Sharp Feature Preservation in Octree-Based Hexahedral Mesh Generation for CAD Assembly Models

This paper describes an automatic and robust approach to convert 3D CAD assembly models into unstructured hexahedral meshes that are conformal to the given B-Reps (boundary-representations) with sharp feature preservation. In previous works, we developed an octree-based isocontouring method to construct unstructured hexahedral meshes for manifold and non-manifold domains. However, sharp feature preservation still remains a challenge. In the current algorithm, boundary features such as sharp curves and NURBS (non-uniform rational B-Splines) surface patches are first extracted from the given B-Reps. An octree-based isocontouring algorithm is then carried out to create unstructured hexahedral meshes, detecting and preserving all the sharp features. After this stage, a two-step pillowing technique is adopted to eliminate triangle-shaped quadrilateral elements along the sharp curves and “doublets”. To further improve the mesh quality, a combination of smoothing and optimization is used. The developed algorithm is robust, and it works for single-component manifold domain, as well as multiple component non-manifold domains. We have applied our algorithm to several complicated CAD models and assemblies. Valid meshes are generated and quality statistics are given.