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Hi,
I am running a simulation of an intake channel.
I have imposed elevation (SL) at the outer boundaries, and negative discharge (Q) at the intake.

The simulation run properly for 1 day of the simulation time.
However after 1 day of simulation tide the flow-rate at the intake boundary points becomes zero, as shown in the attached graph. I have given the discharge through a liquid file for more than 1 day of simulation.

Do I need to change any simulation parameter in the case file.

Gourish

Hello,

Without the geometrie file, I can not conclude about the problem, however, there are some questions about data you have sent.
You impose a negative flowrate but you check the velocity only at one point (your graph). The graph gives probably the right velocity at that point (which vanished after 1 day, maybe because the area around it is drying) and the value of the desired flowate is imposed properly at the remaing nodes of the liquid boundary.
In conclusion:
1-try to verify that there is enough water in your domain and especially in the area close to the intake
2-the velocity at 1 point can not give a complete idea about the correct imposition of the flowrate. you need to check the value of the flux going out of the domain at this location (this information is given, for instance, in the listing).

I hope that it was helpful.
With my best regards.

Riadh Ata

Hi Riadh,

Thanks for the reply.

The flux listing at liquid boundary 2, that is the intake boundary shows a near constant outflow of 5.55 m2/s up to 1 day of simulation, after that the flow-rate varies according to the tidal variation.

I have tried imposing velocities earlier in which case the discharge varies with tidal variation.

I have not checked the velocities and the water level in the region,
I shall analyze these results again as you have have advised.
I am attaching the geometry file of the simulation.

Thanks,
Gourish

Hi,
After analyzing the free surface value a the point mentioned earlier,
I have found that the area indeed becomes dry, as indicated by the attached graph.

The value keeps on persisting after 1 day of simulation even water enters from the entrance of the channel.

I there any method to analyze problem, like writing out the value of any variable in the simulation, so as to see why the nodes shows constant negative value after 1 day of simulation?

I have run the simulation without intake and there is sufficient water at all time step available at the particular mentioned point.

Gourish

Hello,

You should declare TIDAL FLATS = .TRUE. to understand better what happens, maybe it is an oscillation that dries a point and then it goes wrong and stays dry, with even negative depth.

Regards, JMH

Hi Jean Michel Hervouet,

I have already given the option
TIDAL FLATS = YES
in the case file tidebound.cas.
And yes, the results shows oscillation at the boundaries when it goes dry.
Is there any other parameter which influences this effect ?

Thanks and Regards,
Gourish

Hello,

Yes, I had a closer look at your steering file, and you are running with the primitive equations, with a risky solver 2 in that case (primitive equations have a linear system which is not symmetric, and conjugate residual waits for a a symmetric system).

So either you stick with primitive equations but you use :

SOLVER : 7 / GMRES
DISCRETIZATIONS IN SPACE : 12;11 /quasi-bubble for avoiding inf-sup oscillations

or you move to wave equation (much less expensive) :

TREATMENT OF LINEAR SYSTEM : 2
and if it still gives oscillations try:
FREE SURFACE GRADIENT COMPATIBILITY : 0.

With best regards,

Jean-Michel Hervouet

Hi, Jean-Michel Hervouet

Thanks a lot,I shall try the options as you have mentioned.

With best regards,
Gourish

Hello Gourish

I guess that there is a small typo in the last post of Jean Michel (Correct me Jean Michel if I'm wrong).
FREE SURFACE GRADIENT COMPATIBILITY : 0.9 and not 0.
You can decrease this value a little bit more if the observed oscillations are still there.

With my best regards,

Riadh ATA

Hi, JMH,

Currently as you have mentioned earlier I am using primitive equation for the solver option, that is the finite element method. I also intent to use the other solver option that is the finite volume method, so that I can check as how the simulation behaves differently.

What are the other options which I may have to change and include if I use
the finite volume method equations.

Regards,
Gourish