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Unexpected High Flow - WaterGEM

Yoko
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When I was working on Steady State analysis of a system with 8,310 gallon per day demand, I realized that one node with 2.36 gpm demand had 23.6 gpm demand instead. At that time, steady State was working.  I corrected the demand at that node, which should decrease the total demand by 30,585.6 gallon.  But, when I re-run the steady state, 3,600 gpm flow is trying to go to the node.  We could not figure out why. There is no such demand assigned.

We need to make this model work as soon as possible. I wonder if someone could give us an advice on what to look for.

Yoko

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  • 0 Offline
    Scott,
     
    This table shows before (the upper table) I changed the demand at Junction Southeast from 23.6 gpm to 2.36 gpm and the initial elevation of the 3,000 gallon Tank at WTP from 1,397.00 ft to 1,400.86 ft.  The lower table show the results afterword and the initial elevation of the same tank is back to 1,397.00 ft now.  The results did not change much after I change the tank initial elevation back to 1,397.00 ft.
     
    Thanks again for looking at the model.
     
     
    Yoko Nomura, E.I.T.
    Project Engineer
     

    PCE, Inc. | 6120 Earle Brown Drive, Suite 629, Brooklyn Center, MN 55430 | www.pce.com
    (763) 560-9133 Phone | yokonomura@pce.com
     
  • 0 Offline in reply to Yoko
    Hello Yoko,

    I assume the scenario that you are running is "1-Stead State Analysis". This appears to have a demand of 2.36 gpm and a tank level of 1397 ft. If you are looking at a different scenario, please let me know.

    When I compute the model as is, I get a "Network Unbalanced" message, meaning the results cannot be trusted. I made a few changes to the calculation options to fix this. First, I increased the number of trials to 100. Second, I set the Damping Limit to 0.01. With this changes, the model was able to compute without an error message.

    After the changes, the pump flow results for pump "PMP-Distribution" was about 47 gpm. Flows in WaterGEMS will always satisfy the demands, but it will also balance the hydraulic grade across the system. The additional flow not going to demand is filling the three tanks downstream of the pump. The general results appear to be reasonable based on what I am seeing.

    Regards,
    Scott

    Answer Verified By: Sushma Choure 

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  • 0 Offline in reply to Yoko
    Hello Yoko,

    I assume the scenario that you are running is "1-Stead State Analysis". This appears to have a demand of 2.36 gpm and a tank level of 1397 ft. If you are looking at a different scenario, please let me know.

    When I compute the model as is, I get a "Network Unbalanced" message, meaning the results cannot be trusted. I made a few changes to the calculation options to fix this. First, I increased the number of trials to 100. Second, I set the Damping Limit to 0.01. With this changes, the model was able to compute without an error message.

    After the changes, the pump flow results for pump "PMP-Distribution" was about 47 gpm. Flows in WaterGEMS will always satisfy the demands, but it will also balance the hydraulic grade across the system. The additional flow not going to demand is filling the three tanks downstream of the pump. The general results appear to be reasonable based on what I am seeing.

    Regards,
    Scott

    Answer Verified By: Sushma Choure 

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