Modal Analysis - Interpretation of Stability Diagrams

[abiszett]

Hello!

I'm doing a modal analysis and I'm trying to extract modal parameters from my aqcuired data. I'm using the Pulse Reflex Software.

I got to the point where the Software provides me with a MIF and a stability diagram and I am to choose the parameters. However, I am unsure how determine the parameter that represents the each mode the best in terms of damping and frequency.

Although there is an auto-pick feature, I don't necessarily want to use it because usually auto-picking isn't as good as doing it yourself ;)

So my question is: How do I determine what mode to pick?

Thanks
abiszett

 

[Zinov]

Hi Abiszett,
First look where your correlation function decreases significantly,
Find that frequency let's say, F_ds, all values greater than F_ds
should be ignored as the measurement over there is not accurate (due to either you sensor or your hammer tip , your impact or other reasons).
This means that only value before F_ds shoudl be considered.
Now look at your imaginary part of the FRF and pick the ones with high amplitude.

Start your analysi with auto-pick (just to have an idea about the modes)
Than do the steps listed above and compare.

Take care about anti-resonance,

Good luck,

'i have good links but cannot submit here'

 

[abiszett]

Hi,

I think there has been a misunderstanding. For clarification I attached an image, so you can see what I mean. The image shows the Stability diagram overlaid with the CMIF (blue) and a FRF (red). For each points of the stability diagram a value for frequency, damping, and density is provided. The auto-pick feature picks the points that are circled, but I cannot figure out why.
Another software provides a so called mode confidence factor, so there would be a value to go with. But Pulse Reflex somehow does not have such a thing, so I am wondering what attributes to consider for the selection.

If anyone has an idea, it is greatly appreciated.

Thanks

Abiszett