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Nykieta
August 26, 2016, 08:50 AM
New InfoWater user here.

I've been trying to run this model that I'm working on but the model run keeps failing from a "System unbalanced at 0:00:00 hr". I have no idea what is causing this especially since no model error is shown in the analysis report.

A section of the analysis report in provided below. I would greatly appreciate any suggestions. Thanks.

Number of Junctions................ 1123
Number of Reservoirs............... 4
Number of Tanks ................... 1
Number of Pipes ................... 2026
Number of Pumps ................... 5
Number of Valves .................. 746
Headloss Formula .................. Hazen-Williams
Hydraulic Timestep ................ 1.00 hrs
Hydraulic Accuracy ................ 0.001000
Status Check Frequency ............ 2
Maximum Trials Checked ............ 10
Damping Limit Threshold ........... 0.010000
Maximum Trials .................... 200
Quality Analysis .................. None
Specific Gravity .................. 1.00
Relative Kinematic Viscosity ...... 1.00
Relative Chemical Diffusivity ..... 1.00
Demand Multiplier ................. 1.00
Total Duration .................... 72.00 hrs
Reporting Criteria:
No Junctions/Tanks/Reservoirs
No Pipes
No Pumps/Valves

Analysis began Fri Aug 26 10:16:32 2016



Hydraulic Status:
-----------------------------------------------------------------------
0:00:00: Balancing the network:
Trial 1: relative flow change = 1.608633
Trial 2: relative flow change = 1.074902

.
.
.
.
Trial 246: relative flow change = 1.026194
Trial 247: relative flow change = 1.047483
Trial 248: relative flow change = 1.027607
0:00:00: Unbalanced after 249 trials (flow change = 1.027607)
Total Supplied: 4719.67 gpm
Total Demanded: 1025.81 gpm
Total Stored: 3693.79 gpm
0:00:00: Reservoir RES3 is emptying
0:00:00: Reservoir RES4 is emptying
0:00:00: Reservoir RES5 is emptying
0:00:00: Reservoir RES6 is emptying
0:00:00: Tank T1 is filling at 10.00 ft

WARNING: System unbalanced at 0:00:00 hrs.

** Run failed **

I
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Hydraulic Run Warning
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** Hydraulic Run Failed or Aborted : only partial results available **
** Available Run Result Duration : 0:00:00 hrs. **

Patrick Moore
August 26, 2016, 12:21 PM
Nykieta,

It was good to talk to you today to help troubleshoot your model issue.

For the benefit of the Forum, I will post the solution.

The model in question had all isolation valves modeled as General Purpose Valves (GPVs) which use a headloss vs. flow curves. These valves when a lot are used in a model can cause issues with model instability because with multiple GPVs in a loop make it difficult for the model to converge head and flow as every time the flow changes this changes the headloss which causes another check of the flow balance, etc. A few GPV's here and there are not an issue, but GPVs are known to cause instability in EPANET when there are a lot used in a model.

The solution for this model was simply to convert the GPV's to Throttle Control Valves (TCV's). Use of TCVs are the typical way that isolation valves when modeled as valves when they are modeled as valves rather than junctions. These TCVs are much more stable especially when two or more of the valves are associated with any pipe loop in the model.

Once all of the GPV's in this model were converted to TCVs the model converged with a green light.

Thank you again for posting your question to the user forum.

Patrick Moore