General Mechanical

General Mechanical

Inaccurate results

Tagged: 

    • kimkarimi9574
      Subscriber

      Hi there,

      I'm trying to validate my settings with attached paper. I get inaccurate results and I don't where is the problem. could you please help me out. In fluent part, the settings include gravity -9.81 in y dir, k-epsilon model with enhanced wall treatment for viscosity, water as fluid and steel as solid (the solid part in article was rubber, so I selected steel then I changed the properties to rubber properties) for materials, inlet 7.19m/s and 300K - inner wall with coupled thermal condition- outter wall 300K for BC.

      In static structural part, the settings include gravity -9.81 in y dir, fluid solid interface, remote force of 7.63N and remote displacement of 0-free-0-free-free-free condition at the left end, remote displacement of 0-0-0-0-0-0 at the right end.

      In harmonic response part, the settings include prestress from static structural, min 58(rad/s)- max 88(rad/s)- solution intervals 5 for frequency, nodal displacement of 0.012m in y dir at the left end for harmonic excitation.

      for these settings I got the attached results.

      thanks a million!


    • Ashish Khemka
      Ansys Employee


      Ansys employees cannot download the attachments. If you can share the snapshots directly in the post and the details of what you are trying to achieve and what you have modeled - it will be useful and easier for us to comment.

      Regards Ashish Khemka
    • kimkarimi9574
      Subscriber

      I'm trying to get amplitude-frequency plot of a pipe conveying fluid. Couldn't you open the screenshots aswell? Because 3 last files are images.

    • Ashish Khemka
      Ansys Employee


      We are not allowed to download the files.

      Regards Ashish Khemka
    • Erik Kostson
      Ansys Employee
      Hi
      PLease post them in-line like below:


      As we said before to see the change in eigen-frequencies and response due to the flow in a pipe that is conveying fluid (so dynamic beam bending differential equation + Centripetal and Coriolis terms due to fluid flow) we just need a vibroacoustic (acoustic harmonic system ) analysis with structure (pipe) and fluid (water say), and we need to add the BF,ALL,VMEN,,, command to the acoustic nodes, for the mean flow in the acoustics - of course if the amplitudes are high and you have some nonlinear effects then this approach (vibroacoustic - linear theory) will not work.

      Hope this helps:

      So nonlinear vibrations (say high amplitudes) -> 2 way FSI (E.g., Fluent+Transient Structural Mechanical)
      Linear vibrations (small amplitude vibrations) -> vibroacoustics.

      All the best
      PS:If you are using Fluent/CFD to mechanical coupling and why (due to nonlinear vibrations), then it is better to post under the fluids forum also.

    • kimkarimi9574
      Subscriber

      These are the images one of them is problem description, one of them is the paper result and one of them is my result. Please accept my apologies for sending the files.
      Thank you so much!


    • Erik Kostson
      Ansys Employee
      No worries at all - we can not see exactly what you want to do but we said if it is nonlinear dynamic effects or one is just looking into linear (so effect of fluid flow on vibration) then these are the two options that you can use for a fluid conveying pipe:

      So nonlinear vibration effects on fluid conveying pipe (say high amplitudes) -> 2 way FSI (E.g., Fluent+Transient Structural Mechanical - you can not use Harmonic since that is linear analysis)
      Linear vibrations for fluid conveying pipes (small amplitude vibrations) -> vibroacoustics + BF,ALL,VMEN command
      using the harmonic acoustic system - but you have nonlinear effects then we can not use the linear vibrations approach only this is what one can try and use:
      2 way FSI (E.g., Fluent+Transient Structural Mechanical (large deflections on) - you can not use Harmonic since that is linear analysis)
      All the best

      Erik
    • kimkarimi9574
      Subscriber

      Ok, then I try acoustic.
      Thank you very much!


    • Erik Kostson
      Ansys Employee


      No we can not use acoustics as we said since there are nonlinear effects here so we have nonlinearities due to large amplitudes of vibration here. In the response shown in the second image above labelled Fig.6 one can see probably such nonlinear effect being present.
      So:
      Linear vibrations for fluid conveying pipes (small amplitude vibrations) -> vibroacoustics + BF,ALL,VMEN command
      Can not be used here!

      so you need to:
      Nonlinear vibration effects on fluid conveying pipe (say high amplitudes) -> the only option that might be able to capture this is a 2 way FSI (E.g., Fluent+Transient Structural Mechanical (with large deflections))
      SO a full 2 way FSI analysis as shown here:
    • Erik Kostson
      Ansys Employee
      Hi
      See my response above - so the only option to try (not sure if it will capture it) and model this is:
      a 2 way FSI (E.g., Fluent+Transient Structural Mechanical (with large deflections)-you can not use Harmonic Analysis since that is a linear analysis so we need a Transient Structural coupled to Fluent)
      SO a full 2 way FSI analysis as shown here:


    • kimkarimi9574
      Subscriber

      Ok, so I'll try with transient structural. Thanks a million!
    • kimkarimi9574
      Subscriber

    • Erik Kostson
      Ansys Employee
      Yes, it will be very hard but you can try - as always do not forget to activate for large deflections in the transient structural.

      All the best of luck

      Erik
Viewing 12 reply threads
  • You must be logged in to reply to this topic.