• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2001년도 학술발표회 논문집(II)
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• pp.949-954
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• 2001

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.22-27
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• 2006

This paper describes the development of the stream-tube based dispersion model for modeling contaminant transport in open channels. The operator-splitting technique is employed to separate the 2D contaminant transport equation into the pure advection and pure dispersion equations. Then the total variation diminishing (TVD) schemes are combined with the second-order Lax-Wendroff and third-order QUICKEST explicit finite difference schemes respectively to solve the pure advection equation in order to prevent the occurrence of numerical oscillations. Due to various limiters owning different features, the numerical tests for 1D pure advection and 2D dispersion are conducted to evaluate the performance of different TVD schemes firstly, then the TVD schemes are applied to experimental data for simulating the 2D mixing in a straight trapezoidal channel to test the model capability. Both the numerical tests and model application show that the TVD schemes are very competent for solving the advection-dominated transport problems.

• 한국수자원학회논문집
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• 제36권5호
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• pp.777-785
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• 2003

본 연구에서는 비구조격자 좌표계상에서 천수방정식 해석을 위한 수치모형을 개발하였다. Fractional step method를 이용하여 이차원의 천수방정식을 두개의 일차원 문제로 분리하여 계산 효율이 우수한 수치연산을 수행하였다. 분리된 일차원 문제는 이차정확도의 TVD 기법을 이용하여 해석하였다. TVD 기법은 HLLC 기법을 이용하여 Riemann 해를 구한후 WAF 기법을 기반으로 이용하였으며 WAF 흐름율 제한자를 이용하여 이차정확도 문제에 수반되는 비물리적인 수치진동을 제어하였다. 개발된 모형을 다양한 문제에 적용한 결과, 해석해와 계산된 결과가 매우 잘 일치하였으며, 본 모형이 불연속해나 상류사류의 혼합흐름 및 이동경계 문제 등에 이용될 수 있음을 보였다.

• 한국전산유체공학회지
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• 제2권2호
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• pp.59-72
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• 1997

A numerical model is constructed to simulate the interactions of oblique shock wave / turbulent boundary layer on a strongly heated wall. The heated wall temperature is two times higher than the adiabatic wall temperature and the shock wave is strong enough to induce boundary layer separation. The numerical diffusion in the finite volume method is reduced by the use of a higher order convection scheme(UMIST scheme) which is a TVD version of QUICK scheme. The turbulence model is Chen-Kim two time scale model. The comparison of the wall pressure distribution with the experimental data ensures the validity of this numerical model. The effect of strong wall heating enlarges the separation region upstream and downstream. In order to eliminate the separation, wall suction is applied at the shock foot position. The bleeding slot width is about same as the upstream boundary layer thickness and suction mass flow is 10% of the flow rate in the upstream boundary layer. The final configuration of the shock reflection pattern and the wall pressure distribution approach to the non-viscous value when wall suction is applied.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.169-177
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• 2005

A high resolution scheme for solving gas-liquid two-phase flows with cavitation is described. This scheme uses the curvilinear coordinate grid and solves the density based momentum equations for mixture of gas-liquid medium with a preconditioning method to treat both compressible and incompressible flow characteristics. The present preconditioned method is based on the Runge-Kutta explicit finite-difference scheme, and is improved by using the diagonalization, the flux difference splitting and the MUSCL-TVD schemes to save computational effort and to increase stability and resolvability, especially at gas-liquid contact surfaces. A homogeneous equilibrium cavitation model is used to treat the gas-liquid two-phase medium in cavitating flow as a locally homogeneous pseudo-single-phase medium. Therefore, it is easy to solve cavitating flow, including wave propagation, large density changes and incompressible flow characteristic at low Mach number. Some numerical results obtained by the present scheme are shown.

• 한국전산유체공학회지
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• 제15권2호
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• pp.55-61
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• 2010

A dependence of weighting parameter in preconditioning method for solving low Mach number flow with incompressible flow nature is investigated. The present preconditioning method employs a finite-difference method applied Roe‘s flux difference splitting approximation with the MUSCL-TVD scheme and 4th-order Runge-Kutta method in curvilinear coordinates. From the computational results of benchmark flows through a 2-D backward-facing step duct it is confirmed that there exists a suitable value of the weighting parameter for accurate and stable computation. A useful method to determine the weighting parameter is introduced. With this method, high accuracy and stable computational results were obtained for the flow with low Mach number in the range of Mach number less than 0.3.

• 대한기계학회논문집
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• 제18권3호
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• pp.612-623
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• 1994

Shock-wave focusing from a two-dimensional parabolic reflector was simulated using an explicit finite volume upwind TVD scheme. Computations were performed for three different incident shock speeds of $M_s$ = 1.1, 1.2 and 1.3, corresponding to the relatively weak, intermediate, and strong shock waves, respectively. Numerical solutions nicely resolved all the waves evolving through the focusing process. As the incident shock strength increase, a transition was observed in the shock-fronts geometry that was caused by the change in the reflection type of converging shock fronts on the axis of symmetry, from regular-type to Mach-type reflection. The computed maximum on-axis pressure amplification and the trajectories of three-wave intersections showed good agreement with experimental results. The strong nonlinear effect near the focal region which determines the shock-fronts geometries at and behind the focus and at the same time confines the pressure amplification at the focus was clearly revealed from the present numerical simulation.

• 한국전산유체공학회지
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• 제4권3호
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• pp.35-43
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• 1999

In this study, the shock wave focusing of an elliptic reflector is numerically simulated by solving the Euler equations. The numerical method is the second order upwind TVD scheme with a finite volume discretization. For the verification of the present method, we simulate the moving shock wave passing through a two-dimensional corner. The computed isopycnics are compared with the earlier experiment. Numerical results of the elliptic reflectors show that the density and pressure at the focusing point increase linearly as the aspect ratio of the reflector becomes deep. On the other hand, the gas dynamic focal length decreased with the increase of the reflector aspect ratio.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.233-236
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• 2008

To analyze the saline intrusion in the place, such as an estuary, the three-dimensional numerical model is developed. In this study, the advection terms of the governing equations are discretized by upwind scheme. By using an explicit scheme for the longitudinal direction and an implicit scheme for the vertical direction, the numerical model is free from the restriction of temporal step size caused by a relatively small grid ratio. The equation of state is used to consider the density, and the scalar transport equation for salinity is employed the third order TVD to scheme to prevent unphysical oscillation near discontinuity. In order to verify saline intrusion, the numerical model is conducted to compare the previous model in the lock exchange. The present model generally show a good agreement with the previous one.

• Water Engineering Research
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• 제3권1호
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• pp.23-30
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• 2002

A numerical model for the solution of two-dimensional dam break problems using fractional step method is developed on unstructured grid. The model is based on second-order Weighted Averaged Flux(WAF) scheme with HLLC approximate Riemann solver. To control the nonphysical oscillations associated with second-order accuracy, TVD scheme with SUPERBEE limiter is used. The developed model is verified by comparing the computational solutions with analytic solutions in idealized test cases. Very good agreements have been achieved in the verifications.