Technology : Pushing the boat out with penguin power

时间:2019-02-27 06:07:01166网络整理admin

By Howard Baker PICKING up on the penguin’s propulsion system could help engineers create highly efficient ships and submarines. American researchers are now planning to build craft driven by flapping flippers rather than propellers after successful trials of a miniature ship last month. Michael Triantafyllou, a professor at the department of ocean engineering at the Massachusetts Institute of Technology, and graduate student James Czarnowski have built a prototype vessel called “Proteus the penguin boat”. Proteus is powered through the water by two “foils” that hang over the stern of the boat and look like rudders. The foils propel the boat forwards by mimicking the movements of the pectoral flippers of penguins and turtles. Each foil is powered by its own motor and is capable of two types of motion. One is a side-to-side flapping, which Czarnowski calls a “heave”, and the other is a twisting motion. The movements are synchronised by an onboard computer to maximise forward thrust. In a submarine, the system could also make the craft dive or rise. Triantafyllou and Czarnowski’s penguin-like system is one step on from the working model of the tuna fish they built while studying the mechanics of fish propulsion (Technology, 1 October 1994, p 22). “Robo-tuna” was propelled by an undulating body and flipper. Although it was a success, the moving body was difficult to adapt for boats. “It was while watching the penguins at the New England Aquarium that I realised nature had already developed the necessary system,” says Czarnowski. In tests, the flipper-like foils have an efficiency of 87 per cent compared with 70 per cent for a propeller, says Triantafyllou. According to 1992 US fuel and shipping statistics, improving efficiency by just 10 per cent on only 3 per cent of vessels in the American fleet would save 120 million litres of fuel a year, worth $15 million. As a foil flaps, it sweeps through a greater area of water than the blades of a propeller. Consequently, more water is thrown backwards, giving a larger forward thrust. And whereas a propeller forces the water to rotate, wasting energy, with the foils there is no rotation so energy losses are smaller. The flipper-like foils have similar hydrodynamics to fish, which are very efficient swimmers. Proteus is just under 4 metres long and about 50 centimetres wide. It is powered by two car batteries and controlled by a modest PC. It flaps its foils about 200 times a minute to generate a top speed of 2 metres per second. Scaled up to a full-sized ship, this would translate to a top speed of 30 knots, with the foils flapping once every two seconds. Triantafyllou believes that the propulsion method could be easily developed for any size of ship. “From our studies, the system can accommodate the forces needed to drive an oil tanker,” he says. The system could be particularly useful in helping military submarines avoid detection. Propellers generate a “signature” wake which can be used to locate them, whereas the wake from the flipper setup looks more like that from a large marine animal. As the next step towards constructing a full-scale vessel,