Hi,
I have been trying to perform a structure-structure interaction coupling CalculiX and another structural solver. I am using my solver to read forces and write displacements, and CalculiX to read displacements and write forces (opposite to classic FSI problems).
I started from the elastic beam tutorial.
Suppose I compute the resultant of the forces on both sides of the interface. In that case, I can see that it has the same modulus (which is ok) but the same direction while, to ensure equilibrium, it should have the opposite sign on the two faces (or at least inverted from the CalculiX side).
When I tried to couple to another solver, I had to invert the sign of the forces read at the interface to make the simulation run and converge, but, this way, I need to distinguish between FSI and SSI problems.
My idea is that the CalculiX adapter, when sending forces, should invert their sign on the interface.
With some guidance, I could try to update the adapter to test this condition.
Thank you
Claudio
We have the same challenge in many similar situations: heat flux (CHT), velocity (flow-flow coupling), and more. We typically make assumptions that, e.g., reading is incoming and writing is outcoming, and one of the two makes the conversion.
This is something we should find a more consistent solution for, and would be something for the ecosystem standardization project. I opened an issue, let’s continue the discussion there: Assumptions for direction of incoming/outcoming fields · Issue #42 · precice/preeco-orga · GitHub