Frequently Asked Questions

• How do I run GridEx?
• What platforms does GridEx support?
• What are the system requirements to run GridEx?
• How does GridEx differ from other grid generation packages?
• What CAD packages does GridEx support?
• Can GridEx be used to develop my geometry?
• Must I have a solid model?
• What unstructured meshing options does GridEx support?
• How do I control the mesh generation process?
• Can GridEx be used to perform mesh adaptation?
• What is the purpose of model regeneration if you cannot develop my geometry?
• How can I tell if my Unigraphics part contains valid solids?
• Who should I contact to request GridEx or if I have questions regarding use of the software?

How do I run GridEx?

GridEx is run from the command line by entering 'GridEx' followed by the solid model format to invoke the proper geometry kernel.

The GridEx GUI was developed using X/Motif with 3D rendering performed using OpenGL and is therefore currently available only for UNIX operating systems.  Executables are available for Intel Linux (2.4 Kernel) and the SGI series of graphics workstations running IRIX 6.5.  Future ports to MS Windows are planned.  It should be noted that GridEx execution on a specific architecture presupposes the existence of the desired geometry kernel on the same.

The GridEx GUI was developed using X/Motif with 3D rendering performed using OpenGL.  As such, X Windows and Motif are required along with OpenGL support.  Linux binaries were built against XFree86 4.0.2 (provides OpenGL dso's) and Lesstif (source compatible OSF/Motif clone) using RedHat 7.1 (2.4.9-12 kernel).  SGI executables were built against the standard IRIX64 n32 ABI system installation.

GridEx integrates grid generation packages with geometry modeling - it is not a geometry preprocessor.  GridEx relies exclusively on external CAD to provide a solid Boundary Representation (BRep) suitable for meshing.  GridEx was not designed to duplicate functionality readily available in most common CAD packages.

GridEx supports solid models developed with I-DEAS from SDRC, Parasolid from UGS, Pro/Engineer from PTC, and CATIA from Dassault Systems.  In addition, a native format allows GridEx to communicate with GridTool, an unstructured mesh pre-processing package produced by GEOLAB, when working with non-manifold geometry descriptions.

GridEx offers no geometry tools per se as it is assumed that all geometric description is performed in the CAD environment.  GridEx does offer simple tools for the creation and manipulation of geometric primitives used to generate computational domain boundaries and other simple shapes.

The basic design of GridEx assumes that the geometry will be provided in the form of a manifold Boundary Representation (BRep) of the model.  This decision was made so as to decouple the mesh generation process from the details of geometry description.  Providing a BRep allows the automation of domain topology extraction.  As such, the geometry of interest is typically provided in the form of a CAD solid model.  This may come directly from the originating CAD system.  A BRep may also be obtained as a result of pre-processing by a geometry preparation tool such as GridTool.  GridEx does offer simple tools for the creation of geometric primitives  and subsequent performing of solid Boolean operations.  These capabilities provide the GridEx user the ability to augment a given subject CAD model with the desired physical domain required for computation.

GridEx incorporates the FELISA, AFLR3, TetGen, Triangle, and VGRID, meshing algorithms.  At the moment, meshes suitable for Navier-Stokes analysis can only be generated via AFLR3.

GridEx offers customized panels which facilitate the interactive placement and specification of mesh sources.  These sources permit control of the characteristics of the resulting mesh at given key locations and are subsequently used to define the character of the mesh over the entire domain.

GridEx is based upon a common software framework that is currently being developed in conjunction with adaptive refinement research.  It is the goal of this effort to eventually incorporate the mesh adaptation process into an automated loop.  In this scenario, GridEx would be used to generate a rough initial mesh that is then handed off to the adaptation loop.  As the adaptive refinement research matures, it is envisioned to add the ability to interactively adapt the mesh using GridEx for debugging and other informational practices.

Model regeneration is useful when dealing with a "e;smart"e; model. Such a model is feature based and may have exposed parameters. Both the suppression state of features and the values of parameters can be modified followed by model regeneration within GridEx without the need to revisit the CAD system proper. An example may be seen in this movie. In the movie (developed by Dr. Juan Alonso at Stanford University) a single Pro/Engineer model (developed at MIT) is subject to 254 linear parameter modifications to produce the distinct frames of the video. This example shows the power of parametric modeling as the model is morphed from a Supersonic Business Jet to a facimile of a Boeing 717 transport.

Load your model into Unigraphics. Load the modeling application by selecting Application->Modeling from the main menu bar. Next, select Analysis->Examine Geometry.... From the resulting dialog, check Set All Checks and Ok. From the selection dialog, Select All followed by Ok. Analyse the resulting report. Look for any anomalies. Bodies, and Faces/Self-intersection are most import and must be eliminated. Edges/Smoothness is usually not a problem. You may also want to eliminate Tiny Objects if they are found as they will produce a poor triangulation since a grid node will be placed at the endes of all of the tiny edges. A quick way to elimate tiny objects is to Export->Heal Geometry. This technique can also be applied to Parasolid files once imported into Unigraphics.

The NASA lead for the development of the GridEx software package is Bill Jones who can be reached at w.t.jones@nasa.gov or at (757) 864-5318.