The Use of Non-Uniform Rational B-Splines in Overset Grid Generation
by
Bruce Vu
Engineering Research Center, Mississippi State University
Coauthors: Bharat K. Soni

The accuracy of CFD simulations involving complex three-dimensional configurations depends on the quality of the computational grids. It is desirable to generate a mesh with simple topology. However, for complex geometry it is difficult to generate a single-block grid with simple topologies. Multi-block grid can resolve the problem of skewness and remove the grid-crossing but it requires time and effort to generate a structured grid with matching interface between blocks; especially in the case of two different grid with different topologies embedded on each other.

To address this problem, in the early 1980s, Steger, et al. have developed a method of domain decomposition methodology called ``Chimera'' or ``Overset Grid''. The Chimera scheme uses a system of relatively simple body-fitted grids. Each grid is generated for a particular component of the overall geometry, making the initial grid generation much simpler. The component grids overlap and, once combined, cover the entire computational domain. Changes in geometry or configuration influence modifications only to one or a small number of component grids, leaving the other individual grids untouched. Therefore, during a design process, these features allow computational grids to be generated quickly and easily.

Overset grid technique has been in use for more than a decade now. Although there have been many advances during that time, there are still many problems both in generation of good overlapping grids and their use for accurate solution of Partial Differential Equations (PDEs). The development of a more robust and efficient algorithm of generating overlapping grids will be presented. A Non-Uniform Rational B-Spline (NURBS) technique is introduced in overset grid generation. The hole-cutting process, which is crucial in overset grid generation, is performed entirely on the NURBS surface.

Included in the NURBS hole-cutting technique is the binary search algorithm. This allows the embedded grids to be located quickly and efficiently. An ``unblanking'' procedure to identify grid points that lie outside the hole boundary surface is also described. These methodologies and computational examples will be reported in the final paper.

References

J.A. Benek, J.L. Steger, F.C. Dougherty, and P.G. Buning, ``Chimera: A Grid-Embedding Technique'' AEDC-TR-85-64, Arnold Engineering Development Center, Arnold Air Force Station, TN, April 1986.

William Chan, ``A Unified Overset Grid Generation Graphical Interface and New Concepts on Automatic Gridding Around Surace Discontinuities'' 4th Symposium on Overset Composite Grid & Solution Technology, Arberdeen, MD, September 1998.

Date received: April 20, 1999

Copyright © 1999 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cacr-77.