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The mesh shown was included in the winning poster presented by Ted Blacker entitled "Octree Based Size Functions". This poster highlighted new advances in mesh density controls available within the GAMBIT preprocessing package from Fluent, Inc. These controls, termed size functions, are aimed at eliminating automation obstacles during meshing, particularly when generating a tetrahedral mesh. Historically, most of the volume meshing problems are related to a bad surface mesh. The problematic surface mesh typically doesn't capture the geometry well, or isn't sized appropriately for thin regions of the geometry. It is also particularly important in CFD analysis that the gradation of the mesh be tightly controlled. This control limits transition rates from small to large elements, allowing capture of the boundary layer phenomenon as well as control over solution accuracy.
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Although density control is not new in the meshing community, this technique is unique in how grading controls radiate or propagate to surrounding regions in a tightly controlled manner. For example, the eye brows on the clown have a tight curvature which is captured through a curvature based size function. But, not only is the eyebrow adjusted, but portions of the geometry in close proximity are also included in the sizing effects. The forehead near the eyebrow attachment and even the interior of the eyelid show a graceful, controlled gradation of size. This insures that the volume tet mesher can successfully fill this region with well shaped elements. The user interactions were minimal in the generation of the clown mesh. A simple size function was defined to capture curvature and set the gradation rate. This size function was attached to the volume and the volume meshing initiated. The software then generated the needed octree background grid and then automatically guided the meshing based on these controls.
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This technical advance is accomplished by imposing individual size functions (e.g. curvature of individual surfaces) on an underlying octree based background grid. The octree depth adjusts automatically to capture regions of importance in the size function. With the aid of this octree background grid, the size functions can then radiate to accomplish the control and effects as desired. Size functions can be of various types, including 1) proximity control (refinement to provide small sizes near thin regions), 2) curvature control (refinement to capture surface changes well) and 3) specific source controls (refinement based on distance to a vertex, edge or face). Any number or combination of size function types can be specified by the user. The edge, face and volume meshing tools then obtain sizing information directly from the background in a highly efficient manner.
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The technology was developed at Fluent, Inc. by Richard Smith, Yongheng Shao, Jin Zhu and Ted Blacker.
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