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Re: [PSUBS-MAILIST] Pressure Hulls
The crush depths listed in chapter four of Busby may perhaps be much
shallower than the depths calculated by Alec Smyth due to through-hulls and
other things in the hull not being built as sturdily as the pressure hull.
After all, you can test the through-hulls in a tank to be sure they are
properly built, even destroy several penetrators to make sure you have a
good design. But the hull itself proves a little bit more difficult to
test, and therefore may have been built to withstand more pressure than its
windows and penetrators, just to make sure that it could keep up with them.
I don't know what I'm talking about,
but it seems half-way believable,
Shin
----- Original Message -----
From: "Alec Smyth" <Asmyth@changepoint.com>
Sent: Monday, July 01, 2002 10:55 AM
> Actually I didn't use any particular page of Busby as a reference for the
> theory. I got my formula if I recall correctly from Submersible Vehicle
> Systems Design (Allmendiger). All I did was pick a few spherical-hulled
subs
> in which Busby listed hull diameter and thickness as well as the collapse
> depth. Then I ran the numbers and compared results. My numbers were way
too
> high every time.
>
> More later when I get a chance to do this exercise again using this
formula,
> perhaps this evening.
>
>
> thanks,
>
> Alec
>
> -----Original Message-----
> From: Captain Nemo [mailto:vulcania@hawaii.rr.com]
> Sent: Monday, July 01, 2002 3:46 PM
>
> Alec,
>
> Ian would be the man to ask. He presented the formula; I was just trying
it
> out.
>
> One likely area for error might be in determining variable U. In my
> example, I used boiler plate steel with 0.4% carbon content, with a
Tensile
> Strength of 44K and a Yield Point of 30K psi. If I'd used milder steel,
say
> 0.2% carbon, those numbers would be about 30K and 22K psi, respectively.
> That would have an effect on the result.
>
> One thing I wondered about while setting up the equation was what they
> really meant by the Minimum Yield Point of the steel; and is it less than
> what's commonly called Yield Point? If MYP were less than YP, that would
> have an effect on the result.
>
> According to STRENGTH OF MATERIALS, Singer 1960: "Ultimate Compressive
> Strength for ductile materials like steel may be taken as the Yield Point
> which is slightly GREATER than the Proportional Limit in Tension." In
this
> case, according to the table of material strengths I used (from MODERN
> WELDING by Althouse, Turnquist, and Bowditch 1980) YP is LESS than TS.
That
> seems to contradict Singer's basics, so again, I'm wondering.....
>
> Another factor effecting U is whether the steel was hot-rolled or
> cold-rolled. Changes the numbers substantially.
>
> What pages did you reference in Busby? I'll go check them out. If they
> cite particular sub hulls, they may have used another formula, or the
> properties of the steel used may be a consideration.
>
> About the possibility of inordinately high safety factors for spheres
> necessitated by sensitivity to out-of-round conditions: I don't know.
> Sorry.
>
> Pat
>
>
>
>
>
> ----- Original Message -----
> From: "Alec Smyth" <Asmyth@changepoint.com>
> To: <personal_submersibles@psubs.org>
> Sent: Monday, July 01, 2002 8:34 AM
> Subject: RE: [PSUBS-MAILIST] Pressure Hulls
>
>
> > Pat,
> >
> > About a year ago, I looked up the formula for spheres (can't remember
if
> it
> > was the same one you just used though) and ran some numbers based on
> > examples of sperical-hulled boats in Busby. The formula was simple
enough,
> > but the pressure ratings I got were way higher than the ratings given
in
> the
> > book, which left me a bit puzzled. Its hard to mis-calculate with such
a
> > simple formula. D'you know whether common practice might be to use an
> > inordinately high safety factor with spheres, given they're so
sensitive
> to
> > out-of-roundness? I'd pull out my Busby and run some numbers with this
> > formula to see how it jibes, but I'm at the office. So I really should
get
> > back to work! But I'll try doing this later.
> >
> > rgds,
> >
> > Alec
> >
> > -----Original Message-----
> > From: Captain Nemo [mailto:vulcania@hawaii.rr.com]
> > Sent: Monday, July 01, 2002 2:05 PM
> > To: personal_submersibles@psubs.org
> > Subject: Re: [PSUBS-MAILIST] Pressure Hulls
> >
> >
> > Dewey,
> >
> > I wasn't worried about that; just clarifying that mine was an exercise
> with
> > the formula, not an estimate of your particular hull's capabilities.
> >
> > Pat
> >
> >
> >
> > ----- Original Message -----
> > From: "Dewey Mason" <drmason2001@yahoo.com>
> > To: <personal_submersibles@psubs.org>
> > Sent: Monday, July 01, 2002 7:25 AM
> > Subject: Re: [PSUBS-MAILIST] Pressure Hulls
> >
> >
> > > Hey All,
> > > I assure you I think highly of you all, HOWEVER,,,,
> > > I will double check ALL math on my sub, I promise. Not
> > > that I don't belive you, just that I don't breath
> > > water, and feel no desire to be smooshed inside a
> > > steel ball. Sounds unpleasant.So you need not worry
> > > that I will kill myself and then blame you.
> >
> >
>
>
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