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Hi everybody !

I am trying to modelize tides with TPXO, but velocities and free surface oscillate at some points near islands for example (shallow water) (start from 5 hours of simulation at some points). I thought it could be because of tidal flats but I have tried several options and the oscillations still appear…
I don’t know what could be the reason for these oscillations, does anyone have any idea ?

Every answer will be appreciated !

Pictures of velocity, free surface oscillations are attached (bathymetry represented as isolines from -200m (blue) with 25m interval), and a time series of velocities extracted between the islands. My steering file is also attached.

Thank you for your time everyone.

Best regards,
Ophélie

Hi Ophélie,

Can you also plot free surface and velocities time series for a boundary point and for an interior point ?

Do you know why the 5 first hours are correct ? is it the time that the tide spends to reach the islands ?

Can you identify where are generated these oscillations (a node or group of nodes) ? and when (at a moment where there is almost no water) ?

Do you have high bathymetric gradients around the islands ? is the resolution of your mesh enough over these slopes ?

Hope it helps !
Laurent

Hello Laurent !

Thank you very much for your answer !

I attach free surface and velocities time series at a boundary point and for an interior point.

I don’t know why the first hours look correct… The tide has already arrived to the island before…

I can’t see which node causes the oscillation, I attach a small video of the apparition of these oscillations. The bathymetry is plotted on it (from -100m (blue) with 10m steps). I think the bathymetric gradient is not too high according to this plot but I would be glad to hear your opinion.

There is water everywhere around the island when the oscillations appear, except where free surface is colored in red in the video, because bathymetry values here are positive and go up to +55m. Maybe this is a problem actually..?

Thank you so much for your time !
Ophélie

The video is available here : we.tl/il96QP6yva , because I can't attach it in the forum

Can you upload your geometry and boundary conditions files please ?
Laurent

My TIME STEP was too small (1s). This must have been creating some instabilities... When I set TIME STEP at 10s, the free surface and velocity oscillations disappear.

Thank you very much for your help Laurent.
Ophélie