Adaptive Shrink-Wrapping for Automatic Extraction of Surfaces from Assemblies

Abstract

The pacing item in the application of computational fluid dynamics (CFD) to new configurations is the pre-processing phase, of which preparation of the geometry is the most time-consuming step. This is especially true for configurations that are defined in a computer-aided design (CAD) system. The primary reason for this difficulty is the existence of both large and small features, some of which are not needed to achieve the results desired by the customer. Users can sometimes remove small unwanted features by suppressing them in the CAD system; this however is not an option when the features emerge during the assembly of parts into a whole model. In a previous paper, a new technique called nested geometric refinement was introduced for automatically extracting a computational model from an assembly of parts with features of varying resolutions. When first applied, the technique generates a configuration approximation that has a globally-applied user-defined resolution that is independent of the local feature size. A simple adaptation process is then applied to resolve geometric features only where needed. The technique is somewhat similar to the shrink-wrapping technique that has become available recently. The further development of the technique is shown as well as the enhancement from two-dimensional to three-dimensional configurations. In these cases, the effects of both global refinement and adapted refinement are shown. The new technique is very efficient, since small features are ignored in the initial representation. Grids can be generated on assemblies, regardless of how well the parts fit together. Through the use of an adaptation method, the configuration can be refined such that only the pertinent features are resolved.