Re: pressure hull design (Fwd)

[Mike Young <tvcmikey@yahoo.com>]

Joe (and John)!
Mike here,
If one is looking for "perfect" hemis, as I understand (John, you may
correct me if I'm wrong), doesn't the government have a whole bunch of
'slightly imperfect' parts of rocket assemblies sitting in storage
which could be bought as surplus. I mean, the reason these cylinders
and such were labeled as'imperfect' was because in the process of
making them they were off by a few millimeters and had to be discarded
or could burn up in atmosphere on re-entry. Couldn't they be used for
submarines instead?

FWAFS,
Mike in Malaysia 




---Marsee Skidmore <heyred@email.msn.com> wrote:
>
> John,
> 
> I'm asking Santa for the Nash book. Thanks for the recommendation.
Can you
> provide Ray with the info that he needs to list it on the "Sources"
page? I
> understand your reluctance to use available hemispheres, but I'm
curious how
> you intend to fabricate yours. My boat is an unscheduled, unbudgeted
paper
> project until I win the lottery, but I intend to start with the
pressure
> hull, and build in both directions. I'm designing for an operating
depth of
> 1000 ft, but my experience is with deep divers. As a result, I have
a bias
> toward a spherical pressure hull supported by an exoskeleton, with a
bare
> minimum of equipment enclosed in the pressure hull. Hydrostatic
testing of
> the pressure hull is a must. I've contemplated towing it out to deep
(>1000
> ft) water, tying a rock to it, and depending on some Tom Swift release
> device to get it back to the surface. However, this violates my
"Don't take
> it into the water if you can't afford to lose it" SCUBA training, so
I'm
> less than thrilled with this approach. I may be a Polyanna, but I'm
assuming
> that there are testing facilities that will rent pressure chamber
time for
> components that are smaller than a pressure hull.
> 
> Joe (from Marsee's computer)
> 
> -----Original Message-----
> From: John Brownlee <jonnie@chronic.lpl.arizona.edu>
> To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
> Date: Wednesday, September 16, 1998 4:54 PM
> Subject: Re: pressure hull design (Fwd)
> 
> 
> > Hi Marsee,
> >
> > My point in suggesting that someone who did not know where to
> >find/derive such a formula probably needs a little more than a
formula in
> >a book to be safe. For example, if you don't know a little about the
> >mechanics of materials and structures, the Nash book (which
incidentally
> >DOES treat surface irregularities and tolerances, more later) will be
> >largely useless to you. It is wonderful, but very rigorous with a
good
> >deal of multivariable calculus in the beginning. For those who
don't need
> >this sort of rigorous analysis, don't bother. Desigining in a huge
safety
> >margin is always a good insurance policy.
> > The Nash book is VERY rigorous, and more or less shows how to set
> >up analyses for all the hull geometries you can name. More
importantly, it
> >has an amazing bibliography, pointing to many papers on both the
theory
> >and experimental trials on the buckling of imperfect shells under
> >hydrostatic pressure. It does not address tolerances per se, but
presents
> >a general way to address geometric imperfections of many kinds.
Indeed,
> >the chapters on spheres are pretty interesting that way; the
emphasis is
> >not solely on the size of the imperfection (the tolerance), but the
> >-nature- of it. For example, considering the crush depth for a sphere
> >which has been flattened by a clamp on opposing sides is very
different
> >than for one which has a dimple on one side. The bits on
reinforcing rings
> >for cylinders and cones are also pretty cool.
> > Don't get me wrong, the Nash book is NOT for everyone. But, if you
> >suffered through senior-level analysis or calculus, it's a chance to
> >exercise the math muscles and learn a lot about the mechanics of
pressure
> >hulls. It is largely geared towards someone with a strong
engineering, or
> >at least mathematical, background. If you never took much calculus,
or
> >don't want to get your 'hands dirty' in the hull design process,
don't
> >bother. Hire a licensed engineer to do the analysis for you, etc.
Also,
> >much of his emphasis on high pressure regimes (like hundreds of
PSI) is
> >serious overkill for the 100' boat.
> > With regard to whether or not forged vessels intended for holding
> >compressed gasses and the like are good enough, I must confess I
don't
> >know exactly. There's a lot of unknowns there, but I suppose with the
> >proper bent you could find out. I'd just rather build the thing from
> >square one using known steels, etc. myself, but that's how I've
operated
> >all along. I am sure that there are several COTS products which
work fine,
> >but somehow the ol' propane tank leaves me a little on edge, as I'd
like
> >to dive deeper than 200' in the best of all worlds.
> > I should qualify all this by saying that I have probably in one
> >form or another designed and built everything BUT the hull for my own
> >boat. Being a computer/optics wonk I started with what I knew and
went
> >back to school for what I didn't. Started with life support, of all
> >things, and built from there. Of course, working at a university
helps;
> >when I knew I needed to know more about statics, I could sit in
> >on a class over at the engineering college and pick it up.
> > This raises an interesting question: in designing, you obviously
> >start with the hull (well, you -START- with a spec, but that's
different
> >than what I mean) but in BUILDING, does everyone start with the
hull and
> >move inwards? Has anyone done it 'backwards,' like I have?
Moreover, does
> >anyone test their components hydrostatically during construction?
> >
> > John
> >
> >John Brownlee
> >Lunar and Planetary Lab
> >University of Arizona
> >jonnie @ lpl . arizona . edu
> >
> >
> 
> 
> 

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