Optimized finite element model updating method for damage detection using limited sensor information

Cheng, L.,Xie, H.C.,Spencer, B.F. Jr.,Giles, R.K. Techno-Press 2009 Smart Structures and Systems, An International Jou Vol.5 No.6

Limited, noisy data in vibration testing is a hindrance to the development of structural damage detection. This paper presents a method for optimizing sensor placement and performing damage detection using finite element model updating. Sensitivity analysis of the modal flexibility matrix determines the optimal sensor locations for collecting information on structural damage. The optimal sensor locations require the instrumentation of only a limited number of degrees of freedom. Using noisy modal data from only these limited sensor locations, a method based on model updating and changes in the flexibility matrix successfully determines the location and severity of the imposed damage in numerical simulations. In addition, a steel cantilever beam experiment performed in the laboratory that considered the effects of model error and noise tested the validity of the method. The results show that the proposed approach effectively and robustly detects structural damage using limited, optimal sensor information.

Bio-inspired autonomous engineered systems

Tomizuka, Masayoshi,Bergman, Lawrence A.,Shapiro, Ben,Shoureshi, Rahmat,Spencer, B.F. Jr.,Taya, Minoru Techno-Press 2007 Smart Structures and Systems, An International Jou Vol.3 No.4

Isolation System for Vibration Control of Stay Cables

Hwang, Inho,Lee, Jong Seh,Spencer Jr., B. F. American Society of Civil Engineers 2009 Journal of engineering mechanics Vol.135 No.1

Real-time hybrid testing using model-based delay compensation

Carrion, Juan E.,Spencer, B.F. Jr. Techno-Press 2008 Smart Structures and Systems, An International Jou Vol.4 No.6

Real-time hybrid testing is an attractive method to evaluate the response of structures under earthquake loads. The method is a variation of the pseudodynamic testing technique in which the experiment is executed in real time, thus allowing investigation of structural systems with time-dependent components. Real-time hybrid testing is challenging because it requires performance of all calculations, application of displacements, and acquisition of measured forces, within a very small increment of time. Furthermore, unless appropriate compensation for time delays and actuator time lag is implemented, stability problems are likely to occur during the experiment. This paper presents an approach for real-time hybrid testing in which time delay/lag compensation is implemented using model-based response prediction. The efficacy of the proposed strategy is verified by conducting substructure real-time hybrid testing of a steel frame under earthquake loads. For the initial set of experiments, a specimen with linear-elastic behavior is used. Experimental results agree well with the analytical solution and show that the proposed approach and testing system are capable of achieving a time-scale expansion factor of one (i.e., real time). Additionally, the proposed method allows accurate testing of structures with larger frequencies than when using conventional time delay compensation methods, thus extending the capabilities of the real-time hybrid testing technique. The method is then used to test a structure with a rate-dependent energy dissipation device, a magnetorheological damper. Results show good agreement with the predicted responses, demonstrating the effectiveness of the method to test rate-dependent components.

Issues in structural health monitoring employing smart sensors

Nagayama, T.,Sim, S.H.,Miyamori, Y.,Spencer, B.F. Jr. Techno-Press 2007 Smart Structures and Systems, An International Jou Vol.3 No.3

Smart sensors densely distributed over structures can provide rich information for structural monitoring using their onboard wireless communication and computational capabilities. However, issues such as time synchronization error, data loss, and dealing with large amounts of harvested data have limited the implementation of full-fledged systems. Limited network resources (e.g. battery power, storage space, bandwidth, etc.) make these issues quite challenging. This paper first investigates the effects of time synchronization error and data loss, aiming to clarify requirements on synchronization accuracy and communication reliability in SHM applications. Coordinated computing is then examined as a way to manage large amounts of data.

MR damping system for mitigating wind-rain induced vibration on Dongting Lake Cable-Stayed Bridge

Chen, Z.Q.,Wang, X.Y.,Ko, J.M.,Ni, Y.Q.,Spencer, B.F.,Yang, G.,Hu, J.H. Techno-Press 2004 Wind and Structures, An International Journal (WAS Vol.7 No.5

The Dongting Lake Bridge is a cable-stayed bridge crossing the Dongting Lake where it meets the Yangtze River in southern central China. Several intensive wind-rain induced vibrations had been observed since its open to traffic in 1999. To investigate the possibility of using MR damping systems to reduce cable vibration, a series of field tests were conducted. Based on the promising research results, MR damping system was installed on the longest 156 stay cables of Dongting Lake Bridge in June 2002, making it the worlds first application of MR dampers on cable-stayed bridge to suppress the wind-rain induced cable vibration. As a visible and permanent aspect of the bridge, the MR damping system must be aesthetically pleasing, reliable, durable, easy to maintain, as well as effective in vibration mitigation. Substantial work was done to meet these requirements. This paper describes field tests and the implementation of MR damping systems for cable vibration reduction. Three-years reliable service of this system proves its durability.

Feedforward actuator controller development using the backward-difference method for real-time hybrid simulation

Phillips, Brian M.,Takada, Shuta,Spencer, B.F. Jr.,Fujino, Yozo Techno-Press 2014 Smart Structures and Systems, An International Jou Vol.14 No.6

Real-time hybrid simulation (RTHS) has emerged as an important tool for testing large and complex structures with a focus on rate-dependent specimen behavior. Due to the real-time constraints, accurate dynamic control of servo-hydraulic actuators is required. These actuators are necessary to realize the desired displacements of the specimen, however they introduce unwanted dynamics into the RTHS loop. Model-based actuator control strategies are based on linearized models of the servo-hydraulic system, where the controller is taken as the model inverse to effectively cancel out the servo-hydraulic dynamics (i.e., model-based feedforward control). An accurate model of a servo-hydraulic system generally contains more poles than zeros, leading to an improper inverse (i.e., more zeros than poles). Rather than introduce additional poles to create a proper inverse controller, the higher order derivatives necessary for implementing the improper inverse can be calculated from available information. The backward-difference method is proposed as an alternative to discretize an improper continuous time model for use as a feedforward controller in RTHS. This method is flexible in that derivatives of any order can be explicitly calculated such that controllers can be developed for models of any order. Using model-based feedforward control with the backward-difference method, accurate actuator control and stable RTHS are demonstrated using a nine-story steel building model implemented with an MR damper.

사장교에서 다양한 불확실성에 대한 μ-제어기의 강인성 해석

박규식(Park Kyu Sik),Spencer B. F. Jr,김춘호(Kim Chun Ho),이인원(Lee In Won) 대한토목학회 2006 대한토목학회논문집 A Vol.26 No.5A

본 연구에서는 벤치마크 사장교를 이용해 다양한 불확실성에 대해서 복합시스템에 사용된 μ-제어기의 강인성 해석을 수행 하였다. 복합 시스템에 추가적으로 사용된 능동제어 장치로 인하여 전체 시스템의 강인성이 저하되거나 불안정성이 발생할 수 있다. 따라서 본 연구에서는 복합 시스템의 강인성을 향상시키기 위해 기본적으로 신뢰성이 확보되는 수동장치와 함께 불확실성을 포함한 시스템의 성능과 안정성(강인성능)을 보장하는 μ-합성법을 능동제어 장치에 사용하였다. 교량상판에 추가적인 질량, 구조물 강성행렬에 대한 섭동, 능동제어 장치의 시간지연, 그리고 이들의 조합을 이용하여 μ-합성법의 강인성을 조사하였다. 수치해석 결과 다양한 불확실성에 대해 제안된 시스템은 제어성능의 저하 없이 뛰어난 강인성을 보여 주었다. 또한 제어시스템의 강인성은 다른 불확실성에 비해 구조물의 강성행렬 섭동에 더 큰 영향을 받는다. 따라서 μ-합성법으로 제어되는 복합 시스템은 불확실성이 많은 지진하중을 받는 사장교에 개선된 제어기법으로 제안될 수 있다. This paper presents an extensive robust analysis of a ,μ-controller in the hybrid system for various uncertainties using the benchmark cable-stayed bridge. The overall system robustness may be deteriorated by introducing active devices and the active controller may cause instability due to small margins. Therefore, a ,μ-synthesis method that simultaneously guarantees the performance and stability of the closed-loop system (robust performance) with uncertainties is used for active devices to enhance the robustness in company with the inherent reliability of passive devices. The robustness of the μ-synthesis method is investigated with respect to the additional mass on the deck, structural stiffness matrix perturbation, time delay of actuator, and combinations thereof. Numerical simulation results show that the proposed control system has the good robustness without loss of control performances with respect to various uncertainties under earthquakes considered in this study. Furthermore, the control system robustness is more affected by the perturbation of structural stiffness matrix than others considered in this study. Therefore, the hybrid system controlled by a ,μ-synthesis method could be proposed as an improved control strategy for a seismically excited cable-stayed bridge containing many uncertainties.

Middleware services for structural health monitoring using smart sensors

Nagayama, T.,Spencer, B.F. Jr.,Mechitov, K.A.,Agha, G.A. Techno-Press 2009 Smart Structures and Systems, An International Jou Vol.5 No.2

Smart sensors densely distributed over structures can use their computational and wireless communication capabilities to provide rich information for structural health monitoring (SHM). Though smart sensor technology has seen substantial advances during recent years, implementation of smart sensors on full-scale structures has been limited. Hardware resources available on smart sensors restrict data acquisition capabilities; intrinsic to these wireless systems are packet loss, data synchronization errors, and relatively slow communication speeds. This paper addresses these issues under the hardware limitation by developing corresponding middleware services. The reliable communication service requires only a few acknowledgement packets to compensate for packet loss. The synchronized sensing service employs a resampling approach leaving the need for strict control of sensing timing. The data aggregation service makes use of application specific knowledge and distributed computing to suppress data transfer requirements. These middleware services are implemented on the Imote2 smart sensor platform, and their efficacy demonstrated experimentally.

해석적인 정보를 고려한 다중입력을 받는 다자유도계 구조물의 시스템 규명 기법 개발

김상범(Kim, Saang-Bum),스펜서(Spencer, B. F., Jr.),윤정방(Yun, Chung-Bang) 한국소음진동공학회 2005 한국소음진동공학회 논문집 Vol.15 No.6

This paper presents a system identification method for multi-input, multi-output (MIMO) systems, by which a rational polynomial transfer function model is identified from experimentally determined frequency response function data. Analytically determined information is incorporated in this method to obtain a more reliable model, even in the frequency range where the excitation energy is limited. To verify the suggested method, shaking table test for an actively controlled two-story, bench-scale building employing an active mass damper is conducted. The results show that the proposed method is quite effective and robust for system identification of MIMO systems.