User Forum of Software BASEMENT

Gnoebbas

User

From: Wuppertal

Registered: 2022-05-03

Posts: 6

Mass Balance Problem when switching from Internal to Linked boundary

Hey there,

I just ran into a problem when switching my boundary conditions. I set four string defs in total inflow and outflow at the edges with uniform in and out and two internal boundaries. However, for the first simulation I set it to internal and used only one of the two remaining boundaries and a hq-relation file. For this scenario, I get a running simulation and results. For another simulation where I generated a new mesh with a hole between the two internal boundaries and switched the conditions in Basement from internal to linked using the same hq-relation file as before it fails. The Simulation runs for a while then crashes with mass balance error.

I have read through most of the topics concerning the mass balance problem but I can not manage to analyse my failing simulation as described in other topics. As far as I know running the debug mode is not possible, since i use the interface/GUI?

Thanks in advance
Jan

Lukas Vonwiller

Developer

Registered: 2014-09-04

Posts: 127

Re: Mass Balance Problem when switching from Internal to Linked boundary

Hi Jan

Try to run the model using "safe_mode": "off" (HYDRAULICS -> PARAMETER). This will prevent the model from stopping due to mass balance errors. This can make sense in the beginning when you have a 'dry' start. However, make sure that these errors stop at some time during the simulation, e.g. when you reach a quasi steady state. Then try to restart from this state for further simulations (INITIAL: "type": "continue"). This will possibly avoid further mass balance errors. Another possible source of mass balance errors is your 'hqrelation' at the linked boundary, especially when you start from 'dry' initial conditions.

Hope this helps!
cheers, Lukas

Gnoebbas

User

From: Wuppertal

Registered: 2022-05-03

Posts: 6

Re: Mass Balance Problem when switching from Internal to Linked boundary

Hi Lukas,

a first runtrought with save_mode disabled resulted in the simulation running two steps further but crashing Basement after reaching big negativ numbers for h. A second attempt does not look promising either.
So i was thinking about the stringdef upstream directions and how to determine the correct direction as described in the manual. However i have no information about the nodes, when meshing with the basemesh plugin using quality meshing in QGIS, am i right?
So most likely the hq-relation file is causing the error. Any suggestion how to improve/adjust/"repair" the hq-relation file?

Greetings
Jan

Last edited by Gnoebbas (2022-09-23 14:00:19)

Lukas Vonwiller

Developer

Registered: 2014-09-04

Posts: 127

Re: Mass Balance Problem when switching from Internal to Linked boundary

Hi Jan

your nodes are in the 2dm file (lines starting with ND), you can plot the coordinates in QGIS and checkout the node ids (first row after ND).

Try to start the 'h' (water surface elevation) in the hq-relation from (or slightly above) the mean bottom elevation at your nodestring. Maybe try to get some idea of the mean watersurface elevation or mean bottom elevation using BMv3GaugeExtract.py.

hope this helps!
cheers, Lukas

Gnoebbas

User

From: Wuppertal

Registered: 2022-05-03

Posts: 6

Re: Mass Balance Problem when switching from Internal to Linked boundary

Hi Lukas,

i caclulated the mean bottom elevation of the profile and adjusted my DEM in very short range before the In and at the Out of the Linked condition strings. In addition i set the starting point of the hq-relation file 10 cm higher than the mean value. After several runtroughs with various input Q, it looks like my results are fine now.

Thanks
Jan