different results Freecad and Solidworks

[Eduardo1]

Good Afternoon everybody, I am doing a thermical simulation, but the weird thing is the difference of results between Freecad and Solidworks. I made the same simulation in both, but the numerical result are totally different, being correct results in Solidworks, however in Freecad the results are illogical. Both simulation using the same temperatures, materials, etc. I attached an image of Solidworks and freecad file on Drive. What is happening really?

https://drive.google.com/file/d/1hwliuN ... sp=sharing


Beforehand thank you so much.

OS: Windows 10 Version 2009
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24267 +99 (Git)
Build type: Release
Branch: Branch_0.19.3
Hash: 6530e364184ce05ccff39501e175cf2237e6ee4b
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.3
Locale: Spanish/Mexico (es_MX)

[NewJoker]

It's not the fault of CalculiX because I solved your model using another preprocessor for this solver and the results agree with SolidWorks Simulation very well. Be extremely careful when applying heat fluxes (concentrated or surface fluxes) to multiple faces unless you are sure that you know how particular software handles it. In SolidWorks you have the "per item" option so you can be sure that the specified value is applied to each face. Otherwise, it's common in FEA software that the specified value is uniformly distributed on all the selected faces (so that each face is loaded with a fraction of total specified flux). The same applies to nodes within a face - sometimes the specified concentrated heat flux may be applied to each node while sometimes it will be distributed over the face so that each node receives a fraction of the specified flux. I'm not sure how it works in FreeCAD since it's not mentioned in the documentation and there might be some bugs. I will try to take a closer look at this if I have time, some simple tests and examination of the exported input file will be needed to verify how it works here.

[Eduardo1]

It's not the fault of CalculiX because I solved your model using another preprocessor for this solver and the results agree with SolidWorks Simulation very well.

What solver did you use?

[NewJoker]

PrePoMax, it's another open-source pre- and postprocessor for CalculiX. This analysis should work in FreeCAD FEM as well but it will likely require some investigation regarding heat fluxes.

[Eduardo1]

PrePoMax, it's another open-source pre- and postprocessor for CalculiX. This analysis should work in FreeCAD FEM as well but it will likely require some investigation regarding heat fluxes.

Thanks I will try with PrePoMax solver and I am going to share the results, but do you think SolverCalculix has a bug?

[NewJoker]

Thanks I will try with PrePoMax solver and I am going to share the results, but do you think SolverCalculix has a bug?

There might be a bug in FreeCAD FEM module as a preprocessor for CalculiX solver (as I've mentioned, the solver itself works fine). The definition of heat fluxes may be working incorrectly - it's possible that the specified value is not being distributed to the surfaces properly. But I would have to do some further checks to confirm that it's actually a bug.

[Kunda1]

@Eduardo1 any chance you can test on v0.20dev?
The FEM subforum guidelines recommend that you do

[Eduardo1]

@Eduardo1 any chance you can test on v0.20dev?
The FEM subforum guidelines recommend that you do

that is true!!!, I am going to try it I will share that results too. Thanks

[Eduardo1]

@Eduardo1 any chance you can test on v0.20dev?
The FEM subforum guidelines recommend that you do

I don't know why I can't use the v0.20dev, I download it but it has errors inside the file.

[Eduardo1]

It's not the fault of CalculiX because I solved your model using another preprocessor for this solver and the results agree with SolidWorks Simulation very well. Be extremely careful when applying heat fluxes (concentrated or surface fluxes) to multiple faces unless you are sure that you know how particular software handles it. In SolidWorks you have the "per item" option so you can be sure that the specified value is applied to each face. Otherwise, it's common in FEA software that the specified value is uniformly distributed on all the selected faces (so that each face is loaded with a fraction of total specified flux). The same applies to nodes within a face - sometimes the specified concentrated heat flux may be applied to each node while sometimes it will be distributed over the face so that each node receives a fraction of the specified flux. I'm not sure how it works in FreeCAD since it's not mentioned in the documentation and there might be some bugs. I will try to take a closer look at this if I have time, some simple tests and examination of the exported input file will be needed to verify how it works here.

if it is not a nuisance, Could you tell me what numbers did you added in each heat fluxes? because I am having the same error.