Re: [PSUBS-MAILIST] Pressure Hulls

["Captain Nemo" <vulcania@hawaii.rr.com>]

Cool.  I'll check back after I get off work tonight.

If you've got time, how about sharing Allmendiger's formula with us?

Mahalo,

Pat
----- Original Message -----
From: "Alec Smyth" <Asmyth@changepoint.com>
To: <personal_submersibles@psubs.org>
Sent: Monday, July 01, 2002 10:55 AM
Subject: RE: [PSUBS-MAILIST] Pressure Hulls


> 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
> To: personal_submersibles@psubs.org
> Subject: Re: [PSUBS-MAILIST] Pressure Hulls
>
>
> 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.
> >
> >
>
>