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Inflatable Submersible

Inflatable submersible hull.
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The idea of an inflatable submersible seems contradictory and I'm not even sure it would work myself, so bear with me here...

The idea is not at all dissimilar to the Zorb® balls. I realized that the passenger compartment is maintaining it's shape because it is 'stretched' by the pressurized outer sphere. Now I suppose this would work as long as the pressurized compartment has a higher internal pressure than ambient pressure.

For underwater use there are a number of obvious changes that would have to be made. For starters, the passenger compartment would have to be sealed off from the water to keep it at 1 atmosphere equivalent. Furthermore you'd need life support systems, as well as a method of controlling the air pressure in the pressure hull.

You would also need massive amounts of ballast for such a large sphere, which would probably prove to be the Achilles heel..

Oh, and some form of propulsion. That's going to be interesting. A sphere is hardly the most hydrodynamically efficient shape.

On top of all that, I can really not think of a practical use for it.. Oh well, it's 3am whatcha gonna do, eh?

akumabito, Jun 17 2008

ZORB structure http://img.photobuc...0712151852_zorb.jpg
An image showing the structure of a ZORB ball for clarification. [akumabito, Jun 18 2008]

[link]






       http://www.zorb.co.nz/ <-- The inspiration for the idea.
akumabito, Jun 17 2008
  

       "Oh, and some form of propulsion. That's going to be interesting"   

       How about letting the air that you used to inflate with escape out the back as a propellant?
normzone, Jun 17 2008
  

       It could be done. But you'be pretty soon be in to saturation diving and gas mixtures; decompression would be slow ......   

       The buoyancy is going to try and rip the "bubble" off its base; it may need to be contained in a net to limit the forces on the junction.
8th of 7, Jun 17 2008
  

       Interesting. I like it. Don't understand it. But I like it.
Moonguy, Jun 17 2008
  

       ...Not sure exactly what you're suggesting here. it's either of two things. First <and what I think you're suggesting> is a system with a double-hull, whereby the gap between the two skins is highly pressurised, but the inner zone in at a more moderate pressure.   

       ..which will encounter all sorts of structural problems. You've still got the inner skin with XXXPsi acting on it's outer wall, trying to collapse it. Yes, it's attached via some method to the outer skin, but we're talking huge forces for a thin walled vessel to withstand. - And also your vessel will be horribly sensitive to impact, puncture, etc. That said, it's worth a look - maybe your ties between the hulls could be made strong enough to make this viable.   

       The other option is simply a sub where you've matched inner pressure to the outside pressure. This works beautifully. Only problem is, our bodies aren't so suited to the high pressures. Deep scuba diving involves exotic gas mixes, delicate procedures, and high risk. But every extra PSI you put inside your sub is one less PSi your walls need to withstand. That's why breathable liquid is a bit of a holy grail. Liquids generally don't change volume much with pressure changes <bulk moduli in the gigapascal range, or higher> - and so were we able to make a breathable liquid to fill your sub with, most of the high-pressure environment issues just go away.   

       Anyhoo, sometimes it helps to draw what engineers call a "free body diagram" - which is a simple sketch of the thing you're designing. Now draw on it all of the loads it's subjected to from outside influences. <in this case, outside water pressure, gravity>. Now, in all directions, unless you're accelerating, forces sum to zero. So, look at your diagram. Where do those forces go? What is "holding back" the loads? - That's what design is about. Looking where the loads are and counterracting them. I reckon you've forgotten that your inner sphere will want to collapse - and quite simply, if you make it strong enough to withstand the pressure between the two skins - you didn't need to worry about the double-pressure hull in the first place. The ties between the skins is the critical issue in this design. Hell, maybe it'll work.   

       Lastly, you'd almost certainly use hydraulic pressure in between the walls - less stored energy <read - less power required to make/maintain pressure>.   

       Bun for distracting me on a crappy wednesday.
Custardguts, Jun 17 2008
  

       Hey, how come you get to have wednesday early???   

       I live in australia, which makes me very very special.   

       but not in a <lisp> thpecial </l> way.
Custardguts, Jun 17 2008
  

       I don't think the problems are insurmountable. The pressures involved of both water and air aren't too high. Obviously this isn't a machine for deep-sea exploration.   

       The key to maintain normal structural integrity would be to maintain the pressure differential between the pressure 'hull' and the outside environment.   

       For example, assuming the sphere would hold its shape on the surface when filled to 2 Atm (a +1 atmosphere pressure differential with the environment), then at a depth of 10 meters it should maintain the same shape and volume when filled to a pressure of 3 Atm. and at a depth of 20 meters when filled to 4 times atmospheric pressure.   

       The passenger compartment would maintain its shape and (assuming a way could be found to close it off successfully), internal shape should be maintained at 1 atmosphere.   

       The ZORB idea of having two flexible 'hulls' joined together by hundreds of cables could be scalable and adaptable to a large number of designs, including the traditional cigar or blimp shapes for submarines.
akumabito, Jun 18 2008
  

       Pardon me for going into a different context with this. . . There is a lunar/planetary base shielding concept which utilizes the idea of inflating a double-hulled, cylindrical balloon with cable ties between the two hulls. After inflation, the gas is displaced out of the inflatable by filling it with regolith. The cables prevent the filled structure from collapsing under its own weight. To date tests have been done with 1/10th scale units filled with sand and it works.   

       I mention this concept here because one of the interesting features is a built-in airlock that is sort of like the internal bubble of the inflatable submersible.
Moonguy, Jun 19 2008
  
      
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