Mesh-Based Geometry: A Systematic Approach To Constructing Geometry From A Finite Element Mesh

A new system for defining geometry based on feature s of a finite element mesh is described. A systemat ic approach to building a complete geometric and topologic representation of a model given only the finite element description i s proposed. Geometry and topology entities including volumes, surfaces, curv es and vertices, can be implied based on user defin ed boundary conditions or surface features. Curve and surface geometry is de scribed by either linear triangular facets or G 1 continuous 4th order Bezier patches. The proposed Mesh-Based Geometry (MBG) sy stem serves as an alternative to the CAD-based syst em currently in use in Sandia National Laboratory's, CUBIT mesh generat ion toolkit. CGM enables the mesh-based geometry t o work seamlessly with existing geometry and meshing tools already de veloped within the CUBIT environment. * Sandia is a multiprogram laboratory operated by San dia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000. 1.INTRODUCTION CAD programs and libraries provide an ideal geometr ic foundation for finite element mesh generation. Mos t automaticmeshingalgorithmsrequireageometry framework upon which the mesh may be developed. I n some cases, the analyst or designer may be unable t o take advantage of CAD geometry, consequently precluding the useofautomaticmeshingormeshimprovement algorithms. The basis for precluding the use of CA D geometry may include one or more of the following: 1. The finite element model may be legacy data. In some cases, old archived mesh files may be the only representation of the model available to the analys t. Design modifications or more advanced computational methods may require changing or modifying the mesh. Where associated CAD data is not available, or geometryformatshavebecomeobsolete,mesh modificationsmaybeimpracticalorextremely tedious. 2. Remeshing of deformed finite element data is requir ed. For dynamic remeshing problems, although an initial CAD-based geometric model may have been used to define the model, computed deformations may change curve and surface definitions, such that the origin al geometry is no longer valid. 3. Interoperabilitybetweenpreprocessingprograms. Designers and analysts will frequently use several software tools to develop a finite element mesh for analysis. For example, an analyst may generate the mesh in one system and smooth it in a second or generate a structured grid in one and an unstructur ed grid in another. Although these tools may support CAD geometry, even small modifications to the geometry may preclude its use in other software. T he …