I am trying to validate my fluid and structure mesh for the FSI1 case of cylinder-flap test. As the refinement of the fluid and structure mesh increases, it is difficult for implicit FSI coupling to converge. Therefore, my idea is to use a lenient tolerance of 10^-3 for the first 2 seconds of coupled simulation, and gradually make the tolerance much stricter (10^-4 for 2-4[s], 10^-5 from 4[s]). To accomplish this, I have to restart coupled FSI simulation at 2[s] as well as at 4[s]. As Benjamin mentioned in the gitter chatroom, I have activated the initialize option in the exchange data field as follows:
<exchange data="Displacements0" mesh="Calculix_Mesh" from="Calculix" to="Fluid" initialize="1" />
However, the restarted coupled simulation does not converge in the 1st time step (2.01[s]) and it crashes in the second time step(2.02[s]) after 11th sub-iteration due to the failure of the rbf spatial coupling at the interface. The original coupled simulation from 0[s] was doing well, requiring only 4 sub-iterations for the coupled simulation to converge at 200th time step (2[s]). I understand that IQN-ILS post processing does not function well when it does not have solution history from previous time steps to rely upon on. But if it works well at the first time step with 11 sub-iterations for convergence (0.01[s]), I am puzzled why it does not function similarly for the 201th time step(2.01[s]).
Therefore, I was wondering if my restart procedure for OpenFOAM and CalculiX are correct to begin with. For restarting OpenFOAM, I simply change the parameter
latestTime. Whereas for CalculiX, I followed the procedure described in an earlier discussion from preCICE community.
Also, since my objective here is to make the relative tolerance stricter gradually, is it possible to change the tolerance value by simply editing the
precice-config.xml file during an active simulation like OpenFOAM, thereby avoiding the need for me to restart coupled FSI simulation. I have attached the necessary log and config files for the original as well as restarted simulation for your reference.