• Wind and Structures
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• 제6권6호
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• pp.419-436
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• 2003

Large-eddy simulations of the flow around a circular cylinder at a Reynolds number, based on cylinder diameter and free-stream velocity, $Re_D=2{\times}10^4$ are presented. Three different dynamic subgrid-scale models are used, viz. the dynamic eddy-viscosity model and two different mixed two-parameter models. The sensitivity to grid refinement in the spanwise and radial directions is systematically investigated. For the highest resolution considered, the effects of subgrid-scale modeling are also discussed in detail. In particular, it is shown that SGS modeling has a significant influence on the low-frequency modulations of the aerodynamics loads, which are related to significant changes in the near wake structure.

• 한국전산유체공학회지
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• 제13권3호
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• pp.69-78
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• 2008

The high-order numerical method based on the adaptive mesh refinement(AMR) on the quadrilateral unstructured grids has been developed in this paper. This adaptive-grid method, originally developed with MUSCL-TVD scheme, is now extended to the WENO (weighted essentially no-oscillatory) scheme with the Runge-Kutta time integration of fifth order in spatial and temporal accuracy. The multidimensional interpolation was studied in the preliminary research, which allows us to maintain the same order of accuracy for the computation of numerical flux between two adjacent cells of different levels. Some standard benchmark tests are done to validate this method for checking the overall capacity and efficiency of the present adaptive-grid technique.

• 한국분무공학회지
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• 제16권4호
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• pp.186-194
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• 2011

This study performed the numerical analysis of the internal nozzle flows including cavitation phenomena by using the automated body-fitted grid generator and the multi-fluid model. The effect of grid refinement and the validation of multifluid model were investigated using four computational meshes under two test conditions. The mesh #3 was chosen as the optimum which can reduce the computational time and have good prediction ability to identify the cavitation region simultaneously. In addition, the computed results using multi-fluid model were compared with the reference experimental observations and numerical simulation results using homogeneous equilibrium model. From the distribution of volume fraction and velocity field, the multi-fluid model predicted the internal nozzle flows well when the liquid quality parameters were selected as $1.0{\times}10^{12}$ for initial number density and 25 ${\mu}m$ for bubble diameter.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.182-187
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• 1995

The present paper explains some advancement made by the authors for the compressible flow computation of the Euler equations based on the unstructured grid and vertex- centered finite volume method. Accurate solutions to the unsteady axisymmetric shock wave propagation problems and three-dimensional airplane flows have been obtained by a high-order upwind TVD and FCT schemes. Unstructured grid adaption is made for the unsteady shock wave problems by the dynamic h-refinement/unrefinement procedure and for the three-dimensional steady flows by the Delaunay point-insertion method to generate three-dimensional tetrahedral mesh enrichment. Some physics of the shock wave diffraction phenomena and three-dimensional airplane flow are discussed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 춘계학술대회논문집
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• pp.129-133
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• 2000

It is reasonable to use the stereo vision and image processing technique to digitize 3D coordinates of grid points and to evaluate surface strains on a sheet metal parts. However this method has its intrinsic problems such as the difficulty in enhancement of bad images inevitable error due to digital image resolution of camera and frame grabber unreliability of strains and thickness evaluated from coarse grid on the corner area with large curvature and the limitation of the area that can be measured at a time. Therefore it is still hard to measure strain distribution over the entire surface of a medium,- or large-sized stamped part at a time even by using an automated strain measurement system. In this study the curvature correction algorithm based on the grid refinement and the geometry assembling algorithm based on the global error minimization (GEM) scheme are suggested. Several applications are presented to show the reliability and efficiency of these algorithms.

• 한국항공우주학회지
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• 제42권3호
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• pp.191-198
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• 2014

본 연구는 유체-고체 연성 해석이 활발히 진행되고 있는 고체로켓의 3차원 연소실 상경계면 형상에 대해 정보 전달 기법 중 하나인 공통세분 기법의 적용을 목적으로 수행되었다. 본 기법은 불일치하는 경계면간 정보 전달에도 보존성과 정확도를 동시에 만족시킬 수 있다는 장점을 갖는다. 기법 구현은 상경계면에 공통표면을 구성하고 특정 오차를 최소화 시키는 최소화 내삽법을 적용하는 과정으로 수행되었다. 이를 바탕으로 다양한 다차원 상경계면 형상에서 연속 및 불연속 함수를 이용한 정보 전달 실험을 수행하였고, 다른 기법들과 해석 결과를 비교하였다.

• 대한조선학회논문집
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• 제51권5호
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• pp.409-418
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• 2014

Simulation of flow past a complex marine structure requires a fine resolution in the vicinity of the structure, whereas a coarse resolution is enough far away from it. Therefore, a lot of grid cells may be wasted, when a simple Cartesian grid system is used for an Immersed Boundary Method (IBM). To alleviate this problems while maintaining the Cartesian frame work, we adopted an Adaptive Mesh Refinement (AMR) scheme where the grid system dynamically and locally refines as needed. In this study, We implemented a moving IBM and an AMR technique in our basic 3D incompressible Navier-Stokes solver. A Volume Of Fluid (VOF) method was used to effectively treat the free surface, and a recently developed Lagrangian Dynamic Subgrid-scale Model (LDSM) was incorporated in the code for accurate turbulence modeling. To capture vortex induced vibration accurately, the equation for the structure movement and the governing equations for fluid flow were solved at the same time implicitly. Also, We have developed an interface by using AutoLISP, which can properly distribute marker particles for IBM, compute the geometrical information of the object, and transfer it to the solver for the main simulation. To verify our numerical methodology, our results were compared with other authors' numerical and experimental results for the benchmark problems, revealing excellent agreement. Using the verified code, we investigated the following cases. (1) simulating flow around a floating sphere. (2) simulating flow past a marine structure.

• 소성∙가공
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• 제9권4호
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• pp.362-371
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• 2000

In order to reduce weight of a high-speed railroad vehicle, the main body has been manufactured by hollow section extrusion using aluminum alloys. A porthole die has utilized for the hollow section extrusion process, which causes complicated die geometry and flow characteristics. Design of porthole die is very difficult due to such a complexity. The three-dimensional finite element analysis for hollow section is also an arduous job from the viewpoint of appropriate mesh construction and tremendous computation time. In the present work, mismatching refinement, an efficient domain decomposition method with different mesh density for each subdomain, is implemented for the analysis of the hollow section extrusion process. In addition, a modified grid-based approach with the surface element layer is utilized lot three-dimensional mesh generation of a complicated shape with hexahedral elements. The effects of porthole design are discussed through the simulation for extrusion of an underframe part of a railroad vehicle. An experiment has also been carried out for the comparison. Comparing the velocity distribution at the outlet with the thickness variation of the extruded part, it is concluded that the analysis results can provide reliable measures whether the die design is acceptable to obtain uniform part thickness. The analysis results are then successfully reflected on the industrial porthole die design.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.146-152
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• 2000

Two and Three dimensional dynamic adaptation code is developed for transient computations. This code involves mesh refinement and coarsening to either add points in high gradient regions of flow or remove points where they are not needed, for high spatial accuracy. Temporary cell algorithm is used to maintain the original grid quality. To show the assessment of the accuracy and efficiency, two dimensional study and unsteady flows are computed. Also, three dimensional steady computations are made to assess the refinement using temporary cell algorithm. The result shows the high spatial accuracy primarily in discontinuity regions in steady and unsteady computation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 압출 및 인발 심포지엄
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• pp.5-8
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• 1999

The present work is concerned with three-dimensional finite element analysis of the hollow section extrusion process using a porthole die. For economic computation, mismatching refinement, an efficient domain decomposition method with different mesh density for each subdomain, is implemented. The proposed method improves the computational efficiency significantly, especially fur the three-dimensional analysis of extrusion problems. As a numerical example, extrusion of the underframe part of a railroad vehicle are analyzed. For three-dimensional mesh generation of a complicated shape with hexahedral elements, a modified grid-based approach with the surface element layer is utilized. The analysis results are then successfully reflected on the industrial porthole die design.