
Electromagnetic Water Cloak Eliminates Drag and Wake - hardtke
https://pratt.duke.edu/news/water-cloak
======
oroup
I'm fascinated by how this ended up with the same name as the fictional
stealthy propulsion technology from the Hunt For Red October. They're both
called "magneto hydrodynamic" propulsion.

The book was published in 1984. Was this widely theorized? Did Clancy speak to
someone with non public information? Were the researchers at Duke fans of the
book / movie? Did they just copy the name of his technology or did the
fictional description of how it worked actually inspire their research?

~~~
qubex
Magnetohydrodynamics (MHD) is a real branch of physics that deals with the
motion of charged fluids (which could be ions dispersed in a fluid, but more
typically involve the high-temperature plasmas of stars and experimental
fusion reactors). Mathematically it fuses Maxwell’s Laws of Electromagnetism
with Navier-Stokes for fluid flow (if that is insufficiently nauseating,
relativistic and quantised complications are available upon request).

The idea of moving water by running a current through it and subjecting it to
magnetic fields was “diffusely known” in the late 1970s/early 1980s. Japanese
researchers eventually built such a device in the 1990s and discovered it to
be hideously inefficient. I myself knocked together a means of getting
electricity out of a flame by means of electrodes and a magnetic field as a
high-school science in the late 1990s. It really isn't as exotic as it sounds.

Tom Clancy isn’t actually who conceived of MHD propulsion for the fictional
_Red October_ : in his book, the boat made use of an impeller (essentially a
propeller, perhaps contra-rotating, inside a cowling much a kin to a jet
engine nacelle). It was only revised to be a MHD system for the film.
Interestingly, impellers have now become mainstream methods of propelling a
submarine, and it seems that the next frontier is to use brushless engine
designs to drive the rotor by oscillating magnetic fields generated by housed
coils and not need to run an axle through the pressure hull.

MHD meanwhile, as you can see, has been relegated to a supporting role of
perhaps aiding stealth.

So, remarkably, Clancy was entirely accurate in his technological predictions
and the later film-makers screwed up.

~~~
oroup
Great answer, thanks!

~~~
qubex
Glad to have been of service!

~~~
mcguire
" _Mathematically it fuses Maxwell’s Laws of Electromagnetism with Navier-
Stokes for fluid flow (if that is insufficiently nauseating, relativistic and
quantised complications are available upon request)._ "

Quote of the day, too!

------
sitkack
Not to geek out, but this is basically warp drive from star trek.

By interacting with the medium the object is passing through, this could
effectively change its shape or foil. I wonder if this implications for having
orbiting bodies around gas giants (offsetting atmospheric drag) or a shield
for a sun probe ?

Could also allow for modifications to the leading edge of a hypersonic plane
or a re-entering spacecraft. Relevant research in MHD control of the plasma
layer during hypersonic flight [0]

[0] [http://sci-hub.la/10.1016/j.ast.2014.03.008](http://sci-
hub.la/10.1016/j.ast.2014.03.008)

------
zkms
So I skimmed the paper ([http://sci-
hub.la/10.1103/PhysRevE.96.063107](http://sci-
hub.la/10.1103/PhysRevE.96.063107)) and it involves passing current through a
conductive fluid whilst exposing it to magnetic fields. However, unlike
mercury or NaK, seawater behaves interestingly when current is passed through
it. How do you prevent the water from being chemically changed from the
exposure to electricity; given that such changes will make the vessel easier
to detect (especially if they involve the evolution of gasses)?

~~~
rsynnott
Reducing drag would presumably be useful in itself, even outside the context
of avoiding detection.

