Addressing some current issues in linear and high-order meshing

Abstract

The thesis explores the generation of anisotropic and boundary conforming Voronoi regions and Delaunay triangulations, high-order mesh quality and the development of mesh enhancement techniques which incorporate quality measures to preserve mesh validity longer. In the first part an analogy with crystal growth is proposed to handle mesh anisotropy and boundary conformity in Voronoi diagrams and Delaunay mesh generation. A Voronoi partition of a domain corresponds to the steady-state configuration of many crystals growing from their seed points. Mesh anisotropy is incorporated and the shape of the boundary of an isolated crystal is guided by re-interpreting a user-defined Riemann metric in terms of the velocity of the crystal boundary. A straightforward implementation of conformity to boundaries is achieved by treating the boundary of the computational domain as the boundary of a stationary crystal. The second part attempts to answer the question: what is a good highorder element? A review of a priori mesh quality measures suitable for high-order elements is presented. A systematic analysis of the quality measures for interior and boundary elements is then carried out utilising a number of test cases that consist of a set of carefully selected elements with various degrees of distortion. Their ability to identify severe geometrical distortion is discussed. The effect of boundary curvature on the performance of quality measures is also investigated. The last part proposes improvements to a conventional mesh deformation method based on the equations of elasticity to maintain highorder mesh validity and enhance mesh quality. This is accomplished by incorporating additional terms, that can be interpreted as body forces and thermal stresses in the elastic analogy. Different test cases are designed to prolong mesh validity, and their performance is reported. A proposal of how to formulate these terms to incorporate anisotropy is also presented.