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Frequently Asked Questions
Some commonly asked questions
regarding the execution and operation of GridEx.
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.
platforms does GridEx support?
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.
are the system requirements to run GridEx?
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.
does GridEx differ from other grid generation packages?
GridEx integrates grid
generation packages with geometry modeling - it is not a geometry preprocessor. GridEx relies
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 does GridEx support?
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 be used to develop my geometry?
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
I have a solid model?
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
unstructured meshing options does GridEx support?
At the moment, meshes suitable for Navier-Stokes analysis can only be
generated via AFLR3.
do I control the mesh generation process?
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 be used to perform mesh adaptation?
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.
is the purpose of model regeneration if you cannot develop my geometry?
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.
How can I tell if my Unigraphics part contains valid solids?
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.
Who should I contact to request GridEx or if I have questions regarding use
of the software?
The NASA lead for the development
of the GridEx software package is Bill Jones who can be reached at
or at (757) 864-5318.
NASA Official: William T. Jones
Site Curator: William
Last Updated: Dec