User Forum of Software BASEMENT

Deborah

User

Registered: 2020-03-21

Posts: 8

Error of Mass balance problem

Hello,

I tried to do a hydraulic simulation in a large river.  Horewer, I have a long list of mass balance problems at the first iteration. No problems appear for the next iterations and I can run the simulation until the end.

-> Progress: 0/100, dt = 0.02, RTS = 0
MASS BALANCE PROBLEM: h = -0.610542 < 0.0
MASS BALANCE PROBLEM: h = -0.573999 < 0.0
MASS BALANCE PROBLEM: h = -0.731428 < 0.0
MASS BALANCE PROBLEM: h = -0.791608 < 0.0

I set up an initial "dry" condition and I have two uniform_in boundary conditions.

What could be the problem ? Is it really a problem as I could run it until the end ?

Thanks for your hep in advance

Déborah

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Error of Mass balance problem

Hi Déborah,

you can try starting the simulation with other conditions, such as "region_defined" (BM3.x) or index_table (BM2.8) with which you can set x and y velocities (u and v) and either the water depth (h) or water level (wse).

Dry initial conditions could give some warning, but if everything runs and you get reasonable results I would not be much concerned about the mass balance warning!

Cheers

Matthias Bürgler

Developer

From: Zürich

Registered: 2019-04-04

Posts: 150

Re: Error of Mass balance problem

Hi Déborah

Are you using the safe_mode option in Hydraulics/Parameters with "off" or "on"?

Best regards
Matthias

Deborah

User

Registered: 2020-03-21

Posts: 8

Re: Error of Mass balance problem

Hi

No I'm not using the safe_mode

Best regards,
Déborah

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Error of Mass balance problem

Hi

I have played around with the initial conditions and minimum water depth: I had mass balance problems when I started from region defined conditions, I tried to use dry intial conditions and I got no problems.

So my answer is not completely correct, I am sorry.

However, I have to set the minimum water depth to a value larger than 1 cm (which makes perfectly sense), otherwise I got the mass balance problems.

Last edited by Matteo Facchini (2020-04-09 14:59:03)

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Error of Mass balance problem

Still I cannot run the Flaz tutorial from the command line because of the mass balance problem, while it works if I run it from the GUI

Deborah

User

Registered: 2020-03-21

Posts: 8

Re: Error of Mass balance problem

Hi Matteo,

Thank you for feedback.

I set up a minimal depth of 0,1m, but I still have the problem.

I didn't try to run from the command line.

I changed one boundary conditions, I still have mass problem balance at the beginning however the results seem to be quite good. Then I think I wouldn't take into consideration the mass problem balance.

Déborah

Matthias Bürgler

Developer

From: Zürich

Registered: 2019-04-04

Posts: 150

Re: Error of Mass balance problem

Still I cannot run the Flaz tutorial from the command line because of the mass balance problem, while it works if I run it from the GUI

That's strange, I don't get a mass balance error regarding of CLI or GUI (omp with 7 cores, double). Which backend and precision are you using Matteo?

Regards
Matthias

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Error of Mass balance problem

Hi Matthias,

I posted a complete reply here