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The US Navy is developing "stealth submarines" that have no propellors but are equipped with artificial muscles, enabling them them to swim silently through the water like a fish, New Scientist says. A metre- (3.25-feet) long prototype, built by Texas A and M University at College Station, can flap its tail like a fish, the British science weekly reports in next Saturday's issue. Propellors are submarines' weak spot as they cause noise and a wake of disturbed water, leaving the vessels vulnerable to enemy sonars or aircraft. Fish, however, have evolved in favour of efficiency, using muscles to move their tail and fins and propel themselves sleekly through the water. The Texas prototype comprises a hull divided into six sections like vertebrae. They are rigid but each can be deflected with respect to their neighbouring sections. They are pushed in and out by wire "muscles" made from shape-memory alloys. These alloys are a novel mixture of strong, resilient metals that contracts when it is heated beyond a certain temperature and then expands, recovering its original shape, when it cools back down below that point. The prototype's wires, made from nitinol, an alloy of nickel and titanium, are electrically heated, which causes them to shorten and thus pull the section in.
A built-in cooling system then brings the wires down to below their critical temperature, which, with help from a spring, causes them to expand and thus push the section out again. By carefully controlling the heating and cooling and coordinating the movements of each section, the prototype can be made to wriggle forward, fish-like. The top rate, so far, is five tail-flaps a second, although the researchers are tight-lipped about what speed that gives, New Scientist says. "Initially, we are focussing on unmanned water vehicles," it quotes one of the development team, Othon Rediniotis, as saying, adding that the potential is there to make a bigger version that would be manned. One of the biggest challenges is finding a power source. Rediniotis is interested in clean, light and silent sources such as fuel cells and hydrogen to drive the alloy actuators. All rights reserved. © 2000 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse. Related Links Fluid Dynamics Research Group Application of Active Materials and Neural Networks to Aquatic Biomimetics SpaceDaily Search SpaceDaily Subscribe To SpaceDaily Express 
Does Europa's Rosy Glow Betray A Flourishing Colony Of Bugs
London - Dec 5, 2001The red tinge of Europa, one of Jupiter's moons, could be caused by frozen bits of bacteria New Scientist reported today. Their presence would also help explain Europa's mysterious infrared signal. Europa is mostly frozen water, but it absorbs infrared radiation differently to how normal ice does. |
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