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1.
Based on the Hilbert–Huang spectral analysis, a method is proposed to identify multi‐degree‐of‐freedom (MDOF) linear systems using measured free vibration time histories. For MDOF systems, the normal modes have been assumed to exist. In this method, the measured response data, which are polluted by noises, are first decomposed into modal responses using the empirical mode decomposition (EMD) approach with intermittency criteria. Then, the Hilbert transform is applied to each modal response to obtain the instantaneous amplitude and phase angle time histories. A linear least‐square fit procedure is proposed to identify the natural frequency and damping ratio from the instantaneous amplitude and phase angle for each modal response. Based on a single measurement of the free vibration time history at one appropriate location, natural frequencies and damping ratios can be identified. When the responses at all degrees of freedom are measured, the mode shapes and the physical mass, damping and stiffness matrices of the structure can be determined. The applications of the proposed method are illustrated using three linear systems with different dynamic characteristics. Numerical simulation results demonstrate that the proposed system identification method yields quite accurate results, and it offers a new and effective tool for the system identification of linear structures in which normal modes exist. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
2.
The primary objective of this paper is to develop output only modal identifi cation and structural damage detection.Identif ication of multi-degree of freedom(MDOF) linear time invariant(LTI) and linear time variant(LTV—due to damage) systems based on Time-frequency(TF) techniques—such as short-time Fourier transform(STFT),empirical mode decomposition(EMD),and wavelets—is proposed.STFT,EMD,and wavelet methods developed to date are reviewed in detail.In addition a Hilbert transform(HT) approach to determine ... 相似文献
3.
The energy transmitting boundary used in programs such as FLUSH and ALUSH is a very accurate and useful technique for the earthquake response analysis of soil–structure interaction systems. However, it is applicable only to linear analyses or equivalent linear analyses, because it can be calculated only in the frequency domain. The author has proposed methods for transforming frequency-dependent impedance into the time domain. In this paper, an earthquake response analysis method for a soil–structure interaction system, using the energy transmitting boundary in the time domain, is proposed. First, the transform of the transmitting boundary matrices to the time domain using the methods proposed by the author is studied. Then, linear and nonlinear time history earthquake response analyses using the boundary are performed. Through these studies, the validity and efficiency of the proposed methods are confirmed. 相似文献
4.
A technique to improve the empirical mode decomposition in the Hilbert-Huang transform 总被引：2，自引：0，他引：2
The Hilbert-based time-frequency analysis has promising capacity to reveal the time-variant behaviors of a system. To admit
well-behaved Hilbert transforms, component decomposition of signals must be performed beforehand. This was first systematically
implemented by the empirical mode decomposition (EMD) in the Hilbert-Huang transform, which can provide a time-frequency representation
of the signals. The EMD, however, has limitations in distinguishing different components in narrowband signals commonly found
in free-decay vibration signals. In this study, a technique for decomposing components in narrowband signals based on waves’
beating phenomena is proposed to improve the EMD, in which the time scale structure of the signal is unveiled by the Hilbert
transform as a result of wave beating, the order of component extraction is reversed from that in the EMD and the end effect
is confined. The proposed technique is verified by performing the component decomposition of a simulated signal and a free
decay signal actually measured in an instrumented bridge structure. In addition, the adaptability of the technique to time-variant
dynamic systems is demonstrated with a simulated time-variant MDOF system. 相似文献
5.
A step-by-step integration method is proposed to compute within the framework of the conventional mode superposition technique the response of bilinear hysteretic structures subjected to earthquake ground motions. The method is computationally efficient because only a few modes are needed to obtain an accurate estimate of such a response, and because it does not require the use of excessively small time steps to avoid problems of accuracy or stability. It is developed on the basis that the non-linear terms in the equations of motion for non-linear systems may be considered as additional external forces, and the fact that by doing so such equations of motion can be interpreted as the equations of motion of an equivalent linear system, excited by a modified ground motion. These linear equations are then subjected to a conventional modal decomposition and transformed, as with linear systems, into a set of independent differential equations, each representing the system's response in one of its modes of vibration. To increase the efficiency of the method and account properly for the participation of higher modes, these independent equations are solved using the Nigam-Jennings technique in conjunction with the so-called mode acceleration method. The accuracy and efficiency of the method is verified by means of a comparative study with solutions obtained with a conventional direct integration method. In this comparative study, including only a few modes, the proposed method accurately predicts the seismic response of three two-dimensional frame structures, but requiring only, on an average, about 47 per cent less computer time than when the direct integration method is used. 相似文献
6.
Techniques developed for structural identification of a structural model are typically based on information regarding the response and the forcing actions. However, in some situations it can be necessary, or simply useful, to refer only to the measured responses. In this paper we describe a technique suitable for identifying the modal model of a spatial frame in the frequency domain when the seismic input is unknown both in time contents and direction. In some previous theoretical works we established that this identification problem has a unique solution when at least three time‐history responses are known. Here numerical techniques are developed which allow the evaluation of the modal quantities in practice. Numerical applications are carried out on plane and spatial framed structures by using a modal model which may be complete, including all the structure's modes, or incomplete, including only the lowest modes. In most cases the obtained results are satisfactory. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
7.
The non‐linear analysis of single‐degree‐of‐freedom (SDOF) systems provides the essential background information for both strength‐based design and displacement‐based evaluation/design methodologies through the development of the inelastic response spectra. The recursive solution procedure called the piecewise exact method, which is efficiently used for the response analysis of linear SDOF systems, is re‐formulated in this paper in a unified format to analyse the non‐linear SDOF systems with multi‐linear hysteresis models. The unified formulation is also capable of handling the P‐delta effect, which generally involves the negative post‐yield stiffness of the hysteresis loops. The attractiveness of the method lies in the fact that it provides the exact solution when the loading time history is composed of piecewise linear segments, a condition that is perfectly satisfied for the earthquake excitation. Based on simple recursive relationships given for positive, negative and zero effective stiffnesses, the unified form of the piecewise exact method proves to be an extremely powerful and probably the best tool for the SDOF inelastic time‐history and response spectrum analysis including the P‐delta effect. A number of examples are presented to demonstrate the implementation of the method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
8.
In this article two new approaches are presented for time domain identification of base isolated buildings from recorded response during earthquakes: (1) a least squares technique with time segments is developed to identify the piece-wise linear system properties; and (2) an observer is used to estimate the unmeasured states and initial conditions of different time segments. In base isolated buildings changes in dynamic properties occur during earthquake response due to nonlinear behavior. Hence, a multi-input and multi-output technique using time segments is developed for piece-wise linear system identification. The primary advantage of the developed time segmented technique is that it can be applied to windows of time history instead of the entire duration of earthquake response. The developed technique (1) starts with identification using the entire duration of the earthquake response; (2) evaluation of time segments during which the identified response differs significantly from the recorded response to establish windows of time history during which refined identification is necessary; and (3) identification of the change in dynamic properties in the established windows using the observer based time segmented least squares approach. Only partial state measurements are usually available for identification. Hence, an observer is used to estimate the unmeasured states and initial conditions needed for different time segments. By comparing identified response with recorded response, of an actual base isolated building which experienced Northridge earthquake, it is shown that the change in dynamic system parameters, such as periods and damping ratios, due to nonlinear response, are reliably estimated using the presented technique. 相似文献
9.
Fiona J.L. Reid Alexandre Bertrand † Alan T. McInally ‡ Colin MacBeth 《Geophysical Prospecting》2005,53(2):253-263
A new method for time‐lapse signal separation and enhancement using singular‐value decomposition is presented. Singular‐value decomposition is used to separate a 4D signal into its constituent parts: common geology, time‐lapse response and noise. Synthetic tests which demonstrate the advantages of the singular‐value decomposition technique over traditional differencing methods are also presented. This signal separation and enhancement technique is used to map out both the original and moved oil–water contacts across the Nelson Field. The singular‐value decomposition technique allows the oil–water contact to be mapped across regions which would have been missed using traditional differencing methods. In particular, areas toward the edges of the field are highlighted by the technique. The oil–water contact is observed to move upwards across the field, with the largest movements being associated, as anticipated, with natural production. The results obtained are broadly consistent with those predicted by the reservoir simulator model. Singular‐value decomposition is demonstrated to be a useful tool for enhancing the time‐lapse signal and for gaining confidence in areas where traditional differencing fails. 相似文献
10.
11.
A general step-by-step solution technique is presented for the evaluation of the dynamic response of structural systems with physical and geometrical nonlinearities. The algorithm is stable for all time increments and in the analysis of linear systems introduces a predictable amount of error for a specified time step. Guidelines are given for the selection of the time step size for different types of dynamic loadings. The method can be applied to the static and dynamic analysis of both discrete structural systems and continuous solids idealized as an assemblage of finite elements. Results of several nonlinear analyses are presented and compared with results obtained by other methods and from experiments. 相似文献
12.
An iterative solution method is presented and illustrated to analyse the dynamic response of bridge–vehicle systems. The method consists in dividing the whole system into 2 subsystems at the interface of the bridge and vehicles; these 2 subsystems are solved separately; their compatibility at the interface is achieved by an iterative procedure with under-relaxation or with Aitken acceleration. The characteristics of this method are explained on a simplified system with 2 degrees of freedom (DOF). The numerical results for a simple example demonstrate the high performances of the proposed method: good convergence rate and high accuracy. Finally, the method is applied to a practical example: the linear dynamic response of the Yangtze-River Bridge at Wuhan under a moving train with 2 locomotives and 4 freight cars. The efficiency is attained because neither formation nor factorisation of the coefficient matrices for the equations of the system are needed at every time step in linear analysis. The Aitken acceleration technique is more efficient in systems with multi-degrees of freedom than the relaxation technique. The proposed method will be even more efficient in non-linear dynamic response because, in this case, the iterations are necessary whether the system is solved as a whole or not. 相似文献
13.
The response/transfer function of a coastal site to a remote open-ocean point is introduced, with the intent to directly convert open-ocean measurements into the wave time history at the site. We show that the tsunami wave at the site can be predicted as the wave is measured in the open ocean as far as 1,000+ km away from the site, with a straightforward computation which can be performed almost instantaneously. The suggested formalism is demonstrated for the purpose of tsunami forecasting in Poverty Bay, in the Gisborne region of New Zealand. Directional sensitivity of the site response due to different conditions for the excitation of the shelf and the bay’s normal modes is investigated and used to explain tsunami observations. The suggested response function formalism is validated with available records of the 2010 Chilean tsunami at Gisborne tide gauge and at the nearby deep-ocean assessment and reporting of tsunamis (DART) station 54401. The suggested technique is also demonstrated by hindcasting the 2011 Tohoku tsunami and 2012 Haida Gwaii tsunami at Monterey Bay, CA, using an offshore record of each tsunami at DART station 46411.
相似文献14.
时域高阶双渐近透射边界能够同时模拟层状介质中行波和快衰波的传播,具有很高的计算精度和计算效率.本文将高阶双渐近透射边界推广应用到多层层状地基系统弹性波传播问题的模拟,采用广义特征值分解分析该透射边界的数值稳定性,通过移谱法消除导致数值不稳定的虚假模态.将高阶双渐近透射边界以超单元的形式直接嵌入到近场有限元方程,建立了有限元-高阶双渐近透射边界时域耦合分析模型,并将其应用到重力坝-层状地基动力相互作用分析.数值算例分析结果表明,该时域耦合分析模型具有很高的精度和计算效率,适用于实际重力坝工程的地震响应分析. 相似文献
15.
Derived herein is the integral representation solution of a Rayleigh-damped Bernoulli–Euler beam subjected to multi-support motion, which is free from calculation of a quasi-static solution, and in which the modal participation factor for support motion is formulated as a boundary modal reaction, thus making efficient calculation feasible. Three analytical methods, including (1) the quasi-static decomposition method, (2) the integral representation with the Cesàro sum technique, and (3) the integral representation in conjunction with Stokes' transformation, are presented. Two additional numerical methods of (4) the large mass FEM simulation technique and (5) large stiffness FEM simulation technique are easily incorporated into a commercial program to solve the problem. It is found that the results obtained by using these five methods are in good agreement, and that both the Cesàro sum and Stokes' transformation regularization techniques can extract the finite part of the divergent series of the integral representation. In comparison with the Mindlin method and Cesàro sum technique, Stokes' transformation is the best way because it is not only free of calculation of the quasi-static solution, but also because it can obtain the convergence rate as rapidly as the mode acceleration method can. 相似文献
16.
A dynamic analysis of elastic–viscoplastic systems, incorporating the modal co-ordinate transformation technique, is presented. The formulation results in uncoupled incremental equations of motion with respect to the modal co-ordinates. The elastic–viscoplastic model adopted allows the analysis not to involve yielding regions and loading/unloading processes. An implicit Runge–Kutta scheme together with the Newton–Raphson method are used to solve the non-linear constitutive equations. Stability and accuracy of the numerical solution are improved by utilizing a local time step sub-incrementing procedure. Applications of the analyses to multi-storey shear buildings show that good results can be obtained for the maximum displacement response by including only a few lower modes in the computation, but the prediction of the ductility factor response tends to underestimate the peak values when too few modes are used. In addition, stable and valid results can be obtained even with a sizable time step increment. 相似文献
17.
《Journal of Applied Geophysics》2000,43(1):15-32
Fast S-inversion is a method of interpretation of time-domain electromagnetic (TDEM) sounding data using the thin sheet model approach. Within the framework of this method, the electromagnetic (EM) response measured at the surface of the earth at every time delay is matched with that of a thin sheet model. The conductivity change with depth is obtained using the conductance, S, and depth, d, of the equivalent thin sheet. We analyze two different numerical techniques, the differential S-transformation and the regularized S-inversion, to determine the parameters of the thin sheet. The first technique is a direct differential transformation of the observed data into conductance and depth values. It is fast and requires no iterations or starting model. The second technique uses a regularized inversion scheme to fit the measured response with that of a thin sheet. In both techniques, the retrieved conductance values are differentiated with respect to depth to obtain the conductivity change with depth. We apply S-inversion to three-dimensional synthetic data and we successfully locate the local conductors. We also demonstrate a case history by interpreting TDEM data obtained at the Nojima fault zone in Japan. The results clearly indicate the location of the fault zone. 相似文献
18.
Nonstationary stochastic response of structural systems equipped with nonlinear viscous dampers under seismic excitation 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Nonlinear viscous dampers are supplemental devices widely used for enhancing the performance of structural systems exposed to seismic hazard. A rigorous evaluation of the effect of these damping devices on the seismic performance of a structural system should be based on a probabilistic approach and take into account the evolutionary characteristics of the earthquake input and of the corresponding system response. In this paper, an approximate analytical technique is proposed for studying the nonstationary stochastic response characteristics of hysteretic single degree of freedom systems equipped with viscous dampers subjected to a fully nonstationary random process representing the seismic input. In this regard, a stochastic averaging/linearization technique is utilized to cast the original nonlinear stochastic differential equation of motion into a simple first‐order nonlinear ordinary differential equation for the nonstationary system response variance. In comparison with standard linearization schemes, the herein proposed technique has the significant advantage that it allows to handle realistic seismic excitations with time‐varying frequency content. Further, it allows deriving a formula for determining the nonlinear system response evolutionary power spectrum. By this way, ‘moving resonance’ effects, related to both the evolutionary seismic excitation and the nonlinear system behavior, can be observed and quantified. Several applications involving various system and input properties are included. Furthermore, various response parameters of interest for the seismic performance assessment are considered as well. Comparisons with pertinent Monte Carlo simulations demonstrate the reliability of the proposed technique. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
19.
The maintenance of integrity and functionality of nonstructural components during earthquake excitations is of paramount importance since mechanical failure of those systems can have dramatic consequences in terms of property damage and life safety of the buildings' occupants. This paper explores the dynamic response of nonstructural elements attached on multistory buildings with well‐established floor diaphragm action. Depending on the type of support conditions, seismic response of nonstructural components may be controlled either by acceleration or displacement: Nonstructural components that are subjected to uniform support excitation are controlled primarily by the absolute spectral acceleration developing at their point of attachment on the supporting building. On the contrary, seismic response of multiply supported nonstructural components depends primarily on the relative displacements between successive support points that are imposed by the supporting building during lateral sway. These findings are illustrated from the analytical formulation and its solution through time history analysis of the governing dynamic equation of motion of the primary and secondary components of a system modeled using finite elements. The model encompasses the assembly of a multistory building along with a multiply supported gas pipeline network. It is shown that the dependence of the seismic response of nonstructural components may be linked to the deformed shape of the supporting building at the state of its maximum lateral roof displacement, thereby enabling the definition of design procedures for these systems. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
20.
A modal decomposition method for computing the solution to an eddy-current problem is presented. Modes are computed using the finite element method and the modes produced are simplified to a magnetic polarizability dyadic in the form of a singularity expansion. This reduced form is a very compact and easily-implemented model for the scatterer's reaction to an arbitrary magnetic field. Due to scaling properties, a single model can be applied to scatterers with different sizes and conductivities. The modal decomposition method could be used to compute a variety of parameterized simple models for canonical shapes to assist in algorithm design for clutter discrimination in buried object detection systems. The method is verified using analytically known formulas for the dyadic of a sphere and a loop. The code is then used to predict the behavior of cylinders with arbitrary conductivity and size, showing excellent agreement with a set of measured cylinders. 相似文献