open TELEMAC-MASCARET The mathematically superior suite of solvers

Dear all,

how do we decide which treatment (TREATMENT FOR NEGATIVE DEPTH) is best for tidal flat (TIDAL FLAT) simulation.

Thanks,
Sathish

Hello,

Well generally the negative depths of treatment 1 are not a problem (order of minus a few centimeters) and do not absolutely spoil mass conservation as these negative depths are integrated in the mass balance, and this treatment is chepar in computer time (see e.g. the test case malpasset). Now people prefer to have positive depths and also in 3D it is better because the mesh is based on the depth. Note that treatment 2 is a post-processing of treatment 1 where the fluxes that would bring negative depths are eliminated, and a better continuity equation is obtained, and this gives a second difference :

with treatment 1, the accuracy of mass conservation depends on your accuracy of the solver.

with treatment 2, the accuracy of mass conservation is the machine accuracy.

With best regards,

Jean-Michel Hervouet

Dear Jean-Michel Hervouet,

So treatment 1 (smoothing) is good for telemac2D and treatment 2 (masking) is good for telemac 3D, right?

I read a paper titled "Review of wetting and drying algorithms for numerical tidal
flow models" mentioned ELEMENT REMOVAL method is excellent in telemac2D for all the schemes (FD,FE and FV).

Hello,

Hum, I do not like very much the element removal or masking option, e.g. because the mass balance of water remaining in removed elements is not well done. This option is rather for steady state (but by the way it is a different keyword : OPTION FOR THE TREATMENT OF TIDAL FLATS, while we were talking about TREATMENT OF NEGATIVE DEPTHS...).

Regards,

JMH

Dear JMH,

Yes it is. I am just confused what kind of combination have to take for the simulation.
TIDAL FLAT =YES
OPTION FOR THE TREATMENT OF TIDAL FLATS =1
TREATMENT OF NEGATIVE DEPTHS =1
THRESHOLD FOR NEGATIVE DEPTHS = 0 ( is it ok to keep zero???)

should i use H CLIPPING and MINIMUM VALUE OF DEPTH ??

thanks,
Sathish

Hello,

So :

TIDAL FLATS =YES
OPTION FOR THE TREATMENT OF TIDAL FLATS =1
TREATMENT OF NEGATIVE DEPTHS =1 or 2 (2 for strictly positive depths)
THRESHOLD FOR NEGATIVE DEPTHS = 0 / yes, this is a treatment to avoid too negative depths that is used with the option TREATMENT OF NEGATIVE DEPTHS =1, as 0. is the default value, you can remove it.

should i use H CLIPPING and MINIMUM VALUE OF DEPTH ?? No, this is not mass conservative.

Regards,

JMH

Dear Jean-Michel Hervouet,

Can you tell me if one uses:

Option for tidal flat TIDAL FLATS =YES
OPTION FOR THE TREATMENT OF TIDAL FLATS =1
TREATMENT OF NEGATIVE DEPTHS = 2

So the WET-DRY Condition used here is Element removal algorithm or Negative depths algorithm.

Regards
Preeti