• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.815-821
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• 2009

하천의 2차원 흐름 및 하상변동, 오염확산 해석을 위한 유체의 수치해석법에는 유한요소법, 유한차분법, 유한차분법의 변형인 유한체적법, 경계적분법 등이 있으며, 국내의 경우 비구조적 요소망(unstructured mesh)을 이용하여 복잡한 형상을 표현하기가 상대적으로 용이한 유한요소법이 널리 사용되고 있다. 하천을 유한 요소화 하는 전처리 과정은 전체 해석 과정을 자동화 하는데 있어 필수적인 요소이며, 주로 삼각 요소망 또는 사각 요소망을 이용하여 해석을 수행하게 된다. 삼각 요소망의 경우 상대적으로 자동화하기 쉬운 반면 사각 요소망의 생성은 절점 생성 자체가 삼각 요소망 보다 더 많은 기하학적 제한 요소를 가지고 있기 때문에 상대적으로 완성도 높은 알고리즘을 구현하기가 어렵다 할 수 있다. 이에 따라 본 연구에서는 2차원 상에서 사각 요소망(quadrilateral elements)을 생성할 수 있는 Paving method를 중심으로 한 요소망 생성 알고리즘에 대해 고찰하고, 국내 최초의 범용 수치해석 모형인 RAMS(River Analysis and Modeling System)에 적용하였다. Paving method는 1990년에 Blacker and Stephenson에 의해 제안되었으며, Sandia National Laboratories에 의해 완성되었다. Paving Method는 advancing front style의 요소망을 생성하게 되고, 바깥쪽에서 안쪽으로 element layer를 생성하면서 채워나간다. 본 연구에서는 기존의 요소망 생성 프로세스에서 element 삽입 전의 검증 기능을 강화한 새로운 버전의 paving method를 적용하엿다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.2
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• pp.247-256
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• 2019

In this study, 2-D Godunov type finite volume model which can apply the mixed mesh including triangular and quadrilateral meshes for flood inundation modeling is used to compare and analyze the flood height, flood extent and model execution time according to mesh type and resolution. The study area is the Upton-upon Severn watershed in Great Britain, where the flood occurred for 22 days from October 29 to November 19, 2000. For the flood modeling, topographic data were constructed using high resolution LiDAR (Light Detection And Ranging). The results of the 2-D flood modeling by the mesh type and resolution were compared with four ASAR (Airborne Synthetic Aperture Radar) images captured during the flood period. This study has shown that flood height and extent can vary greatly depending on the mesh type and resolution, even if identical topography and boundary conditions are used, and that the selection of appropriate mesh type and resolution for the purpose and situation of the 2-D flood modeling is necessary.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.10a
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• pp.1-8
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• 1994

A variable-node-flat shell element designated as CLS which has variable mid-side nodes with drilling freedom has been presented in this paper. The shell element to be applied in finite element analysis has been developed by combining a membrane element named as CLM with drilling rotation d.o.f. and plate bending element. The combined shell element possess six degrees of freedom per node. By introducing the variable-node elements which have physical midside nodes, some difficulties associated with imposing displacement constraints on irregular nodes to enforce interelement compatibility in common adaptive h-refinement on quadrilateral mesh are easily overcome. Detailed numerical studies show the excellent performance of the new shell elements developed in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.9 s.240
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• pp.1057-1064
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• 2005

A conservative finite-volume numerical method using unstructured meshes, which is developed by the authors, is evaluated for its application to several 2-D benchmark problems using a variety of quadrilateral, triangular and hybrid meshes. The present pressure-based numerical method for unstructured mesh clearly demonstrates the same accuracy and robustness as that fur typical structured mesh.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.865-870
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• 2004

This paper describes the generation of chordal surface for various shell structures, such as automobile bodies, plastic injection mold components and shell metal parts. After one-layered tetrahedral mesh is generated by an advancing front algorithm, the chordal surface is generated by cutting a tetrahedral element. It is generated one or two elements at a tetrahedral element and the chordal surface is composed with triangular or quadrilateral elements. This algorithm has been tested on several models with rib structure.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.71-76
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• 2004

An extension of our recently developed locally linear reconstruction scheme to 2 dimensional incompressible flow solver is presented. The solver is based on a semi-implicit fractional step method in which the convective term is discretized by Adams-Bashforth method and the diffusion term by Crank-Nicolson method. Several numerical examples are tested to demonstrate the mesh type independent accuracy of the solver, which include decaying vortex flow, square cavity flow, and flow around a circular cylinder. The above examples are solved on quadrilateral or hybrid meshes. For all numerical examples, we obtained reasonable results.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.6 no.2
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• pp.144-149
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• 2006

This paper describes a novel automated analysis system for bellows of piping system. An automatic finite element (FE) mesh generation technique, which is based on the fuzzy theory and computational geometry technique, is incorporated into the system, together with one of commercial FE analysis codes and one of commercial solid modelers. In this system, a geometric model, i.e. an analysis model, is first defined using a commercial solid modelers for 3-D shell structures. Node is generated if its distance from existing node points is similar to the node spacing function at the point. The node spacing function is well controlled by the fuzzy knowledge processing. The Delaunay triangulation technique is introduced as a basic tool for element generation. The triangular elements are converted to quadrilateral elements. Practical performances of the present system are demonstrated through several analysis for bellows of piping system.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.6 no.1
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• pp.58-63
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• 2006

This paper describes a novel automated analysis system for bellows of piping system. An automatic finite element (FE) mesh generation technique, which is based on the fuzzy theory and computational geometry technique, is incorporated into the system, together with one of commercial FE analysis codes and one of commercial solid modelers. In this system, a geometric model, i.e. an analysis model, is first defined using a commercial solid modelers for 3-D shell structures. Node is generated if its distance from existing node points is similar to the node spacing function at the point. The node spacing function is well controlled by the fuzzy knowledge processing. The Delaunay triangulation technique is introduced as a basic tool for element generation. The triangular elements are converted to quadrilateral elements. Practical performances of the present system are demonstrated through several analysis for bellows of piping system.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.4
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• pp.69-76
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• 1994

Thermal elasto-plastic analysis of axi-symmetric body by the finite element method is presented in this paper for analyzing the process of upset forming of circular section extruded bar. The example of calculation for upset forming of Nimonic extruded bar is also presented. It is shown that remeshing of quadrilateral finite element is necessary because the very highly distorted element by plastic deformation disturbs the calculation. Calculated values for nodal points in new mesh are obtained from nodal points of old mesh by linear interpolation method. The experimental results are compared with calculated values. The appearance of upsetupset forming obtained by experimental method is very similar to that obtained by calculations. So, it is proved that the thermal elasto-plastic analysis of axi-symmetric body by the finite element method is very useful for finding the optimum upsetting condition.

• Structural Engineering and Mechanics
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• v.76 no.3
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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.