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The Study and Application of Unstructured Mesh Generation Technique

Author: DongLiang
Tutor: LiuHouLin
School: Jiangsu University
Course: Fluid Machinery and Engineering
Keywords: Surface mesh Mesh generation Mesh refinement Sliver element remove Mesh output
CLC: TH166
Type: Master's thesis
Year: 2010
Downloads: 384
Quote: 8
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Abstract


Mesh generation technique is widely used in the domain of Computational Fluid Dynamics(CFD). It’s also one of the key factors to constrict the development of this domain. The accuracy and computational efficiency of numerical simulation primarily depend on the grid and the numerical algorithm. At present , the research of CFD mesh generation in pump is relatively few., and there isn’t yet a general commercial software of mesh generation in pump at home. Resulting from the complex structure of pump, the existing commercial mesh generation software is difficult to generate high-quality pump mesh, and sometimes can not mesh the pump model directly. Therefore, the mesh generation technique of pump have important theoretical significance and social economic benefits.In this paper, the main research contents and results are the following:(1) On the basis of analyzing a great deal of literature, mesh generation methods in the fluid mechanical CFD were comprehensively summarized. The principle, characteristcs and scopes of application of these methods were systematically analysed. Special mesh generation techniques wer疤?presented, such as curve surface mesh, dynamic mesh, adapt??mesh etc. Moreover, the characteristics of good mesh generation method were pionted out.(2) The shortcomings of the current two-dimensional Delaunay refinement algorithm are that it can not simultaneously control mesh-size and the quality of the mesh. A new two-dimensional Delaunay refinement algorithm which quality coefficient method was proposed with limited mesh-size method. In the process of refining, triangular elements were divided into three kinds of element types, such as equilateral triangles, isosceles triangles and regular triangles. Different strategies of inserting nodes were used for different types of triangles, which can improve the efficiency of the refinement algorithm more significantly.(3) Nowadays, the most common unstructured surface mesh generation method is mapped method. However, mapped method tends to generate distortion elements, which leads to poor quality meshes. Based on mapped method, the Riemannian metric was applied. It triangulates parametric plane fields by making use of the relationship between the curve length of parameter plane and that of physical space. After that, the resulting grid is mapped to the physical space to remove distortion.(4) There are certain amount of Sliver elements in Delaunay triangulation, affecting the overall quality of meshing. In this paper, the adoption of refinement algorithms to eliminate the Sliver elements were comprehensive analyzed, and the existing algorithms, which could not completely eliminate Sliver elements, were pointed out. Then a better existing algorithm of elimination Sliver was improved, and the Sliver elements could be completely eliminated after the refinement.(5) In order to achieve data communication between mesh generation software and finite element software, the output formats of three staple grid file which are Neutral file, Nastran bulk data file and Universal file were deeply studied. Their internal structure form were described. Additionally, the interface program from mesh output file to the solver was developed, and the key codes of the interface programs were given.

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