[f_sizer]

Hello CFD Online,

I'm having a bit of trouble trying to create a 3D mesh of our Formula Student (SAE in America) car at University. The CAD model has been created in Pro Engineer Wildfire 3.0 and saved as a STEP file:

1st Question - When I save the STEP file, is it easiest (for creating a mesh) to save it as Solids, surfaces etc. or a combination.

2nd Question - I have been attempting to create the mesh for over a week now and thus far have managed an incomplete mesh that has several geometry errors as follows -
face.xxx has less than 3 boundary nodes on one or more face node loops.
v_edge.xxx less than 3 intervals, which prevents it from being meshed.

I think it is worth me mentioning how I created the STEP file in Pro Engineer so that any kind answers will have a bit to work from. Basically, I created a single part in Pro Engineer by shrinkwrapping the cars assembly, followed by cutting the shrinkwrap from a large extrusion for the block. I did this because I thought it would save me from having to create a new face on the symmetry plane (the car is cut down the centre as symmetry is assumed).

Thank you so much for any answers in advance! Have a nice day.

[-mAx-]

1- Select solid. It will import volume. If you also select surface, Gambit will import cosmectics surfaces such as threads, etc...

2-Is your cut out operation successfull? Have you done it with ProE or with Gambit?

If you want you can provide your step file, and I can take a look

[f_sizer]

Hi thanks for the fast reply!

The cutout was done in ProE and appears to be successful. I may have been applying too big a spacing on my mesh. Is there a general rule for mesh sizing?
I was up all night thinking about it and the idea came into my mind that the spacing should be smaller than the smallest edge, it seems logical but I'm not sure whether I'm right? If so I take it you cleanup small edges so that you can use a coarser mesh?
Please don't laugh if I'm talking rubbish!!!!
I would love to send you my STEP file but son't know how!

Look forward to hearing from you again!
Sincerely
Freddie

[-mAx-]

ok if you did the cut-out in Proe, then the imported step file should give you a Volume "ready" to be meshed.
Basically you can mesh a surface and choose the cell size, which will be the global size of the mesh.
Then you will mesh the volume with this cell's size (The mesh generation will failed because of small edges etc... but Gambit will tell you where it's failed, resp. on which surface)
Apply Size Function on these surfaces for preventing Gambit to fail, or merge surfaces/edges, if you have small angle.
This is a "quick" method, but you can spend more time on your mesh be spliting it into basics volume which can be meshed with hexa.
You can upload your step file on www.rapidshare.com

[f_sizer]

Hi,

The volume is created, but only when I select make tolerant and heal geometry upon import.
I've just had a go and managed to mesh the symmetry face and the volume. Does it matter that the face is tri and the volume is tetra or is that just the 2d 3d difference in words?
If you mesh different features with different size functions do you have to do any operations to bring the different mesh together?
I've printed out the list of faces that didn't mesh so I'm going to work through them trying to create size functions for each one that will allow a mesh to form.
The biggest problem comes where I have an extrusion, in this case for a wishbone, that goes through the surface, where this happens the following error message is displayed:
Face has less than three boundary nodes on one or more of face node loops, which prevents it from being meshed.
What does this mean!?
http://rapidshare.com/files/223910274/volume.stp.html
Thank you so much again!

[-mAx-]

Ok, I can't import the volume. Just surfaces and 2 small volumes.
I think the best way for you is to import the solid parts in gambit, and then you do the cut out in gambit.
Normally if you export in step file, you choose the "solid" option.
Then for the import, you choose the "make tolerance" option.
It you don't get a volume, then there is a problem, and you can check in ProE if the part you imported has a mass.

[f_sizer]

Oh dear, thats weird, when I import it I get three volumes - every time I've done the import I've selected heal geometry and make tolerant.

I'll have a go at creating the volume in gambit.

What does this error message mean?:

ERROR: Face has less than three boundary nodes on one or more of face node loops.

Thanks.

[-mAx-]

I am using Gambit 2.4
Regarding your issue, I think (but not sure) that you have a small face with less than 3 nodes on outer edges.
For example you have a circe and on this circle you ust have 2 nodes. Gambit don't know how to mesh it.
Once again I am not sure

[f_sizer]

I think that I'm going to go back through the model and simplify it as much as possible, so that I have less things to go wrong! I'll let you know the progress.
Thank you very much for your help, it's been very useful!

[pupul_b]

Hi, you said there is a "quick" way of meshing the volume and there is a longer way which involves splitting the volume and creating a hexa mesh. I'm trying to mesh an SAE car as well, but was hoping you could direct me to some 3D hexa meshes of simpler structures which involves the splitting of volumes. So far, I have followed the Sedan tutorial (http://my.fit.edu/itresources/manual...guide/tg05.htm), but I realised that the mesh quality from that isn't good enough and its a much more simplified model than what I'm trying to achieve.

Any help would be much appreciated. Thanks.

[-mAx-]

If you followed the tutorial, then you have skewness below 0.8, which isn't bad.
you can swith to tet-hexcore schema, and apply a size function on the car-body.
But it is still a quick way.
If you need hexa, then you need splits and more work