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Hi,

I am trying to simulate sediment resuspension caused by wind in a shallow lake but I am getting results files with nil values (zeros).

Below are my Telemac2D and SISYPHE cas files.

I don't really know how to specify the boundary conditions but I followed the examples and I am using the same CLI file I was using for the hydrodynamic simulation. I am not sure if this file needs to be modified when coupling with SISYPHE. In my model, currently all boundaries are wall type and the CLI file looks like:

2 2 2 0.000 0.000 0.000 0.000 2 0.000 0.000 0.000 169 1 #

With only the last two numbers changing in a list of 240 lines.

Any help much appreciated!

Jose

****************Telemac 2d CAS FILE ******************

WIND =YES

COEFFICIENT OF WIND INFLUENCE =1.2615E-5

LAW OF BOTTOM FRICTION =0

TURBULENCE MODEL =1

VELOCITY DIFFUSIVITY =0

INITIAL CONDITIONS ='CONSTANT ELEVATION'

INITIAL ELEVATION =0.05

TYPE OF SOURCES =2

ABSCISSAE OF SOURCES =1993952

ORDINATES OF SOURCES =5668392

WATER DISCHARGE OF SOURCES =0

FORTRAN FILE ='user_fortran-v7p3'

DROGUES FILE ='Drogues.dat'

STEERING FILE ='Whakaki_50m_test.cas'

GEOMETRY FILE ='geometry_Whakaki_50m.slf'

RESULTS FILE ='Whakaki_5m_test_results.slf'

BOUNDARY CONDITIONS FILE ='bc_Whakaki50m.cli'

SISYPHE STEERING FILE = 'Whakaki_sediment_test.cas'

COUPLING WITH='SISYPHE'

COUPLING PERIOD FOR SISYPHE=1

VARIABLES FOR GRAPHIC PRINTOUTS =B,U,V,H,S

NUMBER OF DROGUES =100

GRAPHIC PRINTOUT PERIOD =60

TIME STEP =10

NUMBER OF TIME STEPS =6000

THRESHOLD DEPTH FOR WIND =0.05

SPEED AND DIRECTION OF WIND =5;45

*********************

******SISYPHE CAS FILE************************

SEDIMENT DIAMETERS =0.00005

COHESIVE SEDIMENTS=
true;false;false;false;false;false;false;false;false;false

CRITICAL EROSION SHEAR STRESS OF THE MUD=0.001

BED-LOAD TRANSPORT FORMULA =1

BED LOAD =false

BOUNDARY CONDITIONS FILE ='bc_Whakaki50m.cli'

SECONDARY CURRENTS =YES

GEOMETRY FILE ='geometry_Whakaki_50m.slf'

VARIABLES FOR GRAPHIC PRINTOUTS =E,CS1,TOB,CSAT

TITLE ='Whakaki Test'

ZERO =1e-12

TETA =0

RESULTS FILE ='Whakaki_5m_test_res_sed.slf'

MASS-BALANCE =YES

SECONDARY CURRENTS ALPHA COEFFICIENT =1.0E-00

SLOPE EFFECT =YES

FORMULA FOR SLOPE EFFECT =1

BETA =1.3

SUSPENSION =true

*****************

Hello,
Assuming that you only have wind as external forcing of your problem, the BC file seems to be OK.
Check if your hydrodynamic field gives physical results. Then, clean-up a bit your Sisyphe's file (secondary currents, etc.).
It seems that you're dealing with cohesive sediment. In this case, set COHESIVE SEDIMENTS=YES and remove SUSPENSION =true.

Hope it helps,

Pablo

Hi Pablo,

Thank you for your prompt reply.

The HD results are realistic (perhaps a bit overestimated with respect to reality). I am getting velocities of the order of 0.5 m/s.

I added more output variables to see the sediment concentration and thickness of the layer and I get a non-zero thickness and a non-zero bed concentration.

However, the bed shear stress is zero for all times. I think this may be the problem. With non-zero flow velocities this should not be zero. I cannot see parameters to modify the bed shear stress formulations. In Telemac2D there is no bed shear stress output. I am using version v7p3.

Model files attached.

Any clues much appreciated!

Jose

Hello,
You can visualize the shear velocity (u* = \sqrt(tau_b/rho))

cheers

Pablo

Thanks Pablo,

I could not see how to get the friction velocity as an output variable from Telemac2d but I figured out the problem. I did not specify the LAW OF BOTTOM FRICTION in the Telemac2D CAS file and it was using the default value which is 0 (No friction).

Now I am having blow up issues that I hope to resolve.

Cheers

Hello,
FYI, you can use the flag "US" in your VARIABLES FOR GRAPHIC PRINTOUTS to plot the friction velocity.

Best wishes,

Pablo

Now I am having blow up issues that I hope to resolve.

your time step is probably too high...

Hi again Pablo,

I am now stuck with some weird results. I am starting a simulation with an initial 0.15 Kg/m3 of sediment concentration, the bed shear stress is enough to erode the first mud layer (set with critical shear stress, settling velocity is set very low as well as critical shear stress for deposition. Therefore sediment concentrations are expected to increase from its initial value but this is not happening, they are decreasing.
the layer thickness is decreasing and there are no other sinks of mass or water so I don't know where the sediments are going.

Any clues much appreciated!

SISYPHE CAS file below

Jose

///////////////
SEDIMENT DIAMETERS =0.0001

SETTLING VELOCITIES=0.000005

COHESIVE SEDIMENTS=YES

CRITICAL EROSION SHEAR STRESS OF THE MUD=0.001;10000

NUMBER OF LAYERS OF THE CONSOLIDATION MODEL=2

MUD CONCENTRATION PER LAYER=50;1000

CRITICAL SHEAR VELOCITY FOR MUD DEPOSITION=0.0005;0.0005

ACTIVE LAYER THICKNESS=0.3

CONSTANT ACTIVE LAYER THICKNESS=YES

SEDIMENT DENSITY=1500

INITIAL SUSPENSION CONCENTRATIONS=0.15

BED LOAD=NO

MASS-BALANCE =YES

SUSPENSION =true

BOUNDARY CONDITIONS FILE ='bc_Whakaki50m.cli'

GEOMETRY FILE ='geometry_Whakaki_50m.slf'

VARIABLES FOR GRAPHIC PRINTOUTS =E,CS1,TOB,CSAT,*ES,*CONC,D50

TITLE ='Whakaki Test'

RESULTS FILE ='Whakaki_5m_test_res_sed.slf'

///////

Hello,
Try adding in your Sisyphe's cas file:
TYPE OF ADVECTION = 14 (or 15).
Take also a closer look to your time step.

Hope it helps,

Pablo

I think the keyword
INITIAL SUSPENSION CONCENTRATIONS
assumes a volume concentration, not a mass concentration. Even if the output is in g/l.

Michiel