open TELEMAC-MASCARET The mathematically superior suite of solvers

Good morning!
I have two simple questions. I read the manual, but I coudn't find the answer there.
1. How does the model handle an "open boundary with free depth (LIHBOR=4)" mathematically? Does it use the average bottom slope to estimate flow depth?
2. In setting a flow hydrograph as upstream boundary condition (Q [m3/s] vs. t [sec.]) in FUDAA, I see that the units displayed on the y-axis in the Time Curves Editor are "RATE [m2/s]". Is this a "misprint" or am I supposed to actually enter flux values (i.e., Q/width; m2/s) instead of flow (Q; m3/s)?
Thanks in advance
Roberto

Hi
I couldn't answer to the first question but i'm sure Jean-michel will do this soon.
For the second question in Fudaa i could tell you that this is a misprint and the entered value for discharge are in m3/s

Hope this helps

Hello,

To answer the first question : a point with free depth is treated like any degree of freedom, regardless of the fact that it is on a boundary, so the depth is computed here as for other points.

JMH

Good afternoon.
I have three small questions regarding the stage-discharge curve at the lower boundary of a simple river model:
1) what type of boundary should I select in FUDAA to impose a stage-discharge curve?
3) a boundary of type "Liquid" in FUDAA creates a boundary of type 4 5 5. However, I found a post that says one should use a 5 4 4 configuration. Which one is correct?
2) what is the difference between Q(Z) and Z(Q) in STAGE DISCHARGE CURVES and how does this affect the columns in the stage discharge curves file?
Thanks a lot.
Roberto

Hello,

The natural way to have a stage-discharge curve at an exit is to have Z(Q), thus a boundary of 5 4 4, the columns being Q(1) and Z(1) for example. Beware initial conditions, it is better to start without stage-discharge conditions if you do a cold start (Q = 0), otherwide Z corresponding to Q=0 will be imposed at the beginning. It is thus better to restart from a steady state within the range of the curve.

Regards,

Jean-Michel Hervouet

Good morning!
Thanks a lot for your help!
Unfortunately, the model still produces some strange results:
If I set the boundary nodes to 5 4 4 in the conlim file, what value for HBOR should I give there? FUDAA sets HBOR to zero, as well as PRESCRIBED ELEVATIONS for that boundary. Are these values automatically overridden by STAGE-DISCHARGE CURVES? I ask because I am getting zero depth at the lower boundary after ca. 25% of the simulation time.
I took the liberty of attaching my case, maybe you'll find a moment to have a look?
Thanks again!
Roberto

Hello,

You seem to have the problem of a cold start. Your stage-discharge curve states that Z=0 for Q=0, so if you start with Q=0 you will have Z=0. You should try to have an initial condition with water everywhere (Fudaa can do that), and tend to some steady state before running a case with the stage-discharge curve. In this case you will have to give also :

PRESCRIBED ELEVATIONS = ... in your steering file.

With best regards,

Jean-Michel Hervouet

Good afternoon.
I am trying to run a river model with a stage-discharge curve as downstream boundary condition and a discharge curve upstream. When the model starts, everything looks fine, and the listing printout shows the values of the stage-discharge curve.
The problem is: when I look at the results, the water surface at the downstream boundary is equal to the first water surface value of the stage-discharge curve, and stays like this throughout the whole simulation even though more water is coming in from upstream. It is as if the model reads only the first value in the stage-discharge curve.
What would you suggest?
I attached the data for this model.
Thanks a lot.
Roberto

Before using the stage discharge curve, run a first simulation in order to obtain a non zero discharge at the output.
Then make a hot start with the stage discharge curve

Dear J.M. Hervouet,

I have a problem with my simulation...



Here my files

CAS FILE

BOUNDARY

GEOMETRY

DISCHARGE CURVE



I still can not figure out where mistake.

Best Regards