open TELEMAC-MASCARET The mathematically superior suite of solvers

hou to insert a hydrograph in telemac2d?

Hello,

First you must have the keyword PRESCRIBED FLOWRATES in your parameter file (otherwise Telemac will just look at the boundary conditions file). So if you have 2 liquid boundaries, just put :

PRESCRIBED FLOWRATES : 0.;0.

to start with, the values given will have no importance.

Then you can program function Q or more simply you can have your hydrograph stored in a file called LIQUID BOUNDARIES FILE:

This is a text file edited by the user, it has the following format:
A line beginning with the sign # is a line of comments.
It must contain a line beginning with T to identify the value provided in this file. Identification is by a mnemonic identical to the name of the variables: Q for flow rate, SL for water level, U and V for velocities and T for tracer. An integer between brackets specifies the rank of the boundary in question. This line is followed by another indicating the unit of the variables.
The values to be prescribed are provided by a succession of lines that must have a format consistent with the identification line. The time value must increase, and the last time value provided must be the same as or greater than the corresponding value at the last time step of the simulation. When TELEMAC-2D reads this file, it makes a linear interpolation in order to calculate the value to be prescribed at a particular time step. The value actually prescribed by the code is printed in the control printout.
An example of an open boundaries file is given below:
# Example of open boundaries file
# 2 boundaries managed
#
T Q(1) SL(2)
s m3/s m
0. 0. 135.0
25. 15. 135.2
100. 20. 136.
500. 20. 136.


Make sure that the boundary number you give is correct (it is the order of the boundary conditions file, the first liquid boundary appearing in this file is number one).

That should do it and if not, just ask,

Regards,

Jean-Michel Hervouet

Thank you. I would like to simulate a dambreak case with a big dry area. Could you help me with the boundary and initial conditions. I have a hydrograph derived by the breach simulation.

OK, so in this case the breach should be an open liquid boundary of your initially dry domain. In this case it could be that the flow will be supercritical and you should probably also prescribe the free surface elevation at the breach.

Regards,

Jean-Michel Hervouet

Thank you Jean. The problem is the initial water surface level. Inlet has the hydrograph as liquid boundary condition. Initial water surface must be zero, as well the depht, but the results are also zero water level. How can I put just initial water level on the breach?

Regards, Debastiani

Hello,

You can prescribed any form of the initial water level by programming it in the subroutine condin.f, provided that you say in the parameter file :

INITIAL CONDITIONS : SPECIAL

Then go into condin.f and follow instructions.
Another possibility is to start a few time steps prescribing both discharge and depth, and then you can do a second computation where the free surface elevation is released.

You can also build initial conditions in the Fudaa interface.

Hope this can help,

Jean-Michel Hervouet

OK, thank yiu againg, Jean Michel.
You mean build the initial condition in Matisse?
Do you have any project or report about a problems that looks like mine. Imagine you have a rectangule as dry bed and a hydrogrpah located in part of one face of the rectangule. No more data. My mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Thank you

Hello,

No, the initial conditions can be built in Fudaa, not in the mesh generator, but forget this, your case is very standard, just try the LIQUID BOUNDARIES FILE as explained in my previous posts, and to start with give the discharge and a temptative free surface elevation at the entrance. Your boundary conditions file must start with 5 5 5 on the lines corresponding to points of your entrance (so that velocities and depth are prescribed). You should then see the water entering your domain.

With best regards,

Jean-Michel Hervouet

thank you. just one question: and what about the other boundary number? could i insert 4 4 4 for the other and 5 5 5 for the breach? i dont know why, but it doesent work with that configuration.

Hello,

In your case, the exit of the canal has no depth at the beginning, and then the flood will come, and you do not know whether it will be fluvial or supercritical flow. It may work if you put all free (4 4 4) but sometimes it will blow up. If you have no data of free surface elevation, I would advise to try the "incident wave" boundary condition, i.e. 1 1 1 in the boundary conditions file. However used in these conditions it will tend to give lower elevations than reality. Once there is a flow at the exit, you can then change the condition at the exit, e.g. by prescribing the observed elevation.

Try all this and if you are stuck, send your files and we'll look at it.

Regards,

Jean-Michel Hervouet