Strange phenomenon during multiphase FSI

Hi all,
Recently I’m doing wave-struction simulation using our in-house solver and OpenFOAM. At first, the wave propogates normally. However, the water near the structure suddenly collapses.
The red part is water and the blue part is air.
1.95s


2.00s

Since the displacement and stress results obtained from our in-house solver seem to be fine, I guess this may be related to the fluid part but I haven’t found mistakes in case setting. May it be that the data mapping doesn’t converge?

Has anyone encountered the similar situation? Any suggestions will be appreciated! :blush:
precice-config.xml (2.6 KB)

Are you maybe using a modified version of the adapter? How did you make the FSI module work with multiphase?

I could imagine that there is a bug here, but I need to understand the context first.

Hi Makis,

Yes, I’ve modified the adapter to pass Pressure to the solid participant, and read the Velocity and Displacement on the interface from the solid.

I didn’t change much. In brief, I adopted a multiphase solver and modified some initial files.

Today, I’m sure basically that the problem is due to the Velocity passed to the fluid part, not the openfoam adapter. For some points on the interface, the velocity values calculated by our in-house solver are quite large which could lead to the non convergence in the fluid part. Once I removed the Velocity from the coupling data, the simulation converged well.

Is the discontinuity maybe related to implicit coupling and redoing iterations? Just thinking in the direction of checkpointing.

Since our solid solver doesn’t have checkpoint function at present, I only use explicit coupling to do my tests ( It may change the structure of our solver in order to do implicit couping, but it’s on the to do list). In my simulations, I found that there is unreal oscillation for the structure. For example, the flap is supposed to vacillate to the left and right once it’s hit by waves. However, when the flap should continue to vacillate to the right, there is a sudden movement to the left. May it be the problem of the discontinuity you mentioned?

Are your code changes available online anywhere?

The changed openfoam-adapter is uploaded here. I mainly changed the files in FSI module to write Pressure to the solid and read Displacement and Velocity from the solid.
openfoam-adapter_modified.zip (2.8 MB)

Since our solid solver is an in-house code and it is directly modified in the source code to adopt functions in preCICE library, I’m sorry this cannot be uploaded.

To be more clear, the strange phenomenon is shown in the figures. Fig.3 shows that the flap suddenly vacillate to the left when it should have vacillated to the right. Then, there is a kind of discontinuity of the water phase near the flap as shown in Fig.4.


Fig.1 & Fig.2

Fig.3 & Fig.4