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PostPosted: Mon Dec 11, 2017 6:30 pm 
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Proved to be a inefficient propulsion system but, turned inside out...
quote:
Electromagnetic water cloak eliminates drag and wake
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while simultaneously helping it avoid detection.

The idea originated at Duke University in 2011 when researchers outlined the general concept. By matching the acceleration of the surrounding water to an object's movement, it would theoretically be possible to greatly increase its propulsion efficiency while leaving the surrounding sea undisturbed. The theory was an extension of the group's pioneering work in metamaterials, where a material's structure, rather than its chemistry, creates desired properties.
Six years later, Yaroslav Urzhumov, adjunct assistant professor of electrical and computer engineering at Duke, has updated the theory by detailing a potential approach. But rather than using a complex system of very small pumps as originally speculated, Urzhumov is turning to electromagnetic fields and the dense concentration of charged particles found in saltwater.

Read more at: https://phys.org/news/2017-12-electroma ... k.html#jCp
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PostPosted: Mon Dec 11, 2017 7:17 pm 
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The initial blurb had me throwing the 'conservation law violation' flag. Doesn't appear to actually do that on close reading, but I'm still smelling some sort of a rat.

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PostPosted: Mon Dec 11, 2017 7:49 pm 
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I have read of a crazy person who built a kayak with a hull shape designed in Michlet to reduce the wave drag to zero at one speed. Nice try, but typically only 20% of a kayak's drag is wave resistance. Theses guys may be doing something similar using emf to accelerate or decelerate the flow locally.

I admit it does seem a bit like breaking CoE.

Here's the abstract:

Theory and practical implementations for wake-free propulsion systems are proposed and proven with computational fluid dynamic modeling. Introduced earlier, the concept of active hydrodynamic metamaterials is advanced by introducing magnetohydrodynamic metamaterials, structures with custom-designed volumetric distribution of Lorentz forces acting on a conducting fluid. Distributions of volume forces leading to wake-free, laminar flows are designed using multivariate optimization. Theoretical indications are presented that such flows can be sustained at arbitrarily high Reynolds numbers. Moreover, it is shown that in the limit
Re≫10^2
, a fixed volume force distribution may lead to a forced laminar flow across a wide range of Re numbers, without the need to reconfigure the force-generating metamaterial. Power requirements for such a device are studied as a function of the fluid conductivity. Implications to the design of distributed propulsion systems underwater and in space are discussed.


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PostPosted: Mon Dec 11, 2017 8:51 pm 
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No issues with COE, they must put a lot of power into moving the boundary layer. But, in theory, they can throttle back the main drive and get the same or higher speed, plus some stealth.

Never mind a huge sub, would such be handy for torpedoes ? Faster run, harder to track for counter-measures, can still be guided, unlike the Russian rocket things...

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PostPosted: Mon Dec 11, 2017 9:44 pm 
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I was talking CoM, not CoE. But now I remember that wake is dragged along with the ship, and race is the bit going backwards.

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PostPosted: Mon Dec 11, 2017 10:27 pm 
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Torpedoes don't really run on the surface, I'd be interested to see how much drag they have that is wavemaking resistance. For collins class they dd look at periscope-depth wake, since satellites can detect wakes.


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PostPosted: Tue Dec 12, 2017 9:44 pm 
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I suppose the old rule still applies, throw enough power at something and it'll fly

https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive

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PostPosted: Wed Dec 13, 2017 12:31 am 
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I did a lab on it at uni, it was a cute little perspex channel with some reasonable sized coils around pushing water through it. I preferred running the steam engine.


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PostPosted: Thu Dec 14, 2017 2:33 pm 
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The Argus wrote:
I suppose the old rule still applies, throw enough power at something and it'll fly

https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive


Reminds me of what a jarhead Flyboy LTCol said to a bunch of us at the Amphib school on Coronardo circa 1972.
"The F4 is proof that if you put big enough engines in it, YOU CAN FLY A BRICK".

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PostPosted: Fri Dec 15, 2017 2:38 pm 
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I see your F-4 and raise you a Starfighter. :geek:

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PostPosted: Fri Dec 15, 2017 8:49 pm 
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M.Becker wrote:
I see your F-4 and raise you a Starfighter. :geek:


I call with F-111B.

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PostPosted: Sat Dec 30, 2017 3:52 pm 
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jemhouston wrote:
M.Becker wrote:
I see your F-4 and raise you a Starfighter. :geek:


I call with F-111B.


Raise you a Scimitar.

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PostPosted: Sat Dec 30, 2017 10:53 pm 
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Image

That'd need a fair bit of thrust to get airborne.


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PostPosted: Sun Dec 31, 2017 12:55 am 
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https://youtu.be/pJdrlWR-yFM


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