# Problem to perform a Random Vibration Test

Question asked by Xavier Laurand on May 30, 2017
Latest reply on May 30, 2017 by Ryan Dark

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 :

.

Then, I defined a global damping as :

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

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 ?