Using conjoint meshing primitives to generate quadrilateral and hexahedral elements in irregular regions

The parameter-space mapping technique used in most finite element mesh generation programs requires that the geometry be subdivided into either rectangular areas in 2-D or rectilinear volumes in 3-D to produce, respectively, quadrilateral or hexahedral elements. Since subdivision occurs in parameter space, the edges bounding the areas and volumes need not be straight or parallel lines. Simple geometries may be subdivided easily while irregular features challenge the analyst. This paper presents the formulation and application of conjoint meshing primitives that assist the analyst in meshing in and around irregular features. The term conjoint is applied to these primitives because each is composed of several rectangular areas or rectilinear volumes. Interval assignments may vary from side to side, within a set of constraints, for each primitive. Thus, all of them are useful for transitions between other regular areas or volumes. In 2-D, the primitive areas are the triangle, pentagon, semi-circle, circle, and rectangular transition. These primitives are implemented in the Sandia meshing program FASTQ and are used in regular production work. They are also the basis for decomposition regions in the developing artificial intelligence Automated Meshing Knowledge System, AMEKS. In 3-D, the primitive volumes are the 2-D primitives extended in depthmore » together with the tetrahedon and two rectilinear transition volumes. These primitives are the foundation for extending AMEKS to 3-D. 9 refs., 14 figs.« less