open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi, all.

I have some problems that need your help.

1. How to determine how large the time step should be set? Is there any formula?

2. How to determine the value of the keyword {COEFFICIENT TO CALIBRATE SEA LEVEL}? Should it be set to zero If the water level datum in the geometry file is MSL?

3. I compared the tide levels from TELEMAC3D and TPXO at boundary node 61 and found that they are very different. My understanding is that the water level at the open boundary is completely controlled by tidal forces. Is that right? So why is there such a big difference, is there something wrong with my steering file, and what should I modify?


Thanks!
Chuangwu Deng

It's really interesting...

Are you sure that the time for both model is coherent ? Since it's more like an offset of time. If I know well, it's UTC+0 for TELEMAC using TPXO model.

Hope it helps,
Grebe

Hi Grebe,

I'm not sure, because I don't know whether the time of TELEMAC will be affected by the keyword {ZONE NUMBERE IN GEOGRAPHIC SYSTEM}? Or has it always been UTC+0?
But the time of TPXO is UTC+0.

Thanks for your reply,
Chuangwu Deng

It's also UTC+0 for TELEMAC, you can use the keyword ORIGINAL HOUR OF TIME to set the exact time you want.
Do you have satisfying results compared with the mesured data or the astronomic tide ? If yes, you don't need to worry to much.

I'm just throwing out a suggestion, maybe someone could solve your problem

Regards,
Grebe

Hi Grebe,

I also compared the observations, but the results were terrible.














Thanks for your reply,
Chuangwu Deng

Hi all,

I finally know the reason for my third question, the keyword {ORIGINAL DATE OF TIME} interval symbol must be ";"

I would be grateful if someone could answer the first and second questions.

Regards,
Chuangwu Deng

Hello,

Good to read that you have succeeded in solving your strange issue. Indeed, you have to read user manuals carefully and follow expected format otherwise results may be wrong.

If the numerical schemes you use have Courant number constraints, you can use its formula to estimate the time step (relation between the time step, the biggest velocity and the smallest size of element, classical formula you can find else where).

If the bottom elevation is expressed in MSL, you can let the keyword COEFFICIENT TO CALIBRATE SEA LEVEL to its default value (0.) for your 1st computations. If you think the mean sea level is not good, you can tune this calibrating parameter to better fit what you expect.

Hope this helps,

Chi-Tuan

Hi Tuan,

Thanks for your help.
Your in-depth explanation has deepened my understanding of the model.

Regards,
Chuangwu Deng