The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Francisco L. Silva-gonzález - One of the best experts on this subject based on the ideXlab platform.
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Modal Response analysis of multi-support structures using a random vibration approach: Analysis of Multi-support Structures Using a Random Vibration Approach
Earthquake Engineering & Structural Dynamics, 2015Co-Authors: Ernesto Heredia-zavoni, Sandra Santa-cruz, Francisco L. Silva-gonzálezAbstract:Summary A formulation is developed for Modal Response analysis of multi-support structures using a random vibration approach. The spectral moments of the structural Response are rigorously decomposed into contributions from spectral moments of uncoupled Modal Responses. An advantage of the proposed formulation is that the total dynamic Response can be obtained on the basis of mode by mode uncoupled analyses. The contributions to the total Response from Modal Responses under individual support ground motions and under cross-correlated pairs of support ground motions can be recognized explicitly. The application and performance of the formulation is illustrated by means of an example using a well-established coherency spectrum model and widely known power spectra models, such as white noise and Kanai–Tajimi. The first three spectral moments of displacement, shear, and bending moment Responses are computed, showing that the formulation produces the same results as the exact solution. Copyright © 2015 John Wiley & Sons, Ltd.
Keith D. Hjelmstad - One of the best experts on this subject based on the ideXlab platform.
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STRUCTURAL DAMAGE DETECTION AND ASSESSMENT FROM Modal Response
Journal of Engineering Mechanics, 2003Co-Authors: Thanyawat Pothisiri, Keith D. HjelmstadAbstract:This paper presents a global damage detection and assessment algorithm based on a parameter estimation method using a finite-element model and the measured Modal Response of a structure. Damage is characterized as a reduction of the member constitutive parameter from a known baseline value. An optimization scheme is proposed to localize damaged parts of the structure. The algorithm accounts for the possibility of multiple solutions to the parameter estimation problem that arises from using spatially sparse measurements. Errors in parameter estimates caused by sensitivity to measurement noise are reduced by selecting a near-optimal measurement set from the data at each stage of the localization algorithm. Damage probability functions are computed upon completion of the localization process for candidate elements. Monte Carlo methods are used to compute the required probabilities based on the statistical distributions of the parameters for the damaged and the associated baseline structure. The algorithm is tested in a numerical simulation environment using a planar bridge truss as a model problem.
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STRATEGY FOR FINDING A NEAR-OPTIMAL MEASUREMENT SET FOR PARAMETER ESTIMATION FROM Modal Response
Journal of Sound and Vibration, 2002Co-Authors: Thanyawat Pothisiri, Keith D. HjelmstadAbstract:Algorithms that estimate structural parameters from Modal Response using least-squares minimization of force or displacement residuals generally do not have unique solutions when the data are spatially sparse. The number and character of the multiple solutions depend upon the physical features of the structure and the locations of the Response measurements. It has been observed that both the number of solutions and the sensitivity of the parameter estimates to measurement noise is greatly influenced by the choice of measurement locations. In this paper, we present a heuristic method to select a near-optimal subset of measurement locations starting from a particular set of measurements, by minimizing the sensitivity of the parameter estimates with respect to observed Response. The statistical properties of solution clusters generated from a Monte Carlo samples of noisy data are used to determine the best candidate measurement to be dropped from the current set. The process is repeated until solution sensitivity cannot be significantly reduced. We also show that the laborious Monte Carlo computations can be avoided in certain cases by using a direct computation of sensitivity estimates. A numerical example is provided to illustrate the method and to examine the performance of the proposed algorithm.
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Optimum Sensitivity-Based Statistical Parameters Estimation from Modal Response
AIAA Journal, 2001Co-Authors: Yoshikazu Araki, Keith D. HjelmstadAbstract:Based on the concept of optimum sensitivity, we present a method for estimating the mean and covariance of parameters of a mechanical system from the statistics of its measured Modal Response. The optimum sensitivity, defined as the sensitivity of system parameters with respect to observed output, is obtained by direct differentiation of the Kuhn-Tucker optimality criteria for a nonlinear least-squares output error estimator. With the optimum sensitivity derivatives up to the second order, we can estimate the second-order approximation of both the mean and covariance of the system parameters by applying methods developed originally for evaluating the output of uncertain systems based on the more conventional notion of sensitivity, the sensitivity of system Response with respect to system parameters. The present approach allows us to assess the bias due to nonlinearities in the least-squares estimator whereas conventional sensitivity-based methods do not. Furthermore, the present method is generally much more efficient than Monte Carlo simulation because nonlinear optimization is performed only once. We demonstrate through example problems that, compared to the conventional sensitivity-based methods, the present method provides statistical indices that are more consistent with those obtained by Monte Carlo simulation.
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CRACK IDENTIFICATION IN A CANTILEVER BEAM FROM Modal Response
Journal of Sound and Vibration, 1996Co-Authors: Keith D. Hjelmstad, S. ShinAbstract:A damage detection and assessment algorithm is developed based on system identification using a finite element model and the measured Modal Response of a structure. The measurements are assumed to be sparse and polluted with noise. A change in an element constitutive property from a baseline value is taken as indicative of damage. An adaptive parameter grouping updating scheme is proposed to localize the damage zones in the structure and a Monte Carlo method is used with a data perturbation scheme to provide a statistical basis for assessing damage. Damage indices computed from the Monte Carlo sample of data perturbations are used to assess damage. The threshold values, which distinguish damage from measurement noise, are established through Monte Carlo simulation on the baseline structure. The proposed algorithm is applied to the problem of locating a crack in a cantilever beam. A Bernoulli-Euler beam model and a plane stress model are employed to illustrate the use of the method and compare the efficacy of the two models for crack detection.
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On building finite element models of structures from Modal Response
Earthquake Engineering & Structural Dynamics, 1995Co-Authors: Keith D. Hjelmstad, Mo. R. BananAbstract:We develope two algorithms for estimating member stiffness and masses of a structure from measured Modal Response in conjunction with a finite element model of the structure. The mathematical model has known geometry and topology and parametized constitutive properties. A few of the natural frequencies are measured and the corresponding modes are sampled at certain locations in space. The proposed algorithms are based on the concept of minimizing the sum of the squares of errors, specified as an index of discrepancy between the model and the structure, over all of the measured modes
Ernesto Heredia-zavoni - One of the best experts on this subject based on the ideXlab platform.
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Modal Response analysis of multi-support structures using a random vibration approach: Analysis of Multi-support Structures Using a Random Vibration Approach
Earthquake Engineering & Structural Dynamics, 2015Co-Authors: Ernesto Heredia-zavoni, Sandra Santa-cruz, Francisco L. Silva-gonzálezAbstract:Summary A formulation is developed for Modal Response analysis of multi-support structures using a random vibration approach. The spectral moments of the structural Response are rigorously decomposed into contributions from spectral moments of uncoupled Modal Responses. An advantage of the proposed formulation is that the total dynamic Response can be obtained on the basis of mode by mode uncoupled analyses. The contributions to the total Response from Modal Responses under individual support ground motions and under cross-correlated pairs of support ground motions can be recognized explicitly. The application and performance of the formulation is illustrated by means of an example using a well-established coherency spectrum model and widely known power spectra models, such as white noise and Kanai–Tajimi. The first three spectral moments of displacement, shear, and bending moment Responses are computed, showing that the formulation produces the same results as the exact solution. Copyright © 2015 John Wiley & Sons, Ltd.
Norden E Huang - One of the best experts on this subject based on the ideXlab platform.
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identification of natural frequencies and dampings of in situ tall buildings using ambient wind vibration data
Journal of Engineering Mechanics-asce, 2004Co-Authors: J N Yang, Ying Lei, Silian Lin, Norden E HuangAbstract:An accurate prediction for the Response of tall buildings subject to strong wind gusts or earthquakes requires the information of in situ dynamic properties of the building, including natural frequencies and damping ratios. This paper presents a method of identifying natural frequencies and damping ratios of in situ tall buildings using ambient wind vibration data. Our approach is based on the empirical mode decomposition (EMD) method, the random decrement technique (RDT), and the Hilbert–Huang transform. Our method requires only one acceleration sensor. The noisy measurement of the building acceleration is first processed through the EMD method to determine the Response of each mode. Then, RDT is used to obtain the free vibration Modal Response. Finally, the Hilbert transform is applied to each free vibration Modal Response to identify natural frequencies and damping ratios of in situ tall buildings. The application of the proposed methodology is demonstrated in detail using simulated Response data of a ...
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system identification of linear structures based on hilbert huang spectral analysis part 2 complex modes
Earthquake Engineering & Structural Dynamics, 2003Co-Authors: J N Yang, Ying Lei, Shuwen Pan, Norden E HuangAbstract:A method, based on the Hilbert–Huang spectral analysis, has been proposed by the authors to identify linear structures in which normal modes exist (i.e., real eigenvalues and eigenvectors). Frequently, all the eigenvalues and eigenvectors of linear structures are complex. In this paper, the method is extended further to identify general linear structures with complex modes using the free vibration Response data polluted by noise. Measured Response signals are first decomposed into Modal Responses using the method of Empirical Mode Decomposition with intermittency criteria. Each Modal Response contains the contribution of a complex conjugate pair of modes with a unique frequency and a damping ratio. Then, each Modal Response is decomposed in the frequency–time domain to yield instantaneous phase angle and amplitude using the Hilbert transform. Based on a single measurement of the impulse Response time history at one appropriate location, the complex eigenvalues of the linear structure can be identified using a simple analysis procedure. When the Response time histories are measured at all locations, the proposed methodology is capable of identifying the complex mode shapes as well as the mass, damping and stiffness matrices of the structure. The effectiveness and accuracy of the method presented are illustrated through numerical simulations. It is demonstrated that dynamic characteristics of linear structures with complex modes can be identified effectively using the proposed method. Copyright © 2003 John Wiley & Sons, Ltd.
Mo. R. Banan - One of the best experts on this subject based on the ideXlab platform.
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On building finite element models of structures from Modal Response
Earthquake Engineering & Structural Dynamics, 1995Co-Authors: Keith D. Hjelmstad, Mo. R. BananAbstract:We develope two algorithms for estimating member stiffness and masses of a structure from measured Modal Response in conjunction with a finite element model of the structure. The mathematical model has known geometry and topology and parametized constitutive properties. A few of the natural frequencies are measured and the corresponding modes are sampled at certain locations in space. The proposed algorithms are based on the concept of minimizing the sum of the squares of errors, specified as an index of discrepancy between the model and the structure, over all of the measured modes