• 대한조선학회논문집
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• 제56권1호
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• pp.47-57
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• 2019

Recent CFD solvers in engineering have to treat geometrically complex domains and moving body problems. In ship hydrodynamics, flow around the stern and ship motions in waves are examples of such cases mentioned before. The unstructured grid scheme is successfully applied for these problems, but it has weakness of inefficient memory usage and intensive computational time as compared to the structured grid method. Overset grid scheme is one of the alternatives for structured grid system taking advantage of fast and memory efficiency. Overset grid scheme is especially useful for moving body problem because there is no need to re-mesh around the body. In this paper, we adopted the Suggar++, the grid connectivity and interpolation utility for the overlapping grid, to WAVIS which is the in-house flow solver of KRISO. Then we introduced some applications using the overset grid method for flow analysis around the ships. The computed results show that WAVIS with Suggar++ is practically feasible and has an advantages for moving geometry cases.

• 한국전산유체공학회지
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• 제11권2호
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• pp.62-66
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• 2006

In this paper an automated hole-finding method for overset grids is introduced which uses recursive octree-cell division. A graphic program which enables the user to do the hole-cutting with ease is also introduced. Using this program it is found that there is an optimum combination of the level of octree division and vector calculation for the efficient and fast hole finding.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.83-86
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• 2004

In this paper an automated hole-finding method for overset grids is introduced which uses recursive octree-cell division. A graphic program which enables the user to do the hole-cutting with ease is also introduced. Using this program it was found that a proper combination of the level of octree division and vector calculation should be used for efficient and fast hole finding.

• Ocean Systems Engineering
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• 제5권4호
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• pp.245-259
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• 2015

The numerical simulation of wave slamming on a 3D platform deck was investigated using a coupled Level-Set and Volume-of-Fluid (CLSVOF) method for overset grid system incorporated into the Finite-Analytic Navier-Stokes (FANS) method. The predicted slamming impact forces were compared with the corresponding experimental data. The comparisons showed that the CLSVOF method is capable of accurately predicting the slamming impact and capturing the violent free surface flow including wave slamming, wave inundation and wave recession. Moreover, the capability of the present CLSVOF method for overset grid system is a prominent feature to handle the prediction of wave slamming on offshore structure.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.95-104
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• 2007

A new design approach of complex geometries such as wing/body configuration is arranged by using overset mesh techniques under large scale computing environment. For an in-depth study of the flow physics and highly accurate design, several special overlapped structured blocks such as collar grid, tip-cap grid, and etc. which are commonly used in refined drag prediction are adopted to consider the applicability of the present design tools to practical problems. Various pre- and post-processing techniques for overset flow analysis and sensitivity analysis are devised or implemented to resolve overset mesh techniques into the design optimization problem based on Gradient Based Optimization Method (GBOM). In the pre-processing, the convergence characteristics of the flow solver and sensitivity analysis are improved by overlap optimization method. Moreover, a new post-processing method, Spline-Boundary Intersecting Grid (S-BIG) scheme, is proposed by considering the ratio of cell area for more refined prediction of aerodynamic coefficients and efficient evaluation of their sensitivities under parallel computing environment. With respect to the sensitivity analysis, discrete adjoint formulations for overset boundary conditions are derived by a full hand-differentiation. A smooth geometric modification on the overlapped surface boundaries and evaluation of grid sensitivities can be performed by mapping from planform coordinate to the surface meshes with Hicks-Henne function. Careful design works for the drag minimization problems of a transonic wing and a wing/body configuration are performed by using the newly-developed and -applied overset mesh techniques. The results from design applications demonstrate the capability of the present design approach successfully.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.357-359
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• 2006

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.77-81
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• 2007

In this paper, helicopter aerodynamics is simulated in hovering and forwarding flighst. The governing equation is the unsteady Euler equation. To consider the blade motion and moving effects, an overset grid technique is applied in this simulation. At the boundary, the Riemann invariants condition is used for inflow and outflow. To validate this method, the result is compared with Caradonna-Tung's experimental data.

• 한국항공우주학회지
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• 제39권11호
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• pp.995-1004
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• 2011

Overset 격자계에서 사용되는 Object X-rays Method는 홀점 탐색의 일부인 교차점 탐색에 복잡한 벡터계산을 사용하고 개별 배경격자점에 대하여 물체 내외부를 판별하여 홀점을 탐색하므로 많은 시간이 소요된다. 특히 격자의 상대운동이 있을 경우 매 시간간격 마다 홀점 탐색을 수행해야 하므로 계산 시간이 가중된다. 이러한 문제를 해결하기 위해 본 연구에서는 홀점 탐색시간을 줄일 수 있는 효율적인 탐색 알고리즘을 제안한다. 빠른 탐색을 위해 격자점 수가 줄어든 가상의 표면을 사용하고 복잡한 벡터계산을 통한 교차점 탐색 대신 논리연산자를 사용하는 내외부 판별법을 사용하였다. 또한 개별 배경격자점에 대해 홀점 판별을 수행하는 대신 일괄로 홀점을 지정하여 탐색속도를 향상시켰다. 물체의 상대운동이 있을 경우 가상의 표면이 상대 운동하여 기존 방법에 비해서 홀점 탐색시간을 감소시킬 수 있었다. 임의의 2차원, 3차원 형상에 대하여 기존의 hole searching 알고리즘과 홀점 탐색속도를 비교한 결과를 제시하였다.

• 한국전산유체공학회지
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• 제5권2호
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• pp.9-19
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• 2000

Transient aerodynamic response of an airfoil to a moving plane-flap is numerically investigated using the two-dimensional Euler equations with conservative Chimera grid method. A body moving relative to a stationary grid is treated by an overset grid bounded by a 'Dynamic Domain Dividing Line' which has an advantage for constructing a well-defined hole-cutting boundary. A conservative Chimera grid method with the dynamic domain-dividing line technique is applied and validated by solving the flowfield around a circular cylinder moving supersonic speed. The unsteady and transient characteristics of the flow solver are also examined by computations of an oscillating airfoil and a ramp pitching airfoil respectively. The transient aerodynamic behavior of an airfoil with a moving plane-flap is analyzed for various flow conditions such as deflecting rate of flap and free stream Mach number.

• 한국전산유체공학회지
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• 제17권1호
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• pp.70-77
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• 2012

In this paper, diagonal implicit harmonic balance method with overset grid technique is applied to analyze helicopter rotor blade flow in hover and forward flight condition. The chimera grid need interpolation time with sub-grid and background grid in moving problem such as forward flight on every time step. Present method is available enough to reduce the grid module interpolation time. In order to demonstrate present method, Caradonna & Tung's and AH-1G rotor blades are used and the results are compared to other researchers' result and experimental data.