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Entry  Wed Feb 18 21:10:21 2009, rana, Update, IOO, MC Drumhead mode lost again 
    Reply  Thu Jul 30 21:26:16 2009, rana, Update, IOO, MC Drumhead mode mc2drum.png
Message ID: 1814     Entry time: Thu Jul 30 21:26:16 2009     In reply to: 1322
Author: rana 
Type: Update 
Category: IOO 
Subject: MC Drumhead mode 
I used COMSOL 3.5a to do a FEA of one of the MC flat mirrors. Should be close to the same for all the mirrors.

The model is very simple- it includes just the cylindrical shape (no magnets, curvature, or coating or bevels).
This is good enough, since we don't really know all of the material properties at the 1% level.

The attached plot shows the MC drumhead mode. The color scale shows the displacement along the optic axis.
The model predicts 28.855 kHz and the measured value was 28.2 kHz.

I used COMSOL in the multiphysics mode which includes the Structural Mechanics and Heat Transfer modules at the
same time. For the material I used the built in properties of Corning 7940 (fused silica). In reality we have
7980 (I don't know all of the material differences). In any case, this model includes the temperature dependence
of the Young's modulus, so it should be possible to use this to predict the absorption numbers.

The model file (mc2.mph) has been added to our COMSOL SVN directory.
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