Re: [PSUBS-MAILIST] FEA Work on Acrylic CT for KLH-500

[Jon Wallace <jonw@psubs.org>]

It looks to me like the bands are appearing where support is called for 
on the ends of the cylinder.  Brent has modeled the top figure as 
displayed in Figure 13.11 on Page 749 of Stachiw's book.  That is the 
simplist and weakest rendition possible which should also produce the 
poorest set of performance numbers.  However, it's not a realistic or 
practical approach for a conning tower given the methods Stachiw 
provides for mounting the cylinder.

Brent, I think a more interesting model would be the middle figure on 
Page 749 which probably represents a more practical mount on the sub, or 
even the bottom figure which would only require you adding a 
strengthening rib on each end made out of the same acrylic material.  It 
would be interesting to see if those two blue bands disappear or at 
least the effects are lessened.

The numbers produced by the test seem to match pretty closely what I can 
extrapolate from Figure 13.15 on Page 753.  However, I think it would be 
more interesting to run your numbers with a t/D of .045 (see bottom page 
753) and compare your FEA numbers with the results Stachiw published on 
Page 754 which were determined by actual testing to failure.  You can 
see that Stachiw's tests matched pretty closely with standards, although 
the standards (by calculation) were slightly more conservative.

Also, when I talked to Reynolds Plastics they told me that anything over 
1 inch thick material required special tooling for them to produce.  I'd 
like to see the FEA numbers for all the same dimensions except using 1 
inch thick material if you ever find time to redo the test.

Jon

> Brent
>
> You have an enigma around the top and bottom of your cylinder, note 
> the two thin blue bands.  Something like this usually points out that 
> you might have an issue with your model.  Looking at the numbers along 
> the right side of the image, is this deflection?  What are the units?
>
> R/Jay




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