Researchers at the Woods Hole Oceanographic Institution (WHOI) and Webb Research Corporation (Falmouth, Massachusetts) have tested an environmentally friendly robot that uses heat from the ocean for propelling forward. The success of this test paves way for unmanned robots to perform numerous tasks in the ocean that may not be convenient for humans. This “green” robot is the first of its kind, and can glide across thousands of kilometers uninterrupted.
The prototype of the vehicle was launched in December 2007 off the coast of St. Thomas. The vehicle has been traveling ever since in the 13,000-foot-deep Virgin Islands Basin shuttling between St. Thomas and St. Croix more than 20 times. According to the researchers, the glider can continue its “green-powered” motion for around six months. The glider has been named Slocum after Joshua Slocum, the first man to sail around the world single-handedly.
While there have been numerous unmanned robots that operate underwater, the Slocum vehicle distinguishes itself by utilizing ocean heat to operate for months together and not needing a motor. Conventional ocean gliders rely on motors or pumps to displace water and the increase or decrease in the water displaced is used to propel the glider forward.
The “green” glider relies on thermal stratification to derive energy for propulsion. The difference in temperature between the warm surface waters and the colder deep ocean water provides the necessary energy. The heat energy warms the engine’s wax-filled tubes and the expanding wax converts the heat energy to mechanical energy, which pushes oil stored inside the hull to the one outside thereby changing its buoyancy. The wax is again cooled when the glider moves to the colder deeper waters of the ocean. The robot surfaces periodically to ascertain its position using the Global Positioning System and to communicate with a laboratory on the shore via Iridium-based satellite.
The Slocum can be used for various tasks including testing the salinity of the water, temperature and biological productivity. The silent functioning of the robot adds to its usefulness for acoustic studies.
“Gliders can be put to work on tasks that humans wouldn’t want to do or cannot do because of time and cost concerns,” said Dave Fratantoni, an associate scientist in the WHOI Department of Physical Oceanography. “They can work around the clock in all weather conditions, so we are tapping a virtually unlimited energy source for propulsion.”
Although the “green” glider does not depend on batteries for its propulsion, the standard circuitry inside the vehicle like the computers, radio transmitters, and other electronics use alkaline batteries. Webb Research is working on technologies that can reduce its dependency on batteries.
Currently, the data collected by Slocum is used to study the effect of eddies on regional circulation, larvae of coral reef fish and man-made pollutants. Future plans include launching a fleet of gliders in the waters of the North Atlantic to study the ocean’s response to climate change.
Radhika Raghunath is a contributing editor for TMCnet. To see more of her articles, please visit her columnist page.
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