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bentley water hammer

I have made a model on water hammer software , whole layout I have plotted. pressure and head output I got correctly but HGL line shows equal levels, i don't know why it's done Ithink something I missed while putting input. 

    Anybody please  say me what data need to put for getting accurate HGL (hydraullic gredient line), so I can compared with my input data. Please give me solution as early as possible.

                                                       THANK YOU.....

  • Hello Sanket,

    I am assuming that you were able to successfully compute the transient solver. Based on that, what kind of transient event are you model? Events like a pump shut down or valve closure should show some change in hydraulic grade. If you are not modeling a transient event, you may see no change in the hydraulic grade over time. Further details on what you are seeing would be useful.

    I would make sure that you are animating the transient profile, as that will show you how the hydraulic grade or pressure is changing over time. 

    Regards,
    Scott

  • To make things clearer, here are the observations/problems I'm facing currently:

    1) HGL is show as a straight line in Elevation v/s Distance Profile.

    2) Is there any way to input HGL data available; manually in the software?

    Here's a link to the original file I'm working on: 

    https://drive.google.com/file/d/1cGqGDEr1Xm_nTZVjyjikwncNeeoDmmxf/view?usp=sharing

    Thanks in advance

  • Hi Sanket,

    Your model looks ok. For the pipe diameter and flow you have the friction is very low, that's why the HGL (steady state) seems to be horizontal. If you look carefully the HGL at the pump discharge is 340.27 and at the end reservoir 340. Therefore the friction is only 0.27 m which is correct. For this flow scenario the pipe is too big (not sure if you have other flow scenarios too).

    Answer Verified By: Sanket Shivankar 

  • To add to the reply above, you will want to make sure you are working with a calibrated model. If the flow is accurate but pressures at the downstream nodes are not what you expect, you can adjust the pipe roughnesses to assure accurate input. This will also make sure your transient results are accurate.

    The low headloss also means that that transient pressure results are slow to diminish. You may want to try computing the transient run for longer to gauge how long it will take for the pressure wave to reach a new equilibrium after the pump shut down. This link has some additional information on this.

    Regards,

    Scott

  • I took a quick look at the model and wanted to add a few more points:

    • If you want to see what happens during the transient event (not just the flat HGL from the initial conditions), be sure to use the Transient Results Viewer (see link previously provided by Scott) to animate the results to see the HGL change after the pump shutdown event.  The Transient Results Viewer will also show you the minimum and maximum HGL "envelope" for your profile.
    • In your model, I see a downsurge wave in the transient profile animation, which causes some vapor pockets on the downstream end (due to the low initial pressure at those points). You may need to ensure that your junctions are using pipe elevation instead of ground, and possibly consider a PSV or top-fill tank at the downstream end via a D2A (assuming "res2" represents a tank), to prevent the initially low pressures and subsequent vapor pockets during the transient event..
    • Regarding inputting the "HGL data" manually - you can indeed manually enter the initial conditions by choosing "true" for the "Specify initial conditions" transient calculation option, but if the initial conditions HGL computed by the initial conditions solver is not what you expect, then it is probably best to determine the cause of the discrepancy and amend the model so that the results match your expectations. 


    Regards,

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