• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.894-899
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• 2000

An automatic mesh generation system with unstructured quadrilateral elements on trimmed NURBS surfaces has been developed.. In this paper, NURBS surface geometries in the IGES format have been used to represent model shape. NURBS surface is represented as parametric surface. So each surface could be mapped to a 2D parametric plane through the parametric domain. And then meshes with quadrilateral elements are constructed in this plane. Finally, the constructed meshes are mapped back to the original 3D surface through the parametric domain. In this paper, projection plane, quasi-expanded plane and parametric Plane are used as 2D mesh generation plane. For mapping 3D surface to parametric domain, Newton-Rhapson Method is employed. For unstructured mesh generation with quadrilateral elements on 2D plane, a domain decomposition algorithm using loop operators has been employed. Sample meshes are represented to demonstrate the effectiveness of the proposed algorithm.

• 대한기계학회논문집B
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• 제29권9호
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• pp.1057-1064
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• 2005

A conservative finite-volume numerical method using unstructured meshes, which is developed by the authors, is evaluated for its application to several 2-D benchmark problems using a variety of quadrilateral, triangular and hybrid meshes. The present pressure-based numerical method for unstructured mesh clearly demonstrates the same accuracy and robustness as that fur typical structured mesh.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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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.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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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.

• 한국항공우주학회지
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• 제32권8호
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• pp.1-11
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• 2004

본 연구에서는 비정렬 격자계에서 가장 많이 쓰이는 근사 해법 중에 하나인 LU 기법의 Navier-Stokse 방정식에 대한 수렴성 및 안정성에 관한 연구를 수행하였다. 적절한 스칼라 모델 방정식을 사용하여 LU 기법이 갖는 고유한 특성에 관한 해석적 논의를 수행하였으며, 이를 Navier-Stokes 방정식으로 확장하여 해석하였다. 그 결과 LU 기법의 강성도는 격자 종횡비가 높아짐에 띠라, 그리고 격자 레이놀즈 수 감소함에 따라 증가하게 된다. 또한 내부반복계산을 통해서 이러한 강성도가 부분적으로 극복될 수 있음을 보였으며, 평판 난류 유동 해석을 통해서 해석 결과를 검증하였다.

• 한국항공우주학회지
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• 제30권8호
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• pp.37-45
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• 2002

본 연구에서는 이차원에서 비정상 비점성 유동해석을 위한 비정렬 동적 편자 기법을 개발하였다. 유동해석 기법은 시간에 대해 2차의 정확도를 갖는 내재적인 시간적분법을 사용하였으며, 격자중심의 유한 체적법과 Roe의 풍상차분법을 이용하여 공간에 대한 차분화를 하였다. 시간과 공간에 대한 정확도를 증가시키기 위해서는 해에 따라 원하는 위치에 격자점들을 임의로 추가할 수 있는 비정상 동적 적응격자 기법을 사용하였다. 이를 이용하여 이차원의 2자유도를 갖는 스프링 에어포일 시스템의 와류와의 간섭현상에 따른 공탄성적 변위를 예측하였다.

• 한국전산유체공학회지
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• 제17권1호
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• pp.94-100
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• 2012

In this paper, the cavitating flows around a hydrofoil have been numerically investigated by using a 2-d multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. For this purpose, a vertex-centered finite-volume method was utilized in conjunction with 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing. The Spalart-Allmaras one equation model was employed for the closure of turbulence. A dual-time stepping method and the Gauss-Seidel iteration were used for unsteady time integration. The phase change rate between the liquid and vapor phases was determined by Merkle's cavitation model based on the difference between local and vapor pressure. Steady state calculations were made for the modified NACA66 hydrofoil at several flow conditions. Good agreements were obtained between the present results and the experiment for the pressure coefficient on a hydrofoil surface. Additional calculation was made for cloud cavitation around the hydrofoil. The observation of the vapor structure, such as cavity size and shape, was made, and the flow characteristics around the cavity were analyzed. Good agreements were obtained between the present results and the experiment for the frequency and the Strouhal number of cavity oscillation.

• 한국전산유체공학회지
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• 제19권1호
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• pp.27-33
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• 2014

A new and efficient implicit scheme is proposed to obtain a steady-state solution in time integration and the comparison of characteristics with the approximation ways for the implicit method to solve the incompressible Navier-Stokes equations is provided. The conservative, finite-volume cell-vertex upwind scheme and artificial compressibility method using dual time stepping for time accuracy is applied in this paper. The numerical results obtained indicate that the direct application of Jacobian matrix to the Lower and upper sweeps of implicit LU-SGS leads to better performance as well as convergence regardless of CFL number and true time step than explicit scheme and approximation of Jacobian matrix. The flow simulation around box in uniform flow with unstructured meshes is demonstrated to check the validity of the current formulation.

• 한국항공우주학회지
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• 제32권9호
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• pp.1-11
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• 2004

본 연구에서는 비정렬 격자계에서 가장 많이 쓰이는 근사 해법 중의 하나인 LU 기법의 오일러 방정식에 대한 수렴성 및 안정성에 관한 연구를 수행하였다. 적절한 스칼라 모델 방정식을 사용하여 LU기법이 갖는 고유한 특성에 관해서 해석적으로 논의하였으며, 이를 system of equations 형태인 오일러 방정식으로 확장 해석하였다. 해석 결과 LU 기법의 수렴성 및 안정성은 격자 종횡비와 연관된 특별한 독립변수의 조합으로 표현되며, 이러한 독립 변수의 조합을 사용하여 어떠한 종횡비의 격자에 대해시도 수렴성 및 안정성의 저하 현상이 발생되지 않음을 보였다.

• 천문학회보
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• 제38권2호
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• pp.101.2-101.2
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• 2013

We present a new computational fluid dynamic (CFD) simulation code. The code employs the moving and polyhedral unstructured mesh scheme, which is known as a superior approach to the conventional SPH (smoothed particle hydrodynamics) and AMR (adaptive mesh refinement) schemes. The code first generates unstructured meshes by the Voronoi tessellation at every time step, and then solves the Riemann problem for surfaces of every Voronoi cell to update the hydrodynamic states as well as to move former generated meshes. For the second-order accuracy, the MUSCL-Hancock scheme is implemented. To increase efficiency for generating Voronoi tessellation we also develop the incremental expanding method, by which the CPU time is turned out to be just proportional to the number of particles, i.e., O(N). We will discuss the applications of our code in the context of cosmological simulations as well as numerical experiments for galaxy formation.