Gridgen's Open Access to CAD for CFD Meshing

Interoperability of computer aided design (CAD) models (or the lack thereof) poses significant challenges to the CFD practitioner. Other meshing software forces analysts to interface directly with the CAD system, tying up a valuable software asset and requiring significant software training. Gridgen provides a flexible suite of CAD data access methods, allowing the analyst to select the optimum approach.

Solid Meshing Recovers Engineering Topology

One approach to working with complex geometry models in Gridgen is Solid Meshing. This technique involves recovering the "engineering topology" from the rather arbitrary CAD topology. The engineering topology reduces a geometry model to major components relevant to meshing like wings, blades, and sidewalls. This is accomplished using tools that provide solid model import and creation.

Once a solid model of the geometry has been created, all the seams between adjacent surfaces are closed and meshing can proceed without having to deal with special issues related to gaps and overlaps.

Fault-Tolerant Meshing Eliminates CAD Healing

Another problem with CAD model interoperability is sloppy geometry such as gaps between adjacent surfaces, overlapping surfaces, and missing features. An analyst must be able to mesh a less than perfect model. Even though other software attempts to "heal" the CAD model through a variety of manipulations, healing is an ill-defined problem since design intent is usually unknown. Using a technique called Fault Tolerant Meshing, Gridgen is able to create a fully closed mesh on a sloppy CAD model. Merging automatically identifies adjacent surface meshes, joins them across CAD model gaps, and uses the mesh solver to remove CAD artifacts such as topology and sliver surfaces from the mesh.

Geometry Modeling

Gridgen does not require the use of a CAD model for meshing - the mesh can be created directly in 3D without having to create geometry first. This feature lessens dependence on the CAD system, allowing the analyst to use CAD geometry only where necessary. Furthermore, Gridgen's geometry modeler may be used to supplement the CAD model and create new models from scratch:

• points and lines
• Catmull-Rom and Akima splines,
• offsets, conics, circles,
• intersections,
• ruled, revolution, linear sweep, polyconic, coons, and fit surfaces
• trimmed surfaces

Also, Gridgen's hybrid geometry kernel allows models to be imported in de facto standard formats such as PLOT3D wireframes and STL triangular faceted data.

When meshing complex CAD models, Gridgen can create meshes that are independent of the CAD topology. A mesh may span an entire CAD surface, only a portion of a surface, or multiple surfaces.

Direct CAD Access

Through a partnership with CADNexus, a direct method for obtaining CAD data without translation is available for Gridgen users. CAPRI2NMB is a CAPRI CAE Gateway application that works directly with a CAD system's native kernel. Gridgen's native NMB geometry file is produced automatically by direct queries into the CAD model. The NMB file is then simply imported into Gridgen. Because CAPRI2NMB works directly with the CAD software, it has the potential to provide more robust geometry transfer. CADNexus supports CATIA V5, Pro/E, UG NX, SolidsWorks, Parasolid, and OpenCASCADE.

For more information about CAPRI2NMB including licensing information, please contact CADNexus directly. Contact information is available at www.CADNexus.com.

Learn More About Gridgen and Design Geometry

If you're interested in learning more about how Gridgen interfaces with CAD software and how it works with geometry, here are some additional resources.

Read about how solid modeling simplifies the geometry and makes it easier to mesh.		Whether your geometry is analytic or faceted, geometry modeling tools let you make it analysis reaady.