• 한국전산유체공학회지
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• 제17권1호
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• pp.8-15
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• 2012

A code developed using the flux-difference splitting scheme on the hybrid Cartesian/immersed boundary method is applied to simulate three-dimensional internal waves. The material interface is regarded as a moving contact discontinuity and is captured on the basis of mass conservation without any additional treatment across the interface. Inviscid fluxes are estimated using the flux-difference splitting scheme for incompressible fluids of different density. The hybrid Cartesian/immersed boundary method is used to enforce the boundary condition for a moving three-dimensional body. Immersed boundary nodes are identified within an instantaneous fluid domain on the basis of edges crossing a boundary. The dependent variables are reconstructed at the immersed boundary nodes along local normal lines to provide the boundary condition for a discretized flow problem. The internal waves are simulated, which are generated by an pitching ellipsoid near an material interface. The effects of density ratio and location of the ellipsoid on internal waves are compared.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.683-695
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• 2002

The objective of the present study is to analyze the fluid flow with moving boundary using a finite element method. The algorithm uses a fractional step approach that can be used to solve low-speed flow with large density changes due to intense temperature gradients. The explicit Lax-Wendroff scheme is applied to nonlinear convective terms in the momentum equations to prevent checkerboard pressure oscillations. The ALE (Arbitrary Lagrangian Eulerian) method is adopted for moving grids. The numerical algorithm in the present study is validated for two-dimensional unsteady flow in a driven cavity and a natural convection problem. To extend the present numerical method to engine simulations, a piston-driven intake flow with moving boundary is also simulated. The density, temperature and axial velocity profiles are calculated for the three-dimensional unsteady piston-driven intake flow with density changes due to high inlet fluid temperatures using the present algorithm. The calculated results are in good agreement with other numerical and experimental ones.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.760-763
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• 2010

강내탄도 성능 해석의 정확도를 높이기 위해서 1차원 해석 코드를 2차원 및 3차원으로 확장시키는 작업이 필요하다. 다차원 확장 시 이동경계면 해석에 Cut Cell Method를 적용하였다. 이에 high resolution 기법인 MUSCL-Hancock을 선택하였고 free piston problem에 적용하여 그 타당성을 검증하였다.

• 한국전산유체공학회지
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• 제10권1호
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• pp.24-30
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• 2005

Unstructured grid system is suitable for flows of complex geometries. For problems with moving boundary walls, the grid system must be time-dependently changing and deforming according to the movement of the boundaries when we use a body fitted grid system. In this paper, a new moving-grid finite-volume method on unstructured grid system is proposed and developed for unsteady compressible flows with shock waves. To assure geometric conservation laws on moving grid system, a control volume on the space-time unified domain is adopted for estimating numerical flux. The method is described and applied for two-dimensional flows.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.659-665
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• 2008

The 1-D numerical study of the interior ballistics has been conducted. The unsteady compressible 1-D CFD code using SIMPLER algorithm and QUICK scheme has been developed. The mathematical model of the two-phase flow has been established for the behavior of the interior ballistics. The moving boundary due to the projectile motion as the physical phenomena of the interior ballistics results in the varied control volume. In order to analyze the moving boundary, the numerical codes, which apply the ghost-cell extrapolation method and the Lagrangian method respectively, have been developed. The ghost-cell extrapolation method has been used in the Eulerian coordinate system. The Lagrangian method has been used in Non-Eulerian coordinate system. These codes have been verified through the analysis of the free piston motion problem in the tube. Through this study, the basic techniques of the numerical code for the multi-dimensional two-phase flow of the interior ballistics have been obtained.

• 한국전산유체공학회지
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• 제14권4호
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• pp.93-100
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• 2009

The gridless (or meshfree) methods, such as MPS, SPH, FPM an so forth, are feasible and robust for the problems with moving boundary and/or complicated boundary shapes, because these methods do not need to generate a grid system. In this study, a gridless solver, which is based on the combination of moving least square interpolations on a cloud of points with point collocation for evaluating the derivatives of governing equations, is presented for two-dimensional unsteady incompressible Navier-Stokes problem in the low Reynolds number. A MAC-type algorithm was adopted and the Poission equation for the pressure was solved successively in the moving least square sense. Some typical problems were solved by the presented solver for the validation and the results obtained were compared with analytic solutions and the numerical results by conventional CFD methods, such as a FVM.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.165-169
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• 2009

The effect of the Dirichlet boundary condition for the redistance equation of level set method on the solutionof sloshing problem is investigated by adopting four Dirichlet boundary conditions. For the solution of the incompressible Navier-Stokes equations, P1P1 four-step fractional finite element method is employed and a least-square finite element method is used for the solutions of the two hyperbolic type equations of level set method; advection and redistance equation. ALE (Arbitrary Lagrangian Eulerian) method is used to deal with a moving computational domain. It has been shown that the free surface motion in a sloshing tank is strongly dependent on the type of the Dirichlet boundary condition and the results of broken dam and sloshing problems using various Dirichlet boundary conditions are discussed and compared with the existing experimental results.

• Selected Papers of The Society of Naval Architects of Korea
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• 제2권1호
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• pp.140-155
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• 1994

The hydrodynamic problem is treated here when a pressurized bag is submerged partially in the water and the end points of it oscillate. SES(Surface Effect Ship) has a bag filled with pressurized air at the stern in order to prevent the air leakage, and the pitch motion of SES is largely affected by the hydrodynamic force of the bag. The shape of a bag can be determined with the pressure difference between inside and outside. Once the hydrodynamic pressure is given, the shape of a bag can be obtained, however in order to calculate the hydrodynamic pressure we should know the shape change of the bag, and vice versa. Therefore the type of boundary condition on the surface of a bag is a moving boundary like a free surface boundary. The present paper describes the formulation of this problem and treats a linearized problem. The computations of the radiation problem for an oscillating bag are shown in comparison with the case that the bag is treated as a rigid body. The hydrodynamic forces are calculated for various values of the pressure inside the bag and the submerged depth.

• 한국정밀공학회지
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• 제16권7호
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• pp.158-167
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• 1999

Heat and moisture transfer associated with porous materials are investigated. The heat and moisture transfer in porous materials caused by the interaction of moisture gradient, temperature gradient, conduction, and evaporation are considered. The variations of temperature and moisture not only change the volume but also induce the hygro-thermal stress. The finite element formulation for solving the temperature and moisture transfer as well as the associated hygro-thermal stresses is developed. In order to verify the finite element formulation, the heat and moisture moving boundary problem in a half space and the hygro-thermo-mechanical problem in an infinite plate with a circular hole are analyzed. Temperature profile, moisture profile, and hygro-thermal stresses are compared with those of analytic solution and other investigator. Good agreements are examined

• 한국항공우주학회지
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• 제36권11호
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• pp.1049-1055
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• 2008

최근 다분야 전산유체 역학에서는 설계 최적화, 공탄성, 강제 경계 운동 등에서 요구되어지는 이동경계문제를 다루게 된다. 이동경계의 변위가 클 경우 강건하고 효율적인 격자 변형 알고리즘의 개발이 필요하다. 본 연구에서는 유한 대형요소와 초월유한보간에 근거한 체적격자 변형 코드를 개발하였고, 정렬격자 다중 블록 Navier-Stokes 코드와 연계하였다. 개발된 코드의 검증을 위해 주기적으로 진동 운동을 하는 에어포일 문제에 대해 계산을 수행 하였고 양력, 항력, 모멘트 계수의 이력 계산 결과가 실험 결과와 잘 일치하였다.