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Frequency Response Function (frequency + response_function)
Selected AbstractsStability and identification for rational approximation of frequency response function of unbounded soilEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2010Xiuli Du Abstract Exact representation of unbounded soil contains the single output,single input relationship between force and displacement in the physical or transformed space. This relationship is a global convolution integral in the time domain. Rational approximation to its frequency response function (frequency-domain convolution kernel) in the frequency domain, which is then realized into the time domain as a lumped-parameter model or recursive formula, is an effective method to obtain the temporally local representation of unbounded soil. Stability and identification for the rational approximation are studied in this paper. A necessary and sufficient stability condition is presented based on the stability theory of linear system. A parameter identification method is further developed by directly solving a nonlinear least-squares fitting problem using the hybrid genetic-simplex optimization algorithm, in which the proposed stability condition as constraint is enforced by the penalty function method. The stability is thus guaranteed a priori. The infrequent and undesirable resonance phenomenon in stable system is also discussed. The proposed stability condition and identification method are verified by several dynamic soil,structure-interaction examples. Copyright © 2009 John Wiley & Sons, Ltd. [source] Parameter identification of framed structures using an improved finite element model-updating method,Part I: formulation and verificationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2007Eunjong Yu Abstract In this study, we formulate an improved finite element model-updating method to address the numerical difficulties associated with ill conditioning and rank deficiency. These complications are frequently encountered model-updating problems, and occur when the identification of a larger number of physical parameters is attempted than that warranted by the information content of the experimental data. Based on the standard bounded variables least-squares (BVLS) method, which incorporates the usual upper/lower-bound constraints, the proposed method (henceforth referred to as BVLSrc) is equipped with novel sensitivity-based relative constraints. The relative constraints are automatically constructed using the correlation coefficients between the sensitivity vectors of updating parameters. The veracity and effectiveness of BVLSrc is investigated through the simulated, yet realistic, forced-vibration testing of a simple framed structure using its frequency response function as input data. By comparing the results of BVLSrc with those obtained via (the competing) pure BVLS and regularization methods, we show that BVLSrc and regularization methods yield approximate solutions with similar and sufficiently high accuracy, while pure BVLS method yields physically inadmissible solutions. We further demonstrate that BVLSrc is computationally more efficient, because, unlike regularization methods, it does not require the laborious a priori calculations to determine an optimal penalty parameter, and its results are far less sensitive to the initial estimates of the updating parameters. Copyright © 2006 John Wiley & Sons, Ltd. [source] Response of SDOF system to non-stationary earthquake excitationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 15 2004R. S. Jangid Abstract Earthquake excitation is often modelled by non-stationary random process (i.e. uniformly modulated broad-band excitation) for analysis of structural safety subjected to seismic hazards. In this paper, the non-stationary response of a single-degree-of-freedom (SDOF) system to non-stationary earthquake motion is investigated for different shapes of modulating functions. The evolutionary power-spectral density function (PSDF) of the displacement of the SDOF system is obtained using the time-varying frequency response function and the PSDF of the earthquake excitation. The close form expressions for time-varying frequency response function are derived for different shapes of the modulating functions. In order to study the effects of the shape of the modulating function, a comparison of the non-stationary earthquake response of the SDOF system is also made for different modulating functions having the same energy content. Copyright © 2004 John Wiley & Sons, Ltd. [source] An inverse eigenvalue method for frequency isolation in spring,mass systemsNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 1 2002Juan C. Egaña Abstract The action of external vibrating forces on mechanical structures can cause severe damages when resonance occurs. The removal of natural frequencies of the structure from resonance bands is therefore of great importance. This problem is called frequency isolation problem and is the subject of this paper. A new inverse eigenvalue method is proposed and applied to spring,mass systems, which have generated much interest in the literature as prototypes of vibrating structures. The novelty of the method lies in using the zeros of the frequency response function at the last mass as control variables in an optimization problem to minimize the impact of redesign. Numerically accurate algorithms for computing the sensitivity with respect to the control variables are presented, which form the basis of an efficient multidimensional search strategy to solve the frequency isolation problem. Copyright © 2001 by John Wiley & Sons, Ltd. [source] The dynamic behaviour of stacked shipping units during transport.PACKAGING TECHNOLOGY AND SCIENCE, Issue 5 2004Part 1: model validation Abstract This paper deals with the dynamic behaviour of stacked packaging units when subjected to vertical vibrational inputs as experienced in transport vehicles. Although the vibrational performance of single-unit packaging systems has been thoroughly studied, the behaviour of stacked packaging units is not fully understood. The complexity of the problem is compounded when the effects of vertical restraints are taken into account. The paper presents the development of a numerical computer model designed to predict the dynamic response of stacked package systems when subjected to vertical vibrational excitation. Provisions have been made to account for the effects of vertical restraint tension and stiffness. In addition, a physical model representative of a generic stacked packaging system has been developed to assist in validating the numerical model. The paper includes results from preliminary experiments in which the frequency response functions of the models were evaluated and compared. The validity of the numerical model in the time domain was tested using random burst excitation signals. These preliminary experiments reveal that, when the effects of frictional damping are taken into account, the numerical model can be used to generate reasonably accurate predications of the dynamic behaviour of the equivalent physical system. Copyright © 2004 John Wiley & Sons, Ltd. [source] Simulation and Measurements of Rolling Tire DynamicsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2006Maik Brinkmeier The simulation of rolling tires including stationary rolling, modal analysis, excitation with roughness of road surfaces and sound radiation is presented for state of the art industrial tire models. The target of this research, part of the german project "Leiser Straßenverkehr", is the reduction of trafic noise, whereas the main source, namely the tire/road system, is investigated in contrast to other techniques like sound insulating walls. The needs and methods for the solution of the resulting large scale problems are discussed next to special properties of rotating structures, high frequency behavior of rubber material and approaches for the reduction of computational cost. For the validation of the model measurements of real tires and roads are used. These include shaker tests of the standing tire and acoustics of tires rolling on a drum. The same set,ups are applied to the simulation for the comparison of frequency response functions and sound pressure levels. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||