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Message ID: 3224     Entry time: Wed Jul 14 19:36:17 2010
Author: Gopal 
Type: Update 
Category: Optic Stacks 
Subject: Experimental Confirmation of COMSOL Analysis 

I experimentally determined the spring constant of a single Vitol spring in order to obtain a rough estimate for the natural frequency of single-stack oscillation.

The procedure basically involved stacking metal bars of known mass onto the Vitol and using a caliper to measure deviations from the equilibrium length.

The plot below shows that, for small compressions, the response is linear to an R-squared of 0.98.

Untitled.png

The experimental spring constant came out to be about 270 lb/ft, or 3900 N/m.

Previous documents have listed that the top stack takes on a load of approximately 43 kg. per individual spring. A bit of calculation yields an experimental resonant frequency of 9.5 Hz.

Compared with the theoretical COMSOL first harmonic of about 7.5 Hz, there is a reasonable amount of error. Of course, I used this calculation as a simple ballpark estimate: errors from misplacement onto the Viton were minimized through use of a level, but were still inevitable on the mm scale. Since the two methods yield answers with the same order of magnitude, we are ready to move forward and build the remaining layers of the stack.

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