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Construction Corner: Schools of fish provide valuable energy lessons

0 43 Technology

by Korky Koroluk

Water and energy go hand in hand. We use energy — often hydro power — to treat our water and wastewater. Our treated wastewater is discharged into our rivers where it ends up impounded behind another hydro dam that generates power to treat another city's water.
Construction Corner: Schools of fish provide valuable energy lessons

We use water in the process that separates heavy bitumen from oilsands in northern Alberta. People interested in renewable energy know we use water to wash our solar panels to keep them at peak efficiency.

Of all the renewable energy sources in the world, hydroelectricity holds by far the largest share. It's proven technology and it's abundant — in Canada at least. But dams silt up over time, reducing the amount of water they can hold. Their construction has displaced millions of people worldwide, forced to move as the rising water behind the dam floods their land and their towns.

Run-of-river installations give us hydro power on a smaller scale than dams do. It usually involves modest impoundments to produce the fast flow needed to spin turbines. But it may be possible to generate electricity from slow-moving rivers (or ocean currents).

A small start-up — Vortex Hydro Energy — has been testing a device called VIVACE, which harnesses a phenomenon called flow-induced motion. VIVACE weighs 12 tonnes and spent its summer submerged in eight metres of water in the slow-moving Saint Clair River on the Canada-U.S. border just north of Detroit.

The device is made up of four dimpled steel cylinders mounted on rails welded into a frame that's five metres wide and 3.6 metres tall.

The cylinders slide silently from side to side, pushed by the river's slow current. On a typical day each cylinder can generate one kilowatt — enough electricity to power one home.

VIVACE generates power by harnessing vortex-induced vibrations. These are lateral movements that happen when tiny vortices — think miniature whirlpools — form in a current of water (or air) as it flows past a stationary object. The dimples help the currents push the cylinders back and forth. The vortices exert alternating sideways force on the cylinders, pushing them from side to side.

A second phenomenon is also being exploited. Called "galloping," it occurs when turbulence from one cylinder affects the movement of those behind it, moving them back and forth more quickly and increasing the amount of power generated.

Engineers have long considered these vortices to be dangerous. They've shredded power lines, toppled industrial chimneys and demolished off-shore drilling platforms. They even caused the spectacular destruction of "Galloping Gertie," the Tacoma Narrows Bridge, back in 1940.

But the VIVACE team has turned engineering wisdom on its head. They see flow-induced motion as a way to harness slow-moving water currents and revolutionize hydroelectric power generation. They believe that their device could one day make it possible to generate power from river and ocean currents, most of which flow at speeds far below those needed by a hydro turbine.

Conventional wisdom suggested that to generate power efficiently, VIVACE's cylinders would have to be spaced far apart so the vortices from one wouldn't interfere with the vortices from others. But it didn't work out that way. Ultimately, the team took their lesson from fish.

When moving in schools, fish undulate their bodies to squeeze between the alternating vortices created by others in the school. That pushes them forward efficiently.

The VIVACE team used the same idea and placed the cylinders closer together to take advantage of turbulence rather than fighting it.

VIVACE is still not ready to bring to the market. The prototype spent nearly three months in the Saint Clair River, coming out earlier this month. The researchers are now analyzing their results. More testing will follow.

"We have a good device," says Michael Bernitsas, a marine engineer at the University of Michigan and the founder of Vortex Hydro Energy. "But taking principles from schools of fish and turning them into mechanical devices takes time."

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@journalofcommerce.com.

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