• 대한수학회지
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• 제51권4호
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• pp.665-678
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• 2014

We present a new space-time discontinuous Galerkin (DG) method for solving the time dependent, positive symmetric hyperbolic systems. The main feature of this DG method is that the discrete equations can be solved semi-explicitly, layer by layer, in time direction. For the partition made of triangle or rectangular meshes, we give the stability analysis of this DG method and derive the optimal error estimates in the DG-norm which is stronger than the $L_2$-norm. As application, the wave equation is considered and some numerical experiments are provided to illustrate the validity of this DG method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.181-189
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• 1998

A numerical study based on the three-dimensional Reynolds averaged Navier-Stokes equations is presented to analyze the transonic flowfield through two-stage axial compressor. Explicit four-step Runge-Kutta scheme is used for solution algorithm, and local time step and implicit residual averaging are introduced for enhancing the convergency. Artificial dissipation model is adopted to assure the stability of solution. The solver is coupled with Baldwin-Lomax model to describe turbulence. To avoid calculating the unsteady flow, a mixing process is modeled at a station between rotating and stationary blade rows. Results show a variety of important physical phenomena. Comparison of the flowfields with and without tip clearance shows that the effect is considerable in this flowfield. Comparisons with experimental data carried out to validate the calculational results show reasonable agreements. Some remedies are also suggested to improve the revealed problems.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.81-85
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• 1997

The Computer code KAIST-ADD LUFUNS has been developed to solve 3D compressible turbluent flow. This method employs Harten-Yee's modified upwind scheme in the explicit part and Steger-Warming Splitting in the implicit part. Flow past RAE wing-body aircraft has been computed for three different flow conditions. The result have shown good comparision with the experimental data. Baldwin-Lomax turbluence model is used for this computer code.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.51-56
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• 2000

The Finite Element Solutions Is reported on solid-liquid phase change in porous media with natural convection including freezing. The model is based on volume averaged transport equations, while phase change is assumed to occur over a small temperature range. The FEM (Finite Element Method) algorithm used in this study is 3-step time-splitting method which requires much less execution time and computer storage the velocity-pressure integrated method and the penalty method. And the explicit Lax-Wendroff scheme is applied to nonlinear convective term in the energy equation. For natural convection including melting and solidification the numerical results show reasonable agreement with FDM (Finite Difference Method) results.

• Kyungpook Mathematical Journal
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• 제52권2호
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• pp.167-177
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• 2012

In this article, we propose exponentially fitted error correction methods(EECM) which originate from the error correction methods recently developed by the authors (see [10, 11] for examples) for solving nonlinear stiff initial value problems. We reduce the computational cost of the error correction method by making a local approximation of exponential type. This exponential local approximation yields an EECM that is exponentially fitted, A-stable and L-stable, independent of the approximation scheme for the error correction. In particular, the classical explicit Runge-Kutta method for the error correction not only saves the computational cost that the error correction method requires but also gives the same convergence order as the error correction method does. Numerical evidence is provided to support the theoretical results.

• 동력기계공학회지
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• 제9권1호
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• pp.23-29
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• 2005

Numerical analysis of three-dimensional viscous flow-fields in the turbine rotor passages was carried out to investigate flow physics including the interaction between secondary vortices, tip leakage vortex, and the rotor wake. The blade tip geometry was accurately modeled adopting the embedded H grid system. An explicit four-stage Runge-Kutta scheme was used for the time integration of both the mean flow and turbulence equations. The computational results for the entire turbine rotor flows, particularly the tip clearance flow and the secondary flows, were interpreted and compared with the experimental data from the Penn State turbine stage. The predictions for major features of the flow field have been found to be in good agreement with the experimental data.

• 에너지공학
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• 제6권1호
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• pp.52-57
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• 1997

유동방향으로 초원형 형상을 갖는 잘록한 관내의 압축성 유동에 관한 동특성을 수치적으로 연구하였다. MacCormack의 양해법, 즉 예측자/보정자 단계를 거친 시간 진행법을 이용하여 Euler 방정식의 해를 구하였는데, 관내 유동은 이차원, 비점성, 압축성 유동이라 가정하였다. 관의 직경비와 형상비가 압력분포에 미치는 영향을 광범위하게 고찰하였으며, 본 연구에서 개발한 전산프로그램을 이용한 수치 결과는 상용코드인 FLUENT를 이용한 결과와 비교하여 일치된 결과를 얻을 수 있었다.

• 에너지공학
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• 제24권2호
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• pp.110-114
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• 2015

A numerical investigation has been carried out on recirculation zone formed downstream of a compressible flow over a backward facing step. The study has been performed by solving Two-Dimensional Navier-Stokes equations. The system of governing equations has been solved, using an explicit Harten-Yee Non- MUSCL Modified flux type TVD scheme and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. The recirculation region dimensions are characterized over a range of Mach numbers of fixed step height 5mmThe detail of recirculation zone such as pressure, temperature, recirculation length, strength etc are reported. The variations of these characteristics due to change of Mach number are also presented.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.715-720
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• 2000

Stratified flow past a three-dimensional obstacle such as a sphere has been a long-lasting subject of geophysical, environmental and engineering fluid dynamics. In order to investigate the effect of the stratification on the near wake, in particular, the unsteady vortex formation behind a sphere, numerical simulations of stratified flows past a sphere are conducted. The time-dependent Navier-Stokes equations are solved using a three-dimensional finite element method and a modified explicit time integration scheme. Laminar flow regime is considered and linear stratification of density is assumed under Boussinesq approximation. The computed results include the characteristics of the near wake and the unsteady vortex shedding. With a strong stratification, the separation on the sphere is suppressed and the wake structure behind the sphere becomes planar, resembling that behind a vertical cylinder.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2004년도 가을 학술발표논문집 Vol.31 No.2 (3)
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• pp.328-330
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• 2004

차세대 네트워크는 IP 기반의 무선 네트워크로 진화하고 있다. 이에따라 최근의 internet Engineering Task force (IETF)에서 효율적인 이동성 관리를 위한 Hierarchical Mobile IPv6 (HMIPV6)을 제안하였다. HMIPV6는 Mobile Anchor Point(MAP)영역안에 지역 등록을 통하여 상당한 시그널링을 줄일 수 있고 핸드 오프 지연시간을 줄이면서 MIPv6의 성능을 향상 가져왔다. 그러나 MAP 영역이 고정되어 있고 단일 MAP에 집중적인 트랙픽이 발생하는 문제점을 가지고 있다. 따라서 이동노드의 이동성 및 트래픽에 의해서 동적으로 MAP 영역을 설정함으로써 트랙픽이 분산되어 질수 있다. 또한 HMIPv6는 Idle 이동노드도 불필요한 위치 등록으로 인하여 시그널링 오버헤드를 방생한다. 따라서 IP 페이징 기법을 사용하여 불필요한 위치 등록에 따른 시그널링을 줄이기 위한 방법을 제시한다. 또한 explicit multicast (Xcast) 방법을 사용하여 효율적인 메시지 전달방법을 제시한다.