• 한국CDE학회논문집
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• 제6권3호
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• pp.184-192
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• 2001

In this paper we present a remeshing algorithm for irregular meshes with boundaries. The irregular meshes are approximated by regular meshes where the topological regularity is essential for the multiresolutional analysis of the given meshes. Normal meshes are utilized to reduce the necessary data size at each resolution level of the regularized meshes. The normal mesh uses one scalar value, i.e., normal offset value which is based on the regular rule of a uniform subdivision, while other remeshing schemes use one 3D vector at each vertex. Since the normal offset cannot be properly used for the boundaries of meshes, we use a combined subdivision scheme which resolves a problem of the proposed normal offset method at the boundaries. Finally, we show an example to see the effectiveness of the proposed scheme to reduce the data size of a mesh model.

• 한국농공학회지
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• 제37권2호
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• pp.21-30
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• 1995

In order to save time and efforts in generating finite element meshes in irregular houndaries of domains, it is needed to develop an automatic mesh-generator which can hoth promote the accuracy of solutions and reduce the run-time in operating finite ele- ment models. In this study, the advancing front technique of triangular mesh generation and the transforming technique from triangular meshes to quadrilateral meshes were used to de- velop a computer program for the automatic triangular and quadrilateral meshes in the mixed shape. Furthermore, to enhance the quadrilateral mesh quality, the techniques of Laplancian smoothing and interior mesh modification were employed. The mesh genera- tor was applied to evaluate its applicability to irregular and complex geometries such as Nakdong river bay. In has hoen shown that the automatic mesh generator developed is capable of automatically generating meshes for irreguiar and complex geometries with high qualities of meshes and with the simple input data of arbitrarily specified nodal spacing in bound- aries.

• Journal of Mechanical Science and Technology
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• 제17권7호
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• pp.986-998
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• 2003

In this paper, an adaptive numerical integration scheme, which does not need non-overlapping and contiguous integration meshes, is proposed for the MLPG (Meshless Local Petrov-Galerkin) method. In the proposed algorithm, the integration points are located between the neighboring nodes to properly consider the irregular nodal distribution, and the nodal points are also included as integration points. For numerical integration without well-defined meshes, the Shepard shape function is adopted to approximate the integrand in the local symmetric weak form, by the values of the integrand at the integration points. This procedure makes it possible to integrate the local symmetric weak form without any integration meshes (non-overlapping and contiguous integration domains). The convergence tests are performed, to investigate the present scheme and several numerical examples are analyzed by using the proposed scheme.

• 한국CDE학회논문집
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• 제1권3호
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• pp.224-233
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• 1996

An automatic mesh generation scheme with triangular finite elements on three-dimensional surfaces has been developed. The surface triangulation process is performed as follows. To begin, surfaces with key nodes are transformed to two-dimensional planes and the meshes with triangular elements are constructed in these planes. Finally, the constructed meshes are transformed back to the original 3D surfaces. For the mesh generation, an irregular mesh generation scheme is employed in which local mesh densities are assigned by the user along the boundaries of the analysis domain. For this purpose a looping algorithm combined with an advancing front technique using basic operators has been developed, in which the loops are recursively subdivided into subloops with the use of the best split lines and then the basic operators generate elements. Using the split lines, the original boundaries are split recursively until each loop contains a certain number of key nodes, and then using the basic operators such as type-1 and type-2, one or two triangular elements are generated at each operation. After the triangulation process has been completed for each meshing domain, the resulting meshes are finally improved by smoothing process. Sample meshes are presented to demonstrate the versatility of the algorithm.

• 대한전자공학회논문지SP
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• 제38권2호
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• pp.149-159
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• 2001

기존의 블록기반 움직임 예측방법은 특히 저전송률 비디오 압축에 사용 될 경우 움직임 필드에서의 블록화 현상이나 불안정한 움직임 예측과 같은 문제를 수반한다. 본 논문은 이러한 단점을 극복하기 위해 H.263의 기존 블록기반 DCT부호화 구조를 최대한 유지하면서 비정형 삼각형 메쉬에 기반한 새로운 움직임 보상 방법을 수용할 수 있는 하나의 방법을 제안한다. 제안방법은 복원된 이전 프레임 영상을 최소의 제어점들을 이용해 표현하기 위해, 주어진 영상의 컨텐트에 적응적으로 삼각형 비정형 메쉬를 설정한다. 그리고 Affine변환에 기반한 매칭을 이용해, 설정된 각 제어점의 움직임벡터를 구한 후, 이를 이용해 각 메쉬를 Affine변환하여 예측된 현재 프레임을 얻는 전방향 움직임 보상을 제안한다. 이 방법은 컨텐트에 적응적으로 설정된 메쉬 정보를 보내지 않아도 되는 장점이 있다. 실제 비디오 데이터를 이용해 실험한 결과 제안방법이 객관적 및 주관적 화질 평가에서 기존의 블록기반 H.263 방법보다 개선되었음을 알 수 있다.

• 한국전산유체공학회지
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• 제9권3호
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• pp.73-80
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• 2004

A LS(Level Set) formulation is developed for computing two-phase flows on non- orthogonal meshes. Compared with the VOF(Volume-of-Fluid) method based on a non-smooth volume-fraction function, the LS method can calculate an interfacial curvature more accurately by using a smooth distance function. Also, it is quite straightforward to implement for 3-D irregular meshes compared with the VOF method requiring much more complicated geometric calculations. The LS formulation is implemented into a general purpose program for 3-D flows and verified through several test problems.

• 대한기계학회논문집B
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• 제35권6호
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• pp.561-567
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• 2011

2 차원 비직교 형상에 대해 비정렬 삼각 격자를 이용하여 복사 열전달의 역해석을 수행하였다. 본 논문에서는 확산적으로 방사 및 반사를 하는 벽면으로 이루어진 형상 내부에 흡수 및 방사, 산란하는 매질이 채워져 있는 문제를 고려하였다. 유한체적법을 사용하여 복사전달 방정식을 계산하였고 이 때 얻은 입사복사량을 역해석의 측정 데이터로 사용하였다. 벽면의 방사율을 추정하기 위해 켤레구배법을 적용하였으며, 목적 함수를 최소화하는 과정을 통해 해를 구하였다. 측정값의 측정 오차가 추정 정확도에 미치는 영향을 살펴보았고, 비정렬 격자계의 성능을 확인하기 위해 정렬 격자계를 이용하여 얻은 결과와 비교해 보았다.

• Structural Engineering and Mechanics
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• 제43권3호
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• pp.349-370
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• 2012

Variable-node finite element families, termed (4 + k + l + m + n)-node elements with an arbitrary number of nodes (k, l, m, and n) on each of their edges, are developed based on the generic point interpolation with special bases having slope discontinuities in two-dimensional domains. They retain the linear interpolation between any two neighboring nodes, and passes the standard patch test when subdomain-wise $2{\times}2$ Gauss integration is employed. Their shape functions are automatically generated on the master domain of elements although a certain number of nodes are inserted on their edges. The elements can provide a flexibility to resolve nonmatching mesh problems like mesh connection and adaptive mesh refinement. In the case of adaptive mesh refinement problem, so-called "1-irregular node rule" working as a constraint in performing mesh adaptation is relaxed by adopting the variable-node elements. Through several examples, we show the performance of the variable-node finite elements in terms of accuracy and efficiency.

• Journal of Advanced Marine Engineering and Technology
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• 제23권1호
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• pp.9-18
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• 1999

The present study is aimed to investigate flow characteristics of two-dimensional backward-fac-ing step by numerical approach. A convection conservation difference scheme based upon SOLA algorithm is used for the solution of the two-dimensional incompressible Navier-Stokes equations to simulate the laminar transitional and trubulent flow conditions at which the experimental data can be available for the backlward-facing step. The twenty kinds of reynolds number are used for the calculations. In an effort to demonstrate that the reported solutions are dependent on the mesh refinement computations are performed on seven different meshes of uniformly increasing refinement. also to investigate the result of inflow dependence two kinds of the inflow profile are chosen for the laminar flow. Irregular grid is adopted to minimize the errors on the satis-faction fo the discretized continuity. As criterion of benchmarking the result of numerical simula-tion reattachment lengthis used for the selected Reynolds numbers. The results of the present study prove the fact that the numerical predictions agree well with the experimental data and the flow characteristics are shown at the backward-facing step.

• 한국콘텐츠학회논문지
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• 제9권5호
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• pp.76-83
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• 2009

최근 공동 연결 관계와 연속적인 정점 위치들의 움직임으로 이루어진 메쉬들의 모임, 즉 메쉬 시퀀스를 압축하는 연구가 활발하게 이루어지고 있다. 본 논문은 Khodakovsky 등이 제시한 준균일 메쉬 압축방법에 기반한 메쉬 시퀀스의 압축 알고리즘을 제시하고자 한다. 준균일 메쉬 시퀀스로의 메쉬 재구성을 이용한 메쉬 시퀀스 압축 알고리즘은 크게 두 부분으로 이루어진다. 첫 번째 부분은 주어진 비균일 메쉬 시퀀스로부터 준균일 메쉬 시퀀스를 생성하는 것이다. 준균일 메쉬를 생성하기 위해 본 논문에서는 MAPS 알고리즘을 사용하였다. 하지만 단일 메쉬에 대해 적용이 가능한 MAPS 알고리즘을 메쉬 시퀀스에 그대로 적용할 수 없다. 따라서 주어진 애니메이션에서의 정점 움직임을 고려하여 유사한 움직임을 가지는 영역별로 분할하고, 이 분할 정보과 정점의 움직임을 고려할 수 있도록 MAPS 알고리즘을 확장하였다. 두 번째 단계에서는 웨이블릿 변형과 메쉬 분할 정보를 이용해 준균일 메쉬를 압축하였다. 각 분할 영역의 변환 정보를 고려해 분할 영역 내 정점의 위치를 예측하고, 참조 프레임과의 차이값을 압축함으로써 효율적으로 준균일 메쉬 시퀀스를 압축하였다.