General Mechanical

General Mechanical

Impulse Harmonic Analysis

    • ItalicBike
      Subscriber

      Hi everybody,


       


      I'm new on the forum. I use ansys 18.2. I've some question for my job.


      I've to model a experimental test, in particular the FRF of an aluminium panel subject to a impulsive load (like an hammer test). So the take-away question is:


      It's possible to model an impulse load without carry out a transient analysis? Could you say me which block i'have to use?


       


      Thanks in advance.


      Best Regards


       

    • peteroznewman
      Subscriber

      Use a Harmonic Response system block. That can either be on its own, or linked from a Modal analysis. Here is an example on a Bridge.



      Select a face to be a Fixed Support and apply a unit Force at the point where the hammer would impart an impulse load. The system will treat this as a harmonic forcing function. In Analysis Settings, select the frequency range of interest and how many points to plot over that range. Request a Frequency Response output at the point where you would put the accelerometer. The output will be like an FRF.

    • ItalicBike
      Subscriber

      Thanks for answer peteroznewman,


      it's possible to apply a damping coefficient function frequency?

    • peteroznewman
      Subscriber

      Yes, there are several ways to add damping.  Either as a constant damping ratio or as coefficients to the Mass and Stiffness matrices (Rayleigh Damping) or both. You can also add damping to the material, which will add to these values.


    • ItalicBike
      Subscriber

      Thank you Peteroznewman, but i have to define frequency dependent structural damping. Does it is possible in Workbench o I need to write an APDL command?


      If yes, could you help me to understand the variuos command TBDATA, TBFIELD, TB, SDAMP?


       


      Thanks


       


      Best Regards

    • peteroznewman
      Subscriber

      If you click on the pull down menu on the Stiffness Coefficient line where it says Direct Input, you will see you can input frequency dependent structural damping.

    • ItalicBike
      Subscriber

      Sorry peteroznewman, but only 1 value? I need to input 16 values. Thanks


       

    • peteroznewman
      Subscriber

      Damping is frequency dependent when you use Mass and Stiffness coefficients. Here is the equation that shows how the frequency is combined with the coefficient to calculate a damping ratio.



      Take the table of 16 frequency and damping ratio pairs and fit the three coefficients to your data. I can help with the fitting if you don't get a good fit.


    • ItalicBike
      Subscriber

      Thank you so much, very very very useful. And also thank for you patience.


       


       

    • peteroznewman
      Subscriber

      You're welcome.

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