Slow Water Currents Feed 'Fish Technology'

Slow-moving ocean and river currents could be a reliable and affordable alternative energy source. A University of Michigan engineer has made a machine that works like a fish to turn potentially destructive vibrations in fluid flows into renewable power.

The machine is called Vortex Induced Vibrations for Aquatic Clean Energy (VIVACE). According to the University of Michigan, it is the first known device that can harness energy from most of the water currents around the world 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, and turbines and water mills need an average of 5 or 6 knots to operate efficiently.

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 and creates energy.

These vibrations are also present in wind and toppled the Tacoma Narrows Bridge in Washington in 1940 and the Ferrybridge power station cooling towers in England in 1965. In water, the vibrations regularly damage docks, oil rigs and coastal buildings.

“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 Michael Bernitsas, VIVACE developer and professor in the University of Michigan Department of Naval Architecture and Marine Engineering.

Bernitsas said fish are able to put the vortices that cause these vibrations to good use, and future versions of his machine will have the equivalent of a tail and surface roughness akin to scales.

“VIVACE copies aspects of fish technology,” Bernitsas said. “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.”

Bernitsas said VIVACE energy would cost about 5.5 cents per kilowatt-hour, a competitive rate in the energy industry.

The researchers recently completed a feasibility study that found the device could draw power from the Detroit River. They are working to deploy one for a pilot project at that location within 18 months.

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