[PSUBS-MAILIST] bolt on rings

Fri Nov 11 11:42:41 EST 2016

Yes, I was thinking exclusively of spherical hull shells, but cylindrical hulls work in a similar way. I understand that the two bars on the hatch in your photograph mate with similar reinforcing features inside the hull? Reinforcing rings are required by the rules to be continuous, I think because of stiffener tripping / bending stresses which could cause differential movement of the ends, despite their ability to carry the hoop stresses.  The Burcher & Rydill book addresses this a bit, with discussion about bifurcating a reinforcing ring to carry stress continuously around a hull penetration that would otherwise interfere. In any case, novel or nonstandard designs should always be verified with an exhaustive stress analysis (FEA), but your photo is a good example - just put some thought into carrying the required load and avoiding abrupt geometry changes and stress concentrations, and it will probably work.

Sean

On November 11, 2016 9:15:27 AM MST, "MerlinSub at t-online.de via Personal_Submersibles" <personal_submersibles at psubs.org> wrote:
>Sean you can of course do for example a hatch which close the hole and
>fill 
>the gap..
> 
>We make it exact that way on Sgt.Peppers.
>The tolerance of the hatch bars was just 1/10 of a milimeter. and if
>closed 
>and under outside pressure
>it close the pressure hull cylinder again - even it was made from
>aluminium 
>and not steel as the rest of the hull.
>Under pressure this hatch is blocked mechanical by the outside pressure
>
>which press the cylinder of the shell
>close to the hatch bars and not just the hatch from the top.
>But the stress calculation to do so was done on a F&E Analysis Computer
>
>model.
> 
>vbr Carsten  
> 
> 
> 
> 
>-----Original-Nachricht-----
>Betreff: Re: [PSUBS-MAILIST] bolt on rings
>Datum: 2016-11-11T15:50:56+0100
>Von: "Sean T. Stevenson via Personal_Submersibles" 
><personal_submersibles at psubs.org>
>An: "Personal Submersibles General Discussion" 
><personal_submersibles at psubs.org>
> 
> 
> 
>I will preface these comments with a standard disclaimer that what
>works 
>and what is explicitly permitted by the rules may not be entirely 
>congruent.
>That said, when you cut any opening in your pressure hull, you
>ordinarily 
>must reinforce the opening with additional material, in order to carry
>the 
>additional shell stress which can no longer be carried by the material
>that 
>would have been in the opening. Certainly this is the case for window 
>openings, because an acrylic window is structurally insufficient to
>carry 
>the anticipated hoop stresses. Where the opening is to be filled with 
>material equal or greater in strength than the hull shell material, it
>is 
>less clear cut. We had a discussion some time ago about essentially 
>replacing the cutout shell with an equivalent load path through a 
>substantial hatch, and there is no reason why this shouldn't be 
>permissible, provided the "shell" which is integral to your hatch
>provides 
>an uninterrupted load path. In the case of a spherical pressure hull,
>this 
>means that the hatch "shell" would need to be of equal or lesser inner 
>radius than the hull, of equal or greater ou! ter radius than the hull,
>be 
>appropriately centered on the adjoining shell at the interface, and
>that 
>the interface itself be exactly normal to the spherical surface, so the
>
>angle passes through the centre of curvature and hoop stresses do not 
>induce bending.  Any elastomeric seal would have to be positioned
>outside 
>of the theoretical "shell", so that you retain full bearing area in the
>
>metal to metal interface. You would also have to ensure that the hatch 
>itself is appropriately reinforced if you have penetrations for windows
>or 
>dogging mechanisms in it.  What you would not be able to get away with
>is a 
>hatch which sat substantially proud of the neutral axis within the hull
>
>shell (i.e. a "lid" on top), as that would provided no structural
>support, 
>and thus would require the same reinforcement around the hole, integral
>to 
>the hull shell wall, that would be required for a window or other non 
>structural penetration.
>Apart from that, I imagine that a hatch seat similar to the recommended
>
>methods for penetrating "Nemo" windows, as outlined in PVHO-1 and
>Stachiw's 
>book, would prove adequate. You will note that in no instance do these 
>methods permit screwing or bolting to the acrylic hull shell, and I am
>of 
>the same mind with regard to a metal shell. Whatever you come up with,
>you 
>can bolt two halves of an insert to each other across a hole, but must 
>avoid drilling into your base hull shell, or indeed removing material
>from 
>it for other purposes if not adding material to compensate, or if you 
>already have excess shell thickness, or are prepared to derate the
>hull. 
>Instead of machining sealing features on the hull, I would look at
>using an 
>adhesive sealant to seal to your designed insert (which must already be
>
>structurally seated against the hull opening), and restrict the o-ring 
>features to the insert and hatch exclusively.
>As for sealing two hemispheres together with an o-ring seal, there's no
>
>reason that you can't do that, but you need to pay attention to
>centering / 
>concentricity, and of course your design o-ring gaps / extrusion 
>considerations, etc. I would probably be inclined to simply face the 
>hemispheres, and employ a double sided seat ring which would
>incorporate 
>the sealing features, or attach a ring to each hemisphere with an
>adhesive 
>sealant, and have the rings seal to each other, in which case you could
>
>also incorporate assembly / centering features into the rings so that
>they 
>consistently seat in the correct position.  While not strictly required
>(a 
>seal ring between two hemispheres is functionally a short cylindrical 
>section), I might give consideration to facing the hemispheres slightly
>
>short to account for the ring length, such that in the fully assembled
>and 
>seated condition the hemispheres remain concentric and there is no jog
>in 
>the load path through the se! aling ring(s).
>Hope that helps.
>Sean
>
>
>On November 10, 2016 6:51:51 PM MST, hank pronk via
>Personal_Submersibles 
><personal_submersibles at psubs.org> wrote:
>  Sean, I know we talked a bit about this idea before but I need a
>  refresher.  Can I machine a hole in a heavy sphere and insert a hatch
>land\reinforcing ring assembly that bolts to the sphere.  It looks like
>  Karl Stanley may have done that with his front dome.  This idea if
>feasible makes building a deep diver more realistic.  I am thinking  of
>trying this on my current sphere just to see if I can do it.  Better to
>  screw up a cheap sphere first.  ;-)
>   
>  Next question, when I look at the Deep Rover sub, it has two
>hemispherical domes coming together on a two sided land.  I am sure the
>land also gives the dome! s side support.  Why would this design not
>work
>  with two heavy steel hemispherical domes.  I am talking 3 to 4 inches
>  thick.   The  steel domes can easily be machined with a flat land and
>o-ring grooves.  The idea is to eliminate a very costly weld and it
>would
>  be pretty darn nice to build with the top half of the hull removed.  
>  Hank
>   
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