• Title/Summary/Keyword: Cell-Centered Method

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NUMERICAL BEHAVIOR OF VERTEX-CENTERED AND CELL-CENTERED FINITE-VOLUME METHODS ON UNSTRUCTURED MESHES (비정렬 격자계에서 격자점 중심과 격자 중심 유한체적법의 수치적인 거동에 관한 비교 연구)

  • Kim, J.S.;Lee, H.D.;Kwon, O.J.
    • 한국전산유체공학회:학술대회논문집
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    • 2006.10a
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    • pp.57-60
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    • 2006
  • This paper presents an assessment of vertex-centered and cell-centered finite-volume methods on unstructured meshes. The results indicate that the vertex-centered method is more reliable than the cell-centered method.

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A NEW NUMERICAL APPROXIMATION OF DIFFUSION FLUX IN UNSTRUCTURED CELL-CENTERED METHOD (비정렬 셀 중심 방법에서 확산플럭스의 새로운 수치근사방법)

  • Myoung H.K.
    • Journal of computational fluids engineering
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    • v.11 no.1 s.32
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    • pp.8-15
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    • 2006
  • The existing approximations of diffusion flux in unstructured cell-centered finite volume methods are examined in detail with each other and clarified to have indefinite expressions in several respects. A new numerical approximation of diffusion flux at cell face center is then proposed, which is second-order accurate even on irregular grids and may be easily implemented in CFD code using cell-centered finite volume method with unstructured grids composed of arbitrary convex polyhedral shape.

EVALUATION OF NUMERICAL APPROXIMATIONS OF CONVECTION FLUX IN UNSTRUCTURED CELL-CENTERED METHOD (비정렬 셀 중심 방법에서 대류플럭스의 수치근사벙법 평가)

  • Myong H.K.
    • Journal of computational fluids engineering
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    • v.11 no.1 s.32
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    • pp.36-42
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    • 2006
  • The existing numerical approximations of convection flux, especially the spatial higher-order difference schemes, in unstructured cell-centered finite volume methods are examined in detail with each other and evaluated with respect to the accuracy through their application to a 2-D benchmark problem. Six higher-order schemes are examined, which include two second-order upwind schemes, two central difference schemes and two hybrid schemes. It is found that the 2nd-order upwind scheme by Mathur and Murthy(1997) and the central difference scheme by Demirdzic and Muzaferija(1995) have more accurate prediction performance than the other higher-order schemes used in unstructured cell-centered finite volume methods.

STUDY ON HIGH RESOLUTION SCHEMES SUITABLE FOR AN 3-D CFD CODE(POWERCFD) USING UNSTRUCTURED CELL-CENTERED METHOD AND INTERFACE CAPTURING METHOD (비정렬 셀 중심방법 및 경계면포착법을 사용하는 3차원 유동해석코드(PowerCFD)에 적합한 HR 해법에 관한 연구)

  • Myong, H.K.;Kim, J.E.
    • Journal of computational fluids engineering
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    • v.13 no.1
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    • pp.7-13
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    • 2008
  • Several high resolution schemes such as OSHER, MUSCL, SMART, GAMMA, WACEB and CUBISTA are comparatively studied with respect to the accurate capturing of fluid interfaces throughout the application to two typical test cases of a translation test and a collapsing water column problem with a return wave. It is accomplished by implementing the high resolution schemes in the in-house CFD code(PowerCFD) for computing 3-D flow with an unstructured cell-centered method and an interface capturing method, which is based on the finite-volume technique and fully conservative. The calculated results show that SMART scheme gives the best performance with respect to accuracy and robustness.

Development of a Flow Analysis Code Using an Unstructured Grid with the Cell-Centered Method

  • Myong, Hyon-Kook;Kim, Jong-Tae
    • Journal of Mechanical Science and Technology
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    • v.20 no.12
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    • pp.2218-2229
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    • 2006
  • A conservative finite-volume numerical method for unstructured grids with the cell-centered method has been developed for computing flow and heat transfer by combining the attractive features of the existing pressure-based procedures with the advances made in unstructured grid techniques. This method uses an integral form of governing equations for arbitrary convex polyhedra. Care is taken in the discretization and solution procedure to avoid formulations that are cell-shape-specific. A collocated variable arrangement formulation is developed, i.e. all dependent variables such as pressure and velocity are stored at cell centers. For both convective and diffusive fluxes the forms superior to both accuracy and stability are particularly adopted and formulated through a systematic study on the existing approximation ones. Gradients required for the evaluation of diffusion fluxes and for second-order-accurate convective operators are computed by using a linear reconstruction based on the divergence theorem. Momentum interpolation is used to prevent the pressure checkerboarding and a segregated solution strategy is adopted to minimize the storage requirements with the pressure-velocity coupling by the SIMPLE algorithm. An algebraic solver using iterative preconditioned conjugate gradient method is used for the solution of linearized equations. The flow analysis code (PowerCFD) developed by the present method is evaluated for its application to several 2-D structured-mesh benchmark problems using a variety of unstructured quadrilateral and triangular meshes. The present flow analysis code by using unstructured grids with the cell-centered method clearly demonstrate the same accuracy and robustness as that for a typical structured mesh.

NUMERICAL SIMULATION OF NATURAL CONVECTION IN A CUBICAL-CAVITY BY UNSTRUCTURED CELL-CENTERED METHOD (비정렬 셀 중심 방법에 의한 3차원 캐비티내의 자연대류 현상에 관한 수치해석)

  • Myong H. K.;Kim J. E.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.10a
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    • pp.61-66
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    • 2005
  • Natural convection flows in a cubical, air-filled cavity that has one pair of opposing faces isothermal at different temperatures, Th and Tc, the remaining faces having a linear variation from Tc to Th are numerically simulated by a new solution code(PowerCFD) using unstructured cell-centered method. Solutions are obtained for configurations with a Rayleigh number as high as 105 and three inclination angles ${\theta}$ of the isothermal faces from horizontal: namely ${\theta}=0$, 45 and $90^{\circ}$. Interesting features are presented in detail and comparisons are made with benchmark solutions and experimental results found in the literature. It is found that the code is capable of producing accurately the nature of the laminar convection in a cubical, air-filled cavity with differentially heated walls.

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NUMERICAL SIMULATION OF INCOMPRESSIBLE LAMINAR ENTRY FLOWS IN A SQUARE DUCT OF $90^{\circ}$ BEND BY UNSTRUCTURED CELL-CENTERED METHOD (비정렬 셀 중심 방법에 의한 정사각형 단면을 갖는 $90^{\circ}$ 곡관 층류유동의 수치해석)

  • Myong H. K.;Kim J. E.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.10a
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    • pp.81-85
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    • 2005
  • Three-dimensional steady incompressible laminar entry flows in a square duct of $90^{\circ}$ bend are numerically simulated by a new solution code(PowerCFD) using unstructured cell-centered method. Solutions are obtained with three unstructured grid types of hexahedron, prism and hybrid at a Reynolds number, based on the hydraulic diameter and bulk velocity, of 790. Interesting features of the flow are presented in detail. Detailed comparisons between the computed solutions and the available experimental data are given mainly for the velocity distributions at cross-sections in a $90^{\circ}$ bend of a square duct with fully-developed entry flows. It is found that the code is capable of producing the nature of laminar flow in curved square duct with no grid type dependency.

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Incompressible Viscous Analysis on Unstructured Meshes using Artificial Compressibility Method (가압축성 기법을 이용한 비정렬 격자상에서의 비압축성 점성해석)

  • Moon Young J.
    • 한국전산유체공학회:학술대회논문집
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    • 1995.10a
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    • pp.113-117
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    • 1995
  • Viscous analysis on incompressible flows is performed using unstructured triangular meshes. A two-dimensional and axisymmetric incompressible Navier-Stokes equations are solved in time-marching form by artificial compressibility method. The governing equations are discretized by a cell-centered based finite-volume method. and a centered scheme is used for inviscid and viscous fluxes with fourth order artificial dissipation. An explicit multi-stage Runge-Kutta method is used for the time integration with local time stepping and implicit residual smoothing. Convergence properties are examined and solution accuracies are also validated with benchmark solution and experiment.

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NUMERICAL STUDY ON TWO-DIMENSIONAL MULTIPHASE FLOWS DUE TO DENSITY DIFFERENCE WITH INTERFACE CAPTURING METHOD (경계면 포착법을 사용한 밀도차에 따른 다상유동에 관한 수치해석적 연구)

  • Myong, H.K.
    • 한국전산유체공학회:학술대회논문집
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    • 2007.10a
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    • pp.214-219
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    • 2007
  • Both the bubble rising in a fully filled container and the droplet splash are simulated by a solution code(PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method (CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The present results are compared with other numerical solutions found in the literature. It is found that the present code simulate complex free surface flows such as multi phase flows due to large density difference efficiently and accurately.

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MULTIGRID METHOD FOR TOTAL VARIATION IMAGE DENOISING

  • HAN, MUN S.;LEE, JUN S.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.6 no.2
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    • pp.9-24
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    • 2002
  • Total Variation(TV) regularization method is effective for reconstructing "blocky", discontinuous images from contaminated image with noise. But TV is represented by highly nonlinear integro-differential equation that is hard to solve. There have been much effort to obtain stable and fast methods. C. Vogel introduced "the Fixed Point Lagged Diffusivity Iteration", which solves the nonlinear equation by linearizing. In this paper, we apply multigrid(MG) method for cell centered finite difference (CCFD) to solve system arise at each step of this fixed point iteration. In numerical simulation, we test various images varying noises and regularization parameter $\alpha$ and smoothness $\beta$ which appear in TV method. Numerical tests show that the parameter ${\beta}$ does not affect the solution if it is sufficiently small. We compute optimal $\alpha$ that minimizes the error with respect to $L^2$ norm and $H^1$ norm and compare reconstructed images.

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