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Non-zero flow in closed pipes next to hydropneumatic tanks

Ref: http://communities.bentley.com/products/hydraulics___hydrology/f/5925/t/123522

Thank you for the response.  I was able to get the booster pump to turn on and prevent the hydropneumatic tanks from emptying completely.  All four tanks are connected to the main waterline by individual pipes (one pipe for each tank) that connect to a common junction on the main line.  With the EPS I've been running, the four tanks should be inactive during the day (with one or two booster pumps providing all the needed flows and pressures during the day), and there should therefore be no flow in the pipes that connect to the tanks.  However, whenever I graph the flow for any of these four pipes, I get the plot shown below.  These spikes and drops in flow are causing the tanks to experience abrupt changes in pressure and liquid volume when these parameters should remain constant during the day (due to the pipe being closed).  I have controls set up so that the pipes are set to be closed, so I'm not sure why these spikes and drops in flow are occurring in the first place.  Do you know why they may be occurring?

  • Robert,

    In this case it will probably help us to see a copy of your model files. As suggested by Scott above, there are two options for sharing your model on Communities, whichever you choose please be sure to zip your files first. The first option is to attach the zip file containing your model to your reply on the forum using the Advanced Reply Editor (you'll find the link below and to the right of the reply box). If your data is confidential please use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley employees. Please be sure to reply on this thread with the name of the file after it has been uploaded.

    communities.bentley.com/.../7079.be-communities-secure-file-upload

    If you upload the files to Sharefile, please post here so we know it is available.

    Regards,
    Mark

    Mark

  • I've uploaded the folder to Sharefile. It's called Water Model_RJT.zip.

    Another issue I've been having has to do with the pressures and liquid volumes in the hydropneumatic tanks. Each tank is supposed to have an operating pressure range of 40 - 60 psig. A volume of 31.3 gallons of water is supposed to be discharged from each tank when dropping in pressure from 60 psig to 40 psig. However, the graphs keep showing a liquid volume range of 10 - 15 gallons only. The pressures in the tanks also don't correlate with the operating pressure range.

    Each tank has a total volume of 115.9 gallons and a maximum drawdown of 70.5 gallons. If you know of a way to correct these issues as well, I would greatly appreciate it.

    Thanks,
    Rob Tejano
  • Hello Rob,

    It looks like the zip file only contains the .WTG file. Please include the .WTG.SQLITE file as well, as both are needed to open the model.

    In the meantime, some general suggestions - if the hydropneumatic tanks are offline or "float" on the system, try setting the "treat as junction" property to "true", for the appropriate scenarios.

    For the other issue - try a smaller calculation timestep. This tends to be the cause of many EPS problems with hydropneumatic tanks.

    See also:

    How are surge tanks and hydropneumatic tanks (hydro tanks) used in WaterGEMs and WaterCAD models?


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

  • I've re-uploaded the folder (same folder name) with the .WTG.SQLITE file. Let me know if you need anything else. Thanks.
  • Robert,

    I'm still looking into this model and will give you an update when I have more information.

    Mark