J. T.

ASD values from Random Vibration FEA

Discussion created by J. T. on Nov 27, 2020

I have recently been looking for some information regarding ASD graphs which are derived from Random Vibration analysis. Frequency analysis as Random Vibration FEA simulation is relatively new for me and I was wondering whether someone could help me with the issue I keep getting.


After running the actual simulation, the main output I am interested is acceleration response from various nodes in the model. What I noticed is that at the start of response data taken with Define Response Graph tool there is a difference in respect of the input load – most of the time values which were taken with aforementioned tool are lower than the input load (you can see this in the picture below).


I could be wrong (and please correct me if I am), but up to the first fundamental frequency values from every node in the model should be the same as ones from the input load. Sometimes I get this relationship, sometimes I don’t.

Can someone please explain me what am I missing here? Is it something with the software or the actual decrease in value can be theoretically explained?



Thank you in advance



Info regarding the graph:


- red dashed line is the input load.

- blue, grey and orange lines represent acceleration response from different nodes in the model.

*1st fundamental frequency is not reached.