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TOPIC: problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE"

problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10716

  • tzqncwu
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Hi, everyone,

I want to use the keyword "STOP IF A STEADY STATE IS REACHED" and then set it as "YES", but the run process only take 1 second and tell me the steady state is reached, I don't know what the problem is. the main setting in my cas file is as follows.

INITIAL CONDITIONS = 'ZERO DEPTH'
PRESCRIBED FLOWRATES = 700
PRESCRIBED ELEVATIONS = 0
VELOCITY PROFILES = 2

However, when I set the initial condition as follows, telemac2d will compute for several hours(3 hours plus), the only difference between the two runnings is the prescribed elevations, one is zero, one is non-zero which should be more than 9m, or else the running is the same as above.


INITIAL CONDITIONS = 'ZERO DEPTH'
PRESCRIBED FLOWRATES = 700
PRESCRIBED ELEVATIONS = 10
VELOCITY PROFILES = 2

the attached file is the boundary file, the running state when the prescribed elevation is 9m and 10m seperately, which have different volume in the domain.

I want to set a inflow and start as a dry river to get a steady state of the river, so am I right use the initial condition as zero depth? I have tried many settings in cas file but failed. I don't know how to set the initial condition such as prescribed flowrates, prescribed elevation, etc. when I use the keyword "zero depth" and the "STOP IF A STEADY STATE IS REACHED". I have checked all the validation examples, there is no case using the zero depth. I was still confused.

Any help will be appreciated!
yajuan
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problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10723

  • jmhervouet
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Hello,

This keyword STOP IF A STEADY STATE IS REACHED goes with another one:

STOP CRITERIA : 1.E-4;1.E-4;1.E-4

which is 3 numbers set by default at 1.E-4 but that probably need to be changed in your case. If the difference between two time steps of the depth and 2 components of velocity is less than a given value, the program will stop.

Anyway do not put this keyword to start, you can use it after a first run.

Now you can start with no depth in the river, however you will need some water at the entrance, so that the program deduces velocities to get the correct discharge. Another possibility is to start by a supercritical flow and prescribe both depth and velocity at the entrance (it is nothing but reality if you start from a dry river). Then in a restart you can relax the prescribed depth.

Regards,

Jean-Michel Hervouet
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problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10733

  • tzqncwu
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Dear JMH,

Thank you for your quick reply.

I have tested as you suggested using another keyword STOP CRITERIA as default values, it did run.

The attached files are the result of the running, the running state of telemac2d, and my initial conditions in cas file.

Can you check for me where I am wrong, because all the waterdepth is zero.

Expect your reply again.Thanks a lot.

yajuan
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problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10735

  • pilou1253
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Hi!

I did not have a close look at your case, but I've seen that your solver accuracy is 1E-2.
I think you should try first to decrease it (take default values to start with) so that it is consistent with the stop criteria (1E-4)...

Good luck!
PL
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problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10736

  • c.coulet
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Hi
I do not understand how you could say the water depth is 0?
The mass balance indicates that the volume in your domain at the end of the computation is positive so it seems you have some water somewhere in your model. Any advice?

Regards
Christophe
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problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10737

  • tzqncwu
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Hello,

Thank you for your quick reply!

I checked the results of telemac2d running, the flow should go from the upstream to downstream, however, it goes to the opposite direction in velocity result, am I wrong in the initial conditions? am I wrong in the initial condition files when I set the U and V values for the upstream? and maybe because of this reason, the waterdepth in the area is zero.

The attached files are the velocity direction error, the boundary file and the zero waterdepth.

I am confused, any help will be very appreciated!
Best regards!
yajuan
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problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10738

  • c.coulet
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Hi
Probably due to the option for velocity profile.
Try to use option 1 instead of 2

regards
Christophe
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problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10740

  • tzqncwu
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ok, I will have a try. If I get the correct results, I will tell you. thank you!
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problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10744

  • tzqncwu
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Hi, Coulet,

I have tried to change the velocity profiles to 1, but get the same result. then I think maybe the velocity I prescribed in the boundary file is positive and the velocity direction is not correct, now the velocity is minus value, however, when I run the telemac2d, it shows the following error,

"EXCEEDING MAXIMUM ITERATIONS"

I only changed the velocity from the positive to minus, which can influence the iterations?

the attached files is the error.

Best regards!
yajuan
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problem when using keyword "ZERO DEPTH" and "STOP IF A STEADY STATE" 11 years 1 month ago #10748

  • c.coulet
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Hi

In my opinion, one problem is in the fact you want to impose an important dischage on a dry model...
You could try to use a slow variation of the discharge from 0 to 700, it will help the convergence.
Another problem comes probably from the fact you want to impose Velocity instead of discharge...

The solver reach a maximum iteration because it can reach the convergence criteria, sometimes because the time step is too high, especially if you manage a shock in your model.

Regards
Christophe
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