Re: Various Disconnected

[Dick Morrisson <rmorrisson@unidial.com>]

OK, time to throw my 2 cents worth in and stir the pot!

For those of you who did or will not design their sub out of mouse pads with
"beam" type deflections, the optimum hull will be everywhere in equal
compression.  Yes, I said and meant to say COMPRESSION!  If you can stretch your
imagination a bit, think of the cross section of the hull as a non-linear column.
Failure of a relatively long column is in a buckling mode.  The answer is to
arrange the material to maximize the cross sectional area without going too far
and introducing some localized buckling.  That is why the ribs are added to the
cylindrical hull, to keep it round and therefore keep the (compressive) stress
distribution even (in the cylinder as well as the ribs).  Any deviation from round
will start to make the hull go from a pure compression load to a combination
bending/compression load and the result will avalanche into more deviation from
round to more bending etc....The stiffness of the cross section is to stop this
progression before it gets out of hand (i.e. whump!).
Non-cylindrical/non-spherical shapes are stress concentrators, which is one reason
why view ports and conning towers need extra beefy sections where they connect.
If you build a box sub you can see the beam type stresses, tension on the inside
and compression on the outside, but you still need to superimpose the overall
compressive forces of the water pressure on top of the beam stresses.  That is why
nobody builds a box sub, they are much too heavy in comparison to round ones!

Well, that was my 2 cents worth, thanks for listening (reading).
Dick Morrisson

ps I am still researching the design philosophy of rib spacing and "tee" sections
versus others.  I do not know if there is an optimum design for a particular
material/depth or if it is just a point of "how much can we spend" to squeeze out
that last few pounds of useable payload.  I suspect some of the new sintered and
"metal foam" materials being researched will make close to an optimum hull as well
as help out in the buoyancy department but the price will preclude most of us.
Comments, flames, more details?  Anyone read this far?



Erik Michael Muller wrote:

> Joe!!, help!
>
> > > Pick up your mouse pad and flex it in the middle. The inside surface is in
> > compression and the outside is in tension. Your sub hull isn't deflecting
> > that much, and it starts life curved in the opposite direction, but the
> > tension/compression deal still applies.
>
> AHHGGG!!, now i am confused utterly.
> maybe im just too ignorant, but which way is the sub flexing here?
> Are we talking flexing from the weight of the sub or from water pressure?
>
> i hope its the weight, cos i can understand that..
>
> > >Beer steadies the hand. I won't weld without it.
>
> beats me how you can hang onto the beer and the welding torch with the same
> hand, steady or otherwise.
>
> Thanks for your help though!
> E.M.