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Hello,

I am a fairly new user of both Telemac 2D and Sisyphe, and I am now stuck on a pretty big issue.

I am running both Telemac 2D and Sisyphe at the same time (coupled) on a small part of a river, ended by a dam, and I'd like to simulate the transport of uncohesive sediment (2 classes with the following diameters: 0.001 m and 0.02 m).
My input is the following :
-Water flowrate of 480 m^3/s
-For both my sediment classes, 28 g/L (with the keyword MASS CONCENTRATION set to true)

I expected the sediments to flow through the river, but they just get stuck at the very beginning of the geometry (you can see the pictures attached below)

I can't seem to find a reason why this happens. It looks like the water simply doesn't transport the sédiments that enter the domain at the input.

If anyone has any idea on why Sisyphe behaves this way...
Thanks in advance for your help!

Regards,
Pilavoine.

Hello Pilavoine,

Does your hydrodynamic model work fine? From your hydrodynamic model you can know if it's possible to transport sediment with those diameters (as suspended).
Are you selecting those sediment diameters randomly?
Are you using a hotstart?

Remember that the friction velocity field is very important to determine the zones prone to deposit sediment and where the sediment remains suspended.

According to above mentioned, could be helpful you calculate the settling velocities and compare with the U* field in order to know if it's possible to transport suspended sediment trough the river (with those diameters).

It could be the reason (almost 100% sure). Take a look at Sisyphe user manual v7.2, will be helpful.
As a beginner you should start with an example seemed to your model.

Cheers,

José Andrés.

Hi,

first, you should try to apply equilibirum sediment inflow conditions. Then you can see what are the equilibrium concentations calculated by your chosen formula (e.g. Van Rijn) in Sisyphe at the inflow for both diameters. If calculated concentrations by Sisyphe differ a lot to your wanted imposed values of 28g/L, to say, if they are much lower, then you found the problem. One reason could be that your hydraulic model simply underestimates the shear stress in the inflow area. But there could be also other underlying reasons. The setup of boundary conditions in sediment transport model is a tricky thing.

Other way: you could check the discrepancy by calculating the equilibirum conditions at the inflow for the given diameters manually. So you avoid to run the whole model and this gives you roughly, but fairly well, also an idea about the inflow conditions.

Hope this helps,
Clemens

Thank you both for your replies!

jose2kk wrote:
The hydrodynamic model seems to work fine when running all alone. The sediment diameters are based on a previous study of the case I'm trying to simulate.

What is a hotstart though?

jose2kk wrote:
Doesn't Sisyphe calculate the settling velocities itself? I mean, I do have a value from the study I mentionned above (I could double-check that though), but even without it, Sisyphe should be able to cope with it, right?

konsonaut wrote:
I'll try to see that, but how can I see the result of Sisyphe's calculation of the equilibrium concentrations?

Thanks again,
Pilavoine

I checked the settling velocity, which is way lower than the water velocity, so it shouldn't be a problem.

I might have a hint about why my simulation doesn't work though: it seems I can't make the SUSPENSION keyword to work.

Whenever I turn it on, the simulation doesn't even start. The only thing it displays is:
"DIFFIN : UNEXPECTED CASE"

By searching a bit into telemac source files, it seems this has something to do with my boundary conditions, but I really don't know what's wrong. And when the keyword is set to false, the simulation gives the aforementioned result.

Any idea on that issue?
Thanks in advance!

Without the steering file and your boundary definition file (cli), it is impossible to see what is wrong. I suspect that the boundary setting for the sediment is incorrect. Your upstream boundary should be

4 5 5 0.000 0.000 0.000 0.000 5 0.000 0.000 0.000 1 1
or
4 5 5 0.000 0.000 0.000 0.000 4 0.000 0.000 0.000 1 1

(see SISYPHE examples or the manual for details).

Thanks for your answer, I attached the files to this post.

My boundary file is the same as the example you provided, with the LITBOR column set to 5.

As for my previous issue :
The thing is that I used a modified CONLIT subroutine. Whenever I add a fortran file to the steering file that contains that subroutine, no matter what's written inside that particular subroutine, I get the "DIFFIN : UNEXPECTED CASE" error whenever the SUPSENSION keyword is set to true.

By looking into the DIFFIN subroutine, it seems that Sisyphe pretty much "forget" the array LITBOR which leads me to that error. I've made several different tries :

1) TELEMAC 2D coupled with INTER-SISYPHE, SUSPENSION set to true and a fortran file with the CONLIT subroutine => "DIFFIN : UNEXPECTED CASE".

2) TELEMAC 2D coupled with INTER-SISYPHE, SUSPENSION set to true and a fortran file without the CONLIT subroutine => the simulation runs.

3) TELEMAC 2D alone, SUSPENSION set to true and a fortran file with the CONLIT subroutine => the simulation runs.


Here's what I think it happens in the 3 cases listed above:

1) TELEMAC 2D correctly reads the boundary conditions, both for the initialization and every time steps, but the array LITBOR seemed to be freed from the memory as SISYPHE reads values like 2147483647, hence the DIFFIN error (the subroutine expects something between 1 and 5)

2) Both TELEMAC 2D and SISYPHE correctly read the boundary conditions, the array LITBOR stays in memory and the correct value is read (LITBOR=5).

3) TELEMAC 2D still reads correctly the boundary conditions, and SISYPHE isn't here to make it crash.


I have to admit I am a bit lost here...
What I want to do is to have a variable input of sediment with both bedload and suspension turned on. Does anyone know how to achieve that?

(The two attached files are the following : new_sis.cas is the steering file (in French), new_sis.conlim is the boundary file)

What you are telling now suggests that the modified conlit file is incorrect.

In option 3, the conlit is ignored as telemac doesn't use it. Option 2 uses the default conlit and runs fine. Option 1, uses the modified conlit and gives an error that suggests a mistake in the memory allocation.

Is it necessary to use a modified conlit routine?

Is the modified version based on the conlit of the telemac version you are using, or on an older version?

Check that the right variables are past on, that global variables are allocated correctly, all matrices allocated for the correct size (whatch out when running in parallel).

In short: check your coding of conlit.f

Well, using a modified conlit routine is the only way I found to have a variable sediment input.

I'll try to see what's wrong with that routine. The thing is that it runs fine without suspension, but I haven't seen anything that could have interfere with the LITBOR array Inside the routine.

By replacing the modified conlit with the original routine, the simulation runs. So I guess I'll just re-write the conlit routine myself.


Thanks !

Here I come again with the same problem.

The CONLIT subroutine works fine now, and I currently use it to choose the value of QBOR on my input boundary. You can find it in the "fortran_file.f" file attached below.

With my current parameters, I still find myself in the same case as I was for my first post here: sediments do get inside the domain, but they mostly stay along the boundary (see the attached image below).

I have both the BEDLOAD and SUSPENSION keywords set to true, for a single class of sediments with a diameter of 0.001m (1mm).

I truly don't understand what's not working here... I have also attached my steering file (the "new_sis.txt" file)

Does anyone have any hint on what's wrong?
Thanks in advance!