Re: [PSUBS-MAILIST] endcap/bulkhead question

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

Hi.

As far as I see it, inverting the end-caps is a design 'trick'
which has several benifits for those who choose to use them:

 1)  Structural efficiency, the gains of which include:
       - Potential weight savings.
       - Potential cost savings.
       - Don't need to worry about out of roundness as much.
       - Reduced end-cap buckling risk.

 2)  Reduced displacement, you subtract the end-cap displacement
     rather than add it, the gains of which could include:
       - Potential weight savings.
       - Potentially easier to trailer and tow.


For the downsides:

 1)  Hydrodynamic inefficient, can be countered by design,
     i.e. ballast-tank placement, etc.

 2)  Viewport placement not desirable, can be designed around,
     many subs don't have viewports in the end-caps.

 3)  Welding needs to be done from the inside.


I'm not sure if the traditional way works great, it works and it's
proven, but they are definately draw backs.  It will (unless you have
a hemi-spherical one) be the weakest part of the pressure vessel.
I've found that the traditional convex end-cap doesn't scale well
with depth/pressue increase.  Due to the large radius on the double
curve, the out-of-roundness factor need very small.

The convex end-cap compared to the concave end-cap, is pretty similar
to a positively buoyant hydrobatic compared to a 'sinker' (a sub that
can be positive/netural/negative in buoyancy).  It's not appropriate
to make every design a positively buoyant hydrobatic sub, and it's not
appropriate to make each end-cap inverted.

Saying all that, I don't know if I would use an inverted end-cap in a
psub I was building, and if I did, it would be more to reduce the
displacement than anything else.  Maybe after I get the first psub out
of the way, then I'll look at building novel pressure hulls.  ;-)

Cheers,
  Ian.

On Wed, 17 Dec 2003 08:01:26 -0800 (PST)
Warren Greenway <opensourcesub@yahoo.com> wrote:

> That's true. And you could solve the drag problem with
> a fairing. But...Why? They work great the traditional
> way, and without any of the other drawbacks.
> 
> Warren.
> 
> --- Ian Roxborough <irox@ix.netcom.com> wrote:
> > On Tue, 16 Dec 2003 10:16:38 -0800
> > Ian Roxborough <irox@ix.netcom.com> wrote:
> > 
> > > 
> > > Any additional stress (I'm not sure if there is
> > any), could easy
> > > taken care of by a heavy frame
> > stiffener/re-enforcing ring.
> > 
> > Warren you are correct here, where would be extra
> > stress at the
> > joint of the end-cap and cylinder, but nothing that
> > couldn't be
> > off set with a heavy stiffener.
> > 
> > Ian.
> > 
> > > As for the displacement, it reduces displacement
> > meaning that not
> > > only have you eliminated most of the risk of end
> > cap buckling, but
> > > your sub is now lighter.  And for useful space
> > inside the sub, that
> > > is going to depend on how clever you get packing
> > things in.
> > > 
> > > For people wanting to read more about inverting
> > end-caps on submarines,
> > > I would recomend reading "Pressure Vessels,
> > External Pressure
> > > Technology" by Carl T.F. Ross - Chapter 7 "Novel
> > Pressure Hull Design"
> > > (page 280).
> > > 
> > >   Ian.
> > > 
> > > 
> > > On Tue, 16 Dec 2003 09:15:36 -0800 (PST)
> > > Warren Greenway <opensourcesub@yahoo.com> wrote:
> > > 
> > > > The junction between the caps and hull "tube"
> > will be
> > > > under tremendous stress. There will be shearing
> > forces
> > > > on the wleds. Also, you are creating less
> > useable
> > > > interior space for a given displacement. I think
> > those
> > > > would be some of the basic reasons. Reference
> > Concepts
> > > > of Submarine Design for more specifics.
> > > > 
> > > > Warren.
> > > > 
> > > > --- Emile <2stroke@hetnet.nl> wrote:
> > > > > Hello all,
> > > > > 
> > > > > For my future psub I consider an inverted
> > endcap or
> > > > > bulkhead 
> > > > > See the "drawing"of the pressure part.
> > > > > ______
> > > > > )_____(
> > > > > 
> > > > > At this configuration the sphere shelfs only
> > have a
> > > > > tension loading what is preferrable.
> > > > > I lookt at almost every psub design on the
> > site but
> > > > > no other sub has this configuration, exept for
> > the
> > > > > Spurdog.
> > > > > Am I wrong in my toughts and are there high
> > stresses
> > > > > in the sharp transition from the sphere shelf
> > to the
> > > > > circular hull??
> > > > > 
> > > > > hope someboy knows,
> > > > > 
> > > > > Emile D.L. van Essen
> > > > > www.AiResearch.nl 
> > > > 
> > > > 
> > > > __________________________________
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> 
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