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Getting reliable results from Bentley Hammer

Hi,

I am modelling a simple system to compare the results to some codes that I have. But, despite having all the configurations similar to codes, I cannot get similar pressure fluctuation. Could you please have a look and let me know the reason?

Thanks in advance.

Regards,

Example 1.xlsx8233.Example 1.zip

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  • Thanks for your response. I am using the MOC and I wrote the code in Matlab. I compare my code to some results from other researchers that are very close as you see in the spreadsheet. I want to develop my code more for some research purposes and compare them to results from Hammer. I tried to use the same valve pattern and other specifications. But still, the Hammer result is far from other cases (please see the attached graph too). I am trying to understand how to calibrate the Hammer model with some real or reliable data. I appreciate more comments on this issue. 

  • HAMMER models cavitation (vapor pocket formation) when the pressure reaches vapor pressure (set to -10m by default). That's why your HAMMER pressures stop going down at -10m and instead start to 'flat line'. Then later when the vapor pocket collapses you get a pressure spike. 

    I assume the other calculations you are using don't attempt to model cavitation, which may explain the difference. As a quick workaround you can change the vapor pressure value in the calculation options to some large value (like -100m).

          

    Answer Verified By: Hiwa 


  • Regards,

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

    Answer Verified By: Hiwa 

  • Dear Mal,

    Very good point. I appreciate it. Yes, you are right please see the attachment. I am not using a cavitation model. 

    But for the other one, I didn't have the negative pressure (as you see below). Do you have any comment on improving accuracy?

    Regards,

    Hiwa

  • But for the other one, I didn't have the negative pressure (as you see below). Do you have any comment on improving accuracy?

    It could be due to a difference in how the valve characteristics are modeled, or with the discharge-to-atmosphere (D2A) pressure vs. flow characteristics. What assumptions are you making in your program for these elements? This article explains the Ball valve characteristics and this article explains how the D2A works. If you change the valve type, you will see a large difference in the pressure time history. For example if you try the Globe valve type instead of Ball, the results will be quite close.


    Regards,

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

    Answer Verified By: Hiwa