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I am trying to simulate an experimental flume on Telemac 3D. The flume is 12m long and 1m wide with a average flow depth of 0.1m. I am coupling my Telemac 3D with GAIA for sediment transport.

The problem I am trying to simulate has a sudden increase in depth of flow from 0.1m to 0.2m at middle of the flume. I am getting acceptable result for sediment transport but the velocity profile is not matching with the experimental data. The velocity profile is over estimated by the model and also the depth of flow is a little higher than the experimental data.Moreover, I obsereved some free surface undulations.

Can changing the Free Surface Gradient Compatibility from 0.9 to a lower value be useful. Also, what is the minimum acceptable value of FSGC?

Hi
Free surface gradient compatibility is used to damp numerical wiggles.
To roughly explain this option I would say:
It deals with the numerical management of free surface gradient as a source term in the movement equation. The computation of this term could be done according to the 3 nodes of an element (1) or considered as element-wise as a constant value (0). All values between 1 and 0 is a linear combination of these options.

So 0 is acceptable...
Regards

Thank you so much for clarifying. Also, I have a little doubt regarding boundary conditions. When I am using a boundary condition specifying discharge at inlet (455) and depth at outlet (544) it gives an error saying: Please specify profile at inlet boundary or super critical flow at the boundary.

But when I specify both depth and discharge at inlet (555) the simulation run smoothly, though the result is a little off with physical data.

Can you tell me if this is okay to specify such boundary condition.

I am attaching my cas file for your perusal.

The message occurs when there is no water at the entry. Are you sure about the initial water level... maybe a problem with the bathymetry of your geo file...
Using both depth and discharge is ok for inlet under supercritical flow...

Thank you. The bathymetry is for an experimental channel with mild slope. But I do see high level of scour near the entry of the flume during simulation. Moreover, it is subscritical flow so for that would it be fine to use both discharge and depth?

Moreover, if you can look at my cas file and provide a bit of recommendation on any changes for simulation of exprimetal flume of 1m width and 0.1m depth of flow. Also, there is sudden increase in depth of flow in the experimental problem. Keeping these parameters in mind any suggestions will really help me.

Thank you again for your time.

Hi ravi,

I have run into comparable issues in TELEMAC-2D + GAIA with a flume where entry was subcritical, but Froude was relatively high (around 0.7); upstream nodes would eventually go dry for some reason. I had to provide an upstream depth to ensure the model remained stable, even if it wasn't the most elegant option from a theoretical / physical representation standpoint.