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Modal Analysis - Interpretation of Stability Diagrams

  1. Jun 1, 2012 #1

    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?

  2. jcsd
  3. Jun 6, 2012 #2
    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'
  4. Jun 15, 2012 #3

    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.



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