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Adjustment pressure

Hello everyone

I have a problem with my simulation because I don’t reproduce the discharge pressure using “Periodic head-flow”. I’ve noticed that viscosity is fundamental for the network, logically when I changed the viscosity the discharge pressure changes, however this change is not lineal, it is like a parable, it been not logical, I tried with other fluids and the behavior is lineal how I expects.  I hope someone knows something.

Thanks.

Regards 

  • Hello Lyanne,

    In order to answer this, a bit more information will help.

    1) I assume you're using HAMMER. What version are you using? You can find this under Help > About HAMMER. The latest is 08.11.06.58 (SELECTseries 6)

    2) When you say you "don't reproduce" the discharge pressure, what exactly do you mean? Are you comparing to some field measurements? There are any number of differences between the model assumption and the real system that can cause differences.

    3) What exactly does this Periodic Head-Flow element represent?

    4) When you say "discharge pressure", are you looking at the pressure at the periodic head-flow element during the initial conditions, or something else? (max pressure during transient simulation?)

    5) You mentioned that you did not see this behavior with other fluids. Can you be more specific as to exactly what parameters you're varying?

    6) Can you provide a copy of the model for review? There are two options for sharing your model on Communities. Either way, be sure to zip your files first. The first option is to attach to your reply on the forum using the Advanced Reply Editor (see link below and to the right of the reply box). If your data is confidential, use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley.

    http://communities.bentley.com/help/w/be_communities_help/7079.be-communities-secure-file-upload


    Regards,

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

  • Original TPC-ICAMOR (DCOM).wtg_1_1 (2).zip

    5852.Original TPC-ICAMOR (MEREY).wtg_1_1.zip

    1) I’m using Hammer Bentley V8i SELECTseries 5.

    2) By reproduce, i mean to simulate. I need to simulate the discharge pressure in a displacement positive pump that exists, I have the network in other simulator where I evaluated the steady state and I got the pressures I expected. Now I need to reproduce that network using Hammer. I know that exists a difference between both simulators but using Hammer the viscosity has a totally different behavior at the same initial conditions. that is not expected because I worked with the same fluid in both softwares.

    3) I want to simulate displacement positive pump.

    4) I’m looking at the pressure at the discharge of the periodic head- flow during the initial conditions.

    5) I have two fluids that I need to evaluate in the same network, both are crude 16°API( a) Merey16°API, b) DCOM 16°API). When I run the simulation with the first crude, this doesn't presents any problems but using DCOM 16 it does. I’m only changing the fluid specifications in the simulation (viscosity, temperature, vapor pressure, gravity specific, the wave speed and the discharge coefficient of control valve at the end of the network)

    6) Yes, of course. I sent two simulation for the both fluids. For the first one "Merey" the discharge pressure at  the periodic head-flow should be 750psi, while for the second one "DCOM" should be 577psi.

    Thanks.

  • Hello Lyanne,

    The pressure results for different values of viscosity could be occurring because of a change from laminar to turbulent flow. If you look at the Moody diagram, you can see a discontinuity in friction factor vs. Reynolds number (which contain viscosity). This would only happen at low velocity in small pipes. Note that if you use the Hazen-Williams friction method instead, you would not need to worry about the impact of the change in viscosity.

    That said, if you are trying to calibrate your model to match field results or do a sensitivity analysis, it might be best to leave the viscosity at the actual value for the liquid. The viscosity is likely going to be constant no matter the system. However, factors like pipe roughness are more likely to change over time.

    If this doesn't help, knowing more about what exactly you are trying to do would be useful.

    Regards,
    Scott
  • Hello Scott,

    Thanks for your answer. In fact, the problem is the flow is between at the change from laminar to turbulent flow. What should I do in this case? there is a way to adjust the boundary between laminar and turbulent flow?
  • The boundary between laminar and turbulent flow is a property of nature and you can't adjust that.

    Usually when you have such low velocity that you are in laminar flow, the head loss and transient effects are pretty minor and don't make much difference in your overall results.