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Hi,

I am modelling a river bifurcation in Telemac3d having troubles with the liquid boundary conditions which varies in time.

I set 566 (LHBOR, LIUBOR, LIVBOR) for the inlet and 544 at the outlets (river branches after bifurcation). The problem is that ELEMAC is not reading the .txt file for the liquid boundary condition. Instead, setting the velocity at the conlim file in AUBOR or using the Keywords PRESCRIBED VELOCITY in the .cas file the model run ok but in both cases the boundary condition doesn't varies in time.

What could be the problem?
I attached the .cas and boundary condition file.

Best regards,

Gonzalo

Hi
The keyword PRESCRIBED ELEVATION and PRESCRIBED VELOCITY are missing in the steering file.
They should exists even if you use the LIQUID BOUNDARY FILE. The values given in the steering file are replace by the one in the liquid file.
To be sure of that, give unrealistic values and check the result

Hope this helps

Hello,

Yes, there are many pre-programmed possibilities for boundary conditions and it is somewhat misleading. In your case it is the keyword PRESCRIBED VELOCITIES that triggers the call to function VIT3 where a variation intime can be programmed. You can see this line 361 of subroutine bord3d.f, NVIT is the number of values given for this keyword (if NVIT=0 nothing is done so the values in the boundary conditions file are kept as constant). Then the variations in time depend on what you have programmed in function VIT3.

Note that 5 6 6 is a boundary condition for supercritical flow, is it really what you have ? I would expect rather 4 5 5 with free elevation and prescribed discharge.

With best regards,

Jean-Michel Hervouet

Thanks you both.
I thought that PREESCRIBED VELOCITY values supress the values set in the liquid boundary file.
About the flow regime, we want to study if there is a dependency of the Froude number in rivers bifurcation phenomena specially with the distribution of fluxes, width and solids transport in the river branches.
Because of this, we should model lots of cases in supercrítical and subcrítical flow regime.

Thanks,

Gonzalo

I set arbitray values for preescribed elevation and preescribed velocities, and the SL values in the liquid boundary file are recognized but i can figure out why is not reading VIT values.

I set velocities in the liquid boundary file from VIT=0.3 m/s at t=0 reaching VIt=0.75 m/s at t=70 s. But the result shows a velocity in the vertical W=1.39 m/s at the first time step and in the follwing time steps the velocity is zero at the inlet.

I can't figure out what is happening.

Best regards,

Gonzalo

Hello,

Could it be just a misunderstanding ? VIT and SL are functions called by telemac2d whereas the equivalent in telemac3d is VIT3 and SL3. Another point is that W is free at entrances as a default option, to have W=0 for example you need to uncomment a few lines at the beginning of bord3d.f.

With best regards,

Jean-Michel Hervouet