10th International Meshing Roundtable
Newport Beach, California, U.S.A.
October 710, 2001
Centre for Applied Scientific Computing
Lawrence Livermore National Laboratory
Livermore, CA, 94551
Email: henshaw@llnl.gov
Abstract
We are interested in building structured overlapping grids for geometries defined
by computeraideddesign (CAD) packages. Geometric information defining the boundary
surfaces of a computation domain is often provided in the form of a collection of
possibly hundreds of trimmed patches. The first step in building an overlapping
volume grid on such a geometry is to build overlapping surface grids. A surface
grid is typically built using hyperbolic grid generation; starting from a curve
on the surface, a grid is grown by marching over the surface. A given hyperbolic
grid will typically cover many of the underlying CAD surface patches. The fundamental
operation needed for building surface grids is that of projecting a point in space
onto the closest point on the CAD surface. We describe a fast algorithm for performing
this projection, it will make use of a fairly coarse global triangulation of the
CAD geometry. We describe how to build this global triangulation by first determining
the connectivity of the CAD surface patches. This step is necessary since it often the
case that the CAD description will contain no information specifying how a given patch
connects to other neighbouring patches. Determining the connectivity is difficult
since the surface patches may contain mistakes such as gaps or overlaps between
neighbouring patches.
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