open TELEMAC-MASCARET The mathematically superior suite of solvers

Dear all,

I am trying to simulate the sediment transport in a coastal area and while I am able to succesfully produce results,as far as the sisyphe results are concerned I can only visualise a minimal bed load transport only at the open boundary which doesn't seem right.I would be very grateful if you could have a look in my files an help me locate the error.Please be noted that I am a fairly new user and have used the littoral example as basis.

Due to the large size of the results file I am attaching the following link which contains my files.

www.mediafire.com/file/m6q6d4kf9q38954/aulida_utm.zip

Thank you very much,
Andreas

Dear Andreas,

Your model would be OK if you only wanted to model tidal currents, but for nearshore sediment transport, you need adequate mesh resolution to model wave breaking, thus wave induced currents and sediment transport. If your waves are small, so needs to be your element size. You may need elements in the order of 1-2 m.

If you do so for such a large area, the element would rise significantly and the computation will take weeks. So I suggest to refine your model only near the area of interest and then see if you are getting nearshore sediment transport.

Regards,
Costas

Thank you for your reply Costas I will try to refine my mesh nearshore and see the results I get.One more question about this.If the waves practically don't reach my area of interest but I get results from telemac for the uv velocity components,I will still get some results for the sediment transport in the area is that correct?

Regards,
Andreas

You would get if the velocities are high enough to suspend sediment from the bed. But I expect normal tidal currents alone to be insufficient to suspend sand nearshore, especially with steep bottom gradients.

Besides that, even a 0.5 m wave can cause some sediment transport at the shoreface, which certainly needs high mesh resolution to capture.

Costas

Dear all,

I tried to follow Costas' advice and refine my model (I actually extracted time series from the big model and build a new much smaller model with all the elements being 2m using the limwac subroutine to impose wave height at the boundary).However even If I set a small time step for the simulation I get huge number of subiterations after some time steps,so the model hangs(output.txt).Could I ask to take a look at my files once again and tell me where you think the instabillities occur and what could be a possible cause?

Kind regards,
Andreas

Hello Andreas,

waves_lim.txt file is missing. Please attach.
Costas

Here it is sorry for the inconvenience

I am unable to run your case for some reason, but you certainly need to reduce the timestep. A fine mesh requires small timestep as well and 50s is too large for nearshore areas. Set timestep = 1s in T2D and TOM and increase as long it does not compromise your results. If you set TOM's timestep low enough, then you can set NUMBER OF BREAKING TIME STEPS = 1 or 2.

Costas