• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.175-181
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• 1995

Three-Dimensional Euler equations are solved numerically for the analysis of contraction flows in wind or water tunnels. A second-order finite difference method is used for the spatial discretization on the nonstaggered grid system and the 4-stage Runge-Kutta scheme for the numerical integration in time. In order to speed up the convergence, the local time stepping and the implicit residual-averaging schemes are introduced. The pressure field is obtained by solving the pressure-Poisson equation with the Neumann boundary condition. For the evaluation of the present Euler solver, numerical computations are carried out for the various contraction geometries, one of which was adopted in the Large Cavitation Channel for the U.S. Navy. The comparison of the computational results with the available experimental data shows good agreements.

• 한국전산유체공학회지
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• 제2권1호
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• pp.8-12
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• 1997

The three-dimensional Euler equations are solved numerically for the analysis of contraction flows in wind or water tunnels. A second-order finite difference method is used for the spatial discretization on the nonstaggered grid system and the 4-stage Runge-Kutta scheme for the numerical integration in time. In order to speed up the convergence, the local time stepping and the implicit residual-averaging schemes are introduced. The pressure field is obtained by solving the pressure-Poisson equation with the Neumann boundary condition. For the evaluation of the present Euler solver, numerical computations are carried out for three contraction geometries, one of which was adopted in the Large Cavitation Channel for the U.S. Navy. The comparison of the computational results with the available experimental data shows good agreement.

• 전자공학회논문지D
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• 제34D권4호
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• pp.100-105
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• 1997

3-dimensional finite element mehtod (FEM) elecrical field analysis was performed to obtain electric fields on a field emission display (FED) tip in an array form. Because, unlike a single tip structure, there is no azimuthal symmetry for a tip aary, 3D analysis is necessary. To reduce memory requriement the simulatio was performed by applying the neumann boundary condition to the intermediate plane between tips to take the effect of the array on the electric field into account and corresponding current was calculated. To verify our algorithm, comparison between simulation resutls and experimental data from another paper was made and the difference was discussed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.662-664
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• 1997

3-dimensional finite element method(FEM) electrical field analysis was performed to obtain electric fields on a field emission device tip in an array form. The simulation was performed by applying the Neumann boundary condition to the intermediate plane between tips. To verify our algorithm, comparison between simulation results and experimental data from another paper was made and the difference was discussed. Finally, analysis on triode structure was performed.

• 대한수학회지
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• 제45권5호
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• pp.1255-1274
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• 2008

The purpose of this paper is to discuss the constant term appearing in the BFK-gluing formula for the zeta-determinants of Laplacians on a complete Riemannian manifold when the warped product metric is given on a collar neighborhood of a cutting compact hypersurface. If the dimension of a hypersurface is odd, generally this constant is known to be zero. In this paper we describe this constant by using the heat kernel asymptotics and compute it explicitly when the dimension of a hypersurface is 2 and 4. As a byproduct we obtain some results for the value of relative zeta functions at s=0.

• Kyungpook Mathematical Journal
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• 제48권4호
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• pp.593-611
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• 2008

Global attractivity and oscillatory behavior of the following nonlinear impulsive parabolic differential equation which is a general form of many population models $$\array{\{{{\frac {{\partial}u(t,x)}{{\partial}t}=\Delta}u(t,x)-{\delta}u(t,x)+f(u(t-\tau,x)),\;t{\neq}t_k,\\u(t^+_k,x)-u(t_k,x)=g_k(u(t_k,x)),\;k{\in}I_\infty,}\;\;\;\;\;\;\;\;(*)$$ are considered. Some new sufficient conditions for global attractivity and oscillation of the solutions of (*) with Neumann boundary condition are established. These results no only are true but also improve and complement existing results for (*) without diffusion or impulses. Moreover, when these results are applied to the Nicholson's blowflies model and the model of Hematopoiesis, some new results are obtained.

• 대한조선학회논문집
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• 제32권1호
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• pp.42-57
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• 1995

자유표면의 유동문제는 저항추진성능과 내항성능이 우수한 선박과 파랑중 작업성능이 우수한 해양구조물의 설계와 관련되어 조선해양공학분야에서 지속적으로 관심의 대상이 되어온 연구분야이다. 본 논문에서는 선체주위 유동을 정확하고 효율적으로 해석하기 위한 3차원 수치해법의 개발을 목적으로 하였다. 수치해법으로 경계요소법을 사용하였으며, 그린함수는 간단한 랜킨소오스를 사용하였다. 전 경계요소면은 8점 경계요소로 표시하여 기하학적 특성을 정밀하게 반영하고자 하였다. 자유표면에서 속도포텐셜의 변화를 정규화된 8점 경계요소에서 이중 2차 스플라인함수(bi-quadratic spline function)로 표시함으로써 자유표면에서의 수치감쇠 및 분산오차를 개선하였다. 한편 물체표면에서의 물리량은 8점 경계요소의 특성을 살려 이중 2차 다항식(bi-quadratic function)으로 근사하였다. 이와같이 계산영역에 따라 해의 특성에 부합하는 수치방법을 채택함으로써 수치해의 정확성과 효율성이 향상되도록 하였다. 개발한 수치해법의 효능을 검증하기 위해 계산예로서 정상유동 및 비정상유동의 경우 Neumann-Kelvin문제를 다루었다. 본 방법에 의한 몰수 타원체 및 Series 60선에 대한 조파저항 계산결과는 적은 파넬수를 사용하고도 기존의 계산치는 물론 실험치와 좋은 일치를 보였다. 변형된 Wigley선형에 대한 동유체력 계산결과도 기존의 실험치 및 계산치와 비교적 잘 일치하였다. 비정상 유동의 경우 랜킨소오스법에서 일반적으로 적용하는 상류방사조건은 무차원주파수가 1/4보다 큰 경우에만 유효하므로, 본 논문에서는 파동방정식 연산자를 이용하여 무차원주파수가 1/4보다 작은 경우에 적용할 수 있는 상류방사조건을 유도하였다. 수면하에서 전진하며 동요하는 소오스에 대하여 적용한 결과 본 논문에서 유도한 방사조건이 유효함을 입증하였다.

• 한국해양공학회지
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• 제23권1호
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• pp.16-23
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• 2009

The three-dimensional ship motion with forward speed was solved by a finite element method in the time domain. A boundary value problem was described in the frame of a fixed-body reference, and the problem was formulated according to Double-Body and Neumann-Kelvin linearizations. Laplace's equation with boundary conditions was solved by a classical finite element method based on the weak formulation. Chebyshev filtering was used to get rid of an unwanted saw-tooth wave and a wave damping zone was adopted to impose a numerical radiation condition. The time marching of the free surface was performed by the 4th order Adams-Bashforth-Moulton method. Wigley I and Wigely III models were considered for numerical validation. The hydrodynamic coefficients and wave exciting forces were validated by a comparison with experimental data and the numerical results of the Wigley I. The effects of the linearization are also discussed. The motion RAO was also checked with a Wigley III model through mono-chromatic and multi-chromatic regular waves.

• JSTS:Journal of Semiconductor Technology and Science
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• 제7권4호
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• pp.287-298
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• 2007

A two-dimensional treatment of the potential distribution under the depletion approximation is presented for poly-crystalline silicon thin film transistors. Green's function approach is adopted to solve the two-dimensional Poisson's equation. The solution for the potential distribution is derived using Neumann's boundary condition at the silicon-silicon di-oxide interface. The developed model gives insight into device behavior due to the effects of traps and grain-boundaries. Also short-channel effects and drain induced barrier lowering effects are incorporated in the model. The potential distribution and electric field variation with various device parameters is shown. An analysis of threshold voltage is also presented. The results obtained show good agreement with simulated results and numerical modeling based on the finite difference method, thus demonstrating the validity of our model.

• 대한조선학회논문집
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• 제31권3호
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• pp.87-99
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• 1994

Reynolds Averaged Navier-Stokes 방정식을 수치해석하여 Wigley 선형 주위의 난류유동을 계산하였다. 정규격자상에서 공간의 이산화는 2차 정도의 유한차분법을, 시간의 적분에는 4단계 Runge-kutta법을 이용하였다. 시간 증분을 크게 하기 위하여 Jameson의 잔류항 평균 기법을 사용하였다. 압력 Poisson 방정식으로부터 압력장을 구하였고 난류닫음 조건을 만족시키기 위하여 Baldwin-Lomax의 난류 모형을 사용하였다. 수치계산은 레이놀드수가 $4.5{\times}10^6$에서 수행하였고 계산된 속도와 압력분포는 실험 결과와 비교적 잘 일치하는 것을 확인하였다.