VIVACE (Vortex Induced Vibrations for Aquatic Clean Energy) is a newly invented machine harvesting slow-moving ocean and river currents. A researcher from the University of Michigan has come up with the system that works like a fish, turning potentially destructive vibrations found in fluid flows into electricity.
The water that VIVACE uses has to be slower than 2 knots (2 mph). While most of Earth’s currents have less then 3 knots speed, they can’t be used for their energetic properties, because regular turbines don’t work at that water speed (they need at least 5 to 6 knots).
VIVACE uses the vibrations (the 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.
These vibrations in wind 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 VIVACE developer Michael Bernitsas, a professor in the U-M Department of Naval Architecture and Marine Engineering.
Fish have long known how to put the vortices that cause these vibrations to good use. “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.”
Anyway, mr. Bernitsas says future versions of VIVACE will have the equivalent of a tail of a fish. The current working prototype is just one sleek cylinder attached to some springs. The cylinder floats across the water flow in a tractor-trailer-sized tank, that has about 1.5 knots of speed.
Bernistas says the power of just a few cylinders stacked in a short ladder could be enough to power an anchored ship or a lighthouse. He also says that an array of VIVACE machines that have the size of a running track and two stories high, could be enough to power 100,000 houses. The whole installation doesn’t have to be at the surface, it can also be placed under the water.
The electricity created with VIVACE is also cheap: 5.5 cents/kWh, compared to wind, costing 6.9 cents/kWh, and with nuclear power, costing 4.6 cents/kWh. Of all the alternative energy technologies, solar is the most expensive: 16 to 48 cents/kWh.
“There won’t be one solution for the world’s energy needs,” Bernitsas said. “But if we could harness 0.1 percent of the energy in the ocean, we could support the energy needs of 15 billion people.”
Researchers are studying the possibility to deploy a VIVACE machine for testing on the Detroit River, starting 18 months from now.
Bernitsas is right, there isn’t just one variant that we’re going to apply to our energy consuming lives, but all the interesting ideas have to be invested in, and be brought to scales that could help a significant number of people.
Here’s a video of VIVACE in action: