Wave Glider

Wednesday, May 30th, 2012

Liquid Robotics designed its Wave Glider to set a world record for greatest distance by an autonomous wave-powered vehicle:

The Wave Glider’s design is simple: A surfboard-sized float bobs on waves, big or small. That motion is transferred through a streamlined, 7-meter, rubber-and-steel cable to a submarine that cruises in the deeper, calmer waters. “In the rough open ocean, seven meters down, there’s virtually no up and down wave motion,” Brager says.

Indeed, oceanography teaches us that wave turbulence greatly diminishes below the surface of the water. For example, if you have a wave with a 20-foot length trough to trough, the waters underneath will be only 5 percent as turbulent 10 feet below the surface. The Wave Glider exploits this simple fact of physics to transform wave energy into forward motion.

Here’s how it works: When the floating, surface-skimming portion of the Wave Glider attempts to force the submarine portion to flow with a wave, the sub is forced to carve upward through its relatively still waters. As this happens, an array of pivoting wings on the submarine lock into diagonal angles, transforming the bobbing wave motion into zig-zagging forward thrust at around 1 to 2 knots.

Because the solar array on top of the Wave Glider only has to power the rudder, satellite communications and whatever sensors are plugged into the modular payload, the glider, powered by the ocean’s endless undulations, can theoretically last much longer, and travel much farther, than any other ocean-going unmanned vehicle. That means a Wave Glider can go where a boat can — albeit slowly — but with the longevity of a buoy. This makes a Wave Glider an ideal platform for oceanic data collection.

Sharks and barnacles still pose challenges for the Wave Glider:

Some researchers believe that sharks, using their electromagnetic sensing Ampullae of Lorenzini, sometimes become curious about metallic objects and may bite them. But the sharks normally bite the glider’s wings, doing no more harm than scratching off the anti-fouling paint that keeps the hull clean of microorganism growth so it may slipstream through the water. (When Benjamin was removed from the water, barnacle growth only occurred on the sections where this special paint had come off, or on areas left unpainted. This fouling is a major concern for the longevity of a glider at sea, as a dirty sub can lose up to half of its already meager speed.)

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