[Date Prev][Date Next]
[Chronological]
[Thread]
[Top]
Re: [PSUBS-MAILIST] Calculations
Go to
http://www.restorides.com/~dub/ThjisHull/ThjisHull001.htm
to find out. Also check out the moki picture exchange
for renderings of the craft. Concepts of Submarine
Design can be purchased from Amazon and covers hull
stresses reasonably clearly.
Warren.
--- Brian Cox <ojaibees@ojai.net> wrote:
> What is Thijs's double end cap flying sauser craft?
> And when you're
> speaking about stress concentrations what, for
> example, kind of problems
> are you talking about ?
>
> Thanks, - Brian
> ----- Original Message -----
> From: "Michael Wright" <mwright@smallip.com>
> To: <personal_submersibles@psubs.org>
> Sent: Tuesday, July 08, 2003 5:34 PM
> Subject: Re: [PSUBS-MAILIST] Calculations
>
>
> > First, since air at mean sea level is roughly 14
> PSI, a tank at full
> > vaccume is the same as a tank with 1 atmosphere
> inside at 28 PSI outside
> > (or 32 feet of water).
> >
> > Steel is about the same stregnth and modulus of
> elasticity in
> > compression as in tension.
> >
> > Here's the thought model I use to envision the
> difference between
> > internal and external pressure. Take an empty one
> liter plastic pepsi
> > bottle. It can hold upwards of 55 PSI internal
> pressure. However you
> > can collapse it with your lungs by suckin on it
> (far less than 2 PSI).
> >
> > This should easily illustrate that a tank rated
> for X psi internal
> > pressure is not likely safe to use for X psi
> external pressure. A tank
> > designed for internal pressure needs no structure
> to keep it' shape.
> >
> > The physics of the situation are relatively
> straightforward. If a tank
> > deforms due to internal pressure it becomes a
> shape that is loaded
> > entirely in tension. The force from the internal
> pressure keeps the
> > round shape.
> >
> > If a tank deforms due to external pressure it gets
> less rather than more
> > round, becoming an ellipse. As this deformation
> occurs the tank
> > structure is loaded more and more in bending
> rather than compression.
> > This leads quickly to a posetive feedback loop
> that leaves the tank
> > looking like the soda bottle with the air sucked
> out.
> >
> > The posetive feedback nature of this process is
> what should scare anyone
> > thinking of building an atmospheric submarine. If
> you exceed the
> > capability of your internal structure to maintain
> the round shape, the
> > hull will begin to oval, as it ovals it will be
> loaded in bending rather
> > than compression, and quite rapidly the hull will
> collapse on it's self.
> >
> > So if you wanted to use a tank you'd have to build
> in all the structure
> > to keep it from ovaling under external pressure.
> In doing so you'd have
> > to make sure not to create stress concentrations
> in the skin.
> >
> > It seems to me that you'd rapidly spend more
> effort and more mass
> > stiffening the inside of the hull than would be
> required to build
> > Thijs's double end cap flyin saucer shaped craft
> (a shape that looks
> > quite useful to provide space for a crew of two
> with a minimum of excess
> > air space).
> >
> > I supose if one had access to a plasma or lazer
> cutter you could build a
> > bolt together, laminated steel internal structure
> for the tube section
> > that could be installed via the main hatch
> opening. All this would
> > require 3d solid modeling to get the geometry and
> placement right but
> > would be doable. The modeling will probably show
> that the end caps
> > being spherical makes them less susceptable to the
> posetive feedback
> > loop that would affect the tube section.
> >
> >
> > At any rate, assuming that because a tank is rated
> to a certain internal
> > pressure it will handle that external pressure is
> incorrect and likely a
> > fatal mistake.
> >
> >
> > michael
> >
> >
> >
> > Chris Jackson wrote:
> >
> > > Very good point. Logically, if it thick enough
> steel to be
> > > able withstand internal pressure, it should mean
> that it is thick enough
> > > to withstand an equal amount of external
> pressure.
> > >
> > > ----- Original Message -----
> > > *From:* steve
> <mailto:steve@kobol.worldonline.co.uk>
> > > *To:* personal_submersibles@psubs.org
> > > <mailto:personal_submersibles@psubs.org>
> > > *Sent:* Tuesday, July 08, 2003 4:52 PM
> > > *Subject:* Re: [PSUBS-MAILIST] Calculations
> > >
> > > Hi All
> > >
> > > i noticed a lot of talk recently about
> propane tanks, the thread was
> > > a bit dead but i gathered that the question
> of 'Is it worth using
> > > that old propane tank in the garden', was
> dumped because the
> > > work would probably be more involved to
> convert a tank than to just
> > > buy the tube and end caps.
> > >
> > > My question though is, how does it compare
> with cost? If the cost
> > > of the tank is say 1/2 the price would it be
> a viable option?
> > >
> > > I had the opportunity to check a propane
> tank up close recently; i
> > > keep seeing psubs in all types of pressure
> tanks now...i think it's
> > > called obsessive compulsive disorder.
> > > Anyway, thinking as you do, that it would be
> a great size for a psub
> > > i checked out the plate attached to one end.
> > >
> > > The plate read:
> > > /*Manf: Robert Bros*/
> > > */BS1500 Class 2/*
> > > */210psi and Full Vacuum/*
> > > */TP 310psi/*
> > > */310 Gals/*
> > >
> > > A thought came to me, i remember on previous
> posts, a lot of talk
> > > about the pressure vessel only being rated
> for internal pressure.
> > > If it states that it can also withstand a
> FULL VACUUM, how does that
> > > affect its suitability as a psub hull?
> > >
> > > I may be completely wrong here but, can
> vacuum stresses be compared
> > > with external pressure stresses?
> > > It seems to me that if the internal pressure
> was reduced to 1/2 ATM
> > > then wouldn't that be the same as applying 2
> ATM pressure to the
> > > outside of a hull?
> > >
> > > i understand that once the pressure vessel
> used for a purpose it is
> > > not intended for (ie. cut / welded etc.) the
> figures wouldn't be
> > > valid anyway, but it makes me think
> > >
> > > anybody got any ideas???
> > >
> > > Regards
> > >
> > > Steve Bosworh
> > > UK
> > >
> > >
> > > P.S. I did check out the manufacturer but
> they apparently don't
> > > exist anymore and the BS number is now
> obsolete and doesn't say
> much.
> > >
> > > ----- Original Message -----
>
=== message truncated ===
__________________________________
Do you Yahoo!?
SBC Yahoo! DSL - Now only $29.95 per month!
http://sbc.yahoo.com