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Dear community,
I am trying to model the influence of the tidal wave on a sector of the Bahía Blanca estuary, Argentina, where the aim is to evaluate the impact that the discharge of sediments will have on the sector.
For this, the historical series of water levels in the port sector is available, which will be used as base information.
As a boundary condition, I am only using this series of water levels in the place corresponding to the measurements, as shown in the first picture (Condicion de borde.jpg).



The problem is in the expected velocity distributions in the sector, mainly in the boundary condition, where there are instabilities mainly in the time periods where the sign of the slope of the water level changes, as seen in the images ( Water level at the boundary.jpg - Velocity Distribution at the boundary.





I attach below the CAS, and if there is any kind of idea to improve this behavior it will be welcome.
Thank you very much!

Hello matecz,

I think you set 544 code to your open boundary, do not you? (prescribed elevation and free velocities).

Depending on your local bathymetry close to the open boundary, you may have recirculation as drawn in your figure as you let the velocity components free, it is not surprising.

Perhaps by enlarging the extent in the sea the recirculation may be smaller or disappear but if it is due to bathymetry, it will be difficult to change that for me.

Hope this helps,

Chi-Tuan

hello Chi-Tuan,
Thank you for your quick response.
Exactly, I am considering the boundary as 544.
Regarding the bathymetry, I have extended the study channel a few kilometers, but the same phenomenon continues. Unfortunately I do not have the bathymetric information to generate the complete estuary.
Likewise, I do not consider the recirculation on the boundary as the main drawback, but the instability that it generates in the velocity vectors in the study area.
Here I leave you a comparison of velocity and level in a characteristic node, where the instabilities are observed.





I also think that this is sufficient for the study that is being carried out, but perhaps there is some way to smooth the velocity curve that I don't know about.

Thank you so much for everything!

Hello,

What is the maximum velocity in your figure? Something like 0.5 m/s?

Have you tried to decrease the time step?

Anyway looking accurately at velocity on a boundary where velocity is let free is not always a good idea.

Chi-Tuan

Moreover, what is the bottom elevation on the open boundary?