A New Set of Hexahedral Meshes Local Transformations

The modification of hexahedral meshes is difficult to perform since their structure does not allow easy local refinement or un-refinement such that the modification does not go through the boundary. In this paper we prove that the set of hex flipping transformations of Bern et. al. [1] is the only possible local modification on a geometrical hex mesh with less than 5 edges per vertex. We propose a new basis of local transformations that can generate an infinite number of transformations on hex meshes with less than 6 edges per vertex. Those results are a continuation of a previous work [9], on topological modification of hexahedral meshes. We prove that one necessary condition for filling the enclosed volume of a surface quad mesh with compatible hexes is that the number of vertices of that quad mesh with 3 edges should be no less than 8. For quad meshes, we show the equivalence between modifying locally the number of quads on a mesh and the number of its internal vertices.