• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.2
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• pp.159-171
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• 2001

평면 아치 구조물에 대해 선형 탄성 변분방정식에 기반을 둔 설계민감도 해석을 위한 일반적 이론을 개발하였다. 아치 구조물내의 임의 마디에 정의된 응력범함수를 고려하였고 이에 대한 설계민감도 공식을 유도하기 위해 전미분(material derivative) 개념과 보조(adjoint) 변수 방법을 도입하였다. 얻어진 민감도 공식은 구조해석 결과를 얻고 나면 이들로부터 단순 대수연산을 통해 계산이 되므로 적용이 간편할 뿐 아니라 해의 정확도가 높은 잇점이 있다. 본 방법은 아치의 형상을 매개변수를 통해 표현하므로 얕은 아치에 국한하지 않고 어떠한 형상도 고려가 가능하며, 나아가서 아치의 형상변화를 형상에 대해 수직뿐 아니라 접선방향도 포함하여 일반적으로 고려하므로 다양한 형상설계가 가능하다. 몇 가지 예제에서 민감도 계산을 수행함으로써 본 방법의 정확도와 효율성을 입증하였으며, 두 가지의 설계최적화 문제를 대상으로 실제로 두께 및 형상최적설계를 수행하였다.

• Computational Structural Engineering
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• v.4 no.2
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• pp.87-94
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• 1991

In this paper, a mixed variational principle applicable to the linear elasticity of inhomogeneous anisotropic materials is presented. For derivation of the general variational principle, a systematic procedure for the variational formulation of linear coupled boundary value problems developed by Sandhu et al. is employed. Consistency condition of the field operators with the boundary operators results in explicit inclusion of boundary conditions in the governing functional. Extensions of admissible state function spaces and specialization to a certain relation in the general governing functional lead to the desired mixed variational principle. In the physical sense, the present variational principle is analogous to the Reissner's recent formulation obtained by applying Lagrange multiplier technique followed by partial Legendre transform to the classical minimum potential energy principle. However, the present one is more advantageous for the application to the general anisotropic materials since Reissner's principle contains an implicit function which is not easily converted to an explicit form.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.2
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• pp.36-43
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• 2003

The analytic solution of radial displacements of thin cylindrical pressure vessel with carbon fiber T700/Epoxy orthotropic composites was obtained using equilibrium equations of the orthogonal curvilinear coordinate system. The governing equations with the simplified strain versus displacement relation of 3-dimensional curvilinear coordinate system were derived from the variational principle and the virtual work principle. Some theoretical analyses were presented and compared with the results of hydraulic tests for the pressure vessels with some various thicknesses. The results of the theoretical analysis and the hydraulic test were reasonably matched.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.2
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• pp.170-175
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• 2002

The cut-off frequencies of higher order modes in a symmetrical stripline are calculated using the variational finite element method combined with the conformal mapping. The conformal mapping is used to Improve the modeling of the infinite transverse extents of a stripline. And then the finite element method is employed to solve the variational equation in the transformed finite region. Comparisons with numerical results found in the literature validate the presented method.

• Journal of the korean Society of Automotive Engineers
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• v.11 no.1
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• pp.14-19
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• 1989

본 해설에서는 이와같은 SOlution-Adaptive-Grid 방법중 1982년 Blackbill과 Salzman에 의하여 제안된 변분법을 이용한 Solution Adaptive Grid 방법에 대한 기본방정식 그리고 계산방법들을 소개하고자 한다. 이 방법은 논리적 구조에 있어서 명확하고 2차원 3차원 문제에 쉽게 확장시켜 적용할 수 잇기 때문에 많은 연구자들에 의하여 채택되고 있다.

• Journal of the KSME
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• v.33 no.7
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• pp.600-613
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• 1993

유한요소법은 구조공학분야에서 발전하여 과학기술 전반에 통용되는 수치해석의 한 방법 또는 기술로서 각광받고 있다. 이 기법은 변분원리에 수학적 기초를 두는 미분 방정식의 수치해법의 하나라고 할 수 있다. 이 글에서는 고체역학 부문에 한정하여 유한요소법의 기본체계, 응력계산과 관련하여 중요 수치현상, 그리고 최근 국내외학계의 연구동향 및 상용 패키지 사용시 주의 사항에 관하여 언급한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.3
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• pp.303-309
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• 2007

For the propagation of elastic waves in unbounded domains, absorbing boundary conditions at the fictitious numerical boundaries have been proposed. In this paper we focus on both first and second order paraxial boundary conditions(PBCs) in the framework of variational approximations which are based on paraxial approximations of the scalar and elastic wave equations. We propose a penalty function method for the treatment of PBCs and apply these into finite element analysis. The numerical verification of the efficiency is carried out through comparing PBCs with Lysmer-Kuhlemeyer's boundary conditions.

• The KIPS Transactions:PartA
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• v.13A no.5 s.102
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• pp.429-434
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• 2006

A CCTV system reduces some number of cameras if we use convex-mirror. In this case, convex-mirror Image distorted, we need transformation to flat images. In the center of mirror images, a transformed image has no distortion, but at near boundary image has plentiful distortion. This distortion is caused by occlusion of angled ray and diffraction. We know that the linear filtering approach cannot separate noise from signal where their Fourier spectra overlap. But using a non-linear discretization method, we shall reduce blurred noise. In this paper, we introduce the backward solution of nonlinear wave equation for reducing blurred noise and biased expansion of equilibrium contour. We propose, after applying the introduced method, and calculate with discretization method. To analysis the experimental result, we investigate to PSNR and get about 4dB better than current method.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.2
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• pp.11-15
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• 2009

This paper is concerned with the elastic buckling of thin-walled arches that are subjected to uniform bending. Nonlinear strain-displacement relations with the initial curvature are substituted into the second variation of the total potential energy to obtain the energy equation including initial curvature effects. The approximation for initial curvature effects that the bending normal strain distribution is linear across the cross section is applied consistently in the derivation process. The closed form solution is obtained for flexural-torsional buckling of arches under uniform bending and, it is compared with the previous theoretical results.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.151-156
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• 1994

The equations of motion of a submarine pipeline with the internal flowing fluid and subject to hydrodynamic loadings are derived by using Hamilton's principle. Coupling between the bending and the longitudinal extension due to axial load and thermal expansion are considered. Coupling between the twisting and extension are not considered. The equations of motion are well agreed with the results which are derived by the vector method.