”Fish technology” developed to draw affordable renewable energy from water currents

November 22nd, 2008 - 1:37 pm ICT by ANI  

Washington, Nov 22 (ANI): The day is not far when slow-moving ocean and river currents may become new, reliable and affordable alternative energy source, all thanks to VIVACE - a machine designed by an engineer at University of Michigan that works like a fish to turn potentially destructive vibrations in fluid flows into clean, renewable power.
VIVACE is the first known device that could harness energy from most of the water currents around the globe because it works in flows moving slower than 2 knots (about 2 miles per hour.) Most of the Earth’’s currents are slower than 3 knots. Turbines and water mills need an average of 5 or 6 knots to operate efficiently.
Expanded as Vortex Induced Vibrations for Aquatic Clean Energy, VIVACE doesn”t depend on waves, tides, turbines or dams. It’’s a unique hydrokinetic energy system that relies on “vortex induced vibrations.”
Vortex induced vibrations are undulations that a rounded or cylinder-shaped object makes in a flow of fluid, which can be air or water. The presence of the object puts kinks in the current’’s speed as it skims by.
This causes eddies, or vortices, to form in a pattern on opposite sides of the object. The vortices push and pull the object up and down or left and right, perpendicular to the current.
“For the past 25 years, engineers-myself included-have been trying to suppress vortex induced vibrations. But now at Michigan we”re doing the opposite. We enhance the vibrations and harness this powerful and destructive force in nature,” said VIVACE developer Michael Bernitsas, a professor in the U-M Department of Naval Architecture and Marine Engineering.
Fish excel in how to put the vortices that cause these vibrations to good use.
“VIVACE copies aspects of fish technology. Fish curve their bodies to glide between the vortices shed by the bodies of the fish in front of them. Their muscle power alone could not propel them through the water at the speed they go, so they ride in each other’’s wake,” said Bernitsas.
The working prototype in his lab is just one sleek cylinder attached to springs. The cylinder hangs horizontally across the flow of water in a tractor-trailer-sized tank in his marine renewable energy laboratory. The water in the tank flows at 1.5 knots.
Now, the VIVACE cylinder in the current causes alternating vortices to form above and below the cylinder. The vortices push and pull the passive cylinder up and down on its springs, creating mechanical energy. Then, the machine converts the mechanical energy into electricity.
Bernitsas said that only a few cylinders might be enough to power an anchored ship, or a lighthouse. These cylinders could be stacked in a short ladder.
He estimated that array of VIVACE converters the size of a running track and about two stories high could power about 100,000 houses. Such an array could rest on a river bed or it could dangle, suspended in the water. But it would all be under the surface.
It is believed that the system would not harm marine life like dams and water turbines can, because the oscillations of VIVACE would be slow.
Bernitsas said VIVACE energy would cost about 5.5 cents per kilowatt hour.
“There won”t be one solution for the world’’s energy needs. But if we could harness 0.1 percent of the energy in the ocean, we could support the energy needs of 15 billion people,” said Bernitsas.
The study is published in the current issue of the quarterly Journal of Offshore Mechanics and Arctic Engineering. (ANI)

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