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Reserch on Hexahedral Mesh Generation Method Oriented to Geoscience Study

Author: LiXiang
Tutor: GuoFei
School: Nanjing Normal University
Course: Cartography and Geographic Information Systems
Keywords: Geosciences Simulation Spatial Analysis Mesh Generation Hexahedral Mesh Geometric Feature Constrains Feature
CLC: P208
Type: Master's thesis
Year: 2013
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Abstract

With the development of computer technology and numerical simulation method, the basic idea of geoscience mechanism and process simulation is using two-dimension or three-dimension finite element mesh to discretize geographical space and adapting related numerical methods to complete computer simulation. Therefore the finite element mesh is the basis of geoscience mechanism and process simulation. At the same time, the finite element mesh supports traditional GIS spatial analysis like buffer analysis, overlay analysis. We can see that the finite element mesh plays a very important role in geoscience mechanism, process simulation and traditional GIS spatial analysis. In three-dimensional finite element mesh, hexahedral mesh has obvious advantages in terms of the number of units, the degree of freedom and calculation accuracy. It has become one of the most widely used three-dimensional meshes, and also preferred mesh that ensures efficient complex geoscience studies. However, hexahedral mesh generation has been the difficulty of the field of finite element. Meanwhile because geoscience study objects often have characteristics such as complex boundaries and many constraints, and the problem of unstructured hexahedral mesh generation aiming at geoscience objects is still not well solved, hexahedral meshes especially unstructured hexahedral mesh are less applied in the study of geoscience.To meet the requirement of related geoscience research for hexahedral mesh, to promote further development of geoscience simulation and traditional GIS space analysis on the basis of numerical methods, this paper carries out researches on hexahedral mesh generation method for geoscience study, studies structured and unstructured hexahedral mesh generation of three-dimensional objects for common geoscience entity model. The main achievements are as follows:(1) Combining the own characteristics of geoscience study objects, we extend the traditional grid method, study entity surface models (including constraints) based on geoscience, by designing geometric features identification and constraint processing mechanism, take into account entity boundary characteristics and constraint characteristics such as internal constraints points, constraint lines, constraint surfaces and constraint holes, generate hexahedral mesh of high quality reasonably in entity three-dimensional space, improve traditional grid method boundary fitting ability, finally use mesh quality optimization algorithm to improve the mesh generation quality.(2) We carry out the study of central axis generation in three-dimensional entity based on Voronoi diagram. Firstly we sample from the three-dimensional entity, then calculate the Voronoi diagram of sampling point set, and finally use two filter conditions independent from sampling range and density to select Voronoi subset distributing around entity central axis from the generated Voronoi diagram, generate central axis in three-dimensional entity, prepare for unstructured hexahedral mesh generation algorithm. (3) Combinating the advantages of traditional grid method and the AFT method algorithm, we introduce the idea of the level set method, take geoscience entity surface triangular mesh model as data source, all levels (advanced level isosurface) combining distance fields as guide, start from the internal seed, identify quadrilateral mesh feature on the seed surface, and then use grid advancing templates to generate unstructured hexahedral mesh between front levels, finally ensure the quality of the mesh by the mesh quality optimization algorithm.Finally, taking Nanjing South Station formation data as instance to verify these two hexahedral mesh generation algorithms in the paper. Case has proved that the algorithm in this paper is reliable and effective, can generate hexahedral mesh automatically in general geoscience entities, and to some extent meet the demand of geoscience mechanism, process simulation analysis and the traditional GIS spatial analysis for hexahedral mesh.

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