PGAP vs PBUSH/PBUSHT

Marco Somà
Marco Somà Altair Community Member
edited April 2022 in Community Q&A

Hi,

brief intro: I want to get the eigenfrequencies of a structure which includes cables in tension. Since they are modeled as NL elements I can't use the normal mode analysis, therefore I was thinking on using the Frequency responce (direct or modal) simulation to get the FRF plot. 

In order to simulate the cables I tried:

  • Spring (CELAS - PELAS), it works both for linear static and normal modes, but it sets the same stiffness to tension and compression and this is unreal for me
  • Gap (CGAP - PGAP), it works only for non-linear static while it induces a constant stiffness in all the other simulations (this is what I read from attachment 1) so I can't use it. In addition the preload F0 is only in compression, while I need it in tension and I didn't manage to reverse it
  • Bush (PBUSH-PBUSHT), I tried to model it with PBUSH and PBUSHT by adding the tabel TABLED1 but from what I got it expresses the stiffness in function of the frequency and not in function of the positive or negative displacement

Do you have any ideas on how to model it?

Thank you for your help

Marco

 

 

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Answers

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited April 2022

    Hi again Marco,

     

    Modal, FRF, both are linear analysis, so no contact or nonlinear behavior is allowed in general.

     

    For simulating something like that, you will need to go to NL Transient analysis and impose a input to generate this excitation in your structure, by using OptiStruct NL Transient, or OS Explicit, or Radioss Explicit.

     

    By the way, PBUSHT for NL analysis uses a table for Force x Displacement behavior.

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