How Is the Exchanged Data of Subcycles Generated? | Non-Matching Timesteps & Fixed Time Window

Hi everybody,

I’ve got a question about the coupling with non-matching timesteps with fixed time windows.

About my current case:
I’m creating a FSI coupling with the OpenFOAM adapter. Because the Adapter doesn’t match my needs of coupling additional solid body motion, I’m sending this motion data manually via a seperate socket connection (other displacement data is mapped via preCICE).
This works fine for identical timesteps.

On the documentation page it says “Once both participants reach the end of the time window, coupling data is exchanged.”.
Because I have to send some data manually as stated above, I need to know how this exchange of coupling data is performed in detail.

Question:
Is the data collected over a time window just summed up together and finally exchanged with the other coupling partner? Or are there some algorithms acting in the background to merge the timestep data and if yes, can I neglect them?

Answer is short: preCICE simply uses the last data in the time window and sends this one. All intermediate data is neglected.

Important to understand in this context: “displacement deltas” always means the delta in reference to the last time window (not the last timestep).

Further information:

https://precice.org/couple-your-code-timestep-sizes.html

For future readers: we are currently implementing waveform iteration in preCICE which will makes such scenarios much much better.

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Thank you for the reply :slight_smile:

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