Hi Timouthy, what file format are you using for the transfer from MoI into SimLab?

Those look like triangulation errors in Simlab - try exporting from MoI using .obj format and in the "Meshing options" dialog that pops up in MoI at export time, make sure to change the dropdown option to "Export: Quads & Triangles", and not leave it as "Export: N-gons".

That will make the triangulation happen in MoI instead of SimLab. It's not too unusual for rendering programs to have some difficulty triangulating very complex n-gons (an N-gon is a polygon with more than 4 sides on it), since they are not generated by very many programs.

So if you see what looks like triangles that are sort of "leaking" outside of their trim boundaries, try making the triangulation happen inside of MoI instead by not exporting any n-gons out from MoI.

If that does not solve it, and you were using a CAD file format like STEP or IGES, then it could instead be a damaged trim boundary on that surface. That might be something like a self-intersecting edge that squiggles back over top of itself instead of cleanly dividing a surface into different regions. If that's the case then I'll probably need to see the model file to help you with that. For such a large file you'd need to upload it to a file sharing service like Dropbox or Microsoft OneDrive and then post the link to it here rather than directly attaching the file itself right here.

- Michael