Fish technology draws energy from slow water

A US researcher is using fish tail technology to extract usable energy from water flows down to 1.5 knots

Professor Michael Bernitas in the University of Michigan is the latest engineer to rediscover vortex shedding and fish tails as a means of extracting useful amounts of energy from relatively slow moving ocean and river currents, a subject we have covered in 'Eureka' on at least two previous occasions, in 2003 and 2004 (links below)

This latest machine is called VIVACE, which stands for Vortex Induced Vibrations for Aquatic Clean Energy.

Vortex induced vibrations are undulations that a rounded or cylindrically 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.

The new machine is a cylinder attached to springs. The cylinder hangs horizontally across the flow of water in a tractor trailer sized tank in the professor's marine renewable energy laboratory. The water in the tank flows at 1.5 knots.

The presence of the 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.

The professor estimates that an array of VIVACE converters the size of a running track and about two stories high could power about 100,000 houses. Because the oscillations of VIVACE would be slow, it is theorized that the system would not harm marine life as dams and water turbines can.

Bernitsas says VIVACE energy would cost about 5.5 cents per kilowatt hour as opposed to wind energy at 6.9 cents a kilowatt hour, nuclear at 4.6, and solar at 16 to 48 cents per kilowatt hour depending on the location.

They are working to deploy a unit in the Detroit River as a pilot project within 18 months.

Tom Shelley

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