Robots Plumb the Depths


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Image courtesy of Virginia Institute for Marine Science.

Underwater robots, or remotely operated vehicles, are maturing and proving their value in a wide range of commercial and scientific roles, sometimes at bonecrushing depths in oceans around the world. Earlier this year, two types or underwater ROVs dove to 4,000-m depths in the Atlantic Ocean to locate, map, and raise the wreckage of Air France's doomed Flight 447. Elsewhere, in the Ross Sea off of Antarctica, researchers added to the resume of underwater "gliders" by successfully launching and operating the machines for three months in the frigid seas, sending them beneath the ice to continually monitor and gather a wide range of ocean data.

The machines that found and lifted the wreckage of the Air France Airbus operate on proven technology that now is more than 10 years old. But engineers are adapting it and building smaller, less expensive machines that can operate more cheaply at the same depths, although the smaller machines can only be used for search and survey, not recovery.

Caption to come.

Researchers from Woods Hole Oceanographic Institute used their Remus 6000 machines, torpedo-like tubes fitted with cameras, sidescan sonar, sensors and a fiber-optic tether, working in a grid pattern, to locate the Air France wreckage in a 3,900-sq-mile area. Then, working from an ocean-going cable-laying ship, operators with Phoenix International, Largo, Md., used their Remora 6000 to work the bottom, recover the flight's black boxes and later, rig large pieces of the wreckage to allow recovery by ship's cranes. The Remora is fitted with mechanical manipulators, metal appendages with claw-like devices to grip objects.

High Pressure

Phoenix, a marine services company that conducts manned and unmanned underwater operations, built the Remora to reach depths of 6,000 m. Its 1.7-m-long hull uses a 25-hp electrohydraulic motor to power four lateral and two vertical thrusters as well as the manipulators. It is fitted with an array of lights, sonar, video and fiber-optic system, which is connected to the ship with 6,700 m of fiber-optic umbilical line.

Phoenix builds its own robots, pressure testing all components to 10,000 psi, notes Steve Saint-Amour, a mechanical engineer who has led development and production since the firm's startup in 1997. His earlier machines proved successful at lesser depths; a Phoenix machine located and recovered an Israeli submarine in 9,600-ft depths in the Mediterranean Sea. Since then the firm has been called on for a number of high-profile deep-sea jobs.

Caption to come.

Its newest underwater robot is small, 50,000-lb inspection and identification "xBot," designed to penetrate tight spaces at 6,000-m depths. "We wanted something disposable, because we assumed we would lose a vehicle [at such depths and searching through tight spaces in wrecks]," says Saint-Amour. "We wanted to build it cheap enough so that we could swallow that nut."

Reducing costs—the xBot costs about $100,000—means going smaller and using as much off-the-shelf components as possible, says Saint-Amour. Larger machines require larger deck equipment to store, launch and recover the robots, greatly adding to costs. Another key to xBot's success was development of a flat-cell lithium ion battery system that allows it to work at depth for 12 h, tethered with a fiber-optic cable.

Gliding

Oceanographers and scientists also are increasingly working with another type of less-expensive underwater robot to continually monitor water quality in oceans. Gliders are manufactured by three companies for about $150,000; their low cost and mobility are revolutionizing how oceanic data is accumulated, say researchers.

Caption to come.

Powered by batteries and hydraulics, the gliders move in a zig-zag manner through changes in buoyancy from pumping oil in and out of an inflatable bladder. When oil is pumped forward, the nose tilts down for a dive; to surface, oil is pumped back in the machine to increase buoyancy. Moving the battery fore or aft within the hull shifts the center of gravity, and rotating it controls roll. Fins provide mobility. Top speed is about one-half mile per hour. The machines' low power requirements allow them to stay at sea for months at a time.

They are piloted remotely through a satellite phone network. When they surface, the glider flips its tail out of the water to expose its antennae, through which data is transmitted to the network.

Researchers at Oregon State University, Corvallis, have used 9 gliders over five years, "flying them around the clock" for a total some 45,000 kilometers, says Jack Barth, professor of oceanography. OSU's robots work in very swift currents to depths of 1,000 ft off the Oregon coast. "They allow us to keep our finger on the pulse of the ocean, day by day."

Going Deeper

Edison Hudson, director of strategic alliances for iRobot, which manufactures "SeaGlider," says tests are being done for a glider that can dive to 6,000 m. iRobot licenses the technology from the University of Washington, where researchers pioneered the concept. Hudson says sensors can account for 20% to 50% of SeaGlider costs. Many sensors were developed to be used from large, ocean-going ships, the traditional method researchers have used to study oceans. But ships are expensive, costing about $50,000 per day. iRobot has been working with sensor manufacturers to reduce their sizes.

Walker Smith, a professor of oceanography at the Virginia Institute for Marine Science, was part of a team that used SeaGlider last winter on the Ross Sea, off of Antarctica. The project was to study water conditions beneath the ice shelf and the polynya, open stretches of water within ice. They were unsure how it would operate in water temperatures as low as 28°F.

After launching the glider from a seal's breathing hole, the team was alarmed when they lost contact for three days. But after it surfaced and transmitted its data, Smith discovered the reason. Its sensors interpreted ice crystals in the frigid water as an obstacle, so it continued on a route that took it beneath the ice shelf until it located open water. It operated for three months without any problems and the team was able to recover it from the ice with little effort, he says.

An array of underwater robots—remotely operated vehicles—are proving themselves in commercial and scientific roles, sometimes at bone-crushing depths, in oceans around the world.

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July 2011

by John Kosowatz, Senior Editor, ASME.org