Abstract

We present a tetra mesher for multipart meshing purposes. The method is fully automated and rejects no parts if some simple rules are obeyed. The result is a ready to compute, conformal mesh for all parts and for the fluid outside. This method does not rely on Delaunay ideas but is based on wrapping-, segmentation- and marching volume techniques. At first we give a precise definition of what a part is. Starting with a special single tetra which covers the entire input geometry an adaptive refinement process creates a mesh which is fine near this geometry. This refinement process iterates the subdivision of the first tetra to eight tetras of the same shape and therefore of the same quality. This is just like in the cubic case. This division pattern is not applicable to arbitrary tetras, but for our starting one it works. The Marching Tetra method gives tetras which are assigned to parts. Since our mesh is conformal, imprints, i.e. triangles between tetras of different part-membership, can be derived easily. These imprints allow straight forward load definitions. We discuss the criteria which are necessary for mesh refinement and show how to achieve geometry correctness and good element quality simultaneously, by using edge- and face- collapse algorithms and by edge swapping methods. A special chapter is devoted to the generation of feature lines, i.e. sharp edges and lines where three parts meet. To treat feature points is an extension of this work. The Marching Tetra Multigrid method works for any number of parts. The input geometry must allow an answer to the question for any point, whether this point is inside or outside. If this point is inside for more than one part, we need a precise answer which part wins. This is the way Boolean subtract is performed automatically for overlapping parts. Some case studies of multipart problems are presented in the final section.