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. Described herein is a new technique, called nested geometric refinement, 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 application of the technique to a few configurations is shown. 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.