2 Replies Latest reply on May 30, 2017 1:40 PM by Ryan Dark

    Problem to perform a Random Vibration Test

    Xavier Laurand

      Hello everyone !

       

      Let my introduce my self, my name is Baptiste TROTABAS and I have to perform a Random Analysis for my school project

      So, to make this, I launched a new simulation study > linear dynamic > Random Vibration

      After that, a wrote my excitation curve :

      Frequency --- PSD

                 5 Hz --- 0.040 (g²/Hz)

            100 Hz --- 0.20 (g²/Hz)

            500 Hz --- 0.20 (g²/Hz)

          2000 Hz --- 0.040 (g²/Hz)

      And I obtained this curve :

                                          Curve.PNG.

      Then, I defined a global damping as :

      global damping.PNG

       

      Finally I launched the Random test but I obtained this error message :

      pb.PNG

      I tried to perform this analysis without a curve, but with a constant value (=1) and it was a success.

      Hence, I tried in additionning more points : we can consider my curve as 2 linear functions.

      Thus I determined values regarding to a frequency [ f(20hz) = 0.040 & f(50hz) = 0.20 => f(30Hz) = a.x + b, and so on.. ]

      Now I have the same curve as previously, but describe with 2800 points.. However even with this, analysys doesn't work..

       

      Do you know, how perform correctly this analyse ?

       

      Thank you by advance !

        • Re: Problem to perform a Random Vibration Test
          Keith Frankie

          In the study properties, random vibration options, what upper limit are you using?  You probably want to set that to 2000.

           

          You could also define your excitation curve for points beyond 2 kHz.  Either of these two solutions would solve your error message.


          I do see, though, that your first vibration mode is listed at 10 kHz.  That's way above your input curve, so you won't really be getting any useful data out of this study.  Is your model really that stiff, or might it be over constrained?

          • Re: Problem to perform a Random Vibration Test
            Ryan Dark

            Hi Xavier,

            From your setup it looks as though your highest mode is ~28,000 Hz.  The curve that you have defined would need to be extended above this per the warning you are getting.  You may want to also cover the lower range as well.  A curve like this may help: