• Title/Summary/Keyword: Semi-Analytic Method

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The Semi-Analytic Structural Sensitivity Using Pade Approximation (Pade근사를 이용한 준해석 구조 민감도의 해석)

  • Dan, Ho-Jin;Lee, Byung-Chai
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.12
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    • pp.2631-2635
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    • 2002
  • The semi-analytic sensitivity analysis using Pade approximation is presented for linear elastic structures. Although the semi-analytic method has several advantages, accuracy of the method prevents it from practical application. One of promising remedies is the use of geometric series for the matrix inversion. Though series expansion of order three has been successfully applied to the calculation of the structural sensitivity in the most range of the design perturbation, it is prone to have a slow convergence for large perturbation. To overcome this shortage, Pade approximation is introduced so that it can broaden the trust region of the perturbation without adding expansion terms. Numerical results show that the confident sensitivity can be obtained with tiny expenses of computation effort.

The calculation of refined semi-analytic sensitivity based on the hybrid element (혼합 요소에서의 개선된 민감도 계산법)

  • Cho, Maeng-Hyo;Kim, Hyun-Gi
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.686-691
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    • 2001
  • Structural optimization often require the evaluation of design sensitivities. The Semi Analytic method(SAM) is popular for shape optimization because this method has several advantages. But when relatively large rigid body motions are identified for individual elements, the SA method shows severe inaccuracy. In this paper, the improvement of design sensitivities corresponding to the rigid body mode is evaluated by exact differentiation of the rigid body modes. Moreover, the error of the SA method caused by numerical difference scheme is alleviated by using a series approximation for the sensitivity derivatives and considering the higher order terms.

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Error Estimation for the Semi-Analytic Design Sensitivity Using the Geometric Series Expansion Method (기하급수 전개법을 이용한 준해석 민감도의 오차 분석)

  • Dan, Ho-Jin;Lee, Byung-Chai
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.2
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    • pp.262-267
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    • 2003
  • Error of the geometric series expansion method for the structural sensitivity analysis is estimated. Although the semi-analytic method has several advantages, accuracy of the method prevents it from practical application. One of the promising remedies is the use of geometric series formula for the matrix inversion. Its result of the sensitivity analysis converges that of the global difference method which is known as reliable one. To reduce computational efforts and to obtain reliable results, it is important to know how many terms need to expand. In this paper, the error formula is presented and Its usefulness is illustrated through numerical experiments.

A Refined Semi-Analytic Sensitivity Study Based on the Mode Decomposition and Neumann Series Expansion in Eigenvalue Problem(II) - Eigenvalue Problem - (강체모드분리와 급수전개를 통한 고유치 문제에서의 준해석적 설계 민감도 개선에 관한 연구(II) -동적 문제 -)

  • Kim, Hyun-Gi;Cho, Maeng-Hyo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.4
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    • pp.593-600
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    • 2003
  • Structural optimization often requires the evaluation of design sensitivities. The Semi Analytic Method(SAM) fur computing sensitivity is popular in shape optimization because this method has several advantages. But when relatively large rigid body motions are identified for individual elements. the SAM shows severe inaccuracy. In this study, the improvement of design sensitivities corresponding to the rigid body mode is evaluated by exact differentiation of the rigid body modes. Moreover. the error of the SAM caused by numerical difference scheme is alleviated by using a series approximation for the sensitivity derivatives and considering the higher order terms. Finally the present study shows that the refined SAM including the iterative method improves the results of sensitivity analysis in dynamic problems.

Wave Propagation Analysis in Inhomogeneous Media by Using the Fourier Method

  • Kim, Hyun-Sil;Kim, Jae-Seung;Kang, Hyun-Joo;Kim, Sang-Ryul
    • The Journal of the Acoustical Society of Korea
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    • v.17 no.3E
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    • pp.35-42
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    • 1998
  • Transient acoustic and elastic wave propagation in inhomogeneous media are studied by using the Fourier method. It is known that the fourier method has advantages in memory requirements and computing speed over conventional methods such as FDM and FEM, because the Fourier method needs less grid points for achieving the same accuracy. To verify the proposed numerical scheme, several examples having analytic solutions are considered, where two different semi-infinite media are in contact along a plane boundary. The comparisons of numerical results by the Fourier method and analytic solutions show good agreements. In addition, the fourier method is applied to a layered half-plane, in which an elastic semi-infinite medium is covered by an elastic layer of finite thickness. It is showed how to derive the analytic solutions by using the Cagniard-de Hoop method. The numerical solutions are in excellent agreements with analytic results.

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A Refined Semi-Analytic Sensitivity Study Based on the Mode Decomposition and Neumann Series Expansion (I) - Static Problem - (강체모드분리와 급수전개를 통한 준해석적 민감도 계산 방법의 개선에 관한 연구(I) - 정적 문제 -)

  • Cho, Maeng-Hyo;Kim, Hyun-Gi
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.4
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    • pp.585-592
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    • 2003
  • Among various sensitivity evaluation techniques, semi-analytical method(SAM) is quite popular since this method is more advantageous than analytical method(AM) and global finite difference method(FDM). However, SAM reveals severe inaccuracy problem when relatively large rigid body motions are identified fur individual elements. Such errors result from the numerical differentiation of the pseudo load vector calculated by the finite difference scheme. In the present study, an iterative method combined with mode decomposition technique is proposed to compute reliable semi-analytical design sensitivities. The improvement of design sensitivities corresponding to the rigid body mode is evaluated by exact differentiation of the rigid body modes and the error of SAM caused by numerical difference scheme is alleviated by using a Von Neumann series approximation considering the higher order terms for the sensitivity derivatives.

An Analysis of Seismic Wave Propagation by Using the Fourier Method (Fourier 방법을 이용한 지진파 전달해석)

  • 김현실
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 1998.10a
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    • pp.399-406
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    • 1998
  • Transient acoustic and elastic wave propagation in inhomogeneous media are studied by using the Fourier method. To verify the proposed numerical scheme, several examples having analytic solutions are considered, where two different semi-infinite media are in contact along a plane boundary. The comparisons of numerical results by the Fourier method and analytic solutions show good agreements. In addition, the Fourier method is applied to a layered half-plane, in which an elastic semi-infinite medium is covered by an elastic layer of finite thickness. It is showed how to derive the analytic solutions by using the Cagniard-de Hoop method. The numerical solutions are in excellent agreements with analytic results.

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A Semi-Analytic Approach for Analysis of Parametric Roll (준해석적 방법을 통한 파라메트릭 횡동요 해석)

  • Lee, Jae-Hoon;Kim, Yonghwan
    • Journal of the Society of Naval Architects of Korea
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    • v.52 no.3
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    • pp.187-197
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    • 2015
  • This study aims the development of a semi-analytic method for the parametric roll of large containerships advancing in longitudinal waves. A 1.5 Degree-of-Freedom(DOF) model is proposed to account the change of transverse stability induced by wave elevations and vertical motions (heave and pitch). By approximating the nonlinearity of restoring moment at large heel angles, the magnitude of roll amplitude is predicted as well as susceptibility check for parametric roll occurrence. In order to increase the accuracy of the prediction, the relationship between righting arm(GZ) and metacentric height(GM) is examined in the presence of incident waves, and then a new formula is proposed. Based on the linear approximation of the mean and first harmonic component of GM, the equation of parametric roll in irregular wave excitations is introduced, and the computational results of the proposed model are validated by comparing those of weakly nonlinear simulation based on an impulse-response-function method combined with strip theory. The present semi-analytic doesn’ t require heavy computational effort, so that it is very efficient particularly when numerous sea conditions for the analysis of parametric roll should be considered.

ENHANCED SEMI-ANALYTIC METHOD FOR SOLVING NONLINEAR DIFFERENTIAL EQUATIONS OF FRACTIONAL ORDER

  • JANG, BONGSOO;KIM, HYUNJU
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.23 no.4
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    • pp.283-300
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    • 2019
  • In this paper, we propose a new semi-analytic approach based on the generalized Taylor series for solving nonlinear differential equations of fractional order. Assuming the solution is expanded as the generalized Taylor series, the coefficients of the series can be computed by solving the corresponding recursive relation of the coefficients which is generated by the given problem. This method is called the generalized differential transform method(GDTM). In several literatures the standard GDTM was applied in each sub-domain to obtain an accurate approximation. As noticed in [19], however, a direct application of the GDTM in each sub-domain loses a term of memory which causes an inaccurate approximation. In this work, we derive a new recursive relation of the coefficients that reflects an effect of memory. Several illustrative examples are demonstrated to show the effectiveness of the proposed method. It is shown that the proposed method is robust and accurate for solving nonlinear differential equations of fractional order.