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Phlubmarine

 Peristaltic hyrdo locomotive submarine
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Picture an elongated cylindrical submarine hull which tapers slightly towards the aft. The hull bulges significantly along the length of the base of the cylinder for crew space and ballast, and looks similar to a manta ray with its fin-rays wrapped upwards into a tubular shape.
The inner center of this hull is open to the water and has a flexible bladder extending from fore to aft which contains flaps allowing for a one-way valve effect.
Steam generated is allowed to build and fill the flexible valved bladder in cycles.
The inflation constricts the bladder in a wave while rapid heat loss to the sea water then contracts the bladder in stages creating a standing wave-form travelling rear-wards to generate almost soundless propulsion with layman's terms laminar flow.

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       Peristaltic pumps do not produce laminar flow.
—MechE, Jan 08 2013
   

       Crap. I liked that name.
Ooh, I know...~Phlubmarine~		   

       From the wiki article on Laminar flow:
//When a fluid is flowing through a closed channel such as a pipe or between two flat plates, either of two types of flow may occur depending on the velocity of the fluid: laminar flow or turbulent flow. Laminar flow tends to occur at lower velocities, below the onset of turbulent flow. Turbulent flow is a less orderly flow regime that is characterised by eddies or small packets of fluid particles which result in lateral mixing. In nonscientific terms laminar flow is "smooth", while turbulent flow is "rough".//		   

       I guess I'm using the layman's definition here. I figured that it would be extremely smooth flow compared to a propeller. The turbulance would be in the trail of vortex rings in its wake.   

       Shrouded propellers can produce laminar flow, and you're right that laminar flow produces low noise, but not none.   

       The problem, as your annotation indicates, is that peristaltic pumps produce their flow in discrete pulses. These pulses produce alternating high and low pressure, which, by definition, is noise. You might be able to set the frequency high enough that it didn't carry, but it's definitely noise.   

       Even if you do that though, if the force is high enough to produce the same level of thrust as a propeller that produces cavitation, a peristaltic pump will produce similar levels, usually on the front end (the trailing edge of the wave). This cavitation is what causes most of the noise.
—MechE, Jan 08 2013
   

       "... and then, captain, I thought I heard..."   

       "Heard what, Jonsey?"   

       "... I ... thought I heard a 200-foot octopus. Sir."
—lurch, Jan 08 2013
   

       When MecE slams a door It's very hard to re-open! I believe the Idea is great [+] But in reality it would be loud as shit. Seriously, loud as shit!
—Brian the Painter, Jan 09 2013
   


 

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