Varadan, V.V., Kim, J. and Varadan, V.K. 1997. “Modelling of Piezoelectric Sensor Fidelity,” IEEETransactions on Ultrasonics, Ferroelectrics, and Frequency Control, 44(3):538–547.
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Strain in concrete columns of different strengths, monitored by cement-based strain sensor Xiao Hui-gang, Li Hui* School of Civil Engineering, Harbin Institute of Technology, Harbin, China
Ou Jin-ping School of Civil Engineering, Harbin Institute of Technology, Harbin, China Dalian University of Technology, Harbin, China
25
40
Health monitoring in civil infrastructure need a durable strain sensor. CB-filled cement-based composite has been found a promising strain sensor material for long-term health monitoring for infrastructures. As a cement-based composite, the strength and deformation ability of CCN sensor are limited. The relation between CCN sensor strength and that of structure matrix would affect the destroyed sequence of CCN sensor and structure. Therefore, the strain monitoring property of CCN sensor in different strength concrete column was studied in this paper.
SG CCN
35
20
30
15
25
10
20
5 0
15
∆ρ/ρ0 (%)
INTRODUCTION Compressive stress (MPa)
1
⫺5
10
⫺10
5
Cracking of CCN
0 ⫺10
0
10
20
30
40
50
60
70
80
⫺15 ⫺20 90
⫺4 Compressive strain (10 )
Figure 1. Experimental results of C40 concrete column.
MATERIALS AND METHODS
90
3
RESULTS AND DISCUSSION
Figure 1 and Figure 2 shows the results of C40 column and C80 column during compressive test, respectively.
0
80 SG CCN
70
⫺2
60
⫺4
50
⫺6
40 30
⫺8
20
⫺10 ⫺12
10 Cracking of CCN
0 ⫺10
∆ρ/ρ0 (%)
CCN sensor was made with cement, carbon black (CB), water-reducing agent and other additions. All the components were mixed with special method and form specimens of size 30 × 40 × 50 mm. Strain of CCN sensor was monitored by resistance measurement using four-probe method. Concrete columns of size 100 × 100 × 300 mm were made with concrete of C40 and C80 respectively. During pouring, the smart concrete sensors were putted at the middle of the concrete column. Uniaxial loaded testing was conducted on MTS. During the tests, load and displacement of specimens were measured, the resistance of smart concrete sensor was measured synchronously.
Compressive stress (MPa)
2
0
4
8
12
16
⫺14 20
24
28
32
Compressive strain (10⫺4)
Figure 2. Experimental results of C80 concrete column.
stress-strain curve of “–SG” was obtained by strain gauge and cureve of “–CCN” was obtained by CCN sensor. For C40 concrete column, the monitoring results of strain gauge and CCN sensor agreed well, after the concrete column crashed, CCN sensor went
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on monitoring the strain for a while and then error signals occurred. The resistance-strain curve showed obviously that the resistance of CCN sensor decreased continuously after the column destroyed. As a brittle material, C80 concrete column destroyed abruptly when reached ultimate strength. Resistance curves of CCN sensors showed that CCN sensor damaged before concrete column destroyed.
4
CONCLUSIONS
Strain monitoring results of CCN sensor agreed well with that of strain gauge. The strain monitor ability of CCN sensor was dependent on the strength relation between CCN sensor and structure matrix.
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Vibration reduction of HDD disk-spindle system using piezoelectric shunt damping S.C. Lim, Y.M. Han & S.B. Choi Smart Structures and Systems Laboratory, Department of Mechanical Engineering, Inha University, Incheon, Korea
ABSTRACT Information storage plays a key role of leading toward the networked information society of 21 century. Its capability has been anticipated to be increased more and more according to the demand of digital media with tremendous information such as VOD (video on Demand) service, digital library and so on. The information storage devices (ISD) classified by optical disk drive and magnetic disk drive have been developed to meet the request of the playback of high quality movies as well as conventional data storage. The HDD (hard disk drive), as a representative magnetic disk drive, is widely used as a secondary information storage device such as computer peripherals. Recently, the areal density of HDD has been increasing at a growth rate of 100%. According to the increase of areal density, both active and passive vibration suppressions of highly rotating disk are significantly demanded. In HDD, many vibration modes of the rotating disk exist in frequency region ranging from 500 Hz to 1,500 Hz due to the mode split phenomenon. These vibration modes, which are easily excited from the external shock event by user handling and mechanical defects of the spindle motor, generate severe mechanical problems restricting the servo performance such as head off-track. Consequently, the vibration problem of the rotating disk-spindle system of the HDD has been recognized to be the most important issue associated with a limit of the recording density of the drive. In order to overcome this vibration problem, fluid dynamic bearing and squeeze air bearing damper were frequently adopted. However, these research activities on the vibration suppression of HDD were mainly concentrated upon dynamic characteristic analysis of the suspension or disk-spindle system only. The study about structural coupled vibration between external structures (base plate and drive cover) and disk-spindle system is considerably rare in spite of the importance of the shock resistance of the HDD for mobility.
Recently, smart material structures and systems with inherent adaptive capability to variable environment have made a great progress as a new methodology for vibration control. Among various smart material structures and systems, vibration control devices using piezoelectric materials have been proved to be very effective to the ISD through many theoretical and experimental investigations. The main objective of this work is to propose a new piezoelectric shunt damping methodology for the suppression of the coupled vibration between external structures (base plate and drive cover) and HDD disk-spindle system. The finite element (FE) model of the disk-spindle system is established and its suitability is proved by comparing FE results with modal testing results. The disk-spindle FE model is then incorporated to the external structure model. The coupled vibration characteristics between the disk-spindle system and the external structures are carefully investigated in order to determine a target vibration mode which restricts the recording density increment of the drive. After determining the target vibration mode, the piezoelectric bimorph is designed by considering mode shape of the target mode. The electromechanical coupling coefficient of the drive is then incorporated with the mechanical impedance of the shunted bimorph. Using the coupling coefficient, the shunt damping performance is predicted by investigating the displacement transmissibility on the target vibration mode. The piezoelectric bimorph is then optimally designed using the sensitivity analysis method in order to improve shunt damping performance. By comparing the calculated modal parameters with the target modal parameters, design parameters such as piezoelectric thickness are modified and used for updating the piezoelectric bimorph. After manufacturing the piezoelectric bimorph with optimally obtained design parameters, the shunt damping performance of the rotating HDD spindle-disk system is experimentally evaluated in frequency domain by changing impact and measuring points.
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Shear excitation in piezoelectric ultrasonic motors M. Schönecker Dynamics and Vibration Group, TU Darmstadt, Germany
1
INTRODUCTION
Existing piezoelectric Ultrasonic Motors mainly use the d33 or d13 effect for actuation of the stator, where an electric field in polarization direction causes strain. The d15 piezoelectric effect, where an electric field perpendicular to the polarization causes shear, although having a comparatively high coupling factor, has scarcely been used in resonant driven actuators like Ultrasonic Motors (USM). The literature on USM based on the shear-effect is reviewed briefly and the concepts compared to the presented approach.
2
Figure 1. Displacement shape and surface motion of the proposed actuator.
NEW ACTUATOR CONCEPT AND EQUATIONS OF MOTION
The new actuator concept aims at using the shear deformation induced by the d15 effect directly, so that no usage of asymmetries like bimorph structures or coupling through boundary conditions is made. To this end, a length-polarized block made of piezoceramic material is considered, which has four electrodes on the lateral faces, two opposing electrodes forming an electrode pair. By application of a sinusoidal voltage at one electrode pair, and a voltage with 90 degree temporal phase shift at the other electrode pair, a traveling wave is excited in the actuator which will be used to move an attached rotor. Using Hamilton’s Principle for piezoceramic media, the equations of motion are derived. For a twodimensional model (see Fig. 1), it is shown that only the sinusoidal mode shapes are coupled to the electric field.
3
COUPLING FACTOR OPTIMIZATION AND APPLICATION IN USM
From a quasistatic load cycle, a dynamic coupling factor is defined and applied to the present actuator. For the various vibration modes, distinct optimal geometries can be deduced; for the first resonance mode, an optimal aspect ratio of length to width of
Figure 2. First prototype of a piezoelectric USM using the proposed actuator concept.
the actuator l/a = 0.87 has been found to maximize the coupling between electric and mechanical fields. The proposed concept is tested in a prototype motor that has a very simple structure. It consists of only few additional parts besides the stator, bonded on the actuator to constitute the friction area, and the rotor, which is pressed on the stator and is propelled by its traveling waves (Fig. 2).
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Smart structural systems and materials
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Dynamic analysis of a biology inspired miniature directional microphone Z. Chen, A. Lacher & M. Yu Department of Mechanical Engineering, University of Maryland, College Park, MD, USA
1
INTRODUCTION
Sound source localization is widely applied in many fields, including hearing aid, robot navigation, sensor network, etc. In existing sound source localization methods, like in humans and most other vertebrates, the time delay estimation based locator with microphone array is very widely used to calculate the azimuth of the sound source relative to the microphone array for its ability to achieve real time localization, especially in recent digital systems. In applying these methods, one concern is that noise and reverberation can seriously degrade the microphone reception. For this reason, accurate measurement of time delay between microphones is very important for accurate sound direction detection. In addition the microphones need to be located far away enough such that the difference of the sound signal arriving at those microphones can be detected. This poses a fundamental challenge to the miniaturization of directional acoustic sensor systems. However, in some small insects, the auditory receptors are forcibly set close to each other. In this case, the interaural differences are often too small to be useful as directional cues, if they are to be processed by the nervous system. Such ears can be found in the parasitoid fly Ormia Ochracea, which shows a remarkable ability to locate sound source both in nature and in the laboratory. With a separation of only 520 µm (the best possible ITD (interaural time difference) of 1.45 µs and IID (interaural intensity difference) of less than 1 dB), Ormia’s ears can detect extremely small changes (less than 2◦ ) in the incident sound field direction. In this paper, a novel design of a biologyinspired miniature directional microphone is proposed, which consists of two clamped circular diaphragms
Figure 1. The structure of the miniature biology-inspired directional microphone.
mechanically coupled by one connecting beam pivoting around its center, as shown in Figure 1. An analytical mechanical model is also presented to calculate the response of the proposed directional microphone diaphragms subject to sound incident from different directions. Our simulation results show that the proposed biology-inspired miniature directional microphone has a remarkable ability to amplify the time delay (interaural time difference (ITD)) of the sound induced diaphragm responses. Different parameters such as coupling strength and damp factor are studied to evaluate the performance of the proposed biology-inspired miniature directional microphone. These analyses and results are expected to be valuable for carrying out the design of the biology-inspired miniature directional microphones to achieve high accuracy, high resolution and wide frequency range in various sound source localization applications.
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Magneto-mechanical coupling of smart composites with chain-structured magnetostrictive particles H.M. Yin Transportation Laboratory, Folsom Boulevard, Sacramento, CA, USA
L.Z. Sun Department of Civil and Environmental Engineering, University of California, Irvine, USA
Magnetic particle-filled composites as a class of smart materials have attracted a good deal of attention from engineers and researchers. Composites manufactured by brittle magnetic particles and a strong matrix allow the magnetic properties of the particles to be maintained while keeping overall mechanical performance adjustable. In recent years it has been found that fabricating the composite under an applied electric or magnetic field transforms the randomly dispersed particles into chains parallel to the direction of the applied field due to the interaction force. Upon curing the matrix material, the chain structure is locked into place so that the chain-like microstructures in the composites are obtained. When a magnetic field is further applied, an effective magnetostriction has been observed due to the particle’s magnetostriction and the magnetic interaction force between particles. The objective of this paper is to apply micromechanics principles to investigate the effective magnetomechanical coupling for smart composites containing chain-structured magnetostrictive particles under both magnetic and mechanical loading. Here, the microparticles are assumed to be ideal soft magnetic materials, i.e. the residual magnetic field is always zero when the external magnetic field is removed. For simplicity,
we assume that applied magnetic and elastic loading is in the linear range, both the particle and matrix phases have isotropic magnetic and elastic properties, and the magnetic permeability for each phase is assumed to be independent to the mechanical loading such that the magnetic permeability and elasticity of the particles and matrix are treated constant. For the magnetostatic theory to be applicable, magnetic loading is assumed to be at a low frequency and the size of the particles is much smaller than the wavelength of the magnetic field. A representative volume element containing a chain of infinite particles is introduced to solve averaged magnetic and elastic fields in the particles and the matrix based on the Green’s function technique. Effective behavior of smart composites is estimated by considering the particle’s magnetic interaction force and particle-particle mechanical interaction. Magnetic-field-dependent, transversely isotropic effective elasticity of composites is derived explicitly. Comparisons of model results with the experimental data and other models show the efficacy of the model and suggest that the particle interactions have a considerable effect on the effective magneto-elastic properties of composites.
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Natural frequency of beams with embedded piezoelectric sensors and actuators C.N. Della & D. Shu School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore
INTRODUCTION
vf
Smart structures are important because of their relevance to structural health monitoring, structural vibration control and transportation engineering. This is because these systems incorporate particular functions such as sensing, processing and actuation. The use of piezoelectric materials is a primary focus in the study of smart materials since these materials can function both as sensors and actuators. In this research, a mathematical model for the vibration of beams with embedded arrays of piezoelectric sensors and actuators is presented. The piezoelectric sensors and actuators are analyzed as inhomogeneous ellipsoidal inclusions in a non-piezoelectric matrix (host beam) by using Eshelby’s equivalent inclusion method (Eshelby, 1957; Mura, 1987). The formulation for the piezoelectric inclusion problem is decoupled into two equivalent inclusion problems, an elastic problem and a dielectric problem. An equation for the natural frequency of the beam is determined using the variational principle in Rayleigh quotient form, which is expressed as functions of the elastic strain energy and dielectric energy of the piezoelectric inclusions. These energies are derived using Mura’s formulation for inhomogeneous inclusions. The Euler-Bernoulli beam theory and Rayleigh-Ritz approximation technique are used in the present analysis. In addition, the influences of the size, volume fraction and location of the piezoelectric inclusions on the natural frequency of the beam are studied.
2
MATHEMATICAL MODEL
For stationary solutions, the Rayleigh quotient can be expressed as
Fundamental frequency ω/ωO
1
p 0 ε 2 /ε 2 ⫽ 3
3.0
ε p2 /ε02 ⫽ 2
d
e
1.5%
n ⫽ 20
ε p2 /ε02 ⫽ 1
2.5
2%
1% 2%
2.0
1.5% 1%
1.5
2% 1.5% 1%
1.0 0.2
0.3
0.4
0.5
0.6
0.7
0.8
Actuator location d/e
Figure 1. Influence of the actuator location, d/e, on the fundamental frequency of the beam, ω/ω0 , with various piezoelectric volume fraction vf .
The numerator in Equation 1 is the internal energy of the system, which is the sum of the elastic strain energy and the dielectric energy. These energies will be analyzed using Eshelby’s equivalent inclusion method (Eshelby, 1957; Mura, 1987).
3
RESULTS AND DISCUSSIONS
This section presents the results obtained using the mathematical model described above to study a simply supported beam with embedded piezoelectric sensors and actuators. The host beam is made of Alplex material and piezoelectric sensors/actuators are made of PZT-5H. The normalized fundamental frequency ω/ω0 as a function of the actuator location is shown in Fig. 1, where ω0 is the fundamental frequency of the beam without the actuation effect. The number of actuators, n, is identical to the number of sensors. It can be seen that the frequency ω/ω0 increases as the actuator is located nearer to the beam surface. The frequency further increases with increasing piezoelectric volume
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p
p
fraction vf and ε2 /ε02 , where ε2 /ε02 is the normalized eigenstrain actuation.
Proceedings of the Royal Society of London A 241(1226): 376–396. Mura, T., 1987. Micromechanics of defects in solids 2nd ed. Martinus Nijoff.
REFERENCES Eshelby, J.D., 1957. The determination of the elastic field of the ellipsoidal inclusion and related problems.
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Effects of polarization orientation on the effective electromechanical properties of 1–3 piezoelectric composites C.N. Della & D. Shu School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore
INTRODUCTION
20
Piezoelectric ceramic/polymer composites have been widely studied because of their theoretical interest and technological applications. Piezoelectric composites with 1-3 connectivity have recently received increased attention due to their potential applications in underwater acoustics and biomedical imaging. 1–3 piezoelectric composites have piezoceramic rods, embedded in a piezopassive or piezoactive polymer matrix. Their electromechanical properties of the piezoelectric composites can be tailored to meet specific applications. In addition, their flexibility offers an additional advantage over the brittle monolithic piezoelectric. In this research, we study and compare the effects of polarization orientation on the effective electromechanical properties of 1–3 piezoelectric composites. Piezopolymer matrix and piezoceramic matrix phases are considered. The micromechanics based MoriTanaka model for piezoelectric composites, which was developed by Dunn and Taya (1993) is used in the present study. 2
PZT-7A/BaTiO
3(0°)
15 10 e33 (C/m2)
1
5 0
PZT-7
⫺5
0°)
E)(18
DF-TrF
A/P(V
PZT-7
A/P(V
DF-T
0°) rFE)( 0°)
(18
iO3
⫺10
T /Ba
A
T-7
⫺15
PZ
⫺20 0.0
0.2
0.4
0.6
0.8
1.0
Piezoceramic fiber volume fraction vf
Figure 1. Effective piezoelectric constants of the 1-3 piezoelectric composites as a function of the fiber volume fractionvf˙ .
where S is the eshelby tensor. The components of the eshelby tensor can be found in dunn and taya (1993) and taya (2005).
MATHEMATICAL MODEL 3
For piezoelectric composites, the effective moduli using the Mori-Tanaka method is given by
RESULTS AND DISCUSSIONS
The effective piezoelectric constants e33 of the piezoelectric composite as a function of the fiber volume fraction vf is shown in Fig. 1. For PZT/PVDF composite, the poling orientation do not significantly influence e33 as compared to that of PZT/BaTiO3 .
where E = effective electro-elastic moduli Em = electro-elastic moduli of the matrix Ef = electro-elastic moduli of the inclusion vf = volume fraction of the piezoelectric rod/fiber Af = concentration factor
REFERENCES
The dilute mechanical concentration tensor for the fiber
Dunn, M.L. and Taya, M. 1993. Micromechanics predictions of the effective electroelastic moduli of piezoelectric composites. International Journal of Solids and Structures 30(2): 161–175. Taya, M. 2005. Electronic Composites: Modeling, Characterization, Processing, and MEMS Applications. Cambridge University Press.
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Hybrid damage monitoring in PSC girder bridges using acceleration-impedance signatures J.T. Kim, W.B. Na, J.H. Park, D.S. Hong & H.S. Do Pukyong National University, Busan, Korea
The prestress-loss of the PSC bridges is related to reduce the stiffness for entire structure and the flexural crack is related to reduce the stiffness for local element. Hence, the damage type cannot be classified by using only the changes of vibration characteristic. For promise of exact damage detection, an algorithm, which can classify the damage type, is needed. In this study, a new hybrid damage monitoring system is proposed to alarm the damage, classify the damage type (i.e. prestress-loss or the flexural crack), locate the damage and estimate the damage severity. Figure 1 shows a schematic of the proposed system, which consists of three steps: (1) Step 1 – global damage monitoring, (2) Step 2 – damage classification, and (3) Step 3 – damage estimation. In Step 1, the occurrence of damage is alarmed in global manner by using change of acceleration signatures. As the acceleration signature, we use a newly proposed frequency-response-ratio assurance criterion (FRRAC). In Step 2, the damage type is classified by using change of impedance signatures. In Step 3, the damage classified from Step 2 is examined in detail to estimate the location and the severity of damage by using a modal-strain energy based damage index method and a prestress (PS) loss prediction method. To verify the proposed system, experimental tests are performed for PSC girder with T-type cross-section
and an unbonded tendon. Several damage scenarios are selected for the verification as follows: (1) 5 prestress-loss cases and (2) 2 simulated flexural stiffness-loss cases using added mass. The results of the verification for the proposed hybrid damage monitoring system in PSC bridges are concluded as follows: Step 1: The proposed FRRAC, which is a damage alarming method, successfully alarmed all of damages (PS-loss and flexural stiffness-loss) as shown in Figure 2. Step 2: The EM impedance method using the change of impedance signature such as resonant frequency or RMSD can exactly classify whether the alarmed damage in step 1 is due to prestress-loss or flexural stiffness-loss as shown in Figure 3. Step 3: The methods, which are the DI method and PS-loss prediction method, locate the damages and estimate the severity of damage with a few errors for all damages as shown in Figure 4.
Figure 2. Damage alarming (PS-loss & stiffness-loss).
Figure 3. Damage classification (PS-loss & stiffness-loss).
Figure 1. Schematic of hybrid damage monitoring for PSC.
Figure 4. Damage Estimation (PS-loss & stiffness-loss).
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Probabilistic distribution of displacement response of frictionally damped structures under earthquake loads Sang-Hyun Lee, Kyung-Jo Youn, & Kyung-Won Min Department of Architectural Engineering, Dankook University, Seoul, Korea
Ji-Hun Park Department of Architectural Engineering, University of Incheon, Incheon, Korea
1
INTRODUCTION
The accurate peak response estimation of a seismically excited structure with frictional damping system (FDS) is very difficult since the structure with FDS shows nonlinear behavior dependent on the structural period, loading characteristics, and relative magnitude between the frictional force and the excitation load. Previous studies have estimated that by replacing a nonlinear system with an equivalent linear one or by employing the response spectrum obtained based on nonlinear time history and statistical analysis. In this study, nonlinear time history analyses were performed for the structure with FDS subjected to artificial earthquake loads generated using Kanai-Tajimi filter. An equation for the probability density function (PDF) of the displacement response is proposed by adapting the PDF of the normal distribution. Finally, coefficients of the proposed PDF are obtained by regression analysis of the statistical distribution of the time history responses. Finally, the correlation between PDFs and statistical response distribution is presented.
2
Figure 1. Comparison on probabilistic density function of displacement response of SDOF structure(Tn = 0.5).
PROPOSING THE NEW PDF BASED ON NORMAL DISTRIBUTION
The PDF of the structure with FDS is proposed as follows to consider the variation of PDF according the normalized friction force ρ and the natural period Tn by modifying the PDF of the normal distribution.
Figure 2. Comparison on probabilistic density function of displacement response of SDOF structure(Tn = 1.5).
Where, α is a parameter to reflect the effect of the natural period of the structure.
3
STATISTICAL VERIFICATION OF PDFS APPROXIMATION
The validity of the PDF proposed in this study for the structure with FDS is statistically verified according
141
Considering PDF proposed by Cai and Lin, the propose PDF shows more accurate than pervious one especially in the natural period of structure is 0.5(sec) And in the natural period of structure is 1.5(sec), the accuracy of both PDFs is verified to represent accuracy degree over 95%.
to the friction force and the natural period of the structure. 4
CONCLUSION
PDF of structural response was proposed for estimating the peak displacement of a SDOF structure installed frictional damping system under excitation load defined in probabilistic sense such as earthquake.
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Civil infrastructure monitoring and assessment (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Long-term structural health monitoring of the 2006 Torino’s Olympic pedestrian cabled-stayed bridge L.M. Giacosa, A. De Stefano & P. Civera Polytechnic of Torino, Torino, Italy
F. Ansari University of Illinois at Chicago, Chicago, U.S.A.
1
3
INTRODUCTION
Temporary and most important permanent structural health monitoring of an original cable-stayed bridge is discussed. In this paper it is highlighted the monitoring methodology adopted and the innovative sensors installed to identify the behaviour of the structure under different condition. It is not a structural health monitoring an end of itself, but it is a newer approach and prospective to improve the existing methods of civil engineering structures monitoring. In this paper experimental and finite numerical model results are discussed to strengthen methodologies chosen.
2
STRUCTURE DESCRIPTION
The pedestrian bridge in Torino, designed to connect the Olympic Areas is defined one of the symbol of the modernizing and internationalization of the city. This project takes part to the retraining of the Ex General Market Area (MOI), necessary for the 2006 Torino’s Winter Olympic Games and direct to the carrying out of a Torino Olympic Village. The bridge is realized on an Italian railways property and placed at a distance of 65 m from the railway path Ex General Market side and 150 m from the Lingotto side. Torino pedestrian cable-stayed bridge has several critical point, just verified during its construction: first of all cables behaviour in comparison with the deck behaviour under the normal exercise conditions, but above all under different wind conditions. The structure is principally constituted by a flexible steel frame structure with a curvature change along its longitudinal development. As cable-stayed bridge with a 380 m deck long in curve, the designers decided to install a counter-cable to fix the hollow part directly on the ground to increase the stability. From one side the counter-cable is connected to the deck structure and to the other side on the ground with a solid foundation.
STRUCTURAL HEALTH MONITORING
As above written the principal and critical points to taken into account and analyze with a specific structural monitoring are cables, counter-cable and in general deck behaviour. To perform a complete SHM approach, also, was considered the behaviour of the steel-frame structure of the arch. SHM system provides several type of sensors applied on the structures: making use of the numerical results obtained from designers it was been possible to study properly sensors and technical performance of themselves. Sensors acquisition is simultaneously from all the instruments on the bridge installed, experimental data shall download to a remote acquisition system that elaborating a first pre-processing send to the users the data. Inclinometers and accelerometers sensors are connected among themselves through a single cable able to provided them energy and also to transmit data to the central unit. Fiber optic sensor (FOS) used for the cables monitoring is based on FBG fiber optic technology. Active research plan developed by the University of Illinois at Chicago has develop these type of sensors to monitoring the behaviour of tension of the cable. Others type of FOS were installed by the bridge foundation. Fiber Bragg sensors patches were installed directly on the surface of steel frame pillar, connecting the bridge deck and the foundation. As a permanent monitoring the system was thought with an internet connection and a PHP user interface to better perform acquisition and visualization criteria. The writers performed an ambient vibration test on the pedestrian bridge to establish its dynamic properties (frequencies, mode shapes and damping ratios) for system identification purposes. The dynamic properties determined from the vibration testing provide an objective measure of the in-situ structural characteristics.
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New methods for structural condition assessment of highways and airports Lu Sun Department of Civil Engineering, Catholic University of America, Washington D.C.
This paper introduces new methods for nondestructive testing and evaluation of highway and airport pavements. A state of the practice of pavement structural condition assessment is briefly reviewed. Transient response of multilayered elastic system under positionfixed dynamic loads was obtained analytically using various integral transforms and transfer matrix method. Efficient algorithms were developed to implement numerical computation of dynamic response of pavements under impulse loads. Numerical results have been compared with the literature and results obtained from finite element analysis. Very good consistency has been observed. Structural condition
assessment is then formulated as an optimization problem in which structural and material properties of highway and airport pavement structures need to be identified. A software package has been developed that integrates those efficient numerical algorithms as well as a pool of nonlinear programming techniques to effectively and efficiently invert unknown parameters. The inversion has been compared with several existing computer programs of pavement nondestructive evaluation, demonstrating a superior performance of the developed theory, algorithm and software. It provides a powerful tool for studying structural condition assessment of highways and airports.
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Qinghai-Tibet railway subgrade temperature monitoring system-based on FBG sensors Baochen Sun & Jingyun Dai Shijiazhuang Railway Institute, Shijiazhuang, Hebei
Wentao Zhang State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing
1
INTRODUCTION
0
2
4
6
8
0 ⫺1
It is important to ensure that the structures on the subgrade in the 550 kilometers-long permafrost area should be safety. We are preparing to present a subgrade temperature monitor system based on fiber Bragg grating (FBG) according to the condition of Qinghai-Tibet Railway. We use the advanced technology of FBG measuring, and manage to control the system by computer using fiber network communication. Before the monitoring system is operated, we have to do some experiments on the feasibility of the FBG sensors on the Qinghai-Tibet railway.
Temperature, °C
⫺2 ⫺3 ⫺4 ⫺5
TRTS
⫺6
FBG
⫺7 ⫺8 ⫺9 ⫺10 Depth, m
Figure 1. The result of the TRTSs and FBG temperature sensors.
2 THE PRINCIPLE OF THE FBG TEMPERATURE SENSORS FBG sensor is based on the principle that the FBG is very sensitive to the variety of temperature. The FBG is compact, simple and can be demodulated in a wavelength-coding manner. So we can use only one wavelength spectrometer and inspect all FBGs’ changes of wavelength. It becomes easy to measure the strains of the structure at distributed points.
sensor demodulator which is put in a car and communicated with the sensors with a single fiber. And we use the resistance tester to get the temperature the TRTS measured. The results are shown in figure 1. We can find that difference of the temperature between the FBG sensors and TRTS is less than 0.1◦ . This shows the accuracy of the FBG sensors is less than 0.1◦ .
3 THE EXPERIMENT ON THE QINGHAI-TIBET RAILWAY
4
In order to test the practical stability of the FBG subgrade temperature monitoring system, we made a contrast test of FBG sensors and thermal resistance temperature sensors (TRTS). In the experiment we bound 15 FBG sensors and 15 TRTSs together one by one, and put them in a hole of 20 meter’s depth which is used to measure the subgrade temperature. We can get the temperature of the FBG sensors from the PI-101 FBG temperature
CONCLUSION
The unique advantages of FBG temperature sensors make it possible for us to realize the Qinghai-Tibet railway subgrade temperature monitoring system. The result of the experiment on the Qinghai-Tibet railway shows that the accuracy of FBG sensors can meet the demand of the monitoring system, and the FBG sensors is stable in the permafrost area. We can use a single fiber to collect and transmit the signals, which is very convenient to operate.
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On structural safety assessment of bridges by EWMA control chart and reliability analysis A. Zongbao LiangA,B , Weimin Chen, Yong Zhu & Yumei Fu The Key Laboratory for Optoelectronic Technology & System, Education Ministry of China, Chongqing University, Chongqing, China
B. Jianqiu Cao The Department of Computer and Information, Chongqing Jiaotong University, Chongqing, China
ABSTRACT Recently more and more attentions have been paid in structural safety assessment of bridges, which is one of the key components in structural health monitoring of bridges (SHMB). However because of the high complexity of the structural system of bridges, it is difficult to find the hidden trouble of bridges introduced by many factors such as the increasing vehicles, structural degradation, nature disaster and etc. The traditional model-based assessment methods depend seriously on the precise structural model of bridge and the certain excitation to the bridge system which can not be effectively achieved due to the changes of the structural parameters of bridges in the service and the ambient excitation selected in the SHMB. Actually, according to the theoretical analysis of bridge structure, the procedure of structural assessment of bridges mainly focuses on the shifts monitoring of the structural health information of bridges, such as the change of strain or deflection of the girder under live-load. It means that when the varying tendency of
the structural health information is irreclaimable, the bridge is considered to be unsafe and the respective work must be implemented. It is well known that exponentially weighted moving average (EWMA) control chart is a useful technique for statistical process control and process monitoring when the small shifts need to be detected interestingly. In this paper, a method is introduced to achieve the structural safety assessment of bridges by EWMA control chart associated with reliability analysis. In the context, the effect of live-load deflection and strain of the main girder of bridge are firstly extracted from the total measurement as assessment data by wavelet analysis. And then the EWMA control chart is designed to complete the structural safety assessment of bridge, in which the control limits for primary alarm are set by optimal method and the control limits for safety alarm are estimated by reliability analysis. The results from application in a real bridge show the effectiveness of the proposed method in structural safety assessment of bridges.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Application of wireless monitoring system for the ambient vibration study of the Wuyuan steel arch bridge Y. Lei, W.A. Shen & Y. Song Department of Civil Engineering, Xiamen University, China
J.P. Lynch Department of Civil and Environmental Engineering, University of Michigan, U.S.A.
1
INTRODUCTION
They are connected to the wireless and tethered monitoring systems, respectively.
Traditionally, structural monitoring systems employ coaxial wires to transfer measured data from sensors to centralized repository. Installation and maintenance of such wired-based monitoring system on large scale civil infrastructures, such as large span bridges, is time consuming and expensive, which limit widespread adoption of traditional monitoring systems. With recent development of wireless communication, wireless monitoring systems have been proposed to eradicate the extensive lengths of wires in the tethered systems (Spencer et al. 2006, Lynch et al. 2000, Lynch et al. 2006). Recently, some innovative academic and commercial wireless sensing systems have been developed (Lynch et al. 2006). Among them, the academic wireless sensing unit prototype developed at University of Michigan and Stanford University have received great attention as it emphasizes the design of a powerful computational core, low power consumption and multitasking capability (Lynch et al. 2005, Wang et al. 2006). Due to the low cost and easy installation advantages of the wireless sensing system, it is applied to the identification of modal properties of the bridge. The identification of modal properties of the Wuyuan Bridge is accomplished using ambient vibration data acquired by the wireless sensing units. Wuyuan Bridge, with a total of 810 m long, is a bride on the island ring road in Xiamen, China (Figure 1). At each location, two accelerometers are aligned side-by-side (Figure 2).
Figure 1. Side view of the Wuyuan Bridge.
2
CONCLUSIONS
The academic wireless monitoring system with smart sensing units developed at Stanford University and Michigan University is validated through ambient vibration test on Wuyuan steel arch bridge in Xiamen, China. Acceleration responses of the bridge measured by the wireless units are in close match with those by a wire-based data acquisition system.
Figure 2. The wireless and wired-based sensing units.
Figure 3. Comparisons of acceleration time history.
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In Figure 3, time histories of acceleration recorded by a wireless sensing unit at locations #1 is in close match with those by the traditional tethered systems. Therefore, the wireless monitoring system can be applied to the identification of the modal properties of
the bridge. The identified modal properties are in good agreements with those evaluated by engineers after the bridge was constructed.
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Magnetorheological fluids and dampers (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Analytical study on MR fluid shock absorber with annular channel employing biviscous constitutive relationship C.R. Liao, H.H. Zhang & M. Yu Center for Intelligent Structures of Chongqing University, Chongqing, P.R. China
W.M. Chen & S.L. Huang Key Laboratory for Optoelectronic Technology & Systems, EMC, Chongqing, P.R. China
Magnetorheological (MR) fluids are colloidal suspensions of magnetic particles in a non-magnetic fluid. When they are subjected to a magnetic field, the particles aggregate chains in the direction of magnetic field, which generates rapid liquid to solid transition. The controllability of yield stress has led to substantial application research to various mechanical systems, including shock absorbers. In development MR fluid shock absorber, it is important to accurately model MR fluids. So far, Bingham model is widely used in MR fluid devices design. MR fluid is typically characterized by two distinct flow regimes, which are the pre-yield regime where local shear stress is less than static yield stress and post-yield regime where local shear stress exceeds static yield stress. Alternatively, pre-yield behavior of MR fluids can be described as rigid, post-yield behavior can be described as fluid with static yield stress. Even though the Bingham constitutive model is mathematically simple, it exhibits discontinuous characteristics in shear stress versus shear rate relationship at the zero shear rate condition. In the post-yield region, relationships between shear stress and shear rate are accurately observed, Bingham model cannot account for practical behavior of shear stress versus shear rate in pre-yield region. To mitigate drawback of the Bingham model, Williams et al. introduced the Biviscous constitutive relationship which has two distinct viscosities to depict MR fluid behaviors in pre-yield region and post-yield region respectively. The primary objective of this study is to explore design methodology of MR shock absorber by employing Biviscous constitutive model and
quasi-static flow equations based on the Navier-Stokes equations. According to experimental data from laboratory, the (MR) fluid Biviscous constitutive model parameters have been identified via optimization of error function, which is defined as error sum between shear stresses from experimental tests in laboratory and shear stresses depicted Biviscous constitutive model. Authors have theoretically set up quasi-steady flow equations for MR fluids in annular channel by analyzing force equilibrium on fluid element and obtained analytical velocity profile of MR fluids though annular channel using the Biviscous constitutive model and rational boundary conditions. In accordance with piston velocity and annular channel geometrical parameters, MR fluid shock absorber performances have been predicated by means of analytical methodology in order to determine design parameters. In the light of technical requirements of front suspension of Chanan star minibus, a MR fluid shock absorber, designed and fabricated by Chongqing University according to design method presented in this paper, has tested by electro-hydraulic servo vibrator and its control system in National Center for Test and Supervision of Coach Quality. The experimental results reveal that damping force offered by MR fluid shock absorber can be controlled by application of magnetic field (electric current) and analytical methodology and design theory are reasonable. Key words: Magnetorheological fluid, Bingham model, Biviscous model, shock absorber
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Geometric design of a circular plate MR clutch J.M. He, J. Huang & L.J. Fu Chongqing Institute of Technology, Chongqing, China
1
INTRODUCTION
Altering the strength of an applied magnetic field will precisely control the yield stress of Magnetorheological (MR) fluids. Based on the mechanical characteristics, the fluids can be used in the magnetically controlled devices such as dampers. An MR damper is a semi-active control device that uses MR fluids. Altering the strength of an applied magnetic field will change the damping force of the damper. In order to design an MR fluid damper, A designer must be able to predict the performance of the damper in
consideration of its applied magnetic field and geometry. In this paper, the Bingham model is used to describe characteristics of the MR fluids subject to an applied magnetic field. Based on Navior-Stokes’ equation, the axial flow of the fluids between the piston and the outer cylinder is analyzed. The expression for the damping force is derived to provide the theoretical foundation for the design of the damper. Based on this equation, after mathematical manipulation, the engineering expressions for the gap and effective length of the annular MR fluid between the piston and the outer cylinder are derived.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Research on cylindrical magnetorheological fluids clutch Yan Yang1,2 , Hui Li & Jin Huang 1 Department
of Mechanic, Chongqing Institute of Technology, Chongqing, China
Bo-seon Kang of Mechanical Engineering, Chonnam National University, Gwangju, Korea
Magnetorheological(MR) fluids consist of stable suspensions of particles in a carrying fluid such as silicone oils. They are smart materials that respond to an applied magnetic field in their rheological behavior. In the absence of applied magnetic field, MR fluids exhibit Newtonian-like behavior. Upon application of a magnetic field, the behavior of fluids is often represented as semi-solids having a controllable yield stress in milliseconds. A magnetorheological (MR) fluids cylindrical clutch is a device to transmit power and motion by shear force of MR fluids. A MR fluids cylindrical clutch has the property that its transmitting torque changes quickly in response to an external magnetic field. In the absence of an applied magnetic field, the transmitting torque of clutch is achieved by the viscous force of MR fluids in liquid state. When the external magnetic field is applied, the suspended particles in the MR fluids become polarized and gathered to form chain-like structure. These chain-like structures restrict the movement of the MR fluids, thereby increasing the yield stress of the fluids. The torque can be transmitted by utilizing the shear stress of the MR fluids. The transmitting torque can be adjusted continuously by changing the magnetic field strength. To analyze the transmitting torque of clutch, we first assume: 1. the MR fluids is incompressible; 2. the flows of MR fluids is stable; 3. there are no flows in radius and axis direction; 4. the flows of MR fluids is a function of radius; 5. ignore the gravitation; 6. the magnetic field strength is uniform; 7. the pressure of MR fluids is uniform. By the assumptions, we obtain the torque
Eq. (1) is also regard as the design formulation of cylindrical MR fluids clutch when the torque is known. By this equation, we can see the important effect parameters are width of MR fluid action region, L and radius of outer cylinder and rotor, r1 , r2 . For r1 and r2 , the
Figure 1. The cylindrical MRF clutch. 400
80r/min 120r/min
Torque (N.m)
2 Department
300
200r/min
200 100 0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
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Figure 2. Transmitting torque by cylindrical MRF clutch.
thickness of MR fluids, h is introduced that is equal to r2 − r1 . So the torque is directly proportional to action width of MR fluids and inversely proportional to thickness MR fluids. Based on the equation, we design a cylindrical MR fluids clutch which shown in Figure 1. Using this clutch, we conduct some experiments and obtain these results. By Figure 2, we can see the transmitting torque is very small when there are no magnetic field is applied, because the torque is achieved only by viscosity of MR fluids. The transmitting torque is directly proportional to magnetic field strength and the experimental result is consisting with theory result. Because the limits of input power, we can not obtain the large transmitting torque when the rotate velocity is high. That is also satisfied with the practice situation.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Smart sensing for structural health monitoring (S3HM) A. Deraemaeker Active Structures Laboratory, Université Libre de Bruxelles, Brussels, Belgium
G. De Roeck & E. Reynders Department of Civil Engineering, Katholiek Universiteit Leuven, Kasteelpark Arenberg Heverlee, Belgium
K. Worden & G. Manson Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield
J. Kullaa & V. Lämsä Laboratory for Mechanics of Materials, Helsinki University of Technology, Finland
W. Ostachowicz Institute of Fluid Flow Machinery, Polish Academy of Sciences, Fiszera, Gdansk, Poland
The objective of the ESF Eurocores S3T project “Smart Sensing for Structural Health Monitoring” (S3HM) is to combine the most recent developments in sensor and actuator technology, networks, signal processing and computer techniques to explore new avenues in structural health monitoring (SHM). The consortium involves 5 research centres with complementary expertise: smart materials and structures, signal processing, identification, model updating, damage modelling, wave propagation. The project aims at addressing the following issues: using smart sensing technologies for SHM, extracting features relevant to damage and immune to variability, designing robust methods for autonomous SHM systems.
The expected outputs for the project are: modelling tools for damage and wave propagation; guidelines for the design of optimal sensor networks based on new technologies; robust feature extraction and pattern recognition methods, methods to remove the effect of environment and variability from measurements and experimental validations of the new concepts developed in order to show the feasibility of SHM on real structures. After a description of the S3HM project, this paper presents the results achieved so far in the consortium, as well as the perspectives of the project.
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Structural health monitoring
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Damage monitoring and life predication from nondestructive evaluation to structural health monitoring Gui Yun Tian1,2 , John Wilson1 , Binqiang Zhang2 & Haitao Wang2 1 School 2 School
1
of Electrical, Electronic and Computer Engineering, Newcastle University, UK of Automation, Nanjing University of Aeronautics and Astronautics (NUAA), China
INTRODUCTION
Great advances have been made in recent years in non-destructive testing and evaluation (NDT&E) in the qualitative assessment of stresses, flaws and material properties, many of which can be applied to structural health monitoring. Traditionally, these two research communities are separated. This paper tries to bridge the gap for SHM to detect such damage using non-destructive evaluation (NDE) techniques that usually require a sensor, sensor array or network over the structure or system. The attraction for SHM over NDE is the reduction in inspection cost and the structural ‘down-time’ associated with inspection with quantifiable performance has not been satisfactorily addressed.
2
NDE AND SENSOR TECHNOLOGY FOR SHM
Although there have been major advances in NDE in recent years, full advantage has not been taken of these advances by the emerging SHM community. Coupling these NDE techniques with advances in sensor technology will allow NDE methods to be adapted to SHM requirements. Pulsed excitation presents the opportunity to extend penetration depth and provide depth information through time domain analysis and was originally utilised for pulsed eddy current (PEC) testing. Recent advances in PEC include the introduction of pulse width variation by Li & Tian (2007) at Newcastle, allowing isolation of measurements from different depth layers. The development of MEMS techniques and more specifically the magnetically actuated micro-mirror (Cui et al. 2007) coupled with advances in wireless sensor technology means that it is now practical and affordable to install an embedded sensor network along with miniature excitation apparatus in engineering materials and structures such as bridges and aircraft.
Imaging systems such as magnetic cameras (Lee et al. 2006) and magneto-optic thin film imaging (Cheng et al. 2007), provide an alternate option, where embedding of the sensor system is not practical. Permanently attached imaging systems offer the chance to provide a continuous image of the magnetic field in a particular area, so small areas of stress concentration, pre-crack damage or microstructural disturbance can be identified. Once sensing issues can be practically resolved, implementation of NDE techniques is fairly simple. For example, residual field measurement (Wilson et al. 2007) is a technique where the naturally occurring magnetic field is measured to reflect stresses and defects. It requires no excitation, so is ideal to map stresses developing in a structure over time. Combined acoustic and magnetic Barkhausen emission measurement techniques developed in Newcastle (Wilson &Tian, 2007) are ideal for microstructural and stress evaluation in ferromagnetic materials and PEC offers similar capabilities for paramagnetic materials.
REFERENCES Cheng, Y.H., Zhou, Z.F. & Tian, G.Y. 2007. Enhanced magneto-optic imaging system for nondestructive evaluation, NDT & E International: 40(5): 374–377. Cui, Z., Wang, X., Li, Y. & Tian, G.Y. 2007. High Sensitive Magnetically Actuated Micromirrors for Magnetic Field Measurement, Sensors and Actuators A: Physical: 138(1), 145–150. Li, Y. & Tian, G.Y. 2007. Investigation of pulse eddy current with pulse width variation, 46th Annual British Conference on Non-Destructive Testing, Glasgow, UK. Wilson, J.W. & Tian, G.Y. 2007. Comparative quantification of acoustic and magnetic Barkhausen noise data with respect to various excitation waveforms, BINDT Annual Conference, Glasgow, Sep 2007. Wilson, J.W., Tian, G.Y. & Barrans, S. 2007. Residual magnetic field sensing for stress measurement, Sensors and Actuators A: Physical: 135(2), 381–387.
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Structural health monitoring of aircraft components with the impedance method K.J Xing & C.-P. Fritzen University of Siegen, Germany
Smart materials are widely and successfully applied in SHM. They are able to convert e.g. electrical to mechanical energy and vice versa. The electromechanical (E/M) impedance method is one important approach in damage detection which uses piezoelectric materials and operates in a higher frequency range. One special feature of the impedance method is that a single piece of piezoelectric material can concurrently sense and actuate, which is called self-sensing. The basic concept is to monitor the variations in the structure’s impedance spectrum caused by damage. Comparing the measured impedance to a baseline measurement, the real part of the E/M impedance
reflects the state of structural health in the local area under the influence of the excited sensor, the structural damage can be localized. The impedance method is applied successfully to a laboratory structure and a real aircraft component of an AIRBUS A320. First, a stiffened aluminium panel is used to detect and localize artificial damage. Then the concept is applied to the A320 fuselage component using 9 self-sensing elements on the stringers. Obvious shifts of the impedance spectrum are observed for the damaged state. However, large damage indicator values are found only for the two sensors close to crack.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structural health monitoring on damage evolution of 6 story reinforced building through shaking table test Koichi Morita Building Research Institute, Tsukuba, Japan
Taizo Matsumori National Research Institute for Earth Science and Disaster Prevention, Miki, Japan
1
4
INTRODUCTION
In this paper, damage estimation on damage evolution of 6 story reinforced building is shown through shaking table test. Using the system identification technique, natural frequency and damping ratio, story stiffness of damaging reinforced concrete construction test specimen are carried out, and the change of these characteristics in the damage evolution is examined. Correspondence between identification results and visual inspection & analysis is examined, and the method for estimating the damage state of the building will be proposed.
2
DESCRIPTION OF TEST FRAME AND EXPERIMENTS
The test frame floor height is 1 m, total height is 6 m, floor plan is 6 m × 4 m and there are three spans in excitation direction. Shaking table test is carried out at one direction large-scale earthquake simulator facility of the National Research Institute for Earth Science and Disaster Prevention. We carry out damage detection test by damaging the frame and we measure the evolution of damaging frame.
3
DATA FOR IDENTIFICAIOTN AND IDENTIFICATION METHOD
Two types of identification are tried. One is (a) identification using the data during damage evolution and the other is (b) identification using the data of before and after damage. In both cases, we use identification method by ARX (Auto Regressive eXogenous) model. The ARX model structure is the simple linear difference equation
RESULTS OF IDENTIFICATION
From the results of (a), natural frequency and story stiffness decreases and damping ratio increases as amplitude increases, and natural frequency and story stiffness tend to be smaller and damping ratio tends to be larger during principal motion. Tendency of identified story stiffness from (b) is consistent with visual inspection. Minimum identified stiffness from (a) agrees with the results from push over analysis. Identified stiffness from white noise shaking which is carried out just after earthquake shaking is three times larger than minimum identified stiffness from (a). By using the assumption of Takeda-model, maximum displacement estimation from white noise shaking data is tried. 5
CONCLUDING REMARKS
Results obtained from this experiment can be summarized as follows. 1) Tendency of story stiffness before and after the seismic shaking agreed with tendency by the visual inspection just after the shaking. 2) Story stiffness after the seismic shaking is very different from story stiffness under seismic shaking. 3) Smallest story stiffness under seismic shaking agreed with the story stiffness from the static push-over analysis. Estimation of the maximum drift using the data of white noise shaking after earthquake shaking is examined. Estimation is difficult in this state, but it is shown to be possible by using storage of the static member test data.
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Study on measuring error caused by movement of benchmark for auto total station in health monitoring Xiao-Hua Lei, Wei-Min Chen & Peng Zhang Key Lab for Optoelectronic Technology & System, Chongqing University,Chongqing, China
Ren-Bin Yue& Xian-Cai Xiong College of Civil Engineering, Chongqing University, Chongqing, China
1
3
INTRODUCTION
Auto total station is a kind of intelligent instrument integrates optical/mechanical and electronic technology. It has been gradually introduced to realtime health monitoring for large structure, such as bridge/dam/tunnel etc, due to its character of high precision and reliability. While high measuring precision is achieved only when total station is fixed on a stable point (called instrument base) and no obstacle between total station and measuring points. But in long-term deformation monitoring without guard, large complicate structures or buildings around block light beams to arrive at measuring points, condition of stable instrument base can not insured. Auto total station has to be fixed on unstable area. This unstable settlement of instrument base will introduce measuring error. So it is significant to analyze spread of measuring error and find a way to reduce measuring error caused by unstable settlement of instrument base. 2
PRINCIPLES
To address this problem, a mathematics model of error caused by movement of bench mark in threedimension is set up based on measuring principle of total station. Measuring error caused by movement of benchmark is analyzed. A compensation method to correct coordinate of measuring points is proposed after analyzing transfer principle of this error and establishing relationship between coordinate change of benchmark and the error. Furthermore, a corresponding survey method to improve measuring precision is introduced.
SUMMARY OF RESULTS
To prove analysis above, an experiment with a Leica TCA 1800 total station is carried out. There are one reference base/ four measuring points in this experiment. Three points are used to simulate movement instrument base. Total station is putted on unstable instrument bases in turn to survey all measuring points. Survey results of measuring points are corrected by compensation method introduced above. Experiment results show that mathematics model of error is correct and the compensation method to improve precision is feasible, coordinates error of measuring points is less in 4 mm. REFERENCES Zhao Jingzhan, 2002. Application of TCA2003 Total Station to Surface Deformation Observation for ERTAN Dam. Hydropower Automation and dam monitoring, 26(2):34∼38. Bao Huan, 2005. Application of Intelligentized Total Station Monitoring System for Structure Deformation of Subway, Beijing Surveying and Mapping, (3):19∼22. Jing Hai-tao, 2004. Three-dimensional Position by Two Point Intersection Involving Two Vertical Angles, Science of surveying and Mapping, 29(5):59∼61. Chen Zijin, WU Bing, MEI Lian-you, 2005. Application of Coordinate Difference Method in Safe Monitor of High Slope with Total Station Actively. Journal of Chongqing Jianzhu University, 27(6):130∼134.
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Ultra-wideband communication for wireless sensor networks in structural health monitoring Yue Li Department of Civil and Environmental Engineering, Michigan Technological University, Houghton, Michigan, USA
Zhi Tian & Jindong Tan Department of Electrical and Computer Engineering, Michigan Technological University, Houghton, Michigan, USA
The aftermath of recent natural and man-made disasters and the possibilities of higher losses in the future present challenges to the engineering community on how to rapidly response to such extreme events. In addition to damages caused by extreme events, civil infrastructure ages and deteriorates over time as a result of increasing traffic loads, corrosion, aggressive environmental loads, and deferred or ineffective maintenance. There is an urgent need for health monitoring and diagnosis of civil infrastructure systems to prevent or alleviate the extensive damages sustained to construction. Sensory networks, along with automated condition assessment systems, are highly desired to collect and process vital structural response data for multiple purposes: to detect, locate and assess damages, to provide sustainable long-term monitoring, and to make rapid assessment for post-disaster mitigation, retrofit, and repair. Wireless sensor network (WSN) has shown great promise for structural health monitoring (SHM) of buildings and infrastructure in both severe loading events and progressive environmental deteriorating conditions. Some data are critical to structural monitoring as well as damage detection and assessment, but inaccessible in traditional wired structural sensory systems. To collect near real-time measurements for SHM, it is essential to provision reliable high-speed data transmission among sensor nodes. However, in a massively distributed sensor network, the transmission rate and reliability are severely constrained by the limited power supplied by non-rechargeable batteries. These challenges call for an innovative communication paradigm as the enabling physical-layer air interface for WSNs envisioned for monitoring and diagnosing the structural health of civil engineering facilities. Ultra-wideband (UWB) technology emerges as such a competitive communication paradigm for SHM-oriented WSNs. By virtue of its large bandwidth, UWB signaling comes with many uniquely
attractive features for SHM applications: high data rates, robust and low power communications, resilience to multipath propagation, immunity to electromagnetic interference, and capability of wall and ground penetration. All these benefits inherently come from the ultra wide bandwidth utilized. On the other hand, to realize the potential of UWB for SHM WSNs, UWB radio design has to cope with major technical challenges under stringent ultra-low power constraints and harsh signal propagating environments in complex civil facilities. So far, there has been barely any work on designing and assessing UWB systems tailored for SHM WSNs. Toward filling this gap, this paper presents an overview of the technical challenges in employing UWB radios in sensory units in wireless SHM networks. Novel solutions are provided to cope with some critical issues, including UWB timing synchronization and UWB-based network medium access control (MAC) for reliable and ultra-low-power communications. Specifically, we present high-performance synchronization techniques to accurately acquire timing information at low power and practical radio complexity. Timing synchronization is quite challenging for UWB pulses of ultra-short time-length, but is critically needed in WSNs in order to interpret the data collected from so many sensors. Our timing solutions work well for UWB radios operating in diverse conditions (e.g., dense multipath and low scattering), which are key to the operation of high-precision, all-weather SHM WSNs. To extend the network lifetime, we also develop an adaptive MAC protocol to exploit the different energy and data rate requirements at different operation modes. Our MAC solution maintains ultralow energy consumption during normal operations and attain maximum throughput at emergency situations. Finally, a proof-of-concept field test utilizing the Network for Earthquake Engineering Simulation (NEES) facility is discussed.
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Piezoelectric composite sensors (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Study on abrasion resistance, chloride permeability and microstructure of concrete containing nanoparticles Chengming Lan School of Civil Engineering, Harbin Institute of Technology, Harbin, China
Rongshi Wang Tianjin Highway Bureau, Tianjin, China
Jie Yuan School of Material Science and Engineering, Harbin Institute of Technology, Harbin, China
Huigang Xiao & Hui Li School of Civil Engineering, Harbin Institute of Technology, Harbin, China
SUMMARY As a structure material, the durability of concrete containing nanoparticles is necessary to investigate before it is used to construct civil structures. As an initial study, abrasion resistance, chloride permeability and microstructure of concrete containing nanoparticles were studied in this paper. Concrete mixed with nanoTiO2 in the amount of 5% and 10% and concrete mixed with nano-SiO2 in the amount of 3% by weight of binder were fabricated, and their abrasion resistance and chloride permeability were experimentally studied. In order to demonstrate improvements on these properties of concrete containing nanoparticles, specimens of plain concrete with the same water-binder ratio were also fabricated and their related durability was also studied. The results showed that both the abrasion resistance and resistance to chloride penetration of concrete containing 3% nano-SiO2 and concrete containing 5% nano-TiO2 were higher than that of plain concrete, simultaneity, the results of MIP test showed that the average pore diameter and the most probable pore diameter of cement paste mixed nanoparticles were smaller than that of plain concrete, the pore structures of cement paste were refined by nanoparticles mixed and the SEM study of concrete microstructure also confirmed the results. The origin of nanoparticles improving abrasion resistance and resistance to chloride penetration of concrete was also presented from the microstructure view. The diameter of nanoparticles is very small, so there are much more particles contained in the same amount mass of matter for nano-size materials than common size materials. These nanoparticles would affect the
hydration production features of the cement paste. Supposed that the nanoparticles were uniformly dispersed and each particle was located in a cube pattern, so the distance between each nanoparticle could be calculated and was lessened with increasing nanoparticles content. During hydration process, the crystallization of hydrate production could be controlled, and thus the growth of hydrate production could be prevented from if the distance between each nanoparticle is appropriate. The bulk paste would be more homogeneous and compact, so the performance of concrete containing an appropriate content, e.g. compressive strength, especially abrasion resistance, was improved. From the research in this paper, the results could be obtained that the appropriate content of nanoparticles mixed in concrete was favorable for the compressive strength, abrasion resistance, the resistance to chloride penetration and cement matrix microstructure of concrete. The abrasion resistance and resistance to chloride penetration of concrete containing nanoSiO2 in the amount of 3% and nano-TiO2 in the amount of 5%by the weight of binder were much better than that of plain concrete, especially concrete containing 5% nano-TiO2 . It was confirmed that the optimum content of nano-TiO2 in concrete must be less than 10% by the weight on binder for abrasion resistance and resistance to chloride penetration. The pore size distribution of cement paste was refined and the average pore diameter and the most probable pore diameter were decreased by appropriate content of nanoparticles mixed. It was concluded that nanoconcrete was one of the most excellent civil structure materials for its good mechanical properties and durability.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A study on self-sensing properties of carbon fibre sheet as structural materials in civil engineering W. Zhou & H. Li Harbin Institute of Technology, Harbin, China
J.P. Ou Dalian University of Technology, Dalian, China
1
INSTRUCTIONS
CFRP is used in civil infrastructures can play sensors as well as strengthening structural materials. The electromechanical properties of CFRP used in civil infrastructure are experimentally and analytically investigated in this paper. The CFRP strips are tested under monotonically uniaxial loading. The effect on the relationship of change rate of resistance and applied strain by the number of bundles in CFRP strips is also analyzed based on the test results. A modified parallel DC circuit model is suggested to simulate the relation-ship of change in rate of electrical resistance and applied strain of CFRP strips and the calculated results agree well with the test results. 2
SPECIMENS AND METHODS
Polyacrylonitrile-based carbon fibre sheet is employed in this study. The specimens are fabricated to conform to the operation specification of strengthening columns by CFRP. Tests are conducted in Instron 5569 installed in Harbin Institute of Technology. When the specimen is stretched or unloaded by Instron, the voltage between the copper foils is collected by the DAQ system. 3
EXPERIMENTAL RESULTS AND DISCUSSION
The specimens were subjected to uniaxial tensile loading at a crosshead movement rate of 1 mm per min up to failure. The CFRP strips used in this test also have different electrical resistance-strain relationship from the single fibre filament. The change of electrical resistance of a single filament is attributed to elongation of fibre and obeys to Ohm’s law. However, resistance increment of CFRP strip is attributed to not only the elongation but also the gradual and successive
breakage of fibres. The electrical resistance of CFRP increases linearly with applied strain when the applied strain is small. Carbon fibres elongate only but do not break, so the increment of electrical resistance is attributed to elongation of fibres only in this phase. 4 A MODIFIED ELECTROMECHANICAL MODEL OF CFRP APPLIED IN CIVIL ENGINEERING A DC circuit containing a series of parallel resistance is frequently employed to simulate electrical resistance of a CFRP product. Each fibre acts as a resistor and no fibres are in contact each other at initial condition. In this paper, as analyzed above, the carbon fibres within CFRP consist of two parts: carbon fibres covered by epoxy resin and carbon fibres not covered by epoxy resin. For the first part, the broken fibres may contact with neighboring fibres, and still carry on paths of the circuit and contribute to global electrical resistance of specimen, and for the second part, the broken fibres will drop out from the DC circuit after they break and no longer contribute electrical resistance. The total resistance is decided by two parameters: (1) the ratio of carbon fibres not covered by epoxy resin to all carbon fibres, τ; (2) during loading, the ratio of the unbroken carbon fibres covered by epoxy resin to the all unbroken carbon fibres, u. After analysis with new model, the total change rate of electrical resistance at applied strain can be given by:
This modified parallel DC circuit model can simulate the relationship of change in rate of electrical resistance and applied strain of CFRP strips and the calculated results agree well with the test results.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Effects of cure temperature on magnetostrictive properties of polymer-bonded Terfenol-D composite X.C. Guan & X.F. Dong School of Civil Engineering, Harbin Institute of Technology, Harbin, P.R. China
J.P. Ou School of Civil Engineering, Harbin Institute of Technology, Harbin, P.R. China School of Civil Engineering, Dalian University of Technology, Dalian, P.R. China
INTRODUCTION
1.2
In order to evaluate the influence of the cure temperature on magnetostirctive properties of the composites, polymer-bonded Terfenol-D composites with particulate volume fraction of 20% are manufactured at cure temperature of 15◦ C, 40◦ C, 60◦ C and 80◦ C respectively. At room temperature (15◦ C) and with zero stress bias, magnetostrictive response versus applied field curves are presented as well as magnetic flux density versus applied field curves for the composites cured at varying temperature. By differentiating the fitting curves of magnetic field (H ) vs. strain output (λ) and magnetic field (H ) vs. flux density (B) plot, the relative differential permeability (µrd ) and large field piezo-magnetic coefficient (d33 ) are obtained.
1 0.8 B (T)
1
0.6 15°C 40°C
0.4
60°C 0.2
80°C
0 0
100
200
300
400
500
600
H (kA/m)
Figure 2. Flux density as a function of applied magnetic field. 4 15°C
3.5
EXPERIMENTAL RESULTS
40°C
3 d33(m/A*10⫺9)
2
1200 1000
60°C 80°C
2.5 2 1.5 1
λ (⫻10⫺6)
800
0.5 0
600
100
40°C 80°C 0
100
200
300
400
500
300
400
500
600
Figure 3. Dynamic strain coefficient vs. applied magnetic field.
60°C
200
200
H (kA/m)
15°C
400
0
0
600
3
CONCLUSIONS
H (kA/m)
Figure 1. Strain response vs. applied field.
Cure temperature is an important factor which influences properties of Terfenol-D polymer composite.
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When operating temperature is constant, at the same magnetic field level, the magnetostrictive properties, such as magnetostriction and dynamic straincoefficient increase with increasing cure temperature. The thermal compressive stress results from the difference in thermal expansion coefficients between the matrix and the particle and the difference in temperature between cure and operating are responsible for the difference in the magnetostrictive properties.
ACKNOWLEDGEMENTS This research is financial supported by the National Science Foundation of China under the grant number 50478024.
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Numerical analysis on the cymbal and half cymbal membranes for piezoelectric synthetic jet actuator Huangsheng Qian, Bangfeng Wang, Yong Zhou & Lei Xun Nanjing University of Aeronautics & Astronautics, Nanjing, Jiangsu, P. R. China
1
INTRODUCTION
The need to improve fighter aircraft and missile maneuverability has inspired extensive study of the flow controlling past wings and of methods to enhance their performance. In the field of flow boundary layer control, synthetic jet or zero mass jet is a high potential method at present. However, the application of traditional synthetic actuator with plane membrane has been limited so much by the reason of its low jet output velocity. 2 THEORETICAL ANALYSIS AND RESULTS In this paper, two kinds of new style of piezoelectric ceramic-metal composite material membrane, cymbal and half cymbal style shown in Figure 1, and solid and annular styles of piezoelectric patch are used to improve the driving capability. In this research, models are built byANSYS system. The models are meshed and calculated after geometric models built. Then the results are got and analyzed. From numerical results, the distortion value caused by cymbal style membrane is obviously larger than which caused by plane membrane in the same condition. In addition, for optimizing the structure of half cymbal style membrane, the dimensions of membranes are changed and numerical calculations are done to investigate the influence of different dimensions on the largest distortion value of the membrane. In detail, the change tendency of distortion of half cymbal and cymbal style of membrane with solid piezoelectric patch and annular piezoelectric patch is researched by α and β changing (α is defined as s2/s1, and β is defined as d3/d1, s1 is the area of copper and s2 is the area of piezoelectric patch, d1 is the diameter of copper, d3 is the cymbal cap’s top diameter). From the results, the distortion caused by half cymbal membrane is larger than the distortion caused by cymbal and plane membrane in the same condition. And the distortion caused by membrane with annular piezoelectric patch is larger than the distortion caused by membrane with solid piezoelectric patch in the same
Figure 1. Schematic of two kinds of CYMBAL membrane.
condition. For half cymbal style of membrane with annular piezoelectric patches, the distortion value is the biggest when α is 0.15 and β is 0.25. And for the ones with solid piezoelectric patches, when α is 0.25, the distortion value is largest.
3
EXPERIMENTS
In order to validate the correctness of the theoretical analysis, the experiments of half cymbal and plane membrane with solid piezoelectric patch have been done. The piezoelectric patch is driven by sine wave with different frequencies, which is generated by signal generator and amplified by a power amplifier. And the electrical signal from KD-300 is collected by data collection card. The experimental results validate the correctness of the theoretical analysis and reveal that the half cymbal structure achieves the aim to increase the amplitude, and it can be used in SJA.
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Innovative sensing systems: Fiber sensors (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Fiber optic sensors application on the SHM of a pedestrian cable-stayed bridge in Italy L.M. Giacosa & A. De Stefano Polytechnic of Torino, Torino, Italy
F. Ansari University of Illinois at Chicago, Chicago, U.S.A
1
GENERAL INSTRUCTIONS
in account the effect of deflections of the calculating of the structure in calculating the stresses and forces.
The general idea dealt in the present article concerns the application of smart structure in cable-stayed bridges. Fiber optic sensors normally applied in concrete structure are used here directly to bridges cables to evaluate internal forces, deflection and strain. Theoretical study on the infinite and finite strings are carried out for in-plane and out-of-plane applications, in such a way to obtain the prevalent conditions under wind, rain and above all any type of external dynamic loads. Linear and non linear conditions are the first step to verify static and dynamic stresses directly applied at the cables but also to the entire structure. In parallel an experimental optimization of the sensor’s location is studied to measure in the best way the stress applied at the structure.
2
CABLE THEORY
The significant differences between strand and rope are substantial in that a strand normally has a greater breaking strength, a higher elasticity modulus, less curvature capability and the wires in a strand are larger than in a rope. The modulus of elasticity, E, of a rope is low for low loads and increases as the load is increased into the normal working range. The stiffness of the cable-stayed bridge depends largely upon the tensile stiffness of the stay cables. The displacement of the end of the free hanging cable under an axial load depends not only on the cross-sectional area and the modulus of elasticity of the cable but to a certain extent on the cable sag, as provided by Ernst. Cable-stayed bridges pertain to the category of structures in which the deformation of the superstructure under loading affects the values of the stresses acting in them. Due to this, only in static linear analysis the principle of the superposition may be applied. In dynamic analysis, that concern even the non-linearity of the system, it is necessary and obligatory to consider the second order effects taking
3
FIBER OPTIC BRAGG GRATING SENSORS
A fiber Bragg Grating (FBG) sensor consists of a continuous fiber core surrounded by germanium-doped silica; the grating portion itself consists of modulation in the index of refraction along a short length of that continuous fiber core. The UV light changes the physical characteristics of the doped glass core, specifically the index of refraction in effect, creating precisely-spaced regions of physically-altered, periodically-modulated glass core material. This section is the grating or sensor, and the precise spacing, called the pitch (indicated by ) of the regions of altered material, determines the reflective properties of the grating. The pitch length is the physical space between one region of altered material and the next. FBG sensors reflect light in a very narrow band centered about the “Bragg wavelength”, enhancing the precision of the measurement. Fiber optic sensor (FOS) used for the cables monitoring is based on FBG fiber optic technology. Fiber Bragg sensors patches were installed directly on the surface of steel frame pillar, connecting the bridge deck and the foundation. Displacements fiber optic sensor were also installed on the foundation to measure displacement or in the worse way the detachment of the steel slab of the bridge pillar from the concrete foundations. Bragg fibers mounted on arch shape sensors were installed between the steel frame pillar surface and the concrete foundation to measure displacements. All this system was installed due specific request from the Italian railways interested to monitoring the behaviour of the pillars close to the railway paths.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Analysis on a novel reflective intensity modulated fiber optic temperature sensor Jingyun Dai Key Lab. of Structure Health Monitoring and Control of Hebei Province, Shijiazhuang Railway Institute, Shijiazhuang, Hebei
Wentao Zhang Key Lab. of Structure Health Monitoring and Control of Hebei Province, Shijiazhuang Railway Institute, Shijiazhuang, Hebei State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing
Baochen Sun & Yanliang Du Key Lab. of Structure Health Monitoring and Control of Hebei Province, Shijiazhuang Railway Institute, Shijiazhuang, Hebei
1
INTRODUCTION
Fiber optic sensors have developed rapidly in the past several decades. Fabry-Perot interferometer sensor is widely used in smart structure and materials. In this paper, a novel fiber-mercury temperature sensor is proposed. Experiment was carried out to test the performance of the sensor, and the results present a good correlation between the theoretical and experimental result.
2 THE REFLECTIVE INTENSITY MODULATED FIBER OPTIC TEMPERATURE SENSOR
Figure 1. The result of the temperature measurement.
An optical fiber with outer diameter of 125 µm is inserted into a glass capillary and adhered to the capillary at the end. The inner diameter of the capillary is 138 µm and the outer diameter is 250 µm. The mercury is filled into the capillary from another end where the capillary is sealed by adhesive. The air gap between the surface of the mercury and the fiber end is the initial cavity length of the sensor. The light from the white light source transmits through the isolator and the coupler and illuminates the surface of the mercury, and then is reflected by it. The reflected light is collected by the detector. The length of the air gap changes with the thermal extension of the mercury, which determines the intensity of the reflective light. For the same temperature shift, different length of mercury results in different change of the cavity length.
We assume that the surface of the mercury is an ideal reflective mirror and is parallel to the fiber end, and the axis of the fiber is perpendicular to the reflector. The modulation function can be written as
3 THEORY
4
EXPERIMENT AND RESULTS
To evaluate the performance of the sensors, experiment was carried out in a constant temperature oven. The light from the light source transmits through the isolator and the coupler and into the RIM- FOTS, then is reflected by the sensor head and transmits back into the optical power meter (OPM).
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The experimental result has a good agreement with the simulated (Fig. 1). It also shows the sensitivity increases with the length of the mercury. 5
CONCLUSION
performance and reliability. It can also be found that the sensitivity is the function of the length of the mercury and the length of the air gap. The change of the length of the mercury and the length of the air gap not only determine the sensitivity, but also the dynamic range of the sensor.
A novel fiber mercury temperature sensor is designed and analyzed.The results show that the sensor has good
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A novel all-fiber surface roughness sensor-based on laser scattering Haiying Huang, Uday S. Tata & Ayan Majumdar Mechanical & Aerospace Engineering, University of Texas at Arlington
1
INTRODUCTION
As material subjects to fatigue load, friction, and/or high temperature environment, material surface roughness could be altered. In return, surface roughening could contribute to crack nucleation and fatigue life reduction. Therefore, surface roughness is an important property that can be monitored to evaluate material health state. Sensing techniques that can detect surface roughness changes potentially could help us in early damage detection and prevention of serious accidents. 2
PRINCIPLE OF OPERATION
The surface roughness sensor is constructed from two parallel optical fibers, fiber A & B, placed adjacent to each other (figure 1). A red laser with a wavelength of 635nm is coupled to fiber A that delivers the laser light to the sensing material. Upon impinging on the sensing material, the laser light is reflected and partially collected by optical fiber B. Because light reflection is influenced by the roughness of the reflecting surface, the optical power of the light collected by optical fiber B is directly correlated to the surface roughness of the target. 3 THEORETICAL SIMULATION Assuming the illumination light has a Gaussian in-tensity distribution, the power collected by the re-ceiving fiber is related to distance d for a smooth surface is
Figure 1. Principle of operation for roughness sensor.
A rough surface would scatter the illumination light, resulting in a large reflected light pattern with lower intensity. Moreover, light scattering may increase the incident angle of the reflected light, which in turn reduces the amount of the light that is coupled into the receiving fiber, due to the limited numerical aperture of an optical fiber. Both effects will change the output power of receiving fiber as the surface roughness of the target changes. Therefore, the surface roughness of the target can be monitored by measuring the output power of the receiving fiber.
4
RESULTS AND CONCLUSIONS
Theoretical simulation of the light intensity reflected from a smooth surface agreed very well with experimental results. The intensity of the light scattered from five polished steel samples with different surface roughness were measured. It was found that the light intensity decreases as the surface roughness increases. Annealed samples and plastically deformed samples were profiled. The experimental results indicated that the surface roughness sensor can detect surface roughness changes induced by thermal exposure and plastic deformation.
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Optimized design of configuration parameter for a novel Fiber Ring Laser Gyroscope Ming Zhang, Shufen Chen & Lei Fu Department of Opto-electronics Engineering, Beijing Institute of Technology, Beijing, China
Gyroscope is a key part of Inertial Navigation System (INS). It measures angular velocities in guidance of missiles, satellite orientation, gyroscope compass, robot movement, Auto-Guide and so on. All optical gyros work based on the Sagnac effect. Fiber Ring Laser Gyroscope (FRLG) combines advantages of the Ring Laser Gyro (RLG) which has wide dynamic range and high precision and the Interferometer Fiber Optic Gyroscope (IFOG) which has all solid state
configurations with good anti-strike and vibration characterization, long lifetime and low cost. In this paper, working principle of FRLG is described and analyzed in detail. The mathematical models about laser gain and ring cavity of FRLG are built. The simulating results and discussion will be shown in the following, which is useful to finish the optimized design of structure and parameter selection.
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SHM of civil structures
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Recent progress of bridge structural health monitoring research in Chongqing University Yong Zhu, Weimin Chen, Yumei Fu & Shanglian Huang Key Laboratory for Optoelectronic Technology & System, Education Ministry of China College of Opto-electronic Engineering, Chongqing University, Chongqing, China
ABSTRACT Bridges are key traffic nodes of cities with rivers. They have long service period spanning several decades to over one hundred years. During that period, long-term fatigue and other occasional damage are inevitable. These damages accumulate and could lead to a potential disaster. Therefore, it is necessary to develop nondestructive structural health monitoring techniques for bridges. In the past two decades, China maintained a 10 percent GPD growth. The rapid developing economy leads to an extreme need of communicant civil infrastructure, such as bridges. Recently, more and more attention was paid to monitoring the health of these bridges, not only by Chinese scholars but also by the Chinese government. As a result, much progress was made in this field. In this paper, the recent advances in research, development and implementation of bridge structural health monitoring in Chongqing University were briefly reviewed. After a decade of research work on fiber optics sensors (FOSs), the Opto-electronic Technology Lab of Chongqing University (OTLCU) began to focus on the interdisciplinary field of fiber optical sensing in civil engineering. In 1996, S. L. Huang introduced the concept of health monitoring of civil structures in Mainland China for the first time. This became a milestone, not only by pointing out a new application for FOSs, but also by indicating a promising way to solve sensing problems in civil engineering. In the subsequent ten years, the OTLCU had studied and developed several kinds of fiber optic sensors, such as optic fiber cracks sensing array, distributed tensile strain sensing system, optical fiber modal speckle sensor, fiber optic corrosion sensor, Extrinsic Fiber Febry-Perot (EFPI) strain sensors and so on, for practical use in health monitoring of concrete structures, especially for bridges.
Among all fiber optic sensors studied in the OTLCU, the EFPI fiber optic strain sensor is the simplest but most practicable and most widely used one. With distinguished features of low manufacturing cost, high accuracy, robust, temperature insensitivity, and so on, it became one of the best candidates for long-term bridge strain monitoring in mainland China. The accuracy of the EFPI sensor was carefully studied, and both embedded and surface-mount installation & protecting technique were developed in OTLCU. Deflection is a very important parameter which represents the bridge’s global response to load applied on. A series of opto-electric deflection & displacement monitoring techniques have been developed for different type of bridges. They are high speed large measuring range one dimension laser deflectomenter, large measuring range two dimension laser deflectometer, connected pipe opto-electric deflectometer, and so on. A health monitoring system was developed and implemented on Dafosi Yangtze River Bridge, which was the largest cable stayed bridge in Southwest China. The measurement system consists of four sensing subsystems: (1) Fiber optic Strain sensing subsystem, (2) Displacement sensing subsystem, (3) Temperature sensing subsystem, and (4) Dynamic measurement subsystem. As another example, a remote and group monitoring system for bridges was introduced. The remote-group health monitoring system includes three local sensing networks located on the Masangxi Yangtze River Bridge, the Gaojiahuanyuan Jialing River Bridge and the Xiangjiapo fly-over bridge respectively. Some representative monitoring results of these health monitoring systems were given.
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A study on structural health monitoring scheme of cables and ties of Cai-yuanba Bridge Zongming Huang, Pu Yang & Gang Liu College of Civil Engineering, Chongqing University, Chongqing, P. R. China
The Cai-yuanba Yangtze River Bridge in Chongqing is currently the largest span among the completed tiedarch bridges all over the world (see Figure 1). The steel box arch andY rigid-frame are connected by center and side tied-bars together. The upper chord of steel truss girder is lifted by cables from the steel box arch, and the lower chord is lifted by support cables of Y shaped rigid-frame. These bars and cables are the mainly key components among whole bridge. But it is difficult to select type and position of sensor for cables since there are many cables in the bridge and its force is very great. A three-dimensional finite element analysis model of the bridge is established using program ANSYS. And the sensitivity analysis of tied-bars, arch cables and the support cables is performed. From the sensitivity analysis of tied-bars, we find that: (a) the change of displacement along the steel truss girder and the strain of Y shaped rigid-frame are not sensitive to damage of tied-bars. (b) The change value
Figure 1. The sketch of main components of the bridge.
of tied-bars force is approximately in proportion to the damaged percent of section. (c) Displacement of front cantalever of Y shaped frame is sensitive to damage of tied-bars. From the sensitivity analysis of cable, we find that: (a) the force of damaged cable would decrease rapidly and the force of the bars near it would increase respectively. (b) the vertical displacement of the steel truss girder is only sensitive to damage of the cables which are near the center of steel box arch. From the sensitivity analysis of support cables, we find that: (a) the force of the damaged support cables would be less than undamaged and the force of cable near the damaged support cables would increase. (b) the change model of displacement along the steel truss girder is greater at front cantalever of Y shaped frame is same as when the side tied-bars are damaged. So considering economy and safety of the bridge, several suggestions on structural health monitoring scheme of the tied-bars, arch cables and the support cables are obtained as following: (a) In order to detect health status of tied-bars, its force should be monitored. In addition, the displacement of Y shaped rigid-frame should also be monitored. (b) The force of cables should be monitored to decide whether it has been damaged. (c) Based on the force of the support cable and cable 1#, it can be decide whether the support cable has been damaged.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Multisensor and automated measurement of bridge deck condition Dryver Huston, Jianhong Cui & Dylan Burns School of Engineering, University of Vermont, Burlington, VT, USA
Nenad Gucunski & Ali Maher Civil & Environment Engineering, Rutgers University, Piscataway, NJ, USA
Frank Jalinoos Federal Highway Administration, Turner-Fairbanks Highway Research Center, McLean, VA, USA
1 ABSTRACT This paper presents the results of a study that used multiple sensors to examine the condition of two reinforced concrete bridge decks. Some of the sensor systems were automated – others were manually operated. The Van Buren Bridge in Dumfries, VA was the subject of the most extensive examination. Two different ground penetrating radar (GPR) systems provided an automated noncontacting evaluation. One was the FHWA PERES system that uses microimpulse radar and operates in the frequency range between 500 MHz and 5 GHz. A single antenna pair
Figure 1. PERES ground penetrating radar system onCarter Creek Bridge, Irvington, VA, USA.
mounted on a linear drive mechanically sweeps across a 1.5 meter span, acquiring data every centimeter while the entire system is stepped forward in 1 cm increments. The second GPR system was the 3DGPR. This is a step-frequency ground penetrating radar with 47 antennas that allows high-resolution measurements in a frequency range 100–2000 MHz. Impact echo (IE) measurements implemented in a Portable Seismic Property Analyzer (PSPA) provided complementary data. The PSPA is an ultrasonic/high frequency seismic device that in-corporates ultrasonic surface wave (USW) measurement for elastic modulus evaluation and IE technique for delamination detection and characterization. Additional measurements included chain drag, half-cell and visual inspection. The second bridge was the Carter Creek Bridge in Irvington, VA. The testing involved use of the PERES GPR system, chain drag, half-cell and visual inspection. Preliminary observations during testing indicated that 3D-GPR was the quickest system followed by the PSPA, PERES and the fully manual methods.
Figure 2. Overlay of chain drag and impact echo delamination data for Van Buren Bridge, Dumfries, VA, USA.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A study on joint of steel and concrete box girder of Shi-banpo Bridge in Chongqing Pu Yang The Key Laboratory for Optoelectronic Technology & System, Education Ministry of China, Chongqing University, Chongqing, P. R. China
Zeng-yin Xie & Gang Liu College of Civil Engineering Chongqing University, Chongqing, P. R. China
1
INSTRUCTION
The main span of Shi-banpo Bridge in Chongqing is 330 meters long, which is the longest span among the completed continuous rigid-frame bridges in present all over the world. It is a very important bridge in downtown of Chongqing. Prestressed concrete box girder and steel box girder are adopted in the bridge. In order to decrease the weight of the bridge, steel box girder which is 108 m long is used in the middle of the main span of the bridge instead of concrete one. So there are two joints of steel and concrete box girder. The joint of steel and concrete box girder is 2.5 meters long. Top, ventral, bottom and stiffening steel boards are used in steel box girder to bear the pressure. And the steel shear boards (SSB) are used to transfer the shearing force between concrete and steel girder. And there are several prestressed steel bars in three directions in joint. It is very important for safety of the bridge to avoid the glide between concrete and steel box girder. Since two different types of materials are used and the state of stress in joint is very complicated, two joints of steel and concrete girder are the key components of the bridge. In this paper, a finite element analysis model of Shi-banpo bridge in Chongqing is established to analyze response of the bridge corresponding to different load cases including dead load, vehicle load and crowd load etc. At the same time, a local model of the joint of steel and concrete box girder is established using preprogram ANSYS, and a transition element between concrete and steel shear board is used to simulate the
relative deformation according the experimentation value of shaped steel in concrete by Xi’an University of Architecture and Technology (Yang 2003) . The strain and relative displacement of joint is analyzed under different load case. The limited values at different level of safety of the joint are also gain on the basis of the analysis results. Considering studies on the application at present, several sensors of strain are set in the concrete box girder, the steel box girder and the joint, and sensors of displacement are set between concrete and steel shear board. Based on above results, several conclusions are summarized as following: (a) the gliding values between SSB and concrete are very small under load case I, so it is considered that the glide is not happened. The glide begins to happen under load case II and badly happen in under load case III. So it is suggested that the limited value of gliding is 0.01 mm for general warning and 0.02 mm for damaged warning. (b) the relative displacements of SSB and concrete in the LA and LD parts of the joint are obviously larger than the other parts. The relative displacements of the outside SSB and concrete in LD part of the joint are always larger than the relative displacements of the middle SSB and concrete. But the change of relative displacements in LA part is not obvious. So the focus of health monitoring should be gliding in LA and LD part. The sensors should be set in these two parts, especially the outside SSB and concrete in LD part.
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Appropriateness of shear-building models for ASCE SHM benchmark structure M. Zhang & H.J. Li Engineering College, Ocean University of China, Qingdao, China
S.-L. J. Hu Department of Ocean Engineering, University of Rhode Island, Narragansett, USA
Global structural health monitoring (SHM) methods, attempting to assess the condition of the whole structure simultaneously based on dynamic response data, have the potential to make structures safer by observing long-term structural changes. Because various studies applied different SHM methods to different structures, rendering side-by-side comparison difficult, the IASC-ASCE Structural Health Monitoring Task Group developed a series of benchmark problems providing both simulated and experimental data to facilitate comparison among different methods. The Task Group designated a four-story, laboratory scale-model, steel frame structure to be the test structure. In the first phase of the benchmark study, the Task Group decided that the use of simulated data from an analytical model based on the benchmark structure would allow for future comparisons with real measured data. Two finite element based models for the benchmark structure—one a 12 degree-of-freedom (DOF) 3-dimensional shear-building (SB) model, the other a 120-DOF model—were given. While both 12- and 120-DOF models were used to generate the response data, participants of the benchmark study however were charged with using a 12-DOF shear building as their identification model. While a 12-DOF lumped-SB model is utilized as the identification model, the present article addresses two fundamental issues related to parameter and modeling errors: (1) what and how model parameters should be assigned optimally? and (2) what can or cannot be achieved as far as the damage detection is concerned when measurements are synthesized from a full-order finite-element model? The present study applies a model conversion technique to calibrate the stiffness matrices of a 12DOF shear-building model. The model conversion
technique, which is based on the framework of the cross-model cross-mode method for model updating, is unique in the aspect that it is capable of converting a source model into a completely different, but predetermined target model. In the present study, the source model will be a 216-DOF full-order finite element model, and the target model a 12-DOF shearbuilding model. The objective is to refine the stiffness and mass matrices of the identification model, so that the resulting matrices can yield identical or similar modal properties to those of the 216-DOF model. As producing a 12-DOF undamaged (baseline) identification model is for the purpose of conducting structural health monitoring (or damage detection), the second part of the numerical studies focuses on whether the employment of a 12-DOF identification model can achieve the intended objectives on damage detection. To include modeling errors, data corresponding to damage scenarios will be synthesized from using the full-order 216-DOF FE model. A variety of damage scenarios, including damages occurring at single and multiple stories of the structure, are investigated. Numerical studies demonstrate that only those measurements associated with the particular modes that have been preserved at the baseline shear-building model should be used in the damage detection process, and using other modal measurements would yield false damage locations because of the inconsistence between the synthetic measurements and the identification model. Also, numerical studies indicate that using the shear-building model is only able to detect “uniform” damages (i.e., all members of the same kind in a single story possess identical amount of percentage loss in stiffness) occurring at single and multiple stories, but incapable of detecting “non-uniform” damages.
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Innovative sensing systems (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Design of MOEMS gyroscope Yi Zhao & Shufen Chen Department of Opto-electronics Engineering, Beijing Institute of Technology, Beijing, China
Optic gyroscope and MEMS gyroscope are widely believed to be the best solutions for low and medium precision requirements. It is proved that MOEMS and Optic gyroscope have more advantages than mechanism gyroscope, static electricity gyroscope and magnetoelectricity gyroscope in application. Because of the preponderance in high precision level, laser gyroscope is generally used in long term inertial navigation system and gyroscope compass. Fiber gyroscope lies mainly on medium-precision level and its precision will enter the filed of high precision with the development of technology. In low precision level, the market needs a kind of product which has the characteristics of low cost and high integration, and many types of MEMS gyroscope have been presented yet. But the disadvantages of the current MEMS structure, including its value expensive, products difficult and low precision are limited its application.
This paper presents a novel structure design of Micro-Optic-Electro-Mechanical-System (MOEMS) gyroscope. The gyroscope, consisting of Surface Acoustic Wave (SAW) generator, optical waveguide diffractive component and electro-optical modulator, is integrated on a chip as minimized gyroscope for sensing rotating angular velocity. A special point in this structure is adding a optical readout device based on the traditional SAW typed MEMS gyroscope, it has many advantages, such as higher precision, stronger anti-vibration capacity, and lower difficulty of processing techniques than common SAW gyroscope, and easier integration.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Optimum strain gauges distribution for loading identification following fuzzy pattern recognition and hybrid genetic algorithm Gongbiao Li & Wei Lian Qu Hubei Key Laboratory of Roadway Bridge & Structural Engineering, Wuhan University of Technology, Wuhan, Hubei, China
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INTRODUCTION
In this study, the structural strains under different loading conditions are firstly classified to different patterns to ensure loads can be discerned through the recognition of strain patterns. As the direction connections of the strain patterns and loading conditions are constructed, loads can be discerned through the recognition of strain patterns quickly. Because the strain gauges cannot be placed on every nodes of structure, the representative key nodes on which strain gauges to be installed should be determined properly to distinguish from other nodes. After the objective function is constructed, the optimal results are determined by minimizing the objective function through a genetic algorithm (GA). The illustrative example is composed by numerical analysis based on finite element model (FEM) of a steel bracket. Figure 1. Flow chart of fuzzy pattern recognition procedure.
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LOADING FUZZY PATTERN RECOGNITION AND OPTIMIZATION OF KEY NODES
the small niche count individuals, the population will be more diverse to determine the global Pareto set.
By selecting the x-direction and y-direction stresses or strains of some key nodes to deputize for the stress spaces under different loads, the loads can be identified through the identification of the strains of the selected nodes. The identification procedure followed fuzzy pattern recognition (FPR) is plotted in figure 1. Before discerning loads by the FPR method, the characteristic indices should be established firstly. Strains of key nodes are chosen as the indices in the present so the strains must be representative and can correctly reflect the loading conditions of structure in general. Therefore an objective function changing with the errors between the input loads and recognized loads is constructed and the key nodes are selected by minimizing the objective function. As there are errors of loads values and locations, the key nodes searching problem becomes a multi-object optimization procedure. As GA deals with population, it is an efficient method to solve the multi-object optimization problems. To improve the global search ability of GA, a sharing function is introduced. By assigning more chances to
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NUMERICAL INVESTIGATION AND CONCLUSION
A steel bracket is taken as an example for numerical investigation. The load magnitude patterns are constructed with an interval of 1000 kN and the load position patterns are constructed with an interval of 10 mm, thus there are 8349 loading patterns in total. And there also are 5083 random loading states supposed for optimization. Simulation results show that the load values are identified correctly, but there are errors in the load locations and relative large while the load values are relative small. Therefore the loading identification using the nodes optimized by the proposed method is accurate and secure for engineer application. In the simulation, the objective time to discern the input loads is less than 0.04 seconds, thus the approach is useful for on-line loading recognition.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Quantification of orthotropic characteristic of OPCM sensor Ying Luo, Zhongfang Li, Hongguang Liu & Jiafeng Liang Faculty of Science, Jiangsu University, Zhenjiang Jiangsu, P.R. China
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INTRODUCTION
During the past several years, Piezoelectric ceramic for sensors have received numerous investigations and undergone remarkable advances. Tranditional piezoelectric ceramics offer many advantages including quick response, high-induced stress, low energy consumption and low cost which make them very attractive for a number of applications . However, it is a type of isotropic material with the same piezoelectric capability at direction 1 and direction 2 so that it can not be used to detect the strain of special directions. Piezoelectric composite materials can extend the function of pure piezoelectric sensor by selecting different proportion and special scales of ceramics so as to get different piezoeletric capability to strains of different direction which are called orthotropic piezoelectric composite materials (OPCM). As Fig. 1 shown, the 1-1 OPCM sensor is composed of 30 basal elements which are made from three kinds of material, listing as piezoelectric ceramic, insulate epoxide resin and conducting polymer. The polarization direction run parallel to axis x, the polarization
direction of every two adjacent piezoelectric elements is opposite to each other. Analytical expression of the orthotropic characteristics of 1-1 piezoelectric composite material was got. When only stress σ0 is put on direction 1, the total electrical charge is
When only stress σ0 is put on direction 3, D33 , D31 are
The total electrical charge is
When a stress σ0 is forced on the direction with the angle with the direction 1, the charge is
Figure 1. Structure of 1-1 OPCM sensor.
Figure 2. Mechanics simplifying principle of 1-1 OPCM.
Figure 3. Representative element.
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great academic meaning and established the basis of the design of 1-1 OPCM sensor. The profit has great academic meaning and established the basis of the design of 1-1 OPCM sensor.
Figure 4. Q0◦ and Q90◦ curve.
When the sensor is stressed, the variation curves of Q0◦ and Q90◦ in Fig. 4. It can be seen from fig. 4 that the electric charge will be zero when the sensor is stressed if the length-width ratio L1 /L3 is 7.8125. Experiment showed the theory of the orthotropic degree proposed is right and reliable. The profit has
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Wireless fiber optic acoustic sensors for crack monitoring Il-Bum Kwon, Chi-Yeop Kim, Ung Seomoon, Dae-Cheol Seo, Dong-Jin Yoon & Seung Seok Lee Safety Metrology Group, Korea Research Institute of Standards and Science, South Korea
Fiber optic sensors have many advantages: electromagnetic immunity, chemical inert property, compactness, flexibility etc. Large structures are necessary to use huge number of sensors to get the information about the external condition and the internal structural condition. Such huge number of sensors should be connected by cables between sensor conditioners and sensor probes. This instrumentation is very huge labor-consumable process. In this paper, fiber optic acoustic sensor modules were developed with a probe unit, a sensor control unit, and a wireless unit to detect the change of some acoustic signals from crack growth of structures. The probe unit was constructed with an optical fiber Bragg grating. The sensor control unit had some feed back circuit to control wavelength of the light source. Also, the wireless unit was combined with the probe unit and sensor control unit to communicate the host computer. Crack monitoring experiments were simulated by an impact test of an aluminum plate. The sensor could make some crack growth detection event data and transmit the data to the host computer. The change of crack growth was well detected by the sensor probes, and transmitted by wireless unit to the host computer. A novel and simple crack growth detection technique is to be presented with a FBG sensor system with wireless data transmission unit, which can adopt the wavelength of light source to meet the center wavelength of FBG sensor probe. Plate or shell structures can propagate elastic waves. Some elastic waves are generated and traveled on the surface when some
impact force is given on structures. If a defect is appeared on the surface, then the amplitude of the surface wave shall be changed across this defect. This change, therefore, can give the information of crack growth or not. The experimental setup is prepared to investigate the effects of crack growth as shown in figure 1 (a). The sensor control unit is connected with the FBG probe through a circulator. The FBG probe is bonded on an aluminum plate by using epoxy material. Also, a conventional AE sensor puts on the plate near by the FBG probe. Impacts are induced across the crack and the sensor probe. The sensor data are acquired at every time of impact. Some acquired data is shown in figure 1 (b). In this figure, the wave form of the FBG sensor is different from conventional AE sensor signal. However, the fiber sensor signal could be shown the crack growth effect on other signals. The signal waveforms are acquired at several states of crack lengths, which are 0, 5, 10, 15, 20 mm. These gathered signals were processed to identify the crack growth. The processed signals could give the crack growth information as shown in Figure 2.
Figure 1. Experiments for crack growth detection by FBG sensor (a) and the acquired signal (b).
Figure 2. The number of frequency components over critical amplitude for showing the crack growth.
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Recent advances in structural damage and fault detection in the US
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structural damage detection using eigenstructure assignment method and LMIs technique B. Chen & S. Nagarajaiah Rice University, Houston, TX, USA
Existence of structural damages in civil engineering infrastructures will greatly influence the overall performance of the structure or even lead to disastrous consequences.Therefore, the ability to determine whether a structure is healthy or damaged, and if it is damaged, where the damage is and how severe it is, has become increasingly important from life-safety and economic viewpoints. In this paper, the detection filter theory, which is also called Beard-Jones detection filters (BJDT), is further developed. The observer-based detection filter relies on the idealized mathematical model of the system. In practice, this assumption can never be perfectly satisfied. System disturbances and sensor noise have to be considered in the filter design. In this paper, the
eigenstructure assignment method and LMI technique are combined to design robust detection filter. The detection spaces, which play great roles in structural damage detection and isolation, are first determined. Then the eigenstructures of the detection spaces are carefully studied and then a set of stable eigenvalues are assigned to each detection space. After that, the freedom provided by the complementary space can be used to form linear matrix inequalities, which can be solved using Matlab LMI Toolbox for the detection filter gain, such that the H∞ norm of the transfer function from disturbances to the output residual is bounded. The Simulation example shows that the presented method can successfully perform real-time structural detection and isolation.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structural health monitoring of a reinforced concrete frame using piezoceramic-based smart aggregates Gangbing Song, Haichang Gu & Claudio Olmi Mechanical Engineering, University of Houston, Houston, TX, USA
Argahdeep Laskar & Yi-Lung Mo Civil and Environmental Engineering, University of Houston, Houston, TX, USA
packet analysis is used as a signal-processing tool to analyze the sensor signals. The energy vector for healthy data is Eh = [Eh,1 , Eh,2 , . . . , Eh,2n ]. The energy vector Ei for damage state at time index i is defined as Ei = [Ei,1 , Ei,2 , . . . , Ei,2n ]. The damage index at time i is defined as Figure 1. (a) Three fabricated smart aggregate (b) Illustration of a smart aggregate.
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INTRODUCTION
Concrete structures are the most popular civil structures. It is imperative to quickly assess the severity of the damage and health status of a concrete structure, in real time or near real time after a disaster event to provide vital information for decision making. It is desirable to have an automated and distributive system to perform the task of damage detection and health monitoring. Piezoelectric-based approaches have provided an innovative approach for the structural health monitoring of civil structures. In this paper, a smart aggregate based Distributed Intelligent Active Sensing Network (DIASN) is developed to conduct the health monitoring of concrete structures. The proposed DIASN has been utilized to monitor the health status of a reinforced concrete frame during the loading test to fail the concrete frame. Experimental results have demonstrated the effectiveness of the sensitiveness of the proposed distributed intelligent active sensing network. 2
PRINCIPLES OF HEALTH MONITORING
To monitor the structural health status of concrete structure, in this paper, a piezoelectric-based smart sensor device, called smart aggregate as shown in Fig. 1. is developed. In this proposed smartaggregate-based health monitoring approach, wavelet
To show the damage status at different locations, two kinds of innovative damage index matrices are defined: Sensor-History Damage Index Matrix (SHDIM) and Actuator - Sensor Damage Index Matrix (ASDIM).
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EXPERIMENTAL RESULTS
Two hydraulic actuators are installed at the right corner of the frame to apply horizontal load to the reinforced concrete frame to conduct the so called “pushover” test. Sixteen smart aggregates are embedded at the desired locations in the frame. Traditional health monitoring tools-LVDTs are also installed to detect the displacement at different locations of the frame for comparison purpose. The experimental results of from microscope and LVDTs show that concrete frame yields at the load value of 5 tons. In the proposed smart aggregate-based DIASN, the average sensor-history damage index matrix have shown that the reinforced concrete frame reaches critical damage status at load value of 4 tons, which is ahead of the critical point captured by microscopes and LVDTs. The actuator-sensor damage index matrix results as shown in Fig.2 have shown that around PZT3, PZT6 and PZT14, damage situation is more severe. This is verified by the visual observation of cracks in the surface.
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status with the location information and time information. The critical point captured by the proposed smart aggregate-based approach is ahead of the critical point captured by the traditional approaches. The proposed smart aggregate-based DIASN can perform the structural health monitoring for concrete structures and it has the potential to be implemented to the structural health monitoring of real civil structures to enhance safety.
Figure 2. Actuator-sensor damage index matrix.
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CONCLUSIONS
From the experimental results, the proposed smart aggregate-based DIASN can evaluate the damage
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Experience in introducing smart structures technology into civil engineering curriculum Y. Zhang Department of Civil & Environmental Engineering, Lehigh University, Bethlehem„ Pennsylvania, USA
1 ABSTRACT Most of today’s civil engineering students are unaware of the potential use of smart structures technology in the design, construction and maintenance of civil infrastructure systems. This paper describes recent experiences of the writer in incorporating smart structures technology into civil engineering curriculum. In particular, a civil engineering course titled “Smart Structural Systems” that was taught to undergraduate students in the Spring’06 semester, are briefly described. The goal of this education effort is to prepare the future engineers of the society for this cutting-edge technology, for which they may see broad application in their generation. This paper presents the education activities conducted by the writers at Lehigh University in the area of smart structures technologies, In particular, a civil engineering course titled “Smart Structural
Systems” that was taught to undergraduate students in the Spring’06 semester. Two surveys of the students enrolled in the “Smart Structural Systems” course were conducted. The survey data revealed the need for introducing smart structures technology to civil engineering curriculum, which is important to ensuring the continued development of innovative structural systems for the world’s future. Survey data was also used for developing the course contents. A recent survey on smart structures technology development of students in US, China, Korea, and Japan is also described in this paper. Survey data was also used for developing the course contents. To effectively convey the technology to students and practicing engineers, hands-on experiments are very useful tools. Educators in civil engineering need to make active efforts to prepare the future engineers of the society for the cutting-edge technologies in smart structures technology, for which they may see broad application in their profession.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structural health monitoring with higher harmonics S. Hurlebaus Zachry Department of Civil Engineering, Texas A&M University, College Station, TX, USA
ABSTRACT When damaged bodies are subjected to dynamic loadings, a non-linear structural response is observed in the vicinity of the cracks. This non-linearity is caused by the contact between opposite crack surfaces. In case of a harmonic excitation, higher harmonics can be observed in the frequency spectrum. In nondestructive testing, this phenomenon can be employed to localize damaged areas. In the present paper, a methodology is described for the numerical simulation of non-destructive damage detection in the excitation frequency and the higher harmonics. The approach is based upon a transient Finite Element calculation, followed by an analysis of the structural response with the Fast Fourier transform. The suitable choice of analysis parameters is discussed, and examples are given for the detection of cracks in flat slabs. The occurrence of damage in structural components affects their functionality and can lead to failure of the components and, in the worst case, of an entire system. It is therefore important – especially for securityrelevant components – to detect damages at an early stage so that, by taking appropriate measures, failure can be prevented. The aim of non-destructive testing is the detection of damage in a structural component without changing its properties and functionality. When a structural component is damaged – for instance, by a crack, delamination, corrosion, or impact – its physical properties at the point of damage are altered. In non-destructive testing, it is attempted to visualize these alterations to gain information about the type, position, and size of the damage. Therefore, one has to identify properties whose visualization enables a characterization and localization of the damage. Reliability of the visualization procedure is of utmost importance, since an undetected damage can have serious consequences.
In experimental damage detection, local effects caused by non-linearities in the vicinity of the damage can be employed to visualize the damage, such as the occurrence of higher harmonics in cyclic loading or the increased dissipation due to friction in the crack faces. Test methods using these effects include the ultrasound lock-in thermography (ULT) and the overtone vibrometry. To improve existing methods used in nondestructive testing or develop new ones, a detailed understanding of the processes occurring at the location of the damage is essential. The physical models used to describe the damage – e.g., the material hysteresis and friction models – need to be tested and refined using numerical simulations, since the complexity of the processes at real, non-idealized damages prevents an analytical investigation. In addition, the numerical simulation of non-destructive testing allows a detailed investigation of ‘ideal’ damages and their influence on the structural response. This would be extremely difficult, if not impossible, in real components, where the structural response is influenced by material imperfections and other perturbations. In this paper, a methodology for the numerical simulation of overtone vibrometry based on defect selective imaging is described, which uses higher harmonics of the excitation frequency to localize cracks. The investigations are carried out with cracked twodimensional slabs, which are subjected to harmonic vibrations. First, a simple bar model is employed to determine suitable analysis parameters and establish a methodology for the numerical simulation. The proposed approach is then applied to a plane structure with multiple cracks, where its ability to detect cracks is tested and arising difficulties are discussed.
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Trust-region optimization-based model updating with subset selection and damage functions for SHM Wei Song, Shirley Dyke, GunJin Yun & Thomas Harmon Washington University, St. Louis, Missouri, USA
Finite element model updating techniques are widely used for structural health monitoring (SHM) because the results are directly applicable for locating and quantifying structural damage. And although these problems have been examined for many years, significant challenges remain in their application for real world problems. Choices made in the procedure adopted, such as the objective function, the identification model selection, and the approach used to overcome the ill-posedness are strongly linked to the quality of the results. In this paper, a new approach is proposed as an efficient procedure for implementation of a high-fidelity model updating procedure. Here, subset selection (Lallement 1990), a multivariate regression method, is used in conjunction with a damage function (Teughels 2002), efficiently reducing the size of the original updating problem. This integrated approach has been found to result in an accurate assessment of the damage distribution in a structure. A high-fidelity model of the structures considered is used as the “true” reference model, whereas a model with limited sensor information is used as the identification model. Thus, the effects of modeling errors are included in evaluating the approach. Starting with a simple 1-D beam model, this paper first demonstrates several essential concepts in the proposing model updating approach. However, in order to fully demonstrate the capabilities of the new approach, the complexity of the problem is also increased. Few model updating techniques in the literature have been applied to structures with more than one dimension. The limiting factor affecting current methodologies lies in the ability of the optimization technique to minimize the objective function within a high-dimensional parameter space, and in similarities in the sensitivities of dynamic parameters (frequencies and mode shapes) in the neighboring elements. Here an example using a 2D plane stress model is considered to fully demonstrate the approach. A trust-region based optimization algorithm has been used in solving the related updating problems. The combination of subset selection and damage functions is quite robust for solving this complex model updating problem.
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Figure 1. a) Imposed damage (E) b) Identified damage (E).
Figure 2. a) Imposed damage (E), b) Identified damage (E) c) Imposed damage (G), d) Identified damage (G).
The damage is simulated by a reduction of the elastic (E) and shear (G) (for 2D case) moduli of these elements. The damage detection results for 1-D beam and 2-D plane stress examples are shown in Figs. 1
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Teughels A., Maeck, J. & De Roeck, G. 2002. Damage assessment by FE model updating using damage functions. Computers and Structures, 80(25):1869–1879.
and 2. The damage is successfully identified through the model updating procedure. REFERENCES Lallement, G. & Piranda, J. 1990. Localisation methods for parameter updating of finite element models in elastodynamics. Proc. of IMAC VIII:579–585, Orlando, FL.
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Adaptive damage tracking of structures with unknown excitations: Experimental verification Hongwei Huang Department of Bridge Engineering, Tongji University, China
Jann N. Yang Department of Civil & Environmental Engineering, University of California, Irvine, USA
Li Zhou College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, China
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INSTRUCTION
Damage identification of structures is an important task of a health monitoring system. In particular, online or almost on-line damage tracking of structures will provide valuable information for post disaster emergency responses and management. Recently, a new analysis method, referred to as the adaptive quadratic sum squares error with unknown inputs (AQSSE-UI), has been proposed for on-line identification of structural damages [Yang & Huang (2007)]. Simulation results indicate that this approach is capable of not only tracking the structural damages but also identifying the unknown external excitations. Further, experimental tests have been conducted to simulate the scenarios of structural damages in service [Wu et al. (2006)]. In these experimental tests, a scaled 3-story building model was used and white noise excitations were applied to the top floor. An innovative stiffness element device was proposed to simulate structural damages in some stories during the test. Different damage scenarios had been simulated and tested [Wu et al. (2006)]. In this paper, we present further verifications for the capability of the AQSSE-UI technique in identifying the structural damage using experimental data
obtained in [Wu et al. (2006)]. Based on the measured acceleration data and the AQSSE-UI approach, the tracking results for the stiffness of all stories are compared with the stiffness predicted by the finiteelement method. Experimental results demonstrate that the AQSSE-IU approach is capable of tracking the structural damage with reasonable accuracy.
ACKNOWLEDGMENT This research is supported by the National Science Foundation Grant No. CMS-0554814. REFERENCES Wu, S., Zhou, L., andYang, J. N. (2006), “ Experimental Study of an adaptive Extended Kalman Filter for Structural Damage Identification”, Proc. 4th International Conference on Earthquake Engineering, Paper No. 161, CD Rom, Taipei, Taiwan, Oct. 12–13, 2006. Yang, J. N., and Huang, H. W. (2007), “Adaptive Quadratic Sum Squares Error with Unknown Inputs for Damage Identification of Structures”, Proc. World Forum on Smart Materials and Smart Structures Technology, Paper No. 410, May 22–27, 2007, Chongqing and Nanjing, China.
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Model updating for civil applications
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
On the computation of zeros in systems identified from output signals D. Bernal & O.F. Tigli Northeastern University, Center for Digital Signal Processing, Boston MA, USA
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INTRODUCTION
The paper presents an approach to compute transfer function zeros for systems identified without deterministic information on the input. The method is grounded on the fact that the observed output could have been generated by collocated inputs and that the span of the input to state matrix B associated with this condition is constrained by the {A,C} duplet of the stochastic identification. Two implementations are explored. The first does not compute normalization modal constants as an intermediate step while the second one does. The two implementations are found to provide similar accuracy in the numerical examples considered. 2
COMPUTATION OF ZEROS WHEN INPUT IS KNOWN
Assume that identification results are used to describe the system of interest using a state-space model in the form of {A, B, C, D}. Let’s suppose that the input coordinates are partitioned into sets 1 and 2 and the output coordinates into sets a and b. Then, the zeros of the transfer function relating the inputs of set 1 to the outputs of set a can be computed from the following equation
which is a generalized eigenvalue problem whose solution yields the zeros, the initial condition x0 and the spatial distribution of the loading at the input coordinates. 3
In the Cepstrum approach an output signal is taken to a domain where source and path effects can be approximately separated and then the zeros are obtained by fitting a pole-zero model structure to the bandwidth dominated by the system properties. In its basic form the Cepstrum approach is limited to a single excitation and demands that the log of the spectrum of the input be relatively flat. Extension to multiple inputs and less restricted excitations is feasible but the complexity of the Cepstrum approach makes it an unlikely candidate for routine application in structures excited by ambient sources. The idea exploited in this paper is simply that given an {A, C} duplet the input to state matrix B for collocated inputs has to satisfy the following constraints.
COMPUTATION OF ZEROS FROM OUTPUT MEASUREMENTS ONLY
where p = 0, 1 or 2 for displacement, velocity or acceleration measurements. Once an estimate of B is obtained, zeros are computed following the standard state-space approach (Eq. 3). Two implementations of the basis restriction for the collocated B are examined: one where zeros are estimated directly and one where modal constants are first estimated and then used to get the zeros. We restrict treatment to the situation where sets 1 and a are identical and contain a single element, i.e., we look at zeros for diagonal entries of the transfer matrix. Exact solutions can be obtained provided that a full modal space is available and the number of sensors is more than a certain threshold. In practice, however, exact solutions are not generally feasible, primarily because the identified modal space is truncated. Numerical simulations suggested that the two mentioned implementations offer similar accuracy in the estimated zeros.
Prior research on the extraction of zeros from output data have focused on the use of Cepstral techniques.
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Model updating and damage detection of damped systems using incomplete complex modes S. -L. J. Hu Department of Ocean Engineering, University of Rhode Island, Narragansett, RI, USA
F.S. Liu & H.J. Li College of Engineering, Ocean University of China, Qingdao, China
Many civil and mechanical structures accumulate damages during their service life. These damages would alter the structural modal characteristics such as the modal frequencies and mode shapes. Based on changes in frequencies, mode shapes, or their combination, many structural damage detection techniques have been proposed for predicting damage location and severity. One particular model-based approach to identify the damage location and to assess its severity is the finite element (FE) model updating method. The purpose of FE model updating is to calibrate the mass, damping and stiffness matrices of the FE model based on the test data so as to obtain better agreement between numerical model predictions and measured results. Clearly, comparing the updated matrices associated with a damaged structure to those of the baseline model provides an indication of the damage, for both location and severity. In the study of finite element model updating methods, most papers are devoted to undamped systems; thus, their model updating has been exclusively restricted to the updates for the mass and stiffness matrices. Traditionally, the modal-based FE model updating for undamped systems can be classified into two major groups: direct matrix methods and indirect physical property adjustment methods. A completely different approach developed recently for the simultaneous updating of the stiffness and mass matrices is the cross-model cross-mode (CMCM) method. This method was so named because it involves solving a set of linear simultaneous equations for the physically meaningful correction factors, in which each equation is formulated based on the product terms from two same/different modes associated with the
mathematical and experimental models, respectively. The CMCM method is very cost-effective in computational time. It also has the advantage of preserving the initial model configuration and physical connectivity of the updated model. In modal testing, the measured modes are often few, complex valued, and spatially incomplete. When only a few spatially incomplete complex modes are measured, this paper, considering systems with nonproportional damping, addresses the simultaneous updates for the mass, damping and stiffness matrices of a finite element model. Through the framework of model reduction or modal expansion, this paper theoretically extends the recently developed CMCM method. One theoretical development is an iterative procedure to compute the transformation matrix (between the master and slave degrees-of-freedom) associated with the updated model, instead of that of the baseline model routinely used in traditional studies. A 30 degree-of-freedom (DOF) cantilever beam structure is chosen for the numerical studies. Both the analytical model and the damaged model are generated from using finite element models, with different sets of system coefficients. Model reduction and modal expansion approaches are tested in dealing with spatially incomplete situations. Specifically, the Guyan (static) reduction method and the system equivalent reduction expansion process (SEREP) scheme are included in the numerical studies. The numerical results reveal that (1) applying the CMCM method in conjunction with iterative Guyan reduction approach can yield the best model updating, and (2) employing a model reduction scheme always outperforms employing a modal expansion scheme.
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Non-linear identification of MDOF systems with hysteresis from seismic response data R. Ceravolo & G.V. Demarie Dipartimento di Ingegneria Strutturale e Geotecnica, Politecnico di Torino, Turin, Italy
S. Erlicher Institut Navier / LAMI, Ecole Nationale des Ponts et Chaussées (ENPC), Marne-la-Vallée, Paris, France
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A non-linear dynamic identification presupposes the availability of a huge quantity of experimental data, this being a requirement that is seldom satisfied in structural or earthquake engineering applications. The paper presents a technique for the identification of the hysteretic behavior of Multi-Degrees-of-Freedom hysteretic systems subjected to seismic loading by defining proper instantaneous estimators of the dynamic properties: such estimators are defined by resorting to a Volterra series representation of a polynomial non-linear time-varying system whose dynamics is equivalent, to a certain extent, to the actual hysteretic behavior. A numerical application example consists of the instantaneous identification of a shear type frame with Bouc-Wen law in the interstory drift, subjected to seismic excitation.
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REFERENCES
Case study: shear-type frame subjected to seismic excitation.
Ceravolo, R. 2004. Use of Instantaneous Estimators for the Evaluation of Structural Damping, Journal of Sound and Vibration 274(1–2): 385–401.
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Demarie, G.V., Ceravolo R. & De Stefano, A. 2005. Instantaneous identification of polynomial nonlinearity based on Volterra series representation, Key Engineering Materials, 293–294: 703–710. Erlicher, S. & Point, N. 2004. Thermodynamic admissibility of Bouc-Wen-type hysteresis models, C.R. Mécanique 332(1): 51–57. Erlicher, S. & Bursi, O.S. 2007. Bouc-Wen-type models with stiffness degradation: thermodynamic analysis and applications, Engineering Mechanics ASCE, accepted.
Mallat, S., Papanicolaou, G. & Zhang, Z. 1998. Adaptive covariance estimation of locally stationary processes. The Annals of Statistics 28: 1-47. Masri, S.F., Caffrey, J.P., Caughey, T.K., Smyth, A.W. & Chassiakos, A. G. 2004. Identification of the state equation in complex non-linear systems. International Journal of Non-Linear Mechanics 39: 1111–1127.
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Identification of crack locations and extents by Bayesian model class selection H.F. Lam & C.T. Ng Department of Building and Construction, City University of Hong Kong, Hong Kong, China
L.S. Katafygiotis Department of Civil Engineering, Hong Kong University of Science and Technology, Hong Kong, China
1
INTRODUCTION
This paper puts forward a method for the detection of crack locations and extents on a structural member utilizing measured dynamic responses following the Bayesian probabilistic framework. If the model-based approach is followed for crack detection and the number of cracks is not known, beams with different numbers of cracks have to be modeled by different classes of models, as shown in Figure 1. The model class Mj is employed in modeling a beam with j cracks, and the parameters lj and j are used to describe the location and extent of the j-th crack. The problem is how to identify the “optimal” model class using a set of measurements D. By following the concept of model updating, one may consider carrying out a minimization for each model class to minimize the discrepancy between the measured and modeled responses, and “pick up” the “optimal” model class as that which can give the best fit to the measurement. It must be pointed out that the selection of the “optimal” model class based on a given set of data is not trivial. It is clear that the model class of a beam with
Figure 1. Schematic diagram illustrating the basic strategy for the first stage of the proposed methodology.
more cracks consists of more model parameters (see Figure 1), which will always provide a better fit to the measurement when compared to a model class with fewer parameters. Hence, the selection of model class based solely on the fitting between the modeled and the measured dynamic responses can be very misleading, as the most complex model class will always be selected. In addressing this problem, the proposed methodology relies on the Bayesian model class selection method in selecting the “optimal” model class to identify the number of cracks on the beam. The selection is based on the probability of the model class conditional on the set of measurements D:
where U expresses the user’s judgment about the initial plausibility of the classes of models, expressed as a prior probability p(Mj |U ) on the model class Mj , such M that Nj=1 P(Mj |U ) = 1. Unless there is prior information about the number of cracks on the beam, the prior probability P(Mj |U ) is taken as 1/NM ; 1/p(D|U ) is treated as a normalizing constant. The most important term in Equation (1) is p(D|Mj , U ), j = 1, . . . , NM , which is known as the “evidence” for the model class Mj provided by the data D. The class of models to be used is obviously the one that maximizes the probability P(Mj |D, U ) and this is generally equivalent to the one that maximizes the evidence p(D|Mj , U ) with respect to Mj . This paper presents not only the theoretical development of the proposed method but also the numerical and experimental verifications. In the numerical case studies, noisy data generated by a BernoulliEuler beam with semi-rigid connections is used to demonstrate the procedures of the proposed method. The method is finally verified by measured dynamic
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responses of a cantilever beam utilizing laser Doppler vibrometer. Very encouraging results were obtained from both the numerical and experimental case studies. One of the outstanding advantages of the proposed
methodology is that the uncertainties associated with the identified results can be quantified. As a result, engineers know the confidence level of the crack detection results.
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Probabilistic condition monitoring of smart structural elements D. Zonta & M. Pozzi DIMS, University of Trento, Trento, Italy
This paper presents a damage detection procedure based on Bayesian analysis of data recorded by permanent monitoring systems and validates this method for the condition assessment of a roadway bridge, constructed using smart Precast Reinforced Concrete (PRC) elements. These are prefabricated box-girder elements produced in series and incorporating a fiber optic long-gauge strain sensor system. The concept is to assume a set of possible condition states of the element, including an intact condition and various combinations of damage, such as failure of strands, cover spalling and cracking. Based on these states, a set of potential time response scenarios is evaluated, each described by a vector of random parameters (such as location and extent of damage) and by a theoretical model. Based on the prior distribution of this vector, the method assigns posterior probability to each scenario as well as updated probability distributions to each parameter. To clarify how the Bayesian updating procedure works, we present the application of this method to the single span PRC bridge shown in Fig. 1. The deck structure is made up of 6 precast elements, finished with a 22 cm cast-in-place concrete slab. The two lateral beams are special smart elements specifically designed for this application with embedded instrumentation. In detail, each smart element accommodates 8 long gauge-length fiber optic sensors at the lower edge, each monitoring longitudinal elongation over a 2.8 m span. The optical instrumentation also includes thermometers for temperature compensation. To predict the strain history and distribution, we developed a Finite Element Model (FEM) of the deck accounting for all geometrical and mechanical properties of the structural elements, including pre-stressing, creep, shrinkage and relaxation. In this example, we simulate the failure of a strand located at beam 1 and position xf = 12.4 m from the left hand support, near sensor s3 ; we also suppose the failure to occur at time tf = 37 days after production of the beam. In the Bayesian identification we assume that only two scenarios are allowed: S1 simulates a situation where no damage occurs, using the mechanical properties of
Figure 1. Elevation and cross-section of the case study.
Figure 2. Posterior distribution of damage parameters.
material as parameters; S2 simulates a strand failure scenario. The simulation shows that the assessed probability of damage prob(S2 ) begins to increase immediately after the failure, and is 77.9% at time 51 days. At that time, the final distribution presents a single sharp peak for µxf = 12.4 m and µtf = 37.5 days, with standard deviation σxf = 0.5 m and σtf = 1.5 days, as shown in Fig. 2. The outcomes clearly highlight that parameters such as mechanical properties of material and damage position can be identified with very high precision. However, the specific nature of the problem does not allow us to recognize with the same confidence the time of occurrence of damage.
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Finite element model updating of a truss model using incomplete modal data Y.X. Zhang Civil Engineering Department, Shanghai Normal University, Shanghai, China
S.H. Sim & B.F. Spencer, Jr Civil Engineering Department, University of Illinois at Urbana-Champaign, Urbana, IL, USA
Analytical models often differ greatly from their as-built counterparts. Model updating techniques improve the predictions of the behavior of the actual structure by identifying and correcting the uncertain parameters of the analytical model. In recent years, model updating has attracted significant attention from structural engineers. Current model updating methods can be classified into two broad categories, namely direct methods and sensitivity based methods. The main drawback of direct methods is that by forcing the model updating procedure to reproduce exactly the measured modal data causes any measurement errors to be propagated into the parameters (Friswell et al. 2001). Due to this drawback, direct methods are seldom used in structural dynamics (Friswell et al. 1995). Presently, sensitivity based methods are the most popular because they do not have the limitations of the direct methods. In sensitivity-based methods, the model updating problems are posed as optimization problems. They set the errors between analytical and experimental data as an objective function and minimize it by adjusting a pre-selected set of physical parameters present in the finite element (FE) model. The optimum solution is obtained using sensitivity-based optimization methods. The nonlinear relationship between vibration data and the model’s physical parameters requires an iterative optimization process. This approach is able to both update the relevant physical parameters and locate erroneous regions in the model. Link (1999) gives a clear overview of sensitivity-based model updating methods. This paper applies a two-step FE model updating methodology based on a sensitivity analysis method to a 3D truss bridge model using experimental modal data. The first step analyzes the sensitivity of the modal parameters to the physical parameters. In the second step, Sequential Quadratic Programming (SQP), Newton Iteration techniques, and line search methods are combined to minimize the objective function. While performing the optimization, the gradient matrix of
Table 1.
Parameters before and after model updating.
Initial value updated value
E (×1011 ) MPa
I (×109 ) m4
2.0e11 1.1756e11
3.498e−9 3.556e−9
Table 2. ing.
Natural frequencies before and after model updat-
Order
fe,i before
fe,i after
id,i
MAC
1 2 3 4 5
26.195 53.699 88.425 115.800 176.350
20.143 41.207 67.795 88.672 135.21
21.362 41.571 69.387 94.660 120.161
99.97% 96.87% 97.34% 99.21% 99.41%
the objective function versus each physical parameter is calculated by conducting quadratic curve fitting at each iterative step. Doing so helps to obtain a more precise gradient function. By using experimental data gathered from the physical truss, model updating produced new values for the E and I of the numerical model as presented in Table 1. The elastic modulus experienced significant changes from its original value. Table 2 gives the calculated numerical natural frequencies based on the updated parameters. The updated analytic natural frequencies shown in Table 2 do not exactly match the experimental ones. However, the updated frequencies show greatly improved correlation to the experimental results that represents the best effort when only changing these two aspects of the numerical model.
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Life-cycle performance assessment-based on structural health monitoring
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
State identification by soft computing techniques during service conditions S. Arangio & F. Bontempi Department of Structural and Geotechnical Engineering, University of Roma La Sapienza, Rome, Italy
F. Giuliano Department of Structural Mechanics, University of Pavia, Pavia, Italy
G. Pieri Graduate student, School of Engineering, University of Roma La Sapienza, Rome, Italy
1
INTRODUCTION
A double-step procedure, using in-sequence neural networks (ANN) has been considered for the state identification of a long span suspension bridge. It enables the management to detect and localize damage, and arrange timely intervention by processing the response under wind and traffic scenarios of ordinary service. A series of permanent sensors distributed longitudinally along the bridge provides in real-time the wind response, which is compared to the output of a trained Back Propagation Neural Network. Localized damages (stiffness reductions down to 5% for hangers/transverse, 0.5% for cables) produce increases of the approximation errors in the channels in the neighbourhood of the damage, a timely localization of the damaged section and an alert signal directed to the management unit (First step). In these circumstances supplementary sensors are located transversely in the alerted section by the management staff (Second step). Another Back Propagation Neural Network, trained to approximate the response under a goods train crossing the bridge, enables a refinement of the location and identifies the side of the damage. The errors in the three channels are finally used by a further Neural Network, with a larger number of neurons involved in a pattern recognition procedure. Starting from the vectors of errors in the three input channels, the network is trained to produce in output a six component damage vector, more accurate than in the 1st step. Nonzero components of the damage vector mean to damaged corresponding elements. The accuracy of localization and damage magnitude is evaluated by two scalar quantities. The investigation conducted by unedited damage scenarios emphasize the generalization capabilities of
neural networks, their robustness in front of incomplete and uncertain information. In fact whenever the quantification of the damage is sometimes less precise, the localization of the damaged element is always correct. The performance of the 1st step architecture, the minimum detectable damage and its accuracy are the primary target of the design of this system. The results obtained allow to rely that it could represent an attractive option for the damage localization inside a long span suspension bridge, to be used alternatively or synergically with the classical modal approaches to avoid inappropriate or untimely alerts. ACKNOWLEDGEMENTS The financial supports of University of Rome “La Sapienza”, COFIN2004 is acknowledged. REFERENCES Demuth H. and Beale M. 2006. Neural Network Toolbox for use with MATLAB. User’s Guide. Schalkoff R.J. 1997. Artificial Neural Networks. Ko J.M. and Sun Z.G. 2002. Multi-stage identification scheme for detecting damage in cable-stayed Kap Shui Mun Bridge. Steel Structures, 24, 857–868. Sgambi L. 2005. Artificial intelligence for the analysis and design of complex bridge structures. Proc. of the 9th Int. Conf. on Structural Safety and Relaibility (ICOSSAR05), Rome, Italy. Golden R.M. 1996. Mathematical Method for Neural Networks Analysis and Design. The MIT Press. Petrini F., Giuliano F. and Bontempi F. 2007. Comparison of time domain techniques for the evaluation of the response in long span suspension bridges, Computers & Structures, in press. Stretto di Messina S.pa. 1992 Preliminary Project, available at www.strettodimessina.it.
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Insurance derivatives for buildings to reduce the damage due to large earthquakes A. Mita & H. Tamura Keio University, Yokohama, Japan
Despite the modernity of today’s cities, all kinds of buildings are built without proper hedge strategies against the risk of large disasters such as earthquakes. In order to control such risks, new engineering and economic mechanisms should be developed. On the engineering front recently Structural Health Monitoring (SHM) systems using sensor networks have been proposed and even enacted in many variations. Fortunately, data taken from such systems serve as good candidates as risk indices for each building. The purpose of this study is to propose insurance derivatives to maintain and improve the safety of buildings and to provide a risk hedge instrument for owners.
These derivatives should be able to take advantage of information gained from SHM sensor networks. In this study, hazard information offered by J-SHIS (Japanese Seismic Hazard Information Station), and Weibull distributions associated with Is-WF (Seismic index based on seismic diagnosis), proposed by Okada and Takai as Damage Index Functions, were used for the quantification of risk. This simply defined quantification was used to evaluate the proposed earthquake derivatives. Results showed that the proposed derivative is better than the functions currently used for earthquake insurance, and that it has potential to be used as incentive for seismic strengthening. A mechanism proposed in this paper is depicted in Fig. 1.
Figure 1. Derivative mechanism with incentives to improve the structural strength.
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Condition assessment of buildings using acceleration data for life cycle predictions Y. Qian & A. Mita Keio University, Yokohama, Japan
1
EXTENDED ABSTRACT
Most currently available damage detection methods are global in nature, i.e., the dynamic properties (natural frequencies and mode shapes) are obtained for the entire structure from the input–output data using a global structural analysis. However, natural frequencies and mode shapes are not sensitive to minor damage and local damage. The techniques using time-domain dynamic responses are appealing and promising. Furthermore, the dynamic responses of structures under environmental excitation or smallscale earthquakes are very economical information for structural identification and health monitoring, especially in the place where small-scale earthquakes occur very frequently. Some information about structural parameters and dynamic properties can be identified by the direct use of these time-domain response. There is an approach by directly using dynamic responses in time series without extraction of dynamic properties, which used acceleration, velocity and displacement time histories as the input of the emulator neural network, called acceleration-based emulator neural network (AENN) for free vibration. In this paper, the AENN is extended beyond the limitation of free vibration to forced vibration. The acceleration time histories, which are readily available
in real structures, are only required. This is the first phase, through which the damage occurrence alarm can be obtained by observing the relative root mean square (RRMS) error between the output of AENN and the real value. After knowing the damage occurrence, the next phase is to localize and quantify the damage. Most currently available damage localization approaches are using pattern recognition methods to classify the different damage location. However, such approaches need analytical data for all damage case situations, which can be computationally expensive and even impossible. Therefore, the system identification is utilized. Seeing as the currently available system identification techniques are normally based on the frequency-domain approach, so in this paper the system identification problem is transferred to optimization problem with the convenience for time-domain. The particle swarm optimization (PSO) is utilized. The proposed approach is carried out in two phases as briefly described in Fig. 1. We analyze two five-story shear the structure to verify the proposed method experimentally. Key words: Particle swarm optimization, Neural network, Life cycle prediction, Damage identification
Figure 1. Two-phase damage evaluation approach.
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Safety evaluation of infrastructures-based on long-term measured data of structural health monitoring systems H. Li School of Civil Engineering, Harbin Institute of Technology, Harbin, China
J.P. Ou School of Civil Engineering, Harbin Institute of Technology, Harbin, China Dalian University of Technology, Dalian, China
1
3 AN SHM SYSTEM OF THE BINZHOU YELLOW RIVER HIGHWAY BRIDGE
INTRODUCTION
The structural health monitoring (SHM) techniques have more and more attracted great research and development interests of scientists and engineers in the whole world because of the ability to ensure safety and study damage evolving characteristics of structures. In this paper, safety evaluation methods of bridges, dome roof structure and offshore platforms based on structural health monitoring systems are proposed.The method to assess fatigue accumulative damage index of cables or suspenders is proposed based on structural health monitoring system. The principle component analysis (PCA) in combination with artificial neural networks is employed to obtain the relationship of modal parameters and ambient temperature. In this way, finite element model of a structure can be updated without perturbation of ambient factor. For offshore platforms, a base shear capability obtained based on structural health monitoring is employed to evaluate the safety of platform structures.
2 AN SHM SYSTEM OF THE OFFSHORE PLATFORM CB32A The SHM system developed for a steel jacket platform JZ20-2MUQ an on-line SHM system includes 259 OFBG sensors, 178 PVDF sensors, 56 fatigue life meters, 16 accelerometers. Additionally, the SHM system also includes an anemoscope and wave-current meters for measurement of wind, wave and flow loads. PXI bus technique is employed to collect data synchronously from different sensors. A wireless transmission system is set up for transferring the signal collected on the CB32A to the management agency office.
A SHM system implemented in The Binzhou Yellow River Highway Bridge includes sensors, data acquisition system, signal transmission system, structural performance evaluation module, and database. 96 FBG strain and temperature sensors, 2 anemoscopes, 39 accelerometers and 4 GPS are embedded in or attached to the Bridge. This system can be automatically online operated at website through internet. The system has been operating since the static and dynamic tests for open to traffic on July 18, 2004.
4 AN SHM SYSTEM OF THE HARBIN SONGHUA RIVER CABLE-STAYED BRIDGE A SHM system of the Harbin Songhua River Cablestayed Bridge consists of sensors, data acquisition system, database and structural performance. The sensors include FBG strain and temperature sensors, wireless accelerometer networks and 3 GPS. The data acquisition system and database are the same as those used in the SHM system of the Binzhou Yellow River Highway Bridge.
5 AN SHM SYSTEM OF THE NATIONAL SWIMMING CENTER A structural health monitoring (SHM) system on the National Swimming Center for Olympiad consists of sensors, data collection systems, wireless and wired data transmission system, database and performance evaluation module.
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6
CONCLUSIONS
evaluate structural performance based on utilization of measured data in the future.
It is found that some bridges suffer from heavy traffic loads and stress is little large. Additionally, uncertainties have intensive impact on stress and modal frequencies of structures. It is important to study relationships between uncertainties and structures, which is beneficial to detect damage and update model accuracy. More attention should be paid on how to
ACKNOWLEDGEMENTS This research is financially supported by the National Natural Science Foundation of China under the grant 50538020, 50525823 and 50420120133.
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Novel technologies and methods of SHM for decision making
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Improvement of health monitoring system for environment with noise Hitoshi Furuta & Hiroshi Hattori Kansai University, Takatsuki, Japan
1
INTRODUCTION
In this paper, an attempt is made to develop a structural health monitoring system that can adapt to the structural systems and environments, by introducing the learning ability. By introducing the learning ability, it is not necessary to prepare any previous knowledge and examination for the underlying structures and environment. In other words, it is not necessary to use the precise modeling and analysis method before conducting the health monitoring. Several numerical examples are presented to demonstrate the efficiency and applicability of the proposed system. In the numerical examples, a multiple degree of freedom structure with the same number of sensors is used to examine the performance of detecting the degree and location of deterioration. Through the numerical examples, it is concluded that the proposed system can identify the change of structural characteristics and condition states.
2
Figure 1. Comparison of observed value and predicted value without degradation.
Table 1.
Recognition rates.
PROPOSED SYSTEM
The propose system consists of 1) prediction part; learning the vibration response and predicting the next response, 2) judgment part; detecting the deterioration by analyzing the vibration response and 3) simulation part; analyzing the vibration. Inputs to the proposed system are external force and vibration response; displacement and velocity of structures. Outputs from the proposed system are probability of deterioration and position of deterioration. At the prediction part, it is performed to predict the vibration response; displacement and velocity of structures of next step from current response and external force. In this research, fuzzy-neuro is used for the prediction so that versatile rules are obtained and calculate time becomes shorter. At the judgment part, it is done to detect the deterioration by comparing prediction value and observed value. The system provides the existence of deterioration in probability using fuzzy reasoning with the learning ability. Input data of fuzzy reasoning are error and error rate.
Environment without noise Environment with noise
3
Intact situation
Deterioration situation
0.922 0.902
0.804 0.756
EXAMPLE
Figure 1 shows the difference of prediction value and observed value when external force is wind velocity that is learned under the noisy environment. Table 1 shows the recognition rate. 4
CONCLUSIONS
To validate the ability of the proposed system, several numerical simulations are performed. The proposed system can identify the existence of deterioration. By introducing the learning ability for fuzzy reasoning used for the detection part, the recognition rate can be improved even under the environment with noise.
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Estimation of probability density function of long-term strain measurement for reliability assessment Y.Q. Ni, X.G. Hua, K.W. Chen & J.M. Ko Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
ABSTRACT Cable-stayed Ting Kau Bridge in Hong Kong is instrumented with a long-term structural health monitoring system called Wind And Structural Health Monitoring System (WASHMS) which has collected voluminous data on structural responses as well as the imposed loadings. Obviously, the probability density functions (PDFs) of the measured structural responses under traffic loadings, wind loadings, and environmental effects are indicative of performance and condition of structures, and they play a vital role for probabilistic condition assessment of structures. Among a variety of measurands, the strain response is probably the most important as it directly indicates the safety reserve of the component. This paper presents the reliability-based condition assessment of bridge components directly using PDF of strain measurement data. A non-parametric density estimation approach
based on Parzen window is first applied to estimate the density function of strain data at every measurement point. Then structural reliability method is used to determine the reliability index and failure probability based on the estimated PDF of strain data and the PDF of design stress capacity. Reliability indices are useful parameters to evaluate the damage condition of typical members and to assign the level of maintenance action. Some preliminary results of application to the reliability assessment of instrumented structural components in cable-stayed Ting Kau Bridge are presented by using long-term strain monitoring data. Keywords: Cable-stayed Ting Kau Bridge, structural health monitoring, strain measurement, probability density function, kernel density estimation, reliability assessment.
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Issues in using video images for structural health monitoring R. Zaurin & F.N. Catbas Civil and Environmental Engineering Department, University of Central Florida, Orlando, FL, USA
EXTENDED ABSTRACT Structures are complex engineered systems that ensure society’s economic and industrial prosperity. To design structures that are safe for public use, standardized building codes and design methodologies have been created. However, structures are often subjected to unexpected loading and severe environmental conditions that are not fully anticipated during design. These effects will result in long-term structural damage and deterioration. Novel structural health monitoring strategies for better management of civil infrastructure systems (CIS) are increasingly becoming more important as CIS are aging and subject to natural and man made hazards. Structural health monitoring (SHM) offers an automated method for tracking the health of a structure by combining assessment algorithms with sensing technologies. Very recently, some investigators have introduced the idea of a new paradigm for SHM: the possibility of incorporating imaging and optical devices and combining them with sensing technology however, only a few limited attempts have been tested and implemented. Very soon, computer vision will become an indispensable and common part of any SHM framework. By adding vision capabilities to a SHM framework, correlation between moving loads (traffic) and responses (sensors readings) can be performed and cause/effects relationship can be determined. However, although there are many benefits of using video in conjunction with sensing technology, there are also many issues related with this approach. Technology requirements, algorithm needs, and the amount of data to be handled are increased dramatically. In this paper, some of the most common issues related to computer vision techniques and sensor fusion applications as well as some possible practical solutions are described. First, the use of Background Subtraction (BGS) method for SHM is studied and discussed. In vision
based systems, the most common approach to identifying the moving objects is BGS, where each video frame is compared against a reference or background model. Pixels in the current frame that deviate significantly from the background are considered to be moving objects and belonging to the foreground. Two key issues have to be solved when using this method: first, what value for thresholding is the best, and second how to deal with illumination changes. Another computer vision technique used for SHM is tracking. The main goal for tracking algorithms is establishing correspondence between circulating vehicles (moving loads) in the 3D world and their projection on a 2D space (images). One of the main problems related with tracking is occlusion, also discussed in this paper. One of the big concerns in SHM is handling, processing and storing the data properly so that it can be meaningful and be used in a timely manner. It is known that SHM generally involves per se a large amount of data coming from sensors readings. Acquiring data has become easy and economic because sensors have became cheaper with the advances in its fabrication process technology and massification. By including video information, the amount of data is increased dramatically. A system of structured database is proposed to store only relevant data, and necessary information. To keep record of the time-history, only hourly (or any other desired time-frame) peaks can be stored for each of the sensors. Also a series of image frames describing the significant event should be time stamped and recorded, making it possible to correlate with sensors readings. In addition, any behavior deviating from the normal has to be recorded and time stamped. Finally, an experimental setup which was designed and built by the researchers to investigate the issues concerning with sensor fusion and video monitoring, is described and some laboratory and real life examples are presented and discussed.
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FBG-based distributed sensing system for bridge health monitoring R.J. Sun, Z. Sun & L.M. Sun Department of Bridge Engineering, Tongji University, Shang Hai, China
1
INTRODUCTION
In this paper, a FBG-based acceleration sensing technique is proposed to measure the low frequency response of the engineering structural systems. In the design stage, a special L-type structure is adopted to amplify the vibration response and to ward off the chirped phenomenon. Moreover, some damping liquid is infused into the sensor to broaden the working frequency range. A series of shaking table tests were then conducted to verify the performance of the prototype accelerometers. During the performance tests, the damping liquid with various viscosities is infused into the sensors, and their influences on the sensitivity, linearity and the amplitude-frequency relationship are discussed. Integrating this novel sensor with the FBG strain gauges and FBG thermometers, a distributed sensing system is setup for structure health monitoring. An experimental study on a fixed-fixed beam is conducted to verify the efficiency of the proposed distributed sensing system for structure health monitoring. 2 A FBG BASED ACCELEROMETER A prototype FBG accelerometer was fabricated according to the design strategy explained above. In
order to eliminate the influence of transverse strain, the width of a special L-type structure was bigger than its thickness. To avoid being destroyed for the acceleration measurement of high magnitude, some over load protection device is adopted. In the tests, some damping liquid with various viscosity were infused into the sensor to broaden the working frequency range. As a result, the prototype sensor was successfully developed (Fig. 2). Its performances were examined by a series of shaking table tests. 3 A FBG DISTRIBUTED SENSING SYSTEM For structural health monitoring, this novel sensor is integrated with the FBG strain gauges and FBG thermometers and a distributed sensing system is setup. This sensing system is composed of sensory, data transmission and data acquisition modules. The logic structure of this system is shown in fig.2. The FBG sensors are integrated in series via wavelength multiplexing into one channel and those channels are then integrated into one system in parallel via spatial multiplexing. For wavelength signal demodulating, the filtering demodulating technique is adopted to achieve high measurement resolution. Although this demodulating technique is generally of low dynamic performance, it is still suitable for structural vibration monitoring considering that the vibration modes of engineering structures are generally of low frequency.
Linking optic fiber
FBG demodulator
Figure 1. The prototype FBG accelerometer.
FBG sensors
Computer
Figure 2. A FBG distributed sensing system.
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Smart materials and intelligent systems
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Bio-inspired structural monitoring system architecture R.A. Shoureshi School of Engineering and Computer Science, University of Denver, Denver, Colorado, USA
L. Faravelli Department of Structural Mechanics, University of Pavia, Pavia, Italy
The infrastructure of a nation provides the backbone for its economy, well being and prosperity. Thus, adequacy, health, safety and security of a nation’s infrastructure system have a profound impact on its socio-economic state. New civil engineering construction is the largest industry in the world, accounting for more than 10% of the world’s gross domestic product (GDP). Civil infrastructure systems are generally the most expensive investment and assets in any country. In the USA, this asset is estimated to be about $20 trillion. Over the last century, the United States has invested a significant amount of capital into developing and maintaining the nation’s infrastructure in the form of roadways and bridges. However, this infrastructure is deteriorating at an alarming rate due to material or system deterioration caused by overuse, overloading, aging, damage or failure caused by external loads such as natural or man-made hazards. The field of structural health monitoring (SHM) has experienced significant progress during the past decade. As the development of wireless sensors becomes more rapid and the price of this technology is decreasing, most of the structural health monitoring architecture is now geared toward the utilization of distributed wireless sensor. This paper presents an architectural concept of an anatomical-based structural monitoring and diagnostic system that mimics
human nervous system. For this research, we have examined and attempted to understand some of the intricacies of the human sensory and nervous system. Sensory information is conveyed to the brain as trains of action potentials traveling along individual sensory neurons, with pools of neurons acting together. To savor the richness and diversity of perception, the central nervous system must integrate the activity of an entire sensory population. Among five basic types of sensory receptors in the human body, mechanoreceptors detect mechanical compression and stretching of the receptor, or of tissues adjacent to the receptor. Stimulation of mechanoreceptors in the skin leads to a wide range of touch pressure experiences, deep pressure vibrations, and superficial touch. These mechanoreceptors are highly specialized nerve endings encapsulated in elaborate cellular structures. Activation of rapidly adapting receptors gives rise to the sensations of touch, movement, and vibration; whereas slowly adapting receptors give rise to the pressure sensation. A stimulus that causes or is on the verge of causing tissue damage usually elicits a sensation of pain. The overall design, sensory system, and its selfpowered monitoring technique are presented. Preliminary experimental data from a prototype cable-stayed bridge are discussed.
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Processing of fiber optic dynamic strain records for structural monitoring A. Del Grosso & F. Lanata Department of Structural and Geotechnical Engineering, University of Genoa, Italy
A. Torre & L. Denegri D’Appolonia S.p.A., Genoa, Italy
1
INTRODUCTION
The recent development of dynamic long base fiber optic sensors has made possible to perform some interesting experiences in the field of structural monitoring. The first experience is related to the measurements performed on sample reinforced concrete beams subjected to known levels of damaging by cracking and corrosion. The second experience consists in the recording of dynamic measurements on a cable-stayed bridge in the Port of Venice. The paper addresses specific problems in the processing of the related signals and of the characteristics of the information that can be derived from the related strain time-histories in view of the condition assessment of structures.
2 APPLICATION ON LABORATORY BEAMS The aim of the project was the detection of damage in concrete structures using experimental tests. Three reinforced concrete beams were cast for this investigation. The first specimen was cast without defects and it has been used as the control beam in the undamaged state. The second beam had mechanical damages: three cracks were artificially located around the central section of the beam (Fig. 1). The third beam was mechanically damaged like beam 2 and it was also subjected to accelerated corrosion in the central part of the beam. Dynamic measurements have been performed using output-only tests. Loads have been applied through an hammer in different positions of the beam. SOFO linear deformation sensors temporarily attached to the lower surface of the samples have been used for the measurements.
Figure 1. Geometry and crack locations for beams 2 and 3.
Figure 2. General view of the bridge.
3 APPLICATION ON A STEEL BRIDGE The new cable stayed bridge crossing the West Canal in the Port of Marghera is a cable-stayed bridge, characterized by a circular axis (Fig. 2). Because of the characteristics of the bridge structure it was decided to install a permanent monitoring system. The SOFO long-base fiber optic deformation sensory system was selected also for this particular monitoring project. Through the installed monitoring system an interpretation of the dynamic behaviour of the structure has been carried out and a comparison with measurements obtained by classic accelerometric sensors has been also conducted.
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Experimental applications of a case-based reasoning method for structural damage assessment L.E. Mujica, & J. Rodellar Control, Dynamics and Applications Group (CoDAlab), Technical University of Catalonia, Barcelona, Spain
J. Vehí Modal Interval and Control Engineering Group, University of Girona, Girona, Spain
1
3
INTRODUCTION
Some methods developed for damage identification in Structural Health Monitoring use a numerical model of the structure, others use experimental records. The work presented in this paper presents a hybrid methodology of reasoning, combining the use of a numerical model and/or experiments in the structure with a knowledge-based reasoning scheme to evaluate if damage is present, its severity and its location. The methodology involves some elements related to vibration analysis, mathematics (Wavelets, Statistical Process Control) and signal/pattern analysis/processing (Case Based Reasoning, Self Organizing Maps). Approaches are numerically and experimentally validated considering corrosion, mass reduction, adding masses and impact loads. Structures considered in this work are: an aluminum beam, two pipe sections and a portion of a wing aircraft. 2
DAMAGE ASSESSMENT METHODOLOGY
The methodology for structural assessment (identification of the damage, its location, size and severity) uses Case Based Reasoning as principal tool. First, in a “learning mode”, either a model of the structure is used to simulate damage responses, or previous experiments are performed to generate a set of cases. Using a pattern classification tool, an initial casebase is built which will be used in diagnosing future situations by analogy. To reduce the number of input signals to the casebase, some strategies to extract features or reduce the dimensionality from the measured signal while retaining most of the intrinsic information should be applied. When the system is in the “operation” mode each new experience is retained once the damage has been detected.
RESULTS AND CONCLUSIONS
Five cases are studied, analyzing different kinds of damage. Since the difficulty in each case was increasing, several techniques for reducing the dimension and for building the casebase were developed. The methodology has been validated in simulated and laboratory applications, demonstrating its high accuracy detecting and locating damages and its satisfactory accuracy for industrial applications in evaluating dimension and severity of the damage. In general, if the numerical model (or simultaneous models) of the structure exists, it can be used to build the casebase. However, if it does not exist, the casebase can be loaded with nondestructive experiments. In both circumstances, the casebase can be updated while retaining already-identified experiments, improving the robustness. These case studies have a high diversity of models (FEM and VDM), excitations (sine pulse, windowed sine or known-impact) and damages (mass reduction, added mass and impact loads) showing a high adaptability regardless these issues. Current methodologies for damage identification require a high computational cost every time a new damage appears. This limits their applicability in real time. The developed methodology, which consists of two steps, building the casebase and retrieving and adapting for damage identification, is computational expensive for building the casebase because it demands numerous inputs by simulations and/or experiments. But, once this casebase is built, identification of a new episode of damage is almost immediate. Therefore, it is reasonable to conclude that this methodology can be applied in real time.
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Fiber optic sensing technologies for smart materials and structures D. Inaudi SMARTEC SA, Manno, Switzerland
A. Del Grosso Department of Structural and Geotechnical Engineering, University of Genoa, Italy
1
INTRODUCTION
From many points of view, fiber optic sensors are the ideal transducers for smart materials and structures. Being durable, stable and insensitive to external perturbations, they are particularly interesting for the longterm health assessment of structures. Many different fiber optic sensor technologies exist and offer a wide range of performances and suitability for different applications. A number of these systems have matured to full commercial exploitation and routine application in structural health monitoring. This contribution reviews the most popular fiber optic sensing technologies, for local and distributed sensing, and briefly presents some significant application examples.
aims and during different phases of the structure’s lifetime. Among these examples, the following can be mentioned as representative of the most used technologies. 3.1 Pile loading test A new semi-conductor production facility in theTainan Scientific Park, Taiwan, is to be founded on a soil consisting mainly of clay and sand with poor mechanical properties. To assess the foundation performance, it was decided to perform an axial compression, pullout and flexure test in full-scale on-site condition. Four meters SOFO sensors were used. 3.2 Bitumen joint monitoring
2
FIBER OPTIC SENSING TECHNOLOGIES
The major characteristics of the following fiber optic sensory systems and of their commercial developments are described in the paper: – – – – –
SOFO Displacement sensors; Bragg Grating Strain sensors; Fabry-Perot Strain sensors; Raman Distributed Temperature sensors; Brilloin Distributed Temperature and Strain sensors.
In particular, advantages and disadvantages of the different systems are discussed in the light of their application for the structural health monitoring of real structures. 3
SELECTED PROJECTS
A few projects are introduced, showing an effective use of fiber optic technology for the health monitoring of different types of structures, with different
Plavinu is a dam that belongs to the complex of three most important hydropower stations on the Daugava River in Latvia. This is the largest hydropower plant in Latvia and is considered to be the third level of the Daugavas hydroelectric cascade. One of the dam inspection galleries coincides with a system of three bitumen joints that connects two separate blocks of the dam. In order to increase the safety and enhance the management activities it was decided to monitor the average strain in the concrete arm next to the joints. The DiTeSt system with SMARTape deformation sensor and Temperature Sensing Cable is used for this purpose. 3.3 Gas pipeline monitoring About 500 meters of a buried, 35 years old gas pipeline, located near Rimini, Italy, lie in an unstable area. Distributed strain monitoring proved to be useful in order to improve the vibrating wire strain gauges monitoring system, currently used in the site. Different types of distributed sensors were used: SMARTape and Temperature Sensing Cable.
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Seismic analysis of retrofitted historical masonries using passive control systems C.A. Syrmakezis National Technical University of Athens, Greece
1
INTRODUCTION
The seismic rehabilitation and retrofitting of historical structures is an important issue in the entire Mediterranean basin, which is characterized by its richness in historical masonry structures as well as its high seismicity. The exceptional character of historical structures imposes the respect of their originality, thus any protection measures should comply with the principles of reversibility and compatibility. As a result the application of passive control systems such as dampers is suggested for their retrofitting (Syrmakezis 2006). 2
built during 11th and 12th century. The finite element model was developed using 3D solid elements, failure analysis was performed and its seismic vulnerability was evaluated. The structure’s seismic response was very good. The second one is Nea Moni of Chios, a monastery protected by UNESCO. Its Church of Agios Panteleimonas is connected with a semi-underground Cistern, through a common vertical wall. Analysis results revealed both structures’ high vulnerability and their retrofitting using dampers was proposed. Diminuation of their displacements, failure and seismic vulnerability was achieved.
PROPOSED METHODOLOGIES 4
For the realistic evaluation of historical masonries seismic specialized analytical methodologies are needed. For the analysis of masonry structures the finite element method is recommended. Failure analysis, gives an indication of the masonry susceptibility to damage. The methodology presented in this paper proposes the elaboration of finite element stress data using the FAILURE software and a modified Von Mises failure criterion for masonry structures (Syrmakezis &Asteris 2001). The seismic vulnerability evaluation of a structure is subsequent to its failure analysis. It is associated with the structure’s seismic performance through the definition of a correlation function between this action and the probability of exceeding a certain response level when uncertainties are introduced. The function is illustrated using a fragility curves diagram (Syrmakezis et al. 2004). The developed methodology is based on the statistical elaboration of structural failure results (Syrmakezis et al. 2005). The proposed damage index is the ratio of the wall area that has failed to the total wall area. 3
CONCLUSIONS
In this paper methodologies for the analytical evaluation of historical masonries’ response have been presented. Their application has been used for the evaluation of the seismic response of two historical masonry structures and the investigation of the efficiency of dampers for their retrofitting. REFERENCES Marinelli, K., Syrmakezis & C.A., Antonopoulos, A.K. 2004, Structural Response of Masonry Historical Structure Using Fragility Curves, Proceedings of the third European Conference on Structural Control, Vienna University of Technology, Vienna, Austria, 12–15 July 2004. Syrmakezis, C.A. & Asteris, P.G. 2001. Masonry Failure Criterion under Biaxial Stress State. Journal of Materials in Civil Engineering, ASCE, p. 58–64. Syrmakezis, C.A. 2006. Earthquake Protection of Historical Masonry Structures using Passive Control Systems. Proc. of the 4th Conference on Earthquake Engineering, Taipei, Taiwan, 12–13 October 2006.
CASE-STUDIES
Two case studies are presented. The first one is Moni Kaisarianis Church, part of a Byzantine monastery,
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Optimal experimental design for structural health monitoring applications H.F. Lam City University of Hong Kong, Department of Building and Construction, Hong Kong, China
C. Papadimitriou & E. Ntotsios University of Thessaly, Department of Mechanical & Industrial Engineering, Volos, Greece
1
EXTENDED ABSTRACT
Successful structural health monitoring and condition assessment depends to a large extent on the sensor and actuator networks place on the structure as well as the excitation characteristics. An optimal experimental design methodology deals with the issue of optimizing the sensor and actuator network, as well as the excitation characteristics, such that the resulting measured data are most informative for monitoring the condition of the structure. Information theory based approaches have been developed to provide rational solutions to several issues encountered in the problem of selecting the optimal sensor configuration. The optimal sensor configuration is taken as the one that maximizes some norm (determinant or trace) of the Fisher information matrix. Papadimitriou et al. (2000) introduced the information entropy norm as the measure that best corresponds to the objective of structural testing, which is to minimize the uncertainty in the model parameter estimates. An important advantage of the information entropy measure is that it allows one to make comparisons between sensor configurations involving a different number of sensors in each configuration. Furthermore, it has been used to design the optimal characteristics of the excitation (e.g. amplitude and frequency content) useful in the identification of linear and strongly nonlinear models. The optimal sensor placement strategies depend on the class of mathematical models selected to represent structural behavior as well as the model parameterization within the model class. However, it is often desirable to use the measured data for selecting the most appropriate model class from a family of alternative model classes chosen by the analyst to represent structural behavior. Such classes may be linear (modal models or finite element models), nonlinear elastic or inelastic, each one involving different number of parameters. Model class selection is also important for damage detection purposes for which the location
and severity of damage are identified using a family of model classes with each model class monitoring a specific region in a structure (Papadimitriou & Katafygiotis 2004) or incorporating different mechanisms of damage. The objective in this work is to optimise the number and location of sensors in the structure such that the resulting measured data are most informative for estimating the parameters of a family of mathematical model classes used for structural identification and damage detection purposes. Theoretical and computational issues arising in optimal experimental design are addressed. The problem is formulated as a multi-objective optimization problem of finding the Pareto optimal sensor configurations that simultaneously minimize appropriately defined information entropy indices related to monitoring multiple probable damage scenarios. Asymptotic estimates for the information entropy, valid for large number of measured data, are used to rigorously justify that the selection of the optimal experimental design can be based solely on nominal structural models associated with the probable damage scenarios, ignoring the details of the measured data that are not available in the experimental design stage. Heuristic algorithms are proposed for constructing effective, in terms of accuracy and computational efficiency, sensor configurations. Damage detection results on a shear model of a building structure are used to illustrate the theoretical developments. REFERENCES Papadimitriou, C., Beck, J.L. & Au, S.K. 2000. EntropyBased Optimal Sensor Location for Structural Model Updating. Journal of Vibration and Control, 6(5): 781–800. Papadimitriou, C. & Katafygiotis, L.S. 2004. Bayesian Modeling and Updating. Engineering Design Reliability Handbook, E. Nikolaidis, D.M. Ghiocel and S. Singhal (Eds), CRC Press.
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Data-driven approaches and structural informatics for next generation smart structures (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Image-based spatial-temporal information retrieval for vibration measurement Y.F. Ji & C.C. Chang Department of Civil Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
Modal properties including natural frequencies, damping ratios and mode shapes are important characteristics for civil engineering structures. These characteristics are the fundamentals of structural response analysis under traffic, wind and earthquake induced loads. In addition to analysis, these characteristics have also been used for a variety of other purposes such as finite element model updating, vibration mitigation and control, condition assessment, and health monitoring of structures. Modal properties normally are obtained indirectly through processing some measured responses from the structure. The most frequently used response for such a purpose is the acceleration time history which can be easily and accurately measured by accelerometers. Accelerometers although provide accurate and sensitive acceleration measurements, they are nevertheless discrete sensors that measure acceleration along one direction at the installed locations only. While the discrete measurement does not affect the extraction of natural frequencies and damping ratios, it unavoidably limits the determination of mode shapes which are spatially continuous. Image-based measurement techniques have a long history of development and application. The techniques use images to establish the geometrical relationship between a three-dimensional (3D) object and its two-dimensional (2D) images. As compared with the other sensors, image-based measurement techniques provide several special advantages: (1) they can provide direct displacement measurement in both time and 3D spatial domains; (2) they can measure displacements at multiple locations simultaneously; (3) they resemble a non-contact and wireless sensor and are conducted remotely away from the structure being measured; and (4) they do not need sophisticated setup and are less labor-intensive. Due to these advantages, image-based measurement techniques have attracted
attentions from various disciplines including engineering, medicine, archaeology, biomechanics, astronomy, etc. The use of pre-defined targets that are attached to the structure’s surface is quite common to the imagebased measurement techniques. These targets serve two purposes: to provide coordinates for the point of interest and to establish correspondence for the point of interest within one image sequence or between two image sequences. The use of targets on the other hand confines the acquired information at these targeted locations only even though the recorded image sequences provide ample of information in the spatial domain. In addition, attachment of targets can be troublesome when the measurement locations are difficult to access. This paper presents a non-target stereo vision technique to measure response of a line-like structure in both spatial and temporal domain simultaneously. The technique uses two digital cameras to acquire image sequences of a line-like structure. These images are processed firstly through a sub-pixel edge detection algorithm. A simple non-dimensional length matching approach and the epipolar geometry are used to establish point correspondences within an image sequence and between two image sequences, respectively, without using any specific target. After reconstructing spatiotemporal displacement response from the two image sequences, wavelet transform is then used to extract the modal characteristics of the structure. The proposed technique was illustrated using two tests: free vibration of a steel cantilever beam in the laboratory and free vibration a bridge stay cable in the field. Results showed that the technique could directly measure 3D displacement responses along edges of the two line-like structures without using any specific target.
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A data processing and analysis system for the instrumented suspension Jiangyin Bridge H.F. Zhou, Y.Q. Ni & J.M. Ko Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
1
BACKGROUND
The suspension Jiangyin Bridge with a main span of 1385 m was instrumented a structural health monitoring system in 1999. The system was upgraded in 2005 because it was found malfunction in some sensors and data acquisition units. This paper reports the upgraded system with the focus on the data processing and analysis system. 2
DATA PROCESSING AND ANALYSIS SYSTEM
The data processing and analysis developed with MATLAB consists of eight modules. User friendly graphic user interface was devised with MATLAB GUI to relief end-users from abstruse algorithms. 2.1
Serviceability assessment
The serviceability of wind speed, deflection, expansion joint displacement, and vibration are examined.
2.5 Modeling of modal variability The back-propagation neural network is employed to formulate the model correlating modal properties and environmental conditions. The coupling effects of multiple environmental factors and their relative strength of effect can also be considered. 2.6 Structural damage alarming The auto-associative neural network is employed for structural damage alarming. A parametric approach is proposed for eliminating the environmental effects in the vibration-based structural damage alarming. 2.7 Safety index evaluation of bridge components The safety index of bridge components is evaluated based on the reliability analysis. It is used to decide bridge inspection or maintenance strategy.
2.2 Analysis of wind characteristics The main purpose is to validate design assumptions on the wind characteristics and the bridge responses under the assumed wind loadings. The prediction of extreme wind loadings is another concern. 2.3
to predict the expansion joint displacements under extreme temperatures for design verification. Annual or daily-average cumulative expansion joint movements are estimated for determining the interval for inspection or replacement of expansion joints.
Prediction of extreme lateral displacement
The correlation model between lateral displacement and transverse wind speed is formulated to predict the extreme lateral displacement under the extreme wind speed. 2.4 Assessment of expansion joint The correlation pattern between effective temperature and expansion joint displacement is established
2.8 Analysis of fatigue life expectance The method for probabilistic fatigue life assessment specified in specifications is modified by making use of the long-term stress monitoring data to find the stress range and its probability distribution. 3
CONCLUDING REMARKS
The system has been applied to analyze the monitoring data acquired so far and is proved to be easy to use, maintain and expand. Continuous efforts are made to consummate the system.
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Adaptive quadratic sum squares error with unknown inputs for damage identification of structures Jann N. Yang Department of Civil & Environmental Engineering, University of California, Irvine, USA
Hongwei Huang Department of Bridge Engineering, Tongji University, China
1
EXTENDED ABSTRACT
The ability to detect structural damages real-time online, based on vibration data measured from sensors, will ensure the reliability and safety of structures. Analysis methodologies for structural damage identification based on measured vibration data have received considerable attention recently. The problem is quite challenging, especially when the excitations and the responses are not completely measured and when the prior knowledge of the undamaged structure, i.e., referenced data, is not available. Traditional timedomain analysis techniques, such as the least square estimation (LSE) method and the extended Kalman filter (EKF) approach, require that all the external excitations (inputs) be available, which may not be the case for some structural health monitoring systems. Recently, a new adaptive damage tracking technique, referred to as the adaptive quadratic sum squares error (AQSSE), has been developed by the authors for on-line damage identification of structures, when all external excitations (inputs) are measured. In this paper, we further extend the AQSSE approach to cover the general case, in which external excitations are not measured or not available, referred
to as the adaptive quadratic sum squares error with unknown inputs (excitations) (AQSSE-UI), in order to reduce the number of sensors required in the health monitoring system. In this approach, unknown linear and nonlinear structural parameters are estimated directly from the minimization of a quadratic sum squares error between the measured output data and the theoretical values. Analytical recursive solution for the proposed QSSE-UI method will be derived and presented. The accuracy and effectiveness of the proposed approach will be demonstrated by simulation results using a 2-story plane frame with finite-element model. Simulation results indicate that the proposed approach is capable of tracking the changes of structural parameters accurately leading to the identification of structural damages. The AQSSE-UI method proposed herein is not available in the previous literature, and it is applicable to linear and nonlinear structures. ACKNOWLEDGMENT This research is supported by the National Science Foundation Grant No. CMS-0554814.
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Initialization of multilayer feedforward neural networks to approximate nonlinear functions in engineering mechanics applications J.-S. Pei & E.C. Mai The University of Oklahoma, Norman, Oklahoma, USA
ABSTRACT This paper presents a heuristic initialization methodology for designing multilayer feedforward neural networks in modeling nonlinear functions in engineering mechanics applications. The goal of this study is fulfilled by utilizing the governing physics and mathematics of nonlinear functions and the strength of the sigmoidal basis function. The applications of this exploratory work can be numerous and include those associated with potential interpretation of the inner workings of neural networks, such as damage
detection. A step-by-step graphical procedure utilizing a few neural network prototypes as “templates” to approximate commonly seen memoryless nonlinear functions of one or two variables is developed in this study. Decomposition of complex nonlinear functions into a summation of some simpler nonlinear functions is utilized to better exploit this prototype-based initialization methodology. Training examples are presented to demonstrate the rationality and efficiency of the proposed methodology when compared with the popular Nguyen-Widrow initialization algorithm. Future work is also identified.
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Structural damage and fault detection (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Flexibility-based local damage detection algorithm for structural joints and its decentralized implementation with wireless sensor units A. Masuda & S. Kobashi Kyoto Institute of Technology, Kyoto, Japan
F.-G. Yuan North Carolina State University, Raleigh, NC, USA
1
SUMMARY
This paper presents a modal-based, simplified and practical algorithm to evaluate the local flexibility of structural joints. The algorithm adopts local flexibility indices (LFIs) as damage metrics, that are then extended to define a modified damage index. Because the proposed damage index is evaluated without calculating mass-normalization constant, one can assess the joint integrity by using a couple of sensors only installed in the vicinity of the joint of interest, not deploying many sensors throughout the structure. Moreover, since the information processing is also localized and decentralized in the proposed scheme, it would be suitable for the implementation in the wireless sensor network environment with local computation capability. 2
OUTLINE OF FORMULATION
The LFI is defined as the relative displacement (or the relative rotation angle) induced by a pair of opposite forces (or moments) with unit magnitude applied on two points on the both sides of the structural region of interest. Using the modal expansion form of the flexibility, the LFI between two points x and y is formulated as
where, ωn is the nth natural frequency, cn is the massnormalization constant for nth mode, and ψn,j is the nth relative mode shape between the points with respect to the js axis. To avoid the calculation of mass-normalization constants, the formulation of LFIs is rewritten as follows:
Figure 1. Evolution of modal parameters, i.e., the relative angular mode shapes, mass-normalization constants and the natural frequencies, in function of the damage extent (i.e., joint flexibility) in the third story.
where
where n is the nth mode shape measured at the reference point z. Since it is revealed that an is damage-insensitive (see Figure 1), a modified damage index is defined by only using dn .
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Identification of damages in the vertical links of a CFST arch bridge model S.J. Wang, H.C. Xie & Z.Q. Gong Department of Civil Engineering, Shantou University, Shantou,Guangdong,China
B.F. Spencer, Jr. & Ryan Giles Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA
ABSTRACT The researchers have designed and built a CFST arch bridge model in their laboratory. In this paper, static and dynamic analyses of the model’s vertical links in both undamaged and damaged cases were studied using ANSYS. In the damaged cases, the axial forces in the vertical links that neighbor the damaged link showed a marked difference. However, the axial forces of the links far from the damage location showed little change. In addition, all the natural frequencies of the bridge changed after introducing the damage. The
largest change occurred in the frequency corresponding to the third vertical bending mode. Likewise, the modal curvature of the longitudinal girders is also sensitive to damage in the vertical links – especially the curvature of the second vertical bending mode. By analyzing the changes in the modal curvature, the location of the damaged vertical links can be determined. A method for identifying the locations of damaged vertical links is proposed by using a combination of the changes in the natural frequencies of the structure, the modal curvatures of the longitudinal girders, and the axial forces of the vertical links.
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Smart control systems based on MR fluids (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Research on running attitude control of full vehicle with Magneto-rheological suspensions and road test R. Li, W.M. Chen, M. Yu, X.M. Dong, C.R. Liao & H.H. Zhang Key Laboratory of Optoelectronic Technology & Systems of the Education Ministry of China, Chongqing University, Chongqing,China
ABSTRACT Magneto-rheological (MR) suspension system has great potential application on restraining automotive running attitude. But there are still lots of difficult problems in its control system design. Conventional control strategies, which depend on single control mode, has good result on restraining single vibration state but cannot effectively restrain various vibration attitudes of vehicle body or wheel, are not suitable to solute MR suspensions complicated vibration and does not gain favorable vehicle running attitude. However, the hierarchical controller is likely to solute these difficulties. Considering vertical vibration, pitch vibration and their coupling vibration of vehicle body, and vibration of four wheels, a full vehicle MR suspension vibration dynamics model with six degree of freedom is built. To restrain vehicle vertical vibration and pitch motion, and improve wheel road holding capability, a hierarchical attitude control system of vehicle with MR suspension is proposed, which includes direct control level and parameter correction level. In direct control level, the running attitude is divided into five character states that include aim vibration, vertical vibration, pitch vibration, coupling vibration of vehicle body, and wheel vibration. Then a multi-mode controller is given. The hold mode control is used on aim vibration of vehicle body. The skyhook control and proportion differential (PD) control are adopted to decrease vertical vibration, pitch vibration, coupling vibration of vehicle body according to its vibration velocity and displacement. Similar with vehicle body vibration control, hold control, ground hook control and PD control are adopted to restrain various wheel vibrations. In parameter correction level, the
hybrid factor, which adjusts the vehicle body vibration control force and wheel vibration control force, are corrected by fuzzy reasoning method with the inputs of the root mean square of vibration acceleration of each un-sprung mass and vehicle centroid, respectively. And several other parameters of control level are modified, according to vehicle running attitude and characteristics of MR suspensions vibration in different conditions. To validate the real results of hierarchical attitude control, a MR suspension test and control system is set up and implemented on an automotive vehicle equipped with four MR dampers. According to ISO2631, test automobile is driven on random inputs roads at various speeds along a stretch of straight road in constant vehicle velocity of 50 km/h and 70 km/h. The accelerations of body frame and axles are sampled and analyzed. Test results indicate that compared to passive suspension and hybrid control, the first resonance of vibration accelerations of vertical and pitch motion of the body frame are visibly reduced when attitude control is applied, especially decreasing vibration energy between 4 and 12.5 Hz which is the human vibration sensitive area. And the axle vibration is also effectively be suppressed by attitude control system. Therefore, the hierarchical attitude controller can improve ride comfort and handling stability of vehicle with MR suspensions. It solutes the vehicle running attitude control difficulties without needing accurate vibration model of vehicle with MR suspensions. Keywords: Magneto-rheological suspension, Automotive vehicle, Attitude control, Road test.
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Design approaches of mitigating cable vibration using MR dampers on the cable-stayed bridges X.Y. Wang & Z.Q. Chen Wind Engineering Research Centre, Hunan University, Changsha, Hunan, P.R. China
Y.Q. Ni & J.M. Ko Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon Hong Kong
ABSTRACT Large amplitude cable vibrations have been observed in numerous of cable-stayed bridges worldwide and vibration mitigation has become one of the critical issues in this type of bridges. Mitigating cable vibration using magneto-rheological (MR) dampers on stay cables is a new technique with the good prospects.To facilitate a wide use of MR damper in vibration control of stay cables, design approaches of MR damping mitigating system must be investigated. The design approaches should cover two aspects at least. Firstly, for a given stay cable and special requirements, the input voltage of MR damper and other parameters can be determined conveniently; Secondly, for a given input voltage and some limitation conditions, performance of MR damper can be evaluated easily. Many efforts are devoted to these issues in this paper. The mechanical model of RD-1005 MR damper manufactured by Lord Corporation under sinusoidal excitation was experimentally investigated. The effects of magnetic field (input voltage to MR damper), displacement amplitude and driving frequency on the damping force are experimentally studied. The test results are expressed as a nonlinear biviscous model. To employ viscous damper theory to design MR damper cable mitigating system, the equivalent viscous damping coefficients of MR damper are evaluated for various frequency, amplitude and voltage with the hysteresis loops of force (F) versus displacement (x). For the sagged cable with viscous damper, taking into account of sag, inclined angle and bending stiffness, the plane free motion equation of the cable with damper is founded by using Galerkin’s method, and a numerous of complex eigenvalue analysis are conducted for different cables with a damper so that to investigate effects of parameters such as sag and bending stiffness to modal damping ratio. Then the revised Pacheco’s method for estimating the modal
damping ratio in stay cable with viscous damper is developed. The analytical results show that the first modal damping ratio of stay cable is greatly affected by the cable sag. With the revised Pacheco’s method and the equation of the equivalent viscous damping coefficients of MR damper, the simple design method for mitigating cable vibration with MR dampers is finally proposed for the single damper case and the twin-damper case. On the proposed method, the optimal viscous damping coefficient is acquired with the stay cable parameters, attachment height of damper and control goal of modes, and the optimal voltage input to MR dampers is determined ulteriorly by the equation of the equivalent viscous damping coefficients of MR damper. A prototype stay cable from real bridge is use to demonstrate this design approach. The proposed method also is verified by the field test. The field test indicates that the results are very consistent with the optimal voltages obtained by the proposed approach. Hence, the proposed method is available for actual engineering. The proposed the simple optimal design approach of stay cable vibration control is also available for other MR dampers or nonlinear dampers, which can be summaried as following: Step 1: foundation of nonlinear biviscous model with experiment of damper; Step 2: identification of the empirical formula of equivalent viscous damping coefficient of damper under various frequency, amplitude and voltage; Step 3:determination of the optimal design parameters with the improved Pacheco’s the “universal curve”. Keywords: the stay cable vibration; Magnetorheological (MR) dampers; mitigating vibration; optimal voltages
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Modeling of passive magnetorheological fluid dampers coupled with stay cables in cable-stayed bridges M. Liu1 , H. Li∗1 & J.P. Ou1,2 1 2
1
School of Civil Engineering, Harbin Institute of Technology, Harbin, China Dalian University of Technology, Dalian, China
INTRODUCTION
Stay cables used in cable-stayed bridges are prone to vibration with large amplitude because of their slenderness and lower inherent damping. At present, MR dampers have been proven to be effective in many applications to suppress large amplitude vibration of the stay cables. However, due to stay cable’s flexibility, coupling dynamic performance of the stay cable incorporated with the MR damper occurs frequently. To adequately characterize the MR damper’s intrinsic nonlinear behavior, which is attached with flexible structures, such as stay cables, models must be developed. Experimental investigation was carried out on a stay cable model incorporated with one small size MR damper scaled down from a real stay cable in the cable-stayed bridge. Then utilizing the measured displacement and damping force of the MR damper and based on the modified Bouc-Wen model of MR damper proposed by Spencer et al. (1997b), a model of MR damper coupled with stay cable is developed to predict the behavior of the passive MR damper with the different constant current inputs. The proposed model is validated by the numerical simulations based on the experimental data. 2
EXPERIMENTAL INVESTIGATION OF COMBINED CABLE/MR DAMPER SYSTEM
As shown in Figure 1, one small size MR damper is connected to the stay cable model perpendicularly at the location of 5.3% of the cable length from the lower anchorage. The force and displacement of the MR damper are respectively measured by a load cell and linear variable differential transducers (LVDT).
3
MODELING OF PASSIVE MR DAMPERS COUPLED WIT STAY CABLES
Figure 1. Installation of MR damper and shaker.
Figure 2. Proposed mechanical model of the MR damper coupled with the stay cable.
Bouc-Wen model of MR damper developed by Spencer et al.(1997b), the model of the MR damper coupled with the stay cable is proposed shown in Figure 2 to better predict the MR damper response. 4
CONCLUSIONS
The proposed model of the passive MR damper coupled with the stay cable can well portray and precisely predict the behavior of the passive MR damper attached with a flexible structure, such as a stay cable. REFERENCES
Considering the frame of the MR damper installation shown in Figure1 and based on the modified
Spencer, B.F. et al. 1997b. Phenomenological model for magneto-rheological dampers. Journal of Engineering Mechanics, ASCE, 123, 230–238
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System identification
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Experimental study of tuned mass damper in reducing floor vertical vibration due to machinery M.L. Chang Department of Civil Engineering, National Chung Hsing University, Taichung, Taiwan, China
C.C. Lin College of Engineering, National Chung Hsing University, Taichung, Taiwan, China
J.M. Ueng Department of Civil Engineering, National Chung Hsing University, Taichung, Taiwan, China
K.H. Hsieh Center for Environmental Restoration and Disaster Reduction, National Chung Hsing University, Taichung, Taiwan, China
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INTRODUCTION
Recently, tuned mass dampers (TMD) have been widely used in reducing the structural responses or absorbing and consuming external power and energy. TMD is a passive control device which was initially used to control the vibration of ship’s outside-shell (Fhram 1911). TMD has been applied to different structures in reducing vibrations and protecting civil structures against different loads, such as earthquake and high-velocity wind. In past two decades, theoretical development and experimental studies on its performance have been made. The common applications of TMDs are used as the auxiliary system of civil structures, such as highrise building. The main function of TMD is to reduce structural response in extreme environments, such as typhoon and earthquake. Both activities can cause serious oscillations of the tall buildings, especially the vibration on the top floor. Serious seismic and typhoon activities may damage the structure and cause structural failure. The vibration control in horizontal direction has been well researched and several applications have been facilitated into different civil structures. The TMD which installed in the world’s tallest building, Taipei 101 Building, is a typical example on utilizing TMD to decrease structural vibration due to wind loads. Setareh and Hanson (1992) used TMD to control human induced structural vibration. Bell (1994) utilized TMD to control floor vibration of a museum building and Murray (2001) used similar device on controlling office building’s floor vibration
due to walking pedestrians. Setareh (2002) used ground-hook tuned mass damper (GHTMD) to reduce the floor vibration during human activities. Several typical TMD’s researches can be found at Lin et al. (1994), Kwon et al. (1998), Lin et al. (2000), Wang et al. (2003), Wong and Chee (2004), Lin et al. (2005), and Lin et al. (2006). A general review and overview of different passive damper’s application can be found at Ou et al. (1996). The general purposes for those for those installed TMDs are used to decrease structural vibration and prevent motion sickness in people. There is a need to develop a TMD device to mitigate machine-induced floor vibration. The above studies mostly focus on human-induced floor vibrations on vertical direction and other structural vibration sources, such as vehicle, wind, and train on both horizontal and vertical directions. The floor vibration due to machinery is seldom studied. The purpose of this project is to study how to reduce machine-induced floor vibration using VTMD as mentioned in the abstract. This experimental study includes two case studies of vertical vibration. First and second case studies use simply-supported beam and full-scale concrete floor as examples on showing the successes of reducing vertical vibration.These case studies are presented to reinforce theory and applications. Based on the studied results, both cases show that with the installation of VTMD, the absolute vertical accelerations are significantly decreased by 80% for the steel beam (at middle section) and by 32∼54% (based on various sensor locations) for the school building under harmonic machine loadings.
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A new method to detect natural frequency of bridge-based on connected pipes system Wei-Min Chen, Xiao-Hua Lei, Guo-Ping Liu & Peng Zhang Key Lab for Optoelectronic Technology & System, Chongqing University, Chongqing, China
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INTRODUCTION
Existence structural damage in bridges leads to modification of vibration modes. These modifications are manifested as changes in the modal parameters (natural frequencies/mode shapes). Nowadays only acceleration sensor or velocity sensor is thought to be the useful way to detect those parameters[1–4] . While acceleration sensor or velocity sensor are not sensitive to low frequency, especially frequency below 1 Hz, because sensing element of them is spring. Measuring precision of natural frequency with these sensors for bridges in low frequency range is not so good. Connected pipes system is often used to measuring displacement in vertical direction. It has been gradually applied to bridge/dam health monitoring[5] , due to its high precision/ easy to achieve multi-points monitoring synchronously, etc. Liquid in connected pipe is used as sensing medium. Due to viscidity of liquid, connected pipe system can be looked upon as a low pass filter to filtrate high frequency automatically from complicate surroundings. But natural frequency of connected pipe is in low frequency range. Just when natural frequency of it can be separated from frequency of bridge and frequency response of it is higher than natural frequency of bridge, connected pipes system can be used to detect natural frequency of bridges.
pipes system is set up. Simulations are carried out according to it. From simulations we can see, displacement response is distorted when input frequency is larger than natural frequency of connected pipe system. But frequency is still can be responded by connected pipes system, although there is some amplitude reducing. Frequency in low frequency range can be measured with frequency range above natural frequency of connected pipes system. 3
SUMMARY OF RESULTS
To prove frequency response of connected pipes system, vibration test is carried out on a vibration table which frequency is controllable. Connected pipes system is used to sensing frequency, when vibration frequency is changed from 0.0082∼4.92 Hz. The experimental results show that frequency response error is below 3%.Then, a further application with connected pipes system in Si Banpo Bridge acrossYangtze River is introduced. From experiment and application results we can see, connected pipes system is a potential method to detect model parameters especially natural frequency. REFERENCES
2
PRINCIPLES
Properties of frequency response are the most important factor for connected pipes system to achieve bridges’ frequency detection. So, model of three connected pipes system is set up according to applications. Then, differential equations of liquid flow in connected pipes system is obtained with hydromechanics knowledge. Natural frequency and properties of frequency response are analyzed according to differential equations. Furthermore, transfer function of connected
Bekker, A. & Brinson, L.C. 1998. Phase diagram based description of the hysteresis behavior of shape memory alloys, Acta Mat., 46(10): 3649–3665. P. Galvín & J. Domínguez, 2007. Dynamic analysis of a cablestayed deck steel arch bridge, Journal of Constructional Steel Research, 63:1024–1035. Mistuhiro Yoshimura, Qingxiong Wu, et al. 2006. Vibration analysis of the Second Saikai Bridge—a concrete filled tubular (CFT) arch bridge. Journal of sound and vibration, 290:388–409. Zhu Yong, Fu Yumei, Chen Weimin, et al. 2005. A Health Monitoring System for the Da Fosi Yangzi River Bridge,Chinese Civil Engineering Journal, 38(10): P66–71.
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Cable force identification by global optimization using coupled local minimizers W.Y. Liao, Y.Q. Ni & J.M. Ko Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
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INTRODUCTION
The identification accuracy of cable force by vibration measurement may be significantly affected by inaccurate determination of cable sag-extensibility, bending rigidity, cable effective length, material parameters and boundary conditions (Russell & Lardner 1998, Ni et al. 2000, Zheng et al. 2001, Ren et al. 2005, Geier et al. 2006). For accurate and reliable evaluation of cable tension forces, both the precise finite element model and the systematic identification method are needed. The main idea of coupled local minimizers CLM is to impose upon the multiple design vectors to reach the same final position in which the average objective function value over all the search points is minimized. Though this method was originally developed in the area of neural networks (Suykens et al. 2001), it is successfully applied to finite element model updating using experimental modal data (Teughels et al. 2003). In this study, the theoretical background of CLM and its implementation are described and the method is illustrated with a numerical cable model by comparing a local optimization algorithm. Next, CLM is applied to cable force identification as well as other sensitive parameters on a Dongting Lake bridge cable by using the measured modal frequencies. 2
NUMERICAL VERIFICATION AND APPLICATION TO BRIDGE CABLE
All the parameters that are sensitive to modal frequencies are taken into considered in the numerical verification and case study. According to the numerical verification of cable model, the CLM method is not so sensitive to the noise levels due to its lower standard deviations and stable results with respect to different noise levels. This says that, for the cable structures, the CLM method can obtain more precise identification results and smaller impacts on the uncertainties than the local optimization method. CLM is further demonstrated using the site measurement data of a Dongting Lake Bridge cable. Basing
on the distribution of frequency relative errors with respect to the mode order, one can find that the errors are all lower than 0.1%, which demonstrate that the validity of the optimization algorithm and the accuracy of the identified parameters. It is also observed that the normal distribution is quite good for describing the frequency errors. Considering the central limit theorem, the normal distribution of the small errors, not greater than 0.1%, can be interpreted as a result of many factors, which slightly affect frequency measurements and calculations.
REFERENCES Geier, R., De Roeck, G. & Flesch, R. 2006. Accurate cable force determination using ambient vibration measurements. Structure and Infrastructure Engineering 2(1): 43–52. Ni, Y.Q., Ko, J.M. & Zheng, G. 2000. Dynamic analysis of large-diameter sagged cables taking into account flexural rigidity. Journal of Sound and Vibration 257(2): 301–319. Ren, W.X., Chen, G. & Hu, W.H. 2005. Empirical formulas to estimate cable tension by cable fundamental frequency. Structural Engineering and Mechanics 20(3): 363–380. Russell, J.C. & Lardner T.J. 1998. Experimental determination of frequencies and tension for elastic cables. Journal of Engineering Mechanics 124(10): 1067–1072. Suykens, J.A.K., Vandewalle, J. & De Moor, B. 2001. Intelligence and cooperative search by coupled local minimizers. International Journal of Birurcation and Choas 11(8): 2133–2144. Teughels, A., De Roeck, G. & Suykens, J.A.K. 2003. Global optimization by coupled local minimizers and its application to FE model updating. Computers and Structures 81(24–25): 2337–2351. Zheng, G., Ko, J.M. & Ni, Y.Q. 2001. Multimode-based evaluation of cable tension force in cable-supported bridges. In S.C. Liu (ed.), Smart Structures and Materials 2001: Smart Systems for Bridges, Structures, and Highways; Proceedings of SPIE, Vol. 4330: 511–522.
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Inverse analysis for identification of a truss structure with incomplete vibration strain B. Xu College of Civil Engineering, Hunan University, Hunan, China
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INTRODUCTION
Due to construction materials aging, misuse, lacking proper maintenance, and, in some cases, overstressing as a result of increasing active load levels and changing environments, existing civil infrastructures are now deteriorating. It is critical to evaluate their current safety, reliability, performance and condition for the prevention of potential catastrophic events because the failure of these infrastructures often leads to a high social consequence. In the last decade, researches in structural health monitoring (SHM) with the emphasis on the development of advanced sensing techniques and efficient identification algorithms have been carried out widely as an emerging that could play an essential role in realizing a sustainable society. The increasing use of advanced sensing technologies such as optic fiber Bragg grating and embedded piezoelectric sensors necessitates the development of strain-based identification methodologies. Neural network has been increasingly recognized as one of the system modeling and identification paradigms for a linear or nonlinear structural system. Although several neural-network-based strategies are available for qualitative evaluation of damages that may have taken place in a structure, it was not until recently that a quantitative way of detecting damage with neural networks has been proposed. Recently, a three-step neural networks based structural inverse analysis strategy, called direct soft parametric identification (DSPI), has been presented to identify structural parameters directly from free vibration-induced strain measurements using an evaluation index called root mean square of prediction difference vector (RMSPDV). In reality, because the number of strain sensors is limited and it is difficult to get strain information for all members of a large-scale structure, it is necessary to study the performance of the proposed methodology when incomplete measurements are available.
STRATEGY
The proposed DSPI strategy is carried out in three steps. In Step 1, the strain-based emulator neural network (SENN) is constructed and trained using the time series of free vibration-induced macro-strain of the reference structure under a certain pre-determined initial condition. In Step 2, consider M associated structures that have different structural parameters from the reference structure in Step 1 and the parametric evaluation neural network (PENN) is constructed and trained to describe the inverse relation between the evaluation index called the RMSPDV and the structural parameters. After the PENN has been successfully trained, it will be applied in Step 3 into the object structure to forecast the structural parameters with RMSPDV. 3
CONCLUSION
The performance of a three-step neural networks based DSPI strategy for the identification of structural stiffness parameters with direct use of spatially incomplete free vibration-induced macro-strain time series has been studied with an engineering truss structure by numerical simulation. Based on numerical simulations, the following conclusions can be drawn: 1. The free vibration-induced macro-strain response at current time step can be successfully forecast by a non-parametric identification model, strainbased emulator neural network, using spatially in-complete strain responses at the two previous time steps. 2. The parametric evaluation neural network trained with a number of training patterns that are randomly selected from the interested space can accurately identify the parameters of object structures, even if the object structures are not included in the selected training patterns and incomplete measurements are available.
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Identification of the inter-story stiffness of shear type structures using the extended Kalman filer He Liu University of Alaska Anchorage, Alaska, USA
Mansheng Wang University of Alaska Anchorage, Alaska, USA; University of Science and Technology Beijing, China
Yibin Zheng University of Virginia, Virginia, USA
Xiyuan Zhou Beijing University of Technology, China
Structural health monitoring (SHM) for civil engineering has emerged as a new research area during the last two decades. In recent years, SHM has become an important area of research, offering the potential for continuous and periodic assessment of the safety and integrity of civil infrastructure. The goal of this paper is to apply a powerful structural identification tool, the extended Kalman filter (EKF), to evaluate the inter-story stiffness of shear-type structures and assess the structural health condition. In the EKF procedure, the first-order polynomial difference approximation was used to replace the derivatives. The numerical simulation of the EKF procedure was applied to a 5-story building. The results show that
the modified EKF can identify the inter-story stiffness and damping efficiently. Because EKF can track the change of model parameters due to structural damage, the modified ekf will be an efficient identification tool for structural health monitoring. Comparing the identified stiffness with the initial structural stiffness, it is possible to evaluate the structural health condition and possible damage in the structure. Based on knowledge of the condition of the structure, certain preventative measures can be carried out to prolong the service life of the structure and prevent catastrophic failure.
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Analysis and assessment of structural systems
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Wind pressure distribution rules for complicated roof structures with holed surface J. Teng, M.Y. Qin, Y.H. Zhu & W. Lu Harbin Institute of Technology Shenzhen Graduate School, Shenzhen, China
To estimate the wind load distributions on the large span flexible roof structures is a key problem for designing and monitoring, however, the real wind distribution of a complicated surface of structure isn’t easy to calculate in the theoretical method at present. The general computational fluid dynamics software FLUENT is used to study the wind pressure distribution rule of the roof and the result of the simulation is contrasted with that of the wind tunnel test in analysis the feasibility of CFD. The space roof of Shenzhen Citizen Center is used as an example in this paper, which is 486 m in length, 154 m at two sides changing to 120 m in the middle in width, 2.25 m at two sides changing to 9.00 m in the middle in thickness. The upward and downward surfaces of this roof are both curved and the downward surface is made up of the holed plane with 13.6 percent holed ratio. The model is full scaled and the boundary dimension is 486 m × 154 m × 80 m, where the calculation field is 2000 m × 1200 m × 500 m. The model is established in consideration of (1) the turbulence model is shear stress transport model (SST); (2) the control equation of flow field is dispersed using finite volume method (FVM); (3) the equation solver is the completed implicit expression separate type equation solver which is acceptable for the incompressible and low velocity flow fluidal; (4) the velocity and pressure are combined using PISO method; (5) the flow item is dispersed using the second order upwind; (6) the convergent judgment standard of the calculation result are that the residual of all the physical quantities in calculation process is less than 10−6 and the average wind pressure coefficient of monitoring points is stability or periodic vibration in small amplitude. Boundary condition in the flow field entrance is velocity entrance.
Boundary condition in the flow field exit is pressure exit. The gradient along normal exit is zero for any physical quantity. Non-sliding boundary condition is used for the ground, and free sliding boundary condition is used for the other boundaries. The surface wind pressure distribution rule of large space structure is gotten from the study on the eight models with seven changes in its shape, which indicates that the average wind pressure coefficient distribution rules of all the points are almost the same as the average wind pressure coefficient distribution rule of the real model, though there is large difference of the real model and the other 7 roof model shapes. In order to study on the wind pressure distribution of solid surface and single side holed surface, the pressure variation rule of solid model under different wind attack angles is studied firstly; secondly, the pressure variation rule of model with 13.6 percent holed ratio is studied in contrasted with the result of solid model; finally, the variation of wind pressure according to the change of the holed ratio is studied, the result indicates that the pressure with real holed ratio is closed to the simulated pressures with 6 holed ratios. It can be known that the directions of pressures on the front and behind surface are contrary under almost all wind attack angles, so the combined action is harm to the structure as contracted with solid surface; when the wind attack angle is 90 ± 10 degree, the pressures directions of front and behind surface are the same, so the combined action is benefit to the structure as contracted with solid surface. At last, the wind pressure all-around for single side holed surface structure such as Shenzhen Citizen Centre is studied in this paper, which presents a method for the complicated roof structure based on the wind pressure calculation.
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Serviceability conditions in the design of suspension bridges F. Bontempi Department of Structural and Geotechnical Engineering, University of Roma La Sapienza, Rome, Italy
F. Giuliano Department of Structural Mechanics, University of Pavia, Pavia, Italy
1
INTRODUCTION
The paper discusses the possible improvement of serviceability of extreme long span suspension bridges, focusing attention also on the possible implementation of smart technology solutions, inside the approach of the Performance-based Design. Actually the most noticeable suspension bridge serve only roadway traffic, while the application for railways are limited to light trains like for Tsing Ma Bridge, Hong Kong. It is well known that railways impose a series of restrictions to the design which hinder the implementation of railway long span suspension bridges. For these innovative structures, consequently, the experience is quite limited. In this context, the draft of the Specifications of the Expected Performance of a railway & roadway bridge such as the Messina Strait Bridge contain a challenging jump on innovation, and require a calibration on performance capabilities and load scenarios. For this bridge passive devices are admitted in order to get satisfactory construction, and to improve the Serviceability Performance. Also Active devices are considered as a feasible option, but in case of out-of-service, they must guarantee at least the same Performance of the Passive devices. The main serviceability performance of a roadway+ railway long suspension bridge are outlined and classified according to their scale of description. The global (Macro-level) serviceability performance of the bridge depend on the structural flexibility, damping, inertia and boundary conditions. The deformability of the bridge, and the geometry govern the global serviceability performance. The large size and the high inertia of long span bridges make these features hardly improvable by control actuators.
In the specific case of the Messina Strait Bridge, control provisions can correct the kinematics of the bridge, reducing structural displacements and curvature to increase the serviceability for railway traffic. The availability of the bridge can be only slightly increased if a distributed system of TMD is spread inside the deck girders, because of the small mass ratios in respect the large inertia of the structure. For high wind scenarios, such provisions appear almost useless. REFERENCES Calzona R. 2005. Epistemological Aspects of Safety concerning the challenge of Future Construction: the Messina Strait Bridge. Proc. of the 10th CC2005, Rome. Bontempi F. 2006. Basis of design and expected performance for the Messina Strait bridge. Proc. Int. Conf. on Bridge Engineering – Challenges in the 21st century, Hong Kong. Casciati F. 2006. The challenge of long-span suspended bridges, Proc. 4EWSHM, Granada, Spain. Gimsing N.J. 1983. Cable Supported Bridges, concept and design. New York. J. Wiley & Sons. Petrini F., Giuliano F., Bontempi F. 2007. Comparison of time domain techniques for the evaluation of the response in long span suspension bridges, Computers & Structures, in press. Warburton G.B. 1982. Optimum absorber parameters for various combinations of response and excitation parameters. Earthquake Eng. and Str. Dynamics, 10, 381–401. Giuliano F. 2005. Sensitivity Analysis of Devices and Motion Control for Suspension Bridges. ICOSSAR’05. Rome. Istruzioni FS N◦ I/SC/PS-OM/2298 13/01/1997. Sovraccarichi per ponti ferroviari-…. (Italian Railway Design Code).
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A web-based assessment system of slope stability Qiangxin Zhou & Haiqing Yuan School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan, Hubei, China
Yanyan Tao Wuhan University of Science and Technology Zhongnan Branch, Wuhan, Hubei, China
ABSTRACT The research of slope stability evaluation is fundamental to the research of slope engineering; however, the complexity, fuzziness, inadequacy and uncertainty of slope engineering bring difficulty to the slope stability evaluation. Therefore, how to analyze and evaluate slope stability reliably and effectively is very significant to slope safety and landslide forecast in theory and practice. In this paper, the web technology, intelligent decision support system (IDSS) and group decision support system (GDSS) are introduced into the process of slope stability assessment, and we have built up a Web-Based Assessment System of Slope Stability, which can assess the slope stability scientifically, efficiently and programmatically, and the assessment result nears to reality more. Currently there are many various methods of slope stability analyses, however, for the various factor influence of slope stability, the complexity, fuzziness, inadequacy and uncertainty slope Engineering bring difficulty to the slope stability analysis. The methods of slope stability analysis have been developed form certain analysis methods to uncertain analysis methods, and can be divided into certain analysis methods, uncertain analysis methods and compound analysis methods summarily. The influence factors of slope stability have not only structure characteristics, but also random characteristics, and the computation analysis includes qualitative reasoning and quantitative computation. So the assessment of slope stability belongs to a half-structure decision problem, and the decision support system (DSS) is introduced into assessment system of slope stability. Aim at the characteristics of slope failure, the assessment system of slope stability applies the technologies of IDSS and GDSS to evaluate slope stability, and adopts the technique route of “integral
five databases”(“five databases” consist of data base, method base, model base, knowledge base, expert database) to carry out the process of slope stability evaluation. In the assessment process of slope stability, we can select evaluation object from the data base, and choose appropriate model form model base according to the characteristics, the environment condition and the data condition in the system of concrete evaluation object, and choose from method base according to the need of model or apply the corresponding method directly, then carry out computation analysis and output the computation analysis result. The system applies reasoning machine to match the computation result of model with the knowledge rules in knowledge base, according to certain reasoning strategy, resolving the problems of slope stability, thus getting a system assessment result. Above-mentioned process can be circulated again and again; we can make use of various models to carry out the assessment of slope stability. With the development of the computer and network technologies continuously, web technology has been applied in the engineering realm more and more widely, we can share the information and the application by web. Separating the application logic processing and application display mutually, the system is divided into the distributed B/S structure of four levels, such as user interface level, web server level, application logic level and integrated data level. We can apply the system to assess the slope stability scientifically, efficiently and programmatically, and the assessment result nears to reality more. Presently, with large-scale economy construction, the system has the very important practical value and the application foreground doubtless. Key words: Slope engineering, slope stability, assessment system, DSS, Web.
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Study on measurement system of tilting train-based on math platform Xue Mei Wang, Wen Bo Ni & Fu Li School of Mechanical Eng., Southwest Jiaotong University, Chengdu, Sichuan, China
Jian Hui Lin Traction Power State Key Lab., Southwest Jiaotong University, Chengdu, Sichuan, China
1
INTRODUCTION
Realizing the real-time measurement of the unbalanced centrifugal acceleration of train through curves is the main task of the measurement system of tilting train. Up to now, methods of signal detection of tilting train mainly have two modes that are railway pre-setting and timely measurement respectively. Except Japan’s 383 type tilting train, nearly all of the other tilting trains from various countries adopt the method of timely measurement, which directly measures the unbalanced horizontal centrifugal acceleration of train with accelerometers mounted on the front bogie of train. But affected by railway irregularities, the measured acceleration signals of tilting train contain mounts of random vibration noises. For eliminating the influences of these random vibration noises, ensuring the measurement accuracy, filtering to the measured signals must be done. Since the inherent frequency of vehicle is within 1–10 Hz, corresponding cutoff frequency of low pass filter should be set within 0.5–1 Hz. However after filtered, acceleration signals are typically delayed 0.8 seconds. Therefore this direct detection mode is not preferred because of the time delay caused by filtering. In view of the problems of the existent measurement systems of tilting train, a new measurement method based on math platform is put forward. With three-axis angular rate gyroscopes and accelerometers mounted on the front bogie of train, the angular rates and accelerations of tilting train through curves are measured. With the strict inertial algorithm the instantaneous speeds, positions and attitude angles of train can be accurately obtained. Thereby whether train is in or out curves can be judged. The unbalanced centrifugal acceleration can be further computed. It is shown that the key of this new method is to accurately compute the attitudes and positions of train through curves. Thereby corresponding kinematics differential equations including attitude rate differential equation,
position rate differential equation and velocity rate differential equation are firstly constructed. According to the principles of rigid body centering movement, the methods that describe the orientation relationship of the motion coordinate relative to the reference coordinate are Euler method, direction cosine method and quaternion method. Among them, the quaternion is the most popular for attitude and position computation because of its advantages of simplicity, nonsingularity, and recursive algorithm. But however, the accuracy of quaternion is limited by the coning error, which is an important error source of attitude computation. Introducing the rotation vector concept into the quaternion effectively improves the quaternion algorithm, suppressing the coning error. So for the attitudes and positions computation of tilting train, the quaternion method based on the rotation vector is employed. What’s more, computation of speeds, attitudes and positions are closely relative to each other. Complete math platform is justly the real-time computation of velocity rate differential equation, attitude rate differential equation and position rate differential equation. During the computation, computation time, relationship of parameters, compensation for coning error and its affection to the accuracy should be taken into consideration. For running on the land and having small speed, the affections of coriolis acceleration and gravitational acceleration to titling train are so small that they could be neglected in some situations. Therefore relative five simplified mathematical models are derived and their errors caused by simplification are analyzed. Among these simplified modes, errors with uncouple mode are most serious and accumulate with time. Simulation and analysis show that this new measurement method of tilting train based on math platform is effective and feasible. For ensuring the accuracy, the complete mode instead of the simplified should be employed.
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Real-time substructure testing with equivalent force control method and its application to smart damping G. Xu & B. Wu School of Civil Engineering, Harbin Institute of Technology, Harbin, China
ABSTRACT Real-time substructure testing (RSTing) was proposed in order to reflect the properties of structural or mechanical systems under dynamic loading. RSTing is a hybrid simulation technique, in which a structure is split into a physical test specimen and a numerical model, and the dynamic behavior of the entire structure is simulated in real-time. A key element of the RSTing is the numerical algorithm that is used to perform the stepwise integration of the equations of motion. There are two types of numerical algorithms: explicit algorithms and implicit algorithms. Many explicit integration methods have been proposed for RSTing. Owning to their conditional stability, they are not advisable methods for structures with many degrees of freedom (MDOFs). So an implicit unconditional integration method which avoids complicated and time consuming iteration to solve the equation of motion is highly desirable. The equivalent force control (EFC) method replaces the numerical iteration with a force feedback control loop for solving the nonlinear equation of motion in an RST using implicit time integration algorithm, while displacement control is retained to control the motion of an actuator. The accuracy and effectiveness of the method have been demonstrated with numerical simulation of a linear single-degree-of-freedom (SDOF) structure. The method has also been validated with actual tests of an SDOF structure in which a damper was used as the physical substructure. In this paper, A PD controller is adopted in the EFC loop. The influence of the PD controller parameters on the accuracy and effectiveness of the EFC method is studied with actual tests of a SDOF structure in which spring elements areused as the physical substructure. Two paralleled linear springs were used
as the physical specimen, which were loaded with a servo hydraulic actuator controlled by MTS software. Although the EFC method was experimentally shown effective by the RSTs with a damper as physical substructures, it has yet to be tested with spring specimens. To some extent, the RSTs of lightly damped, especially undamped, structures are more challenging than damped ones, because even a small time delay of the testing system may cause instability. The experimental results show that the EFC method is a very effective method to do RSTing if the controller is properly designed. Then, RSTing with EFC is applied to evaluate the performance of JZ20-2NW offshore platform with semi-active magnetorheological (MR) fluid dampers by numerical simulation. In the test, the damper which had a constant voltage of 0 V to act as a passive fluid viscous dampers formed the experimental substructure and the remainder of the structure is the numerical substructure modeled numerically. So the block diagram of the EFC method for this kind of structure is provided. A PD controller is adopted in the EFC loop in order to enforce the equilibrium condition. A second-order transfer function is used to approximate the dynamics of an actuator- specimen system. For comparison, both the Newmark constantaverage-acceleration integration method with EFC and the central difference method (CDM) with conventional displacement control are considered in the test. The numerical simulations validate the stability and accuracy of the EFC method. The results also show that the seismic and ice induced vibrations of the offshore platform are effectively controlled with the MR dampers. Further experimental studies are needed to verify the numerical simulation of RSTing with EFC for JZ20-2NW platform.
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Motion and vibration control structures (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Designing the tuned mass dampers for towers of suspension bridges F. Casciati & F. Giuliano Department of Structural Mechanics, University of Pavia, Pavia, Italy
1
INTRODUCTION
Tuned Mass Dampers are suitable for the reduction of the gust response of steel towers of long span suspension bridges. Yet these devices are intrinsically non robust, being their effectiveness very sensitive to mistuning. The boundaries of the towers of suspension bridges make the structural frequency very sensitive to the soil flexibility. Soft soils can produce shift of frequencies, inversion of modes, high gradient of the frequencies, insertion of spurious modes, in a different measure along the constructive process. Free-standing towers have robust frequencies, while the wind loading is severe. The service configuration is less critical but more robustness demanding. As a consequence for the service life of the bridge, the adoption of multi-TMD solutions, intrinsically more robust, appears to be the most convenient, also for the installation and maintenance facilities. The choice of opportune frequency ranges allows to enlarge the effective bandwidth. The most effective MTMD configurations, with higher number of devices and optimal choice of the damping and the frequency range, in general do not provide the greatest robustness. Any supplementary provision of robustness, obtained especially by enlarging the frequency range beyond the optimum, is paid by a decrease of effectiveness of the control system. So the final choice will realize an optimal compromise between effectiveness and robustness, whose demand should be limited as much as possible. This task must be pursued by activities of data collection and model updating during the construction. The synergic integration of monitoring and structural control allows to check and keep structural integrity of steel towers of long span suspension bridges, from the early construction stages to the operative life. The model updating of the tower must follow the erection path, in order to limit the uncertainties on
the structural frequencies and permit an optimal design of the control devices for the service life. Monitoring, data processing, progressive numerical sensitivity analysis, parameter selection and constrained optimization for model updating, are a feasible strategy to identify in-progress the natural frequencies of the tower, from the free-standing to the service configuration, in opportune advance to obtain an optimal efficient-robust design of the control system for the operative life. On the basis of the sensitivity analysis conducted (but no updating, since the bridge has not been built yet, neither obviously monitored), a framework of construction/monitoring/control program can be nevertheless outlined. The definitive choice of the design parameters, is completed only at the end of the constructive process. REFERENCES Koshimura K., Tatsumi M., Hata K. 1994. Vibration control of the main towers of the Akashi Kaikyo bridge, Proc. of the 1st World Conf. on Structural Control, Los Angeles. Casciati F. The challenge of long-span suspended bridges, Proceedings 4EWSHM, Granada, Spain. Giuliano F. 2007. Perormance-based design by Structural Control for Suspension Bridges, Ph.D. Thesis, Pavia. Luft R.W. 1979. Optimal Tuned Mass Dampers for Building, J. Struct. Div., ASCE, 105(12), 2766–2772. Warburton G.B. 1982. Optimal Absorber Parameters for Various Combinations of Response and Excitation Parameters, Earthquake Eng. and Str. Dyn., 10, 381–401. Kareem A., Kline S. Performance of Multiple Mass Dampers under Random Loading. J. of Str. Eng., 121, N.2. Allemang R.J., Brown D.L. 1982. A correlation coefficient for modal vector analysis. Proc. 1st Int. Modal Analysis Conference, Orlando, Florida. Stretto di Messina S.p.A. 1992, Preliminary Project.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Semi-active vibration isolation system with stiffness on-off control Yanqing Liu, Hiroshi Matsuhisa & Hideo Utsuno Department of Mechanical Engineering and Science, Kyoto University, Sakyo-ku, Kyoto city, Japan
1
INTRODUCTION
4
In a vibration system, the spring stores the kinetic energy as potential energy. The potential energy is proportional to the spring constant. Then it is not reasonable to consider that the spring stiffness can be changed instantaneously because of the conservation energy law. For the previously proposed systems, the potential energy is stored by the spring in the damper on-state. When the damper is switched to the off-state, the system stiffness is changed and the potential energy has a loss because of dissipation of the damper. In order to analyze the loss potential energy of variable stiffness system, a simple structure only using one controllable damper is studied in this paper.
CONCLUSIONS
The loss potential energy in the stiffness on-off control system was dissipated by the damper in the off-state instantaneously. In order to dissipate the loss energy, the damper should have a damping value in the offstate. The system with stiffness on-off control demonstrated excellent vibration isolation performances in the whole frequency region.
2 VARIABLE STIFFNESS SYSTEM A model of one-degree-of-freedom (1-DOF) vibration isolation system with a controllable damper (corresponding damping coefficient of c) and two springs (spring 1 and 2 corresponding stiffnesses of k1 and k2 ) is proposed and shown in Fig. 1 (a). Figure 1 (b) shows the system equivalent model. Figure 2. Experimental setup.
3
EXPERIMENTS
Figure 2 shows the experimental setup of the vibration system. One MR fluid damper is used to provide the variable damping. Figure 3 shows the frequency responses to a sinusoidal excitation.
Figure 1. Variable stiffness system.
Figure 3. Frequency responses to a sinusoidal excitation.
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Data-driven approaches and structural informatics for next generation smart structures (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Information-driven wireless sensing and control for civil structures Yang Wang Department of Civil and Environmental Engineering, Stanford University, Stanford, CA, USA
Jerome P. Lynch Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, USA
Kincho H. Law Department of Civil and Environmental Engineering, Stanford University, Stanford, CA, USA
Structural monitoring and control have undergone significant research and development over the last few decades. In order to transfer measured response information, monitoring and control systems are installed using coaxial cables as a means for data communication. To eradicate the high installation and maintenance cost of cabled systems, wireless communication technologies have been explored for sensing and monitoring of civil structures. Additionally, wireless systems allow the sensor network to be easily reconfigured for supporting different topological and information requirements. Furthermore, by incorporating an actuation interface, the wireless sensing unit can be extended to command actuators for structural control applications. Fig. 1 shows the overall hardware design of a prototype wireless sensing unit, and the two optional off-board auxiliary modules for conditioning analog sensor signals and generating actuation signals. The wireless sensing unit consists of three functional modules: sensor signal digitization, computational core, and wireless communication. The sensor signal conditioning module assists in amplifying, filtering, and offsetting analog sensor signals prior to digitization.
The actuation signal generation module offers an interface through which the wireless unit sends analog commands to structural actuators. Efficient information flow plays a critical role in the implementation of structural monitoring and control systems. Information constraints, such as bandwidth, latency, range, and reliability, pose many challenges in the selection of hardware technologies and the design of software/algorithmic strategies. The transmission latency and limited bandwidth of wireless devices can impede real-time operations as required by control or monitoring systems. Signal attenuation characteristics of the wireless transceivers used by the wireless sensing unit need to be carefully analyzed according to the operating environment. Hardware and software implementation must be able to handle the needs and requirements of the monitoring and/or control applications. This paper describes an information-driven design for wireless structural monitoring and control networks. Design concepts have been proposed and implemented to address some of the above mentioned issues. These include: 1) embedded computing in the wireless sensing unit for minimizing communication bandwidth and reducing onboard energy consumption; 2) state machine concept for designing efficient and robust communication protocols in wireless sensing and control networks; 3) decentralization of information architecture bypassing the range and latency constraints in large wireless control networks. The efficacy and robustness of the proposed information management schemes have been validated with laboratory and field experiments.
Figure 1. Functional diagram detailing the design of the wireless sensing unit.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structural health monitoring using smart sensors T. Nagayama University of Tokyo, Tokyo, Japan
B.F. Spencer, Jr. & J.A. Rice University of Illinois at Urbana-Champaign, Urbana, IL, USA
Though networks of densely deployed, smart sensors have the potential to improve SHM dramatically, the limited resources of smart sensors present significant challenges. Consider the task of locating a few strategic sensors on structures such as the 2 km long Akashi-Kaikyo Bridge or the 443 m tall Sears Tower so that these sensors can detect randomly occurring damage; such a task is intractable, if not impossible. To effectively detect arbitrary damage in structures, especially complicated structures, a dense array of sensors distributed over the entire structure will be required. However, using the traditional centralized approach for SHM will require a central station to collect tremendous amount of data. Direct application of such centralized SHM strategies cannot be implemented directly on dense arrays of smart sensors. Recognizing that structural damage is an intrinsically local phenomenon, SHM applications using smart sensors may be realized for structures of substantial size. Responses from sensors close to the damaged site are more heavily influenced than sensors far from the damage. Processing data locally will keep communication requirements reasonable. This makes a hierarchical network topology ideal for implementation in SHM applications. In a hierarchical system, smart sensors are divided into hierarchical levels and
Figure 1. SHM system architecture with interchangeable roles.
data processing is coordinated and distributed among the sensors. Large amounts of data are not shared globally, a process that quickly depletes the available power resources, but neither do the sensors act completely independently. Hierarchical organization achieves equilibrium between data sharing to gain better special awareness and independence for better energy efficiency. The essential difference between a standard sensor and a smart sensor is the latter’s flexible communication and information processing capability. Each sensor has an on-board microprocessor that can be used for digital signal processing, self-diagnosis, self-identification, and self-adaptation functions. Furthermore, all smart sensor platforms have thus far employed wireless communication technology. This research chose a homogeneous configuration of hardware consisting of the Imote2 developed by Intel. In addition to the Imote2 smart sensors, a PC serves as a user interface in this architecture. A homogeneous configuration results in the simpler programmability and deployment of the smart sensor nodes. Systems with homogeneous configurations can be programmed so that failure of one node does not result in system failure; neighboring nodes take over the roles of a non-functioning node as shown in Figure 1. This is true even in the function of each smart sensor at any given time is different within the hierarchical framework. This research implements a hierarchical, distributed SHM system employing smart sensors and experimentally verifies it on the Imote2 platform. Realizing this SHM system required various issues and algorithms to be addressed. Middleware services, numerical functions, and algorithms were combined to produce the SHM system. Experimental verification using a threedimensional truss demonstrated the efficacy of the SHM system developed herein.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Interactive sensor data retrieval and management method for integrated structural health monitoring system Jian Li Guangdong Provincial Academy of Building Research, Guangzhou, China
Yunfeng Zhang Department of Civil and Environmental Engineering, Lehigh University, Bethlehem, USA
ABSTRACT The importance of structural health monitoring (SHM) to design, construction, maintenance and post-extreme event repair of civil engineering structures has been recognized in the past decade. With advances in sensor and communication technology, next-generation SHM system will have such features as real-time data transmission and analysis, sensor network data fusion, wireless communication, and interactive data retrieval. Due to its large scale and complexity, structural condition monitoring of civil engineering structures generally requires a substantial number of sensors of different type. Transmitting the huge amount of monitoring data to central data processing station via communication channels with limited bandwidth might cause significant time delay, especially during or immediately after strong earthquakes when communication bandwidth may become scarcely available because of possible damages to communication networks and a rise in emergency communication use. Innovative sensor data transmission and retrieval techniques are thus needed to enable fast and efficient
transmission of sensor data. Furthermore, the huge data size increases the burden on data processing and analysis which may be necessary only for selected sensor data since data users such as engineers or decision makers might have different interests in retrieving sensor data with different resolutions during different time periods. Therefore, an SHM system with integrated sensor data compression, data retrieval and management techniques is highly desired, which provides data users the flexibility to retrieve selected sensor data. This paper presents the concept of such an integrated SHM system which has a few important functionalities including sensor data compression, interactive data retrieval and data management, and second order structural parameter identification. Such an integrated SHM system is comprised of three subsystems: data acquisition subsystem, data management subsystem and data distribution subsystem. A prototype integrated SHM system is described in this paper and its performance was examined using real sensor data collected from this prototype integrated SHM system installed to a steel bridge structure.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
An intelligent framework for knowledge discovery from a large amount of data in SHM N. Yabuki Muroran Institute of Technology, Hokkaido, Japan
As a large amount of civil infrastructures have been constructed in the world so far and they are deteriorating day by day, the problem of structural health of those infrastructures is increasingly being recognized. Many structures will be reaching their longevities and will have to be renewed in the future. However, under the restriction of limited resources, infrastructure administrators need to execute various measures to extend their longevities and postpone their renewal timings. Thus, maintenance of civil infrastructures, including inspection and monitoring, is more and more important in civil engineering. Maintenance of civil infrastructures can be represented as a cycle of the following five tasks: 1 2 3 4 5
inspection investigation, sensing health evaluation decision making execution, construction
In maintenance, engineers and administrators obtain various data about structures by inspection, investigation and sensing, then, evaluate their structural health in terms of material and structural mechanics based on the observed data. And they make decisions whether they will renew, rehabilitate, strengthen, repair, etc., using economical and mathematical models, based on the consideration of life cycle costs. Finally, they execute construction or repair, etc. However, in practice, the inventories and databases of civil infrastructures may not be well prepared or provided. Many decisions are being made based on limited inspection data and little monitoring data. However, thanks to Micro Electro-Mechanical Systems (MEMS) technology, the cost of sensors is decreasing rapidly, and cables, of which cost tends to be the largest part of the current monitoring tasks, can be reduced significantly by adopting wireless sensor networks. Thus, more and more sensors will be
installed in various structures for their structural health monitoring in the future. Since extremely large amount of data will be stored, it will take a long time and effort for administrating engineers to find out and reason some relationships among data items observed at various locations and under various conditions. Then, although ubiquitous sensing may be possible in the future, the number of sensors or the number of structures that sensors will be installed may have to be limited, which is deemed as a waste of opportunity and technological advancement. In order to find meaningful information and knowledge from a large amount of sensor data, data mining has attracted considerable attention. However, simple application of the data mining technique to sensor data may not be successful compared to our expectation from our experience. Thus, in order to facilitate administrating engineers to discover meaningful knowledge from a large amount of sensor data of many civil infrastructures, we propose a framework which closely relates data containing semantics of structural members where sensors are installed and the sensor data. The framework also contains knowledge related to qualitative reasoning in physical systems as well as sensor and product data in order to discover some structurally meaningful findings. This framework consists of the following three models:
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– Data Model, which represents a large amount of sensor and sensor-related data – Product Model, which represents geometry and property data of all the members of a structure and relationships among members. – Knowledge Model, which represents qualitative rules in physical systems and which may contain past failure incidents with comments. In this paper, the overall framework is described.
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Parallel data processing architectures for identification of structural modal properties using dense wireless sensor networks A.T. Zimmerman, R.A. Swartz, D.A. Saftner, J.P. Lynch Department of Civil & Environmental Engineering, University of Michigan, Ann Arbor, MI USA
M. Shiraishi Institute of Technology, Shimizu Corporation, Tokyo, Japan
M. Setareh College of Architecture & Urban Studies, Virginia Polytechnic Institute & State University, Blacksburg, VA USA
In recent years, structural health monitoring systems have become increasingly important to the civil engineering community. These systems, which utilize dense networks of sensing devices to provide estimates of structural health, not only promise to reduce the routine maintenance and inspection costs of a wide variety of structures, but may also serve to increase the level of public safety by drawing attention to potential structural problems before failure occurs. With recent advances in wireless sensing and data acquisition technology, it has become feasible to instrument a large structure with a dense array of wireless sensors. Furthermore, the analog-to-digital conversion and data processing capabilities of current wireless sensing prototypes offer the ability to efficiently distribute data processing tasks across a large network of wireless sensing nodes. In this study, three output-only modal identification techniques are adopted and modified for use within a wireless sensing network: the simple peak picking (PP) method, the random decrement (RD) method, and the frequency domain decomposition (FDD) method. Emphasis is placed on parallel implementations of these typically centralized algorithms to ensure scalability of the approach to networks defined by high nodal densities. This work sets itself apart from current work in distributed data processing using wireless sensors by drawing on parallel processing techniques to extract spatial modal information from a large network of sensors without the need for a central data repository. In order to validate the performance of these embedded algorithms, a 21-node wireless monitoring system is deployed on the balcony of a historic theatre in southeastern Michigan. Over the span of several vibration tests, each of the embedded in-network modal identification techniques is used to determine modal properties of the system. The wireless network is
Figure 1. Schematic representation of embedded output-only modal identification methods.
Figure 2. (a) Offline mode shapes, (b) embedded PP mode shapes, and (c) embedded FDD mode shapes.
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able to autonomously determine modal frequencies using a distributed peak picking algorithm, mode shapes using a distributed frequency domain decomposition method, and modal damping ratios using a distributed random decrement technique. For validation, the results from the embedded algorithms are
compared with similar modal analysis techniques run off-line using time history data recorded by the wireless network. It can be seen that the embedded methods proposed in this paper yield modal parameters comparable to those obtained using traditional offline analyses.
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Structural damage and fault detection (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Damage detection for crane girder subjected to moving load K.J. Shin, C.W. Jung, H.W. Seo & W.J. Kim School of Architecture & Civil Engineering., Kyungpook National University, Daegu, Korea
1
INTRODUCTION
The objective of this paper is to present the dynamic measurement to identify the potential damage of crane girder using piezoelectric sensor. Three types of forced vibration test, such as free vibration testing, forced vibration testing, and ambient vibration testing, were tried to identify the damage of structures. The potential damage identification is carried out according to output measurement data through FFT (Fast Fourier Transformation) in the frequency domain. A coherence-based NDT method is applied to identify the damage of test specimens for both impact load and moving load.
Figure 1. Test setup.
is damaged, it is not easy to identify the location of damage, web or flange. 2
COHERENCE-BASED NDT METHOD
The linear relationship between two adjacent outputs is calculated using the coherence function. The coherence function provides a non-dimensional measure of the linear dependence between two signals at each frequency. 3
CANTILEVER BEAM TEST
Natural frequencies are decreased as the size of notch become bigger because the stiffness of the cantilever is decreased. It is noted that the piezoelectric sensor response very sensitively at very small normal strain and gives the high voltage output at this tested frequency. 4
SIMPLY SUPPORTED BEAM SUBJECTED TO IMPACT LOAD
The damage detection methodology is illustrated experimentally using a simply supported 6000 mm span beam with a bolted splice at the center as shown in Fig. 1. Test variables are that the bolts are ‘tightened (fixed)’ or ‘loosened (free)’. All group bolts are in slip-critical condition, which represents a healthy connection. As the level of damage is increased, the natural period is decreased. However, once the connection
5
SIMPLY SUPPORTED BEAM SUBJECTED TO MOVING LOAD
The frequency 23.2 Hz of the first mode was decreased compared to that of impact test because the mass of system due to weight was increased. When the web bolts are free while flange bolts are fixed the magnitude ratio is increased for all PZTs, however when the web bolts are fixed while the flange bolts are free the magnitude ratio in decreased again. 6
CONCLUSIONS
The frequency is decreasing as the damage is increasing. The amplitude of the first mode is decreasing as the bolts are loosened because the damping is increasing. The magnitude ratios of higher mode to that of lower mode tend to be increased. The coherence between to adjacent PZT signals is decreasing as the stiffness is decreasing due to bolt loosening. REFERENCE Abdel-Ghaffer, A.M. & Scanlan, R.H. 1985. Ambient vibration studies of Golden Gate Bridge. I: Suspended structure. J. of Engrg. Mech., ASCE, 111(4): 463–482.
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Structural damage detection using static strain data S.A. Jang, S.-H. Sim & B.F. Spencer Jr. University of Illinois at Urbana-Champaign, Illinois, U.S.A
Civil infrastructure systems, such as bridges and highways, are valuable national assets that must be maintained to ensure public safety. As the I-35W bridge in Minnesota demonstrated, the impact from a bridge failure is devastating, both economically and socially; therefore, maintenance of infrastructure integrity is of utmost importance. More than 153,000 bridges, mostly short and medium size bridges, are structurally deficient or functionally obsolete based on the 2006 report from the Federal Highway Administration (FHWA, 2006). To date, maintenance has been schedule-driven, often being based on expensive and questionable visual inspections. A more effective way to monitor the structural integrity of civil infrastructure is necessary to carry out maintenance and to ensure public safety. Many researchers have proposed quantitative damage indices to quantify the existence and severity of the damage to civil infrastructure. Pandey and Biswas (1994) used changes in flexibility as a damage indicator. Bernal (2002) also used structural flexibility to develop the damage locating vector (DLV) method. Among these methods, the DLV method has received significant attention. The DLV method, as originally derived, uses measured displacement, velocity, or acceleration records as input and has been experimentally verified by Gao et al (2006). Alternatively, a straightforward strain-based flexibility approach can be considered in which the static strain is used to determine directly the associated flexibility matrix. However, several challenges need to be addressed, including: required density of strain gages and fault tolerance due to sensor failure. Because installing strain gages in all elements is inefficient and the resulting data is unmanageable, a fault tolerant SHM algorithm using a small number of static strain sensors is desirable. This paper proposes a strain DLV method that extends the work of Bernal (2002) to allow use of static
strain measurements. As in the original DLV method, linear damage, e.g. stiffness reduction, is considered. The strain DLV approach determines the set of load vectors that span the null-space of the change in strain flexibility matrix. These load vectors result in the same strain fields before and after damage. To obtain the same strain field even though the structure has damage, the strain DLVs induce zero strain at the damaged members. Using this concept, the elements having zero strain, when they are subjected to the strain DLV, are candidate damage elements. A numerical simulation is conducted for a 56 DOF 2-dimensional statically indeterminate truss structure with 30% stiffness reduction damage. Also, the lab testing using a truss model at Smart Structures Technology Laboratory, University of Illinois at Urbana-Champaign is provided. In conclusion, a strain DLV method has been developed by extending the DLV method to allow for use of static strain data. The performance of this method has been verified through both numerical simulation and laboratory experiments using 2D and 3D planar truss models. From these results, the damaged elements are successfully localized using a limited number of strain sensors, and in particular, without measurements at the damaged elements. The experimental results show that the strain DLV can perform better with improved resolution in the strain measurements. Despite the limited resolution of strain measurement equipment, the potential of the strain DLV method for application to statically indeterminate bridges is successfully verified. This study is supported by National Science Foundation under grants CMS 03-01140 and CMS 0600433, Dr. S. C. Liu, Program Manager. The first author would also like to acknowledge support from a fellowship from the Samsung Scholarship Foundation. This support is greatly appreciated.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Predicting of damages in concrete structure using PZT and motor oscillator Is-Sung Kim, Dong-Eun Lee, Hongjin Kim, Daemin Kim & Whajung Kim School of Architecture & Civil Engineering, Kyungpook National University, Daegu, Korea
1
INTRODUCTION
Concrete is a material that has been widely used, but, is easy to have cracks on and beneath the surfaces caused by deterioration developed during and after construction phase. The damage may result in serious defects of concrete structures, and thus it is very important to detect and repair damages within proper time to assure the structural safety. Defects due to deterioration, however, are usually difficult to find by visual inspection and the non-destructive testing (NDT) has been widely used to detect these cracks as an alternative. In order to emulate the realistic environment, the concrete members are vibrated with traditional sources such as impact and motor and vibrations due to these sources are measured using PZT sensors in this study. Then the damages in the concrete member are identified using measured output only. For the damage identification based on the output only, the coherencebased NDT method is proposed. The performance of predicting damages is evaluated experimentally, and the location of the damages in concrete members is quantitatively identified.
Figure 1. Coherence functions between PZT outputs of specimen N-1 and N-7.
Values near 1 indicate that a relationship between y1 (t) and y2 (t) at frequency ω is almost linear and very correlated, which indicates that there is no defect between two points. If two signals are uncorrelated, their cross-correlation and cross-spectral density are equal to zero and consequently the coherence function is equal to zero, which indicates the existence of local flexibility change. 3
2
COHERENCE-BASED NDT METHOD
The linear relationship between two adjacent outputs is calculated using the coherence function. The coherence function provides a nondimensional measure of the linear dependence between two signals at each frequency. The coherence between y1 (t) and y2 (t) is defined as the ratio of the squared modulus of the cross-spectral density function to the auto-spectral density function as
EXPERIMENTS
Each specimen is vibrated with impulsive input to identify the damage. Each concrete beam is damaged with a notch of 4cm depth at the center. The coherence functions obtained based on PZT output are presented in Figure 1 for the specimen N1 and N7. It can be seen that the coherence between PZT outputs measured near the damage (PZT 3 and PZT 4) is clearly lower than that between PZT outputs measured far from the damage (PZT 1 and PZT 2). In most frequencies, the coherence between two adjacent points in the intact part of a structure is close to one indicating two signals are almost linearly related. On the other hand, the outputs measured from two adjacent points in the damaged part of a structure lose the linear relationship.
where Sy1 y2 (ω) is the cross-spectral density function; and Sy1 (ω) and Sy2 (ω) are the auto-spectral density functions of y1 (t) and y2 (t), respectively. The value of the coherence varies between 0 and 1.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Damage detection in offshore jacket structures using incomplete modal data Junrong Wang & Huajun Li College of Engineering, Ocean University of China, Qingdao, China
Sau-Lon James Hu Department of Ocean Engineering, University of Rhode Island, Narragansett, USA
Steel-jacket type platforms, the most common kind of offshore structures having been used in offshore oil and gas exploitation, continually accumulate damage resulting from the action of various environmental forces during their service life. Clearly the development of robust techniques for early damage detection and localization is crucial to avoid the possible catastrophe due to structural failures. Since the damage may change the stiffness and/or mass of the structural system, consequently the damage would alter the structural modal characteristics such as the modal frequencies and mode shapes. Based on changes in frequencies, mode shapes, or their combination, many structural damage detection techniques have been proposed for predicting damage location and severity. Not all structural damage detection techniques are suitable to be employed for offshore structures. In the particular application to jacket-type offshore structures, damage detection schemes that have been investigated include modal strain energy method, artificial neural networks method and modal strain energy decomposition method. Those methods have been demonstrated to be relatively effective to localizing damaged members, but inaccurate on assessing the damage severity. A recently developed method that can localize and estimate damages accurately is the cross-model cross-mode (CMCM) method, which was originally developed for the finite element model updating. Li et al. demonstrated the effectiveness of applying the CMCM method to the damage diagnosis of a simple steel-jacket platform when only one or two spatially complete “measured” modes were available.
While there are several attractive features of the CMCM method described in Hu et al. (2007), a main drawback is the demand of using spatially complete modes. In practice, measured mode shapes are usually spatially incomplete, for instance, rotational DoFs are often unmeasured. Therefore, there is a theoretical and practi cal need to extend the original CMCM method to being applicable to spatially incomplete modes. This paper studies the damage detection in offshore jacket-type platform when only one or two spatially incomplete modes are measured. In dealing with spatial incompleteness, both model reduction and modal expansion are investigated. Specifically either Guyan (static condensation) or SEREP (System Equivalent Reduction Expansion Process) transformation matrix is employed in the model reduction or modal expansion process. One theoretical development is an iterative procedure to compute the required transformation matrix associated with the damaged structure. The numerical example considers a 36 element jackettype offshore structure with multiple damages, and measurements are taken only at translational degrees of freedom (DoFs). Numerical study covers employing both Guyan and SEREP transformation matrices in the model reduction or modal expansion processes. Numerical results suggested that (i) using Guyan scheme always outperformed using SEREP, and (ii) employing model reduction was always better than modal expansion. Overall, applying the CMCM method in conjunction with iterative Guyan reduction approach yielded best damage localization and severity estimate.
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Magnetorheological fluids and dampers (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Investigation of attitude harmony control of full car for Magnetorheological semi-active suspension XiaoMin Dong, Miao Yu, Zushu Li, Changrong Liao, Weimin Chen, Honghui Zhang & Shanglian Huang Center for Intelligent Structures Dept. of Optoelectronic Engineering, Chongqing University, Chongqing, China
ABSTRACT: Due to the significant nonlinearity, time-delay and uncertainty of magneto-rheological (MR) suspension, one of the main challenges in the application of this technology is the selection of appropriate control strategy. However, some classical semi-active control algorithms are limited when they are implemented in real MR suspension. In this paper, a new intelligent control algorithm, attitude harmony human simulated intelligent control is proposed. A nonlinear full car dynamic model is established and the complex motion control of MR suspension is classified as eight motion attitudes. A reasonable control modal is proposed to control each attitude. Attitude harmony HSIC controller with three levels is designed. As the first level, eight sensory-motor intelligent schemas (SMIS) are proposed to control directly corresponding attitude according to the characteristic mode. The second level, parameters adjusting level, adjusts the parameters of running level. At the third level, nonlinear saturation and time delay of MR damper are compensated. To verify the validity of our approach, other representative five control strategies including skyhook control, groundhook control, hybrid control, LQG control and fuzzy logic control are also proposed to compare to HSIC. Numerical simulation and field test of MR suspension with the six control strategies are carried out on various road grades and different vehicle velocities. The results show that the representative five control strategies can achieve some limited control performance and HSIC exhibits best integrated control performance. The semiactive suspension using HSIC can avoid the effect of nonlineartiy and time-delay and can achieve better ride comfort and stability compared to passive suspension. Root mean square (RMS) sprung mass accelerations are reduced by as much as 22% on B class road, and 28% on D class road.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Design analysis of a Magnetorheological damper J. Huang, L.Q. Liao & C.H. Lin Chongqing Institute of Technology, Chongqing, China
1
INTRODUCTION
Altering the strength of an applied magnetic field will precisely control the yield stress of Magnetorheological (MR) fluids. Based on the mechanical characteristics, the fluids can be used in the magnetically controlled devices such as dampers. An MR damper is a semi-active control device that uses MR fluids. Altering the strength of an applied magnetic field will change the damping force of the damper. In order to design an MR fluid damper, A designer must be able to predict the performance of the damper in
consideration of its applied magnetic field and geometry. In this paper, the Bingham model is used to describe characteristics of the MR fluids subject to an applied magnetic field. Based on Navior-Stokes’ equation, the axial flow of the fluids between the piston and the outer cylinder is analyzed. The expression for the damping force is derived to provide the theoretical foundation for the design of the damper. Based on this equation, after mathematical manipulation, the engineering expressions for the gap and effective length of the annular MR fluid between the piston and the outer cylinder are derived.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Analysis of effect of different connecting ways upon the dynamic response time of MR damper Xi Huang, Miao Yu, Linzhang Mao, Changrong Liao & Wei Min Chen College of Optoelectronic Engineering, Chongqing University, Chongqing, China
Dynamic response time is an extremely important character of MR damper, and it is one of the critical factors that determine the controlling frequency, the application range and the practical effectiveness of automotive MR damper directly. Based on the research of MR damper developed by Center for Intelligent Structures of Chongqing University, the effect of different connecting ways (parallel or serial) of electromagnetic coils on dynamic response time were analyzed theoretically. It is found that in the testing system, the effect of different connecting ways upon the dynamic response time of MR Damper is mainly coming from the effect on the time constant of the current driver. Through a series of calculations, the time constant T is acquired:
(Details of the variables can be found in the context.) In reference to the parameters of real circuit, R is much larger than R0 . So it is extremely convenient to use the first term of above equation to estimate the time constant T. Generally speaking, If R0 and L0 are specified, the time constant of current driver system is in inverse proportion to N 2 . Therefore, the time constant of the current driver in MR damper would reduce when
the electromagnetic coils are parallel connected, and accordingly the dynamic response time of MR damper would reduce too. In order to prove the theoretical analysis above, MR dampers developed by Center for Intelligent Structures of Chongqing University are used to tested based on the testing system shown as the following picture:
The testing result has proved the theoretical analysis: the activation dynamic response time of MR damper when electromagnetic coils are parallel connected is approximately 35% shorter than when serial connected; and the deactivation dynamic response time when parallel connected is approximately 88% shorter than when serial connected.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Design and characterization on inner bypass Magneto-rheological damper with magnetic bias Honghui Zhang & Changrong Liao The Key Lab. of Opto-Electronic Technology and Systems, Ministry of Education, P.R.C
Weimin Chen & Miao Yu College of Opto-electronics Engineering, Chongqing University, P.R.C
1
INTRODUCTION
A good MR damper should have large scalability and fast response, simultaneously, satisfy the requirement of vibration control, which demands a low basedamping force. Low base-damping is helpful to the large scalability; unfortunately, it will lead to a narrow force range for the reduction of maximum damping. In order to obtain large scalability and broad damping range at the same time, a new MR damper featured as inner bypass and magnetic bias is presented, and then the characterization is carried out.
2
DESIGN OF INNER BYPASS MR DAMPER WITH MAGNETIC BIAS
Figure 1. Magnetic distribution in −1A, 0A and 1A.
For the installation of MR damper in automotive suspensions, the cylindrical structure and basic geometry of original damper should be kept, correspondingly, the inner bypass mode are presented, which is combined from the basic working modes. There are two passages for MR fluid flow in inner bypass MR damper, one is outer passage between cylinder and magnetic shielding sleeve, and another is the inner passage, which is between the yoke sleeve and piston, the two passages are both cylindrical with the piston. Totally speaking, the outer passage can be maintained magnetic free and working in the mixed mode, and the inner passage are totally controlled by the magnetic field and which is in the flow mode. At the same time, the magnetic bias is integrated to keep a medium damping without the magnetic excitation applied and to lower the base-damping with inverse current excitation. 3
MAGNETIC AND FLOW ANALYSIS
For the verification of designed magnetic distribution, magnetic analysis is conducted with FEM method;
the following figure shows the magnetic distribution at positive, negative and zero electro-magnetic excitation. The outer passage is always kept magnetic free, and the difference mainly expressed by magnetic change of the inner passage. Assuming the damping force respectively generated from outer and inner passage is f1 and f2 , the damping force of the MR damper can be expressed approximately as:
4
RESULTS OF EXPERIMENTAL CHARACTERIZATION OF MR DAMPER
The quasi-steady and dynamic experiments show that the inner bypass MR damper with magnetic bias meets the desired performance. It can be operated bi-directionally with positive and negative current.
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With the negative excitation, a low base-damping can be obtained to fulfill the requirements of control strategy and a large range can be obtained by the magnetic superposition of magnetic bias and
positive excitation. The flow block can be alleviated partly by the inner bypass structure, which is promising in the flow optimization by the further investigation.
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System identification and damage detection
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structure damage detection method-based on modal strain energy F.Y. Yang Engineering College, Ocean University of China, Qingdao, China Offshore Oil Engineering (Qingdao) Co., Ltd, China
Y.C. Yang & M. Zhang Engineering College, Ocean University of China, Qingdao, China
ABSTRACT This paper deals with the general problem of utilizing changes in modal parameters of structures to locate the position and estimate the severity of damage in structures. Non-destructive structural damage may be defined as any deviation of geometric or material properties that may result in unwanted responses of the structure. During the past decade, many damage detection methods based on vibration analysis were proposed, but problems for only a few modes can be obtained still remain and few damage detection methods can be applied to three-dimensional frame structure. To overcome those problems, a newly
structure damage detection method based on modal strain energy is presented, this method can predict locations and severities of damage precisely in threedimensional structure only making use of pre-and post-damage modal parameters that are available for only three modes of vibration. To verify the proposed method, a finite numerical model (FEM) of a threedimensional frame structure, in which six damage cases are simulated, is employed to verify the proposed method. Simulation results illustrate that the proposed method is accurate in damage localization and preliminary in severity estimation. This method is simple and hopeful to be employed into the offshore platform damage detection.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Information acquisition method-based on space similarity structure J. Teng, W. Lu, H.J. Liu & Y.H. Zhu Harbin Institute of Technology Shenzhen Graduate School, Shenzhen, China
The measured information of sensors is the basic data for the structural health monitoring method, which is interdependence and redundant. It is significant in determining the amount, the sorts and the location of sensors as well as in utilizing the sensors’ information effectively to make optimize between monitoring aim and the cost. Moreover, the question arises as to giving the proper method for sensor systems based on the given structure. The structural health monitoring method based on space similarity structure is proposed in this paper, the aim of which is to utilize the limited members’ information measurement to obtain the whole structural state and make its safety estimation. The space similarity structure is the main researched object, which is taken to mean the similarity in structural style, structural member property and structural analysis results. The structure with six curved steel trusses is an example used in this paper, which is similarity space structure as defined above. The information acquisition method for the space similarity structure is discussed from the information acquisition for single standard truss to six trusses. Truss three with the most member number and larger stress is chosen to be the standard truss. The solution to this single truss falls into three parts. Firstly, the principle component analysis is used in the main factor extraction from those factors which can reflect the extent of working members’ health; secondly, according to the main factors, the members are clustered in the aim to have the same stress changing tendency in each cluster, where seven different hierarchical clustering methods are applied and the identified cluster results are gotten; finally, using the clustering result of members’ stress-changing tendency, the unknown members’ stresses can be forecasted from the limited members chosen from the cluster and the adjacent clusters, and interpretation fitting method introducing definition of prolongation is used as acquisition
method. The advantages of introducing the definition of prolongation are: (1) the result is more smoothness and less error, because not only special members of this cluster, but also the members in the adjacent clusters are chosen for forecasting the unknown members’ information. It makes the information forecasting of this cluster absorb information of adjacent clusters’ members better, consequently, members’ information among adjacent clusters are harmonious and the reliability of forecasting for this cluster members is improved; (2) the members selected for one cluster forecasting may be repeated in the other cluster, which can be obtained two different forecasting values from the forecasting in two different clusters, and the comparison of these two values for single member can examine the sensor system and the forecasting method. The forecasting result from the example is of small relative error. Definition of the space similarity structures of the similar mechanical property is given to be the basis of solution to whole structure. Information acquisition of truss three is conducted with 11 members chosen to be arranged with sensors and standard information for the information acquisition of the other five trusses. By comparing the chosen members’ stress in the target truss and the corresponding members’ measured stress in the standard truss, the stress distribution of the other five trusses can be obtained. In conclusion, the data mining and multivariate statistic analysis are combined to gather the information of members in standard truss, and the definition of prolongation is introduced. According to the solution to the standard truss and the property of space similarity structure, the qualitative method is used in the information acquisition of the other five trusses. The stress information forecasted by limited members’ measured information is high accurate, in which the method used is feasible and valid.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Finite element modal updating of Shibanpo Bridge using experiment test results Gang Liu, Pu Yang & Zongming Huang College of Civil Engineering, Chongqing Univiversity, Chongqing, China
The model of the newly constructed Bridge, with the longest main span (330 m) among the continuous rigid bridges, is built and updated using static and dynamic measurement data. And the main objective of this paper is to present a practical FE model updating technique combination the advantages of FE and math software so it is practical to most engineers in daily use. The parameter optimization converts the problem of parameter updating to objection optimization. And the cost function, consisting of residual of measured data and analytical predictions, is minimized using the least-squares algorithm. Although the relationship between the ith prediction Ui and the kth parameter xk can not expressed explicitly, it may be given by the first order Taylor series when the higher order items are neglected
where Ut0 is the analytical prediction when xk valued the initial xk0 , ∂Ui /∂xk , expressed by Sik in this paper, denotes the sensitivity of Ui toxk . The Sik must be iterative calculated when the xk changes, if there are a number of measured data and parameters in large scale structures, burdensome work have to be done through the optimum process. moreover, cost function can not be solved if there is no optimization function or no nonlinear optimization function in FE software. This paper assumes Sik will be the same when the change range of xk is relative small. Therefore, when
xk is in the same beeline, Sik will not be recalculated in the iterative optimization procedure, the optimization problem can be solved respectively by math software. When there are many parameters need to be modified in large scale structure, it is still not practiced to divide the relationship between Ui and xk to several segment beelines, so the dividing scheme according to the decreasing percent of the cost function denoted by β, is suggested, that is, the process of the optimization is halted when the decreasing percent of cost function reaches β, the Sik is recalculated by FE software using the last solution of optimization, then the optimization process continues adopting the new Sik . This process iterates until the value of cost function is below the tolerable value. The model of the Shibanpo Yangtze River Bridge is built and the engivalues and vertical displacement of this bridge have been measured. A numerical simulation using this method is studied and only three times recalculation of sensitivity Sik is need when the ultimate solutions are obtained, demonstrating the calculation work is reduced tremendously. At last, the model of the Shibanpo Yangtze River Bridge is updated. The difference between the predictions form the updated model and the value of measurement decreases observably. So the technique developed by this paper is only not feasible, but also is practical and user-friendly utilized by engineer to update large scale structures in daily use.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Evaluation of the concrete strength using IE and SASW methods D.S. Kim & S.W. Jin Department of Civil and Environmental Engineering, KAIST, Daejeon, South Korea
E.S. Bang Geotechnical Engineering Division, KIGAM, Daejeon, South Korea
INSTRUCTIONS
700
Evaluation of the integrity in concrete structure using nondestructive testing is becoming increasingly important. One of the most important subjects is to predict the current strength of concrete structure. Several nondestructive methods were introduced for measuring in-place concrete strength. In this paper, Impact Echo (IE) and Spectral Analysis of Surface waves (SASW) method are investigated to evaluate the relations between the wave velocity and concrete strength. IE, SASW and UPV were applied on four wall-type structures of different strengths and the uniaxial compression tests were performed using cores obtained at each structure. The feasibility of IE and SASW method was finally evaluated.
600 500 fc(kgf/m2)
1
Lee Vel. by IE AIJ Vel. by UPV
400 300 200
AIJ : fc⫽0.05695e0.001572Vp
100
Lee : fc⫽0.215Vp⫺620 0 3000 3200 3400 3600 3800 4000 4200 4400 4600 4800 Vp(m/s)
Figure 1. Relation between the strength and P-wave velocity.
4 TEST RESULTS 2
BACKGROUND: IE-SASW METHODS
IE is widely used to evaluate the integrity of concrete and SASW can determine the VS profile of layered system. In this paper, IE-SASW method is proposed to find a relationship between P-wave velocity and the concrete strength. P-wave velocity is determined by SASW test at every location where IE test is performed. In the concrete structure, the surface wave velocity can be easily obtained from the experimental dispersion curve without executing the complicated inversion procedure. Then, the thickness or the location of the defect such as a void in the concrete member can be identified using the nondestructive IE method.
3 TESTING EQUIPMENT AND PROCEDURE At four wall-type structures which design strengths are different, IE, SASW and UPV tests were performed and the cores were extracted at each point. The uniaxial compression tests were performed to find the compressive strength using these cores.
(1) The rod wave velocities from cores and P-wave velocities from the wall are determined by IE tests and the appropriate Poisson’s ratio is evaluated. (2) P-wave velocities measured by SASW and IE methods match well. (3) The relationship between P-wave velocity and concrete strength was evaluated as shown in Figure 1. 5
CONCLUSIONS
(1) Comparing IE test results from core and wall, the appropriate Poisson’s ratio was evaluated and its applicability to concrete is verified. (2) Agreement between measured velocity by SASW and IE shows the applicability of IE-SASW to concrete. (3) The relation between concrete strength and P-wave velocity was developed, but further study on aging and high strength concrete is required. Based on these experimental results, the advantages and applicabilities of IE-SASW method were verified.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Comparison of modal identification of output-only systems with simultaneous and non simultaneous monitoring T. Kuroiwa & H. Iemura Structural Dynamics Laboratory, Kyoto University, Kyoto, Japan
Full-scale dynamic tests were conducted on the 5 story steel frame located at Disaster Prevent Research Institute, Kyoto University. In order to determine the dynamics characteristics of the frame, ambient vibration tests were conducted. Two configuration of monitoring were defined in view of compare the results obtained from simultaneous and non simultaneous measured DOF. The employed system identification procedures are based on output-only measurements since the forcing functions are not available during ambient vibration tests. The modal identification method used in this study is based on auto- and crosscorrelation functions, and it is described step by step. The results are compared with finite element models and with the previous results obtained under harmonic forced vibration applied on the frame through a mass exciter. Were clear identified the 5 fundamental lateral frequencies and the respective mode shapes, related to simultaneous monitoring. Based on non simultaneous recorded data, only natural frequencies were obtained. The system identification obtained under ambient vibration tests are in very good agreement with forced vibration and analytical results, thus providing a reliable set of identified modal properties that can be used as baseline in future health monitoring and damage detection studies.
By uncoupling the recorded time histories data, the mode shapes and natural frequencies obtained were checked in order to validate the proposed modal identification methodology.
Figure 2. Transfer functions 1st.–5th floor.
Table 1. Natural frequencies (Hz)- comparison between ambient vibration, forced vibration and finite element model results. Mode
AVM
Forced
FEM1
FEM2
1 2 3 4 5
1.76 5.27 8.79 13.67 17.96
1.69 5.18 8.72 13.60 17.80
1.69 5.22 9.26 13.26 17.75
1.98 5.92 10.19 13.90 18.17
FEM1 : steel beam acting by itself FEM2 : full interaction between concrete slab and steel beam
Figure 1. View of five story steel frame.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Experimental and theoretical identification of an Italian pedestrian cable-stayed bridge L.M. Giacosa, L. Gioanola, A. De Stefano & P. Civera Polytechnic of Torino, Torino, Italy
1
EXPERIMENTAL AND THEORETICAL IDENTIFICATION
The pedestrian bridge in Torino, designed to connect the Olympic Areas is defined one of the symbol of the modernizing and internationalization of the city. This project takes part to the retraining of the Ex General Market Area (MOI), necessary for the 2006 Torino’s Winter Olympic Games and direct to the carrying out of a Torino Olympic Village. Experimental setups were performed on the bridge deck both on the supported side of the bridge and on the cable-stayed side. Accelerometers acquisition were performed to identify natural frequencies and mode shapes of the structure. Goal of the experimental setups were been the mechanical characterization of the structure though a modal analysis. From the data was been possible to extract the several parameters to know better structure behaviour: – Natural frequencies and mode shapes; – Numerical model validation and modal analysis; – Evaluation of the main parameters of the structure under different loading conditions to achieve threshold values.
2
MODAL ANALYSIS METHODS
Many system identification approaches have been developed over the years: the eigensystem realization algorithm (ERA) is one of the more widely used techniques. Structural Identification methods to identify the natural frequency and mode shapes using the crosscorrelation function. With this the identification software developed by the Polytechnic of Torino, it is possible to select directly the minimum frequency in a graph, that correspond to the natural frequency of
the system, as in the picture for the Torino’s pedestrian bridge. The writers performed an ambient vibration test on the pedestrian bridge to establish its dynamic properties (frequencies, mode shapes and damping ratios) for system identification purposes. The dynamic properties determined from the vibration testing provide an objective measure of the in-situ structural characteristics. The identified dynamic properties were also used to confirm the reliability of the designer’s finite element models of the bridge. Ambient vibrations were conducted using both accelerometers sensors installed on the bridge but also commercial ones, to tests and verify the efficiency of the system, as a final test before conclude the installations works. Damping and sinusoidal dynamic tests were conducted, in this precise case mass applied was produced with the oscillation of the pendulum mass in several direction and its dropping on soft material to evaluate the decay of the forced variation. Registration are reported in the picture below. Another type of impact vibration was planned using an impact hammer directly on the surface of the deck. These test were planned in several position of the cablestayed part of the bridge and in special way close to the TMD structure installed under the deck surface. Different test were carried out moving the oscillation mass on the bridge deck; this type of test was also designed to verify the behaviour of the Tunes Mass. From the experimental data acquired during the dynamic tests on the bridge we were able to use them to identify with the method before described the experimental natural frequencies and the relative mode shapes of the deck. Using both methods in the time domain (ERA) and in the time-frequency domain (TF methods), we were able to close evaluate dynamic parameters. Identifying natural frequencies directly from the experimental data with very stable methods developed and tests during the last five year we were absolutely confident on the results achieved.
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Innovative actuators
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Research on the structures and geometric parameters of synthetic jet actuator Yong Zhou, Bangfeng Wang, Li Zhang, Huangsheng Qian & Xinwei Wang Aeronautical Science Key Lab. for Smart Material & Structure, Nanjing University of Aeronautics & Astronautics, Nanjing, China
1
INTRODUCTION
Synthetic jet actuator (SJA) is a prominent device for active flow control (AFC). Fluid was expelled out of and entrained into actuator through an orifice exit on the top of the cavity by the periodically oscillating of the membrane on the bottom, on which a piezoelectric patch was adhered to drive the SJA. A series of continuous vortex pairs were formed because of the shearing between the expelled fluid and the surrounding fluid. To improve the driving ability of SJA, the current paper studies a kind of cymbal structure membrane SJA. The cymbal structure can make full use of strain parameters d33 and d31 of piezoceramic while only d33 is mainly functioned in the conventional piezoelectric structure. Besides the longitudinally deformation of membrane owe to the function of d33 , the top hat hunches because of sideway extrusion and is hollowed because of cross drawing due to function of d31 , resulting from latitudinal deformation of piezoceramic. Thus, the total distortion is larger than the plat copper membrane. Two sizes of cymbal structure were studied in the paper, 12 and 18 (diameter of top hat). Comparison is made with the flat copper membrane SJA and the effect of geometric parameters on jet velocity for both membranes are experimented.
2
EXPERIMENTAL STUDY
The membrane of SJA was driven by sinusoidal voltage, which was supplied from a signal generator and copper membrane
d33 d31
piezoceramic
Figure 1. The schematic picture of cymbal structure diaphragm.
amplified to 240 V by a power amplifier. The hot wire anemometry (HWA) was employed to measure the jet velocity of SJA along the axial distance from orifice exit. The wire diameter and length are 5.0 µm and 2.0 mm. Considering that the length of the hot wire is greater than the orifice diameter, the instantaneous velocity sensed by the hot wire is actually a spatial average of the velocity over the length of the hot wire. The output signal of HWA was collected by a computer. 3
RESULTS AND CONCLUSIONS
Experiments were performed for the actuators with a flat membrane and three different cymbal diaphragms. Frequency responses were examined for each actuator in various geometric parameters, and the velocity distribution along the axial distance was collected. The results show that each geometric parameter has effect not only on the output velocity, but also on the resonance frequencies of synthetic jet. The detailed trends of effect have difference depending on the cymbal size. As a result of comparison, all the cymbal diaphragm actuators are much more powerful than flat membrane actuators. The HHT method was utilized to analyze the instantaneous centerline jet velocity signals. The Empirical mode decomposition (EMD) results show that alternating signal energy focuses on 2nd intrinsic mode functions (IMF) near the exit. And it is the driving frequency of membrane. For the signal far away from exit, the amplitudes of 9 orders of IMF have not distinct differences. Energy spreads mainly between IMF5∼IMF7, which is far away from membrane oscillation frequency. And in Hilbert spectrum, the jet velocity signal’s fluctuating along time can clearly tells the same results. They show that velocity is fluctuating at oscillating frequency of membrane near the orifice exit, and it is no longer affected by the membrane oscillation at larger distance from exit and a steady jet is sustained.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Research on the variable voltage variable frequency inverter-based on DSP for piezoelectric micro-jet actuator Lei Xun, Bangfeng Wang & Huangsheng Qian Aeronautical Science Key Lab. for Smart Material & Structure, Nanjing University of Aeronautics & Astronautics, Nanjing, P. R. China
1
INTRODUCTION
Utilizing the disturbance of micro-flow to realize the control on the main flow is an important method to the flow control, especially for adaptive wing boundary layer control. Synthetic jet control becomes one of the highest potential methods for flow control, because its actuator has a simple structure and easily to be controlled and less power consume. In general, the synthetic jet is generated through the vibration of the membrane of the actuator driven by piezoelectric materials. In order to realize the adaptive control of micro-flow, the piezoelectric materials must be driven by a signal with high voltage, adjustable frequencies and less harmonic. The fundamental frequencies of the conventional power converters are so low that can not drive the piezoelectric materials, furthermore the weight, power consume and volume of the conventional power converters are also not fit to be integrated into the structure or wing of aircraft. In this paper, the power signal converter is capable of providing a stable ac power with variable amplitude and variable frequency over a wide range according to this different application field. Obviously, driving piezoelectric materials is different from driving motor equipments. Piezoelectric materials show capacitive out, and input resistance of piezoelectric materials is high. Then the driving current will be low. So the driver should be high voltage low current power. In order to optimize microflow actuator, the output signal of inverters should be variable voltage and variable frequency signal. With the speed of aircraft raised, the heat on the surface of aircraft caused by the friction between the air and the aircraft becomes higher Generating electricity is one of effective form for heat utilized and
a thermoelectric generator(TEG), which constructed by Bi-Te based thermoelectric material, was presented to realize the self-power of SJA. The TEG can give about 12v dc power, which can not be used to drive the piezoelectric materials, but it can be used by dc-dc and dc-ac inverter. The dc-dc part is mainly used to boost the voltage to fit the demand of Variable Voltage and the dc-ac part is mainly used to achieve the goal of variable frequency. To realizeVVVF for the SJA,The Pulse Width Modulation (PWM) is selected to modulate the inverter for its easy control circuit than the PulseAmplitude Modulation. In this paper, the sinusoidal PWM (SPWM) and Selected Harmonic Elimination PWM (SHE-PWM) are used to modulate the inverter. Both the SPWM and SHE-PWM have advantages and disadvantages. So a synthetic method for harmonic elimination is proposed in this paper. When the fundamental frequency (sine wave) is less than 1000 Hz, SPWM is adopted. And when the fundamental frequency is more than 1000 Hz, SHE PWM is adopted. By the synthetic method, the sine wave signal could be easily reverted after filtering. In order to convert the low voltage of dc to the high voltage of ac, the power includes dc-dc and dc-ac. The goal of dc-dc is to boost the voltage and the aim of the dc-ac is to make the frequency variable, the two circuits are controlled by DSP. In this paper two figures are given, one figure shows the SPWM after being filtered with the frequency is 635 Hz and the voltage is 150 V, the other figure shows the SHE PWM after being filtered with the frequency is 3831 Hz and the voltage is 156 V. The experimental results verify that using this method the system can generate perfect sine wave to drive the SJA.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Performance characteristics of a piezoelectric-driven dispenser for semiconductor package Q.H. Nguyen, B.Y. Yun & S.B. Choi Smart Structures and Systems Laboratory, Department of Mechanical Engineering, Inha University, Incheon, Korea
EXTENDED ABSTRACT In recent years, a dispensing system has been widely used in many applications to deliver fluid in a precisely controlled manner (Lewis, 2003, Hsu, 2004, Landers, 2002). Especially, in the semiconductor industry, the dispensing system has played an essential role to protect an integrated circuit (IC) chip from external environment and prevent its break away in IC encapsulation and surface mount technology. So far, numerous types of dispensing approaches have been developed and successfully implemented in the semiconductor applications. These are classified, in terms of driving mechanism, into four types: Time-pressure, rotary-screw, positive-displacement and jetting types (Li, 2004). Among these the first three approaches belong to the contact-based dispensing technique in which the dispenser nozzle is required to contact with a substrate or printed circuit board (PCB) via dispensed adhesive. In order to achieve repeatable and good quality dots, the distance between the nozzle and the substrate is required to be very small and same from dispense to dispense, which increases the cycle time. Thus, the jetting type has been proposed as a non-contact dispensing technique (Anthony, 1999). In jetting dispensing, by using a ball-needle and seat mechanism, the fluid is constantly pressurized at a syringe and fills the void as the ball-needle retracts from the seat. As the ball-needle returns, the adhesive is forced to flow through a nozzle. Then, an inertia force breaks the stream of adhesive and forms dots striking the substrate from a distance of 1.0 mm to 3.5 mm above the board. The uniformity and shape of the adhesive dots are unaffected by variances in the board planarity or discrepancies in the needle surface and board surface tension since it never comes in contact with the board. Since there is no motion in the z-axis, the cycle time from dispense to dispense is significantly reduced. Despite the benefits, the modern semiconductor process needs an advanced dispensing system because packaging processes become increasingly dense such as flip-chip, and require to dispense micro-volume of adhesives in high flow rate.
Furthermore, the reduction of noise/vibration and the dispensing of high viscous fluids are also important issues to be resolved. This paper presents a new type of jetting dispenser which is expected to achieve high flow rate and small dot sizes in order to satisfy the requirement in the modern semiconductor technology. In order to achieve this goal, a jetting mechanism driven by a piezoelectric actuator is proposed. As wellknown, the piezoelectric actuator can offer large force, fast response and high operating frequency. However, the primary limitation of the piezoelectric material is its small strain. In order to dispense adhesive fluid, a magnification mechanism should be employed. In this study, a hydraulic magnification mechanism is used. After describing structural components of the dispensing mechanism and the operating principle, a dynamic modeling is undertaken by considering the behavior of the piezoelectric actuator, hydraulic magnification, dispensing needle and adhesive fluid. In the modeling, fluid models for adhesive fluid and hydraulic magnification are derived with a lumped parameter method. The magnification fluid is assumed to be Newtonian fluid while the adhesive is modeled based on its equivalent Bingham model. The governing equation of motion is then derived by integrating the fluid models with structural model of the dispenser. Subsequently, the dynamic behavior of the dispenser and its dispensing amount are investigated by applying a sinusoidal driving voltage input. Based on the developed model, significant geometric dimensions of the dispenser are selected and the proposed jetting dispenser is manufactured. An experimental configuration for the dispenser is then proposed and preliminary test results are demonstrated and compared with the simulated results obtained from the proposed model. Finally, a control system is designed to control the dispensing flow rate of the dispenser by actuating the needle in a controlled motion, which is a sinusoidal trajectory in this study. Firstly, based on the simulation and experimental results the desired trajectory of the needle is determined from the desired dispensing flow
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rate. Then, a PID controller is adopted to achieve the desired trajectory. The controlled results are presented in order to demonstrate the effectiveness of the proposed control system.
Keywords: jetting dispenser, piezoelectric actuator, hydraulic magnification device, lumped-parameter method.
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Motion and vibration control structures (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A design of automatic controller for seismic protection system of towers T. Rengaraja R M D Engineering College, Kavaraipettai, India
P. Devadas Manoharan Anna University, Chennai, India
Keywords: structural control, active tendon system, seismic load, linear quadratic regulator (LQR), soil structure interaction (SSI).
1 ABSTRACT It is common knowledge that civil engineering structures must withstand ever changing environmental loads such as wind, earthquakes etc. during the span of their useful lives. Yet, until very recently, buildings, bridges, and other constructed facilities have been built as passive structures that they rely on their mass and solidity to resist outside forces, while being incapable of adapting to the dynamics of an ever changing environment In recent years, however, a number of factors have emerged that signal and need for considering structures with some degree of adaptability or responsiveness. As a result, new concepts of structural protection and structural motion control, such as supplemental damping, passive control and active control, have been advanced and are at various stages of development. Most of the current active structural control strategies for a seismic protection have been based on either full-state feedback (i.e., structural displacements and velocities) or velocity feedback. However, accurate measurement of the displacement and velocities is difficult to achieve directly, particularly during seismic activity, since the foundation of the structure is moving with the ground. Because accelerometers can readily provide reliable and inexpensive measurements of the structural accelerations at strategic points on the structure, development of control methods based on acceleration feedback is an ideal solution. The controller design is based on optimal control strategies. The objective of this paper is to demonstrate using MATLAB simulation that stochastic control methods based on absolute acceleration measurements are viable and robust, and that they can achieve performance levels comparable to full-state
feedback controllers. The soil structure interaction effect is considered. In this study, the acceleration feedback control strategies previously developed by Spencer, for seismically excited structures are verified by MATLAB simulation on a tendon-controlled, threestory, test structure. As a demonstration of the closed loop control principles a three dimensional three panel tower is taken. The real time earthquake acceleration is applied at the base. The control force is applied to the structure through a set of tendons connected to an actuator placed at the base Fig. 1. The object of control is to reduce the horizontal displacement of the nodal points of the towers relative to the base for safety reasons. The system identification procedure is employed to develop mathematical model incorporating soil structure interaction (SSI) effect Frequency domain optimal control strategies are employed to achieve the control objectives. The result reported for the control design indicates that the controller is robust and that state feedback performance can be effectively recovered using acceleration feedback control strategies.
Active Tendon Actuator
Fig. 1. Controller system.
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Vibration control of pipe line applying SMA energy absorb support Yongfeng Du & Hui Li Institute of Earthquake Protection and Disaster Mitigation, Lanzhou University of Technology, Lanzhou, PR China
ABSTRACT This paper presents a numerical simulation of vibration control of high pressure pipelines applying SMA energy absorb support. The pipe line under discussion is a very important project which supplies high pressure gas for several big chemical plants affiliated to a chemical group. The pipe line is excited by a pulsation loading under working condition, and some similar equipment had encountered trouble because of the vibration caused by the pressure in several other factories. The interruption of the production usually causes heavy losses. Here a kind of vibration control divice was designed to solve the problem, and the numerical simulation was done, and a satisfactory result was gotten. To suppress the excessive vibration, a type of passive energy absorb support is designed applying shape memory alloy (SMA) string combined with polyurethane cushion, and placed at the elbow bend of the pipeline. As we know that SMA has large recoverable deformation ability, and has good ability of energy dissipation. By applying this ability to work out some passive energy dissipation device or applying the shape memory property of SMA to be as actuator, installing the device or actuator to engineering structures or industry facilities, the response of the structure or equipment subjected to various external excitations could be controlled. For the elbow bend of the pipeline under discussion, vibration can be divided into two directions: in-plane and out-of-the-plane. Here, only the out-of-the-plane vibration is discussed. The total length of the pipeline is very long compared to the elbow bend part, and the kickstands are closely spaced along the straight line section, which confined the rotation of the pipe at the kickstands and result in some overhanging beam effect in the elbow bend part of the pipe. Based on this understanding, the restraining effect of other part of
the pipe on the elbow bend section is simplified as a fixed end located at the kickstands of the elbow bend section. The elbow bend of the pipe can be modeled as a crank beam fixed at the two ends. The pipeline is modeled as linear elastic frame, and the energy absorb support is modeled as Bouc-Wen hysteretic model. The main idea of this energy absorbing support is to applying the super-elasticity of SMA, the SMA wires should therefore be pre-tensioned before getting to working condition. Using a random signal as input, the effect of vibration control is compared with different parameters of the SMA energy absorb support, and the control method is shown to be fairly effective for reducing the dynamic response in that not only the peak response is reduced but also the vibration duration is reduced apparently. Here come the conclusions: (1) The vibration response of the pipe is controlled evidently by only installing an energy absorbing support at the corner of the pipe. Not only the peak response value of the pipe is reduced by 46%, and the vibration duration is shortened evidently. (2) Installing an energy absorbing support at the corner of the pipe, not only reduces the vibration response at the supporting point, but also reduces the responses of the straight line section of the pipe. This is because the effect of damping on the responses of any structural system always behaves in a global manner. (3) To compare the effect of the control with different inclining angle of the SMA wires, the response of the pipe is calculated by taking the value of the angle to be 30◦ and 60◦ , respectively. The result shows that energy absorbing support with an angle of 30◦ achieves a better control effect than the other case. Moreover, the result also shows that the selection of the parameters of the support plays an important role in reducing the dynamic response.
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Enhancing the performance capabilities of seismically isolated buildings using multi-stage friction pendulum sliding bearings T.A. Morgan & S.A. Mahin University of California, Berkeley, USA
ABSTRACT One concern in the design of seismically isolated structures is the selection of bearing properties so that optimal performance is achieved over a range of excitations and performance metrics. For example, to withstand very severe near-fault motions, isolation bearings frequently become so large, stiff and strong that they provide little isolation during moderate or severe events. Experimental and numerical investigations are presented to characterize isolation bearings capable of progressively exhibiting different hysteretic properties at different stages of response and the feasibility of targeting these properties to achieve specific performance goals for a range of ground motion intensities and structural dynamic characteristics. A newly developed triple pendulum isolator
incorporates four concave surfaces and three independent pendulum mechanisms. Pendulum stages can be set to address specific response criteria for moderate, severe and very severe events. This paper presents shaking table test results for a 1/4-scale seismic isolated steel braced frame. Three earthquake records were considered, and for each record, different hazard levels and components of excitation were applied. The test results confirm the beneficial effects of having isolator properties progressively change with displacement amplitude. Nonlinear dynamic analyses of the test specimen and more realistic building systems are also presented. Keywords: Seismic isolation, performance based design, friction pendulum, floor acceleration spectra
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Active optimal control of SSI system-based on the finite element model of SSI system F.X. Wang & J.P. Ou School of Civil Engineering, Harbin Institute of Technology, Harbin, Heilongjiang, China
1
GENERAL INSTRUCTIONS
A LQG control strategy based on the finite element model of SSI system is constructed to optimally control the responses of SSI system. The whole finite element model is reduced into a smaller set of DOFs system which can be measured, using substructuring analysis. This reduced DOFs system is used to design the active controller including the complete information of soil structure interaction. Then the modified gain G based on this reduced DOFs system using LQG control strategy is obtained. If only retaining the DOFs of superstructure in reduced DOFs system, gain G has the same dimension as gain Gr obtained by fixed-base assumption system. Therefore gain G is the modified value of gain Gr . 2
SIMULATION ANALYSIS
The influence of the boundary condition and the depth of soil layer on control effectiveness are investigated using the proposed method. A five storey building with SSI effects is used to demonstrate the proposed approach. The results show that different boundary conditions can get almost same control effectiveness, but depth of soil layer will influence the control effectiveness in some degree. And the control effectiveness of proposed method is better than that of lump-parameters model.
foundation is put into the soil box. This system used to simulate the interaction between structure and soil. The AMD is fixed on the top of the structure. The control strategy of test adopts the proposed method to design the AMD controller. The control effectiveness is compared between the proposed control strategy and the lump-parameters model control strategy. From the results, it can be found that the proposed control strategy can more effectively control the acceleration than that based on lump-parameters model. The responses of structure under different earthquake waves are different on account of those different features. Under El Centro wave and Northridge wave, the proposed controller and lump-parameters controller can both effectively control the peak response of the structure. However, under Kobe wave, AMD controller based on lump-parameters model can’t control the peak acceleration very well, even larger than the result of the uncontrolled system. Comparison to the AMD controller based on lump-parameters model, the control effectiveness of the proposed method is stable and obvious. 4
CONCLUSION
Some conclusions can be drawn through the simulation analysis and experimental study:
3 TEST STUDY A serial of AMD control tests of SSI system are performed. The test superstructure is 2-storey frame structure produced by Quanser Inc. of Canada. The small scale shaking table test system matching with this model. In this study, the bottom of the structure is fixed with the pile foundation, and then the pile
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1 The influence of the boundary conditions of soil layer to active control effectiveness is unobvious. Thus, the fixed boundary condition can be conveniently adopted to design the active controller. 2 The depth of soil layer can affect the control effectiveness in some degrees. It should be considered while to design the control strategy. 3 Compared to lump-parameters method, the proposed method can get a stable and effective control result. 4 The effectiveness of the proposed control strategy is experimentally verified.
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Hybrid vibration suppression of multiple vibration modes of flexible structures using piezoelectric elements and analog circuit K. Yamada, H. Matsuhisa & H. Utsuno Department of Mechanical Engineering and Science, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto, Japan
1
INTRODUCTION
Suppression of bending vibration of flexible structures like beams and plates using piezoelectric elements has attracted much attention among researchers. Those methods using piezoelectric elements can be divided into two categories; one is active vibration control and the other is passive vibration suppression. Generally the stability of systems is the most important in vibration suppression. The performance is also important in vibration suppression. From these reasons, several methods of hybrid vibration suppression have also been proposed. Authors proposed one hybrid method based on the passive one, and the effectiveness was validated. However, the method can suppress only a single vibration mode. Therefore, an effective method which can suppress multiple vibration modes was proposed in this study. The proposed method requires only analog circuits. The performance relevant to each vibration mode can be tuned independently. The optimum values of the circuits are formulated by making use of the two fixed points method, and the effectiveness of the proposed method and the theoretical analysis was validated by experimental results.
Figure 1. Model of the proposed hybrid method.
Figure 2. Experimental result with short circuit.
2
MODEL OF THE PROPOSED METHOD
A model of the proposed hybrid vibration suppression method which can suppress multiple vibration modes is shown in Figure 1.
3
EXPERIMENTAL RESULTS
The experimental result of the transfer function with a short circuit is shown in Figure 2. This result means uncontrolled. The experimental result conducted by the proposed hybrid method is shown in Figure 3. From
Figure 3. Experimental result of the proposed method.
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these results, the effectiveness of the proposed method was validated.
4
This method requires only piezoelectric elements and analog circuits. The effectiveness of the proposed method and the theoretical analysis was validated by experimental results.
CONCLUSION
A new method of hybrid vibration suppression which can suppress multiple vibration modes was proposed.
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Innovative sensing systems (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Sensor-integrated biofeedback smart system for measuring human biological expressions Y. Lin∗ & H. Cai Department of Mechanical and Industrial Engineering, Northeastern University, Boston, USA
EXTENDED ABSTRACT In the field of Human-Machine Interaction (HMI), understanding of human state becomes important and essential, especially with the evolving of more and more intelligent machines. Human mental states, such as emotion and mental workload, and cognitive behavior are known to be very sensitive to the task performance of a human-machine system; yet they are less understood and not effectively incorporated into contemporary machine systems. Take the drivervehicle system as an example, on one hand, advanced vehicle safety technologies, such as collision warning systems, can assist drivers in preventing potential crashes; however, the capabilities and limitations of the
∗
driver, to respond to these safety technologies, need to be carefully examined. How to reliably sense human state in real-time and in a non-intrusive way remains a challenge. In the current study, a non-intrusive sensorintegrated system was developed to detect human biological expressions. The following physiological parameters were collected by the biofeedback smart system: heart rate, skin conductance, skim temperature, respiration, gripping force and position. Experiments were carried out on this smart system and results are shown. This smart system has a great potential to be applied and extended to general intelligent human-machine interactions.
The corresponding author
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Study on spectrometer induced periodic fluctuant error in EFPI strain sensing system Xiong Gan, Yong Zhu, Hao Mei, Peng Zhang & Weimin Chen Key Laboratory for Optoelectronic Technology & System, Education Ministry of China College of Opto-electronic Engineering, Chongqing University, Chongqing, China
ABSTRACT The extrinsic Fabry-Perot interferometer (EFPI) strain sensor is a widely used strain sensor in the application of long-term bridge strain monitoring. In calibration experiments with loading step increment larger than 100 µε, the EFPI sensor shows very good linearity and accuracy. However, a periodic fluctuant error with a peak-to-peak amplitude about 12 µε was observed during precise continuous loading experiments with step increment of 0.2 µε. This periodic error restricts EFPI’s application on structures with small strain, such as rigid frame bridges. Furthermore, it decreases the credibility of the EFPI sensor and therefore discourages the spreading of EFPI sensor in new applied areas. It is necessary to investigate the reason and find a way to eliminate of this error. Measured by a spectrometer, the output spectrum of EFPI is a discrete function. Borrowing idea from discrete Fourier transform, a discrete gap transform (DGT) of output spectrum can be obtained with the variable gm , For a specified EFPI sensor with a gap length L, the DGT value of the output spectrum will reach its maximum when gm equal to L. Therefore, The gap length L can be figured out by searching variable gm and find the maximum DGT point. This is called DGT demodulation method. If the light source is an ideal broad band source, the output spectrum of an EFPI sensor is a cosine function, and its DGT curve is an impulse. The x axis position of the impulse represents the gap length of the EFPI sensor. In our EFPI system, the light source has a Gaussian spectrum. The DGT curve of the output spectrum became a Gaussian curve because of the convolution of a Gaussian function and the impulse. The x axis position of the maximum point on the DGT curve represents the gap length of the EFPI sensor. For a practical spectrometer, the CCD detector always has a dark current noise, which will add a background
spectrum noise to the output spectrum. The background spectrum noise could be described as a discrete rectangular function. The DGT transform of practical spectrum signal was the sum of the original Gaussian curve and the addition sine cardinal function coursed by the background spectrum. Therefore, the original max point of the Gaussian curve was changed by the sine cardinal function, and then gap length calculation error occurred. Furthermore, the error changes along with variation of the relative position between the Gaussian curve and the sine cardinal curve. For a specified spectrometer, the DGT curve of background spectrum (i.e. the sine cardinal curve) was fixed, but with the increase of the gap length, the DGT curve of EFPI’s spectrum (i.e. the Gaussian curve) moved continuously. The Gaussian curve is a unimodal function, and the sine cardinal function is a decaying periodic function; the peak of the Gaussian curve will be modulated periodically when there is a relative movement between them. The period of the sine cardinal curve, for the USB2000 spectrometer used in our system, is 1.24 µm, and which led to a maximum gap length calculation error about 0.62 µm. For an EFPI sensor with the sensing length of 50 mm, the 0.62 µm gap length error equal to 12 µε strain measurement error. The theoretical analysis agrees with the experiment results very well. To address the problem, a background spectrum subtraction algorithm was put forward. First of all, collecting a spectrum and then denoise it with a Mexican Hat Wavelet arithmetic. Secondly, calculate the average intensity of the background spectrum, and then subtract the average value from the real signal. Finally, perform DGT transform with the spectrum data without the background, and then calculate the gap length of the EFPI sensor. Demonstration experiments were carried on, and the experimental results showed that more than 95% of the periodic fluctuation error could be eliminated by the improved algorithm.
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Effect of photochemical oxidization on stability and SO2 sensing performance of porous silicon Xue-Ming Li, Xing Xiang & Li-Chun Wang College of Chemistry and Chemical Engineering, Chongqing University, Chongqing
As a novel functional material, porous silicon(PS) has nano-pores, a very large internal surface area and a good bio-compatibility. It has drawn considerable attention because of its strong photoluminescent property at room temperature. It can decrease the photoluminescent degrees of PS with increasing concentration of sulfur dioxide, except some gases such as oxygen, nitrogen and so on, which is the basis of sulfur dioxide sensing. A great amount of work has been done to modify it, because of it own shortages. The lightly oxidized PS is prepared by anodizing p-type single crystal silicon with a current density of 50 mA/cm2 for 20 min in electrolyte and photochemical oxidizing PS used high pressure mercury lamp(125W) to irradiate for 35 min, which is far more stability and sensitivity than the freshly PS made by electrochemical anodic oxidation. Comparing lightly oxidized PS with the freshly PS by means of scanning electron microscopy and infrared spectroscopy, both the structure and morphology are analyzed. The sensing performance is evaluated by the photoluminescence quenching of the lightly oxidized PS quantitatively. The results show that the surface of the freshly PS is covered with much rectangle pieces about 120 × 40 µm regularly. Each piece has imperceptible cracks and some of them burst. Its structure is very unstable because the silicon hydride band (SiHx , x = 1,2,3) on the freshly PS surface react with the ambient air easily. After photochemical oxidation, these rectangle pieces become smaller to decrease
the internal stress on the its surface, the stability is strengthened obviously, and partial Si-Hx band is replaced by Si-O band around 1114 cm−1 and OSiH band around 2249 cm−1 , which is different from natural oxidation in the air. Then PS irradiated by ultraviolet light with a selected wavelength between 240 nm to 300 nm may produce strong luminescence and its peak value is 640 nm which is typical porous silicon glowing. So the photoluminescent spectral measurement with the selected wavelength between 260 nm to 280 nm is feasible. When the lightly oxidized PS contacts with 1000 µL/L SO2 , the photoluminescent peaks intensity quenchs immediately, but when the pure N2 is injected to replace SO2 , the photoluminescent peak intensity recovers rapidly, which suggests that the lightly oxidized PS have good reversibility in SO2 sensing. Another set of experiments, which test the lightly oxidized PS in different concentration of SO2 , reveals the concentration of SO2 has positive correlation with the degree of the photoluminescence quenching. The lightly oxidized PS exposed in air for 60 day can still respond to SO2 , but its sensitivity falls. With the time passing by, the SiO2 film on the surface becomes thicker and size of the nanometer silicon hole decreases. The corresponding photoluminescent peak blue-shift and indeed the ability of photoluminescence loses because Si-Hx is oxidized to SiO2 on surface. It shows that the anti-oxidization of the lightly oxidized PS is obviously stronger than freshly etched PS, but the time exposed to air is limited and it is related to the preparation and after-treatment condition.
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Analysis and design of SMA damper Yan Yang1,2 , Hui Li & Jin Huang 1
Department of Mechanic, Chongqing Institute of Technology, Chongqing, China
Bo-seon Kang∗ 2
Department of Mechanical Engineering, Chonnam National University, Gwangju, Korea
Recently, the self-adaptive intelligent control devices based on smart materials is an active strategy to achieve performance-based structural design. Among all smart materials, shape memory alloy has been widely accepted because of it is a kind of smart material with several particular properties. It not only possesses the high drive force and intelligence, but also has properties of pseudo-elasticity and shape memory effect. SMA has the high damping capacity. The capacity can be used to develop the different kinds of dampers and actuators for structural vibration control. A certain TiNi shape memory alloy that was made by the Institute of Metals of CAS was used in this study. We get the damper force,
The Equation also is the design formula of the SMA wire damper. If we have known the value of F, we can suppose the number of wires and calculate the s, or we can suppose the s and calculate how many wires to be need. And then, we using some practical data calculate a example and design a new SMA damper. It is shown in following figure. Because the structure of damper is symmetrical, so we only explain the upper part. There are four SMA wires thrill through the piston rod 11. The one end of wires combined to make a one wire connect to the power supply 10. The aother end of wires thrill though the end cover 7 individually and connect to the voltage dependent resistor and switch 9. The power supply, SMA wires, voltage dependent resistor and switch make up of a loop. We weld two piston rods together and assemble all parts as shown in Figure 3. When there is pressure acting at piston 1 or ∗
Corresponding author
there is a pull acting at the piston 11, the SMA wires in the bottom will be elongated. At the same time, the check ring 2 will press the spring, switch and voltage dependent resistor, and then the loop switch on. As a result of the voltage dependent resistor’s action, the further the piston moves, the bigger the current transit in the loop. Because of the shape memory effect, the resilience of the SMA wires will be enlarged and the damper force of the SMA damper will be enlarged. By contrary, if there is pull acting at the piston 1or there is pressure acting at piston 11, the SMA on top will generate the SMA effect. Therefore, the damper can counteract the vibrations.
For testing the capacity of the SMA damper, we assemble it and a structure model to the vibration testing table and apply an aperiodic vibration to the structure model. Following figure shows the time histories of the structure displacements.
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The results of experiment indicate that besides a short feedback time, this SMA damper has selfadaptive ability as well as predominant vibration damping capability.
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Wireless thermometer-based on quartz tuning fork resonators J. Xu, B. You & J. Cui College of Automation, Harbin University of Science and Technology, Harbin, China
X. Li Computer Center, Harbin University of Science and Technology, Harbin, China
1
INTRODUCTION
High precise temperature measurement is an important part of modern metrology. In the last decade, advances in Micro-Electro-Mechanical-Systems (MEMS) technology, wireless communication and digital electronics have enabled the development of low-cost, low power, robustness, high-performance sensor nodes that are small in size and communication within short distance. These sensor nodes consist of sensing, data processing, power supply and communicating components. This paper presents the design and implement of a wireless quartz crystal tuning fork temperature sensor (QTFS) using Bluetooth technology. 2
PRINCIPLE AND EXPERIMENT
Wireless sensor network (WSN) is a novel high technology in the future, which is intend to replace the cables connecting the system to the sensor unit. In order to complete high precise temperature measurement through WSN, the resonant frequency temperature dependence of quartz resonators has been used for the measurement of the temperature. The quartz tuning fork temperature sensors are prepared of synthetic quartz with Q-factor over 6.104 on ZYtw-cut plates. The miniature frequencytemperature sensor in the form of thermo-sensitive quartz tuning fork resonators with vibrating in the flexural mode has been developed to design a high performance temperature sensor. The principle of the quartz tuning fork temperature sensor is that the resonant frequency of the quartz resonator will be changed with the variation of temperature. The frequency signal is compatible with digital circuitry eliminating the need for A/D conversion. The resolution achievable using a resonant sensor is much higher than traditional temperature sensors as the frequency can be measured with greater accuracy. Resonant sensors also have high sensitivity, high resolution, better long-term stability and low power consumption, which is very suitable for WSN.
The hardware architecture of the prototype consists of microprocessor, radio, voltage regulation, temperature sensor (QTFS) and battery. The operation of the WSN node is controlled by a TI C8051F020 MCU. Nordic Semiconductor nRF905 operating at 433 MHz license-free frequency band is used as radio transceiver. A CR123A primary lithium Battery specified with 1.5 V/1600 mAh capacity and from −40 degree C to +60 degree C operating temperature is selected as power source. The TinyOS operation is utilized for source management, which is designed for WSN. The TinyOS can be used to realize various applications based on component-based structure and the core program processes a little memory which is suitable for restriction in WSN node. The multi-hop soft uses a shortestpath-first algorithm with single destination node and actives two-way link estimation to realize the router for receiving and transmitting packages. Experimental results show that temperature sensing is implemented by a QTFS. The sensor has 0.05 degree C accuracy from −50 to 50 degree C.A user can examine the temperature measurement of sensors through Web browser.
3
CONCLUSIONS
In this paper, we have presented in detail the architecture of wireless temperature sensor based on quartz tuning fork resonators to utilize remote temperature measurement through WSN. It is more convenient to measure temperature without wire, and the node is easy to be deployed in the experiment. The use of Bluetooth technology for wireless communication ensures reliability which is particularly important in industrial and other critical monitoring application.
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Transformative application of smart sensor technology in health monitoring
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Non-contact ultrasonic rail flaw detection Stefano Coccia, Ivan Bartoli, Piervincenzo Rizzo, Francesco Lanza di Scalea University of California, San Diego, California
Mahmood Fateh Office of Research and Development, Federal Railroad Administration, Washington, DC
Ta-Lun Yang ENSCO, Inc., Springfield, Virginia
Current methods for detecting internal flaws in rails rely primarily on ultrasonic pulse-echo technology operated in a water-filled wheel or sled. Presence and loss of echoes along each tested direction are analyzed in parallel to map internal cracks in the rail. While this technology has served the industry well, several inherent weaknesses exist. Contact heads and cross-sectional inspection limit the speed of the measurement; liquid couplant is required to maintain efficient wave/echo transmission through the contact patch. Even with the couplant, significant transmission loss results from the pulse/echo passing through the contact patch twice. More importantly, ultrasonic beams launched vertically from the top of the rail head can miss internal defects located under horizontal shelling; this was the case, for example, for the disastrous train derailment at Superior, WI in 1991. A system based on non-contact ultrasonic testing and robust feature extraction algorithms is under
development at UC San Diego under a Federal Railroad Administration research and development grant and with the technical support of ENSCO, Inc. This system uses a pulsed laser to excite guided waves traveling along the running direction, and an array of air-coupled sensors to detect these waves. The wave energy propagates equally in either direction from the laser beam impact if there is no blockage anywhere. Presence of cracks or other natural boundaries, such as rail joints or welds, between the two sensors will cause the observed intensity to differ. Thus, by comparing the measurements of two sensors, the presence and approximate size of any defect between the two sensing locations can be determined. Promising field tests were carried out in Gettysburg, PA in March 2006. Ongoing steps include the integration of this technology into a high-speed track inspection vehicle.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Recent developments in theoretical and experimental investigations with ultrasonic sensors T. Kundu, S. Banerjee, S. Das & C.M. Dao Department of Civil Engineering & Engineering Mechanics, University of Arizona, Tucson, USA
For several decades ultrasonic actuators and sensors have been used for nondestructive evaluation and structural health monitoring. In traditional applications longitudinal and shear bulk waves are sent into the structure and the reflected and/or transmitted signals are analyzed for detecting internal anomalies like cracks, inclusions, impurities and other defects. Guided waves have both longitudinal and shear components and propagate through waveguides like plates, rods and cylinders. Material inspection by guided waves is a relatively new technology although body waves have been used for this purpose for decades. Because of some inherent advantages of guided waves over the bulk waves, such as their long distance propagation potential, capability of reaching difficultto-reach regions, and multi-mode propagation characteristics the guided wave based inspection techniques are gaining popularity. To exploit the full potential of this technology good theoretical analyses of guided wave propagations in various structures along with experimental investigations are necessary. A newly developed technique called DPSM (Distributed Point Source Method) is employed in this paper to model few
practical engineering problems in the field of Nondestructive Evaluation (NDE) of structures. In this paper a brief introduction on DPSM method is presented. It is compared with few available techniques in the same arena and superiority of DPSM is proved by comparing the results from FEM (Finite Element Method) and DPSM. Following the basics of DPSM a brief theory on modeling wave field in multilayered solid structure with irregular interfaces is presented. Wave field developed in multilayered solid have been presented considering a practical problem with corrugated multilayered structure. An experimental investigation is performed to prove the benefit, advantage and accuracy of DPSM technique. An aluminum corrugated plate is considered for comparison. Need less to mention that such complicated surfaces can not be handled by existing techniques to model wave field in the referenced structure adequately and accurately. DPSM results and experimental results are presented in this paper in two graphs. These results are closely in consensus. DPSM can be widely used in NDE and real time structural health monitoring problems for better understanding of received signals by receivers.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Effects of environmental temperature fluctuations on vibration properties of concrete bridge structures M.P. Singh & H. Nandan Department of Engineering Science and Mechanics, Virginia Tech, Blacksburg, Virginia, U.S.A.
1
INTRODUCTION
The damage induced changes in the modal parameters such as frequencies and mode shapes obtained from vibration data are often used for damage identification. These dynamic characteristics of a bridge structure, however, are also affected by environmental temperature and humidity fluctuations. The modal properties can change due to thermally induced changes in the material elastic modulus, due to thermal gradients induced by transient thermal conditions, and due to boundary constraints which introduce geometric stiffness effects. It has been observed that these changes can often mask or accentuate the changes that could occur due to damage in the structure. In this study we examine the effects of the transient thermal conditions on the frequencies of a typical concrete T-beam bridge structure. To evaluate these effects the following sequential analyses are required: (a) transient thermal analysis considering radiation and convection boundary effects; (b) thermal stress analysis; (c) the system stiffness matrix formulation considering temperature dependence of material modulus and geometric stiffness effects; and (d) eigenvalue analysis. Based on the analysis of a selected bridge system exposed to the thermal variations recorded on a site in North Carolina, several factors that affect the modal frequencies under transient thermal conditions are identified. The results show that the system frequencies can change significantly due to seasonal variations, e.g. summer versus winter conditions. The most important parameter that affects the estimation of the system frequencies is the boundary condition. The second most important factor is the consideration of the asphalt layer in the model used. Although asphalt is not a structural component of bridge, it can significantly change the structural health monitoring
predictions if it is not include in the model. The effect is more pronounced in the winter months. The radiation is another important factor to consider as it can alter the bridge temperature significantly especially during the summer months. Thermal analysis with radiation shows the well-known fact that the surface temperature can be quite different from the air temperature especially during the summer months. However, this large temperature difference does not translate into a commensurate change in the system frequencies. The convection effects are hard to define as they depend on the wind velocity, but their effect on the frequency is relatively less. Simplified modeling of the thermal environment in terms of harmonic variations was also examined, primarily because thermal analysis for harmonic variations can be easily performed. This modeling approach is observed to be reasonably successful in predicting the frequency variations in the summer months but it requires some adjustments for its use in the winter months. Further refinements in harmonic modeling of the thermal environment to accurately predict the thermal effects on the modal properties are currently under investigation. In summary, the effects of the transient thermal environment on the system dynamic characteristics can be significant, and they must be explicitly considered in a health monitoring scheme. Some factors are more important than others. There is a possibility of including the thermal effects using simpler models of site dependent temperature and radiation variations. A more comprehensive study including other types of concrete bridges and for different site conditions is underway. This research is supported by National Science Foundation through grant no. CMMI-0700558 with Dr. S. C. Liu and Dr. D. Foutch as the Program Directors. This support is gratefully acknowledged.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structural damage identification using curvature flexibilities M.P. Singh & S. Bisht Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
1
INTRODUCTION
Modal parameter-based damage detection and quantification approaches have been of continued interest in structural health monitoring of civil engineering structures. The methods that utilize flexibility matrix to identify the damage are preferred over the stiffness matrix-based approach simply because the flexibility matrix can be more easily calculated with just a few modes than the stiffness matrix. The flexibility based approach, however, can be further improved if the curvature flexibilities are utilized instead of the displacement flexibilities. The paper describes an approach to define the curvature flexibilities and shows how they can be used for damage localization and quantification. Since curvature flexibilities are associated with rotational degrees of freedom which are usually condensed out from a dynamic analysis model and are not measured, an iterative approach is necessary to recover this information. The flexibility matrix of a structural system can be formed from its modal parameters (mode shapes and natural frequencies) as follows,
where [] is the matrix of mass normalized mode shapes and [] is a diagonal matrix consisting of the inverse of the squares of structural frequencies. This flexibility matrix however consists of only the measured degrees of freedom which typically correspond
to translational degrees of freedom. Using this flexibility matrix, the flexibility matrix corresponding to the condensed out (rotational) degrees of freedom can be defined as,
The above expression consists of partitions of the full structural stiffness matrix. Using the two flexibility matrices as given in Equation 1 and 2 a curvature matrix is defined. This is motivated by the fact that for each element change in curvatures at its two ends can be used as an indication of damage. By expanding the curvature flexibility matrix of the damaged structure about some known state, an iterative scheme is utilized to calculate the stiffness values for the damaged structure. Knowledge of the undamaged structure and modal parameters of the damage structure corresponding to the measured degrees of freedom are assumed to be given. The developed methodology is applied to three systems, a framed structure, cantilever beam, and a simply supported beam. In the case of beams the number of stiffness terms to be estimated for damage identification is not significantly more than the number of measured degrees of freedom. In these cases damage is accurately identified for single and multiple damage scenarios. However results from the frame structure seem to indicate that if the number of stiffness terms to be estimated are much more that the measured degrees of freedom the damage identification mythology might not able to correctly identify the damage in some cases.
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Innovative sensors and actuators
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A dynamic strain measurement system using fiber grating sensors and its application in structural health monitoring C.S. Shin, B.L. Chen & C.C. Chiang Department of Mechanical Engineering, National Taiwan University, Taipei, China
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3
INTRODUCTION
Fiber Bragg grating (FBG) sensors have found increasing uses in structural applications. Conventional interrogation systems for these sensors are often slow in speed and can only cope with quasi-static signals. Light intensity detecting techniques have been proposed for interrogating Fiber Bragg Gratings (FBG), but demonstration has been limited to the monitoring of static strain or temperature. In the current work, an all fiber interrogating system taking advantage of the edge filtering effect of a LPFG has been developed. The system is simple, low cost and fast responding. 2
EXPERIMENTS
The FBGs and LPFG were fabricated by side writing on single mode photosensitive fibers. The reflectivity of the FBG was about 95%, and the peak wavelength was about 1552 nm. The characteristic dip spectrum of the LPFG has a center wavelength of about 1540 nm and the dip loss was about 10 dbm. The capability of the system to measure high frequency strain variations was first demonstrated by sticking the FBG onto a multi-layer ceramic piezoelectric actuator, which was driven by a sinusoidal waveform that varied between 0–80 V at different frequencies. The system has also been applied to monitor the occurrence and responses to low energy impact on an aluminum alloy plate and a carbon fiber/Epoxy composite laminate by small missile impact. The FBG was stuck on the surface of the aluminum plate.and was embedded between the two middle 0◦ layers in a quasi-isotropic laminate with the lay-up sequence [90◦ / ± 45◦ /0◦ ]s. Impact was brought about by dropping a 68.8g blunt-headed hammer from a height of 12cm at various (r, θ) locations. Signal output was recorded by a high speed digital storage scope for further analysis.
RESULTS AND DISCUSSION
Test driven by the piezoelectric actuator showed the current system has an acceptable dynamic response at least up to 150 kHz. Small missile impact monitoring in an aluminum plate showed that the pattern of waveforms recorded are different when impact occurred at different distances and angular positions from the FBG. By characterizing the waveform signature it is possible to locate the approximate position of impact. The source localization results are derived from a single sensor. This made the stringent requirement of strict synchronization of the different sensors as in conventional differential time-of-flight technique unnecessary and the equipment cost can be much lowered. For the composite laminate with embedded FBG, the waveform signatures of a diagnostic impact at a fixed location before and after the occurrence of an internal damage showed some subtle differences. Such differences are difficult to discern by comparing the shape of the waveform as before. However, a Fast Fourier Transform showed a marked downshift of every peak frequencies when an internal damage exists. 4
CONCLUSIONS
A low cost and fast responding interrogation system for FBG based on intensity modulation has been developed. The system is capable of measuring dynamic strain variation up to 150 kHz. By using this system, it has been demonstrated the detection and location of small missile impact on a metallic plate can be achieved. Moreover, diagnosis of occurrence of internal damage in a composite laminate can also be made.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Distributed optical fiber sensors for deflection measurement of structure C.Y. Wang, H.L. Wang & M.H. Chen Center for Bridge Engineering Research, National Central University, Chungli, Taiwan China
1
INTRODUCTION
Many fiber optical sensors types and configurations have become available over the past two decades. This article is intended to provide a description of two applications of Fiber Bragg Grating (FBG) sensors on health monitoring of bridge structures. In the first case, there are 18 FBG strain sensors are installed on girders of a concrete bridge to monitor its longterm performance. In the first application example, the long-term variations of strain, girder deflection and truck over loading condition are calculated and reported to the owner to conduct the further maintenance works. Figure 1 shows an Athermal FBG sensor that can be installed on the concrete structure. It is called A-thermal just because of its wave length shifting is insensitive to the variation of temperature from 24◦ to 70◦ . The benefit of using the Athermal FBG sensor is of saving one dummy FBG gauge for temperature compensation in strain measurement. In the second case, the bending gauge, which was designed to measure the relative bending angle between two rods at the joint through the strains measured by the FBG gauges, was applied to develop a device so called “optical slope-deflection meter” to measure the dynamic deflection curve of a structure. The resolution of the bending gauge is 0.0004 degree and the operation range is ±1.5◦ . Structure response within 250 Hz can be measured, if the interrogator MOI SM425 is used. This measuring device and its associated calculation method provide another solution to monitor the transverse deformation along a long direction of a structure. 2
CALCULATION OF DEFLECTION
Through the measured strains, one can calculate the curvature at each cross section of the beam. In this monitoring project, 5 sets of curvature along the edge girder can be calculated. The girder is divided into
two parts. It is assumed that the curvature distribution in each part is a second order polynomial function as shown by Eq. (1).
There are 3 coefficients in each curvature function and can be determined by the measured curvatures in the part of beam. The deflection curve can be determined by integrating the curvature function twice. Those four integration constants can be determined by the boundary conditions and continuity conditions at the connection section. The second calculation algorithm for the deflection is developed based on the data of the relative rotating angle between the two arms at each gauge joint along the optical slope-deflection meter.
Equation (2) is a recursive equation and is used to calculate the deflection value (i = 1-4) by the measured data (i = 1-4). 3
CONCLUSIONS
Three cases of applying FBG sensors on bridge health monitoring and diagnosis are presented. Test results demonstrate that the optical Fiber Bragg Grating sensor is a good candidate for smart structure applications. Due to the small size and weight, electrical isolation, environmental ruggedness, and ability to be multiplexed, the optical fiber sensors enable health monitoring structure systems that would be difficult or impossible to implement using conventional electronic technology. The device has great potential to combine with a wide variety of instrumentation techniques for engineering applications.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Piezoelectric type real-time scouring monitoring sensor at the foundation of bridge pier C.Y. Wang, M.H. Chen, H.L. Wang & W.K. Fan Center for Bridge Engineering Research, National Central University, Chungli, Taiwan China
1
INTRODUCTION
Scour is always the primary threat to bridge piers. Since bridges will experience floods which may cause damage. Some damage from scour holes forming around bridge piers and abutments due to the time flood comes. Because scour holes will be refilled when flood dies away, the inspection of scour depth is not quite adequate to estimate the real scour damage. Therefore we need a monitor sensor to determine the Real-time scour depth and we come up with this piezoelectric type sensor. 2
Magnetic sliding collar: The magnetic sliding collar scour monitor is a simple, mechanical device for measuring maximum scour depth. The device consists of a stainless steel pipe that is placed vertically into the streambed with a sliding collar that drops as the scour progresses. The location of the collar is determined by sensing the magnetic field created by magnets attached to the collar. FBG monitoring system: An optical fiber sensory system, fiber Bragg grating (FBG) sensor which uses the cantilever mechanism to measure the local scour depth incurred during a flood. This FBG scour monitoring system can measure both the process of scouring and the variation in water level.
SCOUR & MONITORING SYSTEM
Here we list some available scour monitoring systems which are widely used: Sonar: The sonar scour monitor is a conventional sonar instrument connected to a datalogger that can provide an ongoing record of scour depth. A sonar instrument (also known as a fathometer or sonic sounder) measures distance based on the travel time of a sound wave through water. Underground radar: The underground radar works like sonar. The difference between them is sonar uses acoustic wave and underground radar uses electromagnetic wave. TDR sensor: Time Domain Reflectometry (TDR) technique operates by generating an electromagnetic pulse and coupling it to a transmission line or cable. The response signal changes if there is any variation in the current or potential. Underwater camera: Use something like web-cam to direct inspect structure members underwater and streambed conditions.
3
CONCLUSIONS
Local scour is the most critical, and it is generally caused by the obstructions of the structures with stream flow, which is one of the major causes for bridge failure. Without prior warning or sign of destruction to the structures, scour failure tends to occur suddenly. Therefore, it is important to measure or monitor the variation of depth of scour in every flood. From the experiment, we can easily find the sensor which is covered by sand, and simply get where the depth of the streambed is. Piezo-film scour monitoring system have been developed and tested in laboratory. This new monitoring system can not only monitor the variation of scour depth but also the depth of water even refill can be estimate. Compared with other systems, it is working without power, real-time, durable, sensitive and cost effective.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Tunable vibration absorber incorporating piezoelectric-magnetostrictive sensoriactuator Siu Wing Or, Ching Yin Lo & Helen Lai Wa Chan Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong
Ping Kong Choy ASM Assembly Automation Ltd., New Territories, Hong Kong
Tuned vibration absorbers are pre-tuned passive vibration absorption devices comprising a predetermined set of passively damped mass and spring to reduce the susceptibility to vibrations of a structure at a particular resonance frequency. Tunable vibration absorbers (TVA) often utilize smart materials as the principal tuning means to provide the distinct feature of tunable stiffness via an external tuning signal. With such tuning means, one may easily and precisely adjust the natural frequency of such a TVA to optimally match a structural resonance frequency and thereby absorb structural vibrations without adding any extra component and affecting the vibration levels of the structure at other frequencies. Unfortunately, the existing TVAs are incapable of self-sensing structural vibrations for the implementation of real-time, closed-loop tuning of their natural frequencies; they are limited to an open-loop mode of operation instead. Although it is possible to establish a closed-loop operation via an installation of vibration sensors (e.g. accelerometers) on the vibrating structures and/or on the TVAs, this method not only increases engineering costs but also leads to difficulties in assuring a reasonably high degree of TVA-sensor collocation.
Figure 1. A smart TVA prototype.
Therefore, we have developed a novel type of TVA, comprising a specifically designed piezoelectricmagnetostrictive (PE-MS) sensoriactuator connected to a mounting frame by two flexible beams coupled to axial ends of the sensoriactuator, to provide the
Figure 2. (a) Tunability, (b) sensibility and (c) absorbability of the smart TVA in Figure 1.
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real-time, closed-loop tuning capability in a simple, cost-effective and reliable manner (Figure 1). The sensoriactuator serves to produce an axial force for tuning of the natural frequency of the TVA, to gather the signals associated with structural vibrations and to provide a lumped damped mass for the TVA. By monitoring the sensoriactuator output voltage while adjusting its input magnetic field, the natural frequency of the TVA is tuned to the targeted resonance frequency of a structure.
In this paper, the working principle, design prototype and operating performance of a 63 Hz TVA are reported.A high tunability of natural frequency of 20% (Figure 2a) and a good sensibility of vibrations comparable to a commercial accelerometer are obtained (Figure 2b), together with a high absorbability of vibrations of 4 dB in a steel plate-neoprene resilient mounts structure (Figure 2c).
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A tailor-made MR damper for bridge cable vibration control: Experiment and modelling Z.H. Chen & Y.Q. Ni Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
S.W. Or & K.H. Lam Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
1
INTRODUCTION
Magnetorheological (MR) dampers have emerged as one of the most promising devices to suppress cable vibration in cable-stayed bridges, owing to their attractive features of minute power requirement, controllability, fail-safe operation, rapid response and low environmental sensitivity. While possessing controllable damping capability, the MR dampers are unable to monitor cable vibrations for implementing semiactive closed-loop controls, and are used merely as adjustable passive dampers in an open-loop mode in the current practices. Hence, a novel self-sensing MR damper system with an embedded PZT sensor has been tailor-made for real-time cable vibration control. Its laboratorial fabrication and characterization are to report. Due to the inherent nonlinear nature of MR dampers, one of the challenging aspects for development of appropriate control strategies that take full advantage of the unique features of MR dampers is to build models that can accurately describe their hysteresis dynamics. A dynamic forward model to represent behaviors of the self-sensing MR damper system is proposed based on both NARX (nonlinear autoregressive model with exogenous inputs) and neural network (NN) techniques. 2
FABRICATION, CALIBRATION AND PERFORMANCE VALIDATION
A self-sensing MR damper system, which is formed by integrating a conventional actuation-only MR damper (RD-1005-3) with a lead zirconate titanate (PZT) piezoceramic force sensor, has been devised and fabricated in the laboratory. After fabrication, the self-sensing MR damper was mounted on a Material Test System (MTS) 810 for calibration and performance tests. Force-control tests were conducted using sinusoidal excitations with various frequencies and
amplitudes for the PZT sensor calibration. Through investigating the experimental data, the PZT sensor is calibrated with a mean charge-to-force sensitivity coefficient of −158.248 pC/N. Performance tests were conducted under sinusoidal stroke excitations with different frequencies, amplitudes and input currents to the MR damper. Experimental outcomes verify the good force sensing capability of the PZT sensor. Characteristics of the MR damper are also observed by its hysteresis behaviors at different input current levels. Therefore, all the results validate the attractive force sensing-while-damping functionality of the self-sensing MR damper system. 3
FORWARD DYNAMIC MODELLING
In terms of NARX-based and neural network (NN) techniques, an NARX NN model is developed to describe the association between the piston displacement, velocity and the damping force at constant input current levels for the self-sensing MR damper system. The NARX NN is trained and validated by the Bayesian regularization with the LevenbergMarquardt optimization algorithm and the early stopping technique using experimental data. Network performances on different input configurations show that the damping force, which is available real-time due to the sensing function of the novel system, is extremely important for the modelling quality. A 9-121 NARX NN is eventually determined by analyzing the network performances over various neuron numbers in the hidden-layer and lag spaces for input quantities. Experimental data sets, with which the NARX NN has not been trained, are used to validate its modelling performance. Results demonstrate the accuracy and good generalization capability of the NARX NN model for the forward dynamics of the MR damper under periodic excitations, which will be further incorporated into a closed-loop control algorithm for real-time semi-active cable vibration control.
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Nano-scale materials for civil infrastructures
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Multifunctionality and smart structures-based on cement filled with nano-materials Hui Li, Huigang Xiao, Maohua Zhang & Baoguo Han School of Civil Engineering, Harbin Institute of Technology, Harbin, China
Jinping Ou School of Civil Engineering, Harbin Institute of Technology, Harbin, China Dalian University of Technology, Harbin, China
1
INTRODUCTION
Many works have been done to improve the compressive strength, flexure strength, ductility, fatigue, abrasion and chloride permeability of concrete, but no method could improve the integration properties simultaneously. Due to an ultrafine size, nanoparticles show unique physical and chemical properties different from those of the conventional materials. Nanophase materials were expected to improve the comprehensive mechanical property of concrete. On the other hand, cement-based composite filled with nanophase materials (CMFN) is strain self-monitoring because its electric resistance changes linearily with applied strain, which is named as “piezoresistivity”. Figure 1. Stress-strain curves of specimens at the 28th day.
2
MECHANICAL PROPERTIES
Figure 1 shows the stress-strain testing curves of Normal concrete and CMFN of 60 MPa strength grade. The full stress-strain curves of concrete containing nano-TiO2 demonstrated larger ductility in comparison with that of plain concrete. The enhanced extent of the strength, abrasion resistance and fatigue life of concrete containing nano-particles is much higher than that of concrete containing PP fibers.
3
STRAIN-SENSING PROPERTIES
The resistivity of CMFN decreased linearly with increasing compressive strain up to failure of the specimens. Strain sensor was prepared with CMFN based on this property. CMFN strain sensor was used to measure the strain of concrete column. CMFN sensors were located at the center of columns when poured concrete. Figure 2 shows the results of C40 column
Figure 2. Experimental results of C40 concrete column.
during compressive test, stress-strain curve of “–SG” was obtained by strain gauge and curve of “-CCN” was obtained by CCN sensor. The monitoring results of strain gauge and CCN sensor agreed well.
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4
CONCLUSIONS
The strength, ductility, abrasion resistance and fatigue properties of CMFN were all improved. The Cementmatrix composite containing nano-size semiconductor
is an intrinsically smart structural materials, it can perform as a highly sensitive stress sensor. The strain measured with CMFN sensor agreed well with that of traditional strain gauge.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Carbon nanotube film sensor S. Nagarajaiah Rice University, Houston, TX, USA
Z. Li J. Ray McDermott, Houston, TX, USA
P. Dharap Sea Engineering, Inc., Houston, TX, USA
E.V. Barrera Rice University, Houston, TX, USA
Carbon nanotubes have been investigated extensively at the nano scale. Several experiments have demonstrated the potential of single wall carbon nanotubes (SWCNT) as strain/stress sensors by relating the strain/stress of nanotube using Raman band shift. The electrical bandgap changes as a function of axial compression, tension stretch, torsion, and bending strain have been computed. It is possible to develop nano electro mechanical sensors because of the strong dependence of SWCNTs’ band structure on the mechanical deformation. SWCNTs exhibit superior mechanical properties in addition to electrical properties. Most of the studies to date relate the mechanical deformation with the change in electrical properties at the nano scale. The main objective of this study is to use the strain sensing capability at the nano scale to develop macro scale strain sensors. We propose the use of carbon nanotube films with isotropic properties due to random orientation of SWCNTs; such films can be applied to structural surfaces such as the skin of an aircraft wing to measure strain at macro scale. It is difficult to implement Raman spectroscopy for strain measurements at macro scale field applications, such as the measurement of strain in an aircraft wing. The use of conventional electrical resistance strain gages is limited to discrete points and fixed directional strain sensing. We propose the use of external probes to measure strain by contact with carbon nanotube films; the probes can be easily moved to a different direction or location to sense multidirectional and multiple location strain at macro scale.Additionally, strain gages are
Figure 1. SEM image of a carbon nanotube film: (a) plan view showing randomly distributed bundles of SWCNTs in a carbon nanotube film (scale 100 nm); (b) cross-section of the carbon nanotube film (scale 20 µm).
separate from the material; hence, not embedded. Carbon nanotube films can be integrated into the material, for example in composites; hence, can function as sensors and structural material as well. We demonstrate by experiments that carbon nanotube films can be used to measure strain at macro scale.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Nanostructured cement-based materials D.D.L. Chung & Sihai Wen Composite Materials Research Laboratory, University at Buffalo, State University of New York, Buffalo, NY, U.S.A
1
INTRODUCTION
Due to the rise of nanotechnology, the nanostructuring of cement-based materials is receiving increasing attention. This paper addresses practical nanostructuring of these materials by the use of admixtures, which include silica fume, carbon black, carbon nanofiber and water-soluble polymer. Both the advantages and disadvantages of the nanostructuring are addressed, as shown by comparative evaluation of materials with and without nanostructuring and materials with conventional microstructuring (such as that using microfiber). Comparison is made in relation to both the structural and functional properties. The properties include the basic mechanical properties, the vibration reduction ability, the electrical-resistance-based strain sensing ability, the electrical conductivity, the electromagnetic interference shielding effectiveness, the steel-cement bond strength, the embedded steel corrosion resistance and the degree of microfiber dispersion. 2
CONCLUSION
Cement-based materials that have been suitably nanostructured by the use of admixtures are attractive for some structural and functional properties. The admixtures include silica fume (0.1–0.2 µm), carbon black (30 nm), carbon nanofiber (0.1 µm diameter) and water-soluble polymer (methylcellulose). Silica
fume causes improvement in the vibration reduction ability (increasing both the damping capacity and the storage modulus), steel-cement shear bond strength, embedded steel corrosion resistance and carbon microfiber dispersion. Carbon nanofiber is superior to carbon microfiber in providing electromagnetic interference shielding, due to the skin effect. At the same content, both carbon nanofiber and carbon black are inferior to carbon microfiber in providing mechanical performance, electrical conductivity and electrical-resistance-based strain sensing. However, carbon black lowers the cost and increases the maximum feasible content of conductive admixture, due to enhanced workability. At the same content, methylcellulose is more effective than latex particles in improving the steel-cement bond strength. Cement-based materials that have been suitably nanostructured by the use of admixtures are attractive for some structural and functional properties. The admixtures include silica fume, carbon black, carbon nanofiber and methylcellulose. Nanostructuring improves the electromagnetic interference shielding effectiveness, the vibration reduction ability (both damping capacity and storage modulus), the bond strength of cement with steel rebar, the corrosion resistance of embedded steel rebar, and the degree of microfiber dispersion. Nanostructuring does not improve the electrical conductivity. Carbon nanofiber is less effective as a reinforcement than conventional carbon fiber.
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In-situ materials monitoring
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Rebar corrosion monitoring using novel embedded filament mini-sensors A. Holst, K. Hariri, H. Budelmann & S. Bruder Institute for Building Materials, Concrete Construction and Fire Protection (iBMB), Technical University of Braunschweig, Germany
INTRODUCTION Reinforcement corrosion is the main cause of premature deterioration of reinforced and prestressed concrete structures. Since a deteriorating infrastructure leads to increased costs, a timely assessment of the corrosion risk and an early detection of corrosion induced damages are of importance. This paper deals with the development, testing and use of novel filament mini-sensors for the evaluation of rebar corrosion initiation and progress in concrete members. Figure 1. Filament-sensors of two different types with varying wire diameter, front and rear side, without connecting cables and epoxy sealing; left: Sensor for initially concrete installation; right: Filament-sensor with prefabricated half-rounded mortar pieces for drill hole instrumentation (Ø 18 mm) with the plastic circuit board (PCB) in the center.
DESIGN AND MEASUREMENT PRINCIPLE OF THE FILAMENT-SENSORS With the newly developed filament sensor, cp. figure 1, consisting of several parallel arranged 0.065 to 0.5 mm thin iron filaments, the risk of the corrosion in the vicinity of the tendon can be monitored. If the depassivation (e.g. chloride) front reaches the sensor the thin wires will corrode very fast. The cor-rosion-induced fracture of each filament causes a significant step-like rise of the transition sensor-resistance. This effect can be measured easily e.g. by a standard ohmmeter or a resistive bridge circuit. The sensing wires are mounted at a plastic board at different depths within the concrete cover of the rebar or tendon. The sensor glued on a concrete spacer will be fixed in the accurate position on the steel reinforcement. For amplification and identification purposes at each wire a different series of SMD-shunt resistors is implemented. By grouping of several wires and by measuring the resulting parallel resistance only one data channel is required. For subsequent instrumentation, a profiled prefabricated double-semicircular, dense mortar cylinder made with ribs and grooves for the protection of the wires was designed. This sensor will be installed into a borehole by a shrinkage-compensated filling grout of very small thickness.
MEASUREMENT RESULTS AND DISCUSSION The functionality of the calibration-free filament sensor was demonstrated at concrete specimens and in a practical long-term experiment at a prestressed slab and at a trial bridge under chloride exposure. The single and multi-wire filament-sensors generally showed a good conformity with conventional electrochemical sensors. The erratic change of resistance due to corrosion fracture of a single wire, computable by Ohm’s law, was determined to 3 or 4 decades. With an increasing diameter of the sensing wire, the response time is ascending. The electric resistance of the multi-wire filament sensor is also affected by the additional parallel resistance of concrete and by the slight conductivity of corrosion products at the point of fracture. The sensor resistance shows a significant dependence on temperature only after the fracture of the filament. This effect can be used as a second fracture indication of the sensing wires. Misinterpretations can arise from voids and cracks in concrete or by deficient epoxy-sealing, thus the defect-free assembly is a prerequisite.
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Using tip-based fiber optic pH probes for the early detection of degradation in civil infrastructure Narissa Puran Polytechnic University, Department of Chemical and Biological Sciences
Gamal Khalil University of Washington, Department of Chemistry
Masoud Ghandehari Polytechnic University, Department of Civil Engineering
INTRODUCTION
UV-VIS Spectrum of Chlorophenol in PMMA/5%MAPTAC Matrix (Film) BKG: PMMA/ 5%MAPTAC (Film) Test Media: Iron (III) Chloride (FeCl3)
Fiber Optics Chemical Sensors (FOCS) are optical fibers that are used to monitor civil infrastructure to detect early degradation of the structure due to the influx of moisture into steel reinforced concrete and the leaching of metal chlorides into the structure due to corrosion and rust from weathering. Tip-based FOCS are optical fibers that are doped with a chromophore at the tip of the fiber which has a silica core, a fluoropolymer cladding and an epoxy resin buffer cladding, Light signals interact with analytes and the choromophore, reflect off of titanium dioxide (TiO2) particles at the tips and then travel along the optical fiber without losing intensity. This facilitates remote monitoring of degradation of civil infrastructure by monitoring the UV-VIS spectrum of the chromophore immobilized at the tip of the sensor in a charged polymer matrix.
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Figure 1.
UV-VIS Spectrumof Chlorophenol in PMMA/5%MAPTAC Matrix (Film) BKG: PMMA / 5% MAPTAC(Film) TestMedia: pH 5.0-7.0 2.5 pH 7.0 (0Min) 2
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EXPERIMENTAL SETUP AND RESULTS
This study analyzes the efficiency of three different low pH sensors which can detect the ingress of chlorides and acid rain into the structural material. The sensor films were doped with phenol red (phenolsulfonphthalein), chlorophenol red and phenol red covalently-linked to 3-trimethylammonium chloride (MAPTAC). Dyes were immobilized into 5% MAPTAC/95% poly (methyl methacrylate) (PMMA) matrix. The low pH sensors were tested for cross-sensitivity of iron chloride (FeCl3 ) of 1%, 2% and 3% media from pH 5.0–pH 7.0. Using UV-VIS spectroscopy, changes in the low pH sensor signal were detected at 550 nm and 575 nm. The results indicated that chloride
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Figure 2.
concentration could be monitored through changes of the absorbance level of 550 nm which is constant in changing pH levels as shown in Figure 1. Changes in pH levels can be monitored in changes of the absorbance level of 575 nm as shown in Figure 2. This demonstrates that this FOCS can be used to assess the
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stage of degradation of civil infrastructure due to the cross-sensitivity of the chlorophenol red.
Ghandehari, Masoud; Cristian Vimer. Molecular Mechanics for In-Situ Measurement of Moisture in Cement Mortar. Presented at American Society of Civil Engineering Proceedings. 2004.
REFERENCES Ganesh , A. Balaji; T.K. Radhakrishnan. Fiber Optic Sensors for the Estimation of pH within natural biofilms on metals. Sensors and Actuators B Chemical (2006) In Press.
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Moisture sensing in porous media S. Zheng Polytechnic University, Brooklyn, NY, USA
P. Spellane NYC College of Technology, Brooklyn, NY, USA
A. Sidelev & M. Ghandehari Polytechnic University, Brooklyn, NY, USA
1
INTRODUCTION
0.000008
Poly-MLM Adsoprtion
0.000006 0.000004 0.000002 2nd deriv absorbance
Molecular Vibration Spectroscopy In this article, vibration spectroscopy refers to the study of selective absorption of infrared light by mo-lecular species. As photons enter a material, some are reflected from its surface, some pass through the material, and some are absorbed. Such absorption ‘finger prints’ provide useful information for the identification of an analyte. The moisture sensor developed is made from a low OH glass 0.6 mm diameter fiber coated with the polymer tip and the stainless steel protective sleeve. The sleeve is glued to the fiber about 0.5 mm from the sleeve opening to overcome any capillarity effects. The fiber is prepared by removing a portion of the original cladding from the tip and polishing it. The uncoated is then coated with poly- MLM® or poly-MLC® and cured. Overall both sensor types using the two polymer types, show good results. In both cases full response time are approximately 5 minutes for ingress
wavelength 0 1775 -0.000002
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and approximately 15 minutes for egress. Yet in comparison the cellulose based sensor Chemsense-MLC showed greater signal level compared to the PMMA type sensor Chemsense-MLM.
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A model-free method for structural damage identification-based on dynamic strain sensing of distributed fiber optic sensors Zhishen Wu Department of Urban and Civil Engineering, Ibaraki University, Japan
Suzhen Li College of Civil Engineering, Tongji University, China
Most of vibration-based damage identification strategies to date are traditionally based on the dynamic responses from accelerometers, velocimeters and displacement transducers. Although various algorithms have been developed to make the most of these dynamic measurements, a challenge remains that these responses in translational degrees of freedom are global quantities of structures and have no clear relationship to a specific local damage even near the transducers. Moreover, the situation for multi-damages will be extremely intricate. The mutual influence of structural damages on these measurements makes it difficult to perform effective structural parametric and damage identification. In contrast, strain is a local response and may be used to concentrate on sensing the structural behavior around a localized region. Furthermore, stain measurements can be directly applied for damage detection with no need for an analytical structural model. A feasible distributed sensing system adaptable to civil engineering application on the basis of fiber Bragg grating (FBG) has been developed in our recent research. Different from most of traditional ways to focus on the usage of FBG sensor as a localized gauge for point or axial strain measurements, this innovative system is devoted to implementing distributed strain measurements by packaging long-gage FBG sensors
and then extending them in series or grids. In virtue of the high sampling rate of FBG interrogator, dynamic macro-strain distribution may be achieved with nice measuring precision. Based on this dynamic distributed strain sensing, a model-free method for damage locating and quantifying algorithm is introduced in this paper. Similar to mode shape, a modal parameter concerning macrostrain distribution is first constructed, named as modal macro-strain vector (MMSV). By taking a component of this vector as reference, MMSV can be then normalized to derive a damage index vector, which provides an indication to damage location and quantification. Numerical simulations as well as experimental studies have been performed to verify the effectiveness of this method. Moreover, this work further investigates the superiority of the proposed strategy for damage identification by comparing with the manners based on various features using acceleration measurements. Three acceleration-based methods, including modal strain energy based damage index method, curvature mode shape method and modal flexibility method, are employed for this comparative study. Numerical examples have shown that in the cases of single and multiple damages, the method using distributed strain measurements presents more effective and satisfied results.
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Educating next-generation engineers on smart structures technology
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Student society for research on intelligent structural systems at SNU J.K. Kim Seoul National University, Seoul, Korea
Seoul National University (SNU) has been offering a course named Structural Information Engineering at the undergraduate level since 2004. At the beginning it was intended to emphasize experiments but soon it evolved into an introductory course on intelligent or smart structural systems. The students had opportunities to become acquainted with sensor technologies, control theory, remote monitoring, and even robotics. In addition to the course, an undergraduate student society for research on intelligent structural systems (SSISS) was founded in fall 2006 with 12 members. The society’s members are expected to engage in the research and study of intelligent structures and systems. They will share information, knowledge and experience with each other and make them available to their fellow students and future society members. The student society and its activities are being supported by the Korea Construction Engineering Development Collaboratory Program (KOCED Program) as the society’s activities are expected contribute to the KOCED Program in many ways. I am currently serving as the director of KOCED PMC and as advisor to the society. At the time of the society’s formation, the KOCED PMC was in need of research assistants to develop application technologies and upload various kinds of data to the KOCED homepage. Hence the members of SSISS were offered the opportunity to work at KOCED during their winter vacation. While working for the KOCED PMC to develop application technologies, they engaged in experimental research on intelligent structural systems. They were allowed access to the experimental facilities owned by KOCED PMC including a desktop shaking table, a test-bed for the structural health monitoring and fiber optic sensor equipment. Even though the society has been in existence for less than a year, the results have been very promising. The students seemed to have gained much through the interaction with graduate students and full-time
researchers of the KOCED PMC. The benefits will increase if they are given the opportunity to participate in research projects early in their undergraduate program. Some important lessons, however, were learned from this experience. Members of the society commented that they should have been offered a wellprepared and well-organized introductory course before they started engaging in advanced experimental research. Some felt that it would have been very helpful if they had knowledge of Labview, CAD or C-Language. Step-by-step guidance by the advisor seems crucial in this context. The success of the society is also dependent on a dedicated advisor or advisors. Another important element of success would be having a committed sponsor. It can be the school itself. It can also be a research center in the intelligent structural engineering field. In order to strengthen the organization and to give its members a wider perspective and to equip them with a strong potential for professional achievement, globalizing the student society may be the next step in its development. This can be achieved by networking with similar student societies at universities distributed worldwide. It will accelerate the formation of a global human network of next-generation leaders in this field. But in order to make it work, appropriate guidance and generous support from various levels are prerequisite. To achieve progress in the globalizing endeavor, it may be very helpful if MOUs are agreed upon between universities pledging to support the student network activities. Initiative by government organizations such as the NSF will be critical to the success of the proposed network of student societies. The first part of this paper summarizes the brief history of SSISS at SNU. Next, the performance and achievement as well as important lessons learned so far are reported. In the last part of this paper, the global networking of student societies is proposed. Topics regarding the organization and operation of the network are also briefly discussed.
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Hysteresis-based structural damage detection using multi-resolution sensor data Yunfeng Zhang Department of Civil and Environmental Engineering, Lehigh University, Bethlehem, USA
Jian Li Guangdong Provincial Academy of Building Research, Guangzhou, China
Yunbyeong Chae Department of Civil and Environmental Engineering, Lehigh University, Bethlehem, USA
ABSTRACT This paper presents the results of a recent study on the performance of a hysteresis-based damage detection method when sensor data with multi-resolution levels is used. Real-time monitoring of hysteresis loop behavior derived from measured structural acceleration responses and ground motion provides a simple yet effective approach to make decisions about the performance and condition of civil engineering structures subjected to extreme events. However, real-time monitoring requires not only efficient damage detection method but also efficient data transmission from remote site. Transmitting huge amounts of monitoring data to central data processing station via communication network with limited bandwidth might cause significant time delay, especially during or immediately after strong earthquakes when communication bandwidth may become scarcely available because of possible damages to communication networks and a rise in emergency communication use. Innovative sensor data compression techniques are thus needed to facilitate
fast and reliable remote transmission of seismic data from monitored structures to central data processing station, especially during strong earthquakes. In this study, the effect of progressive data transmission with increased sensor data resolution levels is researched. Two progressive data transmission method, a wavelet-based method and a PCA-based method, are considered here. The accuracy of the hysteresis-based damage detection method with varying data resolution levels is studied using simulation data from a 6-story steel braced frame building subjected to earthquake ground motion. It is found that both the wavelet-based and PCA-based progressive data transmission method are capable of reducing the raw sensor data size by a significant amount while having only a minor effect on the accuracy of the hysteresis-based damage detection method. Using such a structural health monitoring system with builtin sensor data compression, engineers and rescue managers will be able to retrieve and analyze seismic data in real time during strong earthquakes, which enables rapid decision making regarding structural condition.
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Impact of mechatronics and smart structures on engineering education Victor Giurgiutiu & Lingyu Yu University of South Carolina, SC, USA
Due to the accelerated growth of electronics, computers and information technology industries, a gap has emerged between the teachings of traditional nonElectrical Engineering education (e.g., Mechanical Engineering, Civil Engineering, Chemical Engineering, etc.) and the skills expected of non-EE graduates entering the job market. A deluge of computers, sensors, microcontrollers, actuators has permeated present-day society. Microcontroller-based devices and smart structures are found in all aspects of our everyday life. Even the auto industry, a traditional mechanical engineering fiefdom, is putting tens of microcontrollers in a modern automobile, and plans to increase this number multifold as new technologies are being introduced. As revealed by a recent site visit to our university by BMW auto plant representatives, hybrid propulsion, 42-Volts wiring bus, “steer-by-wire”, “brake-by-wire”, collision avoidance, autopilot, etc. are being currently developed, and automobiles with such capabilities will hit the market in the near future. To acquire the “high-tech” skills required in job market, a proper designed interdisplinary courses to obtain electrical, electronics, and information technology is urgently needed for non-EE engineering students. Mechatronics is an emerging engineering area that will likely alter the fundamental nature of engineering education, particularly (and initially) in the disciplines of electrical and mechanical engineering. As an academic inter-disciplinary model, it has started in conventional engineering institutes in all the developed countries, with a wide acceptance from academic and industrial circles. The Mechatronics area of concentration could offer engineering students a multi-disciplinary education in design and product development processes. The discipline of adaptive materials and smart structures, recently coined as Adaptronics, is an emerging engineering field with multiple defining paradigms. Biological structural systems, for example, are the result of a continuous process of optimization taking place over millennia. Their basic characteristics of efficiency, functionality, precision, self-repair, and
durability continue to fascinate designers of engineering structures to-day. The emerging engineering fields of mechatronics, adaptive materials, and smart structures have captured the attention of many engineering professionals, academics, and government officials in recent years. This emerging engineering fields has known an explosive exposure at national and international levels, has generated a number of impressive technology demonstrators under DARPA, NASA, NSF and DoD sponsorship. Currently, the technologies are being transitioned from aero-space and military applications to the wider areas of civil, mechanical, and electrical engineering applications. A number of national and international engineering schools have already opened centers, laboratories, or units dedicated to research in this emerging technology have attracted millions of dollars of research money, and are producing technology demonstrations in cooperation and/or partnership with industrial firms, government labs, and small business concerns. When considering the interdependence of Mechatronics and Smart Structures, the subject of multidisciplinary programs and teams springs forward. Today’s engineering disciplines are increasingly intermeshed, and Mechatronics as well as Smart Structures are typical examples of such situations. It goes without saying that an engineering professional with Mechatronics specialization needs to have a sound basic knowledge in both Mechanical and Electrical engineering disciplines. The same could be said about a Smart Structures specialization. Much of our present effort is focused on bridging the traditional divide between Mechanical and Electrical engineers, on identifying means and methods to teach multi-disciplinary courses, to have multi-disciplinary teams working together on a common project. We think the case of Mechatronics and Smart Structures offers a very timely opportunity to do this in a continuous improvement effort that is currently taking place across the College of Engineering and Information Technology at the University of South Carolina.
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Connected control method experiment as an international benchmark in smart structures education R.E. Christenson & L.E. Loebach University of Connecticut, Storrs, Connecticut, USA
T. Watanabe & K. Seto Nihon University, Tokyo, Japan
Structural control is one realization of smart structure technology that has been shown to have great promise in reducing unwanted structural vibrations resulting from dynamic loads. The Connected Control Method (CCM) of structural control is where two or more adjacent structures provide interaction forces between one another to more effectively reduce responses. Passive, active and semiactive implementations of the CCM can be realized. Since the Summer 2002, undergraduate researchers from the US have been introduced to smart structure technologies through conducting passive, active and semiactive control experiments employing the CCM as part of joint research efforts between Profs. Seto and Watanabe at Nihon University
in Japan, and Prof. Christenson in the US. Within the context of the CCM experiments, undergraduate researchers learn structural dynamics, structural control (and the theory behind “fixed-point theory”), conduct system identification of bench-scale building models, and design, build and verify the performance of CCM experiment. The paper discusses the effectiveness of the coupled building experiment for teaching students structural dynamics, control and the connected-control method. Specifically this paper will highlight how coupled building experiments at Nihon University in Japan have been utilized as an international learning experience undergraduate US researchers.
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Teleoperation and teleparticipation of instructional shake tables using the NEES cyberinfrastructure S.J. Dyke1 , Z. Jiang2 , R. Christenson2 X. Gao1 & S. Courter3 1Washington 2 3
1
University, St. Louis, Missouri, USA University of Connecticut, Storrs, Connecticut, USA University of Wisconsin, Madison, Wisconsin, USA
INTRODUCTION
Bench-scale shake tables are an engaging tool for educating students at all levels about fundamental concepts in structural response and earthquake engineering. These tools allow for classroom demonstrations and hands-on experimentation on physical structures using modern instrumentation. Demonstrations for K12 students allow students to gain an understanding of earthquake motions. The University Consortium of Instructional Shake Tables (UCIST) was developed by Prof. Shirley Dyke in 1998 to enhance undergraduate and graduate education in earthquake engineering (Dyke et al. 2002, 2003). This consortium, headquartered at Washington University in St. Louis, was initially a cooperative educational effort between 23 universities associated with the three U.S. national earthquake centers and has expanded to over 100 institutions around the world. UCIST has endeavored to enhance the education of undergraduates through the procurement of instructional bench-scale shake tables, the development of curricula, and the dissemination of these tools to other institutions. UCIST has recently partnered with the George E. Brown Network for Earthquake Engineering Simulation (NEES, see Figure 1), a premier cyberenvironment project funded by the NSF. The recent establishment of NEES provides an excellent opportunity to increase the number of students that can be impacted by UCIST educational exercises, and to develop a collaboratory in earthquake engineering education. In partnership with the NEES Consortium, Inc. (NEESinc) we are leveraging the geographicallydistributed network of world-class experimental facilities, its connecting cyberinfrastructure, and its extended community of engineering and crossdisciplinary faculty from academic programs across the nation to provide undergraduates with exceptional learning opportunities. Implementation of the extensive array of cyberinfrastructure tools developed for
NEES research will enhance the learning process at the undergraduate level. Most of these tools are opensource and are being continually updated and improved by NEES, ensuring that updated, secure tools will be available for our needs. Our vision is to develop an international collaboratory of bench-scale earthquake engineering facilities that will engage a broad range of students by creating a series of shared laboratory exercises available for remote operation via the internet. Tools have been developed recently for the remote control (teleoperation) and the viewing and analysis of streaming data and video (teleparticipation) for the instructional shake tables over the internet. These capabilities have been incorporated into formal laboratory exercises, and in the fall of 2007 we will be deploying these exercises to several universities within the US. Over the next couple years, several new exercises using these capabilities will also be developed. Further information about the UCIST, as well as Educational Modules, Lab Exercises, Teleparticipation and Teleoperation Tools, and all documentation for these activities will be made available at: http://cive.seas.wustl.edu/wusceel/ucist/ . For more details on how to participate in or partner with this educational collaboratory please contact Prof. Shirley Dyke at
[email protected]. ACKNOWLEDGMENTS Partial support for this project is provided by the National Science Foundation, DUE 0618605. Support for development of the UCIST was provided by the NSF, DUE 9950340. Undergraduate research assistants involved in the development of these activities have been supported in part by the National Science Foundation Research Experiences for Undergraduates Program at Washington University (NSF Grant No. EEC–9820506). All of this support is gratefully acknowledged.
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Course material development for a graduate course on structural health monitoring H. Huang Dept. of Mechanical and Aerospace Engineering, University of Texas at Arlington
1
INTRODUCTION
Structural Health Monitoring (SHM), having the capability of providing autonomous inspection of critical structural components, has become an increasing important technology in mechanical systems, civil infrastructures, and air-borne vehicles, etc. SHM systems could potentially prevent catastrophic failure, eliminate manual inspection, and reduce unnecessary maintenance, leading to higher confidences on structural safety and significant reduction in operation costs. Moreover, real-time SHM systems could provide in-service loading information of the structural components that can be utilized for better specification of input parameters for simulation models and improvement of design guidelines. In order to realize these advantages, it is of paramount importance that a new generation of researchers is educated and well-trained in applying the fundamental concepts and state-of-the-art SHM technologies to solve real-life engineering problems. Because SHM research is multi-disciplinary by nature, traditional disciplinary-oriented education program at university is no longer sufficient in producing all-around undergraduate students that are well-prepared to participate in graduate studies in the area of SHM. This paper presents a new graduate course on SHM that was delivered at the University of Texas at Arlington in spring 2007.
2
The course does not have any pre-requisite as it was intended to attract students from different disciplines to SHM technology. Among the four students enrolled, two were PhD level graduate students and two were Master level students. Each comes from a different department. Despite active searching for a textbook, no suitable textbook was found. Therefore, course materials were developed using a number of books and published papers as references. Class notes were handed out at each lecture and posted on WebCT in lieu of a textbook. The learning objects were defined as: 1) Understand the basic concepts of SHM and its applications; 2) Have a basic knowledge of data acquisition, sample theory, digital signal processing techniques; 3) Understand the basic characteristics of measurement systems; 4) Familiar with finite element modeling of structural vibration and common vibration testing equipment and techniques; 5) Understand the important applications and limitations of guided stress wave SHM methods; 6) Understand the main concepts in optical fiber sensors and their applications for SHM. Students were evaluated in several different ways, including five homework assignments, one classroom presentation, two mid-term projects, one close-book exam, and one final project. In general, the students performed well in written exams, programming related tasks, and course materials delivered at classes. The projects revealed the weaknesses in the students’ experience with hardware related subjects and their capabilities of applying materials taught in class to solve more complicated problems.
COURSE DESCRIPTION
The course is intended to introduce the basic concepts of SHM technologies with an emphasis on sensor technologies. The course materials were divided into four modules: fundamentals of SHM, vibration-based damage detection, guided stress wave for SHM, and optical fiber sensors. Two projects and one final project were designed to give the students the opportunities to apply the theories taught in classes to practical problems.
CONCLUSIONS Based on the experience of teaching the course for the first time, it is suggested that more projects and lab sessions should be planned to address the students’ weakness in experimental skills. Collaborating with other instructors to develop a curriculum program on SHM is also recommended.
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Signal processing for SHM
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Bridge scour surveillance using guide electromagnetic wave technology X.B. Yu & X. Yu Department of Civil Engineering, Case Western Reserve University, Bingham, Cleveland
1
INTRODUCTION
Bridge scour or bridge sediments scour is the lowering of streambed around bridge piers or abutments. Bridge scour has caused the collapse of many bridges at service. It is also a major factor contributing to the high construction and maintenance costs of bridges in the United States. Proper scour prediction is essential for an economic and safe design of bridge piers and abutments. The current design relies on the empirical scour prediction equations generated from laboratory data, which do not adequately predict the actual scour under field conditions. Collecting scour data from the field is necessary to improve the existing scour prediction theory. The data will also assist the deployment of scour countermeasure and real time surveillance systems. Thus Real time monitoring of bridge scour is important from both safety and economic considerations. 2
METHOD OF INVESTIGATION
In response to the fact that current tools for scour measurement generally do not perform satisfactory under field conditions. This paper introduces the use of guided electromagnetic wave technology called Time Domain Reflectometry (TDR) to accurately monitor the extent of scour, sediment status, and river conditions (Fig. 1). With the use of wave-splitting theory, information including the distribution of sediment with depth can be determined. The system helps to accurately assess the earth pressure on bridge piers and abutments as well as the effectiveness of scour countermeasures. The information provided by the scour monitoring system together with survey of superstructures conditions is integral components of a bridge management system which ensure the safety and cost-effective bridge safety assurance.
Figure 1. Schema of a typical TDR system.
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MAJOR CONCLUSIONS
Based on established theory and relationships, a simply application framework for bridge scour has been developed, which is amendable to be developed into an automatic algorithm. A laboratory experimental program was conducted to validate the theory for scour signal interpretation. Simulated scour/sedimentation tests were performed in tap water and water with different salt concentrations. The theoretical bases and application schema were validated from the collected data. It was found TDR signals changes systematically with the thickness of sediment layer. Application of the analyses algorithm and procedures results in satisfactory results of scour depth. Research will continue to further validate and refine this concept to develop practical instrument for bridge scour monitoring.
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Research of deteriorated data restoring in nonlinear system ShunRen Hu, WeiMin Chen, YuMei Fu & ZongBao Liang Key Laboratory for Optoelectronic Technology & System Under Ministry of Education
1 ABSTRACT Because the service life of the span bridge may last several decades, even hundred years, the bridge structural health monitoring system acquires enormous data automatically and continuously everyday. Despite the acquisition system of the bridge structural health monitoring system is designed by the advanced sensors, the deteriorated data are generated by much reason in data acquisition system and transmission system, and these data are unavoidable. However, the data analyst of the bridge deals with simply the deteriorated data, or don’t do any thing ultimately. So, the distorted data are the main reason to bring the illusive alarm (above 80%), meanwhile, these data are nonlinear and don’t filtered by common methods. In this study, the paper try to study the correlation relation of the bridge deflection checking points from bridge’s enormous deflection data, and take the ChongQing MaSangXi Yangtse bridge’s structural health monitoring systems as research object to
analyze how to restore deteriorated deflection, which is one most parameter of bridge structural health monitoring system, and it occurs vertical displacement when bridge was loaded or self weight. Because the span bridge deflection change is very little and the precision should be below 0.1 mm, the photoelectric imaging deflection meter system is used by the ChongQing MaSangXi Yangtze River bridge, which is composed of the light target, digital camera and compute. According the deflection data character and none-linear approximation of RBF neural networks, a novel method based on the correlation analysis of bridge’s checking points and the RBF neural networks is proposed for restoring nonlinear deflection when this checking point is deteriorated at some times. Compared with conventional methods (its MSE is 4.3815), the proposed approach (its MSE is 0.7973) assures more accurate and accords with practice. Simulation results verify the effectiveness of the designed method and theoretical discussions.
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Development of a signal processing tool to remove vehicle induced vibration signals from recorded seismic data for the vibration-based SHM Mansheng Wang University of Alaska Anchorage, Alaska, USA; University of Science and Technology Beijing, China
Yibin Zheng University of Virginia, Virginia, USA
He Liu University of Alaska Anchorage, Alaska, USA
One of the major problems without satisfactory solutions in structural health monitoring is the fact that environmental changes are responsible for changes in features of interest as much as the damage itself. Especially for bridges, vehicular vibration signals may make the recorded seismic data difficult to use. The objective of this paper is to apply signal processing technology to remove vehicle vibration signals form contaminated recorded seismic response data of bridges. The paper presents the corresponding assumptions and preliminary method of the signal processing to solve this problem. An example application of this method to the recorded data from a bridge with a vehicle passing
during a weak seismic event is given in the paper. By comparing the moving speed of vehicle induced vibration signal calculated from the crosscorrelation sequence functions with the possible driving speed of the vehicle, it is demonstrate that the cross-correlation sequence functions are reasonably effective in the example. The decomposed recorded earthquake response data from the bridge were briefly validated by spectral ratio analysis with the site earthquake acceleration as input and the decomposed earthquake response as output. The work presented here is only preliminary study in signal processing with typical conditions.
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Smart materials and structural systems
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Multi-scale modeling for electro-mechanical coupling of ferroelectrics Yansong He∗ , Jinhong Fan∗∗ , Zhongming Xu∗ & Yuan Wang∗ ∗The
State Key Laboratory of Mechanical Transmission, Chongqing University, ChongQing, China of Engineering, Alfred University, New York, USA
∗∗ School
Multi-scale analysis is motivated by the development of high resolution equipment for microstructure characterization, powerful computers and computational techniques. Although scientists and engineers have been aware of the significance of multi-scale analysis of material properties for some time, the analysis still remains in its infancy. Ferroelectric ceramic is an aggregate of thousands of randomly distributed grains. A multi-scale modeling scheme for electro-mechanical coupling of ferroelectrics is proposed. The scheme is effective for quantitatively analyzing relationships among variables of micro/meso/macroscopic scales. To make the description of the historic dependent switching process simple and accurate, we introduced a parameter that is objective, monotonically increasing, and closely related to the domain switching process. In the α -sort domain switching system the most important physical quantities intrinsically related to the switching process are the increment of normalized remanant strain, dSα and normalized remanant polarization, dPα along that switching system,
where ε0 , p0 are parameters of spontaneous strain and polarization respectively. The definition of the change rate of microstructure may be pertinent for description of the α-sort domain switching process:
where z is a monotonically increasing variable whose increment is defined as follows:
α where Gth is a material parameter indicating the threshold of material switching resistance, M denotes the domain wall mobility, which closely related to the microscopic local environment surrounding the domain switching. It may relate to defects, electronic structure, impurity, and domain/grain boundaries. To make an increase of fα , there must have be sufficient driving force:
The greater the difference between the driving force Gα and the critical resistance Gcα , the more driving force is available to drive more atoms switching. The methodology is exemplified through investigating behavior of ferroelectric material of PLZT. The key for connection of variables at different scales is through the remanant polarization and remanant strain at the meso-cell. This is physically sound in the sense that it can describe progressive domain switching. The meso-micro-linkage is realized by constitutive equation of the meso-cell (grain) through making remanant strain and remanant electric displacement explicitly expressed by microscopic volume fraction. Switching saturation and limited interactions between different switching systems are successfully accounted for. Numerical results showed that the well-known nonlinear butterfly curve of strain versus electrical field is described. It was found that pre-compressive stress will facilitate the domain switching if the switching makes tensile strain reduced, or compressive strain increased. The predicted effects of compressive stress on electro-mechanical coupling are consistent with existing experimental results.
Kf is a weighting coefficient. The evolution law of f α can be proposed as follows:
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Smart ties for the retrofit of arches and vaults M. Dolce Italian Dept. of Civil Protection, Rome, Italy
D. Cardone DiSGG – University of Basilicata, Potenza, Italy
1
INTRODUCTION
Metallic tie-rods are frequently used in arches and vaults to absorb the lateral thrusting forces due to gravity loads or inertial forces caused by an earthquake. Traditional tie-rods, however, have some limitations. First, the pre-tensioning operation is not easy, and the tension force in the tie-rod is often different from the expected value. Second, metallic tie-rods are sensitive to temperature variations, which can produce significant changes in the tensile force. Third, under seismic cyclic actions, traditional tie-rods do not dissipate energy and tend to buckle or to slip with respect to masonry when compressed, while the subsequent recovery of tension in the tie-rod produces impact, and then damage, to the anchorage masonry area. Shape Memory Alloys (SMAs) can be used to enhance the performances of metallic tie-rods both in service and seismic conditions. This is achieved with the Tensioning Control Block (TCB) system, which basically consists of pre-strained superelastic SMA wires, put in series with the metallic tie-rod. The number and diameter of the SMA wires is selected based on the force levels to reach. The length is optimized with respect to the thermal behavior of the system. A number of theoretical and experimental studies have been conducted to fully understand the thermal and mechanical behavior of TCB. In the paper, the main outcomes of these studies are described.
2
as follows: (i) calibrating the stress in the tie-rod during the pre-tensioning process, (ii) avoiding buckling under negative displacements, (iii) applying the force in the tie anchorages without jerks during an earthquake, (iv) restraining the structural deformations, if a given threshold displacement is exceeded, under unexpected earthquakes, (v) dissipating a considerable amount of energy during an earthquake. 3
SUMMARY OF RESULTS
The thermal behaviour of metallic tie-rods equipped with TCB has been examined through both numerical simulations and experimental tests. The force changes in the tie-rod due to temperature variations can be drastically reduced by using the TCB system. By referring to a steel tie-rod with 10 m length, working at 180 MPa at 20◦ C, and subjected to temperature variations of ±20◦ C, for instance, force changes of the order of 15% are found for the tie-rod with BCT, while of the order of 30% for the tie-rod w/o TCB. The effectiveness of TCB in limiting force changes due to temperature variations increases while decreasing the work stress level in the tie-rod. It is also affected by the SMA characteristics, particularly by the transformation temperatures of SMA in the stress-free state. Another advantage of TCB is the possibility to increase the damping capacity of the structure under seismic excitations from about 5–7% to 14–18%. REFERENCES
FUNCTIONAL PROPERTIES OF TCB
The main goal of TCB is that of limiting force changes in the tie-rod caused by temperature variations. This result is achieved by exploiting the thermal behaviour of superelastic SMA wires, which is antagonistic with respect to that of metallic tie-rod (i.e. stress increases, instead of decreasing, while increasing temperature). The TCB system, moreover, allows to achieve a number of additional objectives which can be summarised
Bekker, A. & Brinson, L.C. 1998. Phase diagram based description of the hysteresis behavior of shape memory alloys, Acta Mat., 46(10): 3649–3665. Dolce, M. & Cardone, D. 2001. Mechanical behavior of SMA elements for seismic applications – Part 2 Austenite NiTi wires subjected to tension, Int. J. Mech. Sciences, 43(11): 2657–2677. Funakubo, H. 1987. Shape Memory Alloys. New York: Gordon & Breach Science Publishers.
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Seismic performance of cellular-solid shear walls L. Chen & P. Tsopelas The Catholic University of America, Washington, DC, USA
1
INTRODUCTION
Cellular solids with deterministic periodic topologies show great potential for applications as response modification elements within structural systems, due to their ultra-light and good thermal properties. Response modification elements can provide additional stiffness and strength, resulting in reduced inter-story drifts and accelerations. A light-weight cellular solid shear wall could work efficiently for vibration mitigation in large scale structural systems. 2
CELLULAR SOLID SHEAR WALL SYSTEMS
Utilizing cellular solids to assemble shear wall elements for use in vibration mitigation of large structural systems could offer some advantages over the use of Steel Plate Shear Wall (SPSW) or Composite Shear Wall (CSW) systems. Cellular-solid shear wall systems i) are not prone to out of plane buckling as the SPSWs, ii) can offer flexibility to a designer in achieving a balance between stiffness, strength, and ability to dissipate energy, iii) are light weight compared to CSWs, iv) can be utilized as response modification elements, and iv) could be used as architectural elements within a structural system. Cellular solids are multi-phase composite structures. Although the mechanical properties of unit cells are neither isotropic nor homogeneous on their microstructure, the macroscopic behavior of cellular solids is considered homogeneous. The shape, size, orientation, and geometric properties of a unit cell from a cellular solid influence the mechanical properties of a cellular-solid shear wall. To achieve optimal design, Finite Element models (ANSYS) are developed to predict the stiffness, strength, and energy dissipation effectiveness of shear wall panels with cellular solids.
When cell orientation angles are relatively small, the cell walls are experiencing mainly bending response. For orientation angles is larger than 20◦ , the cell wall deformations are manifested as axial deformations resulting in increased stiffness and yielding strength. The increase in yielding strength is due to a more uniform axial yielding along the length of the cell walls and the increased amount of the material that undergoes plastic deformations. The pre-yielding stiffness, the yield strength, and the post yielding stiffness are strongly affected by (l/t). Higher values of the (l/t) ratio result in an apparent decrease of the density of the cellular solid. The behavior of a cellular solid with the vertical walls of regular honeycomb cells oriented by φ = 30◦ is studied under cyclic loading.The hysteretic response of such a cellular solid is not symmetric. This is due to buckling experienced by a column of cells. When the cell walls are under compression, a number of them buckle. That causes the cellular solids to loose its ability to resist loads through axial actions/deformations. The resulting asymmetric hysteretic behavior is similar to the response of a brace in a braced-frame structure under cyclic loading. Under tension the cell walls yield almost uniformly resulting in stable hysteretic response with significant yielding strength and post yielding stiffness. 3
SEISMIC RESPONSE OF CSSW SYSTEM
To evaluate the performance of a structure fitted with cellular solid shear wall (CSSW), models of a threestory structural frame with/without cellular solids shear wall panel are compared under seismic excitation. The 3rd story responses in terms of drift, shear force and CSSW force are presented. It is observed that the story drift and the story shear were reduced due to the energy dissipation ability of the CSSW system.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Assessment of adhesive bond strength in laminated safety glass S. Huo & H. Reis University of Illinois at Urbana-Champaign, Urbana, Illinois, US
EXTENDED ABSTRACT
Table 1.
Laminated safety glass consists of a plastic interlayer with two adjacent glass plates, and is used in automotive applications as well as in architectural applications, see Figure 1 and Table 1. The level of adhesive bond strength between the plastic interlayer and the two adjacent glass plates plays a significant role in the penetration resistance against flying objects. Penetration is prevented mainly by absorbing the kinetic energy through stretching the plastic interlayer, delamination between the plastic interlayer and the two adjacent glass plates, and fracture of the two glass plates. Laminated safety glass samples with different levels of adhesive bond strength were manufactured and tested using mechanical guided waves. The results were then compared with those obtained using the commonly used destructive testing method, i.e., the pummel test method.The imperfect interfaces between the plastic interlayer and the two adjacent glass plates in laminated safety glass were modeled using a bed of longitudinal and shear springs, and their stiffness characteristics were estimated using fracture mechanics concepts. The area of contact at the interfaces between the plastic interlayer and the two adjacent glass plates for each of the laminates was estimated
Materials properties for the laminated safety glass.
Long. Shear Thickness Denisty E Poisson Attenuation Attenuation np/m np/m (mm) g/cm3 GPa Ratio Glass 2.54 PVB 0.762
2.5 1.1
72 0.25 3.9 0.34
0 8.5106
0 43.478
Figure 2. Predicted and experimentally obtained energy velocities for safety glass samples with different adhesion levels (i.e., different pummel ratings) at 350 kHz.
via surface characterization experiments using atomic force microscopy measurements.The predicted energy velocities were validated using guided wave energy velocity measurements for each of the laminates (with different pummel test ratings) for the S0 mode. The results are shown in Figure 2. The experimentally obtained results were in good agreement with the predicted results, and the experimentally measured energy velocities of the S0 mode showed good correlation with the adhesion level of the laminated safety glass samples. Figure 1. Schematic diagram of guided wave measuring system to assess levels of adhesion in safety glass.
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Smart structural systems
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Development of fragility relationships for smart structures E. Taylor, W. Barnawi & S.J. Dyke Washington University in St. Louis, St. Louis, USA
1
INTRODUCTION
To mitigate the dynamic effects of earthquakes in structures, several classes of response modification strategies have been developed, including passive, active, and semiactive devices. Structures with supplemental control systems have been shown to reduce the responses during large earthquake events. Although recent studies on controlled structures have mainly focused on modeling, performance and control strategies, a systematic study on the vulnerability of controlled structures has not been conducted. Seismic risk assessments are becoming more valuable to mitigate future losses. A fragility analysis considers the conditional probability of a system meeting or exceeding
Data
Extrapolated Data
P(LS|Sa)
0.6 0.4 No Control B1 B2 B3
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0
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0.3
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2
CONCLUSION
Three device placements schemes using control effort as a design criterion, and three increasingly more aggressive controllers with the same device configuration are compared. All controlled cases reduce the vulnerability of the structure noticeably. Furthermore, more aggressive controllers significantly restrict the number of plastic hinges.
1 0.8
a specified performance limit state given the occurrence of a particular demand. Fragility analyses are less complex, less costly, and more easily understood by decision makers than complete risk assessments; however provide information that is primarily useful in an averaged sense. Fragility relationships may be used on systems of structures to determine the risk and identify the pros and cons of potential retrofit strategies. This paper explores fragility functions of actively controlled configurations to more easily depict the reduction of probability of failure compared to a structure without control devices. Results are provided.
0.5
Sa (g)
ACKNOWLEDGEMENTS 0.6
This work was supported by the Mid-America Earthquake Center through NSF EEC-9701785.
Figure 1. Fragility Curve of Different Controllers.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Self-centering building system composed of rocking structural members T. Azuhata & T. Ishihara National Institute for Land and Infrastructure Management, Tsukuba, Ibaraki, Japan
M. Midorikawa Hokkaido University, Sapporo, Hokkaido, Japan
1
INTRODUCTION
It has been pointed out that the effects of rocking vibration (uplift response) may reduce seismic damage of buildings subjected to strong earthquake ground motions by past studies. Based on this knowledge, some rocking structural systems have been proposed and developed as one kind of passive vibration control system. Using effect of building’s self weight, the rocking system can prevent the building structure from yielding residual deformation even after a sever earthquake and can realize a ‘smart’ self-centering system. However, most of them have been generally applied only to slender frame structures with single bay. This study aims to apply the concept of the rocking structural system to wider steel frames with multibays more efficiently. For this purpose, some rocking structural members, the coupled brace units with yielding base plates and the one-side rocking beams, are introduced. The seismic performance of the proposed self-centering system with these members is examined by seismic response analyses on a steel frame model. And the energy dissipation mechanism is investigated. 2
Numerical models of yielding base plates, one side rocking beams and vertical dampers, which are arranged in the coupled brace frame units, are presented in the paper. As input ground motions for seismic response analyses, an artificial ground motion (BCJ L2) and the 1995 Kobe earthquake record (JMA Kobe) are used. The seismic response results of base shear of the SCR model are smaller than those of the F model in the both cases of BCJ and JMA Kobe. However the corresponding roof displacement of the SCR model is almost equal to or smaller than that of the F model. This means the base shear of the frame can be reduced by introducing rocking structural members. Also analytical results show the F model suffers considerable damages especially in the middle stories against the JMA Kobe. In contrast, the SCR frame model almost keeps elastic except base plates. By applying the proposed self-centering system, structural damages can be largely reduced even against the JMA Kobe. In the SCR model, the base plates and vertical dampers dissipate about 70% of the total input energy when it is subjected to the JMA Kobe motions. This large energy dissipation capacity can reduce frame damages.
CASE STUDY 3
A conventional steel braced frame model is picked up as an application example. To improve the seismic performance of this frame model, the proposed self-centering system is introduced. Comparing seismic responses of a self-centering frame model with rocking structural members (SCR model) with those of the original braced frame model with fixed bases (F model), the seismic response reduction effect and the self-centering ability of the SCR model are examined. The frame model has 10 stories and 3 bays. The height is 37.8 m, the width is 18 m and the total weight is 540 t.
CONCLUSION
The seismic performance of the proposed system was successfully demonstrated by earthquake response analyses to a real scale steel frame model. The analytical result showed it can keep the frame almost elastic even against severe earthquake ground motions like the JMA Kobe. The seismic response of proposed system largely depends on the vertical connection dampers arranged in the coupled brace units. Thus to evaluate its performance more appropriately, we need further studies on physical characteristics of these dampers.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Development of the smart maintenance and management system for the soil slope structures S.R. Lee & Y.K. Kim Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
1
INTRODUCTION
In Southeast and Far East Asia such as Singapore, Hong Kong and Korea, very frequent slope failures are occurring in heavy rainy season. Rainfall infiltrates into the unsaturated soil slope in forming the water-wetting front and it reduces the matric suction and hence the shear strength near the surface. Then there may be a possible surface failure. Therefore monitoring and predicting the instability of slope during or after rainfall are very important to prevent the slope disasters. 2
CONCEPT OF UNSATURATED SOIL SLOPE STABILITY
The slope stability analysis can be conducted using the Limit Equilibrium Method with the modified MohrCoulomb shear strength criterion, which includes the matric suction term.
infiltration of rain in rainy period and decreased due to drainage to lower layer and the evaporation to open air in hot and sunny period. This phenomenon occurs less sensitively as the depth increases. The sudden drop of matric suction happened rightly after the rainfall event. This loss of matric suction has the effect on the reduction of strength of soil. 4
SLOPE FAILURE CRITERIA
Numerical results were applied to slope failure criteria. The condition of 3-m depth slip moved from safe zone to suspicious zone. 6-m depth slip was in the dangerous stage and in the possibility of slip failure if the rainfall continues. 5
CONCLUSIONS
We can easily define the stability of current slip using the criteria. If the stage of instability moves to more dangerous zone, there will be an alarming notice to slope management center or organization to prevent from landslides and the possible loss of lives.
where c = cohesion; φ = frictional angle; φb = soil property related to the matric suction; (σn − ua ) = net confining stress; (ua − uw ) = matric suction; zw = depth of infinite slope; α = angle of slope; and γt = unit weight
-25 0
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Pore-water pressure (kPa) -10 -5 0 5 10
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Hydrostatic
3
MONITORING RESULTS
The water content and matric suction in the slope are the most important factors for rainfall-induced slope instability. However, because of uncertainties involved in the affecting factors, we need to directly measure the rainfall condition and its infiltration effects. Matric suction at 15 cm depth showed very rapid variation because the water content increased easily due to the
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Slip depth (m)
-1 -2 -3 -4 -5 -6
FS=1.5 FS=1.2
FS=1 Initial values 12 h 24 h 192 h
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Experimental investigation on hysteretic characteristics of a transmission tower with friction-type reinforcing members Ji-Hun Park Department of Architectural Engineering, University of Incheon, Incheon, Korea
Byoung-Wook Moon, Sung-Kyung Lee & Kyung-Won Min Department of Architectural Engineering, Dankook University, Seoul, Korea
INTRODUCTION
Figure 2. Energy dissipation mechanism of the FRM.
Damper F-D(C)
Damper F-D(T)
15
15
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Force (kN)
In this study, friction-type reinforcing members (FRMs) were installed in a transmission tower to enhance its wind-resistant performance, and their hysteretic characteristics were experimentally investigated. The FRMs are connected to the tower leg by fixed joint at both ends and are divided into two angles connected by slotted bolted connections (SBCs). The FRMs utilize the relative displacement between the two divided angles to exert their energy dissipation capacities on a transmission tower. Cyclic loading tests of the tower substructure with the FRMs are conducted. From the test results, hysteresis loop of the whole substructure and individual FRMs, energy dissipation in the FRMs, increase of the total energy dissipation and participation ratios of the FRMs in the total energy dissipation are analyzed with respect to various design torque values applied to the SBCs and displacement amplitude.
Force (kN)
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CYCLIC LOADING TEST
A 154 kV B2-type transmission tower of height 38.1 m is chosen for the experimental study of the FRMs
Figure 1. Experimental setup.
0 -5
2
-2
-1
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1
2
Displacement (mm)
Figure 3. Force-displacement curves of the SBC in the FRM (C: compression side, T: tension side), (Torque = 20 N-m).
installed in the tower body. Four plane units in the middle of the tower body are extracted from the entire tower structure and reduced on a 1/2 scale in length and a 1/4 scale in section. Detailed energy dissipation mechanism of the SBC in the FRM under the wind-induced bending deformation of the tower structure is illustrated in Fig. 2. A relative displacement in the SBC is induced from the slip in the SBC located in the middle of the FRM corresponding to the flexural deformation of the tower body under lateral loads. The similar relative displacement is induced in the opposite side of the tower structure.
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3 TEST RESULT AND CONCLUSION In this study, cyclic loading tests of a SBC in the FRM and a tower substructure with FRMs are conducted in order to investigate wind-resistant retrofit
performance of the FRM in terms of the energy dissipation and member force share. The FRMs increased the total energy dissipation of the tower substructure by 2.4 times compared to the original one without FRMs.
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Motion and vibration control (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Active vibration control using hybrid mount featured by electromagnetic actuator and piezostack actuator V.Q. Nguyen, Y.S. Paeng, J.Y. Yook, Y.M. Han & S.B. Choi Smart Structures and Systems Laboratory, Department of Mechanical Engineering, Inha University, Incheon, Korea
S.J. Moon Korea Institute of Machinery & Materials, Daejeon, Korea
1
EXTENDED ABSTRACT
Many types of passive mounts have been used to support static load and isolate unwanted vibrations. Rubber mount is one of the most popular and effective passive mounts which is widely used due to its efficient vibration isolation performance against non-resonant and high frequency excitations. However, the passive rubber mount cannot exert good performance at some frequency regions, especially at resonant frequencies. This performance limitation of the passive mount leads to the study on active and semi-active mounts featuring smart materials which include electrorheological fluids and piezoelectric materials. However, control performance of the active and semi-active mounts may be deteriorated at the non-resonant and low-frequency excitation due to low material damping and small displacement. Thus several types of hybrid mounts has been proposed which make use of smart materials such as electrorheological (ER) fluids, magneto rheological (MR) fluid, shape memory alloys (SMA), and piezoelectric materials. In this work, two types of hybrid mount are proposed to evaluate and compare their control performance. One type consists of rubber and electromagnetic actuators, and the other one consists of rubber and piezoelectric actuators. As well-known, the piezo actuator is featured by fast response time, but small displacement; whereas the eletromagnetic actuator has properties of slow response time, but larger displacement. By including these actuators into the passive rubber mounts, the hybrid mounts can be controlled to improve their performance in specific frequency ranges, especially at resonant frequencies. In both cases, the rubber is introduced for the passive element, and the additional actuators are used to enable the active controlled ability of the vibration system. Moreover, the rubber-and-electromagneticactuator hybrid mount is designed to isolate low
frequency vibrations, whereas the rubber-and-piezoactuator one is designed for high frequency isolation. While the rubber element is utilized to mitigate vibrations as its common use in passive mount, the additional actuators are for performance improvement in the whole frequency range of excitation, especially at system resonant frequencies. The frequency range of excitation in this system is from 1 Hz to 1000 Hz. That is a big challenge in active mount design and control implementation for it; an improper choice of controller may cause the system to be unstable. For control implemetation, the actuating force characteristics of the actuators are experimentally identified first; the two proposed hybrid mounts are then manufactured for the vibration control system. In both cases, the system load is assumed to be a lumped mass. In controller design, the dynamic of the rubber stiffness and damping is not considered, the nominal values are used instead, and their variations are considered as uncertainties. Moreover, since the excitation is considered as disturbances, the controlled system must be robust to external disturbances and parameter variations. In such case, a sliding mode controller is a good candidate. After deriving the governing equations of motion of the proposed systems, a sliding mode controller is formulated to control the system. The control simulations are done by using Simulink/Matlab. An experimental system is also set up for evaluating the system performance in both time and frequency domains. A dSPACE DS1104 board hosted in a computer is used for real-time control implementation. Finally, experiments at various frequency excitation are done to verify the simulation results. Keywords: hybrid mount, electromagnetic actuator (EMA), piezoelectric actuator, sliding mode controller.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Control performance evaluation of ER suspension system under road test K.G. Sung, Y.M. Han, J.W. Sohn & S.B. Choi Smart Structures and Systems Laboratory, Department of Mechanical Engineering, Inha University, Incheon, Korea
Y.S. Lee & M.S. Han Department of Mechanical and Automotive Engineering, Keimyung University, Daegu, Korea
1
EXTENDED ABSTRACT
Recently, driver’s and passenger’s attention to ride comfort has been significantly increased in vehicle driving. In order to improve the ride comfort under consideration of the conflict of steering stability, many researchers have studied on the vehicle suspension system whose main function is to attenuate the vehicle vibration caused from various road conditions. So far, three types of suspension systems have been proposed: passive, active and semi-active. The most successfully implemented type is the passive suspension featuring passive dampers and spring elements. However, inevitable performance limitations have been faced by the conflict of vehicle stability versus ride comfort. Therefore, in recent years, electronic control suspension (ECS) has been proposed by adopting controllable active suspension and computer-based control scheme. A typical ECS system is the active suspension which can provide high control performances in wide frequency range, but requires high cost to realize high power source, many sensors, servo-valves and sophisticated control logic. One way to resolve these problems of the active suspension system is to use the semi-active suspension system. The semi-active suspension system offers a desirable performance generally enhanced in the active mode without requiring large power sources and expensive hardware. Recently, a very attractive and effective semi-active suspension system featuring electrorheological (ER) fluid or magnetorheological (MR) fluid has been proposed by many investigators. Petek proposed a monotube type ER damper and demonstrated its superiority over conventional damper by showing that the damping force of the ER damper could be increased with respect to applied electric field regardless of the piston velocity. Sturk et al. proposed a high voltage supply unit for controlling the voltage applied to the ER damper and experimentally evaluated its performance. In order to do this, they manufactured a small-sized ER damper
and applied it to a quarter-car suspension system. Nakano constructed a quarter-car suspension system model using an ER damper and proposed two control strategies: constant control voltage and square root of control voltage proportional to absolute velocity of unsprung mass. Choi and co-workers proposed a cylindrical ER damper for passenger car and its superior controllability of damping force was proved in the laboratory by implementing skyhook and sliding mode controllers. From these research works, the effectiveness of ER suspension system has been proved for vibration control of automotive vehicles. In order to successfully commercialize the ER suspension, its road test should be undertaken on a commercial scale in real and natural environment. However, so far the research on the road test is considerably rare because the real implementation of ER dampers to the full vehicle requires a multidisciplinary effort including ER fluids, ER devices, high voltage amplifiers, sensors, controllers as well as the test vehicle. Moreover, the test on a standardized proving ground (PG) is absolutely required. The main contribution of this work is to present vibration control results of the ER suspension system via the road test undertaken on the standardized proving ground. As a first step, front and rear ER dampers are designed and manufactured based on the damping force levels and mechanical dimensions required for a commercial middle-sized passenger vehicle. After experimentally evaluating dynamic characteristics of the ER dampers, the test vehicle is prepared for road test by integrating voltage amplifiers, realtime data acquisition system and numerous sensors such as accelerometer and gyroscope. Subsequently, the manufactured four ER dampers (two for front parts and two for rear parts) are incorporated with the test vehicle and a skyhook control algorithm is formulated and realized in the data acquisition system. In order to emphasize practical aspect of the proposed ER suspension system, road tests are undertaken
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on proving grounds: long waved, rugged, paved and unpaved roads. The control responses are evaluated in both time and frequency domains by activating the ER dampers.
Keywords: electrorheological damper, semi-active suspension, road test, proving ground, skyhook controller.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Experimental study on semiactive modal neuro-control scheme H.J. Lee, K.M. Choi & I.W. Lee Department of Civil and Environmental Engineering, KAIST, Daejeon, Korea
S.J. Lee Civil Engineering Division, Samsung Engineering & Construction, Kyeonggi-do, Korea
1
INTRODUCTION
Modal control is especially desirable for the vibration control of civil engineering structure, which is usually a large structural system but its vibration is usually dominated by the first few modes. In this paper, a semiactive modal neuro-control scheme which combines the modal neuro-control algorithm and semiactive control device (MR damper) is developed and verified in experiments with scaled shear building model.
2
Figure 1. Block neuro-controller.
SEMIACTIVE MODAL NEURO-CONTROL SYSTEM
Figure 1 shows the block diagram of the proposed semiactive modal neuro-control scheme using MR damper. The proposed control scheme consists of a clipped algorithm and modal neuro-controller. The training of neural network for modal neuro-controller is based on the minimization of a type of new cost function.
3
EXPERIMENTAL VERIFICATION
The test structure model used in the experiment is a scaled three-story shear building model. The frame is constructed of steel and has a height of 105 cm and the floor masses of the model weigh a total of 48.27 kg, which is distributed evenly between the three floors. The control device used in the experiment is a controllable friction MR fluid damper (Model: RD1097-01) from Lord Corporation. The measurements of responses are acquired from the laser displacement sensor, accelerometer, and load cell and converted into the digital data by the NI DAQCard-6062E. Then the controller computes the desired control force with those measurements and finally output signal (in voltage) is sent to wonder box for the MR damper through the output port.
diagram
of
semiactive
modal
In designing the modal neuro-controller, two kinds of controller are considered. The modal neurocontroller type A is designed for reducing the overall responses (both inter-story drift and acceleration), and type B is designed for focusing on reducing the inter-story drift mainly. The control performance of the semiactive modal neuro-control systems is compared with that of the passive-off (0 V), passiveon (8 V), and the optimal passive case (2 V) operated in constant voltage mode. As compared to the optimal passive system, the semiactive modal neuro-control systems achieved satisfactory vibration reductions over the entire range of earthquake intensities considered. Moreover the proposed semiactive modal neuro-controllers show the good adaptability and ability to wide application subjected to specific purpose. These results indicate that the semiactive modal neuro-control systems can be effectively used over a wide range of ground motion intensities and characteristics.
4
CONCLUSION
The experimental results subjected to all of the scaled earthquakes finally indicate the effectiveness
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of the proposed semiactive modal neuro-control system in reducing the inter-story drift and acceleration responses. REFERENCES S. W. Cho, B. W. Kim, H. J. Jung and I. W. Lee, “The Implementation of Modal Control for Seismic Structures using
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MR Damper,” ASCE Journal of Engineering Mechanics, Vol.131, No.2, 2005, pp.177–184.
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
The application of nonlinear energy sinks controller in a full car semi-active suspension system with MR dampers L. Zheng & Y.N. LI State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing, China
A. Baz & A. Elsabbagh Department of Mechanical Engineering, University of Maryland, College Park, MD, USA
1 ABSTRACT In this paper, a Nonlinear Energy Sink (NES) controller is designed and used to control semi-active suspension system with Magneto-Rheological(MR) dampers. A full car model with seven degrees of freedom is developed and used to demonstrate the effectiveness of the NES controller. The proposed controller relies in its operation on specially designed nonlinear spring elements which are attached to the primary suspension system in order to induce optimal nonlinear vibration energy sinks. Four MR dampers are designed, manufactured and integrated with four independent NES controllers. These MR dampers are all twin tube MR dampers with double class magnetic circuits.The MR dampers in the front suspension have different geometricl dimensions from the MR dampers in the rear suspensions. The performance of these MR damper is tested using a servo-hydraulic shock testing dynamometer. The experimental results show that these MR dampers can supply a changeable damping force which can cover the curves of the damping force via velocity from the original passive hydraulic dampers. In order to control the full car semi-active suspension system in a simple way and decrease the computational burden for the whole control system, the control system is divided into four independent subsystems. The four controllers are designed for the four independent subsystems to achieve a rapid response and maintain a good control for body pose. The control effectiveness of semi-active suspension system with MR dampers using NES control strategy is compared with that of using linear LQR control strategy. The optimal feedback gain matrix used in the LQR controller is determined according to classical control theory. The feedback state variables in the NES controller are modified to induce Nonlinear Energy Sinks into subsystems of the primary vibration system of vehicle. That means that two nonlinear stiffness
elements are introduced in the NES controller. In this way, the active control force required by the NES controller is obtained by the feedback control of the new set of state variables. The key question is how to get the feedback gain matrix. In this study, a simplex search method is used to determine the feedback gain matrix in order to minimize the cost function. At each step of the search, a new point in or near the current simplex is generated. The cost function value at the new point is compared with the cost function’s values at the vertices of the simplex, usually, one of the vertices is replaced by the new point, giving a new simplex. This step is repeated until the diameter of the simplex is less than the specified tolerance. The numerical example is given to identify and compare the effectiveness of the NES controller to that of the classical LQR controller.In order to reveal the transient response characteristic. a single rectangular bump is used as the road excitation. The RMS values and the cost function for the different control strategies are caculated.The simulation results show that the control effectiveness using NES controllers is much better than that using LQR controllers. The body heave, roll and pitch accelerations, tire deflection are significantly reduced by the NES controllers. This means that the vibration energy from road excitation is absorbed rapidly. Vibration energy transmitted by road disturbance has been successfully attenuated and the best possible ride comfort and handling performances have been potentially achieved by the proposed NES controller. Furthermore, the calculation for the cost function of energy consumption shows that the total cost function with the NES controllers is about 20% less than that of the LQR controllers and vibration energy using the NES controllers is 28% smaller than that of the linear LQR controllers. This dramatic result suggests that nonlinear NES controllers are much better than linear LQR controllers. It shows the potential of the NES control strategy as an effective means for attenuating vehicle vibration.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A new arching PZT actuator and its application in vibration control of smart structures Wei Wang & ZhiChun Yang School of Aeronautics, Northwestern Polytechnical University, China
1
INTRODUCTION
Piezoelectric materials have piezoelectric effects and inverse piezoelectric effects because of their unique crystalline structures. Their good electromechanically coupling characteristics make them have been widely used in smart/intelligent structures. The holy grail of actuator research is an architecture that can generate high displacement and force through a broad frequency range while not consuming a significant amount of electrical power. There has already been classified three main architectures of piezoelectric actuator design, i.e. externally leveraged, internally leveraged and frequency leveraged. Externally leveraged actuators, such as flexural hinged, Moonie, Cymbal, rely on an external mechanical component for their actuating ability. Internally leveraged actuators, such as stack, bender, RAINBOW, THUNDER, generate amplified strokes through the internal structure without using an external mechanical component. Whereas, frequency leveraged actuators, which include inchworm and ultrasonic motors, rely only upon an alternating control signal to generate motion. Currently, PVDF and PZT play important roles in the active vibration control application in smart structures. Generally these two kinds of piezoelectric materials are used in film or patch form. There are two main coupling approaches for their applications: bonded on or embedded in structures. Both of these two approaches, however, have limits in practical use. For the first method, smooth surface is required, which usually can not be satisfied, especially for aircraft structure where rivets and bolts are widely used. Consequently, the optimal distribution scheme can not be carried out directly, and the implementation of the vibration control system is badly affected. In addition, once the patches are stuck on the structural surface, they can hardly be removed or replaced. In this study a new Arching PZT Actuator (APA) is proposed to deal with the setting restrictions and to improve the actuating ability of PZT patch actuator (PPA) in smart structural vibration control. As shown in fig. 1 the APA consists of an arching pedestal and a PPA. With this configuration it can be mounted on various structural
Figure 1. Sketch of APA.
Figure 2. FRF comparison between control off and on for cantilever beam with APA.
surfaces and be reusable. Firstly, the characteristics of APA are investigated, which include the analysis of the free-end deformation amplifying principle and the test of the deformation output character. The test results accord with the analysis and demonstrate that the deformation output of APA is much larger than that of the PPA. Secondly, comparative active vibration control experiments are implemented with the use of APA and PPA on two same cantilever beams. Experimental results show that the amplitude of the tip-point displacement frequency response function (FRF) at the first three mode frequencies of the beam can be suppressed approximately by 35 dB, 25 dB and 23 dB, respectively, with APA, which can be seen in fig. 2. With PPA only the amplitude of the FRF at the first mode frequency is suppressed by 24 dB.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Research of process controls parameter optimal selection-based on improved genetic algorithm G.F. Yan, X.H. Huang & F. Tan Institute of Automation Engineering, University of Electronic Science and Technology of China, Cheng Du, Si Chuan, China
1
INTRODUCTION
Because of the simplicity, robustness and reliability in PID (proportional, integral, differential) control algorithm, it has been extensively used in process controls. By tuning the PID parameters properly, we can get a satisfying control effect for a certain model system. But it is difficult to tune the PID parameters in this controller because PID parameters influence each other. In fact, this parameter tuning process is a compromise between the proportional, integral, and differential effects. Although there are a lot of methods for PID parameters tuning, they are often piled up and time-consuming as well. Therefore, seeking PID parameters optimal matching is especially important for getting optimal control effect. In this paper, a new optimal selection method for tuning process control parameters is proposed in order to solve the problems mentioned above. This is accomplished by using SA (simulated annealing) for local search and GA (genetic algorithms) for global search. Furthermore, fuzzy reasoning is adopted to modify Pc (crossover probability) and Pm (mutation probability) according to the characteristics of the population in genetic algorithms, rather than using fixed parameters. And so, the global optimum can be converged at quickly. The verified algorithm can be applied to obtain the best control parameters of the fitness function with least-error and least-overshoot optimization criterion. A better control effect is achieved in the process simulation of the second order system’s response using these control parameters.
2 THE CONCRETE METHOD
KP (proportional coefficient), KI (integral coefficient), and KD (differential coefficient) according to their ranges. Pay attention to the relation between chromosome’s length and parameter’s precision; Step 3: Produce initial population, which represents a potential solution set of some optimization problems; Step 4: Compute fitness; Step 5: Reproduce the population according to “survival of the fittest”; Step 6: Operation of crossover and mutation: Select chromosomes randomly to mate, and create new gene combination according to Pc to change part of the old genes. And then select some individuals randomly to produce new genotype according to Pm in order to enlarge optimization range. In this paper, fuzzy reasoning is adopted to modify Pc and Pm according to characteristics of population in genetic algorithms instead of fixed parameters; Step 7: Process SA operation to adjust the created population, which object constraint condition is the least system response by using decoded PID parameters, i.e. to prevent too big overshoot; Step 8: Repeat the above steps until optimization criterion is satisfied, and then decode the max fitness value to solve PID parameters. 3
CONCLUSIONS
This paper presents an improved GA, which combines SA with GA, and uses fuzzy reasoning to adjust Pc and Pm according to the characteristics of the population and individuals in GA, rather than using fixed parameters. The above research indicates that using this algorithm for process control parameters’ optimal selection can obtain better control effect.
The realization steps of this improved GA based process control parameter optimal selection are as follows: Step 1: Set GA’ objective function; Step 2: Code: Construct chromosomes by using binary string to represent PID controller’s parameters
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Bio-inspired structures and materials (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Flapping performance of a flapper actuated by the compressed LIPCA Quoc Viet Nguyen Department of Advanced Technology Fusion, Konkuk University, Korea
Hoon Cheol Park & Nam Seo Goo Department of Advanced Technology Fusion, Konkuk University, Artificial Muscle Research Center & Smart Robot Center, Konkuk University, Korea
1
3
INTRODUCTION
In this work, an insect-mimicking flapping device actuated by a unimorph actuator LIPCA (LIghtweight Piezo-Composite Actuator) has been experimentally investigated. The performances of two flappers actuated by the original LIPCA and the compressive LIPCA, respectively, in terms of vertical force generation, flapping frequency and flapping angle, have been experimentally examined. A highly sensitive and multi-axis load cell and a digital high-speed camera were used for the experiment. The results showed that we could improve the vertical force 22% and increase the flapping angle 22% by using the compressive LIPCA. 2 THE FLAPPING DEVICE The flapping device mimics three important mechanisms of insect flight, which are wing rotation, wing corrugation, and wing clap. All components of the flapping device were made by using lightweight materials. A 4-bar linkage system made of acrylic and machined by CNC was used to amplify and transform the limited up-and-down bending motion of the LIPCA actuator into a large flapping motion. The fully-assembled flapping device is 10 cm long, 12.5 cm wide, and 6.5 cm high with total mass of 10.38 grams. The artificial wings mimicking the vein structure and shape of horse botfly were attached to the flapper for the experiment. The flapper was tested at various flapping frequencies from 6 Hz to 15 Hz and for a prescribed voltage of 300 Vpp (voltage peak-to-peak) to the piezoelectric actuator to search for the best flapping frequency, where the maximum vertical force can be obtained. The high-speed camera images of both front view and top view of the flapper were also taken and examined image by image to find out the kinematics of the wing for both of flapping and wing rotation.
RESULTS
The best flapping frequency was found at around 9 Hz which can be named as the natural frequency of the flapping system, at which the vertical force reached the maximum value. For lower flapping frequency than 9 Hz, the vertical force was smaller due to the low flapping wing speed. For higher flapping frequency than 9 Hz, the vertical force was decreased as the flapping frequency was increased. In this case, due to the faster flapping speed, the time spent for the passive wing rotation during upstroke and downstroke was not enough to fully complete the wing rotation. The average vertical force of the flapper actuated by the original LIPCA is 0.022 N, and that of the flapper actuated by the compressive LIPCA is 0.027 N. The vertical force could be improved 22%. However, the force history of the flapper actuated by the compressive LIPCA with respect to time during downstroke and upstroke could not be clearly seen rather than that of the flapper actuated by the original LIPCA.
4
CONCLUSION
From the test and results, it was found that the flapping device actuated by the compressive LIPCA could improve amount of the vertical force generation over the original flapping device. The passive wing rotation as well as flapping motion can work well in the present flapping device. Even though the measured vertical force includes inertia force, we could deduce that the flapping device can work properly and generate aerodynamic forces. Further CFD simulations and flapping tests in a vacuum chamber are required to separate inertia and aerodynamic forces and to investigate the effect of the wing clap on enhancement of the lift.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Dry adhesive structures designed to reduce the effective stiffness Y.-S. Cho, D.-H. Jung, H. Han, J.-H. Kim & W.-D. Kim Korea Institute of Machinery and Materials (KIMM), Republic of Korea
H.O. Kang National NanoFab Center (NNFC), Republic of Korea
1
INSTRUCTION
In the fabrication of dry adhesive structure, increasing contact-points or contact-area is the primary goal since the adhesive force grows in proportion to the contactarea. The simplest way to extend the contact surface is to utilize a column-array structure made of soft materials. However, the column-array structure could suffer from matting phenomenon where columns are stuck together. Therefore, we need a novel design to reduce the effective stiffness with adequate stiff materials like a gecko’s setae. In this study, we propose a novel design for the dry adhesive structure. The contact behavior between the proposed adhesive structure and a randomly rough surface is analyzed based on finite element method which includes the non-bonding interaction as a body force term. In order to demonstrate the usefulness of the proposed design, the dry adhesive structures made of SU8 are fabricated using optical lithography technique and the resulting adhesive forces are measured using a displacement-controlled indentation technique. 2
Figure 2. (a) Adhesive force graphs of Fig. 1(a) and (b) respectively.
RESULTS
In this study, we demonstrated how the effective stiffness of structure important through some numerical analyses. Figure 2(a) and (b) show the adhesive force of Fig. 1(a) and (b) respectively. Figure 1(a) is the schematics of structure having elastic asperity and rigid hair, while Fig. 1(b) is that of structure having elastic asperity and elastic hair. As depicted in Fig. 2,
Figure 1. (a) A model having rigid hair and elastic asperity, (b) A model having elastic hair and elastic asperity.
Figure 3. Comparison of maximum contact area.
Figure 4. SEM results of the representative structure of novel designed cases.
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the stiffness of structure could affect the adhesive force at randomly rough surface. According to these results, we designed a novel structure to reduce the effective stiffness of dry adhesive structure. As depicted in Fig. 3, we demonstrated numerically the novel design,
which reduces the stiffness, could give us lager contact area than the others. The contact area is related with the adhesive force. Figure 4 shows the representative fabrication structure of derived several cases.
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Damage detection and control of structures
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
The acousto-ultrasonic approach: Several industry applications H. Reis & A. Vary University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
EXTENDED ABSTRACT Analytical ultrasonics implies the measurement of material microstructure and associated factors that govern mechanical properties and dynamic response. It goes beyond flaw detection, flaw imaging, and defect characterization and includes assessing the inherent properties of material environments in which the flaws reside. Acousto-ultrasonics (AU) has been proven to be sensitive to changes in microstructure and damage accumulation due to fatigue and impact. In practice, a broad spectrum ultrasonic pulse is injected with a transmitting transducer mounted on the surface of the specimen. It can be demonstrated that larger amounts of damage (i.e., flaws, changes in the microstructure, etc.) in the specimen produce greater acousto-ultrasonic signal attenuation, resulting in lower stress-wave-factors (SWF), i.e., stresswave-parameter measurements. Figure 1 represents a schematic diagram of a typical acousto-ultrasonic data-acquisition system used to monitor ‘diffuse damage’ in the volume of material between the two transducers in a simple plate-like test sample. It shows the sender and receiver probes as piezoelectric transducers coupled at normal incidence to the surface and on the same side of the test piece. Currently, most of the applications use broad-band sensors for both the sender and the receiver. The time domain signal is then subjected to signal processing by partitioning the time and frequency domains to search for signal features, i.e., stress-wave-factors, which have provable correlations with the material properties being studied. Traditionally, a stress-wave-factor is any stresswave parameter in any domain such as the time and frequency domains that help to characterize the AU signal relative to the property of interest. All stresswave-factors, i.e., waveform features, can be used in conjunction with pattern recognition and adaptive learning systems.
Ultrasonic Pulser
Signal Processing Unit
Sending Transducer Receiving Transducer
180⬚
90⬚
0⬚ 270⬚ Transducer Separation Distance
Figure 1. Schematic of a traditional acousto-ultrasonic data acquisition system to estimate porosity in fiber reinforced polymer matrix composite samples.
Acousto-Ultrasonics is still primarily an empirical and experimental approach. Basically, the mechanical energy in form of an induced stress wave is forced to interact with the test section the specimen. The Acousto-Ultrasonic (AU) approach was originated at NASA Lewis Research Center (today, the NASA Glenn Research Center) and it was developed mainly to evaluate/characterize distributed damage in advanced composites. In this paper, the nature and the underlying rational of the acousto-ultrasonic approach are explained and its principles are explored. The robustness and other advantages of the acoustoultrasonic approach in quality control applications are discussed. A literature review is presented and, as an example, the use of acousto-ultrasonics to assess levels of porosity in advanced polymer composites is discussed in detail. Other examples including applications to steel reinforced radial truck tires, infrastructure, and aerospace industry are also discussed. Because many factors involved in the technique are not yet fully understood AU is currently undergoing experimental investigations to establish theoretical grounds for the purely empirical findings and practical applications now abundant in the literature.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A magnetostrictive sensor for structural health monitoring in a non-ferromagnetic plate Yajie Yang & Li Zhou College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, China
Fuh-Gwo Yuan Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, USA
ABSTRACT Guided wave inspection is a new emerging technology for rapidly assessing the structural damage in structural health monitoring (SHM). Most currently available guided wave sensors are based on piezoelectricity. Recently, a magnetostrictive guided wave sensor has received much attention because of several advantages such as potential non-contact detection and cost-effectiveness. In this work, the development of a magnetostrictive sensor for generating and detecting guided waves in a non-ferromagnetic plate is described. From the theory and experiment it can be proven that the sensor can generate non-dispersive horizontal shear (SH0 ) wave mode for structural health monitoring. The sensor system consists of a nickel
strip, a couple of Nd-Fe-B permanent magnets, Cshaped cores, and the figure-of-eight coil wound on it. The incident wave propagates in the plate and is reflected from the plate boundaries. Since the time of the arrival can be determined from the reflected wave signal through signal processing, the velocity of the wave can be calculated. Comparing the calculated velocity with the theoretical velocity, the mode of the wave can be identified with a priori knowledge of group velocity of the plate. The sensor shows its promise in applying in SHM and nondestructive evaluation (NDE). Keywords: magnetostrictive sensor, guided wave, structural health monitoring, plate.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Vibration and aeroelastic control of composite structures using PZT actuators M. Kameyama & H. Fukunaga Tohoku University, Sendai, Japan
1
INTRODUCTION
The present paper treats the optimal placement method of lead zirconate titanate (PZT) actuators for vibration and aeroelastic control. For effective suppression of vibration of composite structures, a modal actuator is constructed by the optimal placement of a limited number of segmented piezoelectric actuators based on the minimization criterion of control spillover (Sun D. et al. 2001). The experimental verification of vibration control of cantilevered laminated plates is carried out. Moreover, the present method is applied to aeroelastic control of composite wing structures. The validity of the present method for aeroelastic control of cantilevered laminated plates is also examined through the numerical examples.
Figure 1. Results of vibration control (Optimal location of actuators).
0.20 Tip deflection [mm]
2 VIBRATION CONTROL OF COMPOSITE STRUCTURES In the first example, a vibration suppression methodology of cantilevered laminates by using a limited number of sensors and actuators is studied through the experiments. Accelerometers are used as sensors in this example. Figure 1 shows the results of vibration control by an optimal modal actuator, when two actuators control the first and the second mode.
In the next examples, a stable flutter suppression methodology of composite plate wings by using a limited number of sensors and actuators is studied through the numerical simulations. PVDF sensors are used as sensors, and flutter suppression based on the measurement and control of torsional vibration is examined in this example. Figure 2 shows the results of control at the design velocity, when three sensors and three actuators are used. 4
CONCLUSIONS
It has been clarified through the experimental and numerical results that the importance of the locations
0.10 0.00 -0.10 -0.20 0 .0
3 AEROELASTIC CONTROL OF COMPOSITE STRUCTURES
Leading edge Center Trailing edge
0.5
1.0 Time [s]
1.5
2.0
Figure 2. Results of control (Optimal locations of actuators).
of actuators in terms of the influence of the higher residual modes for vibration and flutter suppressions, and that the present method can realize the vibration and aeroelastic control by using a limited number of segmented piezoelectric actuators. REFERENCES Sun, D. et al. 2001. Vibration Control of Plates using Discretely Distributed Piezoelectric Quasi-modal Actuators/Sensors. AIAA Journal 39(9): 1766–1772.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structural health monitoring for composite airframe of next generation space vehicles Jeong-Beom Ihn Phantom Works, Boeing Company, Seattle, WA, USA
Jerry Huang Phantom Works, Boeing Company, Huntington Beach, CA, USA
1
INTRODUCTION
The Boeing Company is funded by Air Force Research Laboratory (AFRL) to perform research and development activities on Structural Health Monitoring (SHM) and Assessment Techniques for Advanced Aerospace Vehicles. This effort includes two SHM aspects, i.e., on-board sensors and ground based NDE techniques. The first aspect focus’s on prototyping a SHM system that integrates several different types of sensors to generate structural health information based on real-time or near real-time sensor data. The second aspect focus’s on a ground system that provides a linkage between the on-board sensors and ground based NDE techniques with a prototype system capable of rapidly gathering and interpreting structural health information. They can be viewed as two parts of a SHM system that are complimentary to one another. Developing such an SHM system is intended to help advance aerospace vehicle’s safety and reliability, satisfy the required turnaround time, reduce cost and cycle time in design, operation and maintenance. In this paper, among other candidate techniques considered, two SHM techniques, acoustic emission and diagnostic imaging based on active piezoelectric network sensors are presented and compared with conventional nondestructive evaluation techniques. 2 TEST ARTICLE For this test series, a 30” × 30” carbon fiber reinforced composite panel served as the primary structure for the TPS test article assembly. The panel is an all bonded Skin-Stringer structure. The sensors installed on test article included an Active Sensor Network (ASN) of 30 piezoelectric actuators/sensors and 9 Acoustic Emission (AE) sensors. Sensor locations were determined based on test conditions, expected failure modes
and coverage of area to be monitored. AE data was recorded during the test using 9 AE sensors bonded on the backside of the composite panel. AE monitoring is based on the phenomenon of rapid energy release from a cracked surface when it occurs in the structural material under stress. On the other hands, active diagnostic imaging technique utilizes the ASN permanently attached to the airframe structure. The ASN scans the structure for any structural anomalies as each piezo elements transmits ultrasonic stress waves into the structure and other neighboring piezo elements record the responses as listeners. When a structural anomaly such as delamination is introduced, wave scattering and attenuation occur at the anomaly location. The diagnostic imaging technique visualizes these local scattering phenomena and characterizes damage in terms of location and size. 3
CONCLUSION
The tested SHM sensors and sensing techniques were selected through a down-select process based on capability, and SHM requirements for the space vehicle. The performance of the sensors has been evaluated through the simulated test condition. The results showed effectiveness of these sensors for the specific failure modes such as cracking and bondline failure, and will be used to conclude our sensor down-select process. ACKOWLEDGEMENTS The authors would like to express their appreciation to the IVHM Lead Mark Derisso, Captain Robert Vandawaker, Lieutenant Nathan Taylor of the Air Force Research Laboratory, and Dr. F-K Chang with Stanford University for their support.
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New sensor technology for civil engineering structures (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Magnetic-field-driven micromachine applying multi-functional Fe-Pd ribbon T. Okazaki & Y. Furuya Hirosaki University, Hirosaki Japan
The ferromagnetic shape memory alloy (FSMA) FePd is expected to be useful as a magnetic-field-drive sensor/actuator material for micromachines and intelligent/smart material systems. To apply the Fe-Pd alloy for a micromachine, we investigated the behavior of the shape memory effect for rapidly solidified Fe29.6 at% Pd alloy ribbons. These ribbons exhibited a reversible two-way shape memory effect in the temperature range of 273 to 403 K, where the transformation from the martensite phase (FCT structure) to austenite phase (FCC structure) is found. On the basis of the development of an actuator of the Fe-29.6 at% Pd ribbon, a small simple-structured micromachine system was fabricated as shown in Fig. 1. A wireless micromachine is controlled remotely by an alternating magnetic field: it is able to swim in a fine liquid pipe and move forward or backward by changing the frequency of the applied alternating magnetic field. Figure 2 shows the moving speed υ of the micromachine vs the magnetic field frequency f . The micromachine of 3.8 mm in length (Fig. 2 (a)) moves backward at a low frequency range of 3 to 7 Hz: a maximum speed of 1.5 mm s−1 arises at f = 5 Hz. Moreover, it moves forward at a high frequency range of 10 to 30 Hz: a maximum speed of 6.3 mm s−1 arises at f = 20 Hz. On the other hand, the micromachine of 1.94 mm in length (Fig. 2(b)) moves backward at a low frequency range of 3 to 55 Hz: a maximum speed of 1.2 mm s−1 arises at f = 50 Hz. Moreover, it moves forward at a high frequency range of 60 to 100 Hz: a maximum speed of 2.1 mm s−1 arises at f = 80 Hz. Lastly, it was also confirmed that the behavior of gripping and releasing a small polymer ball (the diameter, φ = 0.5 mm) occurred by supplying microwave energy from the outside of the water pipe. The micromachine grips the ball in the water tube. When
Figure 1. (a) A transparent polymer-pipe encircled around the concentric electromagnetic coil. The micromachine moves in the pipe filled with static water. (b) Design of simple-structured, fish-like micromachine consisted of a grip, twisted part and a fin.
Figure 2. The moving speed υ of the micromachine vs magnetic field frequency f .
2.45 GHz micro- waves were irradiated outside of the tube, the water was heated up and the grip opened automatically. Finally, the grip released a small ball at a water tem- perature of 340 ∼ 350 K.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Hydrothermal synthesis of Kx Na1−x NbO3 powders for fabrication of lead-free piezoelectric ceramics K.J. Zhu*, J.H. Qiu & Z.L. Meng The Aeronautical Key Laboratory for Smart Materials & Structures, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, P.R. China *Institute of Fluid Science, Tohoku University, Sendai, Japan
K. Kajiyoshi, K. Yanagisawa & N. Li Research Laboratory of Hydrothermal Chemistry, Kochi University, Kochi, Japan
1
INTRODUCTION
Lead zirconium titanate (PZT) ceramics are highperformance piezoelectric materials, which are widely used in sensors, actuators and other electronic devices. From the viewpoint of environmental protection, it is desired that the lead based piezoelectric ceramics should be replaced with lead-free materials. Many lead-free piezoelectric materials have been developed for about 30 years, which include bismuth sodium titanate (Bi1/2 Na1/2 )TiO3 , bismuth layers (Bi4Ti3 O12 ), (Na0.5 K0.5 )NbO3 -LiTaO3 lead-free piezoelectric ceramics and so on. NaKNbO3 ceramics have begun to attract special attention again because of a breakthrough made by Saito et al., who obtained high d33 (∼416 pC/N) in textured NaKNbO3 -based ceramics. However, it is difficult to fabricate high-density ceramics because their poor sinterability and high volatility. It is well known that hydrothermal synthesis can give powder higher sinterability. In this work, K1−x Nax NbO3 powder synthesized by hydrothermal method was used to fabricate lead-free piezoelectric ceramics to improve the piezoelectric properties. The starting materials are Sodium Hydroxide, Potassium Hydroxide, Isopropanol (Wako Pure Chem. Ind., Co. Japan) and Niobium Pentoxide (Soekawa Chemicals, Japan). The 3 g Nb2 O5 powder was added to the mixture solution of KOH, NaOH and isopropanol solution with the pH value 2 M under stirring for 30 minutes. The suspension solution was transferred into a 90 ml Teflon-lined autoclave. Hydrothermal reactions were carried out at 240◦ C for 8 hours.
The resulting powders were repeated washed using centrifugation with deionized water, and they are dried in an oven at 100◦ C for 12 hours. The dried powders were characterized by powder X-ray diffraction (XRD; Model RTP-300RC, Rigaku) with Cu Kα radiation (40 kV and 100 mA).The morphology and size of the powders was observed by field emission scanning electron microscopy (FE-SEM; JSM-7000F, JEOL). The element analysis was carried out using ZAF method (EDS; EX-23000BV). The presence of water and organic group were determined by Fourier transform infrared spectra (FTIR) spectroscopy (FTIR8200PC, Shimadzu). The specimens were sintered by conventional sintering method at 1100˚ C for 2 hours. Electrodes were formed on the specimens by sputtering gold on both surfaces, and then polarized in a silicon oil bath under a DC field of 2 kV/mm at 110◦ C for 10 min. The value of d33 was measured using a d33 meter (Model ZJ-3D, Institute of Acoustic Academia Sinica, China). The pure (Kx Na1−x )NbO3 powders with perovskite structure were synthesized by hydrothermal method at 240◦ C for 8 hours with the addition of isopropanol. With increase of K content in the starting solutions, the morphology of the obtained crystals varied, and the K content in the products increased. The K/(K + Na) molar ratio in the products is lower than that in the staring solutions. The FT-IR spectra indicate that there is not the vibration of organic group in the obtained powders. The specimen with the composition of x = 0.22 exhibited the highest piezoelectric constant of d33 = 120 pC N−1 .
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
External force and displacement estimation for self-sensing control of a piezoelectric actuator A. Badel Institute of Fluid Science, Tohoku University, Japan
J.H. Qiu College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, China
T. Nakano Honda Automobile R&D Center, Tochigi, Japan
1
INTRODUCTION
Piezoelectric actuators (PEA) are commonly used as micro-positioning devices due to their high resolution, high stiffness and fast frequency response. Several methods have been proposed to control the displacement of PEAs. Some of these methods use an inverse model of hysteresis in the controller. This inverse model is sometimes based on a Preisach model of hysteresis (Ge & Jouaneh, 1996 – Cavallo, 2003) or on a “Generalised Maxwell Slip” model of hysteresis (Mayhan, 2000). Other approaches have been investigated, using a neural network (Yu, 2005) or a phase shifting operator (Cruz-Hernandez & Hayward, 2001) for hysteresis compensation. In all these studies, the external force on the PEA is supposed to be zero or constant. However, new applications of PEAs have emerged, in which the dynamic mechanical load cannot be neglected and/or for which the force is to be controlled. The aim of this study is to control the force generated by a multilayered piezoelectric actuator under dynamic mechanical loading. A classical way to control the piezoelectric force would be to use a force sensor in a feedback control loop, as shown in figure 1. The main drawback of this approach is that a
force sensor is a costly and bulky device. The basic idea of the present study is to replace the force sensor by a detection model which computes the piezoelectric generated force as a function of the voltage and electrical charge on the actuator. Such electrical measurements are inexpensive and don’t require much space. The proposed approach synopsis is shown in figure 2. 2
SELF-SENSING FORCE CONTROL
A model of PEA is proposed, that includes a new asymmetric hysteresis operator and that takes the external force into account. A detection model is deduced, which allows to compute in real time the PEA elongation and generated force starting from the measurement of the driving voltage and current. This detection model is used to replace the force sensor for closed-loop force control. Experiments are carried out using a two PEAs experimental setup. The first actuator is the controlled actuator, and the second one is used as a dynamic controllable mechanical load. Experimental results have shown the feasibility of self-sensing force control of piezoelectric actuators. A very effective control has been achieved under dynamic mechanical loading. However, two critical issues have been pointed out. The first one is the very
F
I V
Voltage V Charge Q
Actuator
Figure 1. Classical control – force sensor required.
detection Model
Detected F
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Amplifier
Desired F
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Amplifier
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Figure 2. Self-sensing control – no costly and bulky sensor.
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high precision required for the voltage and charge measurement. The second one is related to the creep effect in the PEA, that can affect the detection model efficiency. REFERENCES
Yu Y.C. & Lee, M.K. 2005. Sliding Mode Control of a Piezoelectric Actuator with Neural Network Compensating Rate-Dependent Hysteresis, presented at IEEE International Conference on Robotics and Automation, Barcelona, Spain. Cruz-Hernandez, J.M. & Hayward V., 2001. Phase control approach to hysteresis reduction, IEEE Transactions on Control Systems Technology, vol. 9, pp. 17–26.
Ge, P. & Jouaneh, M. 1996. Tracking control of a piezoceramic actuator, IEEE Transactions on Control Systems Technology, vol. 4, pp. 209–216. Mayhan, P. 2000, “Dynamic Modeling and Controller Design for a Piezoelectric Actuation System Used for Machine Tool Control,” Journal of Intelligent Material Systems and Structures, vol. 11, pp. 771–780.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Eddy current monitoring toward advanced plant maintenance Toshiyuki Takagi, Hisashi Endo & Tetsuya Uchimoto Institute of Fluid Science, Tohoku University, Japan
An approach of plant monitoring by means of eddy currents is proposed to observe the health of plant elements. Our eddy current monitoring (ECM) system performs a couple of tasks; one is to monitor the behavior of cracks found in the in-serve inspection (ISI); the other is to quantitatively evaluate the crack propagation from both the obtained ECM signals and 3D eddy current field analysis. The 3D eddy current field
analysis also accomplishes the eddy current focusing technique, resulting in the optimal design of probes for the monitored cracks. The software and hardware simulations demonstrate the ECM signals just corresponding to the crack propagation. A benchmark test reveals that our ECM system gives one of the efficient and reasonable tools for the advanced maintenance.
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Morphing structures and systems
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Adaptive aeroelastic structures for improved aircraft performance J.E. Cooper, V. Hodigere-Siddaramaiah, G.A. Vio, S. Miller & G. Dimitriadis School of Mechanical, Aerospace and Civil Engineering, University of Manchester, UK
1
INTRODUCTION
There is a growing interest in the development of adaptive aeroelastic structures to allow aeroelastic deflections to be used in a beneficial manner. Part of the 3AS research program was devoted towards investigating the use of changes in the internal aerospace structure in order to control the static aeroelastic behaviour. Such an approach is desirable and arguably advantageous compared to other possible concepts.
Figure 1. Typical wing cross-section
2 ADAPTIVE AEROELASTIC STRUCTURES The key idea exploited in the Adaptive Internal Structures approach is to make use of the aerodynamic forces acting upon the wing to provide the moment to twist the wing, as shown in Figure 1. Research at the University of Manchester has investigated the use of a number of different adaptive aeroelastic concepts including the use of rotating spars, split spars and spars that can move in a chord-wise manner. A number of different implementations are under consideration.
Figure 2. Typical wing FE model
3 AERODYNAMIC OPTIMISATION
4
A conventional Genetic Algorithm was employed to search for the most suitable stiffness distribution at some particular flight condition for the wing structure shown in Figure 2. The minimum drag was determined whilst maintaining some reference lift through changes in the trim. At some given flight condition and spar orientation/position/distance, an inner loop determines the required trim angle through a simple iterative scheme. Then the Genetic Algorithm loop determines the spar orientation that gives the minimum drag.
An initial investigation has been made into the use of optimisation methods to determine the optimum orientation/position of adaptive spar concepts. It has been shown that it is possible to achieve minimum drag whilst maintaining the same lift at different speeds and altitudes. Further work is continuing to increase the scope of the optimization through the introduction of the fuel condition and an increase in the number of spars and ribs whose stiffness can be adjusted, and the number of cases considered.
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CONCLUSIONS
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Dynamic shape control of thin-walled structures M. Krommer & H. Irschik Institute for Technical Mechanics, Johannes Kepler University Linz, Austria
Keywords:
1
Dynamic shape control, shallow shells, actuation stresses, surface profile
INTRODUCTION
Adaptive and smart structures have become a major subject of contemporary research. Smart structures are structures that like human beings are capable to automatically react to disturbances exerted upon them by the environment they are operating in. Typically, smart structures are put into practice by embedding or attaching smart materials to a substrate structure. These materials have both, actuating and sensing capabilities; a popular example would be piezoelectric material that exhibits the direct and the converse piezoelectric effect. As many of the structures, which are considered as candidates for implementing smart materials, are infinite-dimensional structures there is an inherent need for properly distributing the actuation. A method that has been successfully utilized for the design of distributed actuators is the method of shape control. In general shape control is concerned with finding a distributed actuation such that a structure assumes a desired shape. The latter shape may be the undistorted shape of the structure under the action of external disturbances or it may be a prescribed new shape for the structure. 2
DYNAMIC SHAPE CONTROL OF SHALLOW SHELLS
This paper is concerned with dynamic shape control of thin-walled structures; in particular with shallow shells modeled within the nonlinear theory of v. Karman and Tsien. We ask for a distribution of actuation stresses such that the resulting displacement of the shallow shell follows a desired trajectory in every point and at every time instant. A solution for the distributed actuation stresses is calculated, such that the goal of dynamic shape control is reached exactly. In a first step the simple problem of quasi-static shape control is solved. This solution induces an error
for the dynamic case. An exact solution for the control of the error dynamics is then found from a generalized Neumann-type integral; this formulation enables not only to find this exact solution, but also to proof the stability of the solution in case a PD feedback controller is implemented. 3
DYNAMIC SHAPE CONTROL OF SHALLOW PANELS
As a special example, we study thin-walled shallow panels. We seek for actuation stresses, which can change the surface profile of the panel in a desired manner. This problem is first solved exactly for panels under the influence of an aeroelastic loading proportional to the slope and to the transverse velocity of the surface by using arbitrarily distributed actuation stresses. This exact solution is compared to a quasistatic solution, with the error dynamics not controlled. Finally results are presented implementing an active feedback control of the error dynamics. From the results of the paper we conclude that the goal of dynamic shape control cannot be reached by a quasi-static solution with an uncontrolled error system. Actively controlling the error dynamics on the other hand side gives good results in comparison to the exact solution. In general, the error dynamics must be actively controlled, because it is not possible to use the exact solution; e.g. if we use patch type piezoelectric actuator networks instead of spatially distributed actuators. ACKNOWLEDGEMENT Support from the Linz Center of Mechatronics (LCM) is gratefully acknowledged.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Real-time control performance of a model-reference adaptive structural control system S.Y. Chu & S.C. Lo Department of Civil Engineering, National Cheng-Kung University, Tainan, Taiwan, China
1
INTRODUCTION
Recent publications have presented successful implementations of adaptive control techniques in various applications.The advantage of a model reference adaptive structural control (MRASC) algorithm is to adjust the control command signal while estimating the system parameters of the controlled structure in real time. An adaptive control application based on Lyapunov stability theory is presented in this paper. The Lyapunov equation used to define the adaptation law is designed based on a quadratic Lyapunov function candidate. The adaptive control force is calculated from both the measured states and the adaptive gains estimated from error states. The error states illustrate the trajectory tracking performance between reference model and controlled system. The global asymptotical stability is guaranteed by choosing a positive definite weighting matrix for the time-invariant linear system. 2
MRASC ALGOTRITHM UNDER EARTHQUAKE EXCITATION
The block diagram of a model-reference adaptive structural control (MRASC) system is shown in Figure 1. It is composed of four parts: a controlled structure containing unknown parameters, a reference model structure for specifying the desired output of the controlled structure, an adaptive controller to generate
feedback control force based on system states and adjustable parameters, and an adaptation mechanism (defined as the adaptation loop) for updating the adjustable parameters. For illustration purpose without loosing its generalization, we apply this MRASC algorithm to a linear time-invariant system subjected to earthquake excitation as follow,
The adaptive control force U(t) defined in equation (1) can be calculated according to the adaptive control signal u(t) as where θ T (t)= θdT (t) θvT (t) . Based on the basic philosophy of Lyapunov’s direct method, the necessary and sufficient procedure is to generate a scalar “energylike” candidate function for the dynamic system, and examine the time variation of that function. We choose a positive-definite scalar function as
By applying the Lyapunov’s direct method, the asymptotical stability of the proposed Lyapunov candidate function is ensured. Therefore, the core of adaptation mechanism will lie on the adaptation law defined as
Then the error states will converge to zero as the control process start. 3
Figure 1. Model-reference adaptive structural control system
CONCLUSIONS
The basic idea of a MRASC system is introduced and the derivation the proposed adaptive feedback control algorithm to fulfill the implementation requirement of civil structure under seismic loading is investigated. A systematic procedure to determine appropriate combination of parameters embedded in the weighing matrices of Lyapunov function is suggested.
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Bio-inspired structures and materials (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Numerical analysis for the non-matting condition of dry adhesive pillar-array structures H. Han, Y.-S. Cho & W.-D. Kim Korea Institute of Machinery and Materials (KIMM), Republic of Korea
1
INTRODUCTION
in order to know the relationship between non-matting distance and model parameters.
The most important targets of micro/nano-structure manufacturing are summarized by five design conditions as high aspect ratio of hairs, density of hairs, material properties, high surface energy and orientation of hairs. The density of hairs of these conditions is very important for high adhesion. However, if the hairs are packed too closely, adjacent hair will attract each other. This phenomenon prevent construction of adhesive force because hairs do not contact on the surface if hairs were attached each other. Moreover, we developed a finite element code for the analysis of matting phenomenon using body force by molecular potential. Elastic adhesive contact of a nano-hair model is analyzed with the FE contact model
Figure 1. Matting phenomenon of numerical model.
2
RESULTS
In this study, Matting configuration by the analysis results is similar to the experimental matting configuration as shown in Figure 1. The relation between dimensionless non-matting distance and aspect ratio could be fitted logarithmically. Coefficients obtained from logarithmic equation depicted an exponentially convergent behavior to a certain values. Therefore, we fitted the coefficients using exponential decay equation. We found that the coefficients converge to a certain constant as the width wider than tens nm. It means that a certain case of the width wider than tens nm has not been affected by the width of hair. We have to extrapolation the coefficient with respect to elastic modulus using non-matting distance equation as shown in Figure 2. Consequently, we constructed the non-matting criterion equation with respect to aspect ratio and elastic modulus.
Figure 2. Extrapolation dimensionless non-matting distance with respect to aspect ratio.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Water strider’s (Aquarius paludum) (Heteroptera: Gerridae) stroke force on the water P.J. Perez Goodwyn IBSS (Institute for Bio-Inspired Structure and Surface Engineering), Nanjing University of Aeronautics and Astronautics, Nanjing, Jiangsu, China
J. Wang, Z. Wang, A. Ji & Z. Dai IBSS, Nanjing University of Aeronautics and Astronautics, Nanjing, Jiangsu, China
K. Fujisaki Kyoto University, Grad. School of Agriculture, Lab. of Insect Ecology, Kyoto, Japan
1
EXTENDED ABSTRACT
We measured the force of free-swimming water striders (Aquarius paludum) using a hair attached to their back and a 3D force sensor (Fig. 1). We observed with a high-speed video camera, and chose only those measurements in which the stroke was just completed when the signal was transmitted to the sensor. The error calculated by comparing force and geometrical derived
3D force sensor
data, was estimated as 13%. Females in average were stronger (1.32 mN) than males (0.87 mN), however the ratio force/weight was not significantly different (Fig. 2). Compared to other lighter species’ data available in literature A. paludum seems to be stronger, but the ratio force/weight is actually lower (Fig. 2). A. paludum applies about 0.3–0.4 mN/cm with its midlegs thus avoiding to penetrate the surface tension layer while propelling rapidly over the water.
x
6
y
Fy
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γ2
ir ha
γ3 Fz
5
z force / weigh
Fx
4 3
male female G.lac/A.rem. n.s.
n.s.
2 1
α
0
β P water surface Figure 1. Set-up used for the experiments, showing the forces’ axes and angles considered (see explanation in text).
Figure 2. First two columns from left, average (+ SD) of force/weight (performance) for A. paludum males and females (n.s. not significantly different t-test P > 0.05). Third column: performance of A. remigis and Gerris lacustris (based on literature data) for comparison, not included in t-test.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Self-healing wire and cable insulation D. Huston, D. Burns & D. Hurley University of Vermont, Burlington, VT, USA
B. Tolmie Tolmie Inc., Grand Isle, Vermont, VT, USA
ABSTRACT
Table 1. Typical aircraft wire insulation specifications
Wire and cable failures are major maintenance and safety problems for many engineering systems. These problems are particularly acute in aerospace vehicles and systems. This paper will present results from an effort aimed at developing wire and cable insulations that can autonomously repair themselves after suffering from damage. A variety of potential self-healing technologies have been identified, Figure 1. These include vascular two-part systems, microencapsulated and state changing polymers, gels, expanding foams and pre-compressed foams. Benchtop experiments have confirmed the self-healing action and capability of these various technique, Figure 2. However, the requirements of being able to meet the stringent performance requirements of aerospace applications in terms of temperature range, weight, outgassing, moisture tolerance, arc-tracking, etc. severely limits the range of possible material choices Table 1. Additional restrictions come in the form of manufacturability. The most viable methods in terms of potential for flight certification and cost-effective manufacture have been identified.
Specification Temperature (high) Temperature (low) Smoke Flexure Resistance Arc Resistance Weight Voltage rating Impulse dielectric test Wrap test Shrinkage Hydrolysis Thermal shock Flammability Life cycle Humidity resistance Surface resistance
Figure 1. Possible combinations of self-healing wire and insulation cable technologies.
Figure 2. Elastic recovery of precompressed foam in axial direction following wedge cut.
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Passing Criteria 260◦ C −65◦ C 10 50 75 4 600 Vrms 6.5 kilovolts Mandrel test no cracking 0.125 in at 200 ± 2◦ C 2.0% weight increase 200 ± 2◦ C, 0.06 in change 600 Vrms, 60 Hz 313 ± 2◦ C, pass dielectric 500 M for 1,000 ft 500 M -in (min)
Localization of damage in structural systems: Algorithms
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Compressional wave based-damage identification by migration technique in concrete beam Ying Luo, Zhongfang Li, Ziping Wang & Guoqi Zhao Faculty of Science, Jiangsu University, Zhenjiang, China
1
INTRODUCTION
The state of infrastructure in a country reflects economic progress and stability, and indeed, the quality of its peoples’ lives. Over time, the environment, and mismanagement reduce the load carrying capacity, serviceability and durability of civil infrastructures. Recently, many engineering agencies have become interested in locating and evaluating defects or damage in civil structures. Concrete structures are common components of civil infrastructures. To evaluate the safety of a concrete structure, the locations and dimensions of interior cracks and voids must be estimated using nondestructive detecting techniques. Further more, One of the principal objectives of the development of NDT techniques is a reliable assessment of defects of concrete members even when they are accessible only from a single surface. Up to now, the most popular nondestructive method for detecting interior cracks in concrete element just from a single face is Ultrasonic Pulse Velocity Method which need to read the echo time directly and often
gets in trouble of obscure peak value time because of the high attenuation of the ultrasonic wave. The dominant wavelength in the concrete will be about 2 cm, if the velocity of stress wave in the concrete is 4000 m/s and the dominant frequency of the propagating waves is 200 kHz. The size of the aggregates within the concrete may be greater than 1–2 cm, which is comparable to the wavelength of the waves less than 1–2 cm. The waves propagating in attenuation factor of ultrasonic waves implies that conventional ultrasonic nondestructive techniques are not available to detect small cracks (ex. less than 1–2 cm) in concrete. Simann et al. found that a transducer-array method can effectively locate flaws, while Green suggested using the geophysical array method to measure and process the weak signals. Reflection seismology has proved to be efficient in exploring geological conditions of the earth’s crust. Cracks and aggregates in the concrete may be analogous to faults and gravel in the earth’s crust and can diffract ultrasonic waves as the seismic waves are diffracted in geophysical investigations. Young-Fo Chang used the correcting method in reflection seismology for detecting cracks in concrete
Figure 1. Imaging of concrete specimen by pre-stack migration technique.
Figure 2. Imaging of concrete specimen by pre-stack migration technique.
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structures, but it could only detect some of the horizontal cracks in the concrete in his paper because lost of migration technique and any other special signal processing tool. He suggested that migration and other tool should be adopted for detecting the interior cracks later in study what is we are doing just.
In this study, simulated cracks with different depths, size and dip angles will try to be imaged by an migration signal processing method. Hopefully, the results obtained from this study can eventually provide civil engineers with a high resolution method to detect cracks within concrete structures.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Application of adaptive HHGA–RBF neural network to damage monitoring for composite structures Zheng-qiang Li & Shi-jie Zheng Aeronautical Science Key Lab of Smart Materials & Structures, Nanjing University of Aeronautics & Astronautics, Nanjing, Jiang Su Province, People’s Republic of China
1
INTRODUCTION
Table 1.
Radial basis network output.
Delamination size
Delamination location
Predicted size
Predicted location
30 35 40 45 50
330.6 340.6 360.6 390.6 430.6
29.25 35.26 39.92 44.32 51.87
338.34 353.69 360.23 389.64 433.93
The wide use of neural networks in the field of structural health monitoring is motivated by the fact that neural network is a non-linear dynamics system and capable of mapping non-linear functions. There are many types of neural networks, among them, the back-propagation (BP) network, which is a kind of multi-layer feed forward networks, is probably the most frequently used type of neural network model in practical applications. Although many improved algorithms for BP network have been developed, training MLP networks based on backpropagation learning is still computationally expensive and difficultly to avoid fall into local minimum during training. Radial basis function neural networks (RBFNNs), as an alternative to multilayer perceptions, have been found to be very helpful to many engineering problems.
were computed using finite element method and fed into the radial basis function neural network to predict the delamination location and its extent. The simulation demonstrates that the radial basis function neural network based on hybrid hierarchy genetic algorithm is robust, promising and converges very fast.
2 THE HHGA–RBF NEURAL NETWORK
3
In the learning procedure of an RBF neural network, the determination of the hidden centers and the widths is of particular importance to the improvement of the performance of networks. Therefore, in this research, our main task is to discuss how to optimize the structure of the RBF neural networks, i.e., to determine the hidden centers’ number and their parameter. In this algorithm, an RBF neural network is first constructed with certain numbers of input nodes and output nodes according to real application; while the number of hidden nodes and the values of hidden centers and widths are uncertain and generated at random. Then the determination of the hidden neuron numbers and the hidden centers and widths are both fulfilled by genetic optimization. Finally, a hybrid learning process which combines the genetic optimization and the linear least square (LLS) paradigm is used to determine the weights. The modal frequencies of a beam with varying assumed delamination sizes and locations
The modal frequencies of a beam with varying assumed delamination sizes and locations were computed using a finite element model. The assumed different delamination sizes varied from 30.6 to 60.6 mm in intervals of 5 mm. The damage location for each delamination size varied from 330.6 to 530.6 mm in intervals of 5 mm. Sets of six modal frequencies for 533 delamination cases were found. The training of the RBF neural network was accomplished using the 528 sets of modal frequencies and their associated delamination characteristics as calculated by finite element analysis. Five sets of the 533 generated data were reserved for testing the convergence of RBF neural network and were not used for training. Ultimately, the five sets of reserved modal frequencies were input into the neural network and the results shown in Table 1 demonstrate that the RBF network can successfully predicted the delamination parameters(size and location) of the beams.
P1 P2 P3 P4 P5
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NEURAL NETWORKS IMPLEMENTATION
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
On the Hilbert-Huang transform and its application to system identification X. Fang, Y. Lu & J. Tang Department of Mechanical Engineering, The University of Connecticut, Storrs, CT, USA
EXTENDED ABSTRACT It is well known that a successful system identification requires two key elements: identification strategy/setup, and data processing and interpretation. This paper is focused on the latter. Currently, Fourier transform is widely used in signal processing, which, however, has several major drawbacks. Fourier transform is based on the assumption that the signal to be analyzed is periodic in nature and of infinite length. In practice, many signals are non-stationary or nonlinear. When Fourier transform is used, it may need many spurious harmonic components to represent them. It is well know that for periodic and band-limited signals the Fourier transform yields the true Fourier coefficients when exactly one or multiple periods are processed. A phenomenon called leakage will occur if the signal is non-periodic. This leakage problem can result in severe distortion of the Fourier spectral analysis for signals with few vibration or wave cycles. Recently, there has been significant interest in using the Hilbert-Huang transform (HHT) for system identification, data feature extraction, and damage detection, etc. The essence of HHT is the combination of the so-called empirical mode decomposition (EMD) that decomposes a time domain signal into its intrinsic mode functions (IMFs) and the Hilbert transform (HT) of the decomposed IMFs that leads to a temporal-frequency amplitude/energy distribution of the acquired response. An IMF represents a simple oscillatory mode embedded in the data series similar to a harmonic component in Fourier transform, but is more general and adaptive. In contrary to Fourier transform that only returns the average
amplitude and frequency contents over the entire time span of the signal, the Hilbert amplitude and the Hilbert spectrum (i.e., time-frequency-energy distribution) obtained from the HHT analysis may offer more complete and accurate characterization of the signals. However, one should notice that the Hilbert transform is directly related to the Fourier transform, that is, in frequency domain the analytical signal obtained by the Hilbert transform is essentially a one-sided Fourier transform where the negative frequency contents are removed, the direct component is kept unchanged, and the positive frequency contents are doubled. Therefore, the Hilbert transform may inherit the leakage problem associated with the Fourier transform. In the EMD process of HHT, each IMF is picked out based on the local characteristic time scale of the data (i.e., different frequency oscillation embedded in the signal). Therefore, it is possible to extract signals with discrete and/or continuous frequencies. In this paper, we investigate methods to eliminate the leakage problem in Hilbert transform. For signals with discrete frequencies (e.g., the sinusoidal harmonics), the accurate Fourier series can be obtained by means of regressive Fourier technique, which estimates the amplitude, frequency, and phase all together in the least-square sense. For signals with continuous change of frequency and/or amplitude, an approach based on curve fitting the envelope amplitude is explored. In this paper, we first outline the HHT method including the EMD and the improved Hilbert transform, followed by case studies and discussions on benchmark system identification and damage detection problems.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Hierarchical PSD damage detection methods for smart sensor networks R.K. Giles & B.F. Spencer University of Illinois at Urbana-Champaign, USA
Structural health monitoring (SHM) systems are networks of sensors used to monitor continuously the condition, and thus the safety, of structures. Once built, civil infrastructure immediately begins to age and dilapidate due to its constant exposure to the elements. Systems of manual inspections exist to ensure the public safety but they are costly in terms of human and financial capital and their effectiveness is dependent on the skill and thoroughness of the inspector. Installing a SHM system could improve the efficiency of the inspection process, increase the accuracy of the evaluation, and thus improve the safety levels of the structure. The effectiveness of an installed SHM depends on the type of sensor network installed, the computational model employed, and the damage detection algorithm implemented. Ideally, a SHM system would consist of densely distributed multi-scale sensors performing various algorithms to verify and refine the identification, localization, and quantification of damage. However, the scale of civil infrastructure poses many challenges in developing the ideal SHM system. Two general categories of sensor networks exist: wired and wireless. A bridge wired with a wired network would require considerable lengths of wire to provide power to and communicate with the sensors. A wireless network eliminates the long lengths of wire but has a limited power supply. Both wired and wireless networks have relied on a traditional computing strategy where neither data is stored or calculations performed at the sensor location but transmitted back to a base station where the storage and computation occurs. For small-scale deployments, this strategy is sufficient. However, a large-scale dense network would be unwieldy with a traditional computing strategy. An alternative is a smart sensor network where each sensor consists of a node with an on-board microprocessor and a wireless transmitter. A smart sensor network provided advantages in data aggregation, computation, and transmittance as well as providing a more
fault-tolerant approach to SHM. This new approach is not without problems and a principal task is to develop effective algorithms that can function with in the distributed computing environment of smart sensor networks. A smart algorithm requires that the damage detection occur hierarchically where only limited, local information is available and the computation can occur on the sensors themselves. This paper test an algorithm based on changes in the power spectral density (PSD) using numerical examples to tests its functionality and limitations in a hierarchical environment. The results show that the algorithm is effective in damage detection and location when limitations of node overlap, cluster size, cutoff frequency are properly observed. The minimum overlap of three sensors and minimum group size of five are exactly that – minimums. In full-scale civil infrastructure, the envisioned smart sensor network would consist of thousands of sensors deployed along its length and height. A network of only five sensors would not provide sufficient information to make an educated assessment of the structure’s functionality. However, any software that controls the clustering of the nodes must observe these minimums in order to maintain the accuracy and efficiency of the network as a whole. Being aware of the limitations of the damage detection method used in the hierarchical environment greatly improves the fault tolerance of the smart sensor network. While consisting of thousands of nodes, smart sensor networks will also be multi-scale. This implies that the networks will use various damage detection algorithms using different input data to evaluate the structure’s status. The proposed PSD method, though lacking information on the severity of damage, serves as a computationally and energy efficient method to detect and locate the damage. Implementing other methods using additional data, increased data sharing, or more intense calculations could then supplement the initial damage report.
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New sensor technology for civil engineering structures (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Predicting concrete compression strength using PZT Choong-Jae Cho, Dong-Eun Lee, Chang-Mok Suk & Whajung Kim Sch. of Arch. & Civil Engrg, Kyungpook National University, Daegu, Korea
1
INTRODUCTION
The usage of high strength concrete has been increased, because structures are getting larger in size, longer in span, taller in height, and deeper into underground nowadays. However, it is well recognized and addressed that high strength concrete retain brittleness resulting in sudden failure by nature even when a small damage is occurred. The high strength concrete needs to get special attention in ensuring the maintainability and safety rather than normal strength concrete does because it has much higher probability to be subjected to sudden failure. That is why a new NDT method, which is easy to use, effective and reliable for periodical inspection, is necessary. Therefore, this research aims to develop an economical NDT method applicable to assess the quality (or defect) of the entire concrete member in a short period time relatively. The research agenda is to study and/or assess how well the Impact-Echo method and PZT, which is easy to measure, cheep in price out of Smart sensor, met in predicting the distribution of compression strength occurred in a high strength concrete member.
2
Figure 2. Predicting the velocity distribution in the concrete member using new tomography Method (Styrofoam).
IMPACT-ECHO METHOD WITH PZT
Stress waves are generated by applying mechanical impact on a specific location on the surface of a specimen. When Volume-wave reaches to non-homogenous components or border layers between heterozygote mediums such as crack or void, the reflection ratio is increased because of the acoustic impedance, other than the Volume-wave is transferred into adjacent layer. IE Method evaluates monitors and examines the structural health using the multiple reflection acoustic generated due to the deviation of the acoustic impedance.
3
Figure 1. Predicting the velocity distribution in the concrete member using new tomography Method (mortar).
that the velocity at a part where mortar consist the major component with a lot of air void is subject to 1400 ∼ 1500 m/s velocity, while more than 2000 m/s is achieved in a part where mortar consist the major component with small amount of air void. In addition, the velocity at a part where Styrofoam is embedded and aggregates are placed are subject to low velocity and very rapid velocity (e.g. 4000 m/s) respectively. Therefore, the results show that the testing method is reliable in some sense.
RESULTS
Fig. 1 and 2 shows the velocity distribution inside of the concrete member. The testing results identifies
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Basis and application of GMR sensors for reinforced concrete elements J.S. Popovics & G. Gallo Department of Civil & Environmental Engineering, University of Illinois, Urbana/Champaign, USA
P.L. Chapman & M. Shelton Department of Electrical & Computer Engineering, University of Illinois, Urbana-Champaign, USA
1
INTRODUCTION
Damage to civil structures due to corrosion is a severe problem in American infrastructure. The inability of conventional non-destructive methods and visual inspection to accurately characterize the damage in reinforced concrete structures illustrates the need for a sensing method to determine corrosion. Traditional non-destructive evaluation (NDE) techniques to monitor in-place corrosion in concrete structures have strengths, but must be carried out using the equipment attached to the surface of the concrete above the corroding bar, and require direct electrical connection to the inspected bar. Embeddable, self-contained corrosion sensors have been developed. However, most of the sensor do not monitor the steel reinforcement directly, but rather indicates the presence of a corrosion-inducing environment in the vicinity of the steel. More recently magnetic field sensing has been proposed and applied to monitor corrosion without the need for excavation and connection to the steel.
2
GMR SENSORS
Although several types of magnetic field sensors are commercially available, we chose to study Giant Magneto Resistive (GMR) sensors because of broad sensing range, favorable environmental performance and low power consumption. Miniaturized GMR sensors may be integrated into a single chip.
3 TEST RESULTS Experiments with sandwich GMR sensors were carried out to investigate feasibility for application to corrosion sensing. The tests were carried out with air and a hardened concrete piece placed in between the sensor and the magnet. No effect owing to the concrete placed in between is seen. The expected 1/r (distance)
relationship was seen. The response from the rebar was similar to that obtained using a permanent bar magnet, implying that rebar may contain significant residual magnetic fields. The noise levels were found to be different for each sensor type: signal data variability appears to be independent of distance, but highly dependent on sensor type. Also, the input voltage has a significant effect on the computed output field. The results show that mean output field is properly corrected for the input voltage yielding the same output field response. However the noise (data variability) as characterized by signal standard deviation is greatly reduced by increased input voltage. A US standard #4 rebar was placed in a basic and acid solution to suppress and promote, respectively, active corrosion of the bar. Each test was carried out over a four-day period. Data were acquired from two GMR sensors every two hours. Thevisual comparison of the rebar after the tests indicated that corrosion was successfully induced in the acid environment and suppressed in the basic environment. A clear distinction in the mean field response and the standard deviation for both cases is observed. The corroding bar exhibits higher mean field but lower noise levels. 4
SUMMARY AND CONCLUSIONS
We propose magnetic sensing as a non-destructive method to monitor steel corrosion in concrete. GMR sensors show promise for this application. Initial experimental tests showed that the magnetic fields can be sensed readily, even through concrete. The residual magnetic field emitted by a piece of stock reinforcing steel bar can be significant, comparable to that of a bar magnet. Test data show that signal variability is highly sensitive to sensor type and input voltage. Initial results show that GMR sensor data are capable of distinguishing between passivated and corroding reinforcing steel bars.
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A forensic study of the collision of a cargo ship with the Vincent Thomas Bridge H-B Yun, R.D. Nayeri, S.F. Masri, F. Tasbihgoo, M. Wahbeh & R. Wolfe University of Southern California, Los Angeles, CA, USA
On 27 August, 2006, the Vincent Thomas Bridge, a critical 1850-m suspension bridge, located in the metropolitan Los Angeles region had a collision with a large cargo ship, passing under the bridge. This incident left the transportation authorities wondering about the structural integrity of the bridge. Immediately after the accident, the bridge was closed to traffic until structural engineers from the California Department of Transportation (Caltrans) completed an analysis of the bridge. Interest in the field of structural health monitoring (SHM) has been growing at a fast pace in the recent past due to the great developments in the fabrication of innovative sensors, the ease of deploying sensor networks, and the associated high growth in the computational power that is becoming readily available with personal computers. Furthermore, the development of sophisticated digital signal processing tools for the analysis of vibration signatures of dispersed civil infrastructure system has generated a lot of interest in the application of such analysis tools, in conjunction with real-time monitoring approaches, in order to perform virtually continuous condition assessment of any instrumented structure. A real-time continuous monitoring system has been developed by the researchers at the University of Southern California, and deployed onto the Vincent
Thomas Bridge since 2005. Using the monitoring system, the dynamic response of the bridge was successfully recorded before and after the incident as well as during the collision process. The analysis of these valuable data allows the transportation authorities to quantify the effects of the collision on the bridge structural condition, which would otherwise be infeasible with traditional visual bridge inspection approaches. A forensic study was performed to assess the structural condition of the bridge before and after the incident. Relatively long time history records of the bridge oscillations were used to analyze its nearly stationary response by applying multi-sensor system identification approaches, utilizing the NExT-ERA methods. Both global and local identification methods were applied to detect significant changes in the bridge vibration signature. The identification results show that there are no significant system changes due to the collision. By utilizing a web-based SHM system that is installed on the bridge, it is demonstrated that analysis of the acquired sensor measurements can provide the owners of critical infrastructure system with a forensic tool that enables reliable and rapid assessment to analyze the circumstances and consequences of extreme events to which the target system is subjected.
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Electroactive sensors and actuators (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Fabrication and performance of functionally graded piezoelectric bending actuators J.H. Qiu & K.J. Zhu The Aeronautical Key Laboratory for Smart Materials & Structures, College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, P.R. China
1
INTRODUCTION
Unimorph and bimorph piezoelectric actuators are used for applications which require large displacement output [Uchino K. 1986]. Since these actuators are manufactured by bonding one or two piezoelectric layers to a metal shim layer, the bonding interface has low strength. On the other hand, large stress discontinuity and concentration are induced in the bounding interface due to the difference of material properties between the shim and piezoelectric material. The stress concentration and structural weakness at the bonding interface are the main causes for the breakdown of the bimorph and unimorph actuators in cyclic actuation [Aburatani H. et al.]. To increase the durability of bending actuators, RAINBOW actuators were proposed by Furman, Li and Heartling [Heartling G. H. 1994, Furman E. 1994]. In RAINBOW, the shim layer is produced by chemical reduction at high temperature. Since the shim layer and piezoelectric layer are chemically integrated, the interface has high strength. But the stress discontinuity cannot be relieved due to the discontinuity of material properties. The authors proposed a new type of functionally graded (FG) piezoelectric actuator in the former paper and illustrated that the stress discontinuity could be significantly reduced in the FG piezoelectric actuator using FEM analysis [Qiu J. et al. 1999, Tani J. et al. 2001]. In this study, the FG piezoelectric actuator was fabricated from the materials of Pb(Ni1/3 Nb2/3 )O3 -PbZrO3 -PbTiO3 (PNN-PZ-PT) family. In order to generate a bending deformation, it is required that the piezoelectric material on the opposite sides of the actuator generates different in-plane strains under a given electric field in the thickness direction of the actuator. When the distribution of in-plane strain is linear in the thickness direction, a natural bending
deformation can be produced without internal stress. In the practical manufacturing, continuous distribution of material composition is difficult, and instead, multiplayer structure is used. In this study, four material compositions were selected from the PNN-PZ-PT family and used as the materials of the four layers in the new FG piezoelectric actuator. The layer to generate high strain has large piezoelectric constants but small dielectric constants. On the contrary, the lowstrain layer has small piezoelectric constants but large dielectric constants. The stress distribution in the actuator depends on the thickness ratio of the layers, but for the convenience of manufacturing, the thickness of the four layers was set to the same. Since the internal stress induced by electric field is difficult to measure, the durability of the FG piezoelectric actuators was measured and compared with the traditional bimorph actuators under the condition of the same displacement output. In this study, a functionally graded piezoelectric actuator was fabricated and its performance was evaluated and compared with that of traditional bimorph actuators. Though the FG actuator needs much high voltage to generate the same displacement, it has much higher durability in the condition of the same displacement output. Advantages of the new FG actuators over the traditional bimorph actuator, such as small mechanical damping and heat generation when driven at large vibration amplitude, were exhibited by the measurement results. The disadvantage of small displacement output of the FG actuators at the same input voltage can be overcome by reducing their thickness and increasing the gradation of material properties. As the future work, thinner FG piezoelectric actuators, which require lower voltage, are to be fabricated. It is also important to optimize the thickness ratio and to investigate the inter-layer diffusion during sintering.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Nonlinear dynamics of acoustic compressors A. El-Sabbagh ASU Sound and Vibration Lab, Ain Shams University, Cairo, Egypt
A. Baz Department of Mechanical Engineering, University of Maryland, College Park, USA
1
INTRODUCTION
Extensive efforts have been exerted to analyze and develop a wide variety of standing wave acoustic compressors. For example, Dickens and Baz (2005) and El-Sabbagh and Baz (2006) have utilized smart piezoelectric actuators to generate high-pressure standing waves inside optimally configured chambers by developing linear and nonlinear models. In this paper, the emphasis is placed on analyzing the nonlinear features of acoustic compressors with entirely-driven and piston-driven resonators with cylindrical cavities.
Figure 1. Frequency vs. pressure at 75 g.
3
CHARACTERISTICS OF ACOUSTIC COMPRESSORS
Figure (1) shows the characteristics of the two compressors configurations. 2
NONLINEAR MODELS OF ACOUSTIC COMPRESSORS
4
CONCLUSIONS
The obtained results indicate that the piston-driven cavity AC pushes the threshold of the jump phenomenon to higher acceleration levels whereby higher output pressures can be achieved than the case of an entirely-driven cavity AC. REFERENCES
Equation (1) indicates that entirely driven cavity reduces to a Duffing oscillator with a softening cubic stiffness subjected to simultaneous harmonic and parametric excitations. However, equation (2) shows that a piston driven cavity resembles a Duffing oscillator which is subjected to only harmonic excitation.
Dickens, R. A. and Baz, A.; 2005. Optimization of a piezoelectric acoustical compressor. Smart Structures and Materials Conference, Paper # 5757-11, 6-10 March 2005, San Diego, CA. El-Sabbagh, A. and Baz, A. 2006. “A coupled nonlinear model for axisymmetric acoustic resonators driven by piezoelectric bimorphs”, Journal of Mechanics of Advanced Materials and Structures, 13 (2): 205–217. Acknowledgements, This work has been funded by DARPA under grant number NBCH1040001.
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Guided wave piezoelectric wafer active sensor arrays for damage detection L. Yu & V. Giurgiutiu University of South Carolina
Structural health monitoring (SHM) is able to detect and interpret adverse changes in the structure, which will greatly reduce the life cycle cost. Some of the advantages of SHM over conventional non-destructive evaluation (NDE) would be reduced inspection downtime, elimination of component tear down, and potential prevention of failure during operation. This would well be used in identifying failure in aircraft, where thin plate-like structures find a variety of applications in the aerospace industry. Due to the meticulous through-the-thickness C-scans of large area, structural inspection and damage detection in thin wall structure using conventional NDE techniques are time-consuming. One way to increase the efficiency is to utilize the guided waves, e.g., Lamb waves in thin plates. Lamb waves are guided waves that propagate inside thin-wall plates and shallow shells. Lamb waves can be either symmetric or anti-symmetric across the material thickness (known as Sn and An, respectively, where n represents the number of inflection points across the thickness). Attempts have been made to implement the inspection of large structure from a single point by using phased arrays. The advantages of using a phased array are multiple. The application of phased array such as an EMAT array or a passive piezoelectric wafer array has been made by many researchers. However, it seems impractical and costly to conceive an SHM system based on conventional ultrasonic transducers permanently installed in an aircraft structure in a number suffi-cient to achieve the required structural coverage. The low cost, inexpensive, and small commercially available transducers are needed to construct embedded in-situ phased array for SHM. This paper describes an in-situ method for damage detection using phased arrays of piezoelectric wafers active sensors (PWAS) that are permanently attached to the structure. PWAS are small wafers of piezoelectric material that are permanently bonded to the material surface and can simultaneously act as elastic wave transmitters and re-ceptors. Due to the in-plane surface coupling, PWAS are ideally suited for the generation of guided plate waves (Lamb waves).
Of particular importance is the fact that PWAS are coupled with the material strains parallel to the material surface. Thus transmission and reception of Lamb waves in thin-wall structures are greatly facilitated. This type of coupling, which is parallel to the material surface, is significantly more efficient for the excitation and reception of Lamb waves than that of the conventional ultrasonic transducers which can only impinge normal to the material surface. Here we bring up the construction and implementation of an in-situ embedded phased array using the piezoelectric wafer active sensors. The method uses scanning beams of guided waves that can travel at large distances with little energy loss and hence permit the interrogation of large structural areas from a single location. The novelty of the present method, as different from conventional ultrasonic phased array, consists in use of the unobtrusive and inexpensive permanently attached PWAS to perform interrogation and beamforming as a signal post processing procedure. In order to apply the beamforming theory to guided wave application, a mode tuning technique is employed to obtain the required single mode excitation for the phased array application. After reviewing the principles of the PWAS phased array, its implementation algorithm, the embedded ultrasonic structural radar algorithm (EUSR), is introduced briefly. Based on the developed PWAS phased array beamforming formula, we bring up the practical implementation of PWAS arrays and present analytical and experimental results concerning the omnidirectional damage detection ability. Finally, damage detection on aluminum plates with various PWAS phased arrays is conducted. Results are presented and compared between linear and planar arrays. Results have verified that PWAS phased array can be used to detect single or multiple crack and/or hole defects within 0◦ ∼360◦ range. More studies and experiments should be extended to practical geometries and to composite or hybrid-material structures.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Strain sensing with a piezoelectric biopolymer Hanz Richter Department of Mechanical Engineering, Cleveland State University, Ohio, USA
Fernando G. Torres Department of Mechanical Engineering, Catholic University of Peru, Lima, Peru
Jennifer Sanchez Cleveland State University, USA
ABSTRACT The direct and converse piezoelectric effects have been exploited in a host of technological applications. Piezoelectric actuators, where deformation and/or force are generated in response to the application of electric charge (converse effect) are found in devices ranging from simple buzzers to sophisticated nanopositioners. The direct effect, or the generation of charge in response to force and/or deformation, is used in piezoelectric sensing. Piezoelectricity has long been known to exist in biomaterials. In particular, the piezoelectricity of bone, collagen and cellulose have been extensively studied. In the majority of these materials, charge-stress coupling is significant only in shear. Although the piezoelectric effect in these materials is wellunderstood and substantial literature and data are available, the engineering of bio-based transducers is an emergent field. In this paper, we demonstrate the feasibility of strain sensing using a particular biopolymer -chitin- as the base material. Chitin and its derivative chitosan are amazingly versatile polymers. Aside from their piezoelectric properties, these materials have found many applications in industry and medicine. Chitin is found naturally in the shells of crustaceans like lobsters and crabs and in the exoskeletons of other arthropods like ants and beetles. A remarkable property of chitosan is that it is biocompatible, and further, it accelerates the wound healing process. For this reason, it is used in wound and burn dressings for humans and animals. It is also used as an absorbable suture, exploiting its mechanical strength, biodegradability and biocompatibility. Most biopolymers, and polysaccharides in particular do not show tensile piezoelectricity, due to the absence of an intrinsic polarization in their β crystalline structure. Piezoelectricity, however, is observed when shear stress causes slip between the oriented molecules. The samples used in this experiment were obtained from centollon, a crab species from the southern part of
South America. The chitosan sample had a molecular weight of 860 000 Dalton, measured by viscosity, and a degree of deacetylation of 88%. A 2% (w/w) solution of chitosan in acetic acid (1% v/v) was made by stirring the mixture for 6 hours at room temperature, the solution was then filtered through a glass filter to remove impurities. A nanocomposite film was prepared using chitin whiskers as reinforcement. Sample thickness prior to electroding was uniform and equal to 0.05 mm. Physical Vapor Deposition (PVD) and MagnetronSputtering are techniques commonly used to deposit conductive electrodes on biopolymer and other thin films. Due to the time-consuming and expensive nature of these processes, electrodes were formed on the first sample by application of a silver-based conductive paint on both sides. Upon the success of the first experiment, sputtering was used to coat a second sample with high-purity silver. A steel beam with dimensions 137 × 38 × 0.85 mm was mounted as a cantilever. The biopolymer sensor and a conventional strain gage were bonded to the beam at 4 mm from the fixed end. The silver paint was used as adhesive, so that electrical contact exists between one of the electrodes and the beam, which is part of the ground circuit. The biopolymer sensor terminals were connected to a charge amplifier (PCB Piezotronics 464A). The amplified signal was displayed in a Tektronix digital oscilloscope with storage capabilities. The strain gage was connected to a Vishay signal conditioner and oscilloscope. Upon signal filtering, the vibration data collected from the biopolymer sensor matched that from the strain gage with very good fidelity. Experimental work demonstrates the feasibility of developing biopolymer-based thin-film strain sensors. As mechanical testing data of this family of materials become available, further studies can be conducted to completely characterize the electromechanical transduction properties, in particular the relaxation phenomenon of this kind of fiber-reinforced nanocomposite.
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Motion and vibration control (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
SOGFCMAC Fuzzy artificial neural network for active vibration control of flexible plate Liyuan Deng, Renwen Chen & Zhiwei Hou The Aeronautical Key Lab. for Smart Material & Structure, Nanjing Univ. of Aero. & Astron. Nanjing P. R. China
Flexible plate, a simplified model for the solar array of a satellite, is characterized by its large displacement, low and dense vibration mode frequencies and low damping when it is used in the space. It is a challenge to control the vibration actively. 1
SOGFCMAC ALGORITHM
In this paper, a cerebellum model articulation controller (CMAC) method is used for an active vibration control system of the plate using smart structure concept in which piezo ceramic materials are used as both sensors and actuators. To improve the nonlinear approximating ability of CMAC, a fuzzy CMAC with Gauss basis functions (GFCMAC) is used. After improving the self organizing feature of the Kohonen algorithm, a structural self organized algorithm for GFCMAC(SOGFCMAC) was introduced. The SOGFCMAC defines firstly L fuzzy rule patterns in input space and the degree of its matching with the L rule pattern without involving the complicated discretizing, quantizing, coding and hashing procedures used in traditional CMAC. Then, instead of using absolute distance as the winner selection criteria, the matching degree given is used to determine the g winning patterns (g represents generalization
constant). Finally, the centers and its corresponding weights of g winning patterns are updated. 2
EXPERIMENT RESULTS AND ANALYSIS
To achieve real time vibration control of the flexible plate, the output layer of the network was connected to the estimating layer. First, actuating the plate, and recording the signal from piezo ceramic materials used as sensors. Consequently, the sample of neural network was acquired. After the training over, the network was connected to the system of active vibration control of flexible plate for Real-time control. From the Experiment results, we can find the vibration attenuation was significant difference. The damping was enhanced several times. It shows the network achieve the expectations. 3
CONCLUSION
This paper show the effectiveness of the neural network in active vibration control. In system modeling, the characteristic parameter of the plate wasn’t used. So the precision of the sample tested by experiment is very important. The higher the precision of sample, the more perfect the control effect.
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Adaptive neural network structure-based on sensitivity analysis Xiao-Hua Yu Department of Electrical Engineering California Polytechnic State University San Luis Obispo, USA
ABSTRACT: Artificial neural networks (ANN) have been widely used for system identification and adaptive control in recent years. In general, a larger neural network (i.e., more hidden nodes and weights) may yield faster rate of convergence and is more powerful for solving problems. On the other hand, a smaller neural network requires less computation time that is advantageous in real-time environment where speed is crucial. Therefore, choosing the optimal network dimension becomes a critical issue in the design of artificial neural networks. In this paper, a neural network controller with adaptive size/structure is investigated and applied to regulate a class of DC power supplies. Reducing the size of the neural network can increase its speed of response and thus improve the performance of the overall system. An adaptive pruning algorithm based on sensitivity analysis will be discussed and computer simulation results will be presented. Keywords: Artificial Neural Networks, Sensitivity Analysis, Pruning Algorithm
1
INTRODUCTION
Before an ANN can be applied to solve a particular problem, its size (i.e., the number of hidden layers and the number of neurons in each layer) must be predetermined. In general, neural network (NN) learning is not only a function of training time (or number of training epochs), but also a function of network size. Given a certain set of training pairs, there are many networks that can learn the underlying mapping function; however, their generalization capabilities are different. In practice, we would rather overestimate the network size than underestimate it. 2 THE NEURAL NETWORK PRUNING ALGORITHM BASED ON SENSITIVITY ANALYSIS
the sensitivity of training error with respect to each individual weight, the least relevant weights will automatically be removed to reduce the size of a NN. 3
In this section, the sensitivity based pruning algorithm will be applied to reduce the size of a neural network controller for a class of DC power supplies. Computer simulation results show that the NN dimension can be reduced to only 39.6% of its original size while still maintaining satisfactory accuracy. 4
Sensitivity is a performance measure which indicates the contribution of each individual weight/node to the overall neural network performance. By estimating
SIMULATION RESULTS
CONCLUSIONS
In this paper, an adaptive neural network pruning algorithm is studied and applied to determine the size of a NN controller for a DC power regulator. Future research plan includes applying this approach on hardware to test its performance.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Optimal design method for sensors/actuators placement in the active vibration control of a 2D flexible plate Fangfang Han, Renwen Chen & Qiang Liu The Aeronautical Key Lab. for Smart Material & Structure, Nanjing Univ. of Aero. & Astron. Nanjing, P. R. China
1
3
INTRODUCTION
Active vibration control is applied to the vibration control of the flexible structure extensively. Several sensors and actuators are adopted to suppress the system vibration with infinite distribution parameter. It is of great importance for an active vibration control system to properly select its control gain parameters, and design optimally the placement and numbers of the sensors/actuators used in this system. In this paper, optimal design method for sensors/actuators placement in the active vibration control of a 2 D flexible plate is studied, including set up systematic model, improved genetic algorithms, numerical analysis based on 2 D flexible 2
IMPROVED GENETIC ALGORITHMS
The genetic algorithms is an effective global optimization method. Its basic content is to make the colony evolve to high adaptive value through natural selection, reproduction, and aberrance, etc, and reach the optimum state finally. The characteristic of simple genetic algorithms is to choose with turntable, to intercross at one point, it’s easy and simple but its convergence is too slow. An improved genetic algorithms is put forward. To reproduce code according to adaptive value order, so the optimum result is kept. To intercross with a test code, so the fine characteristic of the parent is contained in new code. It is better in global convergence than simple genetic algorithms.
MODEL OF THE SYSTEM 4
An energy based optimal positioning strategy is adopted. Maximization of the consume energy in the system means minimization of the total energy stored in the system. To express vibration response with total energy stored in the system, vibration can be regarded as scalar quantity. The change of total energy storage along with time is a differential coefficient that one scalar quantity function to time and this scalar quantity function reflect the result of vibration control.
CONCLUSION
Vibration control of 2 D flexible cantilever plate is studied using piezoelectric ceramic sensors/actuators. Matlab language is used to work out the improved genetic algorithms procedure. Numerical analysis shows that the proposed method is effective.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Research on controller of active probe of AFM for micro-manipulation Lina Hao & Wenlin Chen Northeastern University, Shenyang, Liaoning Province, China
Jiangbo Zhang & Ning Xi Department of Electrical and Computer Engineering, Michigan State University, East Lansing MI, USA
1
INTRODUCTION
AFM (Atomic Force Microscopy) has been used in micro-manipulation system of MEMS (Microelectro-mechanical System) and NEMS (Nano Engineered and Molecular Systems) structure assembly, and biology cell manipulation. A soft cantilever can provide sensitive force feeling while pushing nanoobjects, but on the other hand, the tip is very easy to slip over the nano-objects due to flexibility of the cantilever and makes the nano-manipulation inefficient. Of course, a relative rigid cantilever may overcome the tip slipping over the nano-objects, but the rigid cantilever is insensitive to the manipulation force. Therefore, the rigid cantilever is not suitable for haptic enhanced nano-manipulation. Thus, it is in a dilemma whether to use soft or relative rigid cantilever for haptic facilitated nano-manipulation. The traditional way is to use a soft cantilever and apply a preloaded normal force on the tip to keep the tip contacting the
x 10
surface and overcome the tip slipping over the nanoobjects. Since the preloaded force is generally much stronger than the tip-object interaction force, the haptic force feeling is dominated by the preloaded force. It becomes very difficult to feel the actual tip-object interaction force during manipulations. Consequently, it also becomes very difficult to precisely control the tip position in the lateral direction during manipulation because the preloaded force not only causes the cantilever to bend in the normal direction but also causes the tip to move in the lateral direction [Li G. Y. et al. 2004]. Furthermore, the preloaded force will wear out the tip and cause contamination easily. Hence, any technique that can actively change the nominal rigidity of the cantilever will help to perform the AFM based nano-manipulation without the preloaded force on the cantilever-tip. Therefore, it is necessary to take the deformation into account or find some way to eliminate the deformation.
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Figure 1. Real displacement of tracking square wave under POF controller.
Figure 2. Real results of scratching a line.
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Active probe of AFM is a kind of smart structure, and has unique characteristics than common probe.
We find that the method of periodic-output-feedback control based on infinite dimension system is a good way of inhabiting probe vibration and decreasing collision force of the tip. The results of this paper will be beneficial to the design of common controller of automatic micro-manipulation system and other smart structures.
3
CONTROLLER OF AFM ACTIVE PROBE
Several design methods of controller such as PD, LQR and Periodic output feedback (POF) controller have been addressed. Figure 1 shows the real results of tracking responses of square wave. Figure 2 shows the real results of scratching a line.
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CONCLUSIONS
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Modelling, identification and control of mechatronic systems equipped with smart actuators: research advances in Spain Ningsu Luo & Mauricio Zapateiro Institut d’Informàtica i Aplicacions, Universitat de Girona, Girona, Spain
José Rodellar & Fayçal Ikhouane Departament de Matemàtica Aplicada III, Universitat Politècnica de Catalunya, Barcelona, Spain
Micropositioning control and vibration reduction are subjects of special practical interest in automotive industry, mechanics, aeronautics, aerospace and civil engineering, as well as in nanotechnologies. Smart actuators based on piezoelectric and magnetorheological materials are particularly useful in high performance control applications, due to their high precision and fast response. These advantages can only be exploited through a fine constructive process and if appropriate theoretical tools are available. Indeed, smart actuators have a complex nonlinear dynamics. Due to the high performance required in closed loop, these actuators are prone to the uncertainties in the models and in the operation conditions. Thus it is essential to have appropriate analytical tools for the study and robust identification of their dynamic models. Moreover, the design of controllers needs the use of advanced control methodologies to be able to guarantee rigorously the narrow specifications in terms of stability, precision and robustness. Among various types of smart actuators, MR dampers are versatile devices that take advantage of the constitutive MR fluid to generate high forces with low energy requirements, simple mechanical design, few moving parts, and at a low cost. This characteristics together with the those of MR fluids make these devices of special interest for structural control applications. One of the most active research fields is related to the modeling of MR damper. These devices exhibit a high nonlinear behavior that can be observed in the hysteresis loop of the force-velocity response. Several models have been proposed. On one side, parametric approaches generally consider the damper as a viscous damping device and add some parameters that describe in some way the hysteresis behavior. On the other side, non-parametric models do not take into account the physical behavior of the device, but try to make a model based on the experimental observations. The use of one approach or the other depends on the ability to reproduce the dynamics of the damper
and the possibility of being part of a control loop. In general, parametric approaches are more complex than their parametric counterparts and further, it is rather difficult to find the inverse model, i.e., the equations that compute the current or voltage necessary to produce the desire force. This is in the end what is needed in a structural control system that makes use of these dampers. On the other hand, the flexibility of non-parametric approaches not only permits the construction of the inverse model in an easy way but builds a less complex model that can be used in real-time control. This paper has summarized the research activities developed by research group MICE at University of Girona and research group CoDaLab at Technical University of Catalonia in the field of vibration control of civil engineering structures equipped with smart actuators. The ongoing research is done within the research project “Analysis, identification and control of mechatronic systems with hysteresis and friction.Application to piezoelectric and magneto- rhelogical actuators”. It follows three complementary directions: the development of new theoretical tools for dynamic analysis, robust identification and intelligent control of systems with hysteresis and friction; the construction of prototypes of piezoelectric and magnetorheological actuators integrated in mechatronic systems and the experimental validation in these systems of the developed methods and algorithms. The paper is organized as follows. First, the experimental setups are described. Then, it is introduced the representative parametric models such as BoucWen model, hyperbolic tangent model, Dahl friction model, etc., and nonparametric models such as neural network models for characterizing the nonlinear hysteretic behavior of MR dampers. Some constructive comments on semiactive control are also given. Finally, conclusions have drawn and some future research outlines are remarked.
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Innovative sensing systems (3)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Influences of thermoelectric parameters on property of gas sensor H. Huang, W.L. Luan, S.J. Mao & S.T. Tu School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai, P.R. China
1
INTRODUCTION
of the lack of reliable method to measure thermal conductivity for thin film.
Thermoelectric (TE) materials have been employed as TE power generator and Peltier cooler. TE gas sensor, which was composed of TE materials as feedback part and catalyst as sensitive part, was approached by integrating TE effects with exothermic reaction of testing gases. However, the influences of TE parameters have not been reported as yet. It was commonly taken consideration of the whole performance of TE materials, which greatly constrained the selection and preparation of TE feedback part. The influences of TE parameters on property of sensor were studied by comparing the output voltage of sensors. The result would be meaningful on improvement of TE gas sensor. 2
EXPERIMENTAL
Bulk TE materials Ba1 -xSrxPbO3 (0 < x < 1) slats were prepared by solid reaction, and BiyTe1 -y (0 < y < 1) films were deposited on quartz substrate via RF magnetron sputtering. Pt film and Pt/ACC were respectively prepared as catalyst parts of bulk and film type H2 sensors, and then tested in 3vol% H2 /Air mixed gases. Fig 1 shows the photo of bulk H2 sensor and SEM picture of Pt/ACC catalyst. TE parameters of both bulk and film materials were measured at room temperature. The thermal conductivity of film were supposed as 1.5 w/m · K, because
3
DISCUSSIONS
The influences of Seebeck coefficient and electrical conductivity were measured simultaneously. The output voltage increased obviously with the increase of Seebeck coefficient, while partly decreased with the enhancement of electrical conductivity. Because Seebeck coefficient is related with carrier concentration, but electrical conductivity was dependent on both concentration and mobility of carriers. The influence of thermal conductivity was measured on bulk TE materials, where the output voltage monotonously reduced with the rise of thermal conductivity. The higher thermal conductivity would quicken the heat transfer, then result in the low temperature difference and voltage. Complicated changing trends of output voltage were gotten with the increasing power factor and ZT, which indicated that the property of sensor was independent on the energy transfer efficiency of TE materials. After the research on relationships between output voltage of sensor and TE parameters, the Grey relational analysis (GRA) were carried out, and the GRA degrees between sensor property and TE parameters were calculated as following order: r(V , α) > r(V , κ) > r(V , α2 σ) > r(V , ZT ) > r(V , σ) 4
Figure 1. Photo of bulk sensor and SEM of Pt/ACC.
CONCLUSIONS
The property of sensor was more or less depended on these TE parameters, and the monotonous changing relationship is valuable for selection of materials for TE gas sensor. Grey relational analysis was carried out to compare the effecting degree of each parameter. The calculating results indicated that the Seebeck coefficient and thermal conductivity showed more close relationship with the property of TE gas sensor.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A blocked beacon discovering scheme for sensor localization C. Wan & A. Mita Department of System Design Engineering, Keio University, Hiyoshi, Kohoku-ku, Yokohama, Japan
1
INTRODUCTION
Many earthquake resistant structures have been destroyed by the recent earthquakes, so that the reliability of the structures during earthquakes must be checked again using rational design methods. For this purpose, E-defense, which has the world largest shaking table, was built. EDgrid standing for E-Defense grid and inspired by the NEES was recently developed. It is the cyber infrastructure to support full-scale experiments to be conducted at the E-Defense. The EDgrid may deal with more than 1000 sensors, 27 cameras and 2 High-Definition (HD) cameras. With so many sensors and other devices available, automation including self-installation, self-organization and selfmanagement of the sensor grid becomes necessary. There is no doubt that embedded sensor network systems are always coupled to the physical world. To acquire the sensor’s position information is important and necessary. With more and more sensors are deployed in the buildings, manual sensor localization is not practical any longer. An automatic sensor localization system for structural health monitoring is needed to be developed. For the indoors sensor localization, accuracy and cost are two key issues. In order to improve the accuracy, advanced equipments can be applied, but the cost increases dramatically accordingly. Usually, people prefer to densely deploy the beacons instead. A beacon means a node whose position is already known so that it can be used as a reference point. However, as the beacon should be placed accurately, deploying beacon itself is a very annoying job. Other methods used widely to improve the accuracy are statistics method and the triangle rule. However, statistics method can do the work only when most of the estimate errors are within the permitted range. Also the triangle rule can only get rid of the outliers conceiving very large errors. For the localization algorism, line-of-sight between the nodes and a beacon is required to ensure the localization correctness. However, for the indoors environment, it is very hard to avoid all the beacons from being blocked, which will consequently make the distances overestimated. It should be noted that a beacon being blocked here does
not mean the receiver can not receive the signal sent by the transmitter at all, it only means that the receiver will receive the signal being reflected, refracted or diffracted, instead of receiving the direct path signal. Hence, if a beacon is blocked, the distance between the beacon and a receiver will become much larger than it actually should be. In this case, the final localization results will definitely been distorted. In this paper, a blocked beacon discovering scheme is proposed. With the blocked beacon discovering scheme, blocked beacons in a beacon grid may be found out and ruled out, thus the final result can be rectified and the accuracy can be improved. This blocked beacon discovering scheme will be helpful in the real sensor localization for health monitoring of large structures, especially for the system that the beacons are sparsely deployed.
2
SENSOR LOCALIZATION ALGORISM
For the localization systems, generally speaking, two kinds of schemes can be used, i.e., range-based localization scheme which uses absolute point-to-point distance estimates or angle estimates for calculating location and range free localization scheme which uses only the connectivity and proximity. Compared with the range free localization scheme, the range-based localization scheme can achieve a better accuracy, which makes it used widely for the indoors localization systems. Considering the facts that angles will be distorted by the reflection which can hardly be avoided in the indoors environment, and a small angle error may result in a big distance error, usually, distance estimates are often used for localization instead. In this case, lateration is applied to locate a node with several known distances. Figure 1 shows a two dimensional lateration with three beacons. For a three dimensional localization problem, which can be depicted as Figure 2 shows, following equations stand:
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Development of a PVDF-based rubber-tread deformation sensing system for understanding wheel/ground interactions Jingang Yi Department of Mechanical Engineering, San Diego State University, San Diego, California, USA
Hong Liang Department of Mechanical Engineering, Texas A&M University, College Station, Texas, USA
1
EXTENDED ABSTRACT
Understanding the fundamentals of wheel/ground interactions plays an extremely important role for not only efficient vehicle design but also for vehicle safe operations in transportation systems. Fundamental understanding of wheel/ground interactions is a challenging task because of highly nonlinearity in wheel/ground interactions and lack of in situ sensing mechanisms. The recently developed tire pressure monitoring systems can only sense very limited information and cannot be used for studying the real-time wheel/ground interactions. Tread deformation is the most critical information for understanding the wheel/ground interactions. In Moon et al. (2007), the use of polyvinylidene fluoride (PVDF)-based micro-sensor to measure the tread deformation has been presented. Figure 1 shows two different sensor placement locations inside the tire developed in Moon et al. (2007): one PVDF sensor is completely glued with the tire tread (Fig. 1(a)) and the other sensor glued and clamped only at the ends along the sidewall of the rubber tread (Fig. 1(b)). The first type of sensors can be used to measure the contact patch geometry and the traction/braking friction forces and the second type of sensors can be used to capture the radial deformation of the rubber tread.
In this paper, we present analytical models for the PVDF-based tread deformation sensors developed in Moon et al. (2007). We present two types of sensor models, namely pre-curved bending and buckling sensors. The analytical models can provide a relationship between the sensor measurements and the information of wheel/ground interactions, such as wheel radius change and the size of wheel/ground contact patch etc. For the bending sensor, we derive the relationship between the sensor output electric charge and kinematic motion of the PVDF film sensor. Figure 2(a) shows the schematic diagram of the PVDF-based deformation sensor attached to the tire tread inner surface. The PVDF sensor is initially curved along the tire tread inner surface. When the tire rotates, the tread deforms flat on the tire/ground contact patch as shown in Figure 2(a). By measuring the generated charge, we can estimate the deformation information and the dynamic interactions between the tire and ground. For the buckling sensor shown in Figure 1(b), we consider a PVDF-based buckling elastica shown in Figure 2(b). One end of the PVDF elastica is clamped at a fixed platform and the other end is also clamped with a moving platform. Based on the heavy-elastica buckling theory, we derive an analytical closed-form formulation to capture the relationship between the output charge and the sensor endpoint deformation.
Figure 1. PVDF-based deformation sensors. (a) Sensor under bending, and (b) sensor under buckling.
Figure 2. A schematic of (a) the bending sensor and (b) buckling heavy-elastica sensor.
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We have developed a deformation sensor characteristic testing kit to experimentally validate and capture the relationship between the deflection of the sensor and the output charge. We also demonstrate some experimental results of the proposed sensors on a mobile robot. The experimental results and development show the feasibility of the proposed sensing techniques.
REFERENCES Moon, K., H. Liang, J. Yi, and B. Mika (2007). Tire Tread Deformation Sensor and Energy Harvester Development for “Smart Tire” Applications. In SPIE Proc. of Sensors and Smart Struc. Tech. for Civil, Mech., and Aerop. Syst., Volume 6529, San Diego, CA.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Design of intelligent flow auto-monitoring system-based on GPRS wireless network Xu Tian & Renwen Chen The Aeronautical Key Lab. for Smart Material & Structure, Nanjing Univ. of Aero. & Astron. Nanjing, P. R. China
Tigao Lei Nanjing Research Center of Mechanical, Electrical and Hydraulic Engineering
1
INTRODUCTION
Remote flow data collection in industrial field usually needs multi measuring points, which are distributed widely. In view of the characteristic of flow data acquiring in project, an intelligent flow auto-monitoring system is designed, which integrated with GPRS technology. The auto-monitoring system through GPRS is quicker and more cost-efficient than through manual work or wire network and has the merits of simple to build up, low running cost, always online, easy to extend and maintain. 2
of initialization are as follows: ➀ accessing the access point “AT + APN = user VPN”; ➁ address and port of server “AT + IPAD = server IP”, “AT + PORT = port number”; ➂ identification of GPRS DTU, “AT + IDTN = 8 bit Modem ID” and “AT + PHON = 11 bit Phone ID”.After setting of the parameters, GPRS DTU can be started up and automatically connected to the server.
3.1
Socket communications between GPRS DTU and data center
For more reliable transmission, the TCP protocol with connection oriented will be used in the system. The communications between application program and
SYSTEM COMPOSITION AND WORKING PRINCIPLES
The system consists of three parts: data acquisition terminal, data transmission network, data center. GPRS DTU(GPRS data terminal unit) communicate with flowmeters by RS485 bus, which make up of data acquisition system in field. In accordance with task of data acquiring, data center send collection commands to GPRS DTU through GPRS network. GPRS DTU transmits the orders to appointed instrument by RS485 bus. The flowmeters answer and return results of data to GPRS DTU. Then the packet data will be sent to data center by GPRS network. Meanwhile, data center can transmit remote configuring commands to GPRS DTU and flowmeters running in field in order to control the state of instrument.
3
3.2
KEY TECHNOLOGY OF SYSTEM Initialization of GPRS DTU
When GPRS DTU starts up, IP of GPRS inner net will be automatically acquired and it actively connects the server with certain IP. Firstly, GPRS DTU is connected to PC via RS232 serial interface, and its parameters are initialized by PC. AT commands
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TCP/IP must use sockets. In the system, data center is as the server and GPRS DTU is as the client. 4
CONCLUSIONS
data rate, always online, real- time communication, charging by flow quantities, high security and wide networks coverage. It achieves data acquiring of flow and unified management of data and information in field. The system has wide application prospects.
Intelligent flow auto-monitoring system takes full advantage of merits of GPRS technology such as high
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Development of integrated wireless sensor powered by MsM energy harvester Shuntao Liu, Lei Wang & F.G. Yuan Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, USA
1
INTRODUCTION
a multi-layered MsM. The circuit design is shown as Figure 2.
In this paper, a new class of wireless sensor powered by energy harvester based on amorphous Metglas 2605SC is developed. In experiments, the average power and power density during charging the ultracapacitor can achieve 576 W and 606 W/cm3 at high frequency.
4
2
For a working prototype, the average power and power density during charging the ultracapacitor can achieve 576 µW and 606 µW/cm3 respectively as shown in Figure 3.
FRAMEWORK OF WIRELESS SENSOR POWERED BY ENERGY HARVESTER
EXPERIMENTAL STUDIES ON ENERGY HARVESTER
2.1 Wireless Sensor with Dual-Controller A new dual-controller based architecture for wireless sensor design is motivated, which takes advantages of conventional wireless sensors for low speed applications, whereas it should enable power efficient operations for high speed applications. 2.2 Energy Harvester As proposed in Figure 1, an energy harvesting wireless sensor has a architecture including an energy harvesting module with two built-in units: harvesting device unit and energy harvesting circuit unit.
Figure 2. Electrical circuit for the MsM harvester. 3 Charge
Discharge
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ultra
(V)
DESIGN OF WIRELESS SENSOR POWERED BY ENERGY HARVESTER
V
3
A new class of energy harvester module based on MsM is presented. It has two units: a harvesting device and
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0 3.3V DC output
Self shutdown
Self startup
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DC DC
(V)
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t (hr)
Figure 1. General architecture of an energy harvesting module and compatible wireless sensor nodes.
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t (min)
Figure 3. Experimental results of the charging/discharging of the ultracapacitor and output performance of the smart voltage regulator.
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5
CONCLUSIONS
A new class of wireless sensor powered by energy harvester is designed, developed, and tested in magnetostrictive vibration. The wireless sensor with
dual-controller is suitable for the high-speed data acquisition and the harvester holds a promising as an alternate scheme of energy harvesting apart from the common piezoelectric energy harvesters.
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Paradigms and technologies related to the engineering and management of intelligent infrastructures and constructed systems (1)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Current status and future issues on bridge management H. Furuta Kansai University, Takatsuki, Japan
M. Kayano Road Bureau, MLIT, Tokyo, Japan
E. Watanabe Kyoto University, Kyoto, Japan
1
INTRODUCTION
This paper presents the current status of bridge maintenance and bridge management system or asset management system. The outline of bridge management system is illustrated and defects and problems to be overcome are clarified. In Japan there are 150,000 bridges with spans of more than 15 meters are in use so that it requires an enormous budget to maintain them in satisfactory conditions. Furthermore, sufficient data, experienced maintenance engineers, special technologies, and good ordering system are needed. In order to develop a bridge management system or asset management system, the concept of Life-Cycle Cost (LCC) has been paid attention as a promising tool for the achievement of rational maintenance programs. The basic concept and advantage of LCC are discussed. Several suggestions are provided to realize the rational and economic maintenance program and to develop a practical bridge or asset management system.
2
PROBLEMS OF BRIDGE MAINTENANCE
In Japan, there are severe environments surrounding bridge maintenance as follows: 1) 2) 3) 4)
Reduction of investment for infrastructures Increase of renewal investment Increase of maintenance cost Increase of stock of infrastructures.
Considering the above situation, it is necessary to overcome the following problems: 1) Economic problems enormous budget is necessary to maintain a great number of infrastructures. For
2) 3) 4)
5)
3
instance, there are 150,000 bridges (span length is greater than 15 m) in Japan. Labor problems it is difficult to collect a sufficient number of experienced maintenance engineers. Lack of data no satisfactory data is available due to old structures. Technical problems it is difficult to assess the integrity of existing bridges and to select appropriate repair methods, because each member has its own characteristic of deterioration. System Problems mismatching to the actual ordering system or estimating system.
PRESENT STATUS AND FUTURE OF BRIDGE MAINTENANCE IN JAPAN
Ministry of Infrastructure, Land and Transport (MLIT), Japan decided to publish a bridge inspection manual in which inspection should be made every five years for about 20,000 bridges. To establish a strategic bridge maintenance program, Bridge Management System (BMS) has been being built. Local governments also have been attempting to develop their own BMS or Asset Management System (AMS). AMS differs from BMS in the point that AMS focuses on the value of bridge as an asset. Namely, AMS aims to manage infrastructures, one of which is bridge, effectively and efficiently from the longterm vision. To establish a practical and useful BMS or AMS, it is necessary to overcome some problems like the variation of inspection results. Furthermore, new technologies such as IT and sensing technologies can be available to make the bridge maintenance more effective. Enormous data can be handled by using the recent database technology, and graphical information can be utilized as well as text information. Advanced sensing and
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monitoring system can provide us with useful quantitative information. Nevertheless, the most important is the education for the inspectors or maintenance engineers to obtain satisfactory knowledge and experience.
Sense of responsibility and passion of engineers may play an important role. Engineers should have a wider and overall perspective as well as the knowledge and skill based upon the ability of accountability.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A new maintenance and management methodology of smart infrastructures due to performance-based design Atsushi Kawamoto Aratani Construct Consultant Inc., Tottori, Japan
Wataru Shiraki Kagawa University, Kagawa, Japan
Keiichi Yasuda Newjec Inc., Tokyo, Japan
Norio Ito CAE Inc., Tottori, Japan
Masahiro Dogaki Kansai University, Osaka, Japan
Emin A. Aktan Drexel University, Philadelphia, USA
1
OUTLINE OF RESEARCH
In Japan, the Specifications for highway bridges have been revised from specification-based design to a performance-based approach, in order to accommodate smart structures. One of the important revision
tasks is to introduce the limit state concept into specification and structural performance level at limit states during and after hazards. However, sufficient attention does not pay to limit states of smart structures. As main revision tasks for performance-based design, is considered the manifestation of limit sates and required
Figure 1. Relation between live design and control of maintenance.
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performance levels, the proposition of methods for guaranteeing safety of each structure, and the planning of escape for disaster. A lot of infrastructures have been constructed with economic growth after the Second World War in Japan. Nowadays, it is an important how to effectively maintain such a huge stock of infrastructures as aging ones increase rapidly. Many studies, e.q., the life cycle cost analysis and asset management has been carried out on the maintenance and management of existing/aging infrastructures. Although a lot of management methods have been developed up to the present, there are few studies dealing with the structural performance level such as the load-carrying capacity of structures and the change of service conditions. In this paper, a new concept for maintenance and management of infrastructures is described.
A management process for maintaining the infrastructures is presented for satisfying multiple demand performances during the reference time. Two concepts such as current maintenance for with service in run and live design in emergency are fused into a new maintenance management concept of highway bridges under performance-based design concept (fig.1 reference). This is based on the performance-based maintenance of infrastructures, and is applied to the maintenance and management of infrastructures with normal service in run and during/after hazards. This method is introduced in the soft disaster prevention after the terror attacks on 11th Sept. 2001 in New York, and is named as live design.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
The frontiers of smart monitoring technology N. Miyamoto & T. Okamoto Keisoku Research Consultant Co., Ltd, Hiroshima, Japan
S. Sumitro Smart Structures LLC, Illinois, USA
H. Matsuda Nagasaki University, Nagasaki, Japan
ABSTRACT In recent years, many infrastructures have been deteriorating. In order to maintain sustainability of those infrastructures in which have significant influence to social lifelines, an economical and rational maintenance management should be carry out to evaluate their life cycle cost (LCC) (Sumitro, et al, 2001). Expected Structural Diagnostic techniques to retrieve degradation information, such as, crack separation, corrosion, carbonation, saltination, stress, flexure, displacement and vibration, can be considered as the first step in resolving the above problem. In this paper, the field application of optical base sensor technology, i.e., Laser scanner, LDV, optical wave, thermography, stick scanner, CCD camera, Satellite portrait, Electromagnetic wave diagnostic, X-ray, are introduced and compared. The field-applicability problems (solution, accuracy, speedy and safety) were summarized and discussed.
The field application of each evaluation techniques are categorized as observational, hazard prevention, cultural assets, and maintenance (Okamoto, et al, 2007). Furthermore, base on application experiences, significant features of suitable diagnostic technique are proposed for a reliable structural monitoring purposes. The features of the proposed optical_base diagnostic techniques are confirmed by comparing with several conventional techniques. The degradation information related to structural health monitoringbased maintenance (SHMBM) such as, crack propagation, delamination of concrete layer, carbonation, saltination, stress, flexure, displacement and vibration characteristic at either surface or inner of a existing structure, can be explored by full field optical measurement devises, e.g., infra-red, ultra-sonic wave, elastic-wave, laser, electromagnetic wave, and magnetic wave.The output information can be stress and/or other visible parameters in remote and non-contact media as shown in Figure 1.
Figure 1. Structural Degradation Information that can be detected by optical base sensory technology.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Concepts and issues of structural health monitoring for structural reliability and decision making F.N. Catbas University of Central Florida, Orlando, Florida, USA
D.M. Frangopol Lehigh University, Bethlehem, Pennsylvania, USA
EXTENDED ABSTRACT Bridge owners and engineers are challenged by the maintenance, repair or replacement needs of aging highway bridge inventories. Meanwhile, growing realization of the necessity for efficient management of infrastructure systems is leading engineers and researchers towards seeking novel approaches. Lifetime cost evaluation is required for optimum allocation of maintenance and repair budgets. Objective decision-making for life-cycle requires accurate and detailed data and reliable prediction tools. Reliability methods have been employed in the past for optimizing the repair and maintenance actions to minimize the life-cycle cost of highway bridges. However, available data for condition assessment comes mainly from visual inspections, which are the standard practice for today. Visual inspections are proved to be limited and subjective by research studies. Structural Health Monitoring (SHM) offers accurate information on structural condition via various sensors and analysis techniques. SHM provides tools for obtaining critical response quantities and data pertaining to structural characteristics accurately. Therefore, it is expected to become a valuable practice for bridge management practice in the near future. Previous SHM applications involve various methods for data collection, communications and analysis, however, there has only been a very few SHM development and demonstrations that have led to making critical decisions about maintenance and structural reliability. In order to make decision, data should be collected and processed to address specific concerns by considering the uncertainties in data as well as in the
final results. Sensor networks and data acquisition systems generate the required data from the structure. The data should be used to define the statistical distributions of the limit states for the reliability analysis. The procedure is described as generating the data, producing field calibrated analytical models with monitoring data, and then conducting a reliability analysis. Making reliable predictions are the critical needs for decision making in bridge management. The predictions can be improved with proper sensor data to fine-tune the prior distributions. This way, predictions will be more accurate, since the information source is more objective than the predictions based on visual inspections. Bayesian updating method is perfectly suitable for updating the condition with sensor measurements. An automated system can be coded, which would continuously update and adjust the parameters with the continuous input of sensors. Updated component reliability indices also form the updated system reliability automatically from parallel/series modeling. In this paper, example SHM applications using reliability methods are briefly presented. First, a long-span bridge was analyzed to obtain its system reliability and study the changes in reliability according to the collected temperature data. Then, monitoring the system reliability of a movable bridge was simulated with a calibrated finite element model. Finally, laboratory studies that investigate uncertainty quantification and prediction with reliability methods and Bayesian updating are summarized. In addition, issues concerning the integration of SHM and reliability are briefly discussed in the paper.
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Model updating in hybrid simulation
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Finite element model updating for roof space truss structure of Shenzhen Citizen Center Wei Lian Qu, Jinwen Wang & Hui Liu Hubei Key Laboratory of Roadway Bridge and Structure Engineering, Wuhan University of Technology, Wuhan, Hubei, China
1
3
INTRODUCTION
The FE model of a structure is constructed on the basis of highly idealized engineering blueprints and designs that may not truly represent all the physical aspects of an actual structure. It is difficult to update large span truss structure by traditional updating methods because of the numerous components structure has. The objective of this paper is to establish an appropriate method to update the FE model of large span truss structure according to its actual characteristic. 2 THEORY AND METHOD For truss structure’s material characteristic, sectional dimension and location of nodes can be accurately achieved by FE approach without updating and joint rigidities of nodes between components are unknown quantities because of the exit of articulate or rigid connection precise, the key of FE model updating is to obtain joint rigidities of nodes between components. The structure’s modal information is measured by field dynamic test. For the structure’s huge size and complex structural style, the locations of several sensors are optimized by Effective Independence method. The structure’s frequencies are identified by analyzing the achieved acceleration signal’s spectral response. Then accurate FE model of structure is achieved by following steps: Firstly, nodes are classified according to their size and rigidity, then by changing joint rigidity parameters of different types of nodes and using finite element method, the database which reflects the relationship between joint rigidity parameters and natural vibration frequencies of model is established. Secondly, structural natural frequencies are selected as the input, and joint rigidity parameters of classified nodes are the output, the artificial neural network is obtained by training the samples. Finally, the measured natural frequencies of the structure are inputted into neural network, rigidity parameters are determined.
ENGINEERING CASE STUDY
The roof space truss structure of Shenzhen Citizen Center is the largest steel truss structure in the world so far. According to its characteristic, the support truss’s nodes are regard as rigid nodes, and the other nodes are classified into three categories, each category has its joint rigidity parameter. When the joint rigidity parameter of every category of nodes is varying, the corresponding structure’s frequencies can be obtained by analyzing the FE model. Eventually, the database including nodes’ joint rigidity parameters and the structure’s corresponding frequencies is realized. The frequencies are selected as the net’s input, and as the corresponding three kinds of joint rigidity parameters as the output, three layers BP network will be trained. Taking the tested frequencies as the input, the joint rigidity parameters of three categories of the nodes are obtained by trained neural network. Thus, accurate finite element model of the structure is achieved. 4
CONCLUSIONS
The key techniques of the method are the establishment of the component’s model in which the joint rigidity of the nodes between components is adjustable, the confirmation of the location of testing nodes by optimizing, the accurate identification of the structure’s modal information and the felicitous management of intelligent algorithm for nonlinear mapping. To achieve the accurate FE model, the fundamental element type of the truss structure’s FE model component should be the three-element-combined-model introduced in this paper. Neural network technique provides an effective way to carry out the parameter identification of the structure with a higher precise.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Research on a smart external prestressed bridge with position-adjustable saddles Jing Wu International Institute for Urban Systems Engineering, Southeast University, China
Zhishen Wu International Institute for Urban Systems Engineering, Southeast University, China Department of Urban and Civil Engineering, Ibaraki University, Japan
Xiangke Liang College of Civil Engineering, Southeast University, China
This paper is based on such a widely accepted concept that if the equivalent load of prestressing balances the applied load, the beam structure would have no deflections. Though there are many factors generating deflections, it is still feasible to control the bridge deformation by regulating the magnitude and distribution of equivalent action of external cables. A series of Length-Adjustable Stay Bars (LASBs) are set as the saddles of externally prestressed bridge. When the length of the LASBs varied to some rules, both the configuration and tension of the cable would be affected and vary remarkably, hence the equivalent load and distribution of external prestressing vary correspondingly, then the deformation of the structure can be controlled. The input of the system is the displacements of the Monitored Points (MPs), and then commands to adjust the length of LASBs will be sent out after controlling algorithm. Thereafter, the structural deflection will be checked by the output of displacement of the MPs. This paper mainly dealt with the algorithm of the control system. Therefore, the vertical displacement of the upper points of the LASBs could be used as the control target in the regulating process, and the physical relationship between the length variation of the LASBs and the vertical displacements of the MPs should be found to form effective control arithmetic to reach the control target. The fundamentality of regulating the length of the LASBs is to establish the physical relationship between the lengths variation of the LASBs and the displacements of the MPs.
A numerical example is set up to simulate the process of controlling. The LASBs connecting the cable and bridge can protract or contract with temperature by specially define their material property, while they are set with infinite axial stiffness so as to ignore the length variation under axial load. A tentative calculation is conducted, and the result shows that the vertical displacement variance of the MPs does not remain constant but changes as the temperature rises, which means that nonlinear characteristic should be considered during the simulation and the algorithm of the control system should have the ability to deal with the problem rapidly. An iterative procedure, using the initial stiffness matrix, is introduced to generate a convergent conclusion. In this example, after 3 iterations the displacement at the monitored point converges to 1mm, which shows that the iteration procedure is stable and efficient. The conclusions are as follows. 1. Length adjustable stay bars at the saddle of external prestressed bridge are feasible to adjust the configuration of the external prestressed cable. 2. Evident nonlinearity could be detected in the control procedure of the external prestressed bridge with length adjustable saddles. 3. Establishing the stiffness equation of temperature load vector and vertical displacement vector, the iteration procedure based on initial stiffness matrix is proposed, and the calculation is efficiently convergent.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Stochastic modal parameters identification by frequency-domain spectrum-driven methods Danhui Dan, Limin Sun & Zhihua Min State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China
1
INTRODUCTION
It is accepted notion that the modal parameter identified from both decided excitation and stochastic excitation, whither what method used, must be look as random variable. The variation comes from several reasons; the first reason is the statistic variation, others are attributed to the structure character reasons, can be called system variations (can be seen in Figure 1). Even if in simulation case, whose structure characters maintain no change, the modal parameters identified from time integral data will also takes a prominent variations (can be seen in Figure 2). In this study, a new notion of modal parameter identification routines is proposed. It look all the taches in identification process as stochastic quantities. When considering the time variation characteristics, a stochastic process may be more exactly. Then impenetrate the statistic information throughout the whole process, and extract the information in statistic style. The statistic quality of the modal parameter estimations is evaluated. After that, make the statistical variation minimization as the target, to control the whole identification process in reverse, build the optimized modal parameter identification methodology. In one word, a stochastic modal parameter identification method is an optimized extraction process, which is based on the minimized statistic variation for identified result. Case studies show that the statistic variation of modal parameters is prominent in identifying the
Figure 2. Variation of identified frequency, system and stative variation.
Figure 3. Two modal parameter identification mothodologies, A (unidirectional): Deterministic, Value transfer, no statistic characteristics transfer; B (bidirectional): Stochastic, Value transfer, no statistic characteristics transfer.
system variations. And the minimum of the statistic of modal parameters can be select as the target for controlling and optimizing the process of identification.
Figure 1. Variation of modal para. and its estimation.
Keywords: Deterministic modal parameters identification, stochastic modal parameters identification, system variation, statistic variation.
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Structural damage and fault detection (3)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Successive zooming genetic algorithm in structural damage detection of truss bridge H.W. Kwon & W.J. Kim School of Architecture and Civil Engineering, Kyungpook National University, Daegu, Republic of Korea
Y.D. Kwon School of Mechanical Engineering, Kyungpook National University, Daegu, Republic of Korea
INTRODUCTION
1.05
Many methods have already been developed to detect the existence of structural damage based on monitoring the change in structural responses, it is generally more difficult to find the location and extent of the damage. Accordingly, this paper formulates the detection and identification of structural damage as an optimization problem. Output errors are used to formulate the objective function, where the difference between the measured and computed responses under static loading is defined as the output error. The structural damage detection problem in truss bridges has many variables, requiring many function calculations. Therefore, this study uses a successive zooming genetic algorithm (SZGA) to detect structural damage, as SZGA can search for a global solution without using derivatives and can perform a direct and probabilistic search simultaneously. The effectiveness of the suggested method is also compared with MGA. 2
SMALL-DIGIT CHARACTERISTIC OF SZGA
The SZGA has already been shown to be capable of pin pointing an optimal solution by searching a successively zoomed domain. In addition to its fine-tuning capability, SZGA only requires several chromo-somes for each zoomed domain, which is a very use-ful characteristic for structural damage detection in a large structure that has a great number of solution variables. To demonstrate this characteristic, SZGA and MGA were applied to the objective function of a simple multi-variable polynomial and the results compared. 3
NUMERICAL EXAMPLE FOR PROPOSED METHOD
1.00
Damage index
1
0.95 Exact value MGA SZGA-PDVA
0.90
0.85
1
3
5
7
9
11
Element No. Figure 1. Plane truss with 10% damage in element 3 using MGA and SZGA with four-digit strings.
accurately determined the location and magnitude of the damaged elements in all cases. Even when more than one damaged element occurred in the structure, the SZGA accurately detected and identified a higher level of structural damage than MGA without mistakenly determining a damaged member in the multiple damage cases. 4
CONCLUSION
The SZGA can determine the magnitude of damage at a 10−6 level of accuracy in the case of truss bridge structural damage. In case of damage above ten percent, the SZGA can determine the magnitude of damage at a 10−4 level of accuracy with only four or eight-digit GA strings. REFERENCE
One of the results of the structural damage detection are shown in Figure 1. Unlike MGA, the SZGA
Carroll, D.L. 1996. Genetic Algorithms and Optimizing Chemical Owygen-lodine Lasers. Developments in Theoretical and Applied Mechanics 18: 411–424.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Damage detection of spatial truss structure by using wavelet analysis Dongmei Tan & Wei Lian Qu Hubei Key Laboratory of Roadway Bridge & Structural Engineering, Wuhan University of Technology, Wuhan, Hubei, China
Shujin Li Department of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan, Hubei, China
1
INTRODUCTION
of the data can be retained and it can often compress or denoise a signal.
In this paper, a wavelet-based approach is presented for identification of damage locations or regions of spatial truss structure. The response simulation data employed in this study, It is found that damage due to the tensile failure of welded joints between the bar and the ball node when the damage occurs can be detected by a spike or an impulse in the plots of the variance of higher resolution details from wavelet decomposition of the acceleration response data and the location of the damage region can also be identified. Numerical results illustrate a great promise of wavelet analysis for detecting damage.
2 WAVELET ANALYSIS THEORY The traditional Fourier transform (FT) can also break down a stationary signal into continuous sinusoids of different frequencies, which transforms a signal from a time-based domain to a frequency-based domain, Unfortunately, in transforming to the frequency domain, time information is lost, When looking at a Fourier transform of a signal, it cannot present the time dependency of signals and it cannot tell when a particular event took place.To correct this deficiency, the wavelet transform (WT) is proposed which can be viewed as an extension of the traditional Fourier transform with adjustable window location and size. The wavelet transform has recently emerged as a promising tool for structural health monitoring(SHM) and damage detection. Wavelets are mathematical functions that give a time-scale representation of the time series and their relationships to analyze time series that contain nonstationarities. The wavelet transform can be used for multi-scale analysis of a signal through dilation and translation and it can provide multiple levels of details and approximations of the original signal, such that the time-frequency features of a signal can be extracted effectively. Therefore, the transient nature
3
NUMERICAL INVESTIGATION AND CONCLUSION
The spatial truss structure of Shenzhen Citizen Center serves for the numerical study, The topside of Shenzhen Citizen Center is a large span spatial latticed truss structure with 486 meters long, 154 meters width and 9 meters thickness in the thickest position. In this study, the tensile break of welded joints between the bar and the ball node of spatial truss structure is simulated. The vertical and horizontal acceleration response at different node is analyzed and discovered that the horizontal acceleration response is sensitive to the tensile break of welded joints, which is employed to detect damage. The horizontal acceleration response data is obtained before and after damage by analyzing finite-element model of original structure and which is decomposed into one level of Db4 wavelets. The external excitation is the artificial simulated wind load, the time step is 0.04 second. Simulation results show that the wavelet-based approach can be used for damage detection and demonstrates its application using numerical simulation data from a large span spatial latticed truss structure of Shenzhen citizen center. It shows that the tensile break of welded joints between the bar and the ball node may be detected by spikes in the details of the wavelet decomposition of the response data, and the locations of these spikes may accurately indicate the moments when the structural damage occurred. The damage region can be located approximately by comparing the details of acceleration response at different nodes from wavelet analysis. It can be concluded that wavelet analysis shows a potential of being an effective tool for damage detection.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Damage detection in beam-like structures using deflections obtained by modal flexibility matrices K.Y. Koo & C.B. Yun Korea Advanced Institute of Science & Technology, Daejeon, Korea
J.J. Lee Sejong University, Seoul, Korea
D.S. Hong & J.T. Kim Pukyung University, Busan, Korea
In bridge structures, damage induces an additional deflection which may naturally contain essential information about the damage. However, inverse mappings from the damage-induced deflection to the actual damage location are generally complex, particularly for statically indeterminate systems. In this paper, a new load and deflection concept, so called the positive-bending-inspection-load (PBIL) is proposed to construct a simple inverse mapping from the damage-induced deflection to the actual damage location as follows. Damage occurs at x = xD ⇔
where u (x) is change in the chord-wise deflection defined from the chord connecting two points at x = xa and xb as
where u(x) is change in deflection and = [xa , xb ] is the inspection region. A PBIL in an inspection region is defined as a load or a system of loads which guarantee positive bending moment in the inspection region. For an example, a uniform load is a PBIL for both a cantilever and a simply supported beam. Generally, a PBIL for any continuous beam system can be devised. The modal flexibility matrix Gm is defined as an expansion of the flexibility matrix using modal parameters as follows.
where m = [\ωi2 \], ωi is the i-th natural frequency, i = 1, …, m; m = [φ1 … φm ], φi is the massnormalized i-th mode shape, and m is the total number of modes estimated from a experiment. Then, any deflection profile under an arbitrary load f can be estimated by a simple matrix multiplication as
where u is a deflection vector and f is a load vector. Hence, a novel damage localization method is proposed using Equation 1 and deflections obtained by Modal flexibility. The procedure may be summarized as: (1) identification of the modal flexibility matrices from acceleration measurements, (2) calculation of the chord-wise deflections under the PBIL using the modal flexibility matrices, and (3) damage localization by finding the location with the maximum damage-induced chord-wise deflection with abrupt change in its slope. Numerical verification study was carried out on a simply supported beam to demonstrate its damage detection capability. The damage detection performance was also evaluated based on the spatially sparse and noisy measurements with a comparison of the Damage Index method. It was found that the proposed method was very robust to the measurement noise than the Damage Index method. It can be expected that the proposed method may be preferred in many situations when measurement noise is not guaranteed to be low. Experimental verification has been carried out on a two-span continuous bridge model with a steel boxgirder. The proposed method identified the damage location for relatively small damage cases of 12% reduction in the bending rigidity at a point with a narrow cut.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Application of empirical mode decomposition for structural damage detection: Experimental investigation Jun Chen, Guan-Yu Zhao Department of Building Engineering, Tongji University, Shanghai, China
Smart structures and materials, which can sense and respond to external stimuli, have received great interests among researchers from various disciplines as civil, transportation, mechanic, meteorology, aerospace and even medicine. Structural damage detection is one of the active research topics for smart structures. Due to the complex and difference of smart structures/system among difference disciplines and more important the varieties of damage type, the structural damage detection techniques are still in the research stage rather than application stage. Taking civil structures for examples, many large scale online structural monitoring systems with large numbers of sensors have been mounted on long-span bridges, high-rise buildings and large-span space structures recently, e.g. Hong Kong TsingMa Bridge, Sutong Bridge, JinMao Tower and Shanghai South Railway Station. In most cases, the hardware of these monitoring systems comprises many modern sensors. The damage detection software, however, is still based on the traditional techniques as power spectrum analysis. Thus to develop more effective damage detection method for different kind of structural damage is the primary concern for research on smart structure damage detection techniques. The development of structural damage detection techniques depends on, to a great extent, the improvements of other sciences as mathematic, computer, signal processing and so forth. Therefore, introduction of new idea or new method emerged in the related fields is a main source for developing new damage detection method. The empirical mode decomposition (EMD) is a new signal processing tool recently proposed by Huang (Huang et al. 1998). The EMD in tandem with Hibert transform, denoted as Hilbert-Huang transform HHT, has then been used by researchers (Vincent 1999, Yang 2004, Xu 2004a) in structural damage detection with varying success. The results demonstrate that
this method offers a simple, effective and accurate tool for parametric and damage identification. Nevertheless, the aforementioned studies are based on the numerical studies or for a special structural damage scenario, the possibility of damage detection using the EMD+HT method for general damage cases has not been experimentally investigated. In this connection, an experimental investigation has been carried out on the applicability of EMD+HT for identifying structural damage due to stiffness loss. It is observed from the experiment that: the EMD + HT approach with proper intermittency check can accurately identify the modal frequencies and it is not sensitive to the type of external excitation and the measurement locations. The modal damping ratios identification results are reasonable. The mode shape identification accuracy depends on the proper selection of computation parameters of empirical mode decomposition. The damage severity can be further quantified by the change of natural frequencies. REFERENCES Huang N.E., Shen Z., Long S.R., Wu M.C, Shih H.H., Zheng Q., Yen N.C., Tung C.C. and Liu H.H., (1998), The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis, Proc. R. Soc. Lond. A, 454:903–995 Huang N.E., Shen Z. and Long S.R., (1999), A new view of nonlinear water waves: the Hilbert spectrum, Annu . Rev. Fluid Mech. 21:417–457 Vicent H.T., Hu S.L.J. and Hou Z., (1999), Damage detection using empirical mode decomposition method and a comparison with wavelet analysis, Proc. Of the Second International Workshop on Structural Health Monitoring, Stanford University, Stanford, pp. 891–900 Xu Y. L., Chen J. (2004a), Structural damage detection using empirical mode decomposition: experimental investigation. Journal of Structure Engineering, ASCE, 130(11): 1 279–1 288
482
Civil infrastructure monitoring and assessment (3)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Do online identification on Donghai Bridge anywhere, anytime, and anyway Danhui Dan & Limin Sun State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China
Yang wang Shanghai Juyee Science&Technology Development Co., LTD
1
INTRODUCTION
To extract the characteristic of the measurement data automatically (online and real-time) is the key to realize intelligent monitoring function in Bridge health monitoring system. The dynamic properties of the bridge act as the significant condition indices for structure state identification, so it is necessarily to develop an online identification technique. In this paper, the author developed an internet based computing technique to provide a platform to do online
identification anywhere, anytime and anyway. On the basis of Donghai-Bridge Heath monitoring system (Ab. DHBHMS) integrated environment which is a Browser/Server framework software platform, a web service routine powered by Apache engine was developed in the remote application server, also a parallel remote interface technique in browser endpoint computer are provide for data access arbitrarily. Two set of toolbox in Matlab computing circumstance are developed by author to fetch the historical data stored in remote Database in Donghai-Bridge Heath
Figure 1. Automatically online modal parameter identification.
485
Monitoring System and real-time data just measured from the 478 sensors distributed on Donghai Bridge and thousands of inspection data stored in another remote Database in DHBHMS. By utilized the timer object program technique provided in Matlab 7.0.1, an automatic and scheduled online identification computing platform in browser computer is constructed. A standard interface for different online identification
routines is designed and the online modal parameter identification by PP methods are realized and integrated into this platform. As a result, in any places where the internet are available, by using monitoring data occurred any time (or on anytime you wanted), any arbitrary online identification routines can be done on this computing circumstance, which need the user contributes their own algorithms and programs.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Shake table experimental verification for a structural damage identification technique Li Zhou & Shinya Wu College of Aerospace Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing, China
Jann N. Yang Department of Civil & Environmental Engineering, University of California, Irvine, USA
ABSTRACT An important objective of a structural health monitoring systems is to identify the state of the structure and to detect the damage when it occurs. Analysis techniques for damage identification of structures, based on vibration data measured from sensors, have received considerable attention. Recently, an adaptive extended Kalman filter (AEKF) technique has been proposed for the damage tracking of structures. Simulation studies have demonstrated that the adaptive extended Kalman filter (AEKF) approach is capable of tracking the variations of structural parameters, such as the degradation of stiffness, due to damages. The purpose of this paper is to experimentally verify the capability of the AEKF approach in identifying the structural damage by conducting a series of shake table tests. In this paper, a 400 mm by 300 mm small-scale 3-story building model has been tested on the shake table using the El Centro and Kobe earthquake excitations. During the tests, acceleration and displacement responses of all floors have been measured and recorded. To simulate structural damages during the shake table test, an innovative device not available in the literature, referred to as the stiffness
element device (SED), has been proposed and constructed to reduce the stiffness of some stories of the test model. Prior to experimental tests, a SED device with a pre-determined stiffness is installed in selected story units, so that the stiffness of the selected story units increases by a pre-determined amount. During the experimental tests, the additional stiffness due to SED is reduced to zero to simulate the abrupt changes of the stiffness in the story units. Different damage scenarios have been simulated and experimentally tested, including different damage locations, different damage severities, and different damage time instants. Measured experimental response data and the AEKF approach have been used to track the variation of the stiffness in each story unit during the test. The tracking results for the stiffness of model stories are then compared with the stiffness predicted by the finite-element method. Experimental results demonstrate that the AEKF approach is capable of tracking the variation of structural parameters leading to the detection of structural damages. Likewise, the AEKF approach is also shown to be capable of predicting the structural responses, such as the drifts of all stories, with reasonable accuracy.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Damage assessment of concrete structures by drilling tests C. Kondo & A. Mita Keio University, Japan
1
3
INTRODUCTION
Compressive strength is the most important durability index for concrete structures and also the key factor to assess the quality or condition of concrete. However, existing estimation methods for compressive strength are not so effective due to their problems on variety of concrete material characteristics. In this study, a compressive strength estimation method for concrete structures using drilling tests and pattern recognition techniques is proposed. By observing the drilling behavior and comparing the physical quantity such as mean and/or deviation of drilling speed, torque, rotation speed, etc., the parameters highly correlated to compressive strength can be extracted. In order to evaluate the influence of aggregation, the drilling tests are conducted using concrete and mortar specimens and the compressive strength model which consists of cement and aggregate is created. The feature vectors which have good ability of classifying the compressive strength are then obtained by considering the combination of extracted parameters and drilling sections. Based on it, the Support Vector Machine (SVM) is built. The results show that the classification can reach a very high resolution. At last, applicability of this proposed compressive strength estimation method is well demonstrated.
The feature vectors were classified into different compressive strength classes by means of application of several SVMs. Each SVM classifies a feature vector to the corresponding compressive strength. For creation of the feature vector with high classification accuracy, the combination of the elements of feature vectors were chosen from the parameters which have high correlation with compressive strength. Then the feature vectors were divided into several training datasets, and the performance tests were conducted as the number of training dataset changed. We could recognize that the performance of SVM is getting worse when the number of training data set is less. And also it was revealed that each SVM had different tendency and it depends on the specimen and we can recognize that there are not so differences of the probability of positive outputs when the number of dataset is over 3, and in those cases, each SVM is considered well performed and the probabilities of positive outputs from SVM which includes misclassification are under 20%. In that sense, we could create the well performed classifier. 4
2
DRILLING TEST FOR CONCRETE
In order to obtain the parameters which have high correlation with compressive strength, we calculated the mean values and standard deviations of recoded data in the two directions; horizontal layer direction and depth direction. The correlation coefficients obtained from dataset of analysis of horizontal layers tend to be higher than those from dataset of depth analysis. Comparing mortar and concrete specimens, it is considered that standard deviation of drilling velocity is not related to coarse aggregates.
CLASSIFICATION USING PATTERN RECOGNITION
CONCLUSIONS
In this study, a compressive strength estimation method for concrete structures using drilling tests and pattern recognition techniques was proposed. We could obtain the parameters which have high correlation with the compressive strength by observing the drilling behaviors and corresponding physical quantities. We created the feature vectors considering the combination of extracted parameters and built SVMs, The classification of compressive strength with high accuracy was achieved.
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Electroactive sensors and actuators (3)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Suppression of the snap-through behaviors of composite shell structures using piezoelectric actuator Seung-Hoon Oh, Jin-Ho Roh, In Lee & Jae-Hung Han Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Korea
B
D (Snap-through)
Load
Composite shell structures have been widely applied in aerospace, mechanical and other engineering fields. However, shell panels show uncommon structural instability behaviors due to its geometric characteristics. For example, even if the plate structure subjected to compressive loads shows bifurcation and stable postbuckling behaviors, the compressive response of shell structures shows different instabilities such as snap-through and snap-back, resulting in a sudden jump to another equilibrium states as shown in Figure 1. In snapping-phenomena, a large deflection is induced and the structure configuration is suddenly changed shown as Figure 2. Therefore, it is important to accurately determine the snapping behavior. Moreover, the snap-through phenomenon may affect the appearance of the crack or the delamination that could induce the collapse of the whole structure. Therefore, the snap-through behaviors should be suppressed for the structural stability. In this research, the suppression of the snap-through behaviors of composite shell structures with piezoelectric actuators is investigated by using a finite element method.The arc-length method is applied to predict the snapping behaviors. The effects of attaching positions of Micro Fiber Composite (MFC) actuators are shown to increase the critical snapping load with various curvatures of cylindrical panels.
C
d
b (Snap-back)
c A Displacement Figure 1. Snapping phenomena of cylindrical panel.
Figure 2. Shape change through snap-through behavior.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Profile and placement optimization for piezoelectric shunt damping system Kaixiang Li, Zhichun Yang, Hao Sun & Lingling Zhang School of Aeronautics, Northwestern Polytechnical University, Xi’an, China
1
INTRODUCTION
Vibration control has been a hot topic of engineering research for the past few decades. Recently, the use of smart material components for vibration control has become an alternative to traditional vibration control techniques. Vibration control with smart materials (such as piezoelectric materials) has many advantages such as light weight and low power requirement. They are especially suitable where traditional techniques cannot be applied due to weight and size restrictions. Piezoceramic is an example of the smart material transducer/actuator in passive/active structural vibration control. Hagood and von Flotow (1991) have demonstrated that structural vibrations can be damped by piezoelectric materials with a passive electrical shunt circuit [1]. The piezoelectric patches convert vibration energy into electrical energy and then dissipate the electrical energy in the form of joule heating through the passive electrical shunt circuit; this is also known as passive vibration damping system (PSDS). However, the performance of such system depends on not only the shunt circuit but also the profile and location of the PZT patches. It is known that the amount of induced electric charges of the PZT patches which is representative to the converted vibration energy is decided by its profile and location; furthermore, the bonded PZT patches will change the local stiffness and mass distribution of the structure especially for thin plate/shell structures, so as to change the vibration mode shapes of the structure. Moreover, once a PZT patch is bonded on the structure, the patch can not be removed to another place. So it is necessary to optimize the profile and location of the PZT patches to make the induced electric charges maximum. Recently, some researches have been conducted on theoretical and experimental researches to suppress vibration of structures by piezoelectric shunt damping approach. Wu performed piezoelectric shunt damping experiments on an F-15 underbelly panel which was excited by the high acoustic excitation. Five PZT patches were used with two shunt circuits designed
to control the first and second modes of the structure between 200 Hz and 400 Hz [2]. To determine the locations and the number of PZT patches, J.S.Park used finite element software MSC.NASTRAN® to analyze the modes of a CD-ROM drive base, and then bond the PZT patches at the highest modal strain area to suppress the vibration of its first two modes [3]. Suresh V Venna et al proposed a method to calculate the strain energy distribution at the first bending and torsion modes of a geometrically non-linear structure by finite element software ABAQUS® , and glue the PZT patches on the high strain region. The experiment results show that the vibration amplitude of these two modes is reduced to 30% and 25% respectively [4]. At present, the research of profile optimization of piezoelectric transducers is performed only in the field of piezoelectric active control. Akhilesh K. Jha and Daniel J. Inman try to find optimum placements and sizes of the actuators and sensors attached to an inflated toroidal shell using a genetic algorithm. They demonstrated their optimal control method by using optimal placement of actuators and sensors [5]. Based on the impedance technique, C.C Cheng and C.C Lin determined the optimal locations and shapes of multiple induced strain actuators bonded on a host structure in respect to the smallest power consumption. Numerical examples are presented to show the mass effect caused by the actuators on the power factor and to demonstrate how to determine the optimal bonding placements and parameters for the multiple actuators [6]. Such work has not been conducted in passive vibration control in piezoelectric shunt damping technique. In this paper, we demonstrate a technique for optimum profile and placement of PZT patches for the vibration control of thin plate structures. The equation of electric charges which are induced on the polarized surface of PZT patches is deduced based on the basic piezoelectric equations. The profile and placement of the PZT patches is optimized. The principle of profile and placement optimization is also proposed based on the optimization results.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Experimental study on placement optimization of transducers of piezoelectric shunt damping system for plate vibration Hao Sun, Zhichun Yang, Kaixiang Li & Lingling Zhang Aeronautics School, Northwestern Polytechnical University, Xi’an, China
1
INTRODUCTION
In the study on the piezoelectric shunt damping system, the early researches mostly aimed at the vibration damping of typical beam structures [1] [2] [3], little effort was made for other type of structures. Recently, a few articles focusing on the shunt damping vibration control on plate and shell structures which widely used in engineering were published. Wu [4] conducted experiments on structural vibration damping of an F15 underbelly panel using piezoelectric shunting with five bonded PZT transducers. The panel vibration was excited with an acoustic speaker at an overall sound pressure level of about 90 dB. By using single and multi-modes shunting circuits, the vibration amplitude reductions of 13.45 dB and 10.72 dB were achieved for the first and second modes respectively. Lee [5] tested the noise reduction performance of hybrid panels with PZT shunt circuit at low frequencies in acoustic tunnel and a noise reduction of 5 dB at the second resonance frequency was observed. Park [6] introduced admittance to represent the electro-mechanical characteristics of piezoelectric structures to optimize the performance of the piezoelectric shunt system, he used aluminum plates bonded with different sizes and numbers of piezoelectric patches as the testing structures. The vibration reduction of about 20 dB was obtained for the first mode and the fifth mode vibration. In Ahmadian’s research [7], a test setup in an SAE J1400 facility was used to analyze the vibration reduction and
sound transmission loss by PZT shunt damping system. In his research, the thin plate bonded with three shunted PZT transducers was inserted in a noise isolation window. The test results indicated that shunted PZT transducers can increase damping of the plate and hence the sound transmission loss of approximately 7 dB for a broad band input of 10 ∼ 10000 Hz was achieved. Compared with the conventional constrained layer damping materials, very small additional mass was introduced to the structure in this approach. Note that in the above examples, the placement optimization of the PZT transducers has not been taken into account for the vibration control efficiency of the piezoelectric shunt damping system, hence the energy dissipating performance of the system is limited. In this paper, vibration reduction using piezoelectric shunt damping system for a clamped thin plate with placement optimization of PZT transducers was studied theoretically and experimentally. The reduction of about 11.90 dB, 16.94 dB, 16.94 dB, 19.91 dB and 16.77 dB for the amplitudes of the transfer function at the first five natural frequencies were obtained respectively. The suppression effects of the piezoelectric shunt damping system with PZT transducer placement optimization are also compared with that of the system without optimization for each plate configuration. And the study of this paper demonstrates the significance of placement optimization of piezoelectric transducers in the application of piezoelectric shunt damping system.
493
Motion and vibration control of structures
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
The energy dissipation performance of displacement dependent semi-active hydraulic damper W.P. Sung National Chin-Yi University of Technology, Taiping, Taichung, Taiwan, China
M.H. Shih National Kaohsiung First University of Science and Technology, Nanzih, Kaohsiung, Taiwan, China
S.P. Hsu National Chin-Yi University of Technology, Taiping, Taichung, Taiwan, China
1
INTRODUCTION
In this research, a proposed device of DSHD is a kind of passive control system with controllable energydissipating element. The energy-dissipating behavior is functioned by the damping force which is generated by the flow of fluid through the orifice in the hydraulic jack. In order to assess the performance and verify the shock absorption performance of this proposed damper, the shaking table test (with DSHD in the test system) is conducted under the excitation of Kobe earthquake with different peak ground accelerations.
KA is the stiffness of DSHD, including the stiffness of brace. XA is the elongation of DSHD. XBal is the elongation of DSHD for previous loose state of brace. Practically, the overflow valve is installed in DSHD to protect the components of oil pressure system under normal pressure. Therefore, the internal force does not increase when the internal force of brace induces the oil pressure to overflow. Therefore, the mechanical behavior is similar to yielding plateau of metal. 4
2
PRINCIPLE AND ORGANIZATION OF DSHD
Herein, DSHD system is composed of Hydraulic Jack, Directional Valve, Check Valve, Relief Valve, and Oil cylinder. Particular current is input through directional valves and DSHD will be switched among functions of “tensile restraint,” “compressive restraint,” and “free restraint”.
3
MECHANICAL BEHAVIOUR AND MATHEMATICAL MODEL OF DSHD
DSHD mechanism is designed to provide a negative work that is applying a resistant force opposite to the direction of structure vibration. From element test, the mathematical model should be established as below by considering the brace stiffness and load amplitude.
EXPERIMENAL SETUP
Shaking table test is used to test and verify the seismic proof capability of structure added with DSHD. The test loading is simulated using the Kobe earthquake record with various peak ground accelerations. 5
SHOCK ABSORPTION PERFORMANCE OF DSHD
The shock absorption ratio for structural displacement and that of acceleration is greater than 0.84 and 0.56 respectively when subjected to simulated excitation of the Kobe earthquake with various peak ground accelerations. In accordance with the hysteretic loop of DSHD during the energy dissipation period, it reveals that the energy dissipation ratio of DSHD depends on vibration amplitude of the structure. DSHD still supplies more than 50% of energy dissipation ratio under lightly shaking that approach the same energy dissipation as that exploited by ADAS, even if running out of control elements.
Where: F¯ B represents the resistance force beyond overflow.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Linear control design for regeneratively-actuated structures with energy storage subsystems J.T. Scruggs Department of Civil & Environmental Engineering, Duke University, USA
1
EXTENDED ABSTRACT
A Regenerative Force Actuation (RFA) Network is a system of electromechanical forcing devices used for the purpose of structural vibratory response control. The various actuators are connected through powerelectronic switching circuitry to a common electrical power bus. Also connected to the power bus is an energystoring subsystem, such as a supercapacitor, flywheel, or battery. The actuators may be operated as generators or motors, and the energy removed from the vibrating structure by one actuator may be driven back into the structure by another, or may be temporarily stored for later use. Because the entire system is controlled through the alternation of transistor switches, the system is capable of managing orders of magnitude more electrical power than is required for the control. However, the absence of an external power supply also constrains the forcing capability, and consequently constrains the feasible set of feedback laws the actuation system can impose. This paper models this dynamic force constraint for RFA networks with energy storage subsystems, and characterizes a feasible set of linear structural control laws in terms of hardware parameters. It is shown that the feasibility of a given feedback controller depends on the terminal resistances of each actuator, the terminal resistance of the storage system, and on the dynamics of energy leakage from storage. The control feasibility domain can be expressed in terms of Linear Matrix Inequalities (LMIs) on these parameters, in a manner reminiscent of the constraints arising in classical passivity theory. Regenerative actuation has been examined for automotive suspension systems using hydraulic as well as electromechanical devices, for flexible aerospace structures with the use of a piezoelectric actuators, and for civil applications using large electromagnetic
transducers. Although a number of device realizations have been proposed for RFA networks, the area of control synthesis for these systems has been slower to develop. This paper presents some new results, toward a generalized approach to the design of linear feedback controllers for energystoring RFA networks. An illustrative example is given in which dynamic controllers are optimized, subject to this regenerative constraint, and performance is compared to the optimal performance acheivable with linear viscous damping. The optimization is framed in the context of multiobjective H2 optimal control theory. The example is framed in a Civil Engineering context, in which a 2-actuator RFA network is used to suppress earthquakeinduced structural vibration. The storage system is modeled as a supercapacitor, and controllers are designed for two different values of its associated RC time constant. One of the main results of the example is a quantification of the degree to which storage efficiency affects the ability of an RFA network to simultaneously suppress drifts and accelerations in a structure. The example also shows that even if the energy storage system is highly inefficient, the ability of the RFA network to transmit energy between the two actuators can be used to improve upon optimal viscous damping. There are two conclusions of the paper:
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There is a quantifiable benefit to the use of RFA networks to impose linear control laws on structures, in the sense that they perform superior to the optimal performance attainable with viscous damping systems. • To be effective, the design of the control law for the RFA network must be approached in such a manner so as to exclude controllers which demand a higherefficiency power management system than actually exists.
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Intelligent hybrid control for braking-induced longitudinal vibration response of floating-type railway cable-stayed bridge Wei Lian Qu, Jia Liu, Jian Wei Tu & Qiang Zhou Hubei Key Laboratory of Roadway Bridge and Structure Engineering, Wuhan University of Technology, Wuhan, Hubei, China
Shunquan Qin China Zhongtie Major Bridge Engineering Group Co. Ltd, Wuhan, Hubei, China
1
INTRODUCTION
the identified results match well with the experimental one.
Large longitudinal vibration response in deck of floating-type railway cable-stayed bridge will be induced by earthquakes, train braking and traffic, consequently the response can lead to huge bending moments at the bottom of the towers, which may produce serious adverse effect on the regular service and safety. In order to avoid it, conventional control devices such as fluid dampers are used to suppress the longitudinal seismic response of the deck. But they can not effectively mitigate longitudinal vibration response caused by train braking and traffic. In the paper, the longitudinal intelligent hybrid control system for the braking-induced longitudinal vibration response of deck of floating-type cable-stayed bridge with MR dampers and fluid dampers are proposed, which are applied to the design of Tian Xing-zhou Bridge in China, the longest highway and railway combined cable-stayed bridge in the world.
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FABRICATION AND EXPERIMENT OF 500KN FULL-SCALLE MR DAMPER
The performance of MR fluid is tested in laboratories and several fabricating crucial techniques of 500 kN large-scale MR damper, including inner disk spring accumulator, magnetic-flux leakage prevented design and leading wire protection are introduced. Based on the performance of MR fluid and several crucial techniques mentioned above, a 500 kN full-scale MR damper have been fabricated and its modified Bingham model parameters have been identified through experimental test. It indicates that
3
BASIC THEORY OF INTELLIGENT HYBRID CONTROL FOR DECK
According to the principle of locomotive dynamics, dynamical equations of a group of trains composed of n + 1 trains can be established, and 4th order RungeKutta is used to obtain the instantaneous longitudinal traffic states. Then a finite element model has been adopted to analyze the transferring problem of longitudinal braking load on bridge. Finally the hybrid control system for braking-induced longitudinal vibration response of bridge based on fuzzy semi-active control strategy has been established. 4
ENGINEERING APPLICATION
One DF4 plus Thirty C62 wagon trains full of goods whose braking initial speeds are 80 km/h are grouped and a total of 9 cases are considered to simulate longitudinal vibration response of decks. Based on 9 cases shown in section 4.2, both hybrid control system with MR and fluid dampers and passive control system with only fluid dampers for longitudinal vibration responses in deck of Tian Xingzhou cable-stayed bridge have been simulated. Simulation results show that the hybrid control system used MR and fluid dampers can effectively suppress the longitudinal vibration displacement and the corresponding bending moments of towers to guarantee the regular service and safety of Tian Xingzhou cable-stayed bridge.
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Innovative sensing systems: Fiber sensors (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Analysis on strain transfer of fiber optic Fabry-Perot sensors-based on FEM method Wentao Zhanga,b , Jingyun Daia , Baochen Suna , Yanliang Dua a Key
Lab. of Structure Health Monitoring and Control of Hebei Province, Shijiazhuang Railway Institute, Shijiazhuang, Hebei b State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing
1
INTRODUCTION
30.0
Many kinds of Fabry-Perot sensors were developed in recent years such as strain gauges, extensometers, pressure sensors, hydrophones, accelerometers, and skin friction gauges. In this paper, we report the analysis of the strain transfer of the Fabry-Perot sensors using FEM. And the results of the theory, experiment and FEM is also given.
25.0 20.0 theoretical FEM Experimental
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PRINCIPLES OF THE FIBER OPTIC EFPI SENSOR
Two cleaved multimode fibers were inserted into a steel capillary tube to form an air gap that acts as a low-finesse Fabry-Perot cavity. The ends of the capillary tube were adhered to the fibers. For different housing structures, the sensor head can act as ether the strain sensor or the temperature sensor. A white light source illuminates the Fabry-Perot cavity through a coupler.And for uncoated fiber ends, a 4% Fresnel reflection results at both ends of the cavity. These two reflections interfere and the peak wavelength of the reflective spectrum is dependent upon the length of the cavity. Thus we can use wavelength demodulation method to get the strain or temperature. However, the strain of the structure can not be transferred to the fiber totally. And the strain in the first layer of the epoxy is different from the second layer due to the same reason. This effect is also analyzed in this paper. 3
FEM ANALYSIS
Finite element method is used in the analyzing of the strain transfer of the Fabry-Perot strain sensor. We use the software of ANSYS to build up the model, mesh and calculate.
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Figure 1. Sensitivity comparison of calculated and experimental results.
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EXPERIMENT AND RESULTS
The experiment was performed by attaching the FabryPerot strain sensor to a sample of steel and using a test machine. The result of the experiment is shown in figure 1 with the result by using FEM. It can be found that the result of FEM has a better agreement with the experimental result than the theoretical. And the sensor has good linearity and stability. 5
CONCLUSION
In this paper we analysis the strain transfer of the Fabry-Perot sensors theoretically and by using FEM. The result shows that the thickness of the epoxy, the Young’s modulus, and the Poisson’s ratio are the main factors that influence the strain transfer rate of the strain sensors. And the result of the FEM analysis has a good agreement with the theoretical analysis and experimental results.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Experiment on dynamic response of fiber optic Fabry-Perot sensors and its application in structural health monitoring Wentao Zhang1,2 , Jingyun Dai1 , Baochen Sun1 & Yanliang Du1 1 Key
Lab. of Structure Health Monitoring and Control of Hebei Province, Shijiazhuang Railway Institute, Shijiazhuang, Hebei 2 State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing
1
4
INTRODUCTION
In this paper, we report the applications of the fiber optic EFPI sensors in the monitoring of the Liaohe Bridge. The fiber optic EFPI sensor and the conventional strain gauges were embedded into the bridge during the building of the bridge. Experimental results show that the fiber optic EFPI sensor has good linearity, repeatability, and stability. 2
PRINCIPLES OF THE FIBER OPTIC EFPI SENSOR
Two cleaved multimode fibers were inserted into a steel capillary tube to form an air gap that acts as a low-finesse Fabry-Perot cavity. The ends of the capillary tube were adhered to the fibers. A white light source illuminates the Fabry-Perot cavity through a coupler. And for uncoated fiber ends, a 4% Fresnel reflection results at both ends of the cavity. These two reflections interfere and the number of observed fringes is a function of the Fabry-Perot cavity length. The peak wavelength λ of reflection is Lc = k/2λ. Where k is an integer. It is easy to find that the peak wavelength changes with the Fabry-Perot cavity length. 3
IMPACT TEST
To test the performance of the Fabry-Perot strain sensor, we attach the sensor to the surface of a steel beam, which is impacted by a hammer. This two types of sensors have similar dynamic response and the correlation coefficient of the two signals is better than 0.95.
EXPERIMENTS AND APPLICATIONS IN LIAOHE BRIDGE
The sensors are embedded into a model ferroconcrete beam together with traditional strain gauges. The experiment is carried out using the PEM-500A hydraulic pulsation fatigue test machine after 2 million stress circles. It can be found from the result that the fibre optic sensors have good stability and reliability. The fiber optic EFPI sensors work well after two million stress circles. Then the fiber optic EFPI strain sensors are embedded into the Liaohe Bridge when the bridge is still in building. After the building is finished, the experiment is carried out to monitoring the dynamic strain in the bridge. It can be seen from the result that the strain measured by the strain gauge is in good agreement with that measured by the fiber optic sensor. This proves up that the sensor has good dynamic response and stability in the monitoring of railway bridges. 5
CONCLUSION
In this paper, we analyze the principle of the fiber optic EFPI sensors. Based on the theory of white light interferometry, the fiber optic EFPI sensor is designed and fabricated. Experiment is carried out to test the performance of the sensors. The result shows that the sensor is stable after two million stress circles. Then the sensor is embedded in the Liaohe Bridge, and the field test result shows that the sensor has good stability and dynamic response. In conclusion, this type of fiber optic strain sensor can meet the demand of the structure health monitoring.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Sensitivity enhancement of long-gage FBG sensors for small macro-strain measurements Suzhen Li & Zhishen Wu Department of Urban and Civil Engineering, Ibaraki University, Japan
Different from periodic testing and examination, SHM is supposed to track real-time structural information and issue early warnings on damage or deterioration prior to costly repair or even catastrophic collapse. Generally, the structural degradation is a long-term slow-moving process, accompanying with accumulating fatigue, creep and corrosion, which consequently calls for a reliable sensing system to record effective data reflecting such slight variation. Moreover, environmental uncertainty and disturbance also impose a huge challenge on sensors to extract valuable signals rather than measuring noise. In our recent study the concept of distributed strain sensing techniques has been proposed to utilize the strain distributions throughout the full or some partial areas of structures to detect the arbitrary and unforeseen damage. Compared with most manners for SHM to date including global damage assessment techniques using structural dynamic responses and limited local independent damage detection mechanisms, these techniques put forward a promising novel alternative due to their high sensitivity to local damage and potential to catch comprehensive structural information in virtue of the “distributed” sensors placement and broad-band dynamic measuring ability. However when the strain response is very small or
environmental noise is heavily disturbing, it may be difficult to obtain the effective measurements. Furthermore, as it is well known that ambient vibration testing, which can work under the normal operational state of the structures, is playing more important role than traditional controlled experiment in the current large-scale civil SHM, the developed sensors are increasingly expected to improve the ability to enhance the measuring sensitivity and obtain the small ambient vibrating responses. On the basis of our preceding efforts on the development and application of distributed fiber optic sensing techniques, this work puts forward a novel packaging design for long-gage fiber Bragg grating (FBG) sensors to enhance the measuring sensitivity for macro-strain responses. The basic idea is to utilize two materials of different stiffness to package the optical fiber and impose the deformation within the gauge length largely on the essential sensing FBG part. A series of tests are carried out to verify the ability of the improved sensor to detect the small crack and measure the slight vibration. By comparing with the measurements from the pristine FBG sensor, the influence of environmental noise on those from the novel one is discussed as well.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
An effective method of temperature compensation about long-period fiber grating with strain characteristic Y. Wang, D.K. Liang & B. Zhou Nanjing University of Aeronautics and Astronautics, Nanjing, Jiangsu, China
1
INTRODUCTION
the LPFG while the other end of it was connected to ANDO(AQ6317C,OSA).
A long-period fiber grating(LPFG) are sensitive to sensor such as strain, curvature, temperature or refractive index. By monitoring the shift in the resonance wavelength of the LPG is the basis of LPFG sensors. Separation of various physical effects is, therefore, an important issue in the development of practical LPFG sensors.
The resonant wavelength of LPFG showed a right shift (red shift) when the temperature increases. It is found that the LPFG has a positive temperature coefficient kT is 55.71 pm/◦ .
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PRINCIPLE OF COMPENSATION
We proposed a simple flexible method of reducing the temperature sensitivity of a LPFG. If we glue LPFG on a material, when temperature increase, the resonance wavelength of LPFG shift will affected by two factors, first the wavelength shift because of the temperature increment, in addition, as a result of the difference between the material and the optical fiber thermal expansion coefficient, the resonance wavelength of LPFG will shift because of the applied strain. By properly mounting a LPFG on a suitable material, which thermal expansion coefficient accord with some optimum condition, the temperature dependence of the resonance wavelength of the LPFG can be largely compensated with the strain. 3 3.1
EXPERIMENT OF KT , Kε Preparation of the LPFG
3.2 Measurement of temperature coefficient
Simultaneity, an opposite shift, towards the shorter wavelengths (blue shift) in the resonance wavelength was noticed when the strain increase. That is to say, a negative strain coefficient kε is −0.4878 pm/µε. 4
From the foregoing data, plexiglass laminate was chosen for its thermal expansion coefficient is 130*10−6 /◦ , is just the right material. By gluing the LPFG onto the plexiglass laminate directly, the resonance wavelength shift can be compensated largely by varying the applied strain parallel to the change of temperature. We reduced the temperature sensitivity of the resonance wavelength of a typical LPFG by two orders of magnitude from 55.71 pm /◦ to 3.7 pm /◦ . 5
In this paper, The LPFG with a period is 450 um and length is 6 cm, the initial wavelength is 1548.044 nm. Agilent(83437A,BBS), was launched on one end of
EXPERIMENT OF COMPENSATED
CONCLUSIONS
It is found that the method to compensate temperature is effective, practical, simple and easy to use.
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Paradigms and technologies related to the engineering and management of intelligent infrastructures and constructed systems (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Korean experiences with smart bridges H.M. Koh & H.S. Lee Department of Civil and Environmental Engineering, Seoul National University, Seoul, Korea
W. Park & J.F. Choo Korea Bridge Design & Engineering Research Center, Seoul, Korea
1
INTRODUCTION
Civil engineering projects constituted the backbone of the development and economic growth of Korea. In the domain of transportation infrastructures, and particularly bridge structures, bridge construction activities has been restlessly undertaken in the peninsula. Recently, bridge construction activity has been revitalized by the ambitious plan of the government to link some of the 3,000 islands of the peninsula to the mainland, especially in the southwestern coast. 2
SMART BRIDGES AND SHM OF BRIDGE IN KOREA
Korea has adopted bridge monitoring systems since 1992. Along with the rapid and massive progresses made in the domain of IT technologies for infrastructures, complete and integrated monitoring systems were systematically installed in all major bridges since 2000 in Korea to become one of the leading countries in bridge monitoring. The corresponding database is currently exploited for diverse purposes such as maintenance, evaluation of structural behavior, system identification and feedback for future constructions. A smart structure is defined as one which has the ability to determine its present state, decide in a rational manner on a set of actions that would change its state to a more desirable state, and carry out these actions in a controlled manner and in a short period of time. Owing to such definition, speaking of smart bridges remains somewhat premature in view of the abilities defined for smart structures that are sensing, cognitive interpretation and decision systems, and actuating. Accordingly, continuous efforts have been and are being deployed to enhance Structural Health Monitoring (SHM) of bridge structures and numerous researches are being conducted on emerging smart
technologies. Such ongoing efforts are dedicated to realize future full integration of smart components to produce smart bridges providing realtime continuous sensing, remote sensing, self-diagnostic and decision-making functions with a lifetime perspective. 3
ONGOING RESEARCHES FOR SMART BRIDGES IN KOREA
Research prospects for smart technologies are focusing on new sensing materials and devices, new actuation materials and devices, control devices and techniques, and self-detection, self-diagnostic, selfcorrective and self-controlled functions of smart materials or systems. The domestic leading organizations are the Korea Panel on Structural Control and Monitoring, the Korea Earthquake Engineering Research Center (KEERC), the Smart Infrastructure Technology Center (SISTeC) and the Korea Bridge Design & Engineering Research Center (KBRC). 4
CONCLUSIONS
Today, Korea can be considered as one of the leading countries in bridge monitoring. The corresponding database is currently exploited for diverse purposes such as maintenance, evaluation of structural behavior, system identification and feedback for future constructions. In order to optimize such utilization and realize smart bridges, continuous efforts have been and are being deployed to enhance SHM of bridge structures and numerous researches are being conducted on emerging smart technologies. Some of these researches have already been applied effectively in Korea and ongoing research products will undoubtedly result in numerous real applications of intelligent infrastructures and bridge structures in particular in a very near future.
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Developments and experiments in biomimetic robots
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Effect of artificial caudal fin on performance of a biomimetic fish robot actuated by piezoelectric actuators S. Heo Artificial Muscle Research Center, Konkuk University, Seoul, Korea
T. Wiguna Department of Advanced Technology Fusion, Konkuk University, Seoul, Korea
H.C. Park & N.S. Goo Department of Advanced Technology Fusion Artificial Muscle Research Center & Smart Robot Center, Konkuk University, Seoul, Korea
1
3
INTRODUCTION
First part of this paper explains actuation system of a fish robot actuated by piezoceramic actuators. Then, design, analysis and fabrication of artificial caudal fins are described in detail. The fish robot was tested in a water tank to investigate the effect of the fin stiffness on the performance. The experimentally measured performance of the robotic fish was examined by calculating Strouhal number, Froude number, Reynolds number, net forward force. Power consumption of the fish robot was also measured for various caudal fins with different stiffness.
2 THE FISH ROBOT The present biomimetic fish robot consists of body, actuation system, artificial caudal fin, and ventral fins. The dimensions of the fully-assembled biomimetic fish robot are 27 cm long, 5 cm wide, and 6.5 cm high with total mass of 550 grams. The actuation system is designed such that the limited actuation displacement produced by bending motion of two LIPCAs (Lightweight Piezo-Composite Actuators) is amplified and transformed into a large caudal fin motion. The key elements of the actuation system are the LIPCA, a fixture structure, a rack-and- pinion system, two cranks and two couplers. The artificial fins mimicking a real mackerel fin with various thicknesses were attached to the robotic fish. The fish robot actuated by various artificial caudal fins was tested in a water tank. During the test, 300 Vpp in a square wave form was applied to the piezoceramic actuators at operating frequency range between 0.6 and 1.2 Hz.
RESULTS
The maximum swimming speeds of the robotic fish reached 2.519 cm/s, 2.313 cm/s, 2.426 cm/s, and 2.338 cm/s for variable (VTF), thin (TNF), medium (MDF), and thick caudal fins (THF), respectively. The Strouhal numbers were in between 0.795 ∼ 1.391, 0.890 ∼ 1.511, 0.839 ∼ 1.441, and 0.913 ∼ 1.583 for the robotic fish with variable, thin, medium, and thick caudal fins, respectively. The ranges of the Froude numbers were 0.01326 ∼ 0.01549, 0.01221 ∼ 0.01422, 0.01280 ∼ 0.1491, and 0.01165 ∼ 0.01437 for the robotic fish with variable, thin, medium, and thick caudal fins, respectively. The calculated Reynolds numbers were ranged between 5824.93 ∼ 6801.58, 5362.61 ∼ 6243.82, 5623.03 ∼ 6549.56, and 5115.64 ∼ 6313.43 for the robotic fish with variable, thin, medium, and thick caudal fin, respectively. The maximum net forward forces of the robotic fish at 0.9 Hz were 0.71389 mN, 0.60147 mN, 0.66187 mN, and 0.61507 mN for variable, thin, medium, and thick caudal fins, respectively. The measured power consumptions of the fish robot propelled by variable thickness fin (VTF) were 0.065 W for 10 and 0.053 W for 100 The
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CONCLUSION
From the swimming test of the fish robot, it was found that the performance of the robotic fish propelled by a variable thickness caudal fin (VTF) is the best among the tested fins in terms of forward speed, net forward force, and power consumption. The calculated Reynolds number indicates that the water flow around the present robotic fish is in
transition from laminar to turbulent flow, while the Froude number forecasts that the robotic fish has poor maneuverability. The Strouhal number and net forward force reflect that the present biomimetic robotic
fish is not yet optimized in terms of thrust and speed. However, power consumption of the fish robot could be reduced by adapting a biomimetic design of the caudal fin.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Experimental investigation on a biomimetic flapping wing with macro-fiber composites Dae-Kwan Kim & Jae-Hung Han Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
Ki-Jung Kwon Korea Aerospace Research Institute, Daejeon, Republic of Korea
1
INTRODUCTION
In the present study, an adaptive flexible flapping wing that can change the camber using macrofiber composite (MFC) actuators is designed and manufactured, and then experimental tests are performed to investigate the aerodynamic characteristics. Low speed wind tunnel tests are performed to measure aerodynamic performance and characteristics of the flapping wing. Additionally, particle image velocimetry (PIV) tests are carried out to verify the aerodynamic characteristics. In particular, chordwise flexibility and unsteady effects are discussed. 2
SMART FLAPPING WING
2.1 Wing design and modeling An adaptive flapping wing is designed using some design constraints and flight parameters of birds. MFC actuators are used to change the camber of a local wing section. In order to determine stiffness of the wing, the structural analyses of the wing are performed using MSC/NASTRAN and a thermal analogy for PZT actuators. The maximum camber of chord line is linearly varied from −0.026 Cmax to 0.044. 2.2 Aerodynamic performance Lift coefficient curves are shifted by the variation of camber, much like a trailing edge flap. The maximum lift is increased by the camber effect, up to 24.4%, under static test conditions.An effective angle of attack of a local wing section is reduced by a chordwise flexibility of the wing. Therefore, the flexibility effect decreases the lift coefficients but delays a stall condition in a high angle of attack regime. In dynamic tests, the maximum mean lift is increased by an unsteady
effect, up to 20.8%. Although a flow velocity is constant, maximum lift coefficient increases remarkably more than 5 with increasing flapping frequency and, moreover, a stall angle increases as in static results. 3 AERODYNAMIC CHARACTERISTICS 3.1
Chordwise flexibility effect
From static PIV results, it is clearly found that, under a static condition, the effective angle of attack reduced by chordwise flexibility delays the aerodynamic stall and decreases the drag, so additional aerodynamic benefit can be obtained, especially in high angle of attack. Moreover, under a dynamic condition, the flexibility effect plays a role in producing a passive twisting motion. 3.2
Unsteady aerodynamic effect
In particular, lift coefficients rise remarkably under an advance ratio of less than 1, where a leading edge vortex attached on wing surface exists, unlike a quasi-steady flow condition. The leading edge vortex develops a suction force normal to the wing surface and accelerates the surrounding flow, thus the lift component generated due to circulation of the wing is increased by adding to the suction force. 4
CONCLUSION
Using the camber motion of an adaptive flapping which generated by the MFC actuators, lift coefficients can be increased in static and dynamic conditions, and sufficient aerodynamic benefits can be obtained. The effective angle of attack of a local chord is reduced
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by the chordwise flexibility, and additional aerodynamic benefits can be brought by the flexibility effect in high angle of attack regimes under static conditions. High lift coefficients in unsteady flow conditions are
produced by a leading edge vortex attached on the wing. Notably, the wing flexibility can help the wing stabilize a small leading edge vortex under an unsteady flow condition.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Model identification and control of a fish-like robot Wa Leung Chan, Taesam Kang & Young Jae Lee Department of Aerospace and Information Engineering, Konkuk University, Gwangjin-gu, Seoul, South Korea
INTRODUCTION
14
12 Terminal velocity (cm/s)
The development of underwater vehicles is a big challenge in marine study, ocean investigation and surveillance. Fish-like propulsive method is one of the design options to achieve high swimming efficiency and quiet underwater vehicles. In this paper, a fishlike robot (see Figure 1), which mimics a fish with ostraciiform swimming mode, was built to study its swimming performance and identify its mathematical model for swimming. This robot demonstrated a simple mechanical design for swimming forward and direction steering with the control of a tail fin only. Oscillation of the tail fin about the fish-like robot body axis generated a trusting force to propel the robot moving forward, see Figure 2 for the terminal velocity measurements. With the tail oscillated about an angle, called mean angle, relative to the robot body axis, the swimming direction could be changed. An attitude reference system unit was mounted on the robot to record the swimming direction for different mean angles. The mathematical model of the robot fish steering was constructed via system identification, see Figure 3 for comparison of experimental data and the identified models.
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6 tail length = 5cm tail lenght = 7cm tail lenght = 9cm
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Figure 2. Terminal velocity versus flapping frequency.
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Figure 3. Path angular rate ωp versus time.
Figure 1. The ostraciiform robotic fish in water.
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Motion and vibration control (3)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Investigation of an optimal motion pattern for a robotic fish Cheolheui Han Biomimetics and Aircraft System Engineering Laboratory Department of Aeronautical and Mechanical Design Chungju National University, Chungju, South Korea
Seunghee Lee & Jonghyeon Park Mechatronics Laboratory School of Mechanical Engineering Hanyang University, Seoul, South Korea
An optimal motion pattern for a fish-mimetic robot is investigated as an initial stage to the intelligent control of the robot fish. A mackerel-mimetic robot fish (BASEMACK1: Biomimetics and Aircraft System Engineering laboratory MACKerel 1) is fabricated to understand the relation between the motion parameters and the fluid-dynamic forces generated from the fish robot(See Fig. 1). Hydrodynamic coefficients of the robot fish are measured using the fabricated
robot fish in a water-tank. Using the measured hydrodynamic coefficient data, a hydrodynamic model of the robot fish is established. Then, a numerical simulation is to investigate the adaptation capability of the robotic fish to the given environment(See Fig. 2). Energy consumption ratio is estimated by measuring the motor current consumed during the test. The optimized motion parameter set with minimum energy consumption is obtained using the numerical simulation results and measured data (See Fig. 3). Using the optimized body shape parameters, the propulsion force exerted to the front body of the robotic fish are expressed as a function of the Strouhal number. Present study shows the possible application of the intelligent control of the robot fish. However, present results are only limited to the case of the robot fish stationed to a fixed place. Present method will be extended to the case of a maneuvering robot fish in the future.
Figure 1. BASEMACK1, a mackerel-mimicking robot fish.
Force(N)
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Figure 3. Change in the optimized BSF parameters with which the robotic fish produces the equal propulsion force.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Analysis and testing of shape memory alloy-driven biorobotic fish fins with multi propulsion modes Yong-Hua Zhang, Yan Song & Jie Yang Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, China
1
INTRODUCTION
Darwinian process of natural selection proposes that each species has its own unique and optimum way of interacting with its environment. This gives each fish uniqueness in its body shape, size and propelling styles. Previous studies conclude that the cruising and maneuvering abilities among fish differ both within individuals among behaviors and within behaviors among individuals and species. Whilst the fish body and fin are the major aids in providing cruising and maneuvering control, different combinations in the movement of these aids make the task of mimicking fish movement a complicated task. Shape Memory Alloy (SMA)’s are metals, which exhibit two very unique properties, pseudo-elasticity and the shape memory effect (SME). The shape memory effect is observed when the temperature of a piece of shape memory alloy is cooled to below the temperature Mf (Martensitic transformations finish temperature). At this stage the alloy is completely composed of Martensite which can be easily deformed. After distorting the SMA the original shape can be recovered simply by heating above the temperature Af (Austenitic transformations finish temperature). The advantages of SMA compared to traditional electromechanical devices are their low energy consumption, noiseless motion and continuous flexibility. Since the devices built on SMA actuators have low metal concentration, it is difficult to detect them by metal detectors or radars. Therefore they are promising candidates for reconnaissance, intelligence gathering and surveillance. SMA materials are lightweight and permit building small devices.
Recently, various real-sized fish-like swimming robots are reported in literature. Based on the propulsive structure used, Breder classified swimming movements into body and/or caudal fin (BCF) locomotion and median and/or paired fin (MPF) locomotion. MPF mode is generally employed at slow speeds, offering better propulsive efficiency. In particular, precise maneuver is a feature of MPF specialists. The fins of these fish consist of fin rays with a flexible membrane joining them together. This enables them to provide adequate thrust at low swimming speeds. Based on their motions, it is further subcategorized according to the fins used for propulsive structure, which includes undulatory and oscillatory fin motions. Many undulatory and oscillatory fin swimmers are capable of turning on their own axis with little or no lateral translation of the body. So in the present research, we seek for a good solution to complement these problems by exploring a “smart” fin that can perform both undulating motion and oscillating motion, and thus achieve high propulsion efficiency, maneuvering and stabilization.The left part of this paper is organized as follows: In section 2, a brief introduction on the background of fishes that exploit fin undulating as well as oscillating motion is carried out. In section 3, we mainly discuss on the mechanism of SMA robotic fish fin which has the ability to realize both undulating and oscillating motion with its special controller. And in section 4, we implement an optimal design of a key parameter of SMA fin ray (the thickness). Finally follow by discussion and future work.
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A building with semi-active base isolation using sliding mode control I. Nagashima, Y. Shinozaki, R. Maseki & J. Toyama Taisei Corporation, Shinjuku, Japan
K. Yoshida & Y. Kitagawa Keio University, Yokohama, Japan
Y. Sanui & H. Komatsu Hitachi, Ltd., Kanagawa, Japan
1
INTRODUCTION
Damping force
The authors have developed a semi-active baseisolation system using semi-active hydraulic dampers that can be switched between two primary damping coefficients. This paper discusses the basic performance of the semi-active hydraulic damper, the control system design, and performance verification through shaking table tests. An overview of the building in which the system was used will also be presented, and the damping effectiveness as determined by seismic response analysis is presented.
C2 = 1.67kNs/cm CH CL
1000kN 929kN 785kN C1H = 36.75kNs/cm
C1L = 12.25k N s/cm Velocity 21.3cm/s 63.8cm/s 150cm/s Figure 1. Piston velocity-damping force relationship of semi-active hydraulic damper.
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SLIDING MODE CONTROL WITH SEMI-ACTIVE HYDRAULIC DAMPER
Figure 1 shows the piston velocity-damping force relationships of semi-active hydraulic damper that correspond to the low and high damping coefficients. The time lag of the damping force when the damping coefficient of the semi-active hydraulic damper was changed was measured through triangular wave excitation by means of displacement control. The results of measurement indicate that, in the low velocity range, the values generally correspond closely to time constants evaluated by assuming that the dynamic characteristics of the hydraulic damper is expressed by a Maxwell model. A sliding mode control has been used to reduce the acceleration response of the building, while keeping the deformation of the isolation story relatively small. First the state space equation for an extended bilinear system is devised to take into account the aforementioned time lag. Next, based on the bilinear optimal control theory [Yoshida et. al. 2001], the switching hyper plane is designed for sliding mode control, and the order of this sliding mode controller is reduced
considering the complex modes of the entire system. Finally, a sliding mode controller for simultaneous bidirectional control is presented. The effectiveness of the semi-active control was verified by shaking table tests using miniature semi-active hydraulic dampers as well as seismic response analysis using a pseudo three-dimensional model of an actual building.
3
CONCLUSIONS
A semi-active base isolation system using semi-active hydraulic dampers that can be switched between two primary damping coefficients was developed and an 11-storey university building equipped with this system was completed in April 2005. The time lag of the semi-active hydraulic damper was measured and considered in the design of sliding mode control. Compared to passive base isolation systems, deformation of the isolation story was maintained at the same
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isolation control, Transactions of the Japan Society of Mechanical Engineers C, Vol.67, No.656. pp.96–102. (in Japanese)
level, while at the same time acceleration response was reduced approximately 20–30%. REFERENCE Yoshida K. and Hujio T. 2001. Bilinear optimal control theory and its application to semi-active vibration
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Semi-active vibration isolation using MR damper for a building-like structure H. Nishimura Keio University, Mita, Minato-ku, Tokyo, Japan
H. Aratake Chiba University
J. Nakasone Kumagaigumi Co., Ltd.
N. Inoue National Institute for Land Infrastructure Management
Y. Nakamura Fujita Corporation
M. Watakabe Toda Corporation
H. Ryujin Maeda Corporation
Y. Ito Hazama Corporation
M. Kanagawa Nishimatsu Construction Co., Ltd.
M. Nagaya Satokogyo Co., Ltd.
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INTRODUCTION
In this paper a gain-scheduled (GS) controller for a semi-active seismic isolation system is designed for a multi-degree-of-freedom structure which has twodegree-of-freedom on the horizontal plane without consideration of coupling of the x- and y-directions. The experiments on a x-y shaking table using some kinds of seismic wave are carried out to verify the performance of isolation of the GS controller used simultaneously. It is demonstrated that the GS controller can adaptively vary the damping coefficient according to various earthquakes and can suppress not only the first floor acceleration but also the relative displacement of isolation layer.
CONTROLLED OBJECT
Figure 1 shows the experimental setup with an isolation layer equipped with rubber bearings and semiactive dampers for x- and y-directions. The height of the structure is about 9 m, and the total weight is about 33 tons. The equation of motion of each direction is respectively described as follows:
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Figure 2. Seismic responses of x-direction to Hachinohe NS earthquake.
Figure 1. Experimental setup.
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DESIGN OF GS H∞ CONTROLLER
By introducing a fictitious damper model whose damping coefficient is linear to the open ratio of orifice area, the bilinear system is transformed to a linear parameter varying (LPV) system. For the LPV system a GS controller based on linear matrix inequalities (LMIs) is designed. 4
SIMULATION AND EXPERIMENT
x-direction to Hachinohe earthquake. The solid line indicates the response of the GS controller, and the broken line indicates the response of the passive damping system. From Figure 2 (a) it is seen that the GS controller can suppress the maximum acceleration by 25 % in comparison with the passive damping system. From Figures 2 (a) and (b), we can see that the experimental results are good agreement with the simulation results. 5
CONCLUSION
We designed GS controllers for a semi-active isolated structure in x- and y-directions independently. The effectiveness of our proposed method was verified by carrying out simulations and experiments.
Figures 2 (a) and (b) respectively show simulation and experimental results of the top floor acceleration of
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Gain-scheduled control of smart structures with dynamic characteristic variation I. Kajiwara Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, Japan
R. Tsuchiya Sony Corporation, Kitashinagawa, Shinagawa-ku, Tokyo Japan
ABSTRACT: This study is concerned with a vibration control strategy for a flexible-link systemto achieve effective vibration suppression. It is required that the control system adapts to the dynamic characteristic variation of the system. A smart-link system composed of piezoelectric actuators and gain-scheduled controller is proposed to cope with change of the variable parameters which causes the dynamic characteristic variation of the system. An adaptive control is conducted by scheduling some LTI controllers to keep the stability and performance against the change of the variable parameters. The appropriate actuator location is determined by the target mode shapes. The scheduling gains for the LTI controllers designed at their operating points are optimized to obtain the effective vibration suppression during the motion of the system.
1
INTRODUCTION
Vibration suppression is very important to improve the performance of mechanical systems. In recent advanced mechanical systems, it is difficult to achieve desired vibration characteristics only by structural design. Smart structure using lightweight devices such as piezoelectric sensors and actuators is a key technology to enhance the vibration control performance. By applying an optimal control theory, the control system for a controlled object with the specific dynamic characteristics can be designed. But generally, the structural dynamic characteristics vary continuously in practical working conditions of mechanical systems. Therefore, the control system which adapts to the dynamic characteristic variation is needed. From this background, this study proposes a gain-scheduled control strategy of smart structures with dynamic characteristic variation in order to achieve desirable vibration suppression.
and holding mass at the end of the manipulator. A smart-link system is constructed by piezoelectric actuators and gain-scheduled controller in order to adapt to the change of the variable parameters. The piezoelectric actuators are appropriately placed to control the target mode vibration. The structure is modeled by FEA and then the model reduction with the modal coordinate transformation is carried out. The control system is designed by solving H2 control problem using a reduced-order modal model. An adaptive control is conducted by scheduling some LTI controllers to keep the stability and performance against the dynamic characteristic variation of the system. The design problem for improving the H2 performance is defined and then the scheduling gains for their LTI controllers are optimized by the SQP algorithm, resulting in an enhanced performance for the vibration control. The performance of the proposed gain-scheduled control system is evaluated by simulation and experiment in this study.
2
3
SMART-LINK SYSTEM AND CONTROL
This study considers vibration suppression of a flexible-link manipulator system which has dynamic characteristic variation.The dynamic characteristics of the system are varied according to the configuration
CONCLUSIONS
This study has proposed a vibration control strategy using smart structure technology for a flexible-link system with dynamic characteristic variation. The gain-scheduled controller is employed to cope with
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the dynamic characteristic variation of the smartlink system. The control system is composed of the multiple LTI controllers designed by H2 control problem and their scheduling gains. The optimization method of the scheduling gains has also been proposed in order to enhance the vibration control performance satisfy-
ing the stability during the motion of the system. The simulation and experiment have been carried out with the 2-link smart manipulator. It has been verified by this study that the enhanced vibration suppression can be achieved by the proposed smart-link mechanism and the gain-scheduled control strategy.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Novel method to utilize piezoelectric film as multi-mode displacement sensor and its application to active vibration control S. Kobayashi, M. Nishikiori, T. Watanabe & K. Seto College of Science & Technology, Nihon University, Tokyo, Japan
1
INTRODUCTION
In this paper, a novel method to utilize piezoelectric film as multi-mode displacement sensor is presented. Figure shows an outlook of the experimental transportation system utilized as the control object.
2 ARRANGEMENT OF PIEZO SENSORS First, fix any location of which the displacement is desired and the frequency response at the location is
measured by any kind of displacement sensor. Then a specific location is chosen where the frequency response of stress possesses roughly proportional to the former frequency response of displacement. Pasting a piezoelectric film on the specific location and scaling its output so that it becomes identical to the output of the initial displacement sensor, the film could be used as a displacement sensor by which multi-modal vibration could be detected. To evaluate the validity of the presented method, two piezoelectric film sensors are applied to an experimental structure in order to perform active vibration control. Figure 2 shows the sensor-positioning algorithm.
3
CONTROL EXPERIMENTS
Control experiments with the two piezoelectric sensors located according to the method are performed, and the effectiveness of the piezoelectric sensors for active vibration control is investigated. Figure 3 shows one of the experimental responses.
Figure 1. Schematic diagram of experimental transportation system.
Figure 2. Arrangement of piezo sensor according to stress-displacement relation.
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4
CONCLUSIONS
The control system using piezoelectric sensors arranged by the presented method achieved good control performance. The effectiveness of the presented method is confirmed.
Figure 3. Step responses with vibration control or without control.
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Smart systems and mechatronics
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
All-terrain vehicle robot with controllable auxiliary mass M. Yokoyama & R. Adachi Niigata University, Niigata City, Japan
EXTENDED ABSTRACT This paper presents a control strategy by learning for an all-terrain vehicle robot developed by the authors. As shown Figure 1, this robot consists of two modules: a normal vehicle with wheels or tracks, and a controllable auxiliary mass which is a feature of this vehicle robot. Motion of the auxiliary mass can be controlled by motors with parallel link mechanism in order to improve the vehicle mobility, i.e. the performance of the vehicle in relation to soft terrain, obstacle climbing and avoidance, and so on. That is, the auxiliary mass can be seen as a rider of motorcycle and utilized to change the center of gravity, the moment of inertia, adaptively corresponding to the variation of environmental conditions. There are many major challenges facing to this novel robot. One of them is how to generate the desired trajectories of the auxiliary mass from some information with respect to the vehicle state. The reinforcement learning is adopted to the vehicle robot in this paper. In order to evaluate the reinforcement learning properly, a simple situation that the vehicle robot
Figure 1. All-terrain vehicle robot with controllable mass with parallel mechanism.
climbs a slippery slope with unknown properties of adhesion is considered. Figure 2 shows the proposed control configuration. The points of this configuration are as follows: 1) A tracking system is designed in which the longitudinal slip is used as the variable being controlled, and should follow the optimal slip. 2) Integral action is used to reduce the tracking error in steady state.
3) Action of the actor is not the control input xm but the reference slip ratio to be followed, thus the actor is expected to generate the optimal slip ratio, λop after learning. 4) The state variables for learning are the longitudinal slip and the vehicle acceleration, because the unknown friction coefficient should be estimated implicitly. It was shown through the numerical simulation that the proposed learning controller achieved the desired performance without estimating the unknown properties of the ground adhesion.
Figure 2. Control configuration.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Multi-objective optimal control of semi-active suspension system with MR dampers M.G. Luo, L. Zheng & Y.N. Li State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing, China
A. Baz Department of Mechanical Engineering, University of Maryland,College Park, MD, USA
ABSTRACT Generally speaking, the ride comfort and handing stability of vehicle are conflicting objectives. The ride comfort requires that the car body achieves small acceleration levels and ideally to achieve zero. On the other hands, the handling performance implies that the wheel normal forces are kept as constant as possible. Physically, this means that wheels should follow the road profiles well, so as to achieve as constant tire deflection as possible. The main theme of this paper is how to design algorithms for fullcar semi-active suspension system with magnetorheological(MR) dampers to achieve a balanced ride and handling performance. In this study, mixed mode-type MR dampers are designed, manufactured and integrated into semiactive suspension systems for a middle sized passenger vehicle. They are twin tube MR dampers with the double class magnetic circuits. When not activated, the MR fluid in the MR dampers behaves as a Newtonian fluid. When it is exposed to a magnetic field, micron-size iron particles in carrier fluid align themselves along magnetic flux lines within milliseconds and the flow resistance increases by several orders of magnitude. The control model of the MR dampers is derived and used to calculate theoretical variable damping force applied to semi-active suspension systems with MR dampers. The experiment is carried out to identify the theoretical model. The dynamic curves for both the damping force via the displacement and the damping force via the velocity are obtained by using a servo-hydraulic shock testing dynamometer. The experimental results show that these prototype MR dampers demonstrate wide controllable dynamic range under magnetic field and are ideal actuators for semi-active suspension systems in vehicle. In additional, the experimental results are in close agreement with the theoretical predictions, this means that the theoretical model can describe the dynamic
characteristics of the MR dampers accurately, thus can be used to implement practice semi-active suspension control system with MR dampers in vehicle. In order to balance the ride and handling performances, a multi-objective optimal control strategy based on the linear matrix inequality(LMI) is designed and used to control semi-active suspension systems with MR dampers in vehicle. A vertical vehicle dynamic model with seven degrees of freedom is developed and used to demonstrate the effectiveness of the multi-objective optimal controller. The ride performance is characterized by H2 system norm, and the handling performance is characterized by H∞ system norm, and the control method optimizes the mixed H2 /H∞ performance. The H2 and H∞ system norms used in the mixed H2 /H∞ performance optimization are scaled by the corresponding open-loop norms. In order to simplify the control system of the full-car semi-active suspension with MR dampers, four independent H2 /H∞ optimal controllers are designed. Each controller is used to control one quarter of the full car model. By this means, the computational burden for the whole control system can be reduced. Usually, a rapid response for various road conditions needs to be considered for the practice application of semi-active suspension systems with MR dampers. The performance of the proposed controller is discussed and evaluated both in time and frequency domains. The results show that the body vertical, roll, pitch accelerations and the tire deflections are reduced significantly by adopting the proposed mixed H2 /H∞ controllers. The RMSs also demonstrate the same results. This means that a good balance between the ride performance and the handling stability has been reached. Furthermore, the results demonstrate the potential of multi-objective optimal H2 /H∞ controller as an effective means for attenuating and supressing the vibration of vehicle and improving the ride comfort and the handling performance at the same time.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Virtual reality simulation of a full car active suspension system with nonlinear energy sink controller J. Smoker & A. Baz Department of Mechanical Engineering, University of Maryland, College Park, USA
L. Zheng State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing, P.R.China
This paper presents the design of a Nonlinear Energy Sink (NES) controller and its application to active suspension systems in the Virtual Reality Environment. In this environment, the design engineers are immersed in an audio-visually coupled tele-operated environment whereby direct interaction with and control of the design process is achieved in real time. In this manner, the behavior of synthetic models of the full car can be monitored by literally walking around the car and adjusting the design parameters of the suspension as needed to ensure optimal performance while satisfying design and operational requirements. The control actuators which provide forces equivalent to nonlinear stiffness and damping elements are attached to the vehicle in order to actively isolate it from road excitation. The effect of the parameters of the NES controller on the vehicle performance is studied both in the frequency and time domain. The
effectiveness of the NES controller is validated by numerical simulation. The robustness of the nonlinear energy pumping process is studied by varying the magnitude of road excitation. The simulation results in the Virtual Reality Environment show that under certain conditions, the nonlinear energy pumping can be induced and significant vibration isolation can be achieved. The performance of vehicle including the ride comfort and road holding capability can be improved significantly. When the magnitude of road excitation is increased, the capacity of the NES to absorb energy from the main system is also enhanced. This is very important to achieve vibration isolation objectives. The virtual reality simulation results also show that the nonlinear NES controller performs better than the classical LQR controller particularly as the road condition becomes worst.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Oscillations of piezoelectric microscale resonators B. Balachandran Department of Mechanical Engineering, University of Maryland, College Park, M,D USA
SUMMARY Microscale resonators are attractive for communication, signal-processing, and sensing applications. In the resonators considered here, piezoelectric actuation is used to excite the composite structures on the input side and piezoelectric sensing is carried out on the output side.Analytical and numerical efforts being carried out to understand nonlinear phenomena in these resonators as well as to develop design tools for such systems will be presented. In the first component of the presentation, it will be discussed as to how linear and nonlinear finite element analyses can be used to study the influence of axial loads, predict buckling, and explain experimental observations. In another
component, parametric identification schemes being used to determine residual stresses and linear and nonlinear characteristics of these resonators will be presented. Nonlinear oscillations of clamped-clamped and free-free microelectromechanical filters will also be addressed, and nonlinear analysis being carried out to explain experimental observations of nonlinear phenomena will be presented. To close the presentation, possibilities for intrinsic localized modes in resonator arrays and other work in progress will be discussed. The presentation will draw upon material from the work of the author and collaborators. The research findings can open the doors to new resonator array designs.
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Magnetorheological fluids and dampers (3)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Dynamic performance and control of ER damper in vehicle L. Zheng, Y.N. Li, M.G. Luo & J. Shao State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing, China
1 ABSTRACT As a kind of smart actuators, electro-rheological(ER) devices have been widely researched in the past decades. Their attractive advantages are fast response time, low power consumption, and easy embedding in structures or mechanical systems. So far, they have been developed as automobile shock absorbers, engine mounts, haptic devices, aircraft landing gears and seismic response reduction devices. In this study, the prototype monotube ER dampers are designed and manufactured and characterized. The proposed ER dampers operate in the flow mode. The inner cylinder is concentric to the outer cylinder. The inner cylinder is charged by a high voltage supple unit as the positive electrode, while the outer cylinder is connected to ground as the negative electrode. In this way, a high voltage electric field is produced in an annular gap between the inner and outer cylinders. When an electric field is applied, the rheological properties of the ER fluid in the annular gap is changed rapidly, thus a continuously variable damping force in the ER dampers is produced. A float piston is designed to form an accumulator of the ER fluid induced by the motion of the piston. The two circular rings are used to limit the motions of the piston and the float piston. The ER fluid used in the prototype ER dampers is fabricated in smart system research center in Chongqing University. Its rheological properties are measured using a rotary rheometer. The rheological experiment shows that the ER fluid has a much better ER effect and a lower leaking current density and is available to be used in the prototype ER dampers. The parameters of the ER dampers for the front and rear suspensions are estimated by the expression of controllable damping force derived from the Bingham model. The prototype ER dampers are tested by using a servo-hydraulic shock testing dynamometer. It has a maximum stroke of 12.5 cm and is equipped with a 50 KN load cell that measures the damping forces of the ER dampers and a
displacement transducer that measures displacement. The excitation used is a sinusoidal displacement with constant amplitude of 25 mm. Three different excitation frequencies are used to test the damping force of the ER dampers. They are 0.50, 0.75 and 1.0 Hz respectively. These frequencies correspond to maximum piston velocities ranging from about 100 to 300 mm/s. The applied electric field ranged from 0– 3.0 kV/mm. The dynamic curves for both the damping force via the displacement and the damping force via the velocity are obtained experimentally. The dynamic hysteresis characteristics are demonstrated. The field test results show that the ER dampers can supply an available damping force for semi-active suspension systems of a small sized passenger vehicle. The full vehicle model was established to design and fabricte the sliding mode controllers of semi-active suspension systems with ER dampers. In order to simplify system, four independent sliding mode controllers are designed and used to control semi-active suspension systems with ER dampers in vehicle, each for each corner. By this means, the computational burden for the whole control system and the response time can be reduced, this enhances the effectivess of semi-active suspension systems with ER dampers. The sliding mode surface is defined and the pole assignment method is used to determine the surface gradient so that the sliding surface itself is asymptotically stable. All steps to design the sliding mode controllers are given in this study. Control characteristics for the vibration suppression of the full vehicle system under various road conditions are evaluated in frequency domain. The robustness is investigated by considering parameter uncertainties such as the sprung mass. The simulation results show that the heave, pitch and roll accelerations of the sprung mass and tire deflection are significantly reduced by adopting the proposed sliding mode controllers. The sliding mode control also demonstrates a good robustness against parameter uncertainties and stability.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Optimal design of MR damper and dynamic characteristics L. Zheng, Y.N. Li & J.S. Wei Affiliation State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing, China
S.S. Li & R.G. Li Chongqing Zhongyi Shock Absorber Factory, Chongqing, China
ABSTRACT Many types of semi-active MR dampers have been proposed for the vibration attenuation of various dynamic systems including vehicle suspensions, seat suspensions and various civil structures. Early in 1998, a commercial vibration control system based on linear MR fluid shock absorbers became available for use in the seats of large Class 8, eighteen-wheeler, trucks. In 1999, MR fluid based adjustable shock absorbers for stock car and drag race vehicles were introduced. A semi-active suspension system with MR dampers for Volvo heavy truck was developed in Virginia Tech. Several innovative prototype MR dampers have been designed, manufactured and characterized at the University of Nevada such as MR dampers for mountain bicycles, motorcycles and high mobility multi-purpose wheeled vehicles (HMMWV). These devices usually work according to one of three modes or some combination of them: the shear mode (Couette flow), the flow mode (Poiseuille flow) and the squeeze mode. In this paper, a mixed mode-type magneto-rheological (MR)fluid dampers for a small sized passenger vehicle is designed, manufactured and characterized. The MR damper encompasses a piston with coils, a oriented piston, a piston rod, a foot valve, two housings, one is the inner housing, another is the outer housing. The MR fluid inside the MR damper flows through the space between the outer surface of the piston and the inner surface of the inner housing under pressure, while the MR fluid is also sheared in the space because the piston moves relative to the inner housing. By assuming the MR fluid to follow the Bingham model, the damping force of the MR damper operated in the mixed mode-type can be derived by the combination of the damping forces from the shear mode and the flow mode. Although some dimensions for housings in MR damper can be determined by the conventional hydraulic passive damper in order to do minimum
modification for the structure of the original damper, other parameters such as fluid gap, the total length of damping channel as well as the coil turns, should be specially designed and considered. The optimal design of the MR damper is implemented by using the finite-element method with the help of ANAYS package.Considering the intensity and the required nonmagnetic characteristic of some of the MR damper components, copper is adopted as the material for the oriented piston. Pure iron is selected as the material for the piston. All the housings and the piston rod are made of MILD steel, which is rigid enough to support the whole structure of the MR damper and can be magnetized as well. Different geometrical and material parameters in the MR damper will determine which section (MR duct, piston or housings) is reached magnetic saturation point first. If the MR fluid and the pure iron or the middle carbon steel can reach magnetic saturation at the same coil currents, the goal of optimization design of the MR damper will be achieved. A 2D finite element analysis magnetic flux density is demonstrated. The theoretical analysis shows that both the MR fluid and the middle carbon steel reach their saturation points at the same coil currents, 1.5 A. The flux density in the fluid gap maintains approximately a constant. Therefore, the optimized dimensions of the MR damper are determined. In order to integrate the MR damper into semiactive suspension systems in vehicle, it is necessary to describe the dynamic characteristics of the MR damper accurately. In this study, the dynamic characteristics of the MR damper are modeled by the Bouc-Wen model. The optimized parameters in the model are obtained using a least-squares optimization method by means of the function ‘leastsq’ available in MATLAB. Theoretical and experimental results demonstrate that the proposed model can describe the dynamic characteristics of the MR damper accurately, thus can be used to implement practice semi-active suspension control system with MR dampers in vehicle.
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Effects of water on the rheological properties of oil-based MR fluids H.B. Cheng, X.H. Wang, J.M. Wang, J. Zhang, W.Y. Zhao, W.L. Qu & Q.J. Zhang State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, China
W.X. Gao Jiangsu Tianyun Advanced Materials Company, Jiangsu, China
1
INTRODUCTION
Due to the moisture absorption during the preparation, storage and application for oil-based magnetorheological (MR) fluids, water molecules can more or less enter into the MR fluids. Nonetheless, the effects of water as an impurity on the properties of MR fluids are unclear and usually ignored, and there are few reports on the issue in literature. In this paper, the influence of water on the properties of MR fluids has been investigated and discussed in detail. The results indicate that the effects of water on the rheological properties and stability of oil-based MR fluids are not negligible. 2
Figure 1. Off-state shear viscosities η vs. the φ values of water in MR fluids at different shear rates.
EXPERIMENTAL
Six MR fluid samples were prepared by adding water in different volume fractions (φ) of 0%, 1.5%, 2.5%, 3%, 4%, and 6% into the same oil-based MR fluids and labeled as #0, #1, #2, #3, #4 and #5 samples, respectively. The MR properties of the samples, including off-state viscosity, field-induced shear stress, and response time were measured using a commercial parallel plate rheometer attached to an electromagnetic iron. 3
RESULTS AND DISCUSSION
The off-state shear viscosity of MR fluids decreases smoothly with φ value of water in lower φ value range, and then increases slightly with the φ value in a critical volume fraction range (φc ) of 1.5%–4%, followed by a rapid increase at above 4% (see Fig. 1). Water can improve the sedimentation stability of MR fluids and their responsive rate to field, but does not obviously affect the field-induced shear stress around the critical range φc . These results are in partly agreement with the phenomenon reported by Park et al. (Park et al. 2001).The mechanism of effects of water on the properties of MR fluids would be very complicated, but
the main reasons are due to the formation of emulsion and network structure between water molecules and carrier molecules. 4
CONCLUSIONS
Water has significant effects on the rheological properties and stability of MR fluids, and there is a different critical volume fraction range (φc ) of water for different MR fluid. If the φ value of water is within the critical range φc , water usually decreases the off-state viscosity, increases both the shear stress and response rate to the applied magnetic field; but if the φ value ≤φc or ≥φc , water would increases the off-state viscosity, decreases both the shear stress and response rate. The anti-sedimentation is usually improved when the φ value is around φc . REFERENCES Park, J.H. et al. 2001. Rheological properties and stabilization of magnetorheological fluids in a water-in-oil emulsion. J. Colloid and Interface Sci. 240:349–354.
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Stable oil-based MR fluids with core-shell composite particles H.B. Cheng, J. Zhang, S. Xu, W.Y. Zhao, J.W. Tu, W.L. Qu & Q.J. Zhang State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, China
W.X. Gao Jiangsu Tianyun Advanced Materials Company, Jiangsu, China
1
INTRODUCTION
Magnetorheological (MR) fluid is an unstable suspension. Effectively preventing MR fluids from sedimentation is a key technique for the engineering application of MR fluids. In this study, we have prepared a kind of core-shell composite particles (CSC particles), which were composed of carbonyl iron (CI) particles and N-hexadecayl ethylenediane triacetic acid (HED3A). A novel stable oil based MR fluids were prepared using the above CSC particles and characterized.
2
EXPERIMENTAL
The magnetic CSC particles were prepared with CI particles as core and HED3A as a shell by chemical absorption. A new MR fluid based on CSC particles was prepared with the composition fraction (in volume) of 40% CSC particles, 0.5% additives and 59.5% mineral oil. A contrast MR fluid based on CI particles was also prepared with the same way. The MR characterizations were performed at 25◦ C via an advanced rheometric expansion system attached to a parallelplate measuring system with a diameter of 25 mm. The magnetic field direction was set to be perpendicular to the flow direction.
3
RESULTS AND DISCUSSION
The sedimentation ratios of the new MR fluid and the contrast MR fluid had been measured. For the former, the clear liquid occurred after 24 hours (9 hours for the latter), and the ratio increased slowly with time in the first 10 days and then remained a constant 10% (13% for the latter). Moreover, the former can be easily redispersed after a long period of storage (such as 12 months) by weakly shaking, but the latter was difficulty to become homogeneous even using a strong
Figure 1. Dependence of the shear stress on magnetic field strength for the new MR fluid () and the contrast MR fluid () (shear rate: 0.1 s−1 , t = 25◦ ).
stirring force. It means that the new MR fluid prepared with CSC particles has better anti-sedimentation and redispersion ability than the contrast MR fluid based on CI particles. The field-induced shear stress of the new MR fluid is larger than that of the contrast MR fluid (see Fig. 1). For example, the former is about 10% larger than the latter at 320 kA/m. The results demonstrate that the outer layer chelating surfactant HED3A of coreshell composite particles can not only improve the anti-sedimentation stability but also enhance the MR effects for MR fluids.
4
CONCLUSIONS
Novel stable oil based MR fluid, using the core-shell composite magnetic particles as dispersed phase, was prepared and characterized; this new MR fluid has better stability and redispersibility, and stronger fieldinduced shear stress than the similar MR fluids with CI particles.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Study on the shear behavior of MREs-based on chain-like model Miao Yu, Xiaorui Yan, Linzhang Mao & Hongchang Wen The Key Lab for Optoelectronic Technology and Systems, Ministry of Education, China Department of Optoelectronic Engineering, Chongqing University, Chongqing, China
The magnetorheological elastomers (MREs) which consists of iron particles and rubber is a new class of MR materials. Compared with MR fluids, it has the advantages of having no sealing equipments and good stability at the basis of having the features of MR materials, so it has become a key point in recent years. In the past research, it was indicated that the shear effect of MREs is more obvious than normal strain with the same condition, however the range of shear modulus change caused by applied magnetic field is also limited, the change of absolute shear modulus is less than 2 MPa and the relative shear modulus is less than 50%. Therefore, in order to increase the range of shear modulus change of MREs, the factors influencing shear modulus change of MREs must be analyzed theoretically. In this paper, we also assumed that the iron particles in the rubber form chain-like structure under the external magnetic field (Figure 1). At the basis of considering the interactions between adjacent particles
Figure 1. Chain-like structure of MREs.
within a particles chain, the case is also considered that the particles chain is not completely parallel with the external magnetic field and it is more exact when describing the real case. Based on above discussion, the specific result of shear modulus change caused by the applied magnetic field is calculated at different magnetic fields and initial angles. The result can be expressed as the following equation:
Where µ1 is the relative permeability of the medium, χ is the susceptibility of magnetic particles, θ is the initial angle of particle chains and applied magnetic field, γ is the shear strain of the particle chains, a is the particle radius, H0 is the external magnetic field intensity, ϕ is the volume fraction of particles, r is the distance of the adjacent particles in a chain. According to the equation (1), we can get the conclusion: the shear modulus change caused by the applied magnetic field would diminish if initial angle θ increases, which indicates that the rheological effect of the oblique chains is less than the chains whose initial angle θ is 0. some other factors influencing the shear modulus change are also be analyzed, such as magnetic field intensity, the shear strain, the distance of particles etc. Based on the above analysis and calculation, in order to get better effect, larger magnetic field intensity should be taken to get smaller initial angle of particles chains, which leads to increase the range of shear modulus change of MREs. Furthermore, the factors including magnetic field intensity, particles distance, the volume fraction of particles and susceptibility will all affect the shear modulus change, certain measures to optimize these parameters should be taken to get better effect.
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Data-analysis methods
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Modeling of magnetorheological fluid damper with force lag considerations X.C. Guan, C.F. Bian & P.F. Guo School of Civil Engineering, Harbin Institute of Technology, Harbin, P.R. China
J.P. Ou School of Civil Engineering, Harbin Institute of Technology, Harbin, P.R. China School of Civil Engineering, Dalian University of Technology, Dalian, P.R. China
1
INTRODUCTION
A huge MR damper whose maximum damping force is about 280 kN is tested. According to experimental results of the damper, a new model was presented. The character of the model is that, the factor of slipping at joint bearing and a little residual air in damper of MRF was considered. Using the model, main performance of the MR damper is analyzed.
2
EXPERIMENTAL AND RESULTS
Figure 1. Nonlinear sectional hyperboloid tangent model used to describe the behavior of MR damper.
Where, Cpo is viscous damp coefficient, F is the yield force, K1 is shape factor which indicate slope ratio of zone that damper through slipping stage to full work, K2 is shape factor which indicate slope ratio of zone that damper through full work to slipping stage, K is slope ratio of slipping stage, λ1 is wide of hysteresis curve, λ2 is wide of hysteresis curve, x and x˙ is displacement and relative velocity between piston and cylinder body, respectively.
3
CONCLUSIONS
The nonlinear sectional hyperboloid tangent model can precisely describe damping force lag caused by
Figure 2. Graphic validation of the model for the two amplitude, on force vs. displacement.
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slipping of joint bearing and a little air residual. Analysis using the model shows that, in this experiment, it is slipping caused the huge lag, instead of the little residual.
2006AA03Z103 and National Science Foundation of China under the grant number 50520130296.
ACKNOWLEDGEMENTS Financial supported by High-Tech Research and Development of China under the grant number
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Enhancement of the spatiotemporal resolution of pulse-echo methods by digital filtering Q.F. Li & L.H. Shi Lab of Electromagnetics, Nanjing Engineering Institute, Nanjing, Jiangsu, China
D.K. Liang & G. Li Nanjing University of Aeronautics and Astronautics, Nanjing, Jiangsu, China
1
4 APPLICATION RESULTS
INTRODUCTION
Ultrasonic pulse-echo method provides a powerful tool in detecting the inner structure of concrete elements. Presented here is a digital filtering method to compensate the unwanted frequency response characteristics of transducers and enhance the spatiotemporal resolution of the method. 2 THEORY OF DIGITAL FILTERING The concept of compensation is a system identification method based on digital filtering. According to dynamic characteristics of linear time invariant system, the inverse system with transfer function can be established by a pair of known input and output of the transducers system, and cascade with the test system to compensate the ringing effects. 3
EXPERIMENTAL VERIFICATION
4.1
Measurement of velocity and thickness
The proposed method is applied to measure the thickness of a concrete element. A specimen of concrete are designed and cast with the same compounding ratio as the normal architectural concrete. By pitch-catch method, velocity of ultrasonic waves in concrete can be derived, and then thickness of the specimen can be calculated. It is obvious that the measurement result is more accurate after using the compensation filter. 4.2
B-scan imaging
A B-scan is also carried out. The collected data is compensated by passing through the filter, and then shown by image. From the images, the shape of PVC pipe embedded in the specimen is revealed, and the bottom of the specimen is clearly shown after using the compensation filter.
3.1 Test system To validate the proposed method, a test system, which includes a function generator unit, a signal amplifier unit, two ultrasonic transducers and a receiving unit, is established. 3.2 Establishing model of transducers In order to measure the dynamic response characteristic of the transducers system, water-immersion test is designed. After collecting the input and output, and making their amplitudes uniform, a model of the system can be established by algorithm of system identification, and transfer function can be obtained. Therefore the inverse system can be calculated and cascaded to the test system to compensate frequency response of the transducer. By comparison, the compensated signal is very close to the original signal, and the proposed method works well.
5
CONCLUSION
A compensation method for low-frequency ultrasonic transducers based on digital filtering is presented. The ringing effect caused by transducer system can be effectively suppressed by compensation and the spatiotemporal resolution is enhanced. The method is applied to measurement of the thickness of concrete specimen. After compensation, the reflected signals are intensified and the thickness measurement error is within 2%. The compensation method is also used in B-scan imaging of concrete structure. The effect of compensation filtering is also obvious. This kind of digital compensation filter provides an effective signal processing method for pulse-echo NDT to improve its spatiotemporal resolution.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A new temperature compensation method for flow measurement employing FLNN Zhiwei Hou, Renwen Chen & Yuanyuan Meng Aeronautical Science Key Lab. for Smart Material & Structure, Nanjing University of Aeronautics & Astronautics, Nanjing, China
1
INTRODUCTION
In recent years, people paid much more attention to the accuracy of flow measurement as technology progresses. The intelligent flow totalizer system in this design is combined with the spindle flow meter, a new type of differential pressure flow-meter, which is used as head-end of flow measurement. In the period of measurement, we collect differential pressures as primacy, the absolute pressures and the medium temperatures as compensation signal to calculate flow. Differential pressure is of significance in the flow measurement system, and its measurement accuracy is directly influenced the final calculation result. As to the outputs of the sensor which is used in differential pressure measurement are influenced by the environment temperature, temperature compensation for more accurate measurement is needed. In this paper Functional-link neural network (FLNN) is employed. FLNN has higher compensation accuracy and the mathematical model based on FLNN is flexible. 2 TEMPERATURE COMPENSATION MODELING BASED ON FLNN The additional functions of Up , Ut and interaction product term of that are output variable. After indispensable analysis of sensor’s element and characteristic, we choose proper function expanding terms and link them to output layer by different weights. According to the input-output samples, the network is trained by mentor. Many iterations aren’t done until convergences in the network by making use of e deviation and NN algorithm.
Figure 1. Temperature compensation modeling based on FLNN.
3 THE RESULT OF TEMPERATURE COMPENSATION In this paper three common adopted function expanding forms are applied in simulation based on FLNN. The result of simulations show that employs Chebyshev polynomial in expanding function has higher compensation accuracy than other two function expanding forms. The max error of it is 0.75, which can satisfy thedemand of flow measurement. So Chebyshev polynomial function expanding form is applied in temperature compensation of differential pressure sensor. In fact, the flexibility of FLNN automatically compensates any variation of the sensor response occurring due to change in environmental conditions. It has a potential future in the field of measurement and control.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Research on signal separation of self-sensing piezoelectric actuator Qiang Liu, Renwen Chen & Baocheng Gu The Aeronautical Key Lab. for Smart Materials & Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, P. R. China
1
GENERAL INSTRUCTIONS
3 THE PROBLEM OF BRIDGE CIRCUIT METHOD
The concept for self-sensing actuator has been brought out for several years, where a single piece of piezoelectric element is simultaneously used as a sensor and an actuator. Self-sensing actuator enable the complete collocation of sensor and actuator that would be much advantageous in control aspects. SSA is attractive in active control applications because the actuator and sensor arrangement is a truly collocated pair, and hence avoids nonminimum phase zero dynamics, which degrades tracking performance. So many researchers have tried to apply a self-sensing actuator to vibration control of flexible structures. An electrical bridge is essential to self-sensing actuation that yields an useful information about the strain in the structure.
2
BRIDGE CIRCUIT FOR SSA
However, successful use of SSA relies on well distinguishing the signal to be measured from the controlling outputs, which are always mixed together. A specially designed electric circuit, typically, a bridge circuit, is required to realize the concept.
Figure 1. Bridge circuit.
The problem with the bridge method is that instability can result from capacitance variation in the piezoelectric material, bringing about an imbalanced equilibrium state of the bridge circuit. Since the capacitor and the voltage generator in the electrically equivalent model shown in Fig. 1 cannot be separated, it is difficult to get the accurate value of the capacitance CP .
4 ALGORITHMS AND THEORETICAL DERIVATION OF SSA SIGNAL SEPARATION BASED ON LMS To solve this problem, the adaptive filtering has been proposed. The self-adaptive compensation method is present based on TMS320F2812. The of this system is shown in Fig. 2. In this SSA control system, the SSA is connected to the operational amplifier IC1, the bypass capacitor is connected to the operational amplifier IC2. The voltage V02 from IC2 is got by DSP through A/D. In the
Figure 2. The experimental system.
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DSP, the adaptive algorithm is actualized. Then VDSP , the output of DSP.
system, is approximately equal to the signal got from the sensor.
5 ALGORITHMS The experimental results are shown in Fig. It shows that the signal, which is got from the SSA signal separation
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Smart control systems-based on MR fluids (3)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Structural reliability analysis-based on support vector machine M. N. Noori Dean of the College of Engineering, California Polytechnic State University, USA
Y. Cao Department of Mechanical and Aerospace Engineering, North Carolina State University, USA
F.G. Yuan Mechanical and Aerospace Engineering, North Carolina State University, USA
T. Yokoi & A. Masuda Department of Mechanical and System Engineering, Kyoto Institute of Technology, Japan
Structural reliability and safety play a major role in all facts of human lives. Over the past few decades significant advancements have been made in incorporating and consideration of reliability and uncertainty analysis in a wide range of engineering disciplines and practices. However, due to lack of a complete understanding and predicting the structural response under various environmental impacts, changes and variations occurring in a structure through its life time, and/or modifications and redesign of a structure’s components during its service life, it might be difficult to obtain the up to date information of structural reliability. Therefore, a non supervised approach to evaluate the reliability information is highly desired. In this work, a Support Vector Machine (SVM) based reliability analysis approach is introduced. Support Vector Machine (SVM) is a promising machine learning algorithm for data classification and regression. For the classification problem, the major feature of SVM is its capability of minimizing the training error while simultaneously maximizing the margin between two classes. This leads to the unique characteristic of its ability of generalization from the small data sets. In reliability analysis, on the basis of the simulated data sets, a hyperplane to classify the safety region and the failure region can be found by using SVM. Other testing data can be classified according to this classifier. The advantage of this approach is to classify the new data points without going through the calculation of the limit state function. In this research work, the support vector machine algorithm was implemented to classify the safe region and the failure region. The failure probability for a set of test data was found based on the classifier. The reliability updating can be
performed based on the learning machine function by updating the hyperplane with only a small set of new measurements. The failure probability is evaluated as:
where N is the total number of testing data or collected data for practical cases and Nfailureregion is the number of data which are classified into the failure region. In this work, generalized reliability analysis models were introduced to verify the approach. Hyper planes to classify input data into safe region and failed region can be modeled from training data. As many as 2000 input data were tested. Different kernel functions were compared. It is demonstrated that the proposed SVM based approach leads to an accurate and efficient procedure for reliability analysis. In mechanical and structural reliability, the probability of failure is usually very small, which requires very large samples to achieve the needed accuracy by using Monte Carlo simulation method. However, it is shown that much less training data are required for SVM based approach to obtain the accurate enough results. Moreover, in reality, due to the lack of complete knowledge about the structure or the changes in the characteristics of the structure through time, such as upgrades and redesigns, the information to define a reasonable limit state function could be limited and sometimes non-continuous. It is another advantage of SVM based reliability analysis that failure probability can be obtained without computation of the limit state function.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Study on a Magnetorheological fluid bladder spring for isolation system X.Z. Zhang, W.H. Li & X.Y. Wang School of Mechanical, Materials & Mechatronic Engineering, University of Wollongong, Wollongong, Australia
1
INTRODUCTION
Vibration reduction and isolation plays an important role in protectecting machinery and structures from unwanted vibration related problems. A variety of passive and active isolation systems have been developed for vibration suppression. However, passive systems are only effective for narrow frequencies while passive systems usually have high costs. Semi-active suspensions can be nearly as effective as fully active suspensions in vibration suppression. Furthermore, they do not require either higher-power actuators or a large power supply. When the control system fails, the semiactive suspension can still work in a passive condition. In early semiactive suspension, the tunable damping force can be achieved by using hydraulic semiactive dampers with electromagnetically controlled valves or Friction damper, which damping force is controlled by varying the force normal to a friction interface. More recently, the applications of MR fluids in the controllable dampers were investigated and used as semi-active structural control devices successfully. In this paper, a novel MR fluid bladder isolator is designed and fabricated. A mechanical model for the isolator is constructed and parameters of the model are identified based on the experimental results. A nonresonant control is employed to minimize the vibration amplitude of the system. In numerical simulations, the performance of the sweeping frequency response reduction and the displacement transmissibility is investigated. 2
RESULTS
The developed MR fluid bladder spring is composed of two variable volume rubber bladder filled with MR fluid, a pipe and a MR valve connecting them. One of the bladders supports distur-bance force and the
MR fluid flows between two bladders because of the variation of bladder volume due to deformation. The MR valve has the dimension of 20 mm, 6 mm, 4 mm. The magnetic field applied to the MR fluid is generated by an electronic coil. Based on the Bingham plastic model, the damping ratio of the developed bladder system versus the coil current was derived. An experimental system was set up to investigate dynamic performances of the isolator system. The frequency sweep method was employed to find natural frequencies of the system at various magnetic fields. The results indicate that the natural frequency of the system varied from 5.3 Hz to 8 Hz when the coil current changed from 0 A to 2 A. The damping ratio also shows an increasing trend with the coil current. A control methodology based on non-resonance theory was used to evaluate the isolator system. The simulation results indicated that the developed system can produce very effective effect, particularly compared with conventional passive systems. 3
CONCLUSIONS
In this paper, a new semiactive vibration isolation system, which is fabricated with rubber bladders and an MR valve, is designed and manufactured. A mathematical model of the MR isolator is built for latter theoretical analysis. To describe the practical damping force generated by the MR valve in the isolator, a numerical model of the MR valve is pro-posed. Then, using experimental method, the parameters of MR isolator are identified. Meanwhile, dynamic behavior of MR isolator with different excitation frequency and current input is measured and compared with that resulting from theoretical analysis. It was shown that the model calculation result was in sufficiently good agreement with the dynamic properties of the isolator measured from the experiment.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Fuzzy vibration control of intelligent structures with MR dampers Y.Q. Guo & S.M. Fei School of Automation, Southeast University, Nanjing, Jiangsu Province, China
Z.D. Xu College of Civil Engineering, Southeast University, Nanjing, Jiangsu Province, China
1
INTRODUCTION
A semi-active control system may be defined as a system which typically requires a small external power source for operation and utilizes the motion of the structure to develop control forces, the magnitude of which can be adjusted by the external power source (Michael et al. 1999). The Magnetorheological (MR) damper using MR fluid to provide controllable damping force is a promising semi-active device for vibration control applications. MR fluid is a kind of intelligent material which can change dramatically according to the strength of an accompanying magnetic field. When no magnetic field is applied to the fluid, the MR damper behaves like an ordinary viscous damper; when a magnetic field is applied to the fluid, particle chains form, and the fluid becomes a semisolid, exhibiting plastic behavior. Additionally, when the magnetic field is altered, the transformation of the fluid is completely reversible. The transformation requires only low power requirements and has rapid response time (only few milliseconds). For control systems with MR dampers, how to generate proper command currents (or command voltages) of MR dampers is very important in that it affects directly the effect of vibration mitigation. Many control strategies MR dampers have been proposed over the last decade. Dyke et al. (1996) proposed a semi-active clipped-optimal control strategy based on acceleration feedback for the MR damper. Chung et al. (1998) also used the acceleration feedback control of seismic structures to successfully reduce vibration of structures. Schurter et al. (2001) proposed a fuzzy controller based on acceleration of the building feedback to achieve the vibration mitigation. Xu et al. (2003) proposed the intelligent bi-state control method to solve the time-delay problem of semi-active control.
Wang et al. (2005) presented an inverse neural network models for MR dampers to generate the command voltage when the MR damper is working in a semi-active mode. For structures with MR dampers with inherent time-delay phenomena, how to resolve the system time-delay problem is also very important. This paper presents a fuzzy control strategy based on a neural network forecasting model (NNFM) for the building structure with MR dampers. It is well known that neural networks are capable of performing non-linear mappings between real valued inputs and outputs and can be used to model, identify and predict complex nonlinear systems. So a NNFM is developed to predict system dynamic response to resolve the system time-delay problem. On the other hand, a fuzzy controller is then designed to determine the command current of MR dampers. A five-floor steel structure with MR dampers using the fuzzy control strategy based on the NNFM is modeled and simulated by using Simulink. Simulation results of the fuzzy control system are compared with those of the bi-state control system and the uncontrolled system, and some conclusions are obtained.The NNFM can predict the dynamic response of the structure with MR dampers. The fuzzy control strategy based on the NNFM can reduce displacement responses of the structure equipped with MR dampers effectively. Furthermore, the performance of the fuzzy control structure was found to be modestly better in reducing maximum displacements than that of the bi-state control system. Control forces produced by the fuzzy control strategy are more appropriate than those produced by the bi-state control strategy. Larger control forces do not always produce better results. Additionally, the utilization of Simulink simplifies and visualizes the modeling and simulating course of the system.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Study on multi-field coupled model for Magnetorheological fluids in microchannel Yongqing Su, Yingjie Zhang, Jiguang Yue & Bin He School of Electronics and Information Engineering, Tongji University
EXTENDED ABSTRACT As a part of MEMS, Micro-fluidic system have characteristics of smaller size, higher output power and faster response speed, thereby it has wide application prospect. Magnetorheological Fluids augments controllable character by electromagnetism on the basis of fluid drive, and overcome the defect that fluid is difficult to control in the system of MEMS. Research on the controllable character of magnetorheological fluids and model of hydrodynamic may achieve the high-accuracy aim of micromechanisms.The drive and control of magnetorheological fluid are very different in microcosmic and macroscopical condition. The technology of drive and control is more complication and diversification in microcosmic condition. And with the development of Micro-fluidic system, the drive and control technology has become the key technique Micro-fluidic system. Magnetorheological Fluids augments controllable character by electromagnetism on the basis of fluid drive, and overcome the defect that fluid is difficult to control in the system of MEMS. This paper studies the fluid dynamic model of Magnetorheological Fluid in microcosmic state, develops micro-valve structure based on Magnetorheological Fluid in order to reach the high accuracy in
the operation of micro-machine. And it could not only offer a new kind of drive method of MEMS in medical operation, miniature sensor, robot and automobile sensor, but also achieve the accurate drive and control in micro-fluid. Magnetorheological Fluid is a kind of smart material. With the help of external magnetic field, it could be turned from Newton fluid into semisolid substance with shear yield stress. And it has low viscosity without magnetic field while it has large yield stress within external magnetic field. This kind of character could make up the low controllability of fluid in microchannel. This paper just explore the flowing condition of Magnetorheological Fluid(MRF) in micro-channel according to the situation. Thus, the paper builds experimental platform and study fluid characteristic of magnetorheological fluids in millimeter conduit. Furthermore analyzes coupling relationship between fileds using finite element analysis method, studys key techniques of fluid drive by magnetorheological fluids in microcosmic state, presents main influence factor of systematic control characteristic in microcosmic state, and explore theoretical basis of magnetorheological fluids applying to micro-actuator.
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Applications of smart materials
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Adaptive tuned dynamic vibration absorbers working with MR elastomers W.H. Li, X.Z. Zhang, B. Liu & X.Y. Wang School of Mechanical, Materials & Mechatronic Engineering, University of Wollongong, Wollongong, Australia
1
INTRODUCTION
Tuned dynamic vibration absorbers (TDVAs) have found wide applications in suppressing vibrations of machines and structures. Examples of such systems include machines, automobiles, aircrafts, generators, engines and motors, and building structures. However, the effectiveness of conventional TDVAs is always limited due to the narrow frequency ranges. In many practical applications, off-tuning of TDVAs occurs because of structural changes or varying usage patterns and loading conditions. To overcome these shortcomings, adaptive tuned dynamic vibration absorbers based on magnetorheological elastomers (MREs) are developed and evaluated. The selection of MREs for development of ATDVA is that MREs have unique characteristics that their modulus can be quickly and reversely controlled by varying an external magnetic field. Therefore, the proposed ATDVAs are expected to have many advantages: very fast response (less than a few milli seconds), simple structure, easy implementation, good maintenance, high stability, and effective control. This paper consists of three major parts: (a) fabrication and characterization of MRE materials; (b) design, manufacturing and testing shear-mode ATDVA; and (c) simulation evaluation of vibration suppression effect by analyzing and comparing various control strategies. 2
RESULTS
The RTV silicon rubber and silicone oil were mixed together to work as matrix. The carbonyl iron particle with particle size of 5 µm were mixed with the matrix to form into MRE samples. The prepared MRE sample has the particle volume of 30%. A semiactive dynamic vibration absorber using MREs as adaptable spring was designed and manufactured. This MRE ATDVA worked in a shear mode and the magnetic field was controlled by a coil and a controllable DC power. The controllabledynamic behaviors of the absorber were tested by a vibration
testing system. Experimental results indicated that this absorber can change its natural frequency from 75 Hz to 150 Hz when the applied magnetic field varies from 0 mT to 220 mT, which is 100% of its basic natural frequency. Various control strategies, including passive control, conventional tuning mode and the bang-bang control mode, were employed to validate the vibration suppressing effects of the developed MRE ATDVA. The parameters of the model were firstly calculated according to the experimental results. The identified parameters were used to develop MATLAB simulink models for simulation. Simulation results indicated that the semiactive MREs absorber can trace the disturbance force frequency and absorb the inertial energy transferred from the primary structure and suppress the vibration of primary system. Moreover, the real time bang-bang control logic was found to effectively suppress the vibration amplitude of the system, not only for single-frequency disturbance, but also for multi-frequency disturbances.
3
CONCLUSIONS
In this paper, the MREs based on silicone rubber and carbonyl iron particles were fabricated. The dynamic performances of MREs samples in different magnetic field were tested by a rheological testing system. A semiactive dynamic vibration absorber using MREs as adaptable spring was designed and manufactured. The controllable dynamic behaviors of the absorber were also tested by a vibration testing system. Experimental results indicated that this absorber can change its natural frequency from 7 5Hz to 150 Hz, 100% of its basic natural frequency. A real time bang-bang control logic has been used to minimize the vibration amplitude of the system too. This controller and quick response of MRE ATDVA can provide the system a real time control ability. Numerical simulation results indicate that the proposed semiactive control system produced much better performance than a passive system.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Theoretical and experimental investigation into dynamic characteristics of a rotor supported on a disk-type Magnetorheological fluid damper Changsheng Zhu College of Electrical Engineering, Zhejiang University, Hangzhou, Zhejiang, P.R. of China
A series of experiments on disk-type ER/MR fluid damper operating in shear mode for rotor system of rotational machinery, have been carried out to demonstrate its ability to control the vibration and dynamic characteristics. A model of the disk-type ER fluid damper based on Bingham fluid model has been developed. Unfortunately, there are not enough experimental data to verify the theory. First, some experiment results about unbalance response of the rotor damper system with different applied currents, rotor imbalances and MR fluids are given in this paper. For the lower WPC MR fluids, when a lower current was applied, the journal amplitude smoothly increased when the rotational speed approached the resonance speed and decreased when the rotational speed was away the resonance speed. When a higher current was applied, if the rotational speed of the rotor system was lower than a certain speed, the moving disk did not move, the damper acted like a rigid support. When the rotational speed was over the certain speed, the journal suddenly started to move and the journal vibration amplitude suddenly increased, which is the “break-loose” phenomenon of the disk-type MR fluid damper. As the rotor imbalance increased, the breakloose phenomenon weakened and the break-loose rotational speed moved towards lower rotational speeds. For the higher WPC MR fluids, if rotor imbalance is small, the break-loose phenomenon occurred shows that at the lower rotor imbalances, the higher WPC MR fluids behaved as non-Newtonian fluid even if no current was applied. As the applied current increased, the break-loose phenomenon became more obvious and the break-loose rotational speed greatly increased. If the rotor imbalance is high, when no current was applied, no break-loose phenomenon appeared. Therefore, at higher rotor imbalances, the MR fluid damper even with the higher WPC MR fluids behaved as a linear damper. However, when a small current was applied, the solidified MR fluid in the damper could
significantly change the dynamical behavior of the rotor system and greatly attenuated the disk vibration, and the break-loose phenomenon occurred. The occurrence of the break-loose phenomenon suggests that the MR fluid behaves a non-Newtonian fluid with an initial yield stress. By the application of an external magnetic field in the MR fluid, the damper could change not only the equivalent damping of the rotor system, but also its equivalent stiffness as well. The effects of the applied current on the equivalent damping and the equivalent stiffness of the rotor system were different for different MR fluids. Then, a model of the damper based on the Bingham model, a rotor model, and simulation results are given. It is shown that the fluid force of the damper consists of a viscous damping force and a Coulomb-type friction force. If the equivalent force acting on the moving disk is less then the initial Coulomb-type friction force, the moving disk does not move, the disk-type MR fluid damper acts like a rigid support. It is in quality in good agreement with the experiments. Therefore, the dynamic model of the damper based on the Bingham fluid model can be used to explain some phenomena being observed in experiments. As the Coulomb-type friction force can be equivalent to a viscous damping force, therefore, the fluid force of the damper based on the Bingham model is of damping. The theoretical results are basically in agreement with experiments for the lower weight percentage MR fluids, but there is a great difference for the higher weight percentage MR fluids. For the higher weight percentage MR fluids, a stiffening effect observed in experiments is nor been predicted. The rheological behaviors of a real MR fluid are quite complex and the Bingham fluid model cannot completely represent the rheological behavior of the higher weight percentage MR fluids. The stiffening effect of the MR fluid should be included in modeling the MR fluid based dampers. Finally, some conclusions are obtained.
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Technologies and methods of SHM
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
An analytical and experimental study of TLCD for structural vibration control A.Y.P. Wang & Y.H. Chen Department of Civil Engineering, National Chiao Tung University, Taiwan, China
B.C.L. Lee Department of Natural Hazard Mitigation Research Center, National Chiao Tung University, Taiwan, China
Tuned Liquid Column Damper (TLCD), an integration of vibration control damper with the fire protection hydraulic tank, is considered to be a substitute of the conventional tuned mass dampers (TMD) for vibration control of high-rise buildings. TLCD is a nonlinear system possessing advantageous features such as easy-tuning, dual function, maintenance-free and cost-effective. In this study, the dynamic characteristics of TLCD systems with various orifice sizes have been investigated via component tests. The headloss coefficients have been identified by a proposed system identification procedure based on ARX model. The identified headloss coefficients are consistent with those obtained by a formula proposed by Wu et al. Moreover, numerical predictions of liquid sloshing displacement and structural response by the proposed analytical model with the experimentally identified headloss coefficient agree very well with the test data, verifying adequacy of the proposed analytical model. Furthermore, this study assesses the wind-resisting performance of TLCD on both translational and torsional vibration modes of the world’s tallest building-Taipei 101, with encouraging results achieved. The larger the eccentricity of the structure, the more pronounced the control effect of TLCD on the torsional responses, and the control efficiency increases as the TLCD pair disposes farther from the centroid of the structure.
Figure 1. Configuration of TLCD system.
Figure 2. Setup and instrumentations for TLCD component and performance tests.
Figure 3. Comparison of prediction and experimental results.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Application of smart 3-D laser scanner in structural health monitoring S. Sumitro Smart Structures LLC, Illinois, USA
H. Matsuda Nagasaki University, Nagasaki, Japan
Y. Itoh Saga University, Saga, Japan
S. Nishimura Keisoku Research Consultant, Hiroshima, Japan
ABSTRACT As one of Full Field Optical Stress & Strain Measurement (FFOSSM) technologies, Smart 3-D Laser Scanner measurement technique enables to monitor the shape and dimension measured-objects in noncontact, remotely and globally. By taking its capability in capturing 3-D spatial information, 3-D Laser Scanner has been utilized effectively in numerous field application, such as, landscaping simulation during structural design stage, bridge load test, and maintenance purposes. In order to provide a rational maintenance strategy, it is important to assess current structural properties of existing structures due to long-term structural degradation, static and
dynamic loads. However, they mostly lack of sufficient information of their spatial shapes and dimensions. In this paper, a structural health monitoring-based maintenance scheme is proposed and its schematic description is shown in Fig. 1. The structural health monitoring process is conducted as follows: (i) Conduct initial structural information (shape and dimension); (ii) Capture visible structural degradation factor (crack distribution) and create a data base for current structural condition; (iii) Perform structural analyses to assess its current structural performance;
Figure 1. Proposed Structural Health Monitoring_Based Maintenance Scheme.
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(iv) Monitor their degradation condition periodically (crack propagation), and update to the crack distribution data base; and (v) Execute fractural-based structural analyses on the deteriorated structures.
to capture spatial information of shape-complicated structures. It can be integrated with generic structural health monitoring system to assess the updated structural performance of existing structures.
Through field-application experiences, it is confirmed that 3-D Laser Scanner is an easy-handled device
567
Magnetorheological fluids and dampers (4)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
US-China joint task force on integrated structural health monitoring S.D. Glaser University of California, Berkeley, USA
H. Li Harbin University of Technology, China
M.L. Wang University of Illinois, Chicago, USA
J.P. Ou Dalian Institute of Technology, China
The National Science Foundations of the United States and China are sponsoring a US-China Joint Task Force to develop a five year collaborative research program on integrated structural health monitoring. The program will stress the use of modern sensors, integrated data acquisition and processing, and structural health interpretation schemes with emphasis on earthquake and natural hazards. The US has been leading the research and development of new sensor technology, and China has been leading the application of sensor technology for monitoring real structures. The task force is integrating these strengths by forming strategic groups of Chinese and US researchers to identify the key challenges and research topics. This venture will facilitate international student exchange, technology transfer through complementary research and exchange of research data, educational courses for students, and training sessions for engineers. It will actively involve relevant industry and government agencies.
The anticipated outcome of this joint effort is a comprehensive program outline for cooperative research in this field. The plan could be used by funding agencies as a major reference for determining program priorities and budget distribution, and by interested researchers as a future road map by which to develop joint research projects and related activities. This paper will report on the progress the task force has made towards reaching these goals. There have been several meeting of the sides, and much communication via email, leading to a draft report. The important conclusions of this report will be presented for discussion. New technical approaches in both hardware and software will be addressed. Most importantly, new mechanisms for interchange of ideas and methods of improving working relations between transnational research groups will be reported. Finally some strategies for putting together funding mechanisms for such groupings will be explained.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
An experimental study into dynamic behavior of a magnetorheological fluid squeeze film damper – overhung flexible rotor Changsheng Zhu College of Electrical Engineering, Zhejiang University, Hangzhou, Zhejiang, P. R. of China
The electrological (ER)/magnetorheological (MR) fluid squeeze film damper (SFD) for rotor system of rotating machinery have been presented and the dynamic behavior of rotor system on the ER/MR fluid SFDs has been studied experimentally and theoretically. However, the agreement between theoretical results with experiments is not good. Therefore, there are many issues to be studied, especially for the MR fluid SFD. In order to model the MR fluid SFD, two kinds of experiments are carried out in a flexible rotor with two disks in the first two critical speed regions of the rotor system. One is the experiments on the dynamic behavior of the flexible rotor on the empty SFD with different applied voltages. The other is the experiments on the unbalance responses of the flexible rotor on the MR fluid SFD with different applied voltages, rotor imbalances and MR fluids. From the tests about the effect of applied voltage on the frequency response function and the unbalance response of the rotor system on an empty MR fluid SFD, it is shown that there are an unbalanced magnetic pull force and an eddy current damping force.The former is caused the eccentricity of the journal with respect to the damper housing, the later is caused by the journal moving in the magnetic field. As the applied voltage increased, the resonance peaks at different frequency regions were reduced and the resonance speeds shifted to lower rotational speeds. If the applied voltage is over a critical value, the unbalanced magnetic pull force will make the journal stick to the damping housing and locks up the journal as a rigid support. Therefore, the centralizing spring must be installed in the MR fluid SFD to produce a working region of applied voltages. It is shown that the shift of the resonance speed to the lower rotational speeds is mainly caused by the unbalanced magnetic pull force, and the great decrease in the resonance peak is mainly due to the eddy current damping force.
From tests on the unbalance response of the rotor system on the MR fluid SFD at different applied voltages, rotor imbalances and MR fluids, it is found some important phenomena. The dynamic behavior of the rotor damper system is dominated by the unbalanced magnetic pull force and the eddy current damping force for lower weight percentage MR fluids, but the fluid film force produced by the squeeze effect for the higher weight percentage MR fluids. The effect of the unbalanced magnetic pull force and the eddy current damping force must be considered, especially for the MR fluid SFD with the lower weight percentage MR fluids in modeling the MR fluid SFD. The dynamic behavior of the rotor system with higher weight percentage MR fluids is very sensitive to the applied voltage, the applied voltage which can greatly change the dynamic behavior of the rotor system is much lower, a voltage of less than 10 V is enough to make the MR fluid SFD system be a rigid support. Not only can the MR fluid SFD by the application of an external magnetic field in the MR fluid change the equivalent damping of the rotor system, but also its equivalent stiffness as well. The effect of the applied voltage on the equivalent damping and the equivalent stiffness of the rotor system were different for different MR fluids and the regions of applied voltages. The rheological properties of the MR fluids are very complex, and depend on weight percentage of the MR fluid, magnetic flux density, and journal motion state. The occurrence of the break-loose phenomenon in the rotor system with the higher weight percentage MR fluids suggests that the MR fluid is most like a nonNewtonian fluid with an initial yield stress, such as Bingham fluid. Finally, some issues, such as modeling, unbalanced magnetic pull force, and sediment were discussed. And some conclusions are obtained.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Dynamic performance of Magneto-rheological dampers subject to impact load Lijie Zhang, Jiong Wang & Linfang Qian Departmentl of mechanical engineering, Nanjing University of science and technology, Nanjing, China
1
INTRODUCTION
Since Magneto-Rheological (MR) Dampers for gun recoil mechanisms applications experience impact load, high velocities, there is a need to understand their impact dynamic performance.The purpose of this paper is to examine the impact dynamic performance of MR dampers subject to impact load. The impact test was done, with the special designed long stroke MR damper, as shown in figure 1, and the test setup is shown in figure 2. With test results, the dynamic performance of the MR damper is examined, and several conclusions are achieved as below: 1) Under the same magnitude of the impact energy, the applied current has little influence on the peak value of the recoil velocity, and the control region of the damping force of the MR damper is from a certain moment after the recoil velocity peak to the end of the recoil movement; 2) During recoil, the range of the mean shear strain rates of the MR fluid is 0s−1 ∼ 7966s−1 . At the ascending stage of the recoil velocity, due to the high impact, the MR fluid shows the behavior of the complicated unsteady flow, while at the falling stage of the recoil velocity, by curve fit to experimental results, the MR fluid is shown to exhibit the nonlinear shear thickening behavior; the model of Herschel-Bulkley steady flow equations for parallel plate can accurately describe the dynamic performance of the MR damper in the control region of recoil movement. It’s followed that fluid index parameters and other parameters in this MR damper model were identified with the theory of nonlinear least squares. Since the mathematical expression of the model mentioned above is complicated and has different forms in high and low recoil velocities respectively, which is not benefit for real-time control, a simplified
Figure 1. Schematic of the long stroke MR damper.
Figure 2. Impact test setup.
model with uniform mathematical expression was proposed as Eq.(1).
3) The magnitude of the impact load of this test is identified by energy spectrum analysis and the simulation platform for the recoil movement was established by SIMULINK. By numerical simulation it’s fully verified the validity of the simplified model and the correctness of the parameter identification for this model. The established platform of the simulation and the accurate model of the MR damper have provided effective tools to study the closed-loop recoil control system, by which the recoil dynamics is optimized.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Effect of fluted flow channel on magnetic field in Magneto-Rheological damper Yancheng Li & Jiong Wang School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing, China
Hongsheng Hu College of Mechnical and Electrical Engineering, JiaXing University, JiaXing, China
1
INTRODUCTION
Magneto-Rheological (MR) damper is a promising semi-active device in the application of vibrationreduction (Carlson 2005). The main task for the designer is to develop a small-size and high-efficiency MR damper. Despite many investigations on semiactive MR devices, research work on the systematic or optimal design of MR damper is relatively rare. In particular, the coupling between the magnetic field formation mechanism and the MR effect formation mechanism still lacks much attention (Wang et al. 2006; Yancheng Li 2006). In this paper, the basic principle of FEM analysis is introduced. Two different FEM coupling analyses, which are the analysis considering the flux leakage and the one without considering the flux leakage, are fulfilled to find its influence on the structure design. MR dampers with different fluted flow channel are compared by means of FEM analysis. It is also revealed that the magnetic density in the middle of the passage increases and the magnetic field in two ends of the passage fall down about 40%, as shown in Table 1. An optimal design in which the length of middle damping passage is increased was made to produce a well-proportioned magnetic field. Finally, a magnetic circuit with fluted channel was investigated to see its influence on the magnetic field. It showed that, if we made a fluted damping passage with less space between, the magnetic densities can be increased in a large content. REFERENCES Carlson J.D. 2005. MR fluids and devices in the real world. In: Lu Kunquan, Shen Rong and Liu Jixing. Proc. of the Ninth International Conference-Electrorheological fluids and magnetorheological suspensions. Singapore: World scientific Publication: 531–538
Figure 1. Magnetic field in the MR damper Table 1. Average value of magnetic density in different position. KA/m
Without flute 2 flutes 3 flutes 4 flutes 5 flutes
Near piston 88.6 Passage center 109 Near cylinder 70.3
98.9 104 67.5
110.4 101.2 64.1
119 107 91.5
127 105 87.5
Yancheng Li, Jiong Wang and Linfang Qian. A New Methodology of Modeling a Novel Large-scale Magnetorheological Impact Damper. Journal of Communications in Nonlinear Science and Numerical Simulation. (in press) Jiong Wang, Qianlong Wang and Yancheng Li. 2005. Finite element analysis of magnetorheological damper. In: Lu Kunquan, Shen Rong and Liu Jixing. Proc. of the Ninth International Conference-Electrorheological fluids and magnetorheological suspensions. Singapore: World scientific: 722–727
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Piezoelectric composite sensors (2)
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A two-way controllable Magnetorheological (MR) fluid damper G. Aydar, X. Wang, F. Gordaninejad & C. Evrensel Mechanical Engineering Department, University of Nevada, Reno, Nevada, USA
ABSTRACT: In this study, a disc-type, radial flow-mode magnetorheological (MR) fluid damper comprised a permanent magnet and an electromagnet is designed, built and tested. The proposed MR fluid damper has a MR valve with which two-way controllability through cancellation or enhancement of the magnetic field is obtained. This added feature provides damping forces less than or greater than that of a passive viscous original equipment manufacturer damper. Experimental and theoretical studies have been conducted to demonstrate that this new design can provide softer damping properties by canceling the effect of the permanent magnet, and enhancing the field effect resulting in a stiffer damper.
1
INTRODUCTION
In many MR fluid damper designs, if the controller fails, the damping force reduces to a minimal force, which may not be practical for certain mechanical systems. Particularly, for the vehicle applications, a fail-safe feature for a MR fluid damper must be considered in order for the damper to be utilized in the suspension system. Increasing the viscosity of MR fluids or reducing the orifice size of a MR fluid valve would offer a simple solution to produce a reasonable fail-safe damping force for MR fluid devices at offstate. However, this is at the expense of reduced controllability. One possible solution in satisfying these competing requirements is the use of a permanentand electro-magnet system. With this system one can achieve sufficient off-state force with a permanent magnet, while reducing or increasing the force through canceling or enhancing the magnetic field by applying current to the electromagnetic coils.
2
Figure 1. The force-velocity results for three different cases under ramp excitation tests.
RESULTS
An experimental study of a two-way MR fluid damper is performed. Figure 8 shows the schematic of the twoway MR fluid damper. Figure 1 presents the force-velocity results for three cases: 1) Magnetic field cancellation under 3Amp applied current, 2) Magnetic field enhancement under 4Amp current applied to the coil in reversed direction, and 3) Off-state, with no magnetic field applied.
As can be seen up to 65% damping force can be achieved below the off-state condition. In addition, a 100% increased damping force can be obtained, if the current in the coil is reversed. ACKNOWLEDGMENT This study was partially funded by the Army Research Office.The authors are thankful for the encouragement by Dr. Gary Anderson, the Program Director.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Preparation and characterization of novel aqueous MR fluids-based on core-shell composite particles H.B. Cheng, J.M. Wang, J. Zhang, W.Y. Zhao, W.X. Gao, W.L. Qu & Q.J. Zhang State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, China Jiangsu Tianyun Advanced Materials Company, Jiangsu, China
1
INTRODUCTION
In order to improve the dispersion stability and anti-oxidation ability of aqueous magnetorheological (MR) fluids, in this study, carbonyl iron (CI) particles were encapsulated with N-polyglycol ethylenediamine triacetic acid (PED3A) to make core-shell composite particles (CSC particles). The CSC particles were in turn used as a dispersed phase in the novel aqueous MR fluids.
2
EXPERIMENTAL
The dispersion stability and anti-oxidation ability of MR fluids were evaluated by measuring their sedimentation ratio and TG-DSC; and their MR properties were measured using a parallel-plate advanced rheometric expansion system equipped with a magnetic field supplier at room temperature. In this measurement, parallel-plate fixtures with diameters of 25 mm at a gap of 0.3 mm were used, and the magnetic field direction was set to be perpendicular to the flow direction.
3
RESULTS AND DISCUSSION
Figure 1. Sedimentation ratio versus time for aqueous MR fluids based on CSC particles (a) and CI particles (b).
properties of the novel MR fluids are similar to those of the traditional aqueous MR fluids. It exhibited high field-induced shear stress, low shear viscosity, the Bingham plastic behavior with a nonvanishing yield stress under an applied magnetic field. These results imply that particle cluster structures constructed within fluids under the applied magnetic field are continuously broken and then instantly reformed (Cho, M.S., et al. 2004). 4
The ratio of sedimentation of MR fluids is defined as: Sedimentation ratio (%) = volume of the supernatant liquid/volume of the entire suspension × 100%. It is obvious that the settling rate of the novel aqueous MR fluids is much smaller (about half) than the contrast MR fluids based on CI particles (see Fig. 1). The TGDSC curves show that the transformation peaks of Fe to FeO and Fe to Fe3 O4 occur at 258.7◦ C and 470.2◦ C, respectively. These results reveal that the hydrophilic organic coating of the CSC particles plays an important role in stabilizing the MR fluids and preventing the particles from being oxidized. The results of measuring the rheological properties show that MR
CONCLUSIONS
A novel aqueous MR fluid based on CSC particles have been prepared and exhibited typical characteristics of aqueous MR fluids in field-induced shear stress, shear viscosity, and especially better dispersion stability and anti-oxidation property. The proposed method proved to be good for fabricating aqueous MR fluids. REFERENCES Cho, M. S. et al. 2004. Encapsulation of spherical ironparticle with PMMA and its magnetorheological particles. IEEE Trans. Magn.40 (7): 3036–3038.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Mechanical and stress-sensitive properties of multi-walled carbon nanotubes reinforced cement matrix composites J.L. Luo & Z.D. Duan School of Civil Engineering, Harbin Institute of Technology, Harbin, Heilongjiang, China
Recently, it has been steadily developed in civil engineering to guarantee infrastructure safety in service through diagnosing its significant components by the cement-based sensors incorporated with some conducting materials. Being the well-known nanosize fibers with outstanding mechanical, electrical, and thermal conducting properties, carbon nanotubes (CNTs) have evolved into the most promising candidates for the next generation high performance structural and multi-functional composite materials. However, the pristine CNTs, just like carbon fibers, being nonpolar materials, have weak bondage with, and bad dispersion in cement material, thereby its reinforcing functions to cement matrix composites have ever modestly embodied in the limited documents. In this research, the combination applications of physically ultrasonic mixing and chemically cetyltrimethyl ammonium bromide (C16TAB) surfactant are developed to make some low concentration multi-walled carbon nanotubes (MWNTs) being dispersed in cement as good as possible. Then, MWNTs reinforced cement matrix composites (MWNTRC) with some different amount MWNTs additions are successfully fabricated. Microstructures reveal that, when the addition of MWNTs is lower than 0.5 wt%
by weight of cement, most of MWNTs can be encapsulated and compatible with cement hydration products, mainly amongst the calcium silicate hydrate (C-S-H) gels. Mechanical results show there are some reinforcements to the mechanical properties of the plain cement mortar with small amount MWNTs addition. The maximal enhancements of the flexural and subsequently compressive strength of the MWNTRC, compared with that of the plain mortar, are 17.00% and 28.3%, respectively. A simple DC series-wound circuit is employed joining to LMS instruments to investigate the stress-sensitive properties of the MWNTRC. The resistivity of the specimen is collected with four-electrode method, and the stress is acquired with a pressure transducer. Results show that the relative change in resistivity of MWNTRC steadily falls down by increasing of the compressive monoaxial stress both in its pressure elastic and inelastic range.Yet, the curve between the relative change in resistivity and the compressive stress has the steadily increasing trend for the plain mortar without MWNTs. These stress-sensing attributes and mechanical improvements can develop the MWNTRC into a promising candidate structural and functional sensor for concrete structure health monitoring, in some sense.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Interactions between N coating fibers in fiber piezoelectric composites B.H. Yang & C.F. Gao Nanjing University of Aeronautics and Astronautics, Nanjing, Jiangsu, China
INTRODUCTION
1.5
Studies on coated piezoelectric materials are of theoretical and practical importance with increasingly wide application of composite materials. Much effort has been made. However, previous works are mainly restricted to the case of single inclusion/fiber. In the present work we propose a straightforward and concise approach to analyze the problem of N coating circular inclusions under anti-plane shear and in-plane electric load by the method of complex variable theory.
1.0 R=1.0 r=0.9 --a/R=1.2 -.. a/R=1.4 -a/R=10.0
0.5 τ∞ | σ M z
1
0.0
-0.5 -1.0 2R -1.5
2
BASIC EQUATIONS
2a 0
1
2
3
4
5
6
θ
Consider N fibers embedded in an infinite transversely isotropic piezoelectric material under uniform remote anti-plane shear and in-plane electric loading. Assume that the poling direction is along the positive z axis. In this case, the governing equations are
where σzx , σzy , Dx and Dy are the components of stress and electric displacement, respectively. The constitutive equations are
where k = 1, 2 and u3 is the out-of-plane displacements and ϕ is the electric potential.
3
RESULTS AND DISCUSSION
Using continuous conditions of displacements, stresses and electric potentials one can finally find u3 andϕ, and then all field variables can be obtained inside the fibers and in the matrix. The matrix, coating and fibers are denoted by I, II, III, respectively, and as an example, the model material is chosen as: I: CI44 = 25 GNm−2 , 13 Cm−2 ,
εI11 = 6 ncV−1 m−1 ,
eI15 =
Figure 1. Angular variations of interfacial shear stress between I and II embedded with three fibers in the matrix.
II: CII44 = 30 GNm−2 , 15 Cm−2 ,
εII11 = 10 ncV−1 m−1 ,
eII15 =
−2 III: CIII 44 = 35 GNm , −2 17 Cm .
−1 −1 εIII m , 11 = 15 ncV
eIII 15 =
Based on these material constants some numerical results are shown in figure for the case of three equal fibers. It can be found that when fibers are far from each other, the shear stress along the outer rim is the same as that acted by only one fiber embedded in the matrix. 4
CONCLUSION
It can be found form the present work that the stiffness of coating and the array type of fibers have significant effects on the stress fields in the matrix. When the stiffness of coating downs, the stress concentration falls down quickly. On the other hand, when fibers are far from each other, the shear stress along the outer rim is the same as in the case of a single fiber embedded in the matrix. However, as the fibers are close to each other the interactions among fibers becomes intense.
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World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
A higher order theory for piezoelectric plate Jianping Jiang & Dongxu Li College of Aerospace and Material Engineering, National University of Defense Technology, Changsha, Hunan, P.R. China.
With the increasing use of piezoelectric materials as actuators or sensors in smart structures and other applications, there is a growing need for numerical methods that give accurate and reliable results for multi-layer plate and shell structures where some or all of the layers are made of piezoelectric materials. In this paper, an accurate and reliable piezoelectric plate element is presented. The formulations are based upon the high order displacement field assumptions as follows:
To take into account the potential induced by the bending and shear deformation, a high order electric potential over the thickness is developed. Firstly, the constitutive equations had been modified by assuming σ3 = 0 and D1 = D2 = 0.
The electric charge equation D3,3 = 0 reduces to
Employing the strain tensor and the relation E3 = −φ3 between the electric field vector Ej and the electric potential φ yields
By carrying out the integration over the thickness coordinate, one obtains a biquadratic variation of the electric potential across the thickness
As usual in the finite element process, the dynamic equations had been derived as follows,
The theory presented in this paper was verified by means of a numerical example. The ANSYS coupledfield analysis program ANSYS Multi-physics is used to carry out a full 3D analysis by considering the coupled-field brick elements (Solid5) and the results from the full 3D FEM are taken as accurate in the present numerical comparison. Numerical example shows that 1) the present model can predict the induced parabolic electric potential field across the thickness, which is a good approximation to the nonlinear variation predicted by the full 3D model. 2) Including the potential induced by the bending deformation into the formulation is not only important to get an accurate solution for the electric field, but also influences the elastic deformation. If the linear variation of electric potential is employed, the calculated tip displacement in corresponds to that obtained with the 3D FEM theory was about 20% for thin plate or 17% for thick plate. For many applications, this error cannot be considered negligible. However, the calculated tip displacements by the present model are excellent agreement with the full 3D FEM model.
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Innovative sensors and actuators: shape memory alloys
World Forum on Smart Materials and Smart Structures Technology – Spencer et al. (eds) © 2008 Taylor & Francis Group, London, ISBN 978-0-415-46845-9
Prediction of electrical properties of carbon nanotube/polymer composites N. Hu, Z. Masuda & H. Fukunaga Department of Aerospace Engineering, Tohoku University, Japan
1
INSTRUCTIONS
Carbon nanotubes (CNTs) of high aspect ratio possess excellent electrical conductivity. Therefore, with a little amount of CNTs, which are dispersed in insulating polymers, it is possible to produce the nano-composites with high electrical conductivity. Until now, there have been some experimental studies on this new nano-composite (Qunaies et al., 2003). However, there has been almost no numerical model or theoretical study, which evaluates the percolation threshold or electrical behaviors of composites after the percolation threshold. In the present work, a 3D numerical model is proposed. 2 THEORY OF NUMERICAL METHOD 2.1
Prediction of percolation threshold
In this study, based on a statistical percolation model, we consider a 3D representative element containing randomly distributed CNTs. The percolation threshold is predicted when the first conductive path is constructed by some CNTs. A Monte-Carlo procedure of 100 simulations has been performed to obtain the average percolation threshold for one volume fraction of CNTs. 2.2 Analysis of electrical conductivity of composites To predict the electrical conductivity of nanocomposites after the percolation threshold, a 3D resistor network made from CNTs is employed. A linear algebraic equation system is built up from the relation between the currents and potentials at all nodes in the network from Kirchhoff’s current law. After obtaining the total current passing through the nano-composites, the electrical conductivity of nano-composites can be obtained from Ohm’s law. 3
found that there is almost no serious aggregate in our samples. Moreover, it was found that the following factors remarkably decrease the electrical conductivity of nano-composites: 1) a high mixing speed with a long mixing process; 2) a curing process with low temperature. All of these factors lead to the difficult formation of macroscopic conductive network. 4
RESULTS AND DISCUSSIONS
The present and other experimental are used to check the proposed numerical model. It was found that this model can yield accurate results for the percolation threshold and the electrical conductivity of nanocomposites. Finally, from the numerical results for various aspect ratios of CNTs, i.e., L/D and various conductivities of CNTs, i.e., σ CNT , we can get the following simple percolation theory:
5 APPLICATIONS AS STRAIN SENSOR Finally, we extend our numerical model with the consideration of tunnel effect among CNTs to simulate the resistance change of nano-composites with the prescribed strains. Both experimental and numerical results agree with each other well, and high sensitivity of the present sensors is obtained. 6
CONCLUSIONS
The electrical properties of nano-composites made from dispersed CNTs in polymer are explored using a 3D numerical model which is very successful. REFERENCES
EXPERIMENTS
We have performed the experiments using multi-walled carbon nanotubes (MWNTs). It was
Ounaies, Z. et al. 2003. Electrical properties of single wall carbon nanotube reinforced polyimide composites. Compos. Sci. Technol., 63: 1637–1646.
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Earthquake response modification of bridges using superelastic shape memory alloys J.E. Padgett & R. DesRoches Georgia Institute of Technology, Atlanta, GA
EXTENDED ABSTRACT
Evaluation of bridge damage from past events has shown that one of the primary modes of severe damage is unseating of spans due to limited seat widths and large relative openings. Though there are traditional retrofit devices that target unseating prevention, several limitations of these devices have been identified, such as the accumulation of deformations upon yielding. Superelastic shape memory alloys possess several characteristics that make them appealing for applications in the field of earthquake engineering and for seismic response modification and retrofit of bridges. In particular, devices com-posed of this unique class of material can exploit the large elastic strain range and recentering ability, strain hardening at large strains, excellent low- and high-cycle fatigue properties, and hysteretic damping, among others. Past analytical studies have indicated the potential viability of using nitinol restrainer cables for bridge retrofit. The two phases of testing detailed as a part of this work illustrate the opportunity for experimental evaluation of this new class of retrofits. The first phase examining the use of SMA restrainers at in span hinges utilized a block-bearing model representative of adjacent frames. The results of this testing revealed the promise of SMAs for unseating prevention. The SMA restrainer cables were found to be much more effective than similar steel restrainer cables at reducing both relative hinge openings and block accelerations. Phase 2 provides a large-scale validation of SMA restrainers in a quarter-scale, multi-span concrete bridge (Figure 1). The test program allowed for examination of different configurations of shape memory alloy restrainer cables (with and without pres-straining). While the test data is currently being collected and analyzed, preliminary results indicate that both SMA configurations were effective in
Figure 1. Phase 2 large-scale testing of SMA restrainers.
South Hinge Opening (0.09 g) 0.6 0.50 in 0.4
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Figure 2. Hinge opening at one level of ground motion.
reducing the deck displacements at the abutment which may lean to span unseating. The pre-strained cables were particularly effective in reducing the hinge openings for the set of tests conducted (Figure 2). Future work will provide comprehensive evaluation of the test data. The experimental testing also provides data for refinement of the analytical modeling and offers validation of the use of a new, promising technology in bridge retrofit.
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Applications of shape memory alloys in control of buildings under seismic loads R. DesRoches Georgia Institute of Technology, Atlanta, GA, USA
J. McCormick Disaster Prevention Research Institute, Kyoto, Japan
ABSTRACT This study considered the use of superelastic shape memory alloys for seismic vibration control of typical structures. The ability of superelastic SMAs to undergo large deformations while returning to their original undeformed shape by undergoing a unique displacive (diffusionless) martensitic phase transformation provides a means to control structural vibration through a combination of recentering capability and hysteretic damping. Both small diameter superelastic NiTi wire and larger diameter superelastic NiTi bars showed good superelastic behavior under uniaxial tensile cyclic loads equivalent to an earthquake. Both size specimens produced the flag-shape hysteresis associated with the superelastic effect with only a small distortion to the unloading plateau at larger strain levels. In general, the residual strains for the wire specimens after several 6% strain cycles were between 70% to 80% higher than those found for the larger diameter bar specimens. Although, for all cases the residual strain remained below 1.2% suggesting that both small wires and larger diameter bars can provide recentering capabilities up to strain levels associated with seismic events. The damping capacity was found to be higher for the wire specimens by approximately 2% to 3% equivalent viscous damping as compared to the bar specimens, but the low equivalent viscous damping values suggest that superelastic SMAs in neither form can be used in purely damping devices. The material test results suggest that SMA wire or bars can provide recentering capability and some added damping capacity to a structure when implemented as vibration control or recentering devices.
The results of the materials study were used to calibrate a three-story small scale proof-of-concept model containing superelastic SMA braces which was run on a small scale shaking table. The results showed an increase in the floor accelerations with the implementation of SMA braces as opposed to the unbraced structure. Although the accelerations increased, the rate at which the structural vibrations damped out was faster when the SMA braces were used. Further, an analytical model of a three-story steel frame with either a traditional steel buckling allowed cross-bracing system or an innovative superelastic SMA cross-bracing system was developed. The dynamic performance under seismic inputs of the two bracing configurations is evaluated. The results showed significant decreases in the maximum inter-story drift values with the use of the SMA braces and almost no residual displacements due to the recentering and damping capability of the SMA material. The traditional steel braces underwent yielding and buckling resulting in permanent story drifts and less effective seismic vibration control. The goal of this study was to illustrate the use of superelastic SMAs in seismic response control of civil engineering structures through added damping capacity and recentering capability. The results show that the larger diameter bars perform as well as wire specimens that are currently being used in non-civil engineering applications. More importantly, the unique properties of SMAs provide a means of reducing vibration response of a structure during seismic events.
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Natural frequency analysis of a composite laminated plate with embedded shape memory alloy wires under thermal activation Q. Liu, J.T. Ren & Y.Q. Guo School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an, China
1
INTRODUCTION 1.0
Fraction of Martensite
Composites structures with embedded SMA (Shape Memory Alloy) have the ability to modify the stress and strain state. Recent literature has focus on the topics which are buckling and dynamic response on composite structures with embedded unidirectional SMA wires (Lee et al. 1999, Parka & Kim 2005). However, there is a little work discussing the effect of orientation of the SMA. In the present study, we programmed Liang and Rogers’s constitutive model in the form of anABAQUS UMAT to calculate the natural frequency of the composite plate.
0.8 0.6 0.4 0.2 0.0 Mf 10
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CONSTITUTIVE EQUATION OF SMA
Figure 2. SMA ξ − T curve.
Tanaka’s constitutive equation relates the stress σ to strain ε, temperature T and martensite fraction ξ in the following form:
the kinetic equation based on the cosine model developed by Liang and Rogers (1990)
The stress-strain responses and the thermal transformation cycle are shown in Figure 1 and Figure 2 to verify the program. Fraction of Martensite
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Figure 3. Sketch of geometrical model. ((a)1# (horizontal); (b)2# (cross); (c)3# (diagonal))
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Figure 1. SMA σ − ε curves.
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MODELING OF LAMINATED COMPOSITE PLATE WITH EMBEDDED SMA WIRES
Figure 3 shows the geometrical model with three types of embedded SMA wires.
4
RESULTS AND DISCUSSIONS
0.08
Figure 4 gives the variance of first frequency with temperature. The natural frequency is affected by the SMA wires significantly.
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affect the natural frequency significantly; increasing the number of SMA wires may increase the stiffness of the structures.
375 370
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REFERENCES
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Lee, H.J., Lee, J.J. &Huh, J.S. 1999. A simulation study on the thermal buckling behavior of laminated composite shells with embedded shape memory alloy (SMA) wires. Composite Structures, 47:463–469. Liang, C.& Rogers, C.A. 1990. One-dimensional thermomechanical constitutive relations for shape memorymaterials. J. Intell. Matl. Syst. Struct, 1(2): 207–234. Parka, J.S.& Kim, J.H. 2005. Thermal post-buckling and flutter characteristics of composite plates embedded with shape memory alloy fibers. Composites Part B, 36: 627–636.
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Figure 4. Variance of first frequency with temperature.
5
CONCLUSIONS
The simulation results show that the activation temperature and the orientation of the SMA wires will
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Shape memory alloy devices for monumental cultural heritage retrofitting S. Casciati ASTRA Department, University of Catania at Siracusa, Italy
Ties in shape memory alloy (SMA) material are proposed as convenient devices to improve the modal response of a structure. This retrofitting technique is particularly suitable for historical buildings, which typically result from a simple assemblage of stone blocks, either linked together or retained only by gravity. The approach of retrofitting via SMA ties is well summarized and experimentally investigated in (Auricchio et al., 2001). However, only the practical implementation of the retrofit is discussed, and no guideline for the retrofit design is given. The present paper aims to provide a detailed insight of the design problem, by following a step by step approach. A specific Copper-based, shape memory alloy is selected as appropriate to the envisioned application, due to the temperature window in which it maintains the super-elastic properties. Details on the thermomechanics characterization of the adopted alloy are given in (Casciati and Faravelli, 2007). Laboratory tests are carried out by using an uniaxial shaking table that mounts a scaled masonry specimen. The specimen is constructed by simply assembling commercial bricks, and it supports a steel plate of mass 50 kg. First, the system is tested in its original configuration, and then the effects of adding an increasing number of pre-stressed SMA wires are estimated. For each considered case, the base excitation is the displacement time history obtained from a realization of a filtered white noise acceleration. Its ordinates are multiplied by six different factors, so that six tests of different excitation amplitude are performed on each structural configuration. Each test leads to a different estimate of the first natural frequency of the structural system. A 3D finite element model of the wall specimen is constructed within SAP 2000, by assuming that it behaves as a cantilever beam (fixed at bottom and free at top) of equivalent homogeneous and isotropic material. The values of the equivalent Young modulus are preliminarily calibrated by matching the experimental frequencies of the specimen in its original state. The effects of an increasing number of SMA ties are then introduced by applying compressive forces at
their installation points, but without adding any structural element. The diagrams of the stress-flow vertical component allow to identify the areas interested by the retrofit. The common practice of simulating the damage effects by decreasing the equivalent Young modulus of the affected areas, suggested the author to approach the retrofit design in a converse manner. That is, the retrofit effect translates in an increase or a restoration of the Young modulus initial values. The increase is quantified on an experimental basis, by matching the identified natural frequencies. However, the dependence of the frequency estimates on the excitation amplitude is due to the change of the masonry geometry at the formation of openings between the bricks. Therefore, the corresponding values of the equivalentYoung modulus are just an artifice to capture the masonry behavior, without having to directly account for the openings. By removing the erroneous assumption of a non-null tensile strength of the masonry and by considering a reduced effective cross-section when traction arises, the fictitious dependence of the equivalent Young modulus on the excitation intensity can be eliminated. This paper discusses a procedure that can be applied during the design phase of a retrofit via SMA ties, to investigate the effects of different retrofit solutions on the structural performance, in view of performing a cost-benefit analysis. In order to obtain reliable quantitative results, after the retrofit implementation, the data must be updated on the measurements collected from the whole structural system mounting the SMA devices. The obtained results must then be evaluated on a case-specific basis. REFERENCES Auricchio, F., Faravelli, L., Magonette, G. and Torra, V., 2001, “Shape MemoryAlloys:Advances in Modelling and Applications”, CIMNE, Barcelona, Spain. Casciati S. and Faravelli L., 2007, “Structural Components in Shape Memory Alloy for Localized Energy Dissipation”, accepted for publication in Computer & Structures.
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Study on self-adaptive trigger mechanism of composite tubes Jun-Jie Gong, Xin-Wei Wang & Xin-Feng Wang College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, China
Advanced composite materials are widely used in aerospace and automobile structures, due to their superior property of high-energy absorption to weight ratio. However, the energy absorption abilities of composite structures rely on many factors, the trigger mechanism is one of the key technologies. Proper design of trigger geometry can make composite structures crushed stably and gradually thus absorb more energy. Numerous studies have indicated that composite structures without effective triggers will lead to higher peak load and uncontrollable damage pattern, and will result less absorbent energy. Relative to the traditional triggers, the self-adaptive trigger is presented by embedding with pre-strained SMA wire in glass/epoxy composite tubes. Since the pre-strained SMA wire will shrink back to its original length when it is heated to the transformation temperature, consequently cause the local deformation to form a trigger mechanism. In this paper, several composite tubes with and without SMA wires are designed and fabricated. The composite laminated tubes were fabricated alternating layers of 0–90 cross-weave glass cloth plies. All specimens were laid 10 plies. The SMA wires were wrapped on the inner two layers of SMA-triggered tubes. Baseline E-glass tubes without SMA-triggers were also fabricated for comparisons. The experiments of SMA wire were conducted to investigate the mechanical properties of this material, including the static tensile tests, load-unload tests and recovery stress-temperature tests under the constrained strain condition. The results of experiments indicated that the SMA could produce a maximum of 13% tensile strain and 1300 MPa ultimate stress. When wires were plastically stretched by about 4% of strain at room temperature and then heated through the transformation temperature with both ends fixed, a maximum stress of 550 MPa was produced in the wire.
Baseline E-glass composite tubes, and tubes containing SMA-triggers were tested to failure in compression at room temperature. Tubes containing SMA-triggers were tested under both the martensite phase (SMA wires at room temperature) and the austenite phase (SMA wires heated above 75◦ C). The load-displacement curves were recorded to measure the peak load, sustained load and specific energy absorption, thus to verify the effect of SMA triggers. Test results indicate that the heated SMA composite tubes display appreciably larger Es (the specific energy absorption). But the differences are not quite large. A significant decrease of peak load is observed for the self-adaptive composite tube when the wires are transformed from the martensite to the austenite phase by heating. It can also be seen that the crushing processes were all gradually no matter whether the specimens were set with SMA-triggers or not, perhaps due to the good integrality of E-glass composites. The local deformation of SMA-triggered composite tube was analyzed with the FE software. The shell63 element and the orthotropic material model were selected to simulate the composite tube. The heated SMAs were modeled as a uniformly distributed pressure on the gap area. Numerical results indicate that the maximum local deformation reaches 0.0143 mm, thus to form an obvious trigger mechanism. In conclusion, preliminary test data indicated that composite tubes with SMA-triggers exhibit remarkable decrease in peak load and appreciably increases in strain energy absorption prior to failure. One may conclude that the SMA self-adaptive trigger mechanism can be realized resulting the peak load reduction as well as improving the energy absorption ability. Further research works should be done in the methodology of design better SMA triggers.
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“Stretchable silicon” wired sensor networks for smart materials K. Huang, R. Dinyari, J.Y. Kim & P. Peumans Electrical Engineering, Stanford University, Stanford, California, U.S.A.
J. Feng, G. Lanzara & F.K. Chang Aeronautics and Astronautics, Stanford University, Stanford, California, U.S.A.
Future generations of smart materials will have embedded electronics distributed on a fine scale (e.g. millimeter scale) to realize functions such as structural health monitoring and other types of high-resolution sensing. These sensing functions might be interrogated wirelessly such that no wiring is required. Each of the electronic units that are distributed over the volume of the smart material must be small enough such that its presence does not affect the structural integrity of the material. Furthermore, efficient, low-power operation in a variety of environments requires that this network is wired via durable, monolithic interconnects. If conventional assembly methods such as pick-and-place assembly and wire bonding are used to build such systems on the required fine scale, the cost would be prohibitively high. Moreover, the presence of electrical and adhesive bonds, each prone to failure under mechanical loading, would result in an unreliable network performance. To address the challenges laid out above, we have developed a method to realize dense and cost-effective networks of high-performance sensors based on monolithic silicon. This methodology allows one to deploy miniature (<1 mm) circuits, sensors, and actuators in wired networks that are of the centimeter to meter-scale. The two-dimensional monolithic silicon networks are entirely processed in a semiconductor foundry before they are “stretched” to the target size, “cut” to the right shape and embedded into the structure or material of interest. Due to the relatively high cost per unit area of monolithic silicon, for this approach to be cost effective, the wired monolithic silicon networks must be stretched by orders of magnitude in area. Such a stretchability is achieved by patterning the silicon into a membrane consisting of
a two-dimensional (2D) network of miniature silicon islands interconnected by springs. The springs are realized as spirals wrapped around the silicon islands such that the maximum local strain encountered in the silicon membrane remains well below the yield strain, even for large spring extensions. This approach combines the maturity of semiconductor foundry fabrication techniques with the ability to quickly assemble a fully interconnected 2D sensor network of arbitrary size and shape. The resulting networks are rugged because no wire bonds or solder connections are needed. The individual circuit elements are of the order of 100 µm in size such that they can be integrated seamlessly into structural materials without adversely affecting structural performance. The 2D sensor networks are damage tolerant (insensitive to failure of interconnects), scalable (networks with 100 to ∼106 nodes can be fabricated), reconfigurable (by virtue of embedded logic) and durable (by embedding into composite panels or protective films). The proposed structure consists of a 20 to 100 µm thick silicon membrane that is structured as a 2D network of 200 µm-diameter nodes connected via spiral interconnects. Each of the network nodes can house a high-performance silicon integrated circuit (IC) and sensors/actuators. One or more levels of network electrical connections run on top of the spiral springs that are initially rolled-up around the network nodes. These spirals (and wires) can be unrolled and extended up to a point of maximum extension, given by the total length of the spiral. This approach localizes all the deformation needed to realize the large areal expansion (up to 1000x) in the spiral sections and the deformation remains entirely elastic.
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Author Index
Abe, M. 85 Adachi, R. 533 Agarwal, A.K. 110 Aktan, E.A. 467 Ali, S.F. 110 Ansari, F. 145, 175 Arangio, S. 219 Aratake, H. 525 Ayame, T. 86 Aydar, G. 577 Azuhata, T. 378 Badel, A. 409 Balachandran, B. 536 Banerjee, S. 330 Bang, E.S. 302 Bao, X.X. 117 Barnawi, W. 377 Barrera, E.V. 345 Barros, R.C. 93 Bartoli, I. 329 Baz, A. 390, 442, 534, 535 Bennett, P.J. 96 Bernal, D. 75, 209 Bian, C.F. 547 Bisht, S. 332 Bontempi, F. 219, 266 Bouzidi, R. 95 Bruder, S. 349 Budelmann, H. 349 Burns, D. 185, 423 Cai, H. 321 Cao, B.J. 148 Cao, Y. 555 Cardone, D. 372 Casciati, F. 273 Casciati, S. 590 Catbas, F.N. 229, 470 Ceravolo, R. 211 Chae, Y. 358 Chan, H.L.W. 338 Chan, W.L. 517 Chang, C.C. 241 Chang, M.L. 257 Chapman, P.L. 436 Chen, B. 199 Chen, B.L. 335 Chen, G. 101
Chen, J. 482 Chen, K.W. 228 Chen, L. 373 Chen, M.H. 336, 337 Chen, R.W. 447, 449, 459, 550, 551 Chen, S. 179, 191 Chen, W.M 162 Chen, W.M. 113, 148, 153, 183, 251, 258, 291, 293, 294, 322, 366, 450 Chen, Y.-C. 78 Chen, Y.H. 565 Chen, Z. 135 Chen, Z.H. 340 Chen, Z.Q. 252 Cheng, H.B. 541, 542, 578 Chiang, C.C. 335 Ching, J.Y. 78 Cho, C.J. 435 Cho, S.W. 112 Cho, Y.-S. 396, 421 Choi, K.M. 111, 112, 388 Choi, S.B. 130, 309, 385, 386 Choo, J.F. 509 Choy, P.K. 338 Christenson, R.E. 360, 361 Chu, S.Y. 417 Chung, D.D.L. 346 Civera, P. 145, 304 Coccia, S. 329 Cooper, J.E. 94, 415 Courter, S. 361 Cui, J. 185, 326 Dai, J. 147, 176, 503, 504 Dai, Z. 422 Dan, D. 475, 485 Dao, C.M. 330 Das, S. 330 De Roeck, G. 156 De Stefano, A. 145, 175, 304 Del Grosso, A. 234, 236 Della, C.N. 137, 139 Demarie, G.V. 211 Denegri, L. 234 Deng, L. 447 Deraemaeker, A. 156 DesRoches, R. 586, 587 Devadas Manoharan, P. 313 Dharap, P. 345
593
Dimitriadis, G. 415 Dinyari, R. 592 Do, H.S. 140 Dogaki, M. 467 Dolce, M. 372 Dong, X.F. 169 Dong, X.M. 113, 251, 291 Du, Y. 176, 314, 503, 504 Duan, Z. 106 Duan, Z.D. 579 Dyke, S.J. 204, 361, 377 El-Sabbagh, A. 442 Elgamal, A. 102 Elsabbagh, A. 390 Endo, H. 411 Erlicher, S. 211 Evrensel, C. 577 Fan, J. 371 Fan, W.K. 337 Fang, X. 430 Faravelli, L. 233 Fateh, M. 329 Fei, S.M. 557 Feng, J. 592 Frangopol, D.M. 470 Fraser, M. 102 Fritzen, C.-P 76 Fritzen, C.-P. 160 Fu, L. 179 Fu, L.J. 154 Fu, Y. 148, 183, 366 Fujino, Y. 83, 84, 85 Fujisaki, J. 422 Fukunaga, H. 403, 585 Furuta, H. 227, 465 Furuya, Y. 407 Gallo, G. 436 Gan, X. 322 Gao, C.F. 580 Gao, W.X. 541, 542, 578 Gao, X. 361 Ghandehari, M. 350, 352 Giacosa, L.M. 145, 175, 304 Giles, R.K. 248, 431 Gioanola, L. 304 Giuliano, F. 219, 266, 273 Giurgiutiu, V. 359, 443 Glaser, S.D. 571
Gong, J.-J. 591 Gong, Z.Q. 248 Gongbiao, L. 121 Goo, N.S. 395, 513 Gordaninejad, F. 577 Gu, B. 551 Gu, H. 200 Guan, X.C. 169, 547 Gucunski, N. 185 Guo, H. 119 Guo, P.F. 547 Guo, Y.Q. 557, 588 Haldar, A. 79 Han, B. 343 Han, C. 521 Han, F. 449 Han, H. 396, 421 Han, J.-H. 491, 515 Han, M.S. 386 Han, Y.M. 130, 385, 386 Hao, L. 450 Hariri, K. 349 Harmon, T. 204 Hattori, H. 227 He, B. 558 He, J.M. 154 He, Y. 371 Heo, S. 513 Hodigere-Siddaramaiah, V. 415 Holst, A. 349 Hong, D.S. 140, 481 Hotate, K. 21 Hou, Z. 447, 550 Hsieh, K.H. 257 Hsu, S.-P. 497 Hu, H. 574 Hu, N. 585 Hu, S. 366 Hu, S.-L.J. 187, 210, 288 Hua, X.G. 228 Huang, G.L. 127 Huang, H. 178, 206, 243, 362, 455 Huang, J. 154, 155, 292, 324, 404 Huang, K. 592 Huang, S.L. 3, 113, 153, 183, 291 Huang, X. 293 Huang, X.H. 392 Huang, Z. 184, 301 Huh, Y.C. 111 Hui, L. 128 Huo, S. 374 Hurlebaus, S. 77, 203 Hurley, D. 423 Huston, D. 185, 423
Iemura, H. 303 Ihn, J.-B. 404 Ikhouane, F. 452 Inaudi, D. 236 Inoue, N. 525 Irschik, H. 416 Ishihara, T. 378 Ito, N. 467 Ito, Y. 525 Itoh, Y. 566 Jalinoos, F. 185 Jang, S.A. 286 Ji, A. 422 Ji, Y.F. 241 Jiang, J. 581 Jiang, Z. 361 Jin, S. 104 Jin, S.W. 302 Jin-ping, O. 128 Jung, C.W. 285 Jung, D.-H. 396 Jung, H.J. 111, 112 Jung, K. 31 Kajiwara, I. 527 Kajiyoshi, K. 408 Kameyama, M. 403 Kanagawas, M. 525 Kang, B.-S. 155, 324 Kang, H.O. 396 Kang, T. 517 Katafygiotis, L.S. 213 Katkhuda, H. 79 Kawamoto, A. 467 Kayano, M. 465 Khalil, G. 350 Kim, C.-Y. 195 Kim, D. 31, 287 Kim, D.-K. 515 Kim, D.S. 302 Kim, H. 287 Kim, I.-S. 287 Kim, J.-H. 396 Kim, J.K. 357 Kim, J.T. 140, 481 Kim, J.Y. 592 Kim, K.J. 31 Kim, S.-M. 31 Kim, S.J. 31 Kim, W. 287, 435 Kim, W.-D. 396, 421 Kim, W.J. 285, 479 Kim, Y.K. 379 Kimura, H. 86 Kitagawa, Y. 523 Ko, J.M. 228, 242, 252, 259
594
Kobashi, S. 247 Kobayashi, H. 89 Kobayashi, S. 529 Koh, H.M. 509 Komatsu, H. 523 Kondo, C. 488 Koo, K.Y. 481 Kraemer, P. 76 Krommer, M. 416 Kullaa, J. 156 Kundu, T. 330 Kuroiwa, T. 303 Kwon, H.W. 479 Kwon, I.B. 17, 195 Kwon, K.-J. 515 Kwon, Y.D. 479 Lacher, A. 135 Lam, H.F. 213, 238 Lam, K.H. 340 Lan, C. 167 Lanata, F. 234 Lanza di Scalea, F. 329 Lanzara, G. 592 Laskar, A. 200 Law, K.H. 102, 277 Lee, B.C.L. 565 Lee, D.-E. 287, 435 Lee, H.J. 111, 112, 388 Lee, H.S. 509 Lee, I. 491 Lee, I.W. 388 Lee, J. 31 Lee, J.J. 481 Lee, S. 521 Lee, S.-H. 141 Lee, S.-K. 380 Lee, S.J. 388 Lee, S.R. 379 Lee, S.S. 17, 195 Lee, Y.J. 517 Lee, Y.S. 386 Lei, J.Y. 122 Lei, T. 459 Lei, X.-H. 162, 258 Lei, Y. 122, 149 Li, D. 581 Li, F. 268 Li, G. 192, 549 Li, H. 106, 155, 167, 168, 222, 253, 288, 314, 324, 343, 571 Li, H.J. 117, 187, 210 Li, J. 279, 358 Li, K. 492, 493 Li, N. 408 Li, Q.F. 549 Li, R. 251
Li, R.G. 540 Li, S. 353, 480, 505 Li, S.S. 540 Li, W.H. 556, 561 Li, X. 326 Li, X.-M. 323 Li, Y. 163, 574 Li, Y.N. 390, 534, 539, 540 Li, Z. 119, 193, 291, 345, 427 Li, Z.-Q. 429 Liang, A.Z. 148 Liang, D.K. 506, 549 Liang, H. 457 Liang, J. 193 Liang, X. 474 Liang, Z. 366 Liao, C. 291, 293, 294 Liao, C.R. 113, 153, 251 Liao, L.Q. 292 Liao, W.Y. 259 Lim, S.C. 130 Lin, C.C. 257 Lin, C.H. 292 Lin, J.H. 268 Lin, Y. 321 Liu, 258 Liu, B. 561 Liu, F.S. 210 Liu, G. 184, 186, 301 Liu, H. 193, 261, 367, 473 Liu, H.J. 300 Liu, J. 499 Liu, M. 253 Liu, Q. 449, 551, 588 Liu, S. 461 Liu, Y. 274 Livingston, R.A. 104 Lo, C.Y. 338 Lo, S.C. 417 Loebach, L.E. 360 Loh, K.J. 102 Lu, W. 265, 300 Lu, Y. 430 Luan, W.L. 455 Luo, J.L. 579 Luo, M.G. 534, 539 Luo, N. 452 Luo, Y. 193, 427 Lynch, J.P. 102, 149, 277, 281 Lämsä, V. 156 Maher, A. 185 Mahin, S.A. 315 Mai, E.C. 244 Majumdar, A. 178 Manson, G. 156 Mao, L. 293, 543
Mao, S.J. 455 Martinez-Flores, R. 79 Maseki, R. 523 Masri, S.F. 437 Masuda, A. 247, 555 Masuda, Z. 585 Matsuda, H. 469, 566 Matsuhisa, H. 274, 317 Matsumori, T. 161 McCormick, J. 587 Mei, H. 322 Meng, Y. 550 Meng, Z.L. 408 Midorikawa, M. 378 Miller, S. 415 Min, K.-W. 141, 380 Min, Z. 475 Mita, A. 220, 221, 456, 488 Miyamori, Y. 86 Miyamoto, N. 469 Mizuno, Y. 83 Mo, Y.-L. 200 Moon, B.-W. 380 Moon, S.J. 111, 385 Morgan, T.A. 315 Morita, K. 161 Mujica, L.E. 235 Na, W.B. 140 Nagarajaiah, S. 199, 345 Nagashima, I. 523 Nagaya, M. 525 Nagayama, T. 84, 278 Nakano, T. 409 Nakasone, J. 525 Nakmura, Y. 525 Nandan, H. 331 Nayeri, R.D. 437 Ng, C.T. 213 Nguyen, Q.H. 309 Nguyen, Q.V. 395 Nguyen, V.Q. 385 Ni, W.B. 268 Ni, Y.Q. 228, 242, 252, 259, 340 Nishikiori, M. 529 Nishimura, H. 525 Nishimura, S. 566 Nishitani, A. 109 Nitta, Y. 109 Noori, M.N. 555 Ntotsios, E. 238 Oguni, K. 88 Oh, S.-H. 491 Ohnishi, K. 55 Okamoto, T. 469 Okazaki, T. 407
595
Olmi, C. 200 Or, S.W. 338, 340 Oshima, T. 86 Ostachowicz, W. 156 Ou, J.P. 106, 168, 169, 222, 253, 316, 343, 547, 571 Padgett, J.E. 586 Paeng, Y.S. 385 Papadimitriou, C. 238 Park, H.C. 395, 513 Park, I.-S. 31 Park, J. 521 Park, J.-H. 141, 380 Park, J.H. 140 Park, W. 509 Pei, J.-S. 244 Pellegrino, S. 95 Perez Goodwyn, P.J. 422 Peumans, P. 592 Pieri, G. 219 Popovics, J.S. 436 Pozzi, M. 215 Preumont, A. 95 Pugal, D. 31 Puran, N. 350 Qian, H.S. 171, 307, 308 Qian, L. 573 Qian, Y. 221 Qin, M.Y. 265 Qin, S. 499 Qiu, J.H. 63, 408, 409, 441 Qu, W.L. 192, 473, 480, 499, 541, 542, 578 Ramaswamy, A. 110 Reis, H. 374, 401 Ren, J.T. 588 Rengaraja, T. 313 Reynders, E. 156 Ricci, S. 94 Rice, J.A. 278 Richter, H. 444 Rizzo, P. 329 Rodellar, J. 235, 452 Rodrigues, G. 95 Roh, J.-H. 491 Ryujin, H. 525 Saftner, D.A. 281 Sakai, J. 89 Sanchez, J. 444 Sanui, Y. 523 Scruggs, J.T. 498 Seo, D.-C. 195 Seo, H.W. 285
Setareh, M. 281 Seto, K. 360, 529 Shao, J. 539 Shelton, M. 436 Shen, W.A. 149 Shi, L.H. 549 Shih, M.H. 497 Shin, C.S. 335 Shin, K.J. 285 Shinozaki, Y. 523 Shiraishi, M. 281 Shiraki, W. 467 Shoureshi, R.A. 233 Shu, D. 137, 139 Sidelev, A. 352 Sim, S.-H. 286 Sim, S.H. 123, 216 Singh, M.P. 331, 332 Sittner, P. 97 Smoker, J. 535 Soga, K. 96 Sohn, J.W. 386 Song, G. 200 Song, W. 204 Song, Y. 122, 149, 522 Spellane, P. 352 Spencer, B.F. 84, 123, 216, 248, 278, 286, 431 Stockman, Y. 95 Su, Y. 558 Suk, C.-M. 435 Suleman, A. 94 Sumitro, S. 469, 566 Sun, B. 147, 176, 503, 504 Sun, H. 492, 493 Sun, L.M. 146, 230, 475, 485 Sun, L.Z. 136 Sun, R.J. 230 Sun, Z. 230 Sung, K.G. 386 Sung, W.P. 497 Swartz, R.A. 281 Syrmakezis, C.A. 237 Schönecker, M. 131 Takagi, T. 411 Tamura, H. 220 Tan, D. 480 Tan, F. 392 Tan, J. 163 Tang, J. 430 Tao, Y. 267 Tasbihgoo, F. 437 Tata, U.S. 178 Taylor, E. 377 Teng, J. 265, 300 Tian, G.Y. 159
Tian, X. 459 Tian, Z. 163 Tigli, O.F. 209 Tiwari, R. 31 Tolmie, B. 423 Torre, A. 234 Torres, F.G. 444 Toyama, J. 523 Tsopelas, P. 373 Tsuchiya, R. 527 Tu, J.W. 499, 542 Tu, S.T. 455 Uchimoto, T. 411 Ueng, J.M. 257 Ung, S. 195 Unjoh, S. 89 Utsuno, H. 274, 317 VanHumbeeck, J. 97 Vary, A. 401 Vio, G.A. 415 Vehí, J. 235 Wahbeh, M. 437 Wan, C. 456 Wang, A.Y.P. 565 Wang, B.F. 171, 307, 308 Wang, C.Y. 336, 337 Wang, F.X. 316 Wang, H. 159 Wang, H.L. 336, 337 Wang, J. 288, 422, 473, 573, 574 Wang, J.M. 541, 578 Wang, L. 461 Wang, L.-C. 323 Wang, M. 41, 261, 367 Wang, M.L. 571 Wang, R. 167 Wang, S.J. 248 Wang, S.Q. 117 Wang, W. 101, 391 Wang, X. 307, 577 Wang, X.-F. 591 Wang, X.-W. 591 Wang, X.D. 127 Wang, X.H. 541 Wang, X.M. 268 Wang, X.Y. 252, 556, 561 Wang, Y. 102, 277, 371, 485, 506 Wang, Y.G. 120 Wang, Z. 422, 427 Watakabe, M. 525 Watanabe, E. 465 Watanabe, T. 360, 529 Wei, J.S. 540 Wen, H. 543
596
Wen, S. 346 Wiguna, T. 513 Wilson, J. 159 Wolfe, R. 437 Worden, K. 156 Wu, B. 269 Wu, J. 474 Wu, S. 487 Wu, Z. 353, 474, 505 Xi, N. 450 Xiang, X. 323 Xiao, H. 128, 167, 343 Xie, H.C. 248 Xie, Z.Y. 186 Xing, K.J. 76, 160 Xiong, X.-C. 162 Xu, B. 260 Xu, G. 269 Xu, J. 326 Xu, S. 542 Xu, Z. 371 Xu, Z.D. 557 Xun, L. 171, 308 Yabuki, N. 280 Yamada, K. 317 Yan, G.F. 392 Yan, X. 543 Yanagisawa, K. 408 Yang, B.H. 580 Yang, F.Y. 120, 299 Yang, J. 522 Yang, J.N. 206, 243, 487 Yang, P. 184, 186, 301 Yang, T.-L. 329 Yang, Y. 155, 324, 402 Yang, Y.C. 120, 299 Yang, Z. 391, 492, 493 Yasuda, K. 467 Yi, J. 457 Yim, W. 31 Yin, H.M. 136 Yokoi, T. 555 Yokoyama, M. 533 Yook, J.Y. 385 Yoon, D.-J. 195 Yoon, D.J. 17 Yoshida, K. 523 You B., 326 Youn, K.-J. 141 Yu, L. 359, 443 Yu, M. 113, 135, 153, 251, 291, 293, 294, 543 Yu, X. 365 Yu, X.-H. 448 Yu, X.B. 365
Yuan, F.-G. 247, 402 Yuan, F.G. 461, 555 Yuan, H. 267 Yuan, J. 167 Yue, J. 558 Yue, R.-B. 162 Yun, 437 Yun, B.Y. 309 Yun, C.B. 481 Yun, G. 204 Zapateiro, M. 452 Zaurin, R. 229 Zhang, B. 159 Zhang, H. 291, 294 Zhang, H.H. 113, 153, 251 Zhang, J. 450, 541, 542, 578 Zhang, L. 307, 492, 493, 573
Zhang, M. 120, 179, 187, 299, 343 Zhang, P. 162, 258, 322 Zhang, Q.J. 541, 542, 578 Zhang, W. 147, 176, 503, 504 Zhang, X.Z. 556, 561 Zhang, Y. 49, 202, 279, 358, 558 Zhang, Y.-H. 522 Zhang, Y.X. 216 Zhao, G. 427 Zhao, G.-Y. 482 Zhao, W.Y. 541, 542, 578 Zhao, X. 106 Zhao, Y. 191 Zheng, L. 390, 534, 535, 539, 540 Zheng, S. 352
597
Zheng, S.-J. 429 Zheng, Y. 261, 367 Zhou, B. 506 Zhou, D. 106 Zhou, H.F. 242 Zhou, L. 206, 402, 487 Zhou, Q. 267, 499 Zhou, W. 168 Zhou, X. 261 Zhou, Y. 171, 307 Zhou, Z. 106 Zhu, C. 562, 572 Zhu, K.J. 408, 441 Zhu, Y. 148, 183, 322 Zhu, Y.H. 265, 300 Zimmerman, A.T. 281 Zonta, D. 215
