Shrouded at Sea: Scientists Give Ships Invisibility Cloaks

Shrouded at Sea: Scientists Give Ships Invisibility Cloaks:

For now, vessels like this one — the MV Cape Texas — still need to ride out stormy waters. Photo: U.S. Navy

Someone tell the U.S. Navy that rough waters might become a thing of the past. Scientists think they’ve figured out how to fool the stormy seas.

The breakthrough, courtesy of researchers at the University of California at Berkeley, is the latest in a series of developments in invisibility research — many of them Pentagon-funded. Too bad this one won’t actually address what’s arguably the military’s biggest on-the-water worry: Hiding ships from the watchful eyes of potentially dangerous foes. Instead, these scientists think they’ve figured out how to trick the water itself.

The goal is to make ships immune to the up-and-down motion of waves, an objective that could help the military avoid the kinds of delays or rerouting that, for now, are inevitable during bad weather.

If that sounds different than previous breakthroughs in invisibility, it most definitely is. Before this, scientists focused on shrouding objects from the human eye. They’ve tried harnessing the mirage effect to play tricks on vision, and tried using meta-materials that bend light, in the hope of rendering something impossible to see. But despite some pretty amazing progress (cloaking 3D objects or entire events, for example) invisibility is still largely relegated to the high-frequency realm — not the optical wavelengths visible to us.

This time, instead of cloaking an object from light, scientists are cloaking it from water.

Here’s how the proposed cloak would work. In an ocean, water typically stratifies into layers. The top layer is warmer and lighter, while the bottom layer is cooler and more dense. Waves, of course, ripple along the top of the water. But they also ripple between those two layers — and those waves are known as “interfacial” waves.

Scientists figured they could help protect vessels from turbulent seas by turning surface waves — the ones that get rocky and cause all kinds of shipboard havoc — into those interfacial waves. Using computer simulation, they modeled a process of laying down a carefully sculpted section of ripples along the ocean floor in front of the object in question (a sailboat or an offshore oil rig, let’s say). The transfer of energy between that sea floor section and the waves above — both interfacial and surface — would create a sort of “wave vector,” in the words of Science Magazine.

The researchers don’t specify how, exactly, they’d lay down these rippling “cloaks” on the seafloor. But, according to their calculations, as long as “the wave vector of the ripple [cloak] equal[s] the difference in the wave vectors of the interfacial and surface waves,” a rough wave approaching a vessel will suddenly disappear — and pass far below the vessel.

Sounds kind of mind-blowing. Of course, with research like this, there tend to be caveats. This time around, it’s the fact that real-world oceans are layered in gradients, rather than simply divvied into two layers of waves. Plus, the ocean abounds with waves moving at different speeds — meaning a different “patch” of ocean floor ripples would be required for each one.

Conceivably, however, this kind of cloak could be used around inert structures, like anchored vessels. Or aircraft carriers that’ve been turned into floating luxury hotels.

Photo: U.S. Navy