Mass balance problem

massimo · 2021-10-08 09:08:26

Hi,

i'm using Basement v3 for simulation of a flood event in a river that its leght is 8 km and i've created the computational mesh with Basemesh 2.0

i have 1 inflow and 1 outflow, i started the steady simulation with this hydrogram to have a complete wetted riverbed:

0.0, 8
86400, 8

Afterward i want to simulate a flood event with hq-relation at the outflow with this file, where 206.77 m.s.l.m is the zero hydrometric:

207.03, 2.51
207.03, 2.51
207.03, 2.51
207.03, 2.51
207.02, 2.38
207.02, 2.38
207.02, 2.38
207.03, 2.51
207.03, 2.51
207.03, 2.51
207.05, 2.78
207.06, 2.92
207.04, 2.64
207.06, 2.92
207.06, 2.92
207.04, 2.64
207.05, 2.78
207.05, 2.78
207.05, 2.78
207.07, 3.07
207.05, 2.78
207.06, 2.92
207.06, 2.92
207.04, 2.64
207.04, 2.64
207.04, 2.64
207.05, 2.78
207.04, 2.64
207.04, 2.64
207.04, 2.64
207.04, 2.64
207.05, 2.78
207.25, 6.22
207.2, 5.24
207.26, 6.43
207.32, 7.73
207.35, 8.43
207.38, 9.15
207.35, 8.43
207.36, 8.66
207.43, 12.69
207.46, 13.65
207.56, 17.06
207.85, 28.72
207.98, 34.77
208.17, 44.51
208.4, 57.64
208.61, 70.9
208.89, 90.37
209.06, 103.18
209.33, 125
209.47, 137.02
209.61, 149.51
209.68, 155.93
209.84, 171.04
209.95, 181.77
210.07, 193.8
210.19, 206.17
210.21, 208.26
210.24, 211.41
210.28, 215.65
210.28, 215.65
210.24, 211.41
210.23, 210.36
210.04, 190.77
209.99, 185.75
209.97, 183.76
209.93, 179.8
209.88, 174.91
209.89, 175.88
209.9, 176.86
209.9, 176.86
209.97, 183.76
209.96, 182.76
209.98, 184.75
209.93, 179.8
209.89, 175.88
209.84, 171.04
209.79, 166.25
209.77, 164.35
209.72, 159.65
209.68, 155.93
209.59, 147.69
209.55, 144.1
209.5, 139.65
209.37, 128.38
209.29, 121.65
209.28, 120.82
209.25, 118.35
209.23, 116.71
209.17, 111.85
209.16, 111.05
209.14, 109.46
209.06, 103.18
209.05, 102.4
209.01, 99.34
209, 98.58
208.97, 96.31
208.89, 90.37
208.88, 89.64
208.84, 86.75
208.85, 87.47
208.79, 83.18
208.74, 79.69
208.75, 80.38
208.71, 77.62
208.7, 76.93
208.66, 74.22
208.65, 73.55
208.62, 71.56
208.64, 72.89
208.62, 71.56
208.56, 67.63
208.55, 66.99
208.54, 66.35
208.53, 65.71
208.51, 64.44
208.5, 63.81
208.49, 63.18
208.46, 61.31
208.61, 70.9
208.62, 71.56
208.59, 69.58
208.58, 68.93
208.55, 66.99
208.56, 67.63
208.51, 64.44
208.48, 62.55
208.5, 63.81
208.49, 63.18
208.43, 59.47
208.43, 59.47
208.39, 57.04
208.41, 58.25
208.38, 56.44
208.29, 51.18
208.22, 47.24
208.19, 45.59
208.17, 44.51
208.16, 43.97
208.15, 43.43
208.14, 42.9
208.14, 42.9
208.13, 42.37
208.12, 41.84
208.13, 42.37
208.1, 40.8
208.11, 41.32
208.09, 40.28
208.07, 39.25
208.07, 39.25
208.06, 38.75
208.07, 39.25
208.03, 37.23
208, 35.75
208.03, 37.23
207.98, 34.77
208.02, 36.74
207.98, 34.77
207.95, 33.33
207.96, 33.81
207.93, 32.39
207.93, 32.39
207.95, 33.33
207.93, 32.39
207.91, 31.45
207.92, 31.92
207.9, 30.99

-------------------------------------

the inflow file is:

0, 15.12
3600, 15.12
7200, 15.12
10800, 15.12
14400, 15.12
18000, 15.62
21600, 15.62
25200, 16.14
28800, 16.66
32400, 16.66
36000, 17.2
39600, 17.2
43200, 17.74
46800, 17.2
50400, 17.74
54000, 17.2
57600, 17.74
61200, 17.2
64800, 17.2
68400, 17.74
72000, 16.66
75600, 16.14
79200, 16.66
82800, 16.14
86400, 15.62
90000, 15.12
93600, 15.62
97200, 15.62
100800, 15.62
104400, 15.62
108000, 16.14
111600, 17.74
115200, 18.86
118800, 20.01
122400, 21.81
126000, 22.43
129600, 22.43
133200, 22.43
136800, 23.7
140400, 25.01
144000, 26.35
147600, 29.16
151200, 31.36
154800, 36.05
158400, 41.99
162000, 52.57
165600, 62.13
169200, 74.95
172800, 83.75
176400, 101.43
180000, 114.69
183600, 127.19
187200, 135.34
190800, 143.75
194400, 143.75
198000, 157.75
201600, 159.55
205200, 180.01
208800, 170.55
212400, 174.3
216000, 159.55
219600, 166.84
223200, 176.2
226800, 154.19
230400, 154.19
234000, 152.42
237600, 145.46
241200, 152.42
244800, 140.35
248400, 145.46
252000, 150.67
255600, 148.92
259200, 147.19
262800, 154.19
266400, 150.67
270000, 145.46
273600, 142.05
277200, 133.69
280800, 138.67
284400, 133.69
288000, 135.34
291600, 127.19
295200, 119.3
298800, 122.42
302400, 114.69
306000, 111.67
309600, 116.22
313200, 110.18
316800, 116.22
320400, 111.67
324000, 107.22
327600, 105.75
331200, 101.43
334800, 104.3
338400, 101.43
342000, 94.42
345600, 97.19
349200, 93.05
352800, 93.05
356400, 89
360000, 90.34
363600, 85.04
367200, 82.46
370800, 83.75
374400, 79.91
378000, 74.95
381600, 76.17
385200, 77.41
388800, 74.95
392400, 77.41
396000, 72.52
399600, 71.33
403200, 70.14
406800, 70.14
410400, 72.52
414000, 71.33
417600, 71.33
421200, 64.37
424800, 62.13
428400, 65.5
432000, 63.25
435600, 64.37
439200, 59.94
442800, 62.13
446400, 59.94
450000, 61.03
453600, 61.03
457200, 61.03
460800, 58.85
464400, 57.78
468000, 58.85
471600, 52.57
475200, 52.57
478800, 56.72
482400, 51.56
486000, 55.66
489600, 52.57
493200, 54.62
496800, 51.56
500400, 50.55
504000, 50.55
507600, 49.56
511200, 51.56
514800, 49.56
518400, 48.58
522000, 47.61
525600, 47.61
529200, 49.56
532800, 52.57
536400, 46.65
540000, 44.76
543600, 44.76
547200, 46.65
550800, 43.82
554400, 45.7
558000, 43.82
561600, 46.65
565200, 40.2
568800, 41.99
572400, 41.09
576000, 43.82
579600, 42.9
583200, 41.09
586800, 41.09
590400, 42.9
594000, 44.76
597600, 42.9
601200, 43.82

when i run the simulation gives me a lot of mass balance problems (very many mass balance problems) like:

MASS BALANCE PROBLEM: h = -0.00260568 < 0.0
MASS BALANCE PROBLEM: h = -0.00258805 < 0.0
MASS BALANCE PROBLEM: h = -0.00286564 < 0.0

and i started the simulation and after 10 hours it's stil at 10%

it's a problem of the mesh in the zone of the inflow or outflow? or the file of input?

or there are too many elements in the computational mesh?

how can i resolve this problem?

this is my first post and i don't know how exatly works this platform

in the previous posts i red that is possible send the files (of the mesh, or file model.json for example) for a check

if i could send my files for a check i don't know where i can send them

thanks

best regards

Massimo

Lukas Vonwiller · 2021-10-08 10:11:00

Hi Massimo

I think your downstream h-q relation is the main problem. I recommend to check the documentation on how the h-q relation is working. Maybe consider to apply uniform flow condition for the downstream boundary.

Hope this helps!
cheers, Lukas

massimo · 2021-10-08 13:02:25

Hi Lukas,

thanks for reply

i serached for it but i don't found any specific documentation, examples and tutorials neither

can you suggest me where can i found this doucumentation? because in the manual i didn't found it (h-q relation is only mentioned as option, but i can wrong) or can you send me an email of the documentation?

i prefer work with h-q boundary condition

cheers

Massimo

Lukas Vonwiller · 2021-10-08 13:15:28

Hi Massimo

The documentation on 'hq_relation_out' is a bit short, but it tells you that "The discharge is determined as a function of the water surface elevation, thus a stage-discharge-relation has to be specified." This means that the the discharge is determined by BASEMENT based on the defined water surface - discharge (h-q) relation. But your h-q relation is strange, it seems to be more of a hydrograph of discharge and associated water surface elevation... (hint: water surface elevation should be unambiguous and always increasing!).

cheers, Lukas

massimo · 2021-10-08 14:37:14

you right Lukas,

i interpreted in wrong way h-q relation

i restart the simulation with new h-q relation:

207.85, 28.72
208.4, 57.64
209.06, 103.18
209.33, 125
209.47, 137.02
209.61, 149.51
209.95, 181.77
210.21, 208.26
210.28, 215.65

but still gives MASS BALANCE PROBLEM: h<.....

is it due to the elevation of boundary condition in h-q relation? or is it due to the elevation of the meshes in the outflow?

thanks

massimo

Matteo Facchini · 2021-10-08 15:47:18

Hi massimo

a few thoughts about your problem:

As Lukas suggested you: "Maybe consider to apply uniform flow condition for the downstream boundary."
if you want to stick to the hq relation be careful and check the reference level of your boundary stringdef (for instance open the .h5 file with HDFView or use the python script provided by the basement team to extract the stringdef results)
run basement in debug mode and check for the element(s) causing the mass balance warning
open you results with paraview, look at the SpreadSheet View (there you can sort your elements by e.g. water level and check if you have negative water depth or very high velocities.

If you do not know how to do such things, I suggest you to go through all the tutorials

massimo · 2021-10-08 17:30:18

Hi Matteo,

thanks for reply

it's my first work with Basement and i'm still learning

i hope to resolve these problems with your suggests

best regards

massimo

User Forum of Software BASEMENT

#1 2021-10-08 09:08:26

Mass balance problem

#2 2021-10-08 10:11:00

Re: Mass balance problem

#3 2021-10-08 13:02:25

Re: Mass balance problem

#4 2021-10-08 13:15:28

Re: Mass balance problem

#5 2021-10-08 14:37:14

Re: Mass balance problem

#6 2021-10-08 15:47:18

Re: Mass balance problem

#7 2021-10-08 17:30:18

Re: Mass balance problem

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