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Resulting Force seems wrong in HAMMER.

Normand Chabot
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My model consists of 5 pumps in a pumping station with a lots of piping. Every node was placed perfectly in the correct axis in order to use the "Calculate Transient force" option. Everything is running well. Results are logic, except for one node where I have a surge valve. There are two parallel lines running, one on top of another, and they connect at each end. Each line has a surge valve on it. Wheter I run scenarios where the surge valves open or not, I get the same problem. The valve on the top line sees a force in Y, which I expect since the pressure from the water in the pipe is pushing that way. The valve on the bottom line does not see a force in Y. I would expect it to since it is subject to the same pressure and placed in the same axis as the other valve and I do get a Pressure Result for that node. Both upstream and downstream nodes of the surge valve see forces in the expected axis, including the Y axis. Any ideas?

  • 0 Online
    Hello Normand,

    We are looking into this issue. I will post here when I have an update for you.

    Thanks,
    Scott
  • 0 Online in reply to Scott Kampa
    Hello Normand,

    HAMMER is working as expected. The reason for the difference in force is largely related to the pipe sizes. Pipe SRP_RECIRCULATION has a larger diameter for one of its adjacent pipes. That is why there is a force component in the Y direction. Basically, the pressure force component is greater in the larger diameter pipe (pressure force = pressure * pipe area).

    You may want to double-check that the pipe sizes and pipes lengths are accurate near the SRVs (one of the pipes is also a little longer than the others, though still pretty short for a HAMMER model). Please let us know if you have any questions.

    Regards,
    Scott

    Answer Verified By: Normand Chabot 

  • 0 Offline in reply to Scott Kampa
    Ok. Thanks! I should have seen that. One last thing that I'm a bit puzzled by: If I run it in "steady state", meaning I change the operating rule of TCV-1 from Butterfly to Open and I run Compute (and not Compute Initial Conditions), I still get a force for SRP_RECIRCULATION and no force for SRP_RELACHE, even though neither surge valves open. I'm having trouble understanding how this could be explained by the change in pipe size when no flow goes through the surge valves. Can you enlighten me?
  • 0 Online in reply to Normand Chabot
    Hello Normand,

    Though there may be no flow in the pipes, the pipes are still under pressure. So the pressure difference related to the different pipe sizes will still apply even if there is no flow through this part of the system. As mentioned above, the pressure force component is greater in the larger diameter pipe (pressure force = pressure * pipe area).

    Regards,
    Scott

    Answer Verified By: Normand Chabot 

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