Mass conservation warning in element #

sajjad · 2015-07-10 15:44:10

Hello all,

I am running a simulation with version 2.5.1 (which i previously ran using v. 2.3) and am getting the subject warning repeatedly. There was no such warning with Basement 2.3. Any clues why is it so and what can we do to avoid such warning ?

Regards

Sam · 2015-07-10 15:52:28

please have a look to the release notes here.

for further explanations about the flux correction, please check out the reference manual at 2.3.1.2

cheers

sajjad · 2015-07-10 19:44:53

Hi,

the section ' 2.3.1.2 Evaluation of bed load transport due to stream forces' deals with morphology but I am only dealing with pure water flow so there must be some other reason.
I must report that v 2.5.1 is about five times (or even more) slower than the v. 2.3.

Regards

Sam · 2015-07-13 08:52:21

2.3.1.2 -> NUMERICS KERNEL (RII)

mostly the problem of failing flux corrections is due to very large element slopes.

concerning the performance issue: what machine and operating system are you using?

sajjad · 2015-07-13 15:45:03

Hi, thanks. Yes there are regions in the mesh with large slopes , perhaps v. 2.5.1 is more strict and issues warning while 2.3 was lenient. In any case, the warning stops soon enough. Regarding, slowdown, I must say that due to a local mesh refinement, I reduce the size of cell from 5 sq.m to 0.1 sq.m. So a large mass of very small triangles (about 2000) are created which slow down considerably but I dare say this behaviour is not due to version 2.5.1 being slow but rather due to this change.

I intend to benefit from local time stepping in Basement by isolating that portion of small cells into another subdomain but I am not sure which boundary cond. I use to connect the two subdomains so that the depth and velocities remain same. If u can please guide me on this point, I would be grateful.

Thanks

Sam · 2015-07-23 10:16:53

could you please open a new topic for your coupling question, since it does not belong to the mass conservation issue? thx

alaquas · 2015-08-27 08:06:42

Hi, I get the Warning -> Mass conservation ins not guaranteed! Negative water depth in element ... (slope = 0.5556). Then the program stops working. The slope is rather steep but it represents the modelled area (river bank). Is there a possibility to run the model in rather steep areas?
Thanks

Sam · 2015-08-28 09:41:08

What do you mean by "program stops working"?
could you please give more detailed information about how BASEMENT exits (information in *.log file)?

alaquas · 2015-08-28 10:34:48

Thanks for your answer. Think I found the problem: I tried to remove water (negative source) from an element that has not been completely filled with water yet. If I reduce the number of elements for the negative source to the ones that are totally filled with water the program works perfectly. It was no problem of the steepness of the element itself but of the water level in the element.

kmsar · 2016-03-17 15:54:24

Hi,

I have the same problem as alaquas had. I am working on a steep terrain in mountainous region (10%). The programm sends me warnings (see under) and after a little time. It stops working and crask down. Can you help me to fix it?
Thanks

BASEMENT log output: many warnings like ...
*******************************************************************************
*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Warning !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*
*******************************************************************************
-> Mass conservation is not guaranteed! Negative water depth in element
#29788 (slope = 0.652573).
missing volume to compensate the overdraft: 8.10146

René Kaufmann · 2016-03-18 09:13:09

Try to run the calculations in batch-mode. I think the problem is due to to many windows... The code looks like: "C:\...\BASEMENT_v2.5.1.exe" - f "C:\...\yourBASEMENTfile.bmc" -b

And: Avoid choosing CFL > 1!

sajjad · 2016-03-18 10:20:31

Hi,

how can we run basement in batch mode and what is the advantage to be gained?

Regards

René Kaufmann · 2016-03-23 11:00:04

Hi
i made the experience, that a lot of warning error windows will crash the program.

The advantage is, that the program will not crash, but the error won't be gone!

If you're running on Windows,
- make a new text file,
- write this code: ' "C:\...\BASEMENT_v2.5.1.exe" - f "C:\...\yourBASEMENTfile.bmc" -b '
- write as the last line 'pause' (after running the code, you have to hit a key to Close the window)
- save the file
- change the extension from .txt to .bat
- double click and the calculations will start.

Hope, this will help

Regards
-

Sam · 2016-03-30 08:55:21

as René stated, it is most probably a problem of the many warning windows in the BASEMENT GUI:

René Kaufmann wrote:

Try to run the calculations in batch-mode. I think the problem is due to to many windows... The code looks like: "C:\...\BASEMENT_v2.5.1.exe" - f "C:\...\yourBASEMENTfile.bmc" -b
And: Avoid choosing CFL > 1!

in addition to the batch mode possibility, the new BASEMENT version 2.6 handles the warnings differently in the GUI!
With BASEMENT v2.6 you should be able to run your model in the GUI with all the warnings without crashing. give it a try

cheers

Stefano Zazzara · 2016-04-10 10:48:26

Hi everybody
I'm trying to simulate a test case of "Benchmarking of 2D Hydraulic Modelling Packages" and when I start the simulation it stops with the following errors

*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Warning !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*
*******************************************************************************
-> Mass conservation is not guaranteed! Negative water depth in element #831
(slope = 0.000479107).
missing volume to compensate the overdraft: 0.000752162
TIME = 3.390968e+003 hyd. Time Step = 9.799418e-001 (SD: 2dimensioni)
Qout[1] = -8.085363e+000 [m3/s] (linee)

I have tried to use CFL>1 and to run in batch-mode but the problem remains.
Actually I'm using the version 2.5.3 because the 2.6 version crashes.
I have WINDOWS 10.
How can I solve the problem???

Thanks for the attention.
Regards

lorenzo.scopetani · 2021-09-24 15:55:56

Good morning
I've the same problem in a very slope river. I've just modelled my river with Tr20 years and it run well, but when I insert the Tr200 years hydrograph the program generates a lot of warning "WARNING -> Mass conservation is not guaranteed! Negative water depth in element
#3550 (slope = 8.8878).
missing volume to compensate the overdraft: 0.784939"
and the results are not realistic, because it generates a very large deposition in the first 100m of the model.
I've set Morphology, Bed Load and Gravitational transport block in my model.
How can I solve this problem?
Thanks very much

Matteo Facchini · 2021-09-27 10:04:01

Hi Lorenzo, three suggestions:

1. use the IOUp boundary condition instead of the transport_capacity;
2. build a fake channel with constant slope and regular geometry upstream of your domain with gravitational transport on all elements;
3. try to play with the slope at the inflow boundary

Best
Matteo

User Forum of Software BASEMENT

#1 2015-07-10 15:44:10

Mass conservation warning in element #

#2 2015-07-10 15:52:28

Re: Mass conservation warning in element #

#3 2015-07-10 19:44:53

Re: Mass conservation warning in element #

#4 2015-07-13 08:52:21

Re: Mass conservation warning in element #

#5 2015-07-13 15:45:03

Re: Mass conservation warning in element #

#6 2015-07-23 10:16:53

Re: Mass conservation warning in element #

#7 2015-08-27 08:06:42

Re: Mass conservation warning in element #

#8 2015-08-28 09:41:08

Re: Mass conservation warning in element #

#9 2015-08-28 10:34:48

Re: Mass conservation warning in element #

#10 2016-03-17 15:54:24

Re: Mass conservation warning in element #

#11 2016-03-18 09:13:09

Re: Mass conservation warning in element #

#12 2016-03-18 10:20:31

Re: Mass conservation warning in element #

#13 2016-03-23 11:00:04

Re: Mass conservation warning in element #

#14 2016-03-30 08:55:21

Re: Mass conservation warning in element #

#15 2016-04-10 10:48:26

Re: Mass conservation warning in element #

#16 2021-09-24 15:55:56

Re: Mass conservation warning in element #

#17 2021-09-27 10:04:01

Re: Mass conservation warning in element #

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