User Forum of Software BASEMENT

medrilama

User

Registered: 2016-08-08

Posts: 4

Negative velocities at the outflow

Hi all,
I have a 2D domain, the upstream boundary condition is a hydrograph and the downstream boundary condition is hqrelation with a fixed slope. My problem is that a certain point at the last cross section I start to see negative velocities that means inflow fluxes entering the domain that cause significant floods in the downstream part of the domain. I checked the quotes of the nodes and it seems all ok. I tried also zero_gradient condition but after some time a get huge values of water depth. I tried to edit the DTM smoothing some terrain peaks and creating some sort of ramp for the water but I didn't solve. Here the link to some pictures to clarify.
Velocities at time=t (overview)
Velocities at time=t+600 s (overview)
Velocities at time=t
Velocities at time=t+600 s

I ask if someone can help me understand what's wrong in my setup or can give me some advice.
Thanks in advance
Filippo

Amini

User

Registered: 2017-07-05

Posts: 1

Re: Negative velocities at the outflow

Hi,
I had exactly the same problem. I tried to run the simulation with an old version (2.5 or 2.6) and the problem has disappeared!
Bests
Azin

alaquas

User

Registered: 2015-08-27

Posts: 9

Re: Negative velocities at the outflow

Hi
I have the same problem as mentioned above. I prefer to use version 2.7 because of the movable_bed condition. Is there another possibility using the zero_gradient BC with version 2.7 without having huge amounts of water flowing back into the system?
@developers: Will this bug be fixed in a new version?
Thanks

nicolagroff

User

Registered: 2017-08-07

Posts: 10

Re: Negative velocities at the outflow

Hi,
I had the same problem. I solved diminishing the slope in the hqrelation.

Nicola

alaquas

User

Registered: 2015-08-27

Posts: 9

Re: Negative velocities at the outflow

Hi, thanks for your answer. I am using the zero_gradient BC not hqrelation. Is there a possibility to use zero_gradient with V2.7?