Surface Modeling Geometry Standards and Exchange
Objective: Develop surface geometry standards and tools to facilitate the automation of the Computational Fluid Dynamics (CFD) processes.
Approach: One of the bottlenecks in the automation of the CFD processes is to perform CFD grid generation and analysis on design data directly. Modern designs are usually performed on computers by Computer Aided Design (CAD) systems. However, CAD systems employ a variety of data representations. To facilitate and simplify the CFD grid generation process, a geometry standard is developed, focusing on aerospace geometries. With this standard, CFD grid generators only have to handle a single data representation.
A compatible, simplified subset of the Initial Graphics Exchange Specification (IGES), the most common output data format of CAD systems, is chosen for the CFD geometry standard to ensure communication between CAD systems and CFD grid generators. The chosen subset is centered on an advanced geometry representation capable of representing CAD designs precisely. Tools are developed to translate the CAD geometries from IGES format to the CFD standard format. Grid generators are upgraded to accept this simple, advanced format.
Accomplishment: The NASA Geometry Data Exchange Specification for Computational Fluid Dynamics (NASA-IGES) was published. An IGES to NASA-IGES translator software (NIGEStranslator) has been completed. A viewer software (NIGESview) has been developed to allow the users to interactively view and manipulate geometries in NASA-IGES files. GRIDGEN, a powerful highly interactive grid generator, has been upgraded to accept NASA-IGES files.
Significance: A streamlined process has been established to allow applied CFD engineers to generate analysis grids directly on CAD designs. A user can use the NIGEStranslator to convert the design geometries from CAD systems to NASA-IGES format, examine/manipulate the geometries with NIGESview, and then generate grids directly from the NASA-IGES surface model. This new process expels the past nightmares of endless battles with different geometry data formats. The NASA-IGES standard has been adopted by both the NASA-Lewis and NASA-Langley HPCCP efforts, and by the DT_NURBS software library, developed by Navy Surface Warfare Center. NIGEStranslator, NIGESviewer, and GRIDGEN have been widely distributed to industries and laboratories.
As the CAS project progresses to its goals of the multidisciplinary analysis and optimization of advanced aerospace systems, a common geometric database and the ability to develop computational physics grids (e.g., for fluid dynamics and structures) from that database will be essential. With the NIGES library, the CAS project will be able to accommodate the complex geometric systems of interest to U.S. Aerospace Industry on the most advanced parallel computer systems.
Status/Plans: The current geometry exchange standard does not contain surface connectivity data. Some grid generators can benefit significantly from such data. An effort is underway to incorporate these data into the standard. To make the standard beneficial to CFD analysts, more grid generators should be upgraded to accept NASA-IGES data. Two efforts are underway. One is to incorporate NASA-IGES capability into the Automated AST Structured Technology Project, another HPCCP effort. The other is to incorporate the capability into an unstructured grid generator.
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