• 동력기계공학회지
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• 제16권5호
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• pp.40-46
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• 2012

본 연구에서는 자유표면 유동문제를 효율적으로 계산하기 위한 방법으로서, 수치 파수조를 구현하여 잠수체에 의한 조파현상을 시간영역에서 다룰 수 있는 수치해법에 대하여 소개하였다. 그리고 이를 이용하여 수행된 연구내용들을 검토하고 양력물체의 경우를 포함하기 위하여 개선된 수학적 정식화 및 수치해법의 개요를 다루었다. 임의의 운동을 하는 양력물체에 의한 조파현상을 전산기로 구현하는 수치 파수조는 과중한 계산시간이 문제가 되는데, 이는 수치 Kutta 조건의 구현과 양력표면 후방의 wake 영역을 계산에서 고려해야 하기 때문이다. 따라서 한층 더 수치계산의 효율성이 중요하다고 판단되므로, 본 연구에서 소개된 3차원 고차 스펙트럴/경계요소법(High-Order Spectral/Boundary Element Method)은 자유표면 요소수를 N이라 할 때 그 계산량이 NlogN에 비례(N이 클 때는 거의 선형적으로 비례)하여 증가하므로 기존의 방법들 보다 매우 효율적인 수치해법이라 할 수 있다. 향후, 본 연구의 타당성 검증을 위한 수치코드의 개선과 여러 가지 수치계산결과 비교 등의 노력이 더 필요하다고 생각된다.

• Journal of Advanced Marine Engineering and Technology
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• 제31권7호
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• pp.833-841
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• 2007

The aim of this paper is to analyze the conjugate problems of heat conduction in solid walls coupled with laminar free convection flow adjacent to a vertical flat plate under boundary layer approximation. Using the similarity transformations the governing boundary layer equations for momentum and energy are reduced to a system of partial differential equations and then solved numerically using Finite Difference Method(FDM) known as the Keller-box scheme. Computed solutions to the governing equations are obtained for a wide range of non-dimensional parameters that are present in this problem, namely the coupling parameter P. the Prandtl number Pr and the heat generation parameter Q. The variations of the local heat transfer rate as well as the interface temperature and the friction along the plate and typical velocity and temperature profiles in the boundary layer are shown graphically. Numerical solutions have been consider for the Prandtl number Pr=0.70

• Structural Engineering and Mechanics
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• 제21권3호
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• pp.315-332
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• 2005

The Element-free Galerkin Method has become a very popular tool for the simulation of mechanical problems with moving boundaries. The internally applied Moving Least Squares interpolation uses in general Gaussian or cubic weighting functions and has compact support. Due to the approximative character of this interpolation the obtained shape functions do not fulfill the interpolation conditions, which causes additional numerical effort for the application of the boundary conditions. In this paper a new weighting function is presented, which was designed for meshless shape functions to fulfill these essential conditions with very high accuracy without any additional effort. Furthermore this interpolation gives much more stable results for varying size of the influence radius and for strongly distorted nodal arrangements than existing weighting function types.

• 한국해안해양공학회지
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• 제2권1호
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• pp.11-17
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• 1990

심해 파랑변형으로부터 형성된 Dirichlet 경계치 문제를 free space Green함수를 써서 경계적 분방정식으로 바꾸었으며 이 적분방정식을 Cubic spline 요소법을 사용하여 차분한 수치모델이 제시되었다. 유도된 제 1종 Fredholm적분방정식의 수치계산시 안정도를 높이기 위한 Hsiao와 MacCamy(1973) 방법이 사용되었다. 수치계산 결과의 검증을 위해 엄밀해가 존재하는 두 경우를 택하여 비교하였고, 본 모델의 높은 정밀도가 입증되었다.

• Structural Engineering and Mechanics
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• 제45권4호
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• pp.569-594
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• 2013

The free vibration of axially functionally graded tapered arches including shear deformation and rotatory inertia are studied through solving the governing differential equation of motion. Numerical results are presented for circular, parabolic, catenary, elliptic and sinusoidal arches with hinged-hinged, hinged-clamped and clamped-clamped end restraints. In this study Differential Quadrature element of lowest order (DQEL) or Lagrangian Interpolation technique is applied to solve the problems. Three general taper types for rectangular section are considered. The lowest four natural frequencies are calculated and compared with the published results.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.534-537
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• 2005

Free Vibration Analysis using Non-dimensional Dynamic Influence Function (NDIF) is extended to arbitrarily shaped plates including polygonal plates. Since the corners of polygonal plates have indefinite normal directions and additional boundary conditions related to a twisting moment at a corner along with moment and shear force zero conditions, it is not easy to apply the NDIF method to polygonal plates wi th the free boundary condition. Moreover, owing to the fact that the local polar coordinate system, which has been introduced for free plates with smoothly varying edges, cannot be employed for the straight edges of the polygonal plates, a new coordinate system is required for the polygonal plates. These problems are solved by developing the new method of modifying a corner into a circular arc and setting the normal direction at the corner to an average value of normal direct ions of two edges adjacent to the corner. Some case studies for plates with various shapes show that the proposed method gives credible natural frequencies and mode shapes for various polygons that agree well with those by an exact method or FEM (ANSYS).

• 한국강구조학회 논문집
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• 제12권2호통권45호
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• pp.221-230
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• 2000

자유단이 있는 비등방성 판의 안정성을 검토할 때, 기존의 해석적인 방법으로는 다양한 하중 조건 및 경계조건에 대해 좌굴하중 및 좌굴모드를 구할 수 없다. 이러한 단점을 해결하기 위해 수치해석 기법인 유한차분법을 사용하였다. 유한차분법을 적용할 때, 자유경계의 가상점 처리가 가장 난해하게 되므로 1변이 자유이고 3변이 고정인 경우와 마주보는 2변이 자유이고 다른 2변이 고정인 경우를 해석 모델로 삼아 좌굴해석을 수행하였다. 본 논문에서는 자유경계를 갖는 비등방성 판의 해석 기법으로 유한차분법을 제시하였으며, 다양한 수치해석을 통하여 자유경계의 좌굴하중 및 모드 특성을 규명하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1994년도 봄 학술발표회 논문집
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• pp.128-136
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• 1994

In this study, dynamic boundary element method using mass matrix is derived, using fundamental solutions for the semi-infinite domain. In constituting boundary integral equations for the dynamic equilibrium condition, inertia term in the form of domain integral is transformed into boundary integral form. Corresponding system equations are derived, and a boundary element program is developed. In addition, equations for free vibration is formulated, and eigenvalue analysis is performed. The results from the dynamic boundary element analysis for a tunnel problem are compared with those from the finite element analysis. According to the comparison, boundary element method using mass matrix is consistent with the results of finite element method. Consequently, in tunnel vibration problems, it results in reasonable solution compared with other methods where relatively higher degree of freedoms are employed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.698-703
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• 2000

In a computational fluid dynamics, the imposition of open boundary condition has an important part of the accuracy but it is not easy to find the optimal boundary rendition. This difficult is introduced by making artificial boundary in unbounded domairs. Such open boundary requires us to ensure the continuity of all primitive variables because the nature is in continuum. Here we introduce a revised well-conditioned open boundary condition particularly in FEM and apply it to various problems-entrainment, body force, short domains.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권2호
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• pp.375-389
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• 2015

An improved boundary element method is presented for numerical analysis of hydrodynamic behavior of marine structures. A new algorithm for numerical solution of the finite depth free-surface Green function in three dimensions is developed based on multiple series representations. The whole range of the key parameter R/h is divided into four regions, within which different representation is used to achieve fast convergence. The well-known epsilon algorithm is also adopted to accelerate the convergence. The critical convergence criteria for each representation are investigated and provided. The proposed method is validated by several well-documented benchmark problems.