Finding transfer function of 3D model by Activate/Motionview

Phat Vu_22478
Phat Vu_22478 Altair Community Member
edited November 2020 in Community Q&A

Hi,

I have a model created in Motionview with specified input and output (Supposing I have a body moves with a friction force, the applying force and the velocity of body correspond to input and output). I wonder how can I find the transfer function of this system? I think it can be done by cosimulating with Activate but I don't know exactly the progress. Could anyone help me to deal with it?

Thanks for your attention.

Tagged:

Best Answer

  • Thierry Bernard_21945
    Thierry Bernard_21945
    Altair Employee
    edited November 2020 Answer ✓

    Hello,

    Friction force is a typical non-linear element that is not well suited to be captured by transfer function  .

    So in order to analyse the behavior of a mechanism subjected to friction in the frequency domain, you can use either of the two following way :

    • Modelize friction in Activate :
      • Set friction force to zero in MotionView model
      • Linearize MotionView model with respect to force input and velocity output (see below)
      • Assemble a deidicated Activate model made of :
        • MotionView linear state matrices (without friction)
        • Friction formulation based on saturation, gain, etc ...
    • Modelize friction in MotionView :
      • Simulate the response of the mechanism to some sweepsine excitation force over a meaningfull frequency range
      • Use Compose to plot estimated FRFs between input (excitation force) and output signals (body velocity) by leveraging dedicated "ms_cpsdplot" feature
      • Rerun same analysis with different magnitude of excitation force

    You can linearize your MotionView model the following way :

    • Define a solver variable to be used in the force expression
    • Refer this solver variable in a plant input solver array with flagged "used for linearization"
    • Define a solver variable measuring the velocity of the body
    • Refer this solver variable in a plnat output solver array with flagged "used for linearization"
    • Set linear simulation settings to output Compose OML state matrices (2020.1)
    • Simulate static operating point and linear analysis

    Regards .

    Thierry BERNARD

Answers

  • Thierry Bernard_21945
    Thierry Bernard_21945
    Altair Employee
    edited November 2020 Answer ✓

    Hello,

    Friction force is a typical non-linear element that is not well suited to be captured by transfer function  .

    So in order to analyse the behavior of a mechanism subjected to friction in the frequency domain, you can use either of the two following way :

    • Modelize friction in Activate :
      • Set friction force to zero in MotionView model
      • Linearize MotionView model with respect to force input and velocity output (see below)
      • Assemble a deidicated Activate model made of :
        • MotionView linear state matrices (without friction)
        • Friction formulation based on saturation, gain, etc ...
    • Modelize friction in MotionView :
      • Simulate the response of the mechanism to some sweepsine excitation force over a meaningfull frequency range
      • Use Compose to plot estimated FRFs between input (excitation force) and output signals (body velocity) by leveraging dedicated "ms_cpsdplot" feature
      • Rerun same analysis with different magnitude of excitation force

    You can linearize your MotionView model the following way :

    • Define a solver variable to be used in the force expression
    • Refer this solver variable in a plant input solver array with flagged "used for linearization"
    • Define a solver variable measuring the velocity of the body
    • Refer this solver variable in a plnat output solver array with flagged "used for linearization"
    • Set linear simulation settings to output Compose OML state matrices (2020.1)
    • Simulate static operating point and linear analysis

    Regards .

    Thierry BERNARD

Categories