open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello,

I have download an example of telemac2d which named "bumpcri", I run it and I think it's done by the analytical method. I plot the discharge at the final time and I found that the discharge is not constante. that'is logical?????

I want to do the simulation by numerical method, so I decommented the fortran file and I modified the conditions initiales: 'cote constante' and give 0.132(hcritical+ ZF) to 'cote initiale'. I run it then and the result is so strange..

I upload the cas file I modified.
Can somebody explain to me the two things???

Thank you very much
jie

Hello,

Depending on what you do in the initial conditions, you may trigger a hydraulic jump, or a subcritical flow that will not be compatible with the boundary conditions at the exit, which are meant for supercritical conditions, i.e. all variables are free.

There are several resons why you do not see a constant discharge. The local discharge in the results file is the depth multiplied by the norm of the velocity. The discharge that must remain constant in this case is the integral over y of the depth multiplied by the velocity along x. It is the integral of a quadratic function as both depth and velocity are linear. A post processor considers that the discharge is a linear function, so the integral is different, and sometimes the difference may be of about 15%. The discharge at the exit is also not the discharge given by the depth and the velocity but the value given by the listing when you have the keyword: CONTINUITY CORRECTION=YES
As a matter of fact the exit has a prescribed depth, which precludes solving the continuity equation, so the discharge is computed a posteriori as the flux that solves the continuity equation. When all is taken into account we find that the relative error in the mass conservation is about the accuracy of the solver, or the machine accuracy if you use the option TREATMENT OF NEGATIVE DEPTHS=2, because in this case the continuity equation is recomputed at machine accuracy.

With best regards,

Jean-Michel Hervouet

Thank you for your detailed explaination.

I have still some doubts, I tried different values for the 'cote initial', I have always the subcritical case flow.
And in this case, the exit is free '4 4 4', so I only prescribed a discharge at the enter, while I use the key word 'treatment of negative depths=2', my silumation cant run.

So what can I do for getting a hydraulic jump result if I decomment the fortran file? and If I plot the final discharge from the 'r2d_bumpcri.slf' gotten by the exact solution, the discharge will not be constant as the resons you said?

Thank you for your guiding sir,
jie