VECTIS Mesher – A 3D Cartesian Approach Employing Marching Cubes

Abstract

This paper describes the main principles used in the development of the VECTIS mesher. The mesher produces unstructured 3D meshes suitable for Finite Volume Methods. It is based on the Cartesian approach. In contrary to the traditional approaches which use exact shape of boundary faces of cut cells, this mesher employs Marching Cubes method for generation of majority of boundary faces. Only in problematic parts of the geometry, when the danger of chamfering of sharp features occurs or when watertightness of the cell might not be ensured, the Exact Fit method is used to produce the patches. Because two different methods are used for generation of patches, additional effort needs to be made to tie the boundary polygons to prevent gaps. A new algorithm for determining the most suitable configuration of triangles of Marching Cubes patterns is proposed. In cartesian meshers, a problematic situation occurs whenever triangles of the surface lay exactly on a side of the intersecting box. In order to prevent these collisions, an approach called Dual Levels has been introduced. The implemented method of cell refinement is presented. The paper also explains the way how the problem of cells that are too concave was resolved. The algorithm of the whole meshing task is described in detail. The new mesher has significantly lower time and memory demands in comparison with its predecessor. The main approaches responsible for this improvement are discussed.