open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi
I am tring to learn how to coupled telemac3d with sisyphe.I found an example SISYPHE BUMP2D to learn it.But I got comfused by the command LAW OF BOTTOM FRICTION.
In t2d_bump2d-t2d.cas LAW OF BOTTOM FRICTION was set to 0 means no bottom friction,however in sis_bump2d-t2d.cas LAW OF BOTTOM FRICTION was set to 5 and FRICTION COEFFICIENT was set to 0.025 that means Nikuradse Law was applied and the friction coefficient is 0.025.
My question is the command LAW OF BOTTOM FRICTION,what is the difference between in t2d.cas and sis.cas?


THANKS!!!

Hi Jason,

the example bump2d is a little special because it uses the Grass formula. With this formula the transport capacity is calculated directly from the velocities and not from the shear stress. Usually the roughness is used for the shear stress simulation. Therefore in this special case no roughness is used neither in the hydrodynamic (LAW OF BOTTOM FRICTION = 0) nor in the morphodynamic (due to Grass formula).

Usually the friction coefficient is given from telemac to sisyphe. LAW OF BOTTOM FRICTION and FRICTION COEFFICIENT from sisyphe are not used. The 2 keywords are still in sisyphe in case of BED ROUGHNESS PREDICTION = YES. In this case sisyphe is calculating the bed roughness and gives it back to telemac.

If you start with morphodynamic modelling it would be best to start with gaia instead of sisyphe. Gaia will replace sisyphe in the future.

Best regards,
Rebekka

Hi Rebekka,

Thanks for your reply!

I have tried the example bump2d in Gaia and Sisyphe.I got different result,it should be same right?

Best regards

Hi Jason,

Gaia and Sisyphe give the same results for this test case. Which version are you using ? Have you changed some parameters in the steering file?

Best regards,

Sara

Hi Sara,

Thanks for your reply!

My version is v8p1r0.Is it the lastly version?I just upgraded it from v7p3r1 last month.
I didnt change the parameter.

Best regards,

Hi again,

I've got it, you are right, there is still a bug in v8p1 which has been fixed for the next version (it concerns only this test case).
To fix it, you should just multiply by XMVS (sediment density) the Grass formula which is in the user fortran (user_bedload_qb). Then you should get the same results.

Hope it helps,

Sara