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Re: [PSUBS-MAILIST] FEA Work on Acrylic CT for KLH-500
Hello Jon,
I'll be interesting to work up the models you spoke of on page 749. One key
thing I'm missing in my FEA work this far is what the sealing gasket does
for relieving some localized stress on the inside seating corners of the
domes, frustums, basic flats, and cylinder windows. Giving that the gasket
would yield long before the acrylic, I'll have to isolate the acrylic, in
the test, in such a way, that the stress is allowed to continued to be
applied to the acrylic until it's material yields. Also I need to change how
the part is constrained. Since right now it is fixed to the plate, and not
allowed to slide in as it would in the real assembly. I've now found the
roll slide option, and will see how that changes the results.
Also now that I've run this cylinder with plates on both ends, with the same
pressure applied to there outer surfaces. I'm thinking I need to add a thick
plate like that to the bottom of my dome FEA assembly, and apply the same
pressures. Since the pressure on are subs underside is pushing up towards
the CT dome.
I'll try the t/D of 0.045 you spoke of and get back to you. I can run the
part with the ASME PVHO-1 minimum values, but I would need to run the values
of the cast acrylic Stachiw actually used for a really good comparison.
Regards,
Brent
--------------------------------------------------
From: "Jon Wallace" <jonw@psubs.org>
Sent: Sunday, August 30, 2009 4:07 AM
To: <personal_submersibles@psubs.org>
Subject: Re: [PSUBS-MAILIST] FEA Work on Acrylic CT for KLH-500
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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