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Simple Pipe Pressure Problem

John Green
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I'm doing a simple water system pipe pressure problem with WaterGEMS.  I've entered all pipes, etc and I've computed the model and I'm analyzing the pressure at a junction by looking at it's properties  I now want to change the roughness factor of all pipes uniformly to reduce the pressure at this junction so I've changed the Darcy-Weisbach roughness "e" in the pipe table for all pipes.  I've computed the model and have noticed a different pressure at the junction.  When I change the roughness values a second time and compute the model, the pressure doesn't change at the junction..  Overall, I'm analyzing the pressure at the junction by changing the pipe roughness.  Am I following the correct steps in doing a simple analysis of the junction?  It seems like this is the straight forward process but I'm not sure why the pressures don't change on my second iteration of changing the pipe roughness.  Any help is appreciated...thanks...J

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    What version of the software are you using?

    The version number can be found by going to HELP > About WaterGEMS (File > Help > About WaterGEMS in the CONNECT Edition version) inside your program and locating the number in the lower left hand corner and may be in brackets. It should start like this 08.11.XX.XX (10.XX.XX.XX) where X  are some numbers.  

    Mark

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    Thanks for helping:
     
    I’m using WaterGEMS V8i (Select Series 6).  Having access to the instructor/student version, this is what is available.  I installed stand alone and didn’t integrate with CADD.  Overall, I’m trying to demonstrate a couple fundamental pipe network problems showing how changing variables (i.e. pipe roughness) will  change the model outcome.
     
    I’ve used the application a number of years back but somehow when I’m doing the second iteration, the pressure isn’t changing…any help is really appreciated…thanks…John
     
  • 0 Offline in reply to John Green

    Hello John,

    The change in the junction might be minor, please increase the decimal precision of the pressure.

    In the junction properties>Pressure> Right click>Units & formatting>change the display precision to a higher number like 4 and now observe the difference in junction pressure after changing the Darcy-Weisbach roughness "e" in the pipe table.

    Regards,

    Sushma Choure

    Bentley Technical Suppport

  • 0 Offline in reply to John Green

    John - here are a few other thoughts:

    1) Are you changing the roughness of one pipe, multiple pipes, or all pipes?
    2) What method are you using to change them?
    3) What is the exact change you are making? Meaning what is the original roughness height, the second roughness height and the third roughness height value? As Sushma mentioned, perhaps the change is so small for the flow through the pipes, that the pressure does not change with your current display precision. Perhaps you can provide an example pipe with the data input (roughness height, diameter, length, etc) and the flow value seen with both roughness values.
    4) In the calculation option set that is active for your current scenario, is the friction method set to Darcy-Weisbach?
    5) What is the general layout of the system where you are changing the roughness? For example a pump between a reservoir and a tank, a pump from a reservoir to a closed system with demands, something else?
    6) Are you seeing any red user notifications indicating that the second run failed or was unbalanced?


    Regards,

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

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    Jesse…thanks for your interest.  I’m certain my issue is procedural and I’ve addressed your questions with a combination of the screen shots below and below your original questions in red.  There must be an easy solution to my issue. 
     
    Overall, this is a text book question that utiIizes WaterGEMS.   The problem statement provides the pipe network information that I’ve provided below. The problem statement also indicates that field observations show the pressure at J5 as 288 kPa (reservoir elevation is at 100 m).  Shown below, in the properties dialog, the pressure at J5 with the problem statement is 296 kPa.  So the question is to find the Darcy-Weisbach roughness height (to the hundredth place) to bring model into agreement with the field records.
     
    I hope that you can review my responses below and lead me in the right direction…thanks…J
     
    Pipe Network
     
    Pipe  Table
     
    J5 Properties dialog box
     
     
     
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