• Title/Summary/Keyword: 고유치 민감도

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Structural Topology Optimization Using Two-level Dynamic Condensation Scheme (2단계 동적 축소법을 적용한 구조물의 위상 최적 설계)

  • Park Soo-Hyun;Kim Hyun-Gi;Cho Maeng-Hyo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.19 no.2 s.72
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    • pp.213-219
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    • 2006
  • Topology optimization problem requires numerous repeated evaluations of objective function and design sensitivity for elements within design domain with various density distributions. The recently proposed two-level condensation scheme(TLCS) is very promising for the construction of reduced system and for an accurate and efficient analysis concerned about eigenvalue and dynamic problems. We used the two-level dynamic condensation scheme for the analysis and sensitivity computation part in the structural topology optimization problem. The results of the topology optimization for the reduced system show the TLCS provides high accuracy and computation efficiency compared to the full scale system within engineering accuracy.

A Study on the Support location Optimizations of the Beams using the Genetic Algorithm and the Sensitivity Analysis. (민감도가 고려된 유전 알고리듬을 이용한 보 구조물의 지지점 최적화에 관한 연구)

  • 이재관;신효철
    • Journal of KSNVE
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    • v.10 no.5
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    • pp.783-791
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    • 2000
  • This describes a study on the support location optimizations of the beams using the genetic algorithm and the sensitivity analysis. The genetic algorithm is a probabilistic method searching the optimum at several points simultaneously and requiring only the values of the object and constraint functions. It has therefore more chances to find the global solution and can be applied to the various problems. Nevertheless, it has such a shortcoming that it takes too many calculations, because it is ineffective in local search. While the traditional method using sensitivity analysis is of great advantage in searching the near optimum. thus the combination of the two techniques will make use of the individual advantages, that is, the superiority in global searching form the genetic algorithm and that in local searching form the sensitivity analysis. In this thesis, for the practical applications, the analysis is conducted by FEB ; and as the shapes of structures are taken as the design variation, it requires re-meshing for every analysis. So if it is not properly controlled, the result of the analysis is affected and the optimized solution amy not be the real one. the method is efficiently applied to the problems which the traditional methods are not working properly.

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An Adjoint Variable Method for Eigenproblem Design Sensitivity Analysis of Damped Systems (감쇠계 고유치문제의 설계민감도해석을 위한 보조변수법)

  • Lee, Tae Hee;Lee, Jin Min;Yoo, Jung Hoon;Lee, Min Uk
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.11 s.242
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    • pp.1527-1533
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    • 2005
  • Three methods for design sensitivity analysis such as finite difference method(FDM), direct differentiation method(DDM) and adjoint variable method(AVM) are well known. FDM and DDM for design sensitivity analysis cost too much when the number of design variables is too large. An AVM is required to compute adjoint variables from the simultaneous linear system equation, the so-called adjoint equation. Because the adjoint equation is independent of the number of design variables, an AVM is efficient for when number of design variables is too large. In this study, AVM has been extended to the eigenproblem of damped systems whose eigenvlaues and eigenvectors are complex numbers. Moreover, this method is implemented into a commercial finite element analysis program by means of the semi-analytical method to show applicability of the developed method into practical structural problems. The proposed_method is compared with FDM and verified its accuracy for analytical and practical cases.

A Study for Structural Damage Identification Method Using Genetic Algorithm (유전자 알고리즘을 이용한 구조물 손상 탐색기법에 관한 연구)

  • Woo, Ho-Kil;Choi, Byoung-Min
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.17 no.1 s.118
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    • pp.80-87
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    • 2007
  • In this paper, a method for identifying the location and extent of a damage in a structure using residual forces was presented. Element stiffness matrix reduction parameters in a finite element model were used to describe the damaged structure mathematically. The element stiffness matrix reduction parameters were determined by minimizing a global error derived from dynamic residual vectors, which were obtained by introducing a simulated experimental data into the eigenvalue problem. Genetic algorithm was used to get the solution set of element stiffness reduction parameters. The proposed scheme was verified using Euler-Bernoulli beam. The results were presented in the form of tables and charts.

A study on the improvement of shape design sensitivity in eigenvalue problems using semi-analytical method (반해석적 방법을 이용한 고유치 문제의 형상 설계 민감도 향상에 관한 연구)

  • 김현기;조맹효
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2001.10a
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    • pp.159-166
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    • 2001
  • Structural optimization often requires the evaluation of design sensitivities. The Semi Aanalytic method(SAM) for 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 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. Finally, this paper shows that the refined SA method including the iterative method improves the results of sensitivity analysis in dynamic problems.

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Experimental Verification of Nondestructive Crack Detection Model Using a Few Natural Frequencies (소수의 고유진동수를 사용하는 비파괴 균열발견모델의 유도 및 검증)

  • 김정태
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.12 no.2
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    • pp.149-159
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    • 1999
  • 본 연구에서는 고유진동수를 사용하여 균열의 위치와 크기를 발견하는 비파괴 균열발견모델을 유도하고 Euler-Bernoulli 보를 대상으로 이 모델의 적합성을 검증하였다. 먼저, 균열위치예측모델과 균열크기예측모델로 이루어진 균열발견체계를 제시하였는데, 균열위치예측모델은 모드민감도와 고유진동수 사이의 선형적인 관계로부터 간접적으로 유도되었으며 균열크기예측모델은 균열발생에 의한 변형에너지의 손실을 진동특성치의 변화와 비교하는 동적 파괴역학적 방법으로부터 유도되었다. 다음으로, 기존에 발표된 양단-자유보에 대한 진동모드 실험결과를 사용하여 균열위치와 균열크기를 예측하고 평가하므로 균열발견모델의 적합성과 적용성을 실험적으로 검토하였다. 대부분의 손상시나리오에서 균열위치와 균열크기 예측치는 실제값과 근사하게 일치하였다.

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Algebraic Method for Computation of Natural Frequency and Mode Shape Sensitivities (고유진동수와 모드의 민감도를 계산하기 위한 대수적 방법)

  • Jung, Gil-Ho;Kim, Dong-Ok;Lee, Chong-Won;Lee, In-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.5
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    • pp.707-718
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    • 1997
  • This paper presents an efficient numerical method for the computation of eigenpair derivatives for a real symmetric eigenvalue problem with distinct and multiple eigenvalues. The method has a very simple algorithm and gives an exact solution. Furthermore, it saves computer sotrage and CPU time. The algorithm preserves not only the symmetricity but also the band width of the matrices, allowing efficient computer storage and solution techniques. Results from the proposed method for calculating the eigenpair derivatives are compared with those from Rudisill and Chu's method and Nelson's method which is known efficient one in the case of distinct natural frequencies. As an example to demonstrate the efficiency of the proposed method in the case of distinct eigenvalues, a cantilever plate is considered. The design parameter of the cantilever plate is its thickness. For the eigenvalue problem with multiple natural frequencies, the adjacent eigenvectors are used in the algebraic equation as side conditions, lying adjacent to the multiplicity of multiple natural frequency distinct eigenvalues, which appear when design parameter varies. A cantilever beam is used to demonstrate the efficiency of the proposed method in the case of multiple natural frequencies. Results form the proposed method for calculating the eigenpair derivatives are compared with those from Dailey's method(an amendation of Ojalvo's work) which finds the exact eigenvector derivatives. The design parameter of the cantilever beam is its height. Data is presented showing the amount of CPU time used to compute the first ten eigenpair derivatives by each method. It is important to note that the numerical stability of the proposed method is proved.

Structural Dynamics Modification Using Surface Grooving Technique : The Effectiveness of Check board Pattern and Comparison the Algorithm for Initial Starting Point (그루브를 이용한 표면형상변형 동특성 변경법 : 체크무늬 그루브의 효용성과 초기 시작점의 선택 알고리즘에 대한 비교)

  • Park, Mi-You;Park, Young-Jin;Park, Youn-Sik
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.05a
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    • pp.128-131
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    • 2005
  • Structural Dynamics Modification (SDM) is a very effective technique to improve structure's dynamic characteristics by adding or removing auxiliary structures. changing material properties and shape of structure. Among those of SDM technique, the method to change shape of structure has been mostly relied on engineer's experience and trial-and-error process which are very time consuming. In order to develop a systematic method to change structure shape, surface grooving technique is studied and successfully applied to HDD cover model. To check the effectiveness of this surface grooving technique, the grooved HDD cover design was manufactured using rapid prototyping and experimentally tested to prove the effectiveness of the grooving method as one of SDM techniques. And the modal strain energy and eigenvalue sensitivity method for choosing the initial starting point are compared.

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Sensitivity Analysis of GIUH Model Applied to DEM Resolutions and Threshold Areas (GIUH적용을 위한 DEM 격자크기 및 Threshold Area의 민감도분석)

  • Cho, Hyo-Seob;Jung, Kwan-Sue;Kim, Jae-Han
    • Journal of Korea Water Resources Association
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    • v.36 no.5
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    • pp.799-810
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    • 2003
  • Hydrologic models generally require land surface analysis to different topographic parameters defined as direct or indirect input variables to the model. Specially GIS supply the these parameters from digital data set of land surface The sensitivity analysis to DEM(Digital Elevation Model) resolution and the threshold area are of GIS extracted digital data set applied GIUH(Geomorphological Instantaneous Unit Hydrograph)model is investigated. Also it is compared the responses of GIUH model as input data of stream networks from digital data set(blue line) of NGIS and those extracted from DEM of various grid sizes. The results shows that the GIUH model is significantly affected by the DEM resolution and threshold area. According to the results, DEM grid size is suitable from 25m to 50m. Also threshold area is in the range of 30%∼50% for exceedance probability.

Finite Element Modelling of Axially Compressed GFRP Cylindrical Panels (축방향으로 압축을 받는 GFRP 원통형 판넬의 유한요소 모델링)

  • Kim, Ki Du
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.4
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    • pp.15-25
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    • 1993
  • In order to promote the efficient use of composite materials, effort is currently being directed at the development of design criteria for composite structures. Insofar as design against buckling is concerned, it is well known that, for metal shells, a key step is the definition of 'knockdown' factors on the elastic critical buckling stress accounting mainly for the influence of initial geometric imperfections. At present, the imperfection sensitivity of composite shells has not been explored in detail. Due to the large number of parameters influencing buckling response (considerably larger than for isotropic shells), a very large number of tests would be needed to quantify imperfection sensitivity experimentally. An alternative approach is to use validated numerical models for this task. Thus, the objective of this paper is to outline the underlying theory used in developing a composite shell element and to present results from a validation exercise and subsequently from a parametric study on axially loaded glass fibre-reinforced plastic (GFRP) curved panels using finite element modelling. Both eigenvalue and incremental analyses are performed, the latter including the effect of initial geometric imperfection shape and amplitude, and the results are used to estimate 'knockdown' factors for such panels.

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