KEYWORDS: Structural health monitoring, Data modeling, System identification, Neural networks, Sensors, Bismuth, Motion models, Control systems, Interference (communication), Statistical analysis
Robust and efficient identification methods are necessary to study in the structural health monitoring field, especially when the I/O data are accompanied by high-level noise and the structure studied is a large-scale one. The Support vector Regression (SVR) is a promising nonlinear modeling method that has been found working very well in many fields, and has a powerful potential to be applied in system identifications. The SVR-based methods are provided in this article to make linear large-scale structural identification and nonlinear hysteretic structural identifications. The LS estimator is a cornerstone of statistics but less robust to outliers. Instead of the classical Gaussian loss function without regularization used in the LS method, a novel e-insensitive loss function is employed in the SVR. Meanwhile, the SVR adopts the 'max-margined' idea to search for an optimum hyper-plane separating the training data into two subsets by maximizing the margin between them. Therefore, the SVR-based structural identification approach is robust and accuracy even though the observation data involve different kinds and high-level noise. By means of the local strategy, the linear large-scale structural identification approach based on the SVR is first investigated. The novel SVR can identify structural parameters directly by writing structural observation equations in linear equations with respect to unknown structural parameters. Furthermore, the substrutural idea employed reduces the number of unknown parameters seriously to guarantee the SVR work in a low dimension and to focus the identification on a local arbitrary subsystem. It is crucial to make nonlinear structural identification also, because structures exhibit highly nonlinear characters under severe loads such as strong seismic excitations. The Bouc-Wen model is often utilized to describe structural nonlinear properties, the power parameter of the model however is often assumed as known even though it is unknown in the real world. In the case of unknown-power parameter, the nonlinear structural identification problem is more intricate and few approaches are dedicated to this problem. In this article, a model selection strategy is proposed to determine the unknown power parameter of the Bouc-Wen model. Meanwhile, the optimum SVR parameters are automatically selected instead of tuning manually. Based on the produced power parameter and optimum SVR parameters, the SVR is executed to identify nonlinear hysteretic structural parameters accurately and robustly. The numerical examples for two linear large-scale structures and a five-DOF nonlinear hysteretic structure provided illustrates that the proposed technique has excellent performance in robustness and accuracy for linear and nonlinear structural identifications, even when the noise exits in I/O measurements is high-level and non-Gaussion. Moreover, an incremental training algorithm utilized to solve SVR formulation in a sequential way not only significantly reduces the computation time, but also makes the structural health monitoring on-line.
KEYWORDS: Particle filters, Particles, System identification, Digital filtering, Filtering (signal processing), Nonlinear filtering, Monte Carlo methods, Statistical analysis, Electronic filtering, Systems modeling
The most common choice of importance density is the transition prior density function for particle filter (it is also known as SIR filter, Monte Carlo filter, Bayesian bootstrap filter, condensation, etc.), since it is intuitive and simple to implement, but using the prior as the importance density suffers from drawback of without any knowledge of the observations, and hence the state space is explored without direct knowledge of the observations, maybe lead to poor performance for the particle filtering. To accomplish this, it is necessary to incorporate the current observation in the importance density. In this paper, we propose an auxiliary particle filter (APF) method to identify a non-stationary dynamic system with abrupt change of system parameters. In the APF, the importance density is proposed as a mixture density that depends upon the past state and the most recent observations, and hence which has a good time tracking ability is more suitable for tracking the non-stationary system than the conventional particle filters. The numerical simulations confirm effectiveness of the proposed method for the structural system identification.
Structural identification based on the vibration data is still a challenging topic especially when the input and output (I/O) measurements are corrupted by high-level noise. In this paper, we propose a new structural parameter identification method based on the Support Vector Regression (SVR) which has been found working very well in many fields as an exclusively data based non-linear modeling method. Machine learning technologies such as Neural Networks has been applied widely in the field of health monitoring field. However, most papers just obtain the 'block-box' model of the studied structures from Neural Network training but the structural parameters are not identified actually. In our work, we not only generate the 'block-box' model but also identify the structural parameters by combining ARMA model together with SVR. Due to the “max-margin” idea used, SVR showed powerful properties in ARMA and structural identification under different kinds and amplitude noise. Furthermore, how to choose the parameters of SVR is also studied in this paper. Finally, numerical examples are given to demonstrate that the proposed method based on SVR is effective and powerful for identifying ARMA time series and structural models.
KEYWORDS: Particles, Monte Carlo methods, Data modeling, Algorithm development, System identification, Genetic algorithms, Particle filters, Data processing, Motion models, Computing systems
In this paper, we develop a new structural identification algorithm by improving the defect of the classical Monte Carlo Filter (MCF). In the MCF, we identify the probability density function of the state vector which is approximated by many realizations, called particles. In the classical MCF, however, as the degree of freedom of structural model increases, we have to generate exponential order of particles. This results in extreme increase of computation time. To overcome this problem, we developed the relaxation MCF (RMCF) in which we improve the filtering process of the classical MCF. By using this method, we can reduce computation time drastically. Moreover, we developed the GA-RMCF, in which we combine the Genetic Algorithm (GA) with the RMCF. We apply the proposed algorithm, the GA-RMCF, to identifying the dynamic parameters of a five-story model building using observed data obtained through the shaking table tests. The data processed here are from a linear structural model.
The purpose of this paper is to develop an application implementable to a laptop computer by which we can evaluate a structural system from its responses in situ. To show applicability of the application, we analyze the data obtained by a shaking table experiment of a five-story building model. Four Lead Rubber Bearings (LRBs) are placed at the four corner of 1st and 3rd stories of the model building instead of columns to set a clear nonlinear behavior of the structure. Using the test data and the developed application, we identify the dynamic characteristics of five-story building model.
In this paper we propose a neural network-based approach for damage detection of unknown structure systems. Newly developed global H∞ Filter optimal learning algorithm for the neural network to simulate a structural response is developed. This algorithm is based on the worst-case disturbances design criterion, and is therefore robust with respect to model uncertainties and lack of statistical information to the exogenous signals. Simulation results are presented to identify dynamic response characteristics of nonlinear structural systems corresponding to different degrees of parameters changes, which indicate that damage occurred in the structure. It is shown that the proposed method is highly robust and more appropriate in practical early structural damage detection.
This paper presents a device to measure the dynamic horizontal shear strain of the ground during earthquake. The proposed device consists of a bronze plate with fiber Bragg grating sensors attached on it. The device is vertically installed in the ground, and horizontal shear strain of the ground is measured as deflection angle of the plate. Employment of optical fiber sensors makes the proposed device simple in mechanism and highly durable, which makes it easy to install our device in the ground. We conducted shaking table tests using ground model to verify applicability of the proposed device.
It is essential to study the dynamic behavior of the soil to make clear the characteristics of ground behavior during earthquake. However, the relationship between the dynamic characteristics and the strain of the soil is not completely studied, because there is no device to measure the strain of the real ground directly. Therefore, it is necessary to develop the ground strain measuring system which can be applied to the real ground. This study presents a system to measure the ground strain, using the fiber Bragg grating (FBG) sensors. Using optical fiber sensor makes the devices simple in mechanism and highly durable. We improve the strain measuring device which was proposed by Sato et al. and also develop a new strain measuring device based on a different mechanism. Their applicability is studied in the experiments. The results in the experiment indicate that it is possible to measure the ground strain by the presented systems with the same level of accuracy as that of the systems by Sato et al. It is also important to recognize the necessity to improve the accuracy.
KEYWORDS: Nonlinear filtering, Digital filtering, Filtering (signal processing), Linear filtering, Systems modeling, System identification, Electronic filtering, Motion models, Complex systems, Data modeling
Dynamic behaviors of a 1-story and 4-story steel structures subject to multi-dimensional ground motion excitations were experimentally investigated by using a shaking table. Linear and nonlinear structural responses were obtained as observation data for the identification. Dynamics characteristics of the model structures were identified using the adaptive H(infinity ) filter, which was developed for identifying structural systems with non-stationary dynamic characteristics by adding the function of memory fading (forgetting factor) for past observation data to the H(infinity ) filter. Identification results show that the H(infinity ) filtering technique are very efficient for identifying linear and nonlinear structural systems. Especially, the nonlinear behavior of the model can be traced effectively.
It is widely recognized that the dynamic behavior of the soil is essential to discuss the characteristics of ground behavior during earthquakes, and many research has been conducted for a long period. Many problems, however, remain unsolved about the dynamic property, which is usually treated as stress- strain relationship, of the soil. One of the reasons for this, is lack of a means to measure the strain in the real ground. This paper presents a system to measure the ground strain using the fiber Bragg grating (FBG) sensors. Employment of optical fiber sensor makes the device simple in mechanism and highly durable. Two types of prototypes of the ground strain measuring device are made and their applicability are examined in the dynamic shaking table experiments. Displacement values measured by the displacement meter and the presented system are compared. The experimental results indicate that it is possible to measure the ground strain by the presented system, although necessity to improve the accuracy is also recognized.
To identify dynamic parameters of structural systems, we have to solve non-linear optimization problems because the system transfer equation of a structural system is usually a non-linear function of the system's parameters. The purpose of this paper is to develop a method to linearize an observation equation with respect to structural parameters, which is derived from the system transferequation, and used it to identify the dynamic parameters of linear and non- linear dynamic structural systems. The numerical examples were satisfactory for identifying the dynamic parameters of model structures with eight degrees of freedom.
KEYWORDS: Digital filtering, Filtering (signal processing), System identification, Dynamical systems, Complex systems, Electronic filtering, Nonlinear filtering, Systems modeling, Linear filtering, Algorithm development
The adaptive H(infinity ) filter was established by adding a forgetting factor to the H(infinity ) filter in order to identify structural systems with time-varying dynamic characteristics. The Akaike-Bayes Information Criterion was used to determine the optimal forgetting factor. The behavior of the adaptive H(infinity ) filter in identifying time-varying structural systems was studied in detail by checking digital simulation results obtained using both the adaptive H(infinity ) and Kalman filters. These results show that the adaptive H(infinity ) filter efficiently tracks variation in the structural parameters and is more robust than the adaptive Kalman filter for identifying structural systems with time-varying dynamic characteristics.
By adding a function of memory fading for past observation data to the Kalman filter which has often been used as a time marching identification algorithm we developed an adaptive Kalman filter scheme. The rate of memory fading was defined by a forgetting factor multiplying to pre- information term at each time step. In order to track fast variation in the system parameters the value of forgetting factor should be small. On the other hand, to remove the random noise from the signal, the number of sample points used at any time should be large enough, that is, the large value of forgetting factor should be used. There is, therefore, a trade-off between the time-tracking ability and the noise sensitivity of the identification. The Akaike- Bayes Information Criteria was applied to determine the optimal forgetting factor. Applications of the newly developed identification algorithm to a multi-degree of structural system with non-stationary dynamic characteristic worked out well.
This paper deals with the identification of the dynamic characteristics of structural system. The relevant neural network characteristics of learning algorithm are discussed in the context of system identification. Because of self-learning nature of neural network the identified dynamic characteristics are strongly affected by the level of noise contained in the teaching signals. Using the Kalman filtering technique, a method to identify the dynamic characteristics of structural system proof against contaminating noise in teaching signals has been developed.
A new closed-open-loop optimal control algorithm is proposed that has been derived by minimizing the sum of the quadratic time-dependent performance index and the seismic energy input to the structural system. We modify the developed algorithm as to be able to take into account the dynamic soil-structure interaction phenomena. Structural responses are well suppressed not only for the system with soil-structure interaction effect and also for that without one.
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