VGRID

Overview
Key Features
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Technology Transfer
Contacts

VGRID is a robust, user-friendly computer program for the generation of three-dimensional unstructured (triangular surface and tetrahedral volume) grids in geometrically complex domains. The base code (VGRID3D) has been developed by ViGYAN, Inc. under a NASA Small Business Innovation Research (SBIR) contract. Since completion of that project (1990), considerable extensions to VGRID have been developed at NASA Langley Research Center. These extensions are an outcome of several years of research, development, extensive application, and user-feedback improvements. VGRID is a key component to the NASA unstructured-grid software system TetrUSS, a recipient of the 1996 NASA Software of the Year award. Along with a graphical user interface utility GridTool and a grid post-processing program POSTGRID, the VGRID system provides a reliable tool for the fast and convenient generation of unstructured grids around complex configurations. The code, in conjunction with the unstructured-grid solver USM3D and post-processing visualization program ViGPLOT has been widely used by many researchers and engineers from academia, industry, NASA, and other government agencies for the past several years.

VGRID is based on the Advancing-Front Method (AFM) for the generation of tetrahedral `Euler' grids. The present version of the code incorporates the following salient features:

• Dynamic memory allocation.
  
• Automatically generated Cartesian Background Grids with discrete Source elements for convenient control of elliptically smoothed grid distribution on the surface and in the field. [figure]
  
• Patch `T-connections' for convenient patching of surface definitions. [figure]
  
• Interactive rearrangement of surface patches for obtaining high quality surface triangulations.
  
• Surface mesh quality check.
  
• Interactive generation of both surface and volume grids using Silicon Graphics, Inc. workstations through the mouse-driven graphical and animation capabilities of the codes.[2nd animation]
  
• Graphical display of grid distribution in the field on moving planes prior to generation of the actual volume grid.
  
• Restart capability with an efficient `recurrent' renumbering system allowing the generation of large grids on small workstations.
  
• Grid post-processing with POSTGRID for local remeshing of any void/anomaly in a grid, volume grid quality check, and automatic grid quality enhancement with local remeshing.
  
• Fast and convenient generation of grids around complex configurations on SGI workstations.
  
• Usable by non-experts.
  

While the existing `Euler' grid generation capability with VGRID is mature and fully operational, the improvements/extensions continue as better ideas evolve and new technology becomes available. Work is currently focused on the advancement of the USG methodology (both grid generation and flow solution) towards convenient computation of the Navier-Stokes equations on complex fluid flow problems.

A new version of the grid generator (VGRIDns), currently under final stages of development, is based on the Advancing-Layers Method (ALM) for the generation of thin layered tetrahedral grids. The method benefits from the flexibility of the Advancing-Front technique for automatic generation of viscous grids around complex configurations. In addition to the main features listed above, the new version offers the following capabilities:

• Generation of both 'Euler' and 'Viscous' grids with the same version of the code and input data file. [animation]
  
• Minimal user-prescribed parameters for generating viscous grids.
  
• Reduced viscous grid generation time by an order of magnitude as compared to Advancing Front Method.
  
• Anisotropic stretching of both surface and volume grids for better grid efficiency.
  
• Interactive swapping of surface triangular edges for mesh quality improvement. [animation]
  
• Generation of volume grid on both sides of `zero-thickness' surfaces. [figure]
  
• Dynamic grids by 'spring' analogy. [animation]
  
• Volume grid smoothing with POSTGRID using a Laplacian operation and local remeshing.
  
• Display of volume grid cross-sections through moving planes.
  

VGRID executables are available to the U.S. users free of charge. The technology is disseminated by the government (NASA Langley Research Center.) ViGYAN, Inc. provides technical support, training, and customization of the codes for a fee. Please see Contacts for further information.

For technical information and/or a copy of the VGRID executable, please contact:

Dr. Shahyar Pirzadeh
Mail Stop 499
NASA Langley Research Center
Hampton, VA 23681
USA
Phone: (757) 864-2245
FAX: (757) 864-8469
Email:

For information on VGRID training, please contact:

Edward B. Parlette
ViGYAN, Inc.
30 Research Drive
Hampton, VA 23666
USA
Phone: (757) 865-1400
FAX: (757) 865-8177
Email:

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Last update: June 11, 1996