Output-only structural identification is developed by a refined Frequency Domain Decomposition（rFDD） approach, towards assessing current modal properties of heavy-damped buildings（in terms of identification challe...Output-only structural identification is developed by a refined Frequency Domain Decomposition（rFDD） approach, towards assessing current modal properties of heavy-damped buildings（in terms of identification challenge）, under strong ground motions. Structural responses from earthquake excitations are taken as input signals for the identification algorithm. A new dedicated computational procedure, based on coupled Chebyshev Type Ⅱ bandpass filters, is outlined for the effective estimation of natural frequencies, mode shapes and modal damping ratios. The identification technique is also coupled with a Gabor Wavelet Transform, resulting in an effective and self-contained time-frequency analysis framework. Simulated response signals generated by shear-type frames（with variable structural features） are used as a necessary validation condition. In this context use is made of a complete set of seismic records taken from the FEMA P695 database, i.e. all 44 ＂Far-Field＂（22 NS, 22 WE） earthquake signals. The modal estimates are statistically compared to their target values, proving the accuracy of the developed algorithm in providing prompt and accurate estimates of all current strong ground motion modal parameters. At this stage, such analysis tool may be employed for convenient application in the realm of Earthquake Engineering, towards potential Structural Health Monitoring and damage detection purposes.展开更多
The development of damage detection techniques for offshore jacket structures is vital to prevent catastrophic events. This paper applies a frequency response based method for the purpose of structural health monitori...The development of damage detection techniques for offshore jacket structures is vital to prevent catastrophic events. This paper applies a frequency response based method for the purpose of structural health monitoring. In efforts to fulfill this task, concept of the minimum rank perturbation theory has been utilized. The present article introduces a promising methodology to select frequency points effectively. To achieve this goal, modal strain energy ratio of each member was evaluated at different natural frequencies of structure in order to identify the sensitive frequency domain for damage detection. The proposed methodology opens up the possibility of much greater detection efficiency. In addition, the performance of the proposed method was evaluated in relation to multiple damages. The aforementioned points are illustrated using the numerical study of a two dimensional jacket platform, and the results proved to be satisfactory utilizing the proposed methodology.展开更多
Although a detailed finite element(FE) model provides more precise results, a lumped-mass stick(LMS) model is preferred because of its simplicity and rapid computational time. However, the reliability of LMS models ha...Although a detailed finite element(FE) model provides more precise results, a lumped-mass stick(LMS) model is preferred because of its simplicity and rapid computational time. However, the reliability of LMS models has been questioned especially for structures dominated by higher modes and seismic inputs. Normally, the natural frequencies and dynamic responses of a LMS model based on tributary area mass consideration are different from the results of the FE model. This study proposes a basic updating technique to overcome these discrepancies; the technique employs the identical modal response, D(t), to the detailed FE model. The parameter D(t) is a time variable function in the dynamic response composition and it depends on frequency and damping ratio for each mode, independent of the structure's mode shapes. The identical response D(t) for each mode is obtained from the frequency adaptive LMS model; the adaptive LMS model which can provide identical modal frequencies as the detailed FE model. Theoretical backgrounds and formulations of the updating technique are proposed. To validate the updating technique, two types of structures(a symmetric straight column and an unsymmetric T-shaped structure) are considered. From the seismic response results including base shear and base moment, the updating technique considerably improves the seismic response accuracy of the tributary area-based LMS model.展开更多
Nonlinear behavior is important in the vibration test of engineering structures. In this study, a constant response vibration test is proposed for nonlinear element extraction. The method is based on the principle of ...Nonlinear behavior is important in the vibration test of engineering structures. In this study, a constant response vibration test is proposed for nonlinear element extraction. The method is based on the principle of Harmonic Balance Method (HBM). The stiffness or damping can be regarded as constant for particular steady displacement or velocity response. The displacement or velocity is controlled as a constant in the test. Then the measured Frequency Response Function(FRF) is obtained. The equivalent stiffness or damping is estimated using FRFs for a particular vibration response level. The displacement-dependent stiffness and velocity-dependent damping are fitted to describe the unknown non-linearity. The nonlinear spring and damping force can be obtained by combining the fitting results with HBM using first-order expansion. Constant response vibration test is illustrated through experimental setup to verify its effectiveness. Experimental results show that the procedure is capable of achieving an accurate parameter identification of nonlinear damping and stiffness, which is hopeful for industrial application.展开更多
In most of real operational conditions only response data are measurable while the actual excitations are unknown, so modal parameter must be extracted only from responses. This paper gives a theoretical formulation f...In most of real operational conditions only response data are measurable while the actual excitations are unknown, so modal parameter must be extracted only from responses. This paper gives a theoretical formulation for the cross-correlation functions and cross-power spectra between the outputs under the assumption of white-noise excitation. It widens the field of modal analysis under ambient excitation because many classical methods by impulse response functions or frequency response functions can be used easily for modal analysis under unknown excitation. The Polyreference Complex Exponential method and Eigensystem Realization Algorithm using cross-correlation functions in time domain and Orthogonal Polynomial method using cross-power spectra in frequency domain are applied to a steel frame to extract modal parameters under operational conditions. The modal properties of the steel frame from these three methods are compared with those from frequency response functions analysis. The results show that the modal analysis method using cross-correlation functions or cross-power spectra presented in this paper can extract modal parameters efficiently under unknown excitation.展开更多
In this paper, we show how Operating Deflection Shapes (ODS’s) andmode shapes can be obtained experimentally from measurements thatare made using only two sensors and two short wires to connect them to amulti-channel...In this paper, we show how Operating Deflection Shapes (ODS’s) andmode shapes can be obtained experimentally from measurements thatare made using only two sensors and two short wires to connect them to amulti-channel acquisition system. This new test procedure is depicted inFigure 1. Not only is the equipment required to do a test much more costeffective, but this method can be used to test any sized test article, especiallylarge ones.展开更多
For modal parameter estimation of offshore structures, one has to deal with two challenges: 1) identify the interested frequencies, and 2) reduce the number of false modes. In this article, we propose an improved meth...For modal parameter estimation of offshore structures, one has to deal with two challenges: 1) identify the interested frequencies, and 2) reduce the number of false modes. In this article, we propose an improved method of modal parameter estimation by reconstructing a new signal only with interested frequencies. The approach consists of three steps: 1) isolation and reconstruction of interested frequencies using FFT filtering, 2) smoothness of reconstructed signals, and 3) extraction of interested modal parameters in time domain. The theoretical improvement is that the frequency response function(FRF) of filtered signals is smoothed based on singular value decomposition technique. The elimination of false modes is realized by reconstructing a block data matrix of the eigensystem realization algorithm(ERA) using the filtered and smoothed signals. The advantage is that the efficiency of the identification process of modal parameters will be improved greatly without introducing any false modes. A five-DOF mass-spring system is chosen to illustrate the procedure and demonstrate the performance of the proposed scheme. Numerical results indicate that interested frequencies can be isolated successfully using FFT filtering, and unexpected peaks in auto spectral density can be removed effectively. In addition, interested modal parameters, such as frequencies and damping ratios, can be identified properly by reconstructing the Hankel matrix with a small dimension of ERA, even the original signal has measurement noises.展开更多
Because robotic milling has become an important means for machining significant large parts,obtaining the structural frequency response function(FRF)of a milling robot is an important basis for machining process optim...Because robotic milling has become an important means for machining significant large parts,obtaining the structural frequency response function(FRF)of a milling robot is an important basis for machining process optimization.However,because of its articulated serial structure,a milling robot has an enormous number of operating postures,and its dynamics are affected by the motion state.To accurately obtain the FRF in the operating state of a milling robot,this paper proposes a method based on the structural modification concept.Unlike the traditional excitation method,the proposed method uses robot joint motion excitation instead of hammering excitation to realize automation.To address the problem of the lack of information brought by motion excitation,which leads to inaccurate FRF amplitudes,this paper derives the milling robot regularization theory based on the sensitivity of structural modification,establishes the modal regularization factor,and calibrates the FRF amplitude.Compared to the commonly used manual hammering experiments,the proposed method has high accuracy and reliability when the milling robot is in different postures.Because the measurement can be performed directly and automatically in the operation state,and the problem of inaccurate amplitudes is solved,the proposed method provides a basis for optimizing the machining posture of a milling robot and improving machining efficiency.展开更多
Data-driven damage-detection schemes are usually unsupervised machine-learning models in practice,as these do not require any training.Vibration-based features are commonly used in these schemes but often require seve...Data-driven damage-detection schemes are usually unsupervised machine-learning models in practice,as these do not require any training.Vibration-based features are commonly used in these schemes but often require several other parameters to accurately correlate with damage,as they may not globally represent the model,making them less sensitive to damage.Modal data,such as frequency response functions(FRFs)and principal component analysis(PCA)reduced FRFs(PCA-FRFs),inherits the dynamic characteristics of the structure,and it changes when damage occurs,thus showing sensitivity to damage.However,noise from the environment or external sources such as wind,operating machines,or the in-service system itself,can reduce the modal data's sensitivity to damage if not handled properly,which affects damage-detection accuracy.This study proposes a noise-robust operational modal-based structural damage-detection scheme that uses impact-synchronous modal analysis(ISMA)to generate clean,static-like FRFs for damage diagnosis.ISMA allows modal data collection without requiring shutdown conditions,and its denoising feature aids in generating clean,static-like FRFs for damage diagnosis.Our results showed that the FRFs obtained through ISMA under noise conditions have frequency response assurance criterion(FRAC)and cross signature assurance criterion(CSAC)scores greater than 0.9 when compared with FRFs obtained through experimental modal analysis(EMA)under static conditions;this validates the denoising feature of ISMA.When the denoised FRFs are reduced to PCA-FRFs and used in an unsupervised learning-based damage-detection scheme,zero false alarms occur.展开更多
基金Public research funding from“Fondi di Ricerca d’Ateneo ex 60%” and a ministerial doctoral grantfunds at the ISA Doctoral School,University of Bergamo,Department of Engineering and Applied Sciences (Dalmine)
文摘Output-only structural identification is developed by a refined Frequency Domain Decomposition（rFDD） approach, towards assessing current modal properties of heavy-damped buildings（in terms of identification challenge）, under strong ground motions. Structural responses from earthquake excitations are taken as input signals for the identification algorithm. A new dedicated computational procedure, based on coupled Chebyshev Type Ⅱ bandpass filters, is outlined for the effective estimation of natural frequencies, mode shapes and modal damping ratios. The identification technique is also coupled with a Gabor Wavelet Transform, resulting in an effective and self-contained time-frequency analysis framework. Simulated response signals generated by shear-type frames（with variable structural features） are used as a necessary validation condition. In this context use is made of a complete set of seismic records taken from the FEMA P695 database, i.e. all 44 ＂Far-Field＂（22 NS, 22 WE） earthquake signals. The modal estimates are statistically compared to their target values, proving the accuracy of the developed algorithm in providing prompt and accurate estimates of all current strong ground motion modal parameters. At this stage, such analysis tool may be employed for convenient application in the realm of Earthquake Engineering, towards potential Structural Health Monitoring and damage detection purposes.
基金Financial Support by the Pars Oil and Gas Company(Grant No. 88-065)
文摘The development of damage detection techniques for offshore jacket structures is vital to prevent catastrophic events. This paper applies a frequency response based method for the purpose of structural health monitoring. In efforts to fulfill this task, concept of the minimum rank perturbation theory has been utilized. The present article introduces a promising methodology to select frequency points effectively. To achieve this goal, modal strain energy ratio of each member was evaluated at different natural frequencies of structure in order to identify the sensitive frequency domain for damage detection. The proposed methodology opens up the possibility of much greater detection efficiency. In addition, the performance of the proposed method was evaluated in relation to multiple damages. The aforementioned points are illustrated using the numerical study of a two dimensional jacket platform, and the results proved to be satisfactory utilizing the proposed methodology.
基金Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education,Science and Technology under Grant No.20151D1A3A01020017
文摘Although a detailed finite element(FE) model provides more precise results, a lumped-mass stick(LMS) model is preferred because of its simplicity and rapid computational time. However, the reliability of LMS models has been questioned especially for structures dominated by higher modes and seismic inputs. Normally, the natural frequencies and dynamic responses of a LMS model based on tributary area mass consideration are different from the results of the FE model. This study proposes a basic updating technique to overcome these discrepancies; the technique employs the identical modal response, D(t), to the detailed FE model. The parameter D(t) is a time variable function in the dynamic response composition and it depends on frequency and damping ratio for each mode, independent of the structure's mode shapes. The identical response D(t) for each mode is obtained from the frequency adaptive LMS model; the adaptive LMS model which can provide identical modal frequencies as the detailed FE model. Theoretical backgrounds and formulations of the updating technique are proposed. To validate the updating technique, two types of structures(a symmetric straight column and an unsymmetric T-shaped structure) are considered. From the seismic response results including base shear and base moment, the updating technique considerably improves the seismic response accuracy of the tributary area-based LMS model.
文摘Nonlinear behavior is important in the vibration test of engineering structures. In this study, a constant response vibration test is proposed for nonlinear element extraction. The method is based on the principle of Harmonic Balance Method (HBM). The stiffness or damping can be regarded as constant for particular steady displacement or velocity response. The displacement or velocity is controlled as a constant in the test. Then the measured Frequency Response Function(FRF) is obtained. The equivalent stiffness or damping is estimated using FRFs for a particular vibration response level. The displacement-dependent stiffness and velocity-dependent damping are fitted to describe the unknown non-linearity. The nonlinear spring and damping force can be obtained by combining the fitting results with HBM using first-order expansion. Constant response vibration test is illustrated through experimental setup to verify its effectiveness. Experimental results show that the procedure is capable of achieving an accurate parameter identification of nonlinear damping and stiffness, which is hopeful for industrial application.
基金Item of the 9-th F ive Plan of the Aeronautical Industrial Corporation
文摘In most of real operational conditions only response data are measurable while the actual excitations are unknown, so modal parameter must be extracted only from responses. This paper gives a theoretical formulation for the cross-correlation functions and cross-power spectra between the outputs under the assumption of white-noise excitation. It widens the field of modal analysis under ambient excitation because many classical methods by impulse response functions or frequency response functions can be used easily for modal analysis under unknown excitation. The Polyreference Complex Exponential method and Eigensystem Realization Algorithm using cross-correlation functions in time domain and Orthogonal Polynomial method using cross-power spectra in frequency domain are applied to a steel frame to extract modal parameters under operational conditions. The modal properties of the steel frame from these three methods are compared with those from frequency response functions analysis. The results show that the modal analysis method using cross-correlation functions or cross-power spectra presented in this paper can extract modal parameters efficiently under unknown excitation.
文摘In this paper, we show how Operating Deflection Shapes (ODS’s) andmode shapes can be obtained experimentally from measurements thatare made using only two sensors and two short wires to connect them to amulti-channel acquisition system. This new test procedure is depicted inFigure 1. Not only is the equipment required to do a test much more costeffective, but this method can be used to test any sized test article, especiallylarge ones.
基金the financial support of the Excellent Youth Foundation of Shandong Scientific Committee(Grant no.JQ201512)the National Natural Science Foundation of China(Grant nos.51279188+1 种基金5147918451522906)
文摘For modal parameter estimation of offshore structures, one has to deal with two challenges: 1) identify the interested frequencies, and 2) reduce the number of false modes. In this article, we propose an improved method of modal parameter estimation by reconstructing a new signal only with interested frequencies. The approach consists of three steps: 1) isolation and reconstruction of interested frequencies using FFT filtering, 2) smoothness of reconstructed signals, and 3) extraction of interested modal parameters in time domain. The theoretical improvement is that the frequency response function(FRF) of filtered signals is smoothed based on singular value decomposition technique. The elimination of false modes is realized by reconstructing a block data matrix of the eigensystem realization algorithm(ERA) using the filtered and smoothed signals. The advantage is that the efficiency of the identification process of modal parameters will be improved greatly without introducing any false modes. A five-DOF mass-spring system is chosen to illustrate the procedure and demonstrate the performance of the proposed scheme. Numerical results indicate that interested frequencies can be isolated successfully using FFT filtering, and unexpected peaks in auto spectral density can be removed effectively. In addition, interested modal parameters, such as frequencies and damping ratios, can be identified properly by reconstructing the Hankel matrix with a small dimension of ERA, even the original signal has measurement noises.
基金supported by the National Natural Science Foundation of China(Grant No.52175463)Key R&D plan of Hubei Province(Grant No.2022BAA055)State Key Laboratory of Smart Manufacturing for Special Vehicles and Transmission System(Grant No.GZ2022KF008)。
文摘Because robotic milling has become an important means for machining significant large parts,obtaining the structural frequency response function(FRF)of a milling robot is an important basis for machining process optimization.However,because of its articulated serial structure,a milling robot has an enormous number of operating postures,and its dynamics are affected by the motion state.To accurately obtain the FRF in the operating state of a milling robot,this paper proposes a method based on the structural modification concept.Unlike the traditional excitation method,the proposed method uses robot joint motion excitation instead of hammering excitation to realize automation.To address the problem of the lack of information brought by motion excitation,which leads to inaccurate FRF amplitudes,this paper derives the milling robot regularization theory based on the sensitivity of structural modification,establishes the modal regularization factor,and calibrates the FRF amplitude.Compared to the commonly used manual hammering experiments,the proposed method has high accuracy and reliability when the milling robot is in different postures.Because the measurement can be performed directly and automatically in the operation state,and the problem of inaccurate amplitudes is solved,the proposed method provides a basis for optimizing the machining posture of a milling robot and improving machining efficiency.
基金supported by the Ministry of Higher Education for the Fundamental Research Grant Scheme(No.FRGS/1/2022/TK10/UM/02/29)the SD Advance Engineering Sdn.Bhd.(No.PV032-2018)+2 种基金the SATU Joint Research University Grant(No.ST020-2020)the Impact-Oriented Interdisciplinary Research Grant(No.IIRG007B-2019)awarded to Zhi Chao ONGthe Advanced Shock and Vibration Research(ASVR)Group of University of Malaya.
文摘Data-driven damage-detection schemes are usually unsupervised machine-learning models in practice,as these do not require any training.Vibration-based features are commonly used in these schemes but often require several other parameters to accurately correlate with damage,as they may not globally represent the model,making them less sensitive to damage.Modal data,such as frequency response functions(FRFs)and principal component analysis(PCA)reduced FRFs(PCA-FRFs),inherits the dynamic characteristics of the structure,and it changes when damage occurs,thus showing sensitivity to damage.However,noise from the environment or external sources such as wind,operating machines,or the in-service system itself,can reduce the modal data's sensitivity to damage if not handled properly,which affects damage-detection accuracy.This study proposes a noise-robust operational modal-based structural damage-detection scheme that uses impact-synchronous modal analysis(ISMA)to generate clean,static-like FRFs for damage diagnosis.ISMA allows modal data collection without requiring shutdown conditions,and its denoising feature aids in generating clean,static-like FRFs for damage diagnosis.Our results showed that the FRFs obtained through ISMA under noise conditions have frequency response assurance criterion(FRAC)and cross signature assurance criterion(CSAC)scores greater than 0.9 when compared with FRFs obtained through experimental modal analysis(EMA)under static conditions;this validates the denoising feature of ISMA.When the denoised FRFs are reduced to PCA-FRFs and used in an unsupervised learning-based damage-detection scheme,zero false alarms occur.
