• 산업공학
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• 제16권spc호
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• pp.87-92
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• 2003

Progressive mesh representation and generation have become one of the most important issues in network-based computer graphics. However, current researches are mostly focused on triangular mesh models. On the other hand, solid models are widely used in industry and are applied to advanced applications such as product design and virtual assembly. Moreover, as the demand to share and transmit these solid models over the network is emerging, the generation and the transmission of progressive solid models depending on specific engineering needs and purpose are essential. In this paper, we present a Cellular Topology-based approach to generating and transmitting progressive solid models from a feature-based solid model for internet-based design and collaboration. The proposed approach introduces a new scheme for storing and transmitting solid models over the network. The Cellular Topology (CT) approach makes it possible to effectively generate progressive solid models and to efficiently transmit the models over the network with compact model size.

• 전자공학회논문지SC
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• 제41권6호
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• pp.1-10
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• 2004

본 논문에서는 가상 구멍뚫기 작업의 표현을 위한 햅틱 렌더링 시스템을 제안하였다. 가상 모델을 만들기 위하여 영상 처리기법과 Delaunay 삼각형을 이용하였고, 실시간 어플리케이션에 적용하기 위해 간단하면서도 효율적인 후크의 법칙을 이용하여 힘을 생성하였다. 또한, 직렬형 메커니즘으로 표현하기 어려운 큰 힘을 표현하면서, 병렬형 메커니즘의 특이점 문제를 함께 해결하기 위하여 여유구동 6자유도 병렬형 메커니즘을 햅틱장치로 제안하였고 두 종류의 구멍뚫기 실험을 통하여 큰 힘을 표현할 수 있는 능력을 검증하였다.

• Structural Engineering and Mechanics
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• 제76권3호
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• pp.379-393
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• 2020

In this paper, we propose an automatic procedure to improve the accuracy of finite element solutions using enriched 2D solid finite elements (4-node quadrilateral and 3-node triangular elements). The enriched elements can improve solution accuracy without mesh refinement by adding cover functions to the displacement interpolation of the standard elements. The enrichment scheme is more effective when used adaptively for areas with insufficient accuracy rather than the entire model. For given meshes, an error for each node is estimated, and then proper degrees of cover functions are applied to the selected nodes. A new error estimation method and cover function selection scheme are devised for the proposed adaptive enrichment scheme. Herein, we demonstrate the proposed enrichment scheme through several 2D problems.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2002년도 종합학술발표회 논문집 Vol.12 No.1
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• pp.375-379
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• 2002

본 논문에서는 수 만개이상의 미지수를 필요로 하는 복잡한 3차원 구조에서의 정전용량 추출을 위한 고속화 알고리즘(Fast mutilpole method)과 결합한 효과적인 적응 삼각요소 분할법(Adaptive triangular mesh refinement algorithm)을 제안하였다. 요소세분화과정은 초기요소로 전하의 분포를 구하고, 전하밀도가 높은 영역에서의 요소세분화를 수행하여 이루어진다. 제안된 방법을 이용하여 많은 미지수를 필요로 하는 IC packaging 구조에서의 정전용량을 추출하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 봄 학술발표회 논문집
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• pp.261-268
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• 2003

A first order shear deformable Loop-subdivision triangular element which can handle transverse shear deformation of moderately thick shell is developed. The developed element is general since it includes the effect of transverse shear deformation and has standard six degrees of freedom per node.(three translations and three rotations) The quartic box-spline function is employed as interpolation basis function. Numerical examples for the benchmark problems are analyzed in order to assess the performance of the newly developed subdivision shell element. Both in the uniform and in the distorted mesh configurations.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.121-124
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• 1997

In the present study, a general tool surface contac search ad check algorithm is proposed. A general tool surface is described by triangular FE mesh. To check a proposed algorithm, clover cup and L-shape cup deep drawing processes are calculated. The elastic-plastic FEM using SEAM (Shear Energy Augmented Membrane) element is adapted for numerical stability.

• 대한기계학회논문집
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• 제18권8호
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• pp.2113-2122
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• 1994

The 3-D FEM analysis for simulating the stamping operation of planar anisotropic sheet metals with arbitrarily-shaped tools is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-normal, which compatibly describes arbitrary tool surfaces and FEM meshes without depending on the explicit spatial derivatives of tool surfaces. The consistent full set of governing relations, comprising equilibrium equation and mesh-normal geometric constraints, is appropriately linearized. The linear triangular elements are used for depicting the formed sheet, based on membrane approximation. Barlat's non-quadratic anisotropic yield criterion(strain-rate potential) is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and non-quadratic function parameter. The planar anisotropic finite element formulation is tested with the numerical simulations of the stamping of an automotive hood inner panel and the drawing of a hemispherical punch. The in-plane anisotropic effects on the formability of both mild steel and aluminum alloy sheet metals are examined.

• 소성∙가공
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• 제15권6호
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• pp.445-452
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• 2006

In most of automobile body panel manufacturing, trimming process is generally performed before flanging. To find feasible trimming line is crucial in obtaining accurate edge profile after flanging. Section-based method develops blank along manually chosen section planes and find trimming line by generating loop of end points. This method suffers from inaccurate results of edge profile. On the other hand, simulation-based method can produce more accurate trimming line by iterative strategy. In this study, new fast simulation-based method to find feasible trimming line is proposed. Finite element inverse method is used to analyze the flanging process because final shape after flanging can be explicitly defined and most of strain paths are simple in flanging. In utilizing finite element inverse method, the main obstacle is the initial guess generation for general mesh. Robust initial guess generation method is developed to handle genera] mesh with very different size and undercut. The new method develops final triangular mesh incrementally onto the drawing tool surface. Also in order to remedy mesh distortion during development, energy minimization technique is utilized. Trimming line is extracted from the outer boundary after finite element inverse method simulation. This method has many advantages since trimming line can be obtained in the early design stage. The developed method is verified by shrink/stretch flange forming and successfully applied to the complex industrial applications such as door outer flanging process.

• 한국컴퓨터그래픽스학회논문지
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• 제26권4호
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• pp.17-26
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• 2020

본 논문에서는 GPU(Graphic Processing Unit) 연산을 활용하여 BCC(Body Centered Cubic) 볼륨 데이터로부터 실시간으로 메시 형태의 등가면을 추출하는 개선된 마칭 사면체(Marching tetrahedra) 기법을 제안한다. 본 기법은 고전적인 방법과 비교하여 메모리 사용량은 다소 높지만 더 좋은 성능을 보인다. 본 기법은 다섯 단계로 구성되어 있다. 첫 번째 단계는 단 한번만 수행되는 단계로, 빈 공간을 생략하여 성능을 향상 시키기 위해 최소/최댓값 블록(Min/max block)을 생성한다. 두 번째 단계에서는 등갓값(Isovalue)을 포함하고 있는 유효한 블록을 추려낸다. 이후 두 단계에서는 등가면(Isosurface)을 포함하는 셀(Cell)과 엣지(Edge)를 추출하고, 마지막 단계에서 삼각형 메시(Triangle mesh)를 생성한다. 본 기법은 512³ 이상의 고해상도 볼륨 데이터(Volume dataset)에 대한 등가면 추출 시, 삼각형 집합 형태의 등가면을 추출하는 고전적인 마칭 사면체 기법에 비해 최대 5배 정도의 속도 향상을 보인다.

• Structural Engineering and Mechanics
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• 제39권6호
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• pp.767-793
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• 2011

An efficient edge-based smoothed finite element method (ES-FEM) has been recently developed for solving solid mechanics problems. The ES-FEM uses triangular elements that can be generated easily for complicated domains. In this paper, the complexity study of the ES-FEM based on triangular elements is conducted in detail, which confirms the ES-FEM produces higher computational efficiency compared to the FEM. Therefore, the ES-FEM offers an excellent platform for adaptive analysis, and this paper presents an efficient adaptive procedure based on the ES-FEM. A smoothing domain based energy (SDE) error estimate is first devised making use of the features of the ES-FEM. The present error estimate differs from the conventional approaches and evaluates error based on smoothing domains used in the ES-FEM. A local refinement technique based on the Delaunay algorithm is then implemented to achieve high efficiency in the mesh refinement. In this refinement technique, each node is assigned a scaling factor to control the local nodal density, and refinement of the neighborhood of a node is accomplished simply by adjusting its scaling factor. Intensive numerical studies, including an actual engineering problem of an automobile part, show that the proposed adaptive procedure is effective and efficient in producing solutions of desired accuracy.