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Jay,
The input like you and others are giving, is why I
post this material to the group. One doesn't need to be a professional FEA
analyst to have good input. This group knows I'm not a professional FEA
analyst. They also are well aware by now that they are responsible for there own
submarine designs, and what data they choose to use to design there subs. I
could choose to only send this material to a select few I know and/or suspect
would have good input. But there are many in this group that I don't know at
all, and others I do know that have a wide array of back ground experience in so
many things, that I don't wish to miss out on there input. Besides it's been
said before, why should the select few get all the fun of looking at different
proposed designs?....
Just so every one is covered, I'll consider posting at
the top of my FEA type postings the below warning
WARNING, Material and ideas contained in this
email are for entertainment, and artistic value only.
Do not try this at home with out proper
supervision. Producer of material here contained, has been seen with mountain
folk with no good reason.
Warning!!!! Many colours are used
in the "art" pictures, that might make you crave a rainbow popsicle.
That said there is a fair bit less stress shown on the
outside corners as it is. The same pressure that is being applied to the
exterior surface of the acrylic cylinder is also being applied to the outer
surfaces of the plates. This puts a lot more concentrated pressure on the
seating area. I'm running the test over with out adding pressure to the
exterior surfaces of the plates to see what that looks like, as well as putting
the pressure back on the plates and removing it from the acrylic, also for
obtaining the results.
I was restraining the acrylic seating surface
from moving in towards the axis, which would not reflect real world actions. I
need to change the restraints to allow the part to slide in, and down onto the
seal. Also I feel there is more stress on the inside corner then there should
be, since the real window would be seated on a elastic surface, thus relieving
some of that localized stress.
Regards,
Szybowski
From: Jay K. Jeffries
Sent: Sunday, August 30, 2009 7:11 AM
Subject: RE: [PSUBS-MAILIST] FEA Work on Acrylic CT for
KLH-500 Brent, Thank
you for the explanation of your FEA model, it is what I expected but does not
deal with the particular issue that I am pointing out. The blue bands
should exist on the cylinder but believe that they may be displaced. They
should be at the very outside corner of the cylinder as this would be were the
minimum stress would be located instead of up the cylinder a bit. I cannot
think of any explanation that would have these bands up the cylinder a bit in
the real world. See the exaggerated deformation detail sketch at http://www.flickr.com/photos/bottomgun/.
The other issue that you need to look at is that both metal plates are not
seeing the same displacement. I cannot see how the stress resulting from
the end plate compression would result in the blue bands being
displaced. You
always need to take the output of any FEA program and do a rational check on
it. If there are abnormalities such as in your recent work, you need to go
back and figure out what is wrong with the model. My story that
illustrates this point is several MIT graduate students that I worked with years
ago built a flow model of Lynn Bay found north of Boston. They were trying
to determine why a certain species of algae was washing up in only one location
on the beach, resulting in a foul smell from its decomposition. The FEA
model had all of the correct seawater movements and bottom contours entered
correctly but when the model was run, a water geyser 130 feet appeared in the
middle of the bay. While this would have been a great attraction to the
public if real, it did not reflect the actual world.
Today?s
programs allow almost anyone to run FEA programs very easily but there has to be
some deeper knowledge of the subject by the programmer to get answers that
reflect reality. While your results look very professional, they can be
misleading to those that do not know what to question (my knowledge and
experience with FEA is rudimentary at best and I find issues). In the case
of submarines if these persons act upon your published FEA solutions, it could
be detrimental to their health. I respect all of the effort and research
that you have put into your FEA work but would caution restraint in publishing
your results. R/Jay Resepectfully, Jay K.
Jeffries Andros Is.,
Bahamas Save the whales,
collect the whole set. From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent
Hartwig You can see the blue
bands also on my dome FEA, showing a low stress zone. From: Brent Hartwig
Sent: Sunday, August 30,
2009 2:48 AM Subject: Re: [PSUBS-MAILIST]
FEA Work on Acrylic CT for KLH-500 Hi Jay,
The
design check is done using von Miser stress In the
photos showing the factor of safety distribution, the software takes the part or
assembly to the first material yield point, then stops. (weakest
link) The red area(s) show the area(s) on the part that yielded
first. A part that is mostly orange in a FOS display state, shows a pretty well
balanced stress absorption by the part. The chart on the right, in the FOS
display state, shows the red as being at the max FOS shown in the top left hand
text. The
display state showing Static displacement, I have set to show the real amount of
deformation that the part or assembly should have at the
time, one area or another of the part or assembly has yielded. I can
change the deformation scale for a bigger effect, to better understand what is
moving. But I've not done that in a while, since are parts tend to not give all
that much, and I'm going after a more realistic display. The red shows the
area the has moved the most under load. That doesn't necessarily mean that, the
red area yielded, just moved. In some cases the material around and/or
under the red area gave way. I see this sort of thing when I run FEA work on 2
to 1 heads. I can animate the displacement to show how the progression of
stress is applied as you dive deeper into the abyss or get munched on by
Kraken. The
scale for the Static displacement charts you see, are URES: (Resultant
Displacement), and it was set to metric meters. That is the default display
state, and since I've been looking at FOS, static strain, and static stress
mostly, I usually just leave it on that setting. I can set it to show how far
the part or assembly moved in a particular axis, in some
cases. The
blue bands you speak of on the upper and lower outer surface of the acrylic
cylinder, is matching what you see on my blown dome FEA work. In the bonded on
retaining ring area. That area is not under much stress. If you look at
how the middle is coming in, of which forces the bending part to bind on the
inside seating edges, against the seating material, it will all come clear. The
outer mating edges would actually lift off the mating surface just a bit.
This is also what we see on basic flat, and conical frustum windows, as well as
many domes, like mine. Regards, Brent
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