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Hi everyone,

I am hoping to replicate an amphidromic point within a simple rectangular domain of flat depth.

To achieve this, I made the west and east boundaries as solid wall. North and south boundaries are open allowing water to flow and move out from the domain.

By selecting the open boundaries to be driven by prescribed velocities, I managed to simulate the amphidromes but faced with the problem of water elevation instability (increasing all the time). I tried to manipulate the boundaries with prescribed elevations but this in return diminish the amphidromes.I also used a variety of boundaries option combination which do not solve my problem.

My question to the forum users is have anyone of you tried this exercise before? Will be glad if someone could shed some light or though on this matter.

Thank you in advance.

Regards,
Jack

Hello,

Yes, you need to have an elevation prescribed somewhere. In your case maybe the Thompson boundary conditions would be OK, consisting of prescribing both velocity and elevation, Thompson taking only what is relevant with the theory of characteristics.

Regards,

Jean-Michel Hervouet

Hi Jean-Michel,

Thank you for the reply.

For now, I am prescribing my open boundaries as 'free or prescribed' option 1 for liquid boundaries, through keywords.

Pardon me but are you referring that I should use option 2 instead? If that is the case, I should create a liquid boundary files of velocities and elevations? I tried with selecting option 2 and using prescribed keywords velocities and elevations, the result is relatively similar to that of option 2.

Thank you.

Cheers,
Jack

Hello,

Yes I was refering to option 2. Another solution is to have the elevations prescribed and the velocities free, it is not well posed but sometimes work (generally when the velocities are small).

Regards,

JMH

Hi JMH,

Thank you for the tips. I think I managed to solve the problem partially if not fully.

Cheers,
Jack

Hi JMH,

I ran into a new issue with the liquid boundary files.

I am trying to specify velocities (U and V) within the .lbf file. From the manual of TELEMAC2D, it mentions to use U and V variable names. For my case, I only have one open boundaries to be driven by velocities. I tried with various types of names (U(1), V(1), UV(1), VU(1) and VV(1)) but none of them works hence giving me an error preventing the run execution.

Previous run with flowrate (Q) and water level (SL) works fine.

I attached the .lbf file here as well for your reference.

Hope you could shed some light on this matter.

Regards,
Jack

Hello,

It is VIT. We'll look at the documentation to see if it must be amended.

Regards,

Jean-Michel Hervouet