Three-dimensional Mesh Generation Method For Boundary Face Method

The boundary face method (BFM) based on the boundary integral equation (BIE) exhibits some extraordinary merits. Generally, the BFM only needs to discretize the boundary of the domain. And the mesh can be obtained by discretizing each piece wise continuous panel of the body’s surface without restriction of element connectivity, hence, considerably simplifies the discretization task and the mesh generation method can be much more flexible. BFM also needs three-dimensional mesh to carry out the postprocess and analysis. The tetrahedral mesh can be generated automatically for complex solids. All-hexahedral meshes are preferred than tetrahedral mesh. But all-hexahedra meshing methods have proven to be more challenging. In order to discretize a complex solid, the volume needs to be decomposed manually, which is a time consuming and difficult task. Therefore, this dissertation conducts some useful researches and trials on the automatical three-dimensional mesh generation method for BFM. Based on the advantages of the BFM, some special elements are used to discretize the boudray of the domain. Hence, the discretization of the surface is very simple, resulting in substantial savings in both data preparation and computing costs. As a result, the following studies are carried out in this dissertation.(1) In order to construct an automatical mesh generator, a program framework for three-dimensional mesh generation is developed. In the framework, some C++classes are designed to performing different tasks needed in overall mesh generation, such as mesh data management, feature recognition, virtual decomposition, and mesh generation methods. A mesh data manager is developed, the conflicting requirements of compactness and computational efficiency is well balanced. The uniform mesh database is convenient for modification, maintenance and expansion of the programme. A variety of three-dimensional mesh generation methods can be implemented in this framework. The resulting mesh cells can be converted into elements for analysis and dumped to postprocess module.(2) A Delaunay method coupled with the advancing front method for automatical tetrahedral mesh generation is presented. The internal points are created by advancing front method and inserted into the mesh by Delaunay kernel procedure. To get better efficiency, a front identification and field point generation method is proposed and applied. The background mesh is used to specify mesh size distributions over arbitrarily shaped domains. The grid is applied to manage the background mesh, thus the point can be quickly located in the backgroud mesh. The mesh generation method combines the advantages of the high point placement quality of the advancing front method and the high efficiency and convergence guaranty of the Delaunay algorithm.(3) The sweep method is applied to generate hexahedral mesh. The mesh feature recognition method is proposed to recognize the sweepable part from the complex solid. And the source surface, linking surfaces and target surface can be settled automatically. The virtual decomposition is applied to extract the sweepable part from the solid. Then, the sweepable part can be discretized by sweep method. If all of sub-domains are sweepable, the all-hexahedral mesh can be generated for the solid.(4) A new conforming hybrid mesh generation method is proposed and applied to generate mesh for three-dimensional solids with open-ended tubular holes. A pyramidal element generation method is presented to solve the non-conforming problem. The regions around the tubular holes are presented by hexahedral elements. The tetrahedral mesh is generated to tessellate the rest of the domain. The pyramid elements are constructed at the interface between hexahedral and tetrahedral elements. High-quality hybrid mesh can be automatically created by the proposed method. Two kinds of special surface elements, tube element and triangular element with negative parts, are proposed for modeling solids containing many slender open-ended tubular shaped holes. The discretization of the surface is very simple by using these special elements, resulting in substantial savings in both data preparation and computing costs.(5) The feature recognition method is applied to automatically determine the meshing algorithm for each solid of dams. And the mesh can be generated automatically by the presented methods. Thus, the whole dam can be meshed automatically without user interaction. The BFM is applied to predict the thermal evolution of dams during their construction with the generated mesh.