Perform 2D simulation with Calculix


I want to perform 2D FSI simulation with Calculix, I saw the test case of the perpendicular flap where the mesh provided has a thickness of 1.

What happen if we put a thickness of 0.1 for the solid and we also put a thickness of 0.1 for the fluid domain ?

I wanted to know if there is an explanation for this choice of thickness and if this is also working if I want to perform the HRON&TUREK FSI3 for example?

I also noticed that you use solid element (C3D8I) for your test case, have you tried with shell elements (S4) with thickness=1 ? Because for me, contrary to shell element, having a solid element would introduce Inertia along the “fake third dimension” (If my flow is in the plan XY, the flap could have different position along the z axis).

Thank you for your help.

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Sorry for the delay in answering.

The thickness of “1” is such that in your unit system, the z-axis has no effect. A force of 1N would be interpreted as 1N per meter in SI units for instance. However if your fluid domain works on a different thickness it might make sense to follow the convention of a different thickness. It depends on whether the fluid solver outputs force per thickness of raw forces.

Shell elements should work too, with the same reasoning for thickness. However support for shell is recent, and you’d need to build the adapter from the “develop” branch on Github, as the last release doesn’t contain this update yet.

Hope it helps!


Yes, I understand better, thank you !

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