open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello everyone,

I'm currently acquainting myself with the software by modeling a straight rectangular canal with subcritical flow. I've set the flow rate at the inlet and depth at the outlet. Initially, I calculated the normal and critical depths as 0.091 m and 0.048 m, respectively, with the following parameters:

• flowrate = 0.01 m3/s
• channel width = 0.3 m
• slope = 0.01
• manning coefficient = 0.04

However in the results of the model the depth upstream of the outlet seems to tend towards around 0.075 m:



Shouldn't the results tend towards the normal depth of 0.091 m ?

Thanks in advance.

Hello Jonathan,

I cannot run your example. The boundary conditions file is not consistent with the geometry file you provide.

Anyway, I have a few additional remarks concerning these input files:
- you prescribe a negative elevation at the outlet whereas the minimum bottom elevation is equal to 0, hard to do (in particular if TIDAL FLATS = 0),
- you have 2 overconstrained triangles in your mesh (2 corners of your rectangle),
- option VARIABLE TIME-STEP = YES does not work well with Finite Elements, please use a constant time step if you want to use Finite Elements method (or switch to Finite Volumes method),
- I would not start with STOP IF A STEADY STATE IS REACHED = YES,
- there is a validation example called friction, you can have a look at it in the TELEMAC-2D validation document + folder in the examples.

Hope this helps,

Chi-Tuan

Hello,

in your manual calculation for uniform flow take the water depth instead of the hydraulic radius and you will be happy.

Best regards,
Clemens

Thank you very much, that is the depth the model was reaching.

Does that mean that to include the effect of the walls I would need to activate friction on the walls or add them to the bottom geometry ?

Best regards.

Hi,

You could try to apply a wall friction since Telemac-2D supports that.

Best regards,
Clemens

Thanks, I will give that a try.

Take care,
Jonathan.

Thank you very much for your suggestions. I've applied them, and the model is now running smoother.

The negative elevation at the outlet is because the bottom at that point is at an even lower negative elevation. Would it be a good practice to set the lowest point of the mesh at zero elevation?

Kind regards.

My apologies, the geometry file was not the correct one, which is the one that I'm attaching now.