Article Updated on 30 November 2020
The geometry model determines the shape of your CFD mesh, so it is important to make sure it is correct and accurate. To support this, Pointwise reads native geometry files from a variety of popular CAD systems bypassing the additional conversions needed when using a neutral file format.
There are several benefits to importing CAD geometry from a native file rather than from a neutral file.
Of course, the value of neutral standard formats has not been diminished. There are many instances (legacy data, for example) in which geometry exchange is aided by support for standard formats and that is why IGES and the new STEP reader are supported by Pointwise. Plus, standard formats are very well defined and relatively stable, whereas there is always the issue of updating for new versions of CAD files.
Both native and neutral file CAD support are important and you get them both in Pointwise.
The CAD readers in Pointwise do not use a license of the CAD software – all you need is the file. The file’s contents are imported directly into Pointwise’s geometry kernel, at which time they are usable just like any other bit of geometry whether imported from IGES or created in Pointwise. You can mix geometry data from several files and several formats.
Details of the supported CAD formats are included in the following table.
As mentioned above, by importing geometry from native CAD formats you are likely to import solid models from the file. A solid model is a topological entity that helps you mesh over gaps between surfaces. Of course, automatic and manual solid model assembly and editing are also available in Pointwise so you can create solids or change any solids that were imported.
But when it comes to meshing, you need more than just the solid model. Yes, the model helps you create a watertight mesh. But the automated meshing procedures will create a mesh topology that matches the CAD surface topology – one mesh for each surface. This probably is not what you want because the surfaces in a CAD model are an artifact of the design process and the CAD software. This is where quilts come into play. A quilt is a collection of CAD surfaces to be meshed as a single unit – one mesh per quilt.
Take as an example the racing seat shown in Figure 1. This solid model was imported from a STEP file and consists of 200 individual surfaces delineated by the colors.
The complexity of this CAD model can be reduced by assembling the surfaces into quilts along feature lines. In this particular case, a feature angle of 20 degrees was specified and the 200 surfaces were combined into only 59 quilts, as shown in Figure 2. The quilts now correspond to regions on which a single mesh will be generated. Quilt assembly in Pointwise can be performed either automatically during CAD file import or manually on any portion of the model.
The resulting surface mesh matches the simplified CAD topology (Figure 3) and thereby more accurately reflects the engineering intent rather than the CAD topology. Because the quilts are part of a solid model, the mesh knits together and is fully closed.
For an in-depth look at all the issues related to geometry modeling for CFD meshing, including discussion of the ins and outs of various geometry representation types, sources of errors, and best practices see our resource page on this topic at info.pointwise.com/en-us/preparation-geometry-models-for-mesh-generation-cfd
If you are interested in learning more about preparing CAD geometry for meshing in Pointwise watch our recorded webinar, Mastering Geometry Cleanup in Pointwise. This webinar will show you ways to automate geometry assembly on import, identify possible CAD import problems, and the best approaches to solve any problems you encounter.