Export meshes in patches

I am doing my research with CFD and finite volumes simulations with another application based in C++ language (OpenFOAM).
I have found myself with a current issue, that the meshes I export even with small features from the CAD software I use (Onshape) give me some trouble. and I thought maybe a FEM software could help me to solve it.
what my problems are:

  • I need to export the surfaces of the models separately, so for example of a cylinder, the cylindrical part, and the two planar sizes in separately stls to be able to reconstruct it in OpenFOAM and be able to recognize the different boundaries. here is my first problem, as the meshes in Onshape is done after the separation of the surfaces (can not do it before as the meshing is done at the same time of the exportation) the models are not necessarily watertight after reassembling of them (as they do not share necessarily the same vertexes, normally as the meshing process does not know that they are related surfaces).

*second my stls that I export have really “stretched” triangles, (see image below) and this option I can not control, it is like the triangles are forcibly touching the edge of the model and they can not be “in the middle” of the surface.
what an exported mesh looks like (right) and what i am looking for (left) (obviously they are different models, where the second one has been provided by a collage):

could I export an .STEP model from my CAD software and mesh it with freefem to solve these two issues? (export an “exploited” surfaces from the model and a better mesh?)
Sorry for being a little bit out of subject maybe? but I can not find any open source solution for my issue
best regards, franco

You can mesh your .step file with Gmsh and then import it inside FreeFEM.

thanks! i will have a look :slight_smile: