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Re: [PSUBS-MAILIST] Hull Shape question

Chuck,
ABS pays allot of attention to the out-of- roundness measurement of stiffened cylindrical sections for a reason. Pressure hulls are historically cylindrical; why? Because this configuration minimizes the stresses in the hull for a give external pressure. If you use the oval hull shape that you shown in your folder, the stresses in the smaller radius bends are going to be much higher than in the larger radius bends for a given external pressure. Since the local maximum stress the hull sees will set the max design depth, an oval hull will mean that you will be able to dive to only a fraction of the depth of an equivalently stiffened cylindrical section. I strongly suggest that before you begin fabrication of an oval hull that you have a FE analysis done to determine the maximum operating depth. I think you will be surprised at how much design depth you will give away with this hull design.
There is a cost penalty you will also pay on fabrication as you will have four longitudinal full penetration welds rather than one for the main hull section. The cost of fabricating stiffening rings will also be greater particularly the flange part of the "T" rings. The web portion of an oval stiffener ring is not a problem if you have access to a bed plasma or water jet cutter.
I realize that from a design perspective, a cylindrical hull is boring but you can always use an FRP shell for a more aesthetically pleasing shape or to minimize drag. 


Cliff
----- Original Message ----- From: "Chuck Will" <chuck@bestan.com> 
To: <personal_submersibles@psubs.org>
Sent: Thursday, June 30, 2005 10:36 AM
Subject: RE: [PSUBS-MAILIST] Hull Shape question



Try this location. Look in the my documents folder.
http://f2.pg.briefcase.yahoo.com/bc/aptostechnology@sbcglobal.net

How do you post to Moki?

Chip

-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of Juergen
Guerrero Kommritz
Sent: Wednesday, June 29, 2005 10:17 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Hull Shape question


Hello Chuck
The folder is empty there are no drawings, so it is
dificult to discuss about a drawing that is not
available.
Best wishes
Jürgen

--- Chuck Will <chuck@bestan.com> wrote:


Adam

I am still trying to finalize the shape of the hull.
I still would like to
go with an oval hull. The way I am looking at it is
to use two fixed
diameters to create the oval. It will not be a
random oval pattern. It will
be created from a 48" diameter tube and a 16"
diameter tube. The top and
bottom plate will be cut from a 48" diameter tube
cut at the point of
intersection with the 16" diameter side plates. It's
sort of hard to explain
so I made a drawing. I don't know how to post to
Moki so you can link to it
at http://briefcase.yahoo.com/divetruk. Look in the
folder called drawings.
The file name is "Oval Hull Construction". The first
page is 2D and the
second page has a 3D interpretation.

Basically I am cutting two lengthwise sections of a
large tube and welding
the to two sections of a smaller diameter tube. The
would be extensive
bracing on the interior. I also wondered how I would
do the hull
calculations for strength. Would I use the larger
48" diameter for all
calculations? Or do I need to do some math to figure
a average diameter? Or
am I still crazy to make my hull oval? It just seems
to fit what I want
better.

Chip
  -----Original Message-----
  From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On
Behalf Of Adam Lawrence
  Sent: Tuesday, June 07, 2005 5:00 PM
  To: personal_submersibles@psubs.org
  Subject: Re: [PSUBS-MAILIST] Hull Shape question


  Hi Chip,

  An oval shaped hull would be as strong as the
largest raduis. So if your
hull is 4 feet wide and 2 feet tall it would be
about equivalent to
calculating the strength of a round hull with a 7
foot radius. But then this
isn't exactly true since you can reinforce the heck
out of it. But to
maximize the weight to opperating depth ratio and
usable inside space, the
solution converges on a round hull with simple ring
stiffners.

  Adam
    ----- Original Message -----
    From: Chuck Will
    To: personal_submersibles@psubs.org
    Sent: Tuesday, June 07, 2005 3:48 PM
    Subject: [PSUBS-MAILIST] Hull Shape question


    Hello everyone,

    A quick question on hull shape. I understand
that the best shape for the
pressure hull will be a sphere or a round tube with
braces and with domed
end caps. How much strength is lost with an oval
tube? Imagine pushing down
on a cardboard tube a bit. Flatten it out lengthwise
just a little. It would
have bracing inside as well. Any advice on this?

    Chip






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