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Posts Tagged ‘National Science Foundation’

Scientific Computing, Advantage Business Media, November 2009

The ocean is a potentially vast source of electric power, yet as engineers test new technologies for capturing it, the devices are plagued by battering storms, limited efficiency and the need to be tethered to the seafloor. Now, a team of aerospace engineers is applying the principles that keep airplanes aloft to create a new wave energy system that is durable, extremely efficient and can be placed anywhere in the ocean, regardless of depth.

While still in early design stages, computer and scale model tests of the system suggest higher efficiencies than wind turbines. The system is designed to effectively cancel incoming waves, capturing their energy while flattening them out, providing an added application as a storm wave breaker.

The researchers, from the U.S. Air Force Academy, presented their design at the 62nd annual meeting of the American Physical Society’s Division of Fluid Dynamics on November 24, 2009.

“Our group was working on very basic research on feedback flow control for years,” says lead researcher Stefan Siegel, referring to efforts to use sensors and adjustable parts to control how fluids flow around airfoils like wings. “For an airplane, when you control that flow, you better control flight — for example, enabling you to land a plane on a shorter runway.”

A colleague had read an article on wave energy in a magazine and mentioned it to Siegel and the other team members, and they realized they could operate a wave energy device using the same feedback control concepts they had been developing.

Supported by a grant from the National Science Foundation, the researchers developed a system that uses lift instead of drag to cause the propeller blades to move.

“Every airplane flies with lift, not with drag,” says Siegel. “Compare an old style windmill with a modern one. The new style uses lift and is what made wind energy viable — and it doesn’t get shredded in a storm like an old windmill. Fluid dynamics fixed the issue for windmills, and can do the same for wave energy.”

Windmills have active controls that turn the blades to compensate for storm winds, eliminating lift when it is a risk, and preventing damage. The Air Force Academy researchers used the same approach with a hydrofoil (equivalent to an airfoil, but for water) and built it into a cycloidal propeller, a design that emerged in the 1930s and currently propels tugboats, ferries and other highly maneuverable ships.

The researchers changed the propeller orientation from horizontal to vertical, allowing direct interaction with the cyclic, up and down motion of wave energy. The researchers also developed individual control systems for each propeller blade, allowing sophisticated manipulations that maximize (or minimize, in the case of storms) interaction with wave energy.

Ultimately, the goal is to keep the flow direction and blade direction constant, cancelling the incoming wave and using standard gear-driven or direct-drive generators to convert the wave energy into electric energy. A propeller that is exactly out of phase with a wave will cancel that wave and maximize energy output. The cancellation also will allow the float-mounted devices to function without the need of mooring, important for deep sea locations that hold tremendous wave energy potential and are currently out of reach for many existing wave energy designs.

While the final device may be as large as 40 meters across, laboratory models are currently less than a meter in diameter. A larger version of the system will be tested next year at NSF’s Network for Earthquake Engineering Simulation (NEES) tsunami wave basin at Oregon State University, an important experiment for proving the efficacy of the design.

Compelling images of the cycloidal turbine:

The view from the far downstream end into the test section of the U.S. Air Force Academy water tunnel. Three blades of the cycloidal turbine are visible at the far end. Engineer Stefan Siegel and his colleagues test the turbine using the tunnel, with both steady and oscillating flow conditions simulating a shallow-water wave-flow field. Courtesy of SSgt Danny Washburn, U.S. Air Force Academy, Department of Aeronautics

 

A cycloidal turbine is installed on top of the test section of the U.S. Air Force Academy water tunnel. In the background, Manfred Meid (left) and Stefan Siegel (right) operate the turbine. Courtesy of SSgt Danny Washburn, US Air Force Academy, Department of Aeronautics

 

 

 

A cycloidal turbine prototype with three blades (translucent, at bottom of image), is shown lifted out of the tunnel. One of the blade pitch control servo amplifiers is visible in the foreground, and the servo motors can be seen in the top portion of the image. Courtesy of SSgt Danny Washburn, US Air Force Academy, Department of Aeronautics

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MendoCoastCurrent, November 29, 2008

Ann Arbor, Michigan — Slow-moving ocean and river currents could be a new, 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 clean, renewable power.

The machine is called VIVACE. A paper on it is published in the current issue of the quarterly Journal of Offshore Mechanics and Arctic Engineering.

VIVACE is a device that may 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.

VIVACE stands for Vortex Induced Vibrations for Aquatic Clean Energy. It 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.

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.”

This generation of Bernitsas’ machine looks nothing like a fish, though he says future versions will have the equivalent of a tail and surface roughness a kin to scales. 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.

Here’s how VIVACE works: The very 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.

Just a few cylinders might be enough to power an anchored ship, or a lighthouse, Bernitsas says. These cylinders could be stacked in a short ladder. The professor estimates 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.

Because the oscillations of VIVACE would be slow, it is theorized that the system would not harm marine life like dams and water turbines can.

Bernitsas says VIVACE energy would cost about 5.5 cents per kilowatt hour. Wind energy costs 6.9 cents a kilowatt hour. Nuclear costs 4.6, and solar power costs between 16 and 48 cents per kilowatt hour depending on the location.

“There won’t be one solution for the world’s energy needs,” Bernitsas said. “But if we could harness 0.1% of the energy in the ocean, we could support the energy needs of 15 billion people.”

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 there within the 18 months.

This work has been supported by the U.S. Department of Energy, the Office of Naval Research, the National Science Foundation, the Detroit/Wayne County Port Autrhority, the DTE Energy Foundation, Michigan Universities Commercialization Initiative, and the Link Foundation. The technology is being commercialized through Bernitsas’ company, Vortex Hydro Energy.

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