Re: [PSUBS-MAILIST] Pressure hull materials

[Ian Roxborough <irox@ix.netcom.com>]

On Fri, 20 Dec 2002 14:32:58 -0500
"Jaytron" <jaytron@wideopenwest.com> wrote:

> Ian,
> I wonder if it is of any consequence/design that the "corrugations" are
> shallow and are more like curves than "sharp" corrugation anles?  I'm sure
> that weighs into the formula as well, don't you think?  Where might we find
> this formula described? any clues?

Ross states that "the original tin cans appeared to fail by
general instability.  By increasing the cone angles of the
corrugations of the original tin cans, the wall thicknesses of
the vessels were reduced by between 28.6 and 57.1%.  It is
possible that a different shape of corrugation to the saw
tooth corrugation, may result in even more material savings."

The formula given is for calculating the thinness ratio, based
on a thinness ratio formula by Windenburg and Trilling.  I'm
not going to quote it because I'm not very familar with that
formula (I don't know if it's correct or has typos) and it's
not much use without the rest of the book unless you're somebody
like Prof Ross...  Most of the book is above my level.

> To all,
> Rather than getting a test "fixture" for testing pressures on structures,
> has anyone tried just "dunking" a structure to a depth using a crane to
> lower and raise the test structure?  Are there any studies on various
> geometric designs for subs besides cylinders?  Such as octagons, triangular
> shaped subs, even rectangular hulls? I am also curious about the thickness
> of steel and other metals at various depths.  I've read the Aquarius U/W hab
> has a 3/4" steel outer hull at a depth of 63' but is it possible to build a
> structure with a thinner specification?  What about for no deeper than 33
> foot (1 ATM)?

Octagons, triangles and rectangles are all shapes with flat sides.
Does anybody have a formula for calculating the failure point
of a flat surface under pressure?  Flat surfaces seem to be the
least efficient, with regard to weight to yield pressure ratio.

Ian.

> ----- Original Message -----
> From: "Ian Roxborough" <irox@ix.netcom.com>
> To: <personal_submersibles@psubs.org>
> Sent: Friday, December 20, 2002 1:37 PM
> Subject: Re: [PSUBS-MAILIST] Pressure hull materials
> 
> 
> > On Fri, 20 Dec 2002 12:07:18 -0500
> > Michael B Holt <tlohm@juno.com> wrote:
> >
> > > On Fri, 20 Dec 2002 08:27:31 -0800 (PST) Ray Keefer writes:
> > > >
> > > >Certainly the corrugations would act as ribs to keep the sides from
> > > >caving in. Wouldn't the corrugations pre-dispose the hull to
> > > >collasp acordian style?
> >
> > Well, that sounds like a nice thesis topic for somebodies masters degree.
> > He talks about the different failure modes of tin cans, but doesn't
> > really mention acordian style failures.  Although, if you had end
> > cap surfaces that where greater than the cylinder's surface, I could
> > imagine the longitudinal force could fold the corrugations in a failure
> > as you describe.
> >
> > A little side note on tin cans you get beans and other food in:
> > The reason they have ribs or corrugations is due to the fact that
> > to tin some food you need to suck all the air out of the tin first.
> > The corrugations give the tin extra strenth without making it
> > heavier or using any framing rings (since while there is a vacuum
> > inside it is under external pressure).
> >
> > > Good idea.  I'd not thought of that.   It might be sufficient, then,
> > > to add internal stiffening rods going the length of the thing.
> > >
> > > The book Ian referenced might help here.  Ian, can you give
> > > more information on it?   Is it in print?
> >
> > I posted a mini review of the book in question to the list a
> > while ago, you can read it here:
> >   http://www.psubs.org/mlist/archive/0112/msg00271.html
> >
> > It's probably not everybodies cup of tea, after about page 20
> > it gets pretty advanced and bleeding edged.  I couldn't really
> > imagine any psubs trying out any of the latest ideas talked about
> > in the book (not until they are more proven anyway).  But saying
> > that, I really enjoy reading about what could be future submarine
> > pressure hull design and construction techniques.
> >
> > It's still in print and still costs $55.
> >
> > Ian.
> >
> >
> 
>