CAD -> mesh strategies

I'm going to add an article on this to the wiki, but first I'd like to open up a discussion on the topic.

I've been making some strange models (lofts, sweeps, revolutions) in Inventor in order to run some unsteady flow cases in Saturne, and have run into a few kinks along the way. So far, I've made the following observations, which may or may not be true for other CAD packages...so I'd like to get some opinions here.

So far, I've noticed (while working with Inventor):

1) gmsh seems to work better with IGES files, but is unreliable to begin with, especially when creating 3D meshes. It also tends to crash and close itself relatively easily in Windows while trying to make any kind of refined mesh. I've pretty much stopped using it completely, although it is still a pretty neat program.

2) SALOME seems to work better with STP files, but can still run into meshing errors on occasion. With luck, using certain methods to create the model in your CAD program can help to avoid these errors (see next).

3) When creating your model, try and combine features in order to minimize the number of total features. For example, rotating a profile and subsequently filleting various edges caused SALOME to encounter mesh errors, whereas directly filleting the profile itself and then revolving it allowed SALOME to successfully mesh the model.

4) If possible, avoid using zero or near zero length line or arc segments, as they tend to cause problems when used with lofts, sweeps or other solids operations.

5) Try and avoid the more advanced solids operations (face splitting, stitching, etc.) if possible.

Here are some notes I've came across while doing my meshing. I'm using Solidworks for the normal CAD.

-- I exported to step format and needed to keep step in lower case because STEP doesn't show up, renaming is a bit of a pain, so best if you can name it step when you create it. I could choose step AP203 or step AP214, I choose the AP203 just because.
-- My assembly was reasonably large 60" x 60" x 3" so I wanted to use a larger mesh, however small features tended to cause problems. I simplified my mesh by filling in these holes and suppressing features before saving as a step file. However I'm sure it could have been done with the normal setup if I had known more about the meshing process.
-- To help things out a bit, in Solidworks, I did a saveas on the assembly as a part. I could choose to save external faces, or external components. This was also helpful in keeping it simple. For example, a part with several sub features (revolves, fillets, ect) is converted to one feature. However an assembly is still listed with several several sub parts.
-- When I imported the step file, I had to explode, then fuse several pieces together. Finding ways to keep the model simple will help decrease the fusing time when doing the mesh.<br /><br />Post edited by: Jared Harvey, at: 2009/02/16 16:34

I have a shape that I am trying to mesh (2D). Perhaps we could use this as a bit of an example (I dont want to hijack your thread)? It is an aerofoil in a wind tunnel. My approach was to create the outline of the aerofoil in CATIA, export as an igs file, and then add the boundary and create the surface (was the surface even necessary?) in Salome. I created groups in the geometry for the boundary conditions (CFD so walls for the tunnel walls and aerofoil profile and a velocity inlet and pressure outlet). I have been trying to mesh this with little success. I would like fine meshes on the walls and aerofoil profile but everywhere else can be rather coarse (more so in front than behind). Can anyone suggest a course of action for meshing?

Thanks,
- Matt Bondy<br /><br />Post edited by: Matthew Bondy, at: 2009/03/12 03:22

I was hoping to attach my .hdf file from Salome but it is too large.

I am using this aerofoil for a project where I will be comparing the results of OpenFOAM, Code Saturne, and Fluent to experimental testing.

- Matt Bondy<br /><br />Post edited by: Matthew Bondy, at: 2009/03/12 21:24

Given a sufficient amount of time that wiki will come to be.

- Matt