• 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 2008년도 12th Asian Congress of Fluid Mechanics
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• pp.34.2-34.2
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• 2008

• 한국측량학회지
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• 제13권2호
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• pp.277-283
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• 1995

본 논문에서는 수치지형모델을 이용한 토공량 계산에서 격자간격지형의 보간방법, 토공양 산정방식 토공량의 정확도에 어떻게 영향을 주는 가를 연구하고자 하였으며, 이를 위하여 수치보험을 하였다. 우선 l0m간격의 정규격자로 구성된 지형의 수치모델에 대하여 이동평균법(Moving average)을 사용하여 2m, 5m, 10간격으로 보간 하였으며, 보간된 각 지형에 대해 양단면평균법, 중앙단면법, 각주공식, 심프슨 공식을 사용하여 토공량을 산정하였다. 이들 방법을 비교분석한 결과 이동평균법을 사용한 결과는 보간 방법에서는 1차식이, 토공량 계산방법에서는 양단면 평균법과 중앙단면법보다 각주공식과 심프슨 공식에서 정밀한 결과를 얻었다.

• 대한조선학회논문집
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• 제44권1호
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• pp.8-15
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• 2007

In this paper, numerical calculations are performed to analyze the unsteady flow of NACA airfoil sections. In order to ease the flow computation for the fluid region changing in time, improve the quality of solution and simplify the grid generation for the oscillating foil flow, the computational method adopts a moving and deforming mesh with the multi-block grid topology. The multi-block, structured-unstructured hybrid grid is generated using the commercial meshing software Gridgen V15. The MDM (Moving & Deforming Mesh) and the UDF (User Define function) function of FLUENT 6 are adopted for computing turbulent flows of the foil in pitching motion. Computed unsteady lift and drag forces are compared with experimental data. in general, the characteristics of unsteady lift and drag of the experiments are reproduced well in the numerical analysis.

• 한국분무공학회지
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• 제5권1호
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• pp.13-22
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• 2000

The present study has numerically analyzed the vaporization characteristics of fuel droplets in the high temperature convective flow field. The axisymmetric governing equations for mass, momentum, energy, and species are solved by an iterative and implicite unstructured finite-volume method. The moving boundary due to vaporization is handled by the deformable unstructured grid technique. The pressure-velocity coupling in the density-variable flows is treated by the SIMPLEC algorithm. In terms of the matrix solver, Bi-CGSTAB is employed for the numerically efficient and stable convergence. The n-decane is used as a liquid fuel and the initial droplet temperature is 300K. Computations are performed for the nonevaporating and evaporating droplets with the relative interphase velocity(25m/s). The unsteady vaporization process has been simulated up to the nondimensional time, 25. Numerical results indicate that the mathematical model developed in this study succesfully simulates the main features of the droplet vaporization process in the convective environment.

• 한국전산구조공학회논문집
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• 제20권3호
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• pp.321-327
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• 2007

본 연구는 탄성균열문제를 신속하고 정확하게 해석할 수 있는 새로운 개념의 그리드(grid) 없는 유한차분법을 제시한다. 이동최소제곱법을 이용한 Taylor 전개식 구성을 통해 직접적인 미분계산 없이 근사함수와 그 미분을 손쉽게 계산한다. 그리드로 인한 절점 간의 종속성이 없어 해석영역 내의 불연속면 모델링이 용이하여 차분식 구성시 균열로 인한 불연속 효과를 고려하는 과정도 자연스럽다. 유한차분법에 근간을 두고 있어 지배 미분방정식을 직접 이산화하기 때문에 수치적분이 필요한 수치기법에 비해 계산속도도 빠르다. 모드 I과 모드 II 균열문제 해석을 통해 본 해석기법이 정확하고 효율적으로 응력확대계수를 계산할 수 있음을 보였다.

• 한국전산유체공학회지
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• 제1권1호
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• pp.88-97
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• 1996

This paper treats an adaptive finite-element method for the viscous compressible flow governed by Navier-Stokes equations in two dimensions. The numerical algorithm is the two-step Taylor-Galerkin mettled using unstructured triangular grids. To increase accuracy and stability, combined moving node method and grid refinement method have been used for grid adaption. Validation of the present algorithm has been made by comparing the present computational results with the existing experimental data and other numerical solutions. Four benchmark problems are solved for demonstration of the present numerical approach. They include a subsonic flow over a flat plate, the Carter flat plate problem, a laminar shock-boundary layer interaction. and finally a laminar flow around NACA0012 airfoil at zero angle of attack and free stream Mach number of 0.85. The results indicates that the present adaptive triangular grid method is accurate and useful for laminar viscous flow calculations.

• 한국항해항만학회지
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• 제28권3호
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• pp.199-205
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• 2004

라디에이션(radiation) 문제를 해결하기 위해서 중합격자법을 개발하였다. 중합격자계는 이동격자계와 고정격자계로 이루어져 있으며, 이동격자계는 운동하는 물체에 적용되어 운동하는 물체와 동시에 이동된다. 이러한 수치계산법은 자유표면 부근에서 운동하는 몰수평판에 작용하는 라디에이션 유체력을 계산하는데 응용되었다. 현재의 수치계산법에 의한 결과는 실험값 및 선형포텐셜 이론에 의한 결과와 상호 비교하였으며, 수치계산의 신뢰성을 확인하였다. 그리고, 몰수평판에 작용하는 비선형 점성감쇄효과에 대하여 평가하였다.

• 대한조선학회논문집
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• 제40권5호
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• pp.36-42
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• 2003

A CFD simulation technique has been developed to handle the unsteady body motion with large amplitude by use of overlapping multi-block grid system. The three-dimensional, viscous and incompressible flow around body is investigated by solving the Navier-Stokes equations, and the motion of body is represented by moving effect of the grid system. Composite grid system is employed in order to deal with both the body motion with large amplitude and the condition of numerical wave maker in convenience at the same time. The governing equations, Navier-Stokes (N-S) and continuity equations, are discretized by a finite volume method, in the framework of an O-H type boundary-fitted grid system (inner grid system including test model) and a rectangular grid system (outer grid system including simulation equipments for generation of wave environments). If this study, several flow configurations, such as an oscillating cylinder with large KC number, are studied in order to predict and evaluate the hydrodynamic forces. Furthermore, the motion simulation of a Series 60 model advancing in a uniform flow under the condition of enforced roll motion of angle 20$^{\circ}$ is performed in the developed numerical wave tank.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.179-182
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• 2008

This study simulated the flood inundations of the Nakdong River catchment running through Yangsan, a small city located in the south eastern area of Korea by using the depth averaged two-dimensional hydrodynamic numerical model. The numerical model employs the staggered grid system including moving boundary and a finite different method to solve the Saint-Venant equations. A second order upwind scheme is used to discretize the nonlinear convection terms of the momentum equations, whereas linear terms are discretized by a first order leap-frog scheme(Cho and Yoon, 1998). The numerical model was applied to a real topography to simulate the flood inundation of the Yangsan basin. The numerical results for urban district are visualized in three dimension. These results can be essentially utilized to construct the three dimensional inundation map after building the GIS-based database in local public organizations in order to protect the life and property safely.