• 전산구조공학
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• 제5권3호
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• pp.119-126
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• 1992

교량, 발전소, 해양구조물과 같은 토목구조물은 사용기간중에 지진, 바람, 파랑하중등에 의해 구조적 손상을 받기 쉽다. 장기간에 걸쳐 구조물에 손상이 누적되면 구조물 전체의 파괴를 초래할 수도 있다. 따라서 현존하는 구조물의 안전성을 분석하기 위한 구조물의 손상도를 추정하는 방법이 필요하다. 본 논문에서는 Inverse Modal Perturbation기법을 이용하여 구조물의 손상도를 추정하는 방법에 대하여 연구하였다. Perturbation식은 구조물의 강성 및 질량행렬의 변화량과 구조물의 고유진동수와 모우드형상의 변화량의 식으로 구성된다. 또한 구조물의 손상은 강성행렬의 변화량으로 표현하였다. 본 연구에서는 구조물의 손상도추정의 효율성을 증대시키기 위하여 2차-Perturbation식을 구성하고, 이것을 반복적인 절차를 거쳐 해를 구하는 방법에 대하여 연구하였다. 제안된 방법의 효율성은 일련의 예제해석을 통하여 검증하였으며, 추정된 결과로 부터 본 방법이 구조물의 손상을 적절히 산정함을 알 수 있었다.

• 한국항공우주학회지
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• 제31권3호
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• pp.31-38
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• 2003

본 연구는 최적설계에 사용되는 역섭동법을 구조물의 손상탐지에 적용하였다. 이 방법은 손상의 위치를 정확하게 탐지하기 위하여 미지수보다 많은 수의 구속조건이 필요하므로, 최적설계와는 달리 비선형 회소자승법을 수치기법에 사용한다. 한편 손상탐지의 경우, 모든 자유도의 응답이 측정가능한 것은 아니며 제한된 수의 센서에서 부분적인 진동모드만 측정할 수 있다. 이처럼 부분적인 정보를 사용하여, 손상진단을 성공적으로 수행하기 위해서는 사용될 센서의 수와 위치를 결정하는 연구가 매우 중요한다. 본 논문에서는 센서의 개수가 결정되었을 때, 손상탐지에 적합한 센서 위치의 선정방법에 관하여 연구하였다. 이러한 연구의 결과로 순차적 소거법이 역섭동법을 이용한 손상탐지에 가장 적합한 센서위치의 선정방법임을 수치 예에서 확인하였다.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1520-1528
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• 2000

This study presents a method for determining bearing stiffness and damping coefficients of air-lubricated slider bearing, and shows influences of air-bearing surface geometry(recess depth, crown an d pivot location) on flying attitude and dynamic characteristics. To derive the dynamic lubrication equation, the perturbation method is applied to the generalized lubrication equation which based on linearized Boltzmann equation. The generalized lubrication equation and the dynamic lubrication equation are converted to a control volume formulation, and then, the static and dynamic pressure distributions are calculated by finite difference method. The recess depth and crown of the slider show significantly influence on flying attitude and dynamic characteristics comparing with those of pivot location.

• Journal of applied mathematics & informatics
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• 제23권1_2호
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• pp.141-152
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• 2007

In this paper a numerical method is presented to solve singularly perturbed two points boundary value problems for second order ordinary differential equations consisting a discontinuous source term. First, in this method, an asymptotic expansion approximation of the solution of the boundary value problem is constructed using the basic ideas of a well known perturbation method WKB. Then some initial value problems and terminal value problems are constructed such that their solutions are the terms of this asymptotic expansion. These initial value problems are happened to be singularly perturbed problems and therefore fitted mesh method (Shishkin mesh) are used to solve these problems. Necessary error estimates are derived and examples provided to illustrate the method.

• Smart Structures and Systems
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• 제10권4_5호
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• pp.427-442
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• 2012

An effective approach for updating finite element model is presented which can provide reliable estimates for structural updating parameters from identified operational modal data. On the basis of the dynamic perturbation method, an exact relationship between the perturbation of structural parameters such as stiffness change and the modal properties of the tested structure is developed. An iterative solution procedure is then provided to solve for the structural updating parameters that characterise the modifications of structural parameters at element level, giving optimised solutions in the least squares sense without requiring an optimisation method. A regularization algorithm based on the Tikhonov solution incorporating the generalised cross-validation method is employed to reduce the influence of measurement errors in vibration modal data and then to produce stable and reasonable solutions for the structural updating parameters. The Canton Tower benchmark problem established by the Hong Kong Polytechnic University is employed to demonstrate the effectiveness and applicability of the proposed model updating technique. The results from the benchmark problem studies show that the proposed technique can successfully adjust the reduced finite element model of the structure using only limited number of frequencies identified from the recorded ambient vibration measurements.

• 한국게임학회 논문지
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• 제10권6호
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• pp.169-178
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• 2010

본 논문은 실시간 응용 프로그램에서 사실적인 금속 재질을 렌더링하기 위한 효과적인 기법을 제안한다. 제안된 기법은 금속면의 미세한 흡집을 표현하기 위해 법선 벡터를 섭동(perturbation)하는 방법을 사용한다. 법선 벡터를 섭동하는 일반적인 방법은 범프(bump) 매핑이나 법선(normal) 매핑 등의 방법을 사용하는 것이다. 그러나 이러한 방식은 이방성 반사 특성을 갖는 표면에서는 사실적인 빛의 산란을 보이지 못한다. 금속 특유의 반사를 표현하기 위해서는 미세면 분포 함수를 이용하여 이방성 반사 특성을 모델링하는 것이 일반적이므로 일반적 법선 섭동만으로는 만족스런 결과를 얻지 못한다. 본 논문은 법선 벡터의 섭동과 함께 미세면 분포 함수를 변형하는 기법을 통해 매우 사실적인 금속면 재질 렌더링이 가능한 기법을 제안한 다. 제안된 기법은 쉽게 GPU 프로그램으로 구현되며, 실시간 환경에서 동작한다.

• Nuclear Engineering and Technology
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• 제56권10호
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• pp.4042-4049
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• 2024

A new automatic group structure optimization method based on the perturbation theory was proposed for the few-group structure in two-step nuclear design procedure for VHTR. It applies the sensitivity coefficient of the perturbation theory which includes not only the effect of the cross section on the multiplication factor but also the adjoint weighted reaction rate. The sensitivity coefficient of the fine group for the multiplication factor was calculated and the group boundary for a few-group can be determined so that the summation of the fine group sensitivity for a few-group should be evenly distributed over every few-group. This method was successfully implemented in the ABGO code. VHTR-350 and MiHTR 2D core were used to investigate the performance and applicability of the proposed method. The code generated the new group structures for two cores and the error of the multiplication and reaction rate by the new group structure was compared with the result by the fine group structure. The comparisons indicate that the new group structure by the proposed method can provide the multiplication factor and reaction rates comparable to the existing group structure and more accurate results than the group structure obtained using the Contributon theory.

• Structural Engineering and Mechanics
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• 제37권4호
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• pp.415-425
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• 2011

In this study, the homotopy perturbation method (HPM) is applied to free vibration analysis of beam on elastic foundation. This numerical method is applied on three different axially loaded cases, namely: 1) one end fixed, the other end simply supported; 2) both ends fixed and 3) both ends simply supported cases. Analytical solutions and frequency factors are evaluated for different ratios of axial load N acting on the beam to Euler buckling load, $N_r$. The application of HPM for the particular problem in this study gives results which are in excellent agreement with both analytical solutions and the variational iteration method (VIM) solutions for all the cases considered in this study and the differential transform method (DTM) results available in the literature for the fixed-pinned case.

• 대한수학회지
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• 제54권4호
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• pp.1209-1229
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• 2017

We coupled the so-called Sumudu transform with the homotopy perturbation method (HPM) and the homotopy analysis method (HAM), which are called homotopy perturbation Sumudu transform method (HPSTM) and homotopy analysis Sumudu transform method (HASTM), respectively. Then we show how HPSTM and HASTM are more convenient than HPM and HAM by conducting a comparative analytical study for a system of time fractional nonlinear differential equations. A Maple package is also used to enhance the clarity of the involved numerical simulations.

• 한국소음진동공학회논문집
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• 제16권7호
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• pp.746-753
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• 2006

This paper proposes a method to calculate the stiffness and the damping coefficients of the coupled journal and thrust bearings. The Reynolds equations and their perturbation equations are transformed to the finite element equations by considering the continuity of pressure and flow at the interface between bearings. The Reynolds boundary condition is used in the numerical analysis to simulate the cavitation phenomena. The dynamic coefficients of the proposed method are compared with those of the numerical differentiation of the loads with respect to finite displacements and velocities of bearing center. It shows that the proposed method is more accurate and efficient than the differentiation method.