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Hi, i have a doubt in FREQ3 card. can anyone clarify how it picks the frequency through NEF? and how it get multiplied with PSDF in RANDOM ANALYSIS?

dhinesh.k
Hi,
i have a doubt in FREQ3 card. can anyone clarify how it picks the frequency through NEF? and how it get multiplied with PSDF in RANDOM ANALYSIS?
  • 0
    in exact, where can i find the selected frequencies by NEF?
     
  • 0
    First of all, when doing NEF within SOL108 or SOL111, you are first doing a standard Frequency Response/Random solution.​  This is where the FREQi entries are used.  The Quick Reference Guide describes each of the available FREQi entries, including the FREQ3.  It is a bit confusing, so I'll attach an excerpt from one of our courses that gives a bit more detail and examples.  That being said, I generally prefer to use a combination of FREQ, FREQ1 and FREQ4 entries to define my forcing frequencies for a random analysis.  I use a FREQ entry to define the break points in the input PSD, a FREQ1 to give a nice, regular excitation frequency interval (to make sure all the valleys between normal modes are found) and a FREQ4 to ensure all the peaks are found at each natural frequency.
     
    As far as seeing what frequencies the various FREQi entries result in, you can look at the frequency response portion of the results.  If you allow the run to print a single result to the f06 file, you can search for "     FREQUENCY =" and this will go to each resulting forcing frequency.  Or you can look in the post processor and see the listed frequencies with the results.
     
    I'll also attach a sample showing printing a single frequency response result to the f06 so you can see the frequencies created using a FREQ2/FREQ4 combo.
     
     
     
     
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