frequency response FEA
frequency response FEA
(OP)
Hi
I have carried out a FE frequency sweep analysis of an assembly using modal superimposition. The assembly is shaken using the same acceleration amplitude across a frequency range along one direction only.
When plotting the response (acceleration) Vs frequency for several nodes there are frequency intervals where this becomes NEGATIVE.
Does a negative acceleration make sense in this case?? If so, what is the underlying physical meaning?
Thanks
Gio1
I have carried out a FE frequency sweep analysis of an assembly using modal superimposition. The assembly is shaken using the same acceleration amplitude across a frequency range along one direction only.
When plotting the response (acceleration) Vs frequency for several nodes there are frequency intervals where this becomes NEGATIVE.
Does a negative acceleration make sense in this case?? If so, what is the underlying physical meaning?
Thanks
Gio1





RE: frequency response FEA
If you have plotted the magnitude in dB then it also makes sense, but means something completely different.
Perhaps you could save us some guesswork and post one of these puzzling plots.
Cheers
Greg Locock
I rarely exceed 1.79 x 10^12 furlongs per fortnight
RE: frequency response FEA
All I have done is choosing the nodal response result "acceleration" and picked a node. What I get is a graph with frequency (Hz) on the X axis and acceleration (mm/s2 - consistently with my units) on the Y axis. I can clearly locate the resonances, but the line goes into negative Y a few times. Will post it as soon as I can.
Cheers
Gio1
RE: frequency response FEA
RE: frequency response FEA
Cheers
Greg Locock
I rarely exceed 1.79 x 10^12 furlongs per fortnight
RE: frequency response FEA
RE: frequency response FEA
I think it was some bug that was affecting the session of the postprocessor I had open.
Today (after a reboot) all plots had POSITIVE acceleration magnitude - as I would expect.
I was slightly puzzled by Greg's last post. What do you mean by "linear magnitude"?
Thanks everybody!
Gio1
RE: frequency response FEA
It would be an unusual, but possible, choice.
abs(v)^2 is more common.
Cheers
Greg Locock
I rarely exceed 1.79 x 10^12 furlongs per fortnight