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Automatic unstructured all-hexahedral mesh generation from B-Reps for non-manifold CAD assemblies

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Abstract

This paper describes an automatic and robust approach to convert non-manifold CAD assemblies into unstructured all-hexahedral meshes conformal to the given B-Reps (boundary-representations) and with sharp feature preservation. In previous works, we developed an octree-based isocontouring method to construct unstructured hexahedral meshes for arbitrary non-manifold and manifold domains. However, sharp feature preservation still remains a challenge, especially for non-manifold CAD assemblies. In this paper, boundary features such as NURBS (non-uniform rational B-Splines) curves and surface patches are first extracted from the given B-Reps. Features shared by multiple components are identified and distinguished. To preserve these non-manifold features, one given surface patch may need to be split into several small ones. An octree-based algorithm is then carried out to create an unstructured all-hexahedral base mesh, detecting and preserving all the sharp features via a curve and surface parametrization. Two sets of local refinement templates are provided for adaptive mesh generation, along with a novel 2-refinement implementation. Vertices in the base mesh are categorized into four groups based on the given non-manifold topology, and each group is relocated using various methods with all sharp features preserved. After this stage, a novel two-step pillowing technique is developed for such complicated non-manifold domains to eliminate triangle-shaped quadrilateral elements along the curves and “doublets”, handling non-manifold and manifold features in different ways. Finally, a combination of smoothing and optimization is used to further improve the mesh quality. Our algorithm is automatic and robust for non-manifold and manifold domains. We have applied our algorithm to several complicated CAD assemblies.

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Acknowledgments

We would like to thank Wenyan Wang for useful discussions on NURBS curve and surface parametrization, and Matt Staten for providing the multi-axis, hook2, hook and varco3 models. The research was supported in part by Y. Zhang’s ONR-YIP award N00014-10-1-0698, an ONR grant N00014-08-1-0653, and a NRL contract N00173-08-C-6011 as part of the HPCMP CREATE program.

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  1. Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA

    Jin Qian & Yongjie Zhang

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  1. Jin Qian
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  2. Yongjie Zhang
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Correspondence to Yongjie Zhang.

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A preliminary version of this paper was published in the 19th International Meshing Roundtable conference [20].

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Qian, J., Zhang, Y. Automatic unstructured all-hexahedral mesh generation from B-Reps for non-manifold CAD assemblies. Engineering with Computers 28, 345–359 (2012). https://doi.org/10.1007/s00366-011-0232-z

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  • DOI: https://doi.org/10.1007/s00366-011-0232-z

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