open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi community,

I'm quite a beginner user with Telemac and I would like to get some more information about a model I want to create, and most of all know if this project is possible or not.

I already have been doing a full study on telemac, modelling flooded area of a river due to intense rainfall.

Now I want to improve my Telemac skill, working on another model. This study focus on an hydroelectric plant. I want to make a model including the river which supply water to the plant, the dam and the intake. My main concern is simple. My boundary conditions will be near the study area. Basically I want to create 3 boundary conditions. The first one, in the main channel would be my inflow, which would be constant to make the model simple at first time. My second boundary would be at the dam. I'm wondering if it's possible to set the outflow at the dam by creating a curve-discharge law. Finally, my last boundary condition would be the outflow in the plant, in the downstream part of the intake. Once more I think it would be wise to set a curve-discharge unit to model the turbine.

As I have never made this kind of model, and as I didn't see any example able to confirm it's possible I wanted to get your opinion. Is it possible to create an relevant model with such conditions ? I'm afraid my boundary conditions will be too close to my study area.

I have already been doing a preliminary model, but I don't get the result I was excepted, that's why I'm asking more skilled people about what they think.

I hope I managed to be clear and understandable by everyone. If you want more details on what I want to do, please feel free to ask. I could also upload a little drawing about the study area.

Regards,
PHD

Hello,

Things similar to what you plan to do have already been done in studies. Stage-discharge curves may be used, but probably with some care. I anticipate that you will have to write bits of Fortran to get exactly what you want, or tune the relaxation in stage-discharge curves to avoid wild oscillations (if the discharge depends on the elevation of a very local point, this may trigger an artificial resonance). One decision to make before starting is whether you model the entry and exit of the turbine by liquid boundaries of with sink and source terms. Sink and source terms, or even a culvert with a specific law could perhaps do the job simply.

Regards,

Jean-Michel Hervouet

Thank you for your answer.

I didn't find similar studies, maybe I should try to search a little bit more to have a practical example.

I'm taking notes about your advices. I'm trying to finalize a preliminary study in order to be sure to be able to set up the model.

About the dam, would it be wiser to set up a weir law to determinate the outflow ? I read on the manual that the distance between each point of the weir has to be the same. So if I choose to set up a weir, I should make on BlueKenue the correct meshes, which one allow same distance between each point right ?

Regards,
PHD

Hello,

If the dam is not overflowed with water, it is just an obstacle in the river, the water flowing through a turbine ? In this case the dam is just a solid boundary, and a culvert with ends on either sides of this obstacle will do the turbine ? In this case also the mesh could be in two disconnected parts (Telemac can do it, see e.g. the test case weirs, but for the mesh generators, I am not sure).

JMH

The dam is overflowed even in a steady case. Water going through the turbines take a canal few meters upstream of the dam. I can do a culvert to model the turbines but I should also make a weir law at the dam I think.

I tried to set up the model using a weir. When i run telemac, if I have too much point in my weir file, I have an error running which is maximum iteration. I tried to run the model with only few point as weir (5 or 6 for example) to see if it's running well. On the upsteam part of the dam, the volume keep growing because of the inflow, the water depth at the dam keep growing as feel but the is not overflow on the weir. At the downstream part I set up a boundary condition with prescribed elevation. But as there is no inflow, the downstream part is doing crazy things.

When you create a weir, do you to set a boundary condition at the weir points ? if yes which one of them ? I let a solid boundary thinking that the weir file will change that condition.

Hello,

OK, so if the dam can be modelled as the bottom topography it would be all the better (this assumes that the dam is a kind of underground dyke, not a vertical concrete wall), otherwise yes a weir would be OK, and you need not have many points.

Regards,

JMH

In fact you are right. I have take into account the dam when I created the mesh. The dam is include in the bottom topography.

So, according to you, it would be ok to set up a boundary condition (prescribed elevation) at the dam, isn't it ?

That's the first thing I tried. But my problem is with the stage-discharge unit. Telemac seems to take the stage-discharge file but the is no upper/lower bound. So at the very beginning of the simulation (in the first step of calculation), all the water in my river is going through the turbine. Maybe this come from my stage-discharge file.

Here is it :

#Stage-discharge curve boundary 1
#
Q(1) Z(1)
m3/s m
0 3.95
10 4.10
20 4.20
50 4.30

At the beginning of the simulation, the water depth at my stage-discharge unit is egal to 3.89. So accordind to what I read, the outflow must be 0 at the beggining, until the water level increase. Am I right ?

In the end, it's like there is no dam, because my turbine let all the flow goes. As excepted, the hydraulic gradient is bigger along the intake canal than at the dam which in one hand can explain my result. But in other end, if I understand well how the stage-discharge unit should work, my outflow must have a maximum.

Hello,

If the dam is in the bottom topography, you can just let the water flow over it.

As for the stage-discharge curve, the problem is that you expect it to work as Q(Z) and this will be only in the next version, now it works only as Z(Q). A culvert would work more like what you expect: a discharge increasing when the elevation increases.

Regards,

Jean-Michel Hervouet

Thank you for your help,

I will adapt my model and use a culvert instead of a stage-discharge unit then.

I hope I will not have to bother you anymore.

Regards,
PHD