• 한국해양공학회지
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• 제11권4호
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• pp.141-151
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• 1997

This paper deals with a numerical study of flow-guider applied to controlling current in a bay. Two dimensional numerical model for tidal currents based on the depth averaged equation is developed and standard k-.epsilon. model is adopted to determine the turbulence diffusion. Equations are described in a generalized coordinate system to be implemented by non-staggered grid system and discretized by using finite volume method. Unsteady flow is simulated by fully implicit scheme. Hybrid scheme and central differencing are used to compute the convective terms and source terms, respectively. The tidal current in a rectangular bay is simulated and it gives satisfactory results. The realistic and distinct models of a large structure placed in bay are also exemplified with or without flow-guiders. The simulation results show that the flow-guider gives the residual tidal current in the bay by the different flux with respect to the direction of tidal current.

• 대한토목학회논문집
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• 제13권3호
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• pp.119-127
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• 1993

근래 천수방정식과 같은 2차원 수치해석에서 가장 널리 쓰이는 방법 중의 하나로 ADI 방법을 들 수 있다. 그러나 서해안과 같이 수심의 변화가 심하며 특히 해저협곡이 곳곳에 발달된 해역에서 조석에 관한 문제해결시 ADI 방법을 사용하면 소위 ADI 효과가 크게 우려된다. 이를 극복하기 위하여 완전 음해법으로 차분되고 CGS(conjugate gradient squared) 방법으로 해를 구하는 알고리즘을 개발하였다. 조간대 모의가 포함된 본 모형용 새만금 수역에 적용한 결과 지형의 복잡성에도 불구하고 유속장과 조간대 형성에 관한 수치적 모의가 만족스러운 결과를 보였다.

• Journal of applied mathematics & informatics
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• 제29권5_6호
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• pp.1129-1141
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• 2011

In this paper, a class of large time-stepping method based on the finite element discretization for the Cahn-Hilliard equation with the Neumann boundary conditions is developed. The equation is discretized by finite element method in space and semi-implicit schemes in time. For the first order fully discrete scheme, convergence property is investigated by using finite element analysis. Numerical experiment is presented, which demonstrates the effectiveness of the large time-stepping approaches.

• Nuclear Engineering and Technology
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• 제35권1호
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• pp.45-54
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• 2003

A hyperbolic two-phase, two-fluid equation system developed in the previous work has been implemented in an existing nuclear safety analysis code, MARS. Although the implicit treatment of interfacial pressure force term introduced in momentum equation of the hyperbolic equation system is required to enhance the numerical stability, it is very difficult to implement in the code because it is not possible to maintain the existing numerical solution structure. As an alternative, two-step approach with stabilizer momentum equations has been selected. The results of a linear stability analysis by Von-Neumann method show the equivalent stability improvement with fully-implicit solution method. To illustrate the applicability, the new solution scheme has been implemented into the best-estimate thermal-hydraulic analysis code, MARS. This paper also includes the comparisons of the simulation results for the perturbation propagation and water faucet problems using both two-step method and the original solution scheme.

• 천문학회지
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• 제40권4호
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• pp.91-97
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• 2007

The Fokker-Planck (FP) model is one of the commonly used methods for studies of the dynamical evolution of dense spherical stellar systems such as globular clusters and galactic nuclei. The FP model is numerically stable in most cases, but we find that it encounters numerical difficulties rather often when the effects of tidal shocks are included in two-dimensional (energy and angular momentum space) version of the FP model or when the initial condition is extreme (e.g., a very large cluster mass and a small cluster radius). To avoid such a problem, we have developed a new integration scheme for a two-dimensional FP equation by adopting an Alternating Direction Implicit (ADI) method given in the Douglas-Rachford split form. We find that our ADI method reduces the computing time by a factor of ${\sim}2$ compared to the fully implicit method, and resolves problems of numerical instability.

• Journal of Mechanical Science and Technology
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• 제14권9호
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• pp.985-996
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• 2000

The issue of quench is related to safety operation of large-scale superconducting magnet system fabricated by cable-in-conduit conductor. A numerical method is presented to simulate the thermal hydraulic quench characteristics in the superconducting Tokamak magnet system, One-dimensional fluid dynamic equations for supercritical helium and the equation of heat conduction for the conduit are used to describe the thermal hydraulic characteristics in the cable-in-conduit conductor. The high heat transfer approximation between supercritical helium and superconducting strands is taken into account due to strong heating induced flow of supercritical helium. The fully implicit time integration of upwind scheme for finite volume method is utilized to discretize the equations on the staggered mesh. The scheme of a new adaptive mesh is proposed for the moving boundary problem and the time term is discretized by the-implicit scheme. It remarkably reduces the CPU time by local linearization of coefficient and the compressible storage of the large sparse matrix of discretized equations. The discretized equations are solved by the IMSL. The numerical implement is discussed in detail. The validation of this method is demonstrated by comparison of the numerical results with those of the SARUMAN and the QUENCHER and experimental measurements.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.260-265
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• 2008

A numerical scheme for solid propellant rocket has been studied using preconditioning method to research unsteady combustion processes for the double-base propellant with a converging-diverging nozzle. The Navier-Stokes equation is solved by dualtime stepping method with finite volume method. The turbulence model uses a shear stress transport modeling. The species equation follows up the method of Xinping WI, Mridul Kumar and Kenneth K. Kuo. A preconditioned algorithm is applied to solve incompressible regime inside the combustor and compressible flow at nozzle. Mass flux was evaluated using modified advective upwind splitting method. The simulated result the comparison a fully coupled implicit method and a semi implicit method in terms of accuracy and efficiency. This report shows the result of solid rocket propellant combustion.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 춘계학술대회 논문집
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• pp.315-319
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• 2009

Investigation of the lateral force fluctuations in an axisymmetric overexpanded compressed truncated perfect (CTP) nozzle for the shutdown transient is presented. These nozzles experience side-loads during start-up and shut-down operations, because of the flow separation at nozzle walls. Two types of flow separations such as free shock separation (FSS) and restricted shock separation (RSS) shock structure occur. A two-dimensional unsteady numerical simulation has been carried out over an axisymmetric CTP nozzle to simulate the lateral force fluctuations in nozzle during shutdown process. Reynolds Averaged Navier-Stokes equations are numerically solved using a fully implicit finite volume scheme. Governing equations are solved by coupled implicit scheme. Two equation k-$\omega$ SST turbulence model is selected. Unsteady pressure is measured at four locations along the nozzle wall. Present pressure variation compared well with the experimental data. During shutdown transient, separation pattern varies from FSS to RSS and finally returns to FSS. Several pressure peaks are observed during the RSS separation pattern. These pressure peaks generate lateral force or side loads in rocket nozzle.

• 한국물환경학회지
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• 제23권5호
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• pp.683-688
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• 2007

질량보존의 법칙과 Darcy의 법칙으로 표현되는 Richards 방정식은 비포화대의 토양수분흐름을 모의하는데 널리 사용되어 왔다. Richards 방정식은 압력수두의 항으로 표현되는 방정식, 토양수분의 항으로 표현되는 방정식, 그리고 이 둘을 혼합한 형태의 방정식 등, 세가지 형태로 표현할 수 있다. 고차의 비선형 항들을 포함하는 이 편미분방정식들을 수치해석방법으로 풀 때, 질량 비보존을 수반하는 오류의 결과가 초래될 수 있다. 세가지 방정식들 중 혼합형 Richards 방정식이, 다른 추가적인 계산없이 질량을 온전히 보존하는 것으로 알려져 있다. 이 연구의 목적은 동질성 토양에서의 1차원적 연직방향 비포화수 흐름모의를 위해, Richards 방정식의 질량보존적 수치해석법을 완전음해 유한차분법으로 개발하고, 이를 통해 민감도 분석을 실시하여 토양특성인자들과 토양종류에 따른 침투율의 변화를 살펴보는 데 있다.

• 한국추진공학회지
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• 제21권6호
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• pp.21-31
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• 2017

본 연구에서는 모드 천이가 발생하는 동안 상세한 유동 특성을 조사하기 위해, 이론분석과 수치해석을 수행하였다. 이론분석은 기존의 기체역학과 종래 보고된 이론식들 재정립하였으며, 수치해석은 2차원 비정상 압축성 Navier-Stokes 방정식을 풀기 위해 fully implicit finite volume scheme을 사용해 수행하였다. 해석의 검증을 위하여 실험 결과와 비교하였다. 격리부 입구 전온도와 수소 연료의 당량비를 변화시키면서 모드 천이에 미치는 영향을 조사하였다. 해석과 실험 결과는 정성적으로 잘 일치하였다. 당량비가 증가하면 스크램제트 모드에서 램제트 모드로 천이가 발생하였다. 이 때, 천이는 당량비에 따라 불연속적으로 나타나며, Non-allowable region이 존재하였다. 한편 격리부 입구에서 전온도의 증가는 모드 천이 경계를 변화시켰다.