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Hello everyone,

in my model i want to use a stage discharge curve for the river inlet. I selected for the boundary condition at the inlet a "PRESCRIBED ELEVATION" as recommended in the telemac manual and according option 2 "discharge as function elevation" for this boundary. However in the simulation the discharge at the inlet is different (quite higher) as the according value in the stage discharge curve file. The free surface elevation at the boundary is correct from the liquid boundary file. Is there any reason why this is so?
Or maybe it is better to use for the inlet in my boundary file a 5 5 5 condition and describe the discharge as well as the elevation in the liquid boundary file?


In the following i listed the stage discharge curve file and the liquid boundary file.

#
#Boundary 1
#
Q(1) Z(1)
m3/s m
45 417.77
60 417.97
88 418.27
109 418.47
145 418.77
172 418.97
213 419.27
242 419.47
287 419.77
316 419.97


# Transient liquid boundary conditions file
# Created on May 5, 2015
T SL(1) SL(2)
s m m
0.0 418.24 413.65
1800.0 418.24 415.88
18000.0 418.24 415.88
180000.0 418.24 415.88

Best regards,

Markus

Hello,

This is not well posed. At an entrance you should prescribe the discharge, and let the elevation free, provided that the entrance is in fluvial regime. There is no need of stage-discharge curve here. If it is an outlet, it is better to have the elevation as a function of discharge.

With best regards,

Jean-Michel Hervouet

Hello Jean-Michel,

ok thank you. I thought that it would be a good way for create a stable initial condition, because if i only used discharge at the inlet my simulation gets unreasonable high velocities and water depths at the inlet. But i guess that i have a mistake somewhere in my steering file. Maybe you can give me some hints. I attached my case with all files.

Best regards,
Markus

it is not possible to add the geometry and the initial file. i guess because they are to large?

Hello,

If the conditions at the entrance do not work, is it because the regime is supercritical at the beginning. You have nothing on initial conditions in your steering file, and the question is what is the initial depth at the entrance. If there is no depth, the entrance will be supercritical and in this case you must prescribe both depth and velocity. It is better to have an initial depth.

Regards,

JMH

In this case it is not possible to describe the initial depth with the INITIAL CONDITIONS Keywords because my geometry consists of the river channel as well as the area outside, which is relevant in case of a flood event. I added 2 picures of the bottom mesh.

So i created an initial condition, in blue kenue, mapping a polygon with a value of 2 to a mesh with elevation of 0m and add this as water depth. So i have only in the channel water.

I didn't find any better solution doing this so far.

Best regards
Markus

Hello,

i'm sorry that i have to ask again for some advice. If i want to use now a stage discharge curve at the outlet in order to describe the free surface elevation in dependence on the discharge there. So i prescribed discharges at inlet (positive) and outlet (negative) as well as a stage discharge curve file. Using the according keyword with value 1:Z(Q), the simulation runs with the correct prescribed discharges but the elevation at the outlet is not the according value from the stage discharge curve. So i dont know how to solve this..

Is there an other method to include information on discharge and elevation at the boundaries? Or is this a result of other wrong parameters like friction, numerical schemes..

Best regards

Markus

Hello,

There is no need to prescribe a negative discharge at the exit, it must remain free, only the elevation will be given by the stage discharge curve. Make sure that your initial conditions are within the range of the curve. A typical use of a stage discharge curve at an exit is to start from a steady state flow, then to precribe a flood at the entrance. It is very difficult to have a stage discharge curve working if you do not start from an existing situation with some discharge at the exit.

With best regards,

Jean-Michel Hervouet