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이산화된 Navier-Stokes 방정식의 영역분할법을 위한 병렬 예조건화
최형권,유정열,강성우,Choi, Hyoung-Gwon,Yoo, Jung-Yul,Kang, Sung-Woo 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.6
A finite element code for the numerical solution of the Navier-Stokes equation is parallelized by vertex-oriented domain decomposition. To accelerate the convergence of iterative solvers like conjugate gradient method, parallel block ILU, iterative block ILU, and distributed ILU methods are tested as parallel preconditioners. The effectiveness of the algorithms has been investigated when P1P1 finite element discretization is used for the parallel solution of the Navier-Stokes equation. Two-dimensional and three-dimensional Laplace equations are calculated to estimate the speedup of the preconditioners. Calculation domain is partitioned by one- and multi-dimensional partitioning methods in structured grid and by METIS library in unstructured grid. For the domain-decomposed parallel computation of the Navier-Stokes equation, we have solved three-dimensional lid-driven cavity and natural convection problems in a cube as benchmark problems using a parallelized fractional 4-step finite element method. The speedup for each parallel preconditioning method is to be compared using upto 64 processors.
최형권(H.G. Choi) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.11
In the present study, a least square weighted residual method and Taylor-Galerkin method were formulated and tested for the discretization of the two hyperbolic type equations of level set method; advection and reinitialization equations. The two approaches were compared by solving a time reversed vortex flow and three-dimensional broken dam flow by employing a four-step splitting finite element method for the solution of the incompressible Navier-Stokes equations. From the numerical experiments, it was shown that the least square method is more accurate and conservative than Taylor-Galerkin method and both methods are approximately first order accurate when both advection and reintialization phase are involved in the evolution of free surface.
최형권(Choi Hyungkwon),임대근(Great Root Woods) 한국외국어대학교 외국문학연구소 2013 외국문학연구 Vol.- No.49
Through the film, from the director’s perspective, Wang Xiaoshuai and Jia Zhangke re-embodied and made the new images of the city which is different from the real splendid city and disclosed to us the dark sides that are hidden in that reality. This research is to provide the insights of how Wang Xiaoshuai and Jia Zhangke reproduced the images of ‘Beijing’ which is the common background for Beijing Bicycle 十七歲的單車 and The World 世界 and what kind of forms they gave to the “people in need” or to “the marginals” who lived in that area. Whereas Wang Xiaoshuai’s Beijing Bicycle mainly focused on the people of the lower classes in the underdeveloped city ‘hutong’, Jia Zhangke’s The World mainly paid attention to the people who lived outskirts of Beijing called ‘World Park.’ In Beijing Bicycle, it shows the class conflicts that are aroused by the living gaps between the rich and the poor by emphasizing on characters’ various opinions. The World, unlike Beijing Bicycle, gives us the pictures of individuals’ alienation, frustration, solitude, and ambitions that are caused by extreme modernization of the city. People in The World compromised with the reality and even with love in order to blend in the city life but they felt the loneliness as outsiders due to the failures of blending in. The Beijing of Beijing Bicycle is full of disintegrating and confrontations. Although the native and lower class people coexisted within only one blocks away from each other, the lower class people could not enter the lives of natives. Just like conflicts are aroused by the differences of wealth, ‘the space’ was struggled and divided by the gaps between the rich and the poor. Dissimilarly, the Beijing of The World is a lost space. We can’t find the freedom in the ‘World Park’ and it is distrusted by the people. Due to rapid capitalization there is no more peace. The characters in The World experienced the absolute loneliness in the lost space.
Level Set 유한요소해석의 Redistance 방정식의 Dirichlet 경계조건에 대한 연구
최형권(Hyoung-gwon Choi) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
The proper imposition of the Dirichlet boundary condition of the redistance equation of level set method is a very important factor for an accurate simulation of multiphase flows, especially for the matter of mass conservation. In this paper, a new method which improves the conventional procedure of the imposition of the Dirichlet boundary condition of the redistance equation of level set method is proposed. The key idea of the proposed method is to correct the level set values of finite elements which an interface line/surface intersects using a direct method. For the numerical solution of the incompressible Navier-Stokes equation PIPI four-step fractional method is employed and least-square method is used for the solution of the advection and redistance equation. Some benchmark problems are solved using the proposed method and compared with the results of the conventional method.
[열유체부문] 유한요소를 이용한 MIRA 모델주위의 유동해석
최형권(Hyounggwon Choi),강성우(Sungwoo Kang),유정열(Jung Yul Yoo) 한국자동차공학회 2001 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2001 No.11_1
A finite element code based on P2PI or PIPI tetra element has been developed for the large eddy simulation (LES) of turbulent flows around a complex geometry. Fractional 4-step algorithm is employed to obtain time accurate solution since it is less expensive than the integrated formulation, in which the velocity and pressure fields are solved at the same time. Crank-Nicolson method is used for second order temporal discretizarion and Galerkin method is adopted for spatial discretization. For very high Reynolds number flows, which would require a fom1idable number of nodes to resolve the flow field, SUPG (Streamline Upwind Petrow-Galerkin) method is applied. As a benchmark problem for code validation. turbulent flows around a sphere and turbulent channel flows<br/> have been studied at various Reynolds numbers. Turbulent flow around MIRA model has been solved using P2PI element and Smagorinsky model at Re= 2.6 x 106. Furthermore, a parallel code based on domain-decomposition method using PIPI element has been developed for LES of turbulent flow and tested with turbulent channel flows. Turbulent flow analysis around MIRA model using the present LES-parallel code is ongoing and will be presented in the near future<br/>
최형권(H.G. Choi),김범준(B.J. KIm),강성우(S. W. Kang),유정열(J. Y. Yoo) 한국전산유체공학회 2002 한국전산유체공학회 학술대회논문집 Vol.2002 No.-
For the large scale computation of turbulent flows around an arbitrarily shaped body, a parallel LES (large eddy simulation) code has been recently developed in which domain decomposition method is adopted. METIS and MPI (message passing interface) libraries are used for domain partitioning and data communication between processors, respectively. For unsteady computation of the incompressible Navier-Stokes equation, 4-step splitting finite element algorithm [1] is adopted and Smagorinsky or dynamic LES model can be chosen for the modeling of small eddies in n,rbulent flows. For the validation and performance-estimation of the parallel code, a three-dimensional laminar flow generated by natural convection inside a cube has been solved. Then, we have solved the turbulent flow around MIRA (Motor Industry Research Association) model at Re=2.6×10^6 ,which is based on the model height and inlet free stream velocity, using 32 processors on IBM SMP cluster and compared with the existing experiment.
채널 유동에서 점성이 단일 입자 혼합 유동의 suspension 에 미치는 영향
최형권(Hyoung-gwon Choi) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.3
Suspension of a single solid particle in a channel flow with a constant pressure gradient is studied numerically. The interaction of a circular particle with a surrounding Newtonian fluid is formulated using a combined formulation. Numerical results are presented using two dimensionless variables: the sedimentation Reynolds number and the generalized Froude number. From the present results, it has been shown that a solid particle is suspended at a smaller generalized Froude number as the viscosity of the surrounding fluid increases. The time taken for equilibrium position is found to be smaller as fluid viscosity increases when both : the sedimentation Reynolds number and the generalized Froude number are the same while, at the same situation, the dimensionless time taken for equilibrium position is to be nearly the same regardless of fluid viscosity when a dimensionless time variable is introduced
유체-구조물 상호작용을 위한 유한요소 결합공식화의 예조건화에 대한 연구
최형권(Hyoung-gwon Choi) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.4
AILU type preconditioners for a two-dimensional combined P2P1 finite element formulation of the interaction of rigid cylinder with incompressible fluid flow have been devised and tested by solving fluidstructure interaction (FSI) problems. The FSI code simulating the interaction of a rigid cylinder with an unsteady flow is based on P2P1 mixed finite element formulation coupled with combined formulation. Four different preconditioners were devised for the two-dimensional combined P2P1 finite element formulation extending the idea of Nam et al., which was proposed for the preconditioning of a P2P1 mixed finite element formulation of the incompressible Navier-Stokes equations. It was found that PC-Ⅲ or PC-Ⅳ among them perform well with respect to computational memory and convergence rate for some bench-mark problems.