open TELEMAC-MASCARET The mathematically superior suite of solvers

Dear All:

I'm running the Telemac2d model with three boundaries (one open H(FIRST BOUNDARY), two opne Q(SECOND AND THIRD BOUNDARY)), I put the boundary condition like follow:

PRESCRIBED ELEVATIONS = 0.;0.;0.
PRESCRIBED FLOWRATES = 0.;15.;15.

But when I run my model after two time steps, it give me this error:

DEBIMP : PROBLEM ON BOUNDARY NUMBER 3
GIVE A VELOCITY PROFILE
IN THE BOUNDARY CONDITIONS FILE
OR CHECK THE WATER DEPTHS



PLANTE: PROGRAM STOPPED AFTER AN ERROR

Which I can't understand, because before I run the model with other values of flowrates like :
PRESCRIBED FLOWRATES = 0.,100.;100.
The model can run succeed, but now I only changed the value it stopped.

Does anyone know my problem?

Thanks a lot.
Best wishes,
Qiang MA
2014-7-17

Dear All:

I find the same problem as me post before:

www.opentelemac.org/index.php/assistance...emac-2d-crash-for-bc

I check my initial depth:

INITIAL DEPTH = 0.002
but I also put rainfall in my catchment:

RAIN OR EVAPORATION = TRUE

RAIN OR EVAPORATION IN MM PER DAY = 2400.00

And also I used

VARIABLE TIME-STEP = TRUE

Do I need to modify my initial depth? Or used fixed small time step?

Best wishes,
Qiang MA
2014-7-17

Hello,

Your problem is probably not well posed. Check whether the boundaries are fluvial or supercritical. For example a free depth is not stable if the entrance is supercritical, and even with a discharge prescribed the depth can then tend to 0 and infinite velocities (whatever the initial conditions, I have already seen it).

Regards,

JMH

Thanks for your reply.

Follow your suggestion, we checked the Froude Number at the boundary. Yes, the Fr number at the boundary at very weird. as this picture:



At these two points the Fr values are around 35000.

We would like to ask you about is there any solution for this problem? Because we check the mesh, the mesh in this place seems ok. as follow:



There is nothing block the flowpath.

We wondering is it because my bounary is too short? As it only has 7 points as follow:



But we want to simluation the water from one street which can't be too wide...

Looking forward for your suggestions

Best wishes,
Qiang MA
2014-7-17

Hello,

You must have a prescribed depth at this boundary when the Froude number is greater than 1, so maybe you can start with a given depth, and once the Froude number is below one you can relax the depth and do a second computation.

Regards,

JMH