open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi everybody,

I am trying to make a 2D telemac model in order to modelise the flow on a parking surface. The problem seems simple : I have a river that come upstream of this parking and that overflow in case of flood. I already know the amount of flow that come from the river to parking so I have the hydrograph at the upstream parking. I put this hydrograph into a file.liq but i have still some problems with the boudary conditions.

Using FUDAA, I put a LIQUID boundary condition at the downstream (without Q or V or H prescribed).

For the Upstream BC, still using fudaa I put a prescribed Q (455). The problemù is that when I try to run it, it doesn't work. I have :

DEBIMP : PROBLEME SUR LA FRONTIERE 2
DONNER UN PROFIL DE VITESSES
DANS LE FICHIER DES CONDITIONS AUX LIMITES
OU VERIFIER LES HAUTEURS D'EAU

So I try to add in my parameter file: PROFILS DE VITESSE : 1;1
And I add a Initial depth of 0.1 m but it still doesn't work.

At the end of the simulation I have 0.1m water on the area but nothing come from the hydrograph. I also try to not use the hydrograph by just putting a constant flow but it doesn't work.

I think that the solution is very basic but I try a lot of solutions and it still doesn't work.

Thanks for your help.

JP

Hello,

This is a frequently asked question, and your problem is actually not simple, it is just not well posed. You cannot simply prescribe a discharge on a dry open boundary, because it will be a supercritical flow at the beginning, and then you must prescribe both velocity and depth, or discharge and depth. As you have posed your problem, you could have e.g. a depth of 2 m and a velocity of 1 cm/s or a depth of 2 cm and a velocity of 1 m/s, giving the same discharge, so an infinite number of solutions. At the beginning your boundary conditions need to be 5 5 5, and only if the flow becomes fluvial you then move to 4 5 5. As this may be cumbersome you can also enlarge your domain by a deep zone which is already flooded, with open boundaries that will remain with a fluvial flow.

With best regards,

Jean-Michel Hervouet

Thank you very well for your help.

I made a first computation with upstream boundary condition presribed H and V (555) for a computation time of 10 minutes. And then I use the result file as input for a second computation with my hydrograph and a upstream BC (455). And...it's working !!!

Thanks again for your help !

Best regards,

JP