open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi!

I am modeling an inflow of concentrated sediment without bedload on a rigid bed. I use a previous computation file corresponding to steady state (T2D only, no sediment).
I then run T2D coupled with Sisyphe for modeling an inflow concentration of 200 g/L. This inflow boundary corresponds to an inflow hydrograph on the T2D model. This boundary is defined as LIEBOR = KENT (4), EBOR = 0. I defined my sediment parameters this way:

SUSPENSION =YES
BED LOAD =NO
SEDIMENT DIAMETERS =0.0001
INITIAL FRACTION FOR PARTICULAR SIZE CLASS =1
CONCENTRATION PER CLASS AT BOUNDARIES =0.;0.0755 /corresponds to 200 g/L on boundary nr 2
MASS CONCENTRATION =true /to have results in g/L

I made a first try with INITIAL SUSPENSION CONCENTRATIONS =0. but got wrong results. I made another try with EQUILIBRIUM INFLOW CONCENTRATION =true and REFERENCE CONCENTRATION FORMULA =4 which seems to work better, but the results are still not corresponding to what I expect. I also have wrong initial concentrations at T = 0s.

I want to model a sediment concentration inflow of 200 g/L for a varying discharge. I then expect the sediment concentration to be constant and equal to 200 g/L on my inflow boundary but it is not the case. It seems indeed that my concentrations are deacreasing as my liquid inflow increases. Is the mass of suspensed sediment entering my model equal to C x Q(t) ? It seems that it is rather C x Q(t=0) as my sediment concentrations near the boundary quickly decreases (they are of about 0.1 - 5 g/L whereas I expected maybe 50 - 200 g/L).

I also made a test with a liquid boundary file for sisyphe setting CG(2) to 200 g/L on the whole computation time, but I have the same results.

I join my t2d and sisyphe steering files.

It would be great if someone could tell me if I am doing something wrong is setting my boundary conditions. Especially regarding the units. As Cath wrote on a similar topic, and also by reading the manual, I understand that even with MASS CONCENTRATION =YES, the keyword CONCENTRATION PER CLASS AT BOUNDARIES should give adimensional concentrations whereas CG in liquid boundaries file give concentrations in g/L. Is that right?

Thanks a lot in advance!
PL

Hi!

I fixed my sediment concentration inflow problem, it was due to my boundary condition file. I found some info in a related post (www.opentelemac.org/index.php/kunena/17-...oncentration-imposed).
I hope the new manual will describe a bit more into detail how to define this file according to the T2D boundary conditions.

Regards
PL

Hi again,

I am now facing trouble with a abnormal deposition at the inflow boundary. Basically, material deposits constantly on one of my boundary node. I tried to modify my boundary in several ways but I still get this abnormal deposition which seems to highly affect the results downstream.

Does someone have any tips for that? For information, I have suspension only and non erodible bed.

Thanks in advance,
PL

Dear PL,
Did you take a look to the values of the shear velocity/shear stress near the boundary?

pablo

Hi Pablo,

No, I didn't so far. But I am now testing the option nr 2 for treatment of tidal flats with a minimum water height of 0,01 m and the results are better. Error on volume is now 1E-1 to 1E-3.

I will have a look at the shear velocity/stress.

Thanks,
PL

Hi Pablo,

The shear stresses are ranging from 30 to 70 Pa downstream the boundary but they are between 10 and > 300 Pa on the boundary itself.
My D50 is 0,1 mm. I am also modeling a rather high concentration, 200 g/L in a rather small discharge. The results are strange in the way that the maximum concentration is decreasing quickly downstream of the boundary whereas I don't have that much deposition in these areas.
If you have any tips...

Thanks in advance
PL

Dear PL,
below a couple of hints...:

(1) you can take a look to the recent post about 'dispersion coefficients', www.opentelemac.org/index.php/kunena/17-...efficient-in-sisyphe, probably these physical values have to be adjusted.

(2) I'm not sure about that, but you can explore different ways in which the flow enters into the domain through the use of the keyword 'VELOCITY PROFILES'

Please let me know,

I hope it helps,

Pablo

I had the same problem.

Try with FORME DE LA CONVECTION: 13

Good luck