Automated Geometry Blocking Using an Adaptive Mesh Refinement Algorithm

We describe an algorithm for automated blocking of geometry by using the Adaptive Mesh Refinement (AMR) algorithm in NWGRID. NWGRID is PNNL's mesh generation, mesh optimization and dynamic mesh maintenance code. It was originally designed for unstructured grids on massively parallel platforms, and is now being used to build hybrid grids, including unstructured, structured and block structured grids. Our approach to creating an automated geometry-blocking algorithm is to use a modified AMR algorithm, such that when the dangling nodes are removed the resulting fully-connected unstructured mesh is composed entirely of six-sided blocks. The modification to the standard AMR algorithm involves doing a 27-element subdivision of each six-sided parent element at each successive AMR level instead of the standard oct-tree subdivision. Another important feature to the AMR algorithm is that it operates on an unstructured, non-orthogonal background mesh. This helps later in the boundary process for fitted grids. The only drawback to the current approach is that we make no attempt to minimize the number of blocks. Relative to the tremendous advantage afforded by automating the process, it is not important that we end up with a few extra blocks in the geometry-blocking phase, as this does not increase the computationalmore » complexity of the calculations to be performed on the block structured grids.« less