Metamaterial Mesh Could Erase a Sub's Tell-Tale Wake

By Valerie Ross | August 15, 2011 3:57 pm

What’s the News: Scientists have already bent light to make invisibility cloaks and manipulated sound to hide underwater objects from sonar. Now, researchers have come up with a preliminary design for a mesh shield that would let submarines stealthily maneuver through the seas without leaving any wake, they report in a study published online last week.

How the Heck:

  • When something moves through water, it pulls water along with it, creating drag, and leaves a turbulent wake behind it, where more water rushes in to fill the newly vacated space.
  • To get an object to glide through water wake-free, the researchers propose coating it in a porous mesh of man-made metamaterial. Tiny pumps scattered throughout the mesh would help push water through with variable amounts of force. “The goal is make it so the water passing through the porous material leaves the cloak at the same speed as the water surrounding by the vessel,” Yaroslav Urzhumov, one of the researchers, said in a press release. “In this way, the water outside the hull would appear to be still, relative to the vessel.” The mesh would also reduce drag, letting a cloaked sub or ship cut through the water more efficiently than a traditional vessel.
  • The researchers modeled this technique on a sphere, simulating 10 layers of mesh to show how the shield would function. Essentially, the shield would speed up water at the front of the sphere, then slow the water to about its initial speed as it flows around the back.

Not So Fast:

  • This mesh is still just a simulation; the researchers haven’t actually built a wake-free sphere, much less a full-size submarine, yet.
  • So far, the cloak design would only work for small objects moving at a slow pace. For something four-tenths of an inch wide to stay wake-free, for instance, it would have to move at less than half an inch per minute.

The Future Holds:

  • Even with its limitations, the cloak could prove useful, Urzhumov suggests. Tiny cloaked robots made to look like fish could stealthily dart through the depths, sending back information on enemy vessels without being detected.
  • The mesh could also improve ships’ efficiency and reduce drag, even if it didn’t fully erase their wake.

Reference: Yaroslav A. Urzhumov and David R. Smith. “Fluid Flow Control with Transformation Media.” Physical Review Letters, August 11, 2011. DOI: 10.1103/PhysRevLett.107.074501

Image courtesy of the United States Navy

CATEGORIZED UNDER: Physics & Math, Technology
  • Geoffrey Frasz

    If a mesh connected to some pumps could reduce drag on subs, could a similar feature be put on cars to reduce drag and increase fuel efficiency? I realize that the idea of pumps on car bodies is a bit of a challenge, but anything that could cut down on drag could help.

  • Iain

    A few Billion Dollars has been spent on car drag already, maybe they need to streamline the undercarriage.

  • Jay Fox

    Mythbusters showed that dimpling the car surface like a big golf ball yielded huge drag reduction, and an appropriate savings in gas consumption. The idea is to get the air to “stick” to the surface of the car and roll into the vacuum behind it, reducing that vacuum and the turbulent air. They did it with a layer of clay, which added a lot of weight to the car. The test was done at speed, and did not reflect the extra energy needed to get all that extra clay rolling. If a car had been manufactured with all the dimples already in it, there would be no weight penalty, and real savings would result.

    Cleaning up the underside of cars would also have benefits, for a lot of the same reasons. Some racing cars actually direct the exhaust underneath to reduce the vacuum there. They don’t seem to have a competitive advantage, but then again, rule changes have outlawed that design, so maybe there was an actual advantage, perhaps relating to increased mileage, not performance.

  • Brian Too

    Half-formed thought here. Could this not form the basis of a propulsion system itself? It sounds a bit like a highly modified jet pump.

    Lots of conceptual problems come to mind though.

  • Iain

    @ Brian
    There ain’t no free ride. Energy is expensive.

    The dimple effect was demonstrated on baseball bats. Yet one has to wonder about the logistics of keeping ones (vehicle) dimples effective. Oh, also don’t forget the random chevron distribution that gives aircraft better fuel efficiency.
    Anyway, put these UGLY dimples all over American cars and the first commercial you’ll see is a dimple free (whatever).
    Second is how much distortion (wear and tear) can the dimples take before they are rendered a handicap?
    Third, how do you sell it to the public? Better mileage? HA! They buy SUV’s, Cheaper? HA if it even smells of ‘Green’ it’s +25% price. And it’s ugly.

  • floodmouse

    Iain is correct about the marketing problem. Painting the dimples like polka dots will not help sales. What about a “lady bug” SUV (red with black dimples)? Think it’ll catch on?

  • Brian Too

    @5. Iain,

    I doubt that energy is the constraint here. The article refers to stealth implementations which almost certainly means military implementations. A goodly chunk of the world’s sub fleets are nuclear powered and that means, for all practical purposes, the energy supply is abundant.

    Even in diesel/electric boats, they are already equipped for high speed travel. Unless this new technology has HUGE energy requirements, the military will find a way to make it happen.

  • Kurt

    Sounds a lot like the dimples that are on golf balls. Its known that parasite drag is reduced by these dimples. However, it only applies for small objects since other factors will come into play with more surface area and will actually increase drag on larger objects based on shape (since parasite drag is largely influenced by the shape of the object). So, sounds a lot like the same principle. However, introducing a metamaterial might change those characteristics, and might work out.


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