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Hello,
I am facing the following issue:
I have a model with one inflow (prescribed discharge, 455) and one outflow (prescribed height, 544) boundary.
However, the model outflow is always only around 90% of the model inflow although the simulation seems to be stationary. Additionally, the water volume is constantly decreasing, although the inflow is bigger then the outflow.

I had a different mesh at first, and the issue did not occur. This is why I suspect the issue stems from the mesh, but I do not understand why...
I also tried changing the prescribed elevation value and looked at the hydraulics at the outfow. But nothing really noticable occurs.

Has anyone an idea where the error might be ?

Best regards,
Jakob

Hello Jakob,

If it works with another mesh and not your 1st one, indeed, your 1st geometry file is suspicious.
Are you sure the flow is not supercritical?

It could be interesting to see the differences between the 2 geometry files (in particular if the interpolated bathymetry at the nodes are very different or not.

Chi-Tuan

Hello again,

In your steering file, you use (at least) 1 option that is not recommended:
- TREATMENT OF NEGATIVE DEPTHS = 1 (rather use 2, not to have potential negative depths; in that case, you have to use SUPG OPTION : 1;0;1;1 + CONTINUITY CORRECTION = YES.

You should also read the Recommendations chapter in the TELEMAC-2D user manual.

Hope this helps,

Chi-Tuan

Hi,

- Are you sure of the consistency of your initial condition with the steady state you want to reach?

- Have you tried CONTINUITY CORRECTION = YES?

Alexis

Hi thanks for your help! It works now, there is still an error smaller than 1% but I think this is acceptable.
The reason it worked for one mesh but not the other was a small error in the bathymetry interpolation. Some of the outflow nodes were a little bit too high, so the water was somewhat flowing upwards on some of the last nodes.