Automatic generation of CFD-ready surface triangulations from CAD geometry

Abstract

This paper presents an approach for the generation of closed mani-[old surface triangulations from CAD geometry. CAD parts and assemblies are used in their native format, without translation, and a paws native geometry engine is accessed through a modeler-independent application programming interface (API). In seeking a robust and fully automated procedure, the algorithm is based on a new physical space manifold triangulation technique which was developed to avoid robustness issues associated with poorly conditioned mappings. In addition, this approach avoids the usual ambiguities associated with floating-point predicate evaluation on constructed coordinate geometry in a mapped space. The technique is incremental, so that each new site improves the triangulation by some well defined quality measure. Sites are inserted using a variety of priority queues to ensure that new insertions will address the worst triangles first. As a result of this strategy, the algorithm will return its "best" mesh for a given (prespecified) number of sites. Alternatively, the algorithm may be allowed to terminate naturally after achieving a prespecified measure of mesh quality. The resulting triangulations are "CFD-ready" in that: (1) Edges match the underlying part model to within a specified tolerance. (2) Triangles on disjoint surfaces in close proximity have matching length-scales. (3) The algorithm produces a triangulation such that no angle is less than a given angle bound, a, or greater than _ -2a. This result also sets bounds on the maximum vertex degree, triangle aspect-ratio and maximum stretching rate tbr the triangulation. In addition to the output triangulations lot a variety of CAD parts, the discussion presents related theoretical results which assert the existence of such an angle bound, and demonstrate that maximum bounds of between 25°and 30°may be achieved in practice.

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