• 대한토목학회논문집
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• 제9권2호
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• pp.63-71
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• 1989

본 연구는 국부적으로 한정된 수역의 파동운동 해석시 개방경제의 조건처리에 대한 수치기법을 개선하여 수치실험결과의 신뢰도를 향상시키기 위하여 시도되었다. 개방경계의 적절한 조건을 도출하기 위하여 $L_e-norm$ 및 RMS 오차분석을 통하여 방사이론이 포함된 조건을 비교한 결과, Sommerfeld 방사조건이 우수한 것으로 나타났다. 본 연구에서 이용된 2 차원 유한요소 천수모형에 응용되도록 2 단계 기법이 적용된 개방경제조건을 단순화된 구형만에서 장주기 파동에 대하여 수치실험한 결과 Sommerfeld 방사조건보다 RMS 오차가 30% 정도 감소되는 양호한 결과를 나타냈다.

• 물과 미래
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• 제22권3호
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• pp.315-322
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• 1989

해양수치모형에 적용되는 상이한 방사조건을 포함한 개방경계조건의 영향이 $L^{2_}$-norm과 RMS오차해석에 의하여 비교되었다. 수치실험에서는 M2조석, 격자망의 영향, 해저마찰의 영향 등이 각각 고려되었다. 연구결과 개선방사조건이 고려될 때 단순한 구형만에서 해석해와 비교된 $M_2$조석의 경우는 방사조건이 고려되지 않을때보다 $L^{2_}$-norm에 의하면 40%, RMS오차에 의하면 96%나 신뢰성이 향상되었다. 이는 반격자를 이용할 때 보다도 더욱 만족스러운 결과인 것으로 나타났다. 해저마찰이 고려된 경우도 개선방사조건의 도입이 필요한 것으로 판단되었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권1호
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• pp.22-37
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• 2016

This article investigates numerical modeling of surface piercing propeller (SPP) in unsteady open water condition using boundary element method. The home code based on BEM has been developed for the prediction of propeller performance, unsteady ventilation pattern and cross flow effect on partially submerged propellers. To achieve accurate results and correct behavior extraction of the ventilation zone, finely mesh has generated around the propeller and especially in the situation intersection of propeller with the free surface. Hydrodynamic coefficients and ventilation pattern on key blade of SPP are calculated in the different advance coefficients. The values obtained from this numerical simulation are plotted and the results are compared with experiments data and ventilation observations. The predicted ventilated open water performances of the SPP as well as ventilation pattern are in good agreement with experimental data. Finally, the results of the BEM code/experiment comparisons are discussed.

• 천문학회보
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• 제44권1호
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• pp.46.1-46.1
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• 2019

We present an accurate and efficient method to calculate the gravitational potential of an isolated system in three-dimensional Cartesian and cylindrical coordinates subject to vacuum (open) boundary conditions. Our method consists of two parts: an interior solver and a boundary solver. The interior solver adopts an eigenfunction expansion method together with a tridiagonal matrix solver to solve the Poisson equation subject to the zero boundary condition. The boundary solver employs James's method to calculate the boundary potential due to the screening charges required to keep the zero boundary condition for the interior solver. A full computation of gravitational potential requires running the interior solver twice and the boundary solver once. We develop a method to compute the discrete Green's function in cylindrical coordinates, which is an integral part of the James algorithm to maintain second-order accuracy. We implement our method in the {\tt Athena++} magnetohydrodynamics code, and perform various tests to check that our solver is second-order accurate and exhibits good parallel performance.

• 대한수학회지
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• 제34권1호
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• pp.87-118
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• 1997

This paper is concerned with a mixed Lagrangian formulation of the wiscous, stationary, incompressible Navier-Stokes equations $$ (1.1) -\nu\Delta u + (u \cdot \nabla)u + \nabla_p = f in \Omega $$ and $$ (1.2) \nubla \cdot u = 0 in \Omega $$ along with inhomogeneous Dirichlet boundary conditions on a portion of the boundary $$ (1.3) u = ^{0 on \Gamma_0 _{g on \Gamma_g, $$ where $\Omega$ is a bounded open domain in $R^d, d = 2 or 3$, or with a boundary $\Gamma = \partial\Omega$, which is composed of two disjoint parts $\Gamma_0$ and $\Gamma_g$.

• Korean Journal of Mathematics
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• 제5권1호
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• pp.29-33
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• 1997

In this paper we investigate the existence of positive solutions of a nonlinear biharmonic equation under Dirichlet boundary condition in a bounded open set ${\Omega}$ in $\mathbf{R}^n$, i.e., $${\Delta}^2u+c{\Delta}u=bu^{+}+s\;in\;{\Omega},\\u=0,\;{\Delta}u=0\;on\;{\partial}{\Omega}$$.

• Journal of the korean society of oceanography
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• 제33권4호
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• pp.212-218
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• 1998

Three different outflow boundary conditions are considered in modeling the East Sea circulation. The first one is that of the conventional constant volume transport (CT). The second one is the Orlanski radiation boundary condition (OR). The third one is that of the constant sea level just outside the outflow boundary (SL). In the third condition, the outflow current is set to be driven by the sea level differences across the outflow open-boundary lines, based on the recent knowledge that the Tsushima Current is driven by the sea level differences across the inflow and outflow boundaries. In case of OR it takes too much time to reach the steady state, resulting in a large increase of Tsushima Current Water in the basin and low level of kinetic energy. Both CT and SL reach the steady state in a relatively short time. However, SL is more recommendable, because it is based on physical background and generates less numerical noises than CT.

• 설비공학논문집
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• 제4권3호
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• pp.217-232
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• 1992

A Numerical study on two-dimensional laminar natural convection with and without surface radiation in fully or partially open square cavity was performed. The cavity has one vertical heated wall facing a vertical opening and two horizontal insulated walls. The pressure boundary condition was applied to the opening instead of the velocity boundary condition. The results of this study showed that the increase of partition length decreased the convective and the radiative Nusselt numbers. It was also found that the increase of wall emissivity decreased the convective Nusselt numbers but increased the radiative Nusselt numbers.

• 한국해안해양공학회지
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• 제5권1호
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• pp.39-44
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• 1993

본 논문에서는 경계 damper를 이용하여 파낭의 항내 침입으로 인한 수면교난 현상을 예측할 수 있는 유한요소 수치모형에 대해서 연구하였다. 지배방정식으로는 완경사냉정식을 사용하였으며, 고체 경계면에서의 에너지 손실 효과를 고려하기 위하여 부분반사 경계조건을 도입하였다. 방사 경계조건은 Bando 등(1984)이 개발한 2차원 경계 damper로 처리하였다. 항내 영역은 8절점 등매개변수요소를 사용하여 모형화하였으며, 경계면의 경계조건은 3절점 선요소로 처리하였다. 본 수치모형의 검증을 위하여 완전 개방된 직사각형 모형항만에 대해 수치실험을 수행하였다. 또한, 고체 경계면에서의 반사율 변화 및 경계 damper의 종류에 따른 해석도 수행하여 상호 비교하였다.

• 한국해양공학회지
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• 제9권1호
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• pp.120-131
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• 1995

Numerical simulations on the suspended sediment transport in the Nakdong Estuary are carried out Uncoupled flow model and diffusion model of which the governing equations are two-dimensional depth integrated equations are used int his study. Four cases are tested in this numerical simulations in which the Gaduk waterway open boundary condition and Nakdong Estuary barrage boundary condition are considered as the boundary conditions. The simulated results are compared with the measured data which were obtained by NEDECO at hadan site on 1981.2.19. and by Dong-A university at one station in the study area on 1993.4.3. and show a good agreement with them. The construction of the Nakdong Estuary Barrage may affect to reduce the current near Jinudo an Daemadeung and the suspended sediment inflowed from the upstream in the wet season seems to be transported to the Dadae.