• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2008년도 공동학술대회
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• pp.57-62
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• 2008

탄성파 수치 모형 계산에 있어서 널리 사용되는 엇갈린 격자 방법이 아니라 회전된 엇갈린 격자 방법을 사용하여 탄성파 수치 모사를 수행하였다. 표준 엇갈린 격자 방법에서는 자유 경계조건을 적용하여야 하는 단점이 있지만 회전된 격자 방법에서는 자유 경계조건을 적용할 필요 없이 물성을 부여함으로써 해결될 수 있다. 파동전파에 있어서 유한 경계 조건에서 발생하는 인공 반사파를 제거하기 위하여 최근에 뛰어난 성능을 보이는 PML(Perfectly Matched Layer)법이 많이 적용되고 있다. 이 연구에서는 PML보다 성능이 뛰어나기도 하지만 차분에 있어 파동식을 분리할 필요가 없는 CPML(Convolutional Perfectly Matched Layer)법을 회전된 엇갈린 격자법(RSG : Rotatged Staggered Grid)에 적용하고자 하였다. Cerjan법의 감쇠법과 비교한 결과 매우 효과적으로 인공 반사파를 제거할 수 있음을 알 수 있었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1054-1059
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• 2005

The artificial potential method uses a potential field to guide a robot from a start to a goal configuration respectively. The potential field consists of attractive potential used to pull a robot toward a goal and repulsive potential to keep it away from obstacles. However, there are two problems concerning local minimum and computational cost to be resolved in conventional artificial potential methods. This study proposes a method utilizing a spline surface that interpolates arbitrary boundaries and a domain reduction method that reduces the unnecessary area. The proposed spline surface interpolates arbitrary shaped boundaries and is used as an artificial potential to guide a robot for global motion planning of a mobile robot. A reduced domain process reduces the unnecessary domain. We apply a distance-weighted function as such a function, which blends distances from each boundary with a reduction in computational time compared with other analytical methods. As a result, this paper shows that an arbitrary boundary spline surface provides global planning and a domain reduction method reduces local minimum with quick operation.

• 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.

• 지구물리와물리탐사
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• 제12권2호
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• pp.183-191
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• 2009

탄성파 수치 모형 계산에 있어서 널리 사용되는 엇갈린 격자 방법이 아니라 회전된 엇갈린 격자 방법을 사용하여 탄성파 수치 모사를 수행하였다. 표준 엇갈린 격자 방법에서는 특별한 자유 경계조건을 적용하여야 하는 단점이 있지만 회전된 격자 방법에서는 물성으로 진공 또는 공기층을 부여함으로써 자유 경계조건을 실현가능하다는 것을 확인할 수 있었다. 파동전파에 있어서 유한 경계 조건에서 발생하는 인공 반사파를 제거하기 위해 PML (Perfectly Matched Layer)의 파동식 분해라는 단점을 극복할 수 있고 좋은 성능을 보이는 CPML (Convolutional Perfectly Matched Layer)법을 회전된 엇갈린 격자법(RSG: Rotatged Staggered Grid)에 적용하였다. 회전된 격자 유한 차분법에서 CPML의 고주파수 흡수 특성과 에너지 흡수율 조사, Cerjan법의 감쇠를 비교한 결과 흡수경계조건으로 좋은 성능을 확인하였다. 유체와 고체의 모형에 대한 경계에 대하여서도 매우 효과적으로 경계면에서 발생하는 반사파를 제거할 수 있음을 알 수 있었다.

• 대한수학회논문집
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• 제12권2호
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• pp.427-456
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• 1997

This paper concerns constructing wavelet bases on the unit interval, where a new boundary treatment is provided to overcome certain drawbacks of eariler constructions. Wavelet expansions on the unit interval usually suffer from artificial boundary effects and poor convergence at the boundaries. Many researchers have suggested a solution to the drawbacks. From a practical point of view, their solutions also have a common disadvantage. This paper provides a new solution using biorthogonality near the boundaries, that avoids the disadvantage while preserving their advantages.

• Selected Papers of The Society of Naval Architects of Korea
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• 제2권1호
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• pp.63-78
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• 1994

This paper deals with the treatment of the open boundary in two-dimensional free-surface wave problems. Two numerical schemes are investigated for the implementation of the open boundary condition. One is to add the artificial damping term to the dynamic free-surface boundary condition, in which the determination of suitable damping coefficient and the damping zone is the most important. The other is a modified Orlanski's method, which is known to be very useful for the uni-directional waves. Using these two schemes, numerical tests have been conducted for a few typical free-surface wave problems. To obtain the numerical solution of the free-surface boundary value problem, the fundamental source-distribution method is used and the fully nonlinear free-surface boundary conditions are applied. The computed results are presented in comparison with those of others for the proof of practicality of these two schemes.

• Journal of applied mathematics & informatics
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• 제14권1_2호
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• pp.97-113
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• 2004

In this paper we shall study moving boundary problems, and we introduce an approach for solving a wide range of them by using calculus of variations and optimization. First, we transform the problem equivalently into an optimal control problem by defining an objective function and artificial control functions. By using measure theory, the new problem is modified into one consisting of the minimization of a linear functional over a set of Radon measures; then we obtain an optimal measure which is then approximated by a finite combination of atomic measures and the problem converted to an infinite-dimensional linear programming. We approximate the infinite linear programming to a finite-dimensional linear programming. Then by using the solution of the latter problem we obtain an approximate solution for moving boundary function on specific time. Furthermore, we show the path of moving boundary from initial state to final state.

• Journal of Advanced Marine Engineering and Technology
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• 제24권1호
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• pp.31-40
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• 2000

This paper describes the numerical computations of the interaction between the streamwise vortex and a flat plate 3-D turbulent boundary layer. In the present study, the main interest is in the behavior of the streamwise vortices introduced in turbulent boundary layers. The flow behind a vortex generator is modeled by the information that is avilable from studies on the dalta winglet. An algorithm of the solution of the incompressible Navier-Stokes equations for three-dimensional turbulent flows, together with a two layer turbulent model to resolve the near-wall flow, is based on the method of artificial compressibility. The present results show boundary layer distortion due to vortices, such as strong spanwise flow divergence and boundary thinning, and have a good agreement with the experimental data.

• Structural Engineering and Mechanics
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• 제18권3호
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• pp.303-314
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• 2004

An artificial neural network (ANN) application is presented for flexural and axial vibration analysis of elastic beams with various support conditions. The first three natural frequencies of beams are obtained using multi layer neural network based back-propagation error learning algorithm. The natural frequencies of beams are calculated for six different boundary conditions via direct solution of governing differential equations of beams and Rayleigh's approximate method. The training of the network has been made using these data only flexural vibration case. The trained neural network, however, had been tested for cantilever beam (C-F), and both end free (F-F) in case the axial vibration, and clamped-clamped (C-C), and Guided-Pinned (G-P) support condition in case the flexural vibrations which were not included in the training set. The results found by using artificial neural network are sufficiently close to the theoretical results. It has been demonstrated that the artificial neural network approach applied in this study is highly successful for the purposes of free vibration analysis of elastic beams.

• 대한수학회논문집
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• 제14권4호
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• pp.815-832
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• 1999

High-order weighted difference schemes with uniform meshes are considered for the convection-diffusion problem depending on Reynolds numbers. For small Reynolds numbers, a weighed cen-tral difference scheme is suggested since there is no boundary layer. For large Reynolds numbers, we propose a modified up wind method with an artificial diffusion in order to overcome nonphysical oscilla-tion of central schemes and obtain good accuracy in the boundary later. Existence and corresponding error estimates of the solution for the difference scheme have been shown. Numerical experiments are provided to back up the analysis.