open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello,

I would propose to modify the dimensionless-grain-diameter (DSTAR) dependent calculation of the critical shields stress in init_sediment.f back to the original Van Rijn calculation in which the critical shiedls parameter is 0.055 for DSTAR above 150.
Currently if DSTAR is between 70 and 150, the critical Shields parameter is higher than if DSTAR is higher than 150.

This may cause strange behavior in case of mixed sediment transport calculations?

It could be a discussion point, so it would be also possible to use a continuous function.


Best regards,
Clemens

Dear Clemens,
thanks for point us this issue. After some analysis, I also think it could be better to come back to the classical Shields curve representation by van Rijn, where the critical Shields parameter = 0.055 for D* > 150, even if the limit 0.045 has been proposed for several authors.

We can also propose an uniform distribution, as the one presented by Soulby & Whitehouse (1997). It will be taken into consideration for the new release of the TMS.

Many thanks again,

Pablo

Hello,

to warm up a 2 years old post since I have to write in the context of a report about this topic. I want to propose again to change the upper threshold for the critical Shields stress in init_sediment.f from 0.045 to the original value of 0.055.

It or I may seem pedantic but again I want to illustrate the issue:
given all the default keywords for the densities etc. in the Sisyphe steering file, using the VanRijn parametrization implemented in Sisyphe and doing the exercise for the two diameters:
d=6mm -> Dstar = 151 -> Shields crit = 0.045
d=5mm -> Dstar = 126 -> Shields crit = 0.053

gives a higher critical Shields stress for the smaller diameter.

In my view this is not logical. Other limits for the critical Shields stress proposed by different authors should be discussed independently.

Best regards,
Clemens