SimScale CAE Forum

CAD Issues



I am having some troubles trying to generate the mesh of the CAD model of a car (Solid Edge). I always receive this message " The mesh generation failed as there is faulty topology in the CAD. Try to inspect your model for body faults in your CAD tool or contact our support for assistance.", I understand that the problem comes from the CAD model but I can’t seem to find the source of this issue.
The model is not mine, it is from a student who worked previously on the same project as me. I did make a few changes to the model though.
I tried with the original model and the modified one and they both get the same error.
As i am writing this, I realized that there was a warning when I uploaded the Geometry.

I tried to modify the CAD a few times but never manage to produce a valid one.
Some of the parts of the assembly overlay a bit I believe would that be the reason of my error.

Here is a link to my project (ignore the name I didn’t come up with a good one yet):

Thank you in advance


Thanks a lot for your description!

@CFD-SQUAD, do one of you mind checking the geometry of our user? Thank you :slight_smile:




Since your model is of a car and you are using an in-compressible solver, I am guessing you want to model the air flow around the car. For this you do not need to mesh the car but rather a volume air enclosing the car. To do this, go to geometries, click on the drop down menu on the right of your geometry and under ‘add geometry operation’, choose enclosure. This enables you to form a mesh of the air around the car. There are several tutorials on the website which include use of the enclosure function, I’ve linked one of them below.

Try this and if you still experience problems with meshing then upload your CAD model so I can look at it in detail


Another point I just noticed is that your setup has a warning about shells being present; these are zero thickness parts. All parts of your model MUST have a thicknesses. You need to give those parts a thickness.


Hi everyone,

The same model? and the same problem?
FYI : 'External Flow' simulation project by cmartiso




Yes ! This is actually the previous student who made the original model.
I will try to follow what was done to the CAD to improve it and make it work.
I did try to “add geometry” but it didn’t let me choose this function, so I will modify the model accordingly and come back if I still have issues after that.

Thank you very much


I think your main problem was that your ‘body’ part was not watertight.

I fixed some easy to fix un-joined edges on it but there was a small hole in the left side of the front bumper that refused to ‘join’, I cut the surface around the hole and put a small patch in but then I decided a better way would be to split the body down the L/R symmetry plane, delete the left side and mirror the right side. Then I joined the two halves back into a symmetrical closed solid.

Here is a project with my new watertight geometry.

There are still 10 small surface warnings which I will let you fix (if they are a problem).

Give it a try…



Thank you very much for your help. I wasn’t able to work on the model this weekend so I just connected back.
I am not able to open the link you posted.
I will try to make the same changes on my own.

Thank you



Sorry to bother again but I realise that my level of CAD engineering is well too low to work on the model.
Everytime I attempt to make the changes you advised the entire model change or they simply do not fix my meshing problem. So I am quite lost there.

If someone could give me crash course in CAD that would be generous.


Sorry, I forgot that the default state after a copy of your project is that it results in a private project to me.

I just changed it to public and you should have access now…


Thank you, I tried to generate a mesh with the model you modified but it still did not work.
I think the issue comes from the 10 small surfaces which I will try to fix myself.


Hello again,

I tried fixing the small faces surfaces. But I am not sure to know what they are and where they are and how to fix them.
I made a few changes to what I thought were the issues but they didn’t solve my issue .
Also, by uploading an .STL file instead of a .STEP it let me do a mesh (but not the automatic one which is not really a big problem) and I am not sure why


As you have discovered, STL mesh files are somewhat of a bandaid for poorly constructed watertight CAD files (say a car with, when exploded, individual surface areas as small as 0.0003 mm^2 :wink: ).

Give us a link to the project with your ‘automatic’ mesh file creation error of your STL so we can make some suggestions…


Sad I can’t figure how to fix my CAD so I’ll stick with a .stl file until I find a way to fix it. :sweat:

So it’s the geometry “vehicle assembly” with mesh 3. When I say “automatic” it’s because when using a .step file, most of the settings are already set by Simscale.
Since I don’t know what most of the settings do yet (still learning) I have been trying out a few different setups.
This one is the last one I made but when the mesh is generated, there are no wheels and no bottom of the car.
There’s only half the mesh because I wanted to try to use symmetry for the boundary conditions later on.
Also it doesn’t look like to be an external mesh.
If you can help me it would be great.
thank you,



Hi @vwirth ,

The material point should be in the air, out of the vehicle volume.
The ‘material’ means like ‘fluid area’ to make a volume mesh.




Yes it worked !
Thank you very much, but I believe the mesh could be refined more so I’ll continue trying out some different configurations. I f you have some tips on how to make it better, I am keen to learn them !
I’ll also continue working on the CAD to try to make work in a .STEP format.
Thank you everyone !:grin: