• Journal of computational fluids engineering
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• v.14 no.3
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• pp.33-48
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• 2009

In the present study, a fast grid deformation technique has been incorporated into the unsteady compressible and incompressible viscous flow solvers on unstructured hybrid meshes. An algebraic method based on the basis decomposition of normal edge vector was used for the deformation of viscous elements, and a ball-vertex spring analogy was adopted for inviscid elements among several spring analogy methods due to its robustness. The present method was validated by comparing the results obtained from the grid deformation and the rigid motion of entire grids. Fish swimming motion of an NACA0012 airfoil and flapping wing motion of a generic fighter were also simulated to demonstrate the robustness of the present grid deformation technique.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.17-22
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• 2007

Chimera grid Method is widely used in Computational Fluid Dynamics due to its simplicity in constructing grid system over complex bodies. Especially, Chimera grid method is suitable for unsteady flow computations with bodies in relative motions. However, interpolation procedure for ensuring continuity of solution over overlapped region fails when so-call orphan cells are present. We have adopted MLS(Moving Least Squares) method to replace commonly used linear interpolations in order to alleviate the difficulty associated with orphan cells. MSL is one of interpolation methods used in mesh-less methods. A number of examples with MLS are presented to show the validity and the accuracy of the method.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.252-255
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• 2006

• Wind and Structures
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• v.36 no.3
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• pp.175-200
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• 2023

The large eddy simulation (LES) of the flow around a circular cylinder is not only affected by the sub-grid scale (SGS) model but also by the grid resolution of the computational domain. To study the influence of different grids on the LES results, the LES simulations of the flow around a circular cylinder with different grids at Reynolds number (Re) = 3900 was performed. A circular computational domain with different radial growth rates and circumferential and spanwise grid numbers was adopted for the simulations. Meanwhile, the aerodynamic forces, wind pressure coefficients, mean and instantaneous flow fields, and the effect of grid resolution on them were comprehensively analyzed. The results indicate that the lift coefficient, wind pressure coefficient, and recirculation length are significantly affected by the radial growth rate of the grid and the circumferential grid number. The spanwise grid number has a significant influence on the three-dimensionality of the flow and plays an important role in velocity fluctuations in the wake region. Nevertheless, the aerodynamic coefficients and recirculation length are not sufficiently sensitive to the grid number in the spanwise direction. By comparing the results, it can be concluded that suitable and reliable LES results can be obtained when the radial growth rate is 1.03 or 1.05, the circumferential grid number is 160, 200, or 240, and the spanwise grid number is 64. A radial growth rate 1.05, circumferential grid number 160, and spanwise grid number 64 are recommended to reduce the grid amount and further improve the efficiency.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.386-389
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• 2008

In this paper grid generation of unstructured quadrilateral surface grids is described. The current approach uses conventional Advancing Front Method which is used to generate unstructured triangular grids. Grid cell size control is done by using closeness-based global interpolation method controlled by pre-described control elements. Algorithm and procedure for quadrilateral grid generation using AFM method and cell size control method are described. Examples of quadrilateral grid generation are shown, and difficulties and problems related to the current approach are also discussed.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.136-141
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• 2006

A prediction of store separation trajectory using grid survey method has been conducted. For the grid survey method, store's aerodynamic flowfield data such as freestream and grid data is needed to solve 6 degree of freedom(6-DOF) equations of motion. In the presented study, aerodynamic flowfield data was generated by Euler solver instead of CTS wind tunnel test. The predicted trajectories shows good agreement with CTS test results.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.386-389
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• 2008

In this paper grid generation of unstructured quadrilateral surface grids is described. The current approach uses conventional Advancing Front Method which is used to generate unstructured triangular grids. Grid cell size control is done by using closeness-based global interpolation method controlled by pre-described control elements. Algorithm and procedure for quadrilateral grid generation using AFM method and cell size control method are described. Examples of quadrilateral grid generation are shown, and difficulties and problems related to the current approach are also discussed.

• 한국전산유체공학회:학술대회논문집
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• 2002.10a
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• pp.84-87
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• 2002

When computing the flow around complex three dimensional configurations, the generation of grid is the sunt time consuming part of any calculation. The object of this study is to develop the grid duster techniques capable of resolving complex flows with shock waves, expansion waves, shear layers, and cursive shapes, The Dot insert method of Non-Uniform Rational B-Splines is described as a id control method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.3
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• pp.183-190
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• 2019

This paper introduces a near-tip grid refinement and explores its usefulness in the crack analysis by the natural element method(NEM). As a sort of local h-refinement in finite element method(FEM), a NEM grid is locally refined around the crack tip showing high stress singularity. This local grid refinement is completed in two steps in which grid points are added and Delaunay triangles sharing the crack tip node are divided. A plane strain rectangular plate with symmetric edge cracks is simulated to validate the proposed local grid refinement and to examine its usefulness in the crack analysis. The crack analysis is also simulated using a uniform NEM grid for comparison. Unlike the uniform grid, the refined grid provides near-tip stress distributions similar to the analytic solutions and the fine grid. In addition, the refined grid shows higher convergence than the uniform grid, the global relative error to the total number of grid points.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.245-248
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• 2008

최근 RFID 시스템의 채택이 다양한 분야에서 빠르게 진행되고 있다. 그러나 RFID 시스템의 대중화를 위해서는 RFID 태그의 정보를 무단으로 획득함으로써 발생할 수 있는 프라이버시 침해 문제를 해결해야 한다. 이 문제를 해결하기 위해서 기존 연구들 중에서 가장 안전한 M. Ohkubo 등의 Hash-Chain 기법이 있다. 그러나 이 기법은 태그를 판별할 때 엄청난 태그 수의 증가로 인해 막대한 계산 능력을 요구하는 문제점이 있다. 따라서 본 논문에서는 프라이버시 보호를 유지하면서 태그판별시간 절감을 위해서 그리드 환경으로의 이식과 노드별로 m/k개의 SP를 분할하는 균등분할 알고리즘을 적용한 태그 판별 처리 모델을 제안한다. 제안 모델을 그리드 환경에서 동시에 수행할 수 있다면 이상적인 경우 태그를 판별하는 시간은 1/k로 감소한다.