Questions about multipart FEM modeling for thermal analysis

Mods FEM
1

Hi folks,

I’m trying my first FEM modeling for thermal analysis and I’d like to ask for some help and advice. I have some previous experience with Solidworks workflow but I’m starting with FreeCAD now (congratulation to developers btw, very impressive work!)

I believe most of my difficulties are related to proper modeling the “assembly” for FEM simulation. I read the Transient FEM Wiki and seen some youtube tutorials, but this part is still a bit tricky. I don’t know a canonical way of doing it and I end up with a lot of trial and error that are not really converging to an useful result. The file is here (don’t mind the part shapes, the’re just arbitrary):

http://hg.cptibr.org/~miguel/peca-mais-bloco2.FCStd

http://hg.cptibr.org/~miguel/peca-mais-bloco2.png

  1. I have succeeded in finishing the mesh and simulation by using “Compound” instead of “Boolean Fragments” (https://wiki.freecadweb.org/Transient_FEM_analysis say that both should work). However the two parts are not considered in contact for heat transfer. Where did it go wrong?

  2. When I tried “Boolean Fragments” then I couldn’t really select the parts individually for assigning materials. Empirically I have seen that the “Compound” that works for mesh and has assignable materials is shown as “Solids:2, CompSolids:0, Compounds:1”. Is this the right shape contents “goal” for this kind of simulation?

  3. In solidworks I remember using mechanical constraints for moving parts and have them in contact with each other. For FreeCAD what tutorials I have seen suggested are using third party workbenchs like “A2Plus”. However that sort of workbench doesn’t seem compatible with what FEM expects for a meshable compound (?). Is there any other resources for parts assembling in standard workbench that I’m overlooking, that might help producing a good “assembly” (“compound”) for simulation? any pointers/tutorials are appreciated.

  4. Finally, the simulation does produce a sensible result considering a model that has no contact between parts (each reaches a final constant temperature). What I don’t understand though is why do I need the ResultPipeline to see these temperature variations in colorscale, if other results (like displacement magnitude) can be displayed just fine using “show result” dialog?

Thanks in advance!

regards,

Miguel

2

Quick update: attached alternative version of the same simulation but using BooleanFragments (Mode=CompSolid) and CompoundFilter. Mesh looks better (doesn’t seem like separate solids).

This version, however, fails to simulate with the following errors:

*ERROR in calinput: no material was assigned
to element 1155
*ERROR in calinput: no material was assigned
to element 1172
*ERROR in calinput: no material was assigned
to element 1191
*ERROR in calinput: no material was assigned
to element 1205
(… many more …)

highlighting some of those manually doesn’t help much. Supposedly they belong to a solid that has been assigned material.

Gui.ActiveDocument.FEMMeshGmsh.HighlightedNodes = [1155,1172,1191,1205]

3

Regardless of the approach you use, if the mesh on both parts is not continuous (which can usually be seen by just looking at it, especially if there’s a difference in mesh density of each part) then tie constraint or thermal contact (contact with gap conduction) has to be applied. In FreeCAD, this is normally needed only when there’s a gap between the two parts, even very small.