• 한국해안해양공학회지
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• 제15권3호
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• pp.190-195
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• 2003

연안 및 해안에서 발생하는 파랑변형, 조석 전파, 부유사 이동 및 확산 현상 등을 예측하기 위해서는 수치모형이 주로 사용된다 대표적인 수치모형 기법으로는 유한차분법 및 유한요소법이 있다. 유한차분법을 사용하는 경우에는 관심영역의 각 격자점에서 유한차분 방정식을 풀어야하므로, 격자망 및 경계조건 등이 설정되어야 한다. 유한차분용 격자망은 유한요소법과는 달리 격자망이 간단하지만, 지형이 복잡한 경우에 편리하게 사용 할 수 있는 격자정보 생성기법이 별로 개발되어 있지 않다. 또한, 상업용으로 많이 개발되어 있는 프로그램도 대부분 유한요소법에 근거한 수치모형에서 사용하는 격자생성을 목적으로 하고 있다. 본 연구에서는 디지타이저(Summagrid IV 기종)를 사용하여 유한차분모형을 위한 동일한 간격의 직사각형 격자 수심자료를 만드는 세부과정을 자료로 소개하고자 한다. 필요한 프로그램은 Golden Software사의 Didger(dititiger 지원 S/W)와 Surfer(gridding & contouring S/W)로서, 비교적 간단하게 정확한 수심 자료를 얻을 수 있으며, 임의의 지점 떠는 영역에 제시된 정보로부터 필요한 직사각형 격자정보를 추출하는 방법에 적용이 가능하다.

• 대한기계학회논문집
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• 제14권1호
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• pp.189-196
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• 1990

본 연구에서는 THOMPSON의 방법과는 달리 경계에서 부여된 metric scale fac- tor에 의해서 동적으로 제어되는 제어함수법과 경계에서 Neumann조건을 적용하여, 제 어함수와 비직교성의 문제를 해결하는 새로운 방법을 소개하고, 3차원 단연결영역(si- mply-conneted region)의 실제적이고 관심있는 영역, 즉, 축대칭 물체(axisymmetric body), 익형 물체(wing body), 확대 곡관(diffusing curved duct), 90도 곡관(90 deg. elbow turn)에 대하여 격자생성을 하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.362-367
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• 2011

The aerodynamic performance of the pantograph of the next generation high sped train is analyzed. The calculation of the flow around pantograph is carried cut by FLUENT; by the steady state flow calculation with ${\kappa}-{\omega}$ SST turbulence model, the lift force of the pantograph is computed. For the verification of the numerical schemes am grid systems, flow calculations are performed with the pantograph shape which was used at the experiments performed at Railway Technical Research Institute (RTRI) in Japan. Then, the difference of lift force between numerical am experimental results is about 10%. Therefore, selected numerical schemes and the current grid system is adequate for the analysis am prediction of the aerodynamic performance of panthograph system. Based on these numerical schemes am grid system, the flow around pantograph of the next generation high sped train is calculated and the lift force of the pantograph is predicted; the lift force of the pantograph is about 146N.

• 한국전산유체공학회지
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• 제1권1호
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• pp.19-25
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• 1996

A multiblock grid generation has been developed to be reliably used for a Navier-Stokes simulation of the turbomachinery flow-fields A multiblock structure simplifies the creation of structured H-grids about complex turbomachinery geometries and facilitate the creation of a grid in the tip flow region. The numerical algorithm adopts the combination of the algebraic and elliptic method to create the internal grids efficiently and quickly. The grid refinement process is enhanced by developing strategies to utilized Bezier curves and splines along with weighted transfinite interpolation technique and by formulating the grid-imbedding method for the viscous boundary-layer meshes. For purposes of illustration, the grid generator is applied to the high turning turbine rotor blades. Two different types of computational grids are provided to be compared with respect to the grid adaptation to the flow simulations. Extension to three-dimensions was done to show the possibility of its application to the tip-flow simulations. The grid quality of the multiblock structure is good in the passages, with gloval orthogonality and adequate smoothness.

• 한국항해학회지
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• 제19권2호
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• pp.13-22
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• 1995

This paper presents the numerical analysis results of the viscous flow for a full ship model. The mass and momentum conservation equations are used for governing equations, and the flow field is discretized by the Finite-Volume Method for the numerical calculation. An algebraic grid and elliptic grid generation techniques are adopted for generation of the body-fitted coordinates system, which is suitable to ship's hull forms. Time-marching procedure is used to solve the three-dimensional unsteady problem, where the convection terms are approximated by the QUICK scheme and the 2nd-order central differencing scheme is used for other spatial derivatives. A Sub-Grid Scale turbulence model is used to approximate the turbulence, and the wall function is used at the body surface. Pressure and velocity fields are calculated by the simultaneous iteration method. Numerical calculations were accomplished for the Crude Oil Tanker(DWT 95,000tons, Cb=0.805) model. Calculation results are compared to the experimental results and show good agreements.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.55-60
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• 1998

An elliptic grid generation scheme using Laplace's equations guarantees the resulting grids to be crossing-free as a result of maximum principle in its analytic form. Numerical results, however, often show the grid lines overlapping each other or crossing the boundaries, especially for very sharp convex corners. The cause of this problem is investigated, and it is found that this problem can be handled by properly modifying the coefficients of transformed Laplace's equations in the computational domain.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회 논문집
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• pp.532-537
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• 2005

The techniques of internally generating waves on a curve in a rectangular grid system are developed using the line source method. Numerical experiments are conducted using the extended mild-slope equations of Suh et al. (1997). For five different types of wave generation layout, numerical experiments are conducted in the cases of the propagation of waves on a flat bottom, and the refraction and shoaling of waves on a plane slope. The fifth type of wave generation, which consists of two parallel lines connected to a semicircle, shows the best solutions especially when the grid size is small enough.

• 대한기계학회논문집B
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• 제23권6호
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• pp.703-712
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• 1999

This paper suggests an automatic elliptic grid generation method that is well-suited for the numerical mapping of complex geometries which are easily obtained from general CAD programs. An LBLADI solver is used for the governing mapping equations to have the strong diagonal dominance. The full boundary control method is adopted to determine the control functions of the equations, which allows the control of the grid regarding spacing and angle control at all boundary surfaces. The solution method presented here provides the capability of mapping very complicated geometries by defining grid point locations only along the boundaries. In the automated elliptic grid generation procedure, it is showed that strong diagonal dominance is essential to achieve successful mapping irrespective of the initial grid condition provided. To demonstrate the robustness of this method, it is applied to the thermal flow like the natural convection between eccentric cylinders. The results agree well with others.

• 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.

• 한국해안해양공학회지
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• 제18권1호
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• pp.1-14
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• 2006

본 논문에서 직사각형 격자 체계에서 원호형 내부조파에 의한 선 조파기법을 개발하였다. 총 다섯 가지 조파형식의 수치실험이 다음의 조건에 수행되었다. 즉, 일정수심에서의 파랑의 전파, 일정경사를 가지는 평면에서의 굴절과 천수, 반무한 방파제에서 회절 실험을 수행하였다. 수치실험 수행 시 기본방정식으로 Suh et al. (1997)이 제안한 확장형 완경사방정식을 이용하였다. 두 개의 평행한 직선이 반원으로 연결된 제5형식 조파기법을 사용하면 가장 우수한 결과를 얻을 수 있었다. 특히, 격자간격이 작은 경우에 그 우수성이 확연히 드러났다.