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Searching for an experienced user in experimental modal analysis

  1. Jan 27, 2010 #1
    Hello,

    I'm new to this forum and found it by searching for anyone who is experienced in experimental modal analysis.
    My work has to do with finding the modes of an aluminium cast component and I made a modal model in LMS CADA-X 3.5C, which is a quite old software but the only thing I have at the moment.
    The other things I work with, are an impact hammer and a 1D accelerometer which I use together with the roving sensor method.

    After all the impact measurement I let CADA-X calculate the Sum Block FRF of the part and I have got three clearly visible peaks. The problem is, that I have a "double peak" at 6,2 kHz which I don't exactly know how to interpret now. I first started to select the modes with the SDOF method, which is fast and easy to use but as far as I know, it is not the right choice when having such a double peak, but I thought I should give it a try. Well, the calculated residues are quite similar which is pointed out in a MAC-matrix with a correspondence of 70%. The animation shows the same to me.
    So after that, I started with the "time domain MDOF"-analysis...
    And now I got a stabilization diagram that confuses me even more. It finds stable solutions, one at the second peak in the region of the double peak, but the the other one which I first hoped to find at the other peak (the two peaks have a difference of about 90Hz) can be found a bit lower (about 30Hz below the first peak).

    Has anyone in this forum an answer or a clue what I can tell out of this result ?
    If needed, I can upload a TIFF of the sum block FRF...

    I really appreciate any answers in advance !

    Greetings

    Jarod
     
  2. jcsd
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