• 제목/요약/키워드: finite spectral method

검색결과 148건 처리시간 0.024초

스펙트럴요소법을 이용한 동적집중하중을 받는 평판의 진동해석 (Vibration analysis of the plates subject to dynamic concentrated loads by using spectral element method)

  • 이준근;이우식
    • 대한기계학회논문집A
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    • 제22권3호
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    • pp.635-643
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    • 1998
  • A spectral element method(SEM) is introduced for the vibration analysis of a rectangular plate subject to dynamic concentrated loads. First, the spectral plate element is derived from the relations between the forces and displacements along the two opposite edges of plate element. The global spectral matrix equation is then formulated by assembling two spectral plate elements so that the dynamic concentrated load is located at the connection nodal line between two plate elements. the concentrated load is then spatially Fourier transformed in the direction of the connection nodal line to transform the two-dimensional plate problem into a simplified equivalent one-dimensional beam-like problem. We may benefit from these procedures in that the spectral results from the present SEM is compared with the exact analytical solutions to prove the remarkable accuracy of the present SEM, while this is not true for conventional finite element solutions, especially at high frequency.

LEAST-SQUARES SPECTRAL COLLOCATION PARALLEL METHODS FOR PARABOLIC PROBLEMS

  • SEO, JEONG-KWEON;SHIN, BYEONG-CHUN
    • 호남수학학술지
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    • 제37권3호
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    • pp.299-315
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    • 2015
  • In this paper, we study the first-order system least-squares (FOSLS) spectral method for parabolic partial differential equations. There were lots of least-squares approaches to solve elliptic partial differential equations using finite element approximation. Also, some approaches using spectral methods have been studied in recent. In order to solve the parabolic partial differential equations in parallel, we consider a parallel numerical method based on a hybrid method of the frequency-domain method and first-order system least-squares method. First, we transform the parabolic problem in the space-time domain to the elliptic problems in the space-frequency domain. Second, we solve each elliptic problem in parallel for some frequencies using the first-order system least-squares method. And then we take the discrete inverse Fourier transforms in order to obtain the approximate solution in the space-time domain. We will introduce such a hybrid method and then present a numerical experiment.

Simultaneous Confidence Regions for Spatial Autoregressive Spectral Densities

  • Ha, Eun-Ho
    • Journal of the Korean Data and Information Science Society
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    • 제10권2호
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    • pp.397-404
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    • 1999
  • For two-dimensional causal spatial autoregressive processes, we propose and illustrate a method for determining asymptotic simultaneous confidence regions using Yule-Walker, unbiased Yule-Walker and least squres estimators. The spectral density for first-order spatial autoregressive model are looked at in more detail. Finite sample properties based on simulation study we also presented.

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Fatigue life prediction of horizontally curved thin walled box girder steel bridges

  • Nallasivam, K.;Talukdar, Sudip;Dutta, Anjan
    • Structural Engineering and Mechanics
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    • 제28권4호
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    • pp.387-410
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    • 2008
  • The fatigue damage accumulation rates of horizontally curved thin walled box-girder bridge have been estimated from vehicle-induced dynamic stress history using rain flow cycle counting method in the time domain approach. The curved box-girder bridge has been numerically modeled using computationally efficient thin walled box-beam finite elements, which take into account the important structural actions like torsional warping, distortion and distortional warping in addition to the conventional displacement and rotational degrees of freedom. Vehicle model includes heave-pitch-roll degrees of freedom with longitudinal and transverse input to the wheels. The bridge deck unevenness, which is taken as inputs to the vehicle wheels, has been assumed to be a realization of homogeneous random process specified by a power spectral density (PSD) function. The linear damage accumulation theory has been applied to calculate fatigue life. The fatigue life estimated by cycle counting method in time domain has been compared with those found by estimating the PSD of response in frequency domain. The frequency domain method uses an analytical expression involving spectral moment characteristics of stress process. The effects of some of the important parameters on fatigue life of the curved box bridge have been studied.

Case study on the effects of retrofitting on changing structural dynamic characteristics by microtremor measurements and finite element analysis

  • Hadianfard, Mohammad Ali;Rabiee, Ramin;Sarshad, Azad
    • Structural Engineering and Mechanics
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    • 제55권5호
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    • pp.965-977
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    • 2015
  • Determination of dynamic parameters of a structure such as predominant frequency and damping ratio is one of the most important subjects in dynamics of structures. Different methods are used to determine predominant frequency. These methods are different in the cost, implement accessibility, accuracy, speed, applicability in different conditions, simplicity of calculations and required data accessibility. Calculation of damping ratio by using common experimental procedures is very difficult and costly, then it is assumed as a constant value in most calculations. Microtremor measurements and using spectral ratio method to determine the predominant frequency and damping ratio of structure is of interest in recent years. In this paper, as a case study, the effects of retrofitting on structural dynamic parameters of two four-story buildings by using microtremor measurements and also finite element analysis, is investigated. The results of this study show that microtremor measurements can be utilized to assess the improvement of dynamic behavior of the retrofitted structure and the effectiveness of the method of retrofitting.

Seismic spectral acceleration assessment of masonry in-filled reinforced concrete buildings by a coefficient-based method

  • Su, R.K.L.;Lee, C.L.;Wang, Y.P.
    • Structural Engineering and Mechanics
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    • 제41권4호
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    • pp.479-494
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    • 2012
  • This study explores a coefficient-based seismic capacity assessment method with a special emphasis on low-rise masonry in-filled (MI) reinforced concrete (RC) buildings subjected to earthquake motion. The coefficient-based method without requiring any complicated finite element analysis is a simplified procedure to assess the maximum spectral acceleration capacity of buildings. This paper first compares the fundamental periods of MI RC structures obtained, respectively, from experimental period data and empirical period-height formulas. The coefficient-based method for low-rise masonry buildings is then calibrated by the published experimental results obtained from shaking table tests. The comparison of the experimental and estimated results indicates that the simplified coefficient-based method can provide good approximations of the maximum spectral accelerations at peak loads of the low-rise masonry reinforced concrete buildings if a proper set of drift factors and initial fundamental vibration periods of structures are used.

변분법을 이용한 축방향으로 움직이는 보의 스펙트럴 요소 모델링 (Dynamics of an Axially Moving Bernoulli-Euler Beam : Variational Method-Based Spectral Element Modeling)

  • 최정식;이우식
    • 한국철도학회:학술대회논문집
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    • 한국철도학회 2008년도 춘계학술대회 논문집
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    • pp.831-834
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    • 2008
  • The spectral element model is known to provide very accurate structural dynamic characteristics, while reducing the number of degree-of-freedom to resolve the computational and cost problems. Thus, the spectral element model with variational method for an axially moving Bernoulli-Euler beam subjected to axial tension is developed in the present paper. The high accuracy of the spectral element model is the verified by comparing its solutions with the conventional finite element solutions and exact analytical solutions. The effects of the moving speed and axial tension the vibration characteristics, wave characteristics, and the static and dynamic stabilities of a moving beam are investigated.

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해양환경에서 2차원 유사 스펙트럴 모델링을 이용한 시간 영역 음 전달 해석 (Time Domain Acoustic Propagation Analysis Using 2-D Pseudo-spectral Modeling for Ocean Environment)

  • 김기산;이근화;성우제
    • 한국음향학회지
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    • 제23권8호
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    • pp.576-582
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    • 2004
  • 본 논문에서는 시간영역에서 음파 전달 모델링을 위해 엇갈림 격자에서 유사 스펙트럴 유한 차분 알고리듬을 기반으로 한 전산조직을 개발하였다. 유한 차분 근사는 기하학적으로 복잡한 매질에서 모델링을 가능하게 하고, 엇갈림 격자는 정규 격자에 비해 훨씬 정확한 해를 제공한다. 유사 스펙트럴 방법은 파수 영역에서 파수에 음압의 푸리에 변환을 곱한 후 이를 역푸리에 변환하므로서 공간 도함수를 구하는 방법이다. 이 방법은 매우 안정적이며, 메모리와 계산시간을 감소시키는 장점을 지니고 있다. 무한 및 반무한 영역에서 이 알고리듬에 의한 결과가 해석해와 잘 일치함을 확인하였고, 무한영역과 Pekeris도파관, 거리종속 해양환경에서 시간영역 모델링을 수행하여 스냅사진을 얻어내었으며 이 스냅사진을 통해 복잡한 해양환경에서 신호의 전파 양상을 파악할 수 있었다.

Numerical investigation on multi-degree-freedom nonlinear chaotic vibration isolation

  • Jiang, Guoping;Tao, Weijun
    • Structural Engineering and Mechanics
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    • 제51권4호
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    • pp.643-650
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    • 2014
  • A chaotic vibration isolation system is designed according to the chaotic vibration theory in this paper. The strong nonlinearity is generated by the system. Line spectra in the radiated noise maybe easily detected caused by marine vessels. It is Important to reduce the line spectra by improving the acoustic stealth of marine vessels. A multi-degree-freedom (MDF) nonlinear vibration isolation system (NVIS) system is setup by the experiment and finite element method. The model is established with finite element method. The results show that the behavior of the device gradually varies from period bifurcation into chaotic state and the line spectrum is changed from single spectral structure into broadband spectral structure. It is concluded that chaotic vibration isolation is preferable contrasted on line spectra isolation.

원통형셸의 초고주파 동적특성을 위한 등가평판모델 (An Equivalent Plate Model for the High-Frequency Dynamic Characteristics of Cylindrical Shells)

  • 이준근;이우식
    • 한국정밀공학회지
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    • 제16권6호
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    • pp.108-113
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    • 1999
  • For cylindrical shells, the closed-form solutions are confined to the specific boundary and/or loading conditions. Though the finite element method is certainly a powerful solution approach for the structural dynamics problems, it has been well known to provide the solution reliable only in the low frequency region due to the inherent high sensitivities of structual and numerical modeling errors. Instead, the spectral element method has been proved to provide accurate dynamic characteristics of a structure even at the ultrasonic frequency region. Since the wave characteristic of a cylindrical shell becomes identical to that fo a flat plate as the frequency increases, an equivalent plate model (EPM) representing the high-frequency dynamic characteristics of the cylindrical shell is introduced herein. The EPM-based spectral element analysis solutions are compared with the known analytical solutions for the cylindrical shells to confirm the validity of the present modeling approach.

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