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Entry  Thu Jan 31 14:00:00 2013, Kristen Holtz, Notes, PMC, PMC Longitudinal Testing and Modal Analysis PMCphoto_circclamps.JPGPMC_ringdown_Jan28.JPGPMC_unconstrainedringdown_Jan28.JPGPMC_Excitation_Diagram_1-28-13.JPG
    Reply  Wed Mar 27 01:52:34 2013, tara, Notes, PMC, PMC Longitudinal Testing and Modal Analysis pmc_eigen.png
       Reply  Sun Mar 31 03:03:28 2013, tara, Notes, PMC, PMC Longitudinal Testing and Modal Analysis psl_log.pngpsl_log2.png
          Reply  Sun Mar 31 14:42:05 2013, Evan, Notes, PMC, PMC Longitudinal Testing and Modal Analysis 
             Reply  Sun Mar 31 20:06:16 2013, tara, Notes, PMC, PMC Longitudinal Testing and Modal Analysis 
       Reply  Mon Apr 1 20:59:19 2013, tara, Notes, PMC, PMC Longitudinal Testing and Modal Analysis 
          Reply  Thu Apr 4 23:55:12 2013, Evan, Notes, PMC, PMC Longitudinal Testing and Modal Analysis mirrorsag_coarse.pdfmirrorsag_fine.pdf
    Reply  Thu Apr 4 11:44:14 2013, Evan, Notes, PMC, 270 Hz clamped PMC twisting mode pmc_clamp_twist_mode.jpg
Message ID: 1131     Entry time: Wed Mar 27 01:52:34 2013     In reply to: 1097     Reply to this: 1134   1137
Author: tara 
Type: Notes 
Category: PMC 
Subject: PMC Longitudinal Testing and Modal Analysis 

I use COMSOL to find the first longitudinal mode of a stainless steel PMC,  it is about 16 kHz. I'll find an analytical solution and compare them to make sure that the FEA result gives us a reasonable answer or not.

The FEA result in psl:1088 does not show the right body mode of the PMC. The frequency of 440 Hz is from some weird mode as seen from the figure in the entry. Evan checked the body mode of a simplified steel PMC, and I also check independently. Our results agree quite well that the first longitudinal mode is at ~16kHz.

pmc_eigen.png

However, this does not answer what we measured in PSL:1097, where the longitudinal motion is around 300Hz. I checked the body frequency of the base blocked and it is even higher than the PMC body modes' frequencies (this should be expected since the base is even bulkier).

Note: I just learned from Zach that the PMC in GYRO setup does not have 3-point support. It just sits on the base block. But this has not given me any clues about the possible modes yet.

 I'm writing some background and requirement for the PMC[coming soon]

 

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