Friday, September 14, 2007

2007 Eel feel helps wave power go with the flow

Eel feel helps wave power go with the flow

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  • 16 April 2007
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  • Paul

The simulated mutant fish slithers through the water, wriggling faster as it detects a change in the sea conditions (3MB .MPG video). It may sound like some Hollywood special effect, but the idea behind this fish is in fact to squeeze more energy out of wave power.

Leena Patel and her colleagues at the University of Edinburgh in the UK are using a genetic algorithm computer program, which mimics the way natural selection breeds fitter creatures, to improve the way their virtual lamprey swims in different sea conditions. They want to use these swimming motions to boost the efficiency of a novel type of wave-power device - a long, thin, eel-like machine called the Pelamis.

Made by Ocean Power Delivery of Edinburgh, the 140-metre-long Pelamis consists of four floating tubular segments (New Scientist, 20 September 2003, p 33). As the waves flex the segments (3.14MB .avi video, divx or xvid codec required), hydraulic rams inside them move in and out of power converters in the joints between the segments, generating up to 750 kilowatts of electricity. Three Pelamis machines are already generating power at a site off Portugal, while four will begin operating in the Orkney islands of northern Scotland in 2008.

However, oscillating machines like this cannot adapt when the wave speed changes. "So they operate at less than optimum efficiency," says Patel. To overcome this, she turned to the lamprey, which uses skin sensors to adjust its swimming motion as the current changes. Lampreys have a cluster of neurons in their spinal cord called a central pattern generator (CPG), which produce signals that drive the muscles to contract rhythmically and make them swim (Neurocomputing, vol 70, p 1139).

Patel took a computer model of a lamprey CPG and applied a genetic algorithm to mutate its connections repeatedly to see if she could "breed" successively better swimming motions under different conditions. This greatly extended the lamprey's repertoire of swimming patterns, and made it wriggle at up to 12.7 times per second, compared with just 1.7 times a second previously.

Initial simulations show that altering the flexibility of Pelamis's joints in line with these fitter swimming patterns could improve energy capture under different wave conditions, Patel says. The principles could be applied to any bobbing wave-power generator, she adds.

Max Carcas, a director of Ocean Power Delivery, thinks the idea may hold promise, but he says the company's own engineers are also working to improve the device's efficiency.

Peter Bentley, a computer scientist at University College London, says the work shows how much genetic algorithms have become accepted in engineering.

From issue 2599 of New Scientist magazine, 16 April 2007, page 28

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