Perpendicular - flap case display problems

[daxiangxiang]

Hello, preCICE developers：

I try to run the precice perpendicular - flap case, I only changed the fluid preservation time interval in the case, after the completion of the coupling, for Calculix results, I use the “frdConvert” convert Calculix Frd files to VTK files. Then，open the two results with paraview, One problem I found was that there was a gap between the fluid grid and the solid grid:

I thought it was the problem of data format. After my investigation, I found that for the same grid point of fluid and solid, the node displacement was different at the same time.

For example, at 0.72s, for the coordinate point of (0.05,1)

The pointdisplacement of the solid node in the X direction is 0.19852952920230785, and the pointdisplacementof the fluid node in the X direction is 0.19337, which is obviously different. May I ask how to achieve the complete overlap of the FLAP interface? This seems to be an error problem caused by the large grid scale, right? Could you please explain why this problem occurs?
Thank you

[boris-martin]

Outside of the synchronization issue, this could be explained by a too low tolerance in the implicit coupling. If you reduce the tolerance on displacement in the precice-config file (e.g. <relative-convergence-measure limit="5e-8" data="Displacement" mesh="Solid-Mesh" /> ) you should get more accurate results, but a more expensive computation.

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