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Air Force Academy Harnesses Ocean Wave Energy
Air Force Academy, CO (SPX) Sep 19, 2011
Washington DC (SPX) Sep 19, 2011

A technician at the Offshore Technology Research Center positions his boat to remove the brackets which secured the wave energy converter's blades after the 5-ton crane lifted it into position over the test pool, while other members of the Academy's wave energy team and testing center staff make preparations to lower the converter into the testing pool. (U.S. Air Force Photo/John Van Winkle).

Air Force Academy aeronautics researchers have finished the largest test of their Ocean Wave Energy Converter to date at the Offshore Technology Research Center in College Station, Texas.

The two weeks of testing proved the fundamental mechanics of the Academy's ocean wave energy converter on the largest scale to date.The Ocean Wave Energy Converter is the brainchild of Dr. Stefan Siegel, a researcher at the Academy's Aeronautics Department.

The project started in 2008 with a National Science Foundation grant to create the world's first free-floating, fully submerged wave energy converter that generates electrical power from deep ocean waves. Siegel and other Aeronautics researchers - Drs. Juergen Seidel and Casey Fagley and retired Col. Rob Fredell - accomplished this and tested it at a 1:300 developmental scale."

We are now at the 1:10 scale, which is the scale that off-shore industry consider when they test their devices, and really the last step before building a full-size ocean-going device," Siegel said. "The main goal is really to demonstrate how much power we can extract with wave energy and convert it to shaft power."

A research grant from the U.S. Department of Energy is designed to increase the converter's technology readiness level, or TRL, from Level 3 to Level 4. TRL is a one-to-nine scale measuring an invention's readiness to enter the market: Level 1 signifies a technology for which basic principles have been observed and reported, while Level 9 designates a mission-ready product that is ready for full-size, large-scale use. Level 4 signifies that a component of a system has been validated in a field environment.

To get the funding to further develop this technology, Siegel and the other researchers incorporated, forming the Atargis Energy Corporation. With the company and funding, the Atargis team got to business in the same manner as many other startups. They built parts of the current wave energy converter in Siegel's garage and tested components in a neighbor's swimming pool.

With the change to a larger scale, difficulties increased exponentially. One person could lift the 1:300 scale wave energy converter without any assistance, but the 1:10 scale model required 10 men to assemble and a 5-ton crane to transport.

"This is expected. Inherent in any new technology, not everything scales up linearly," Siegel said. "Suddenly the effort and design goes up drastically when you build something at a much larger scale. At the 1:10 scale, you are at the level where you need to carefully analyze every single part that's in there: you need to design it for strength, you need make sure we don't have too much twist or flex in your blades when they are in the water.

At this level already, we're seeing some of the full-scale design requirements hit us."Peripheral design issues slowed the testing and put the team's problem-solving skills to the test.

During the generator's first submerged test, the team discovered bubbles coming from one of the gear boxes. After removing the entire assembly from the water, Seidel discovered the gear box was half full of water when he opened it. The team applied additional silicon sealing to eliminate the leak.After the converter went back underwater, the team discovered additional leaks in the pylons, impacting the actuators that control the blades' pitch.

This forced a bit of on-the-fly reengineering: the Academy team huddled, examined the problem, goals and resources and came up with a solution in a matter of minutes. Rolling up their sleeves, they removed some of the electronics from the parts that would be below water level as a short-term fix, with the help of the research center staff.

Leak proofing had been tested on many parts in the design and construction phases prior to this testing, with attention given to balance buoyancy and weight. But in the long-term, the team admits that more attention will be applied to waterproofing turbine and electronics areas.

"This is by no means a deal-breaker. This is the part of testing that you don't normally hear about, but is quite normal in commissioning a new model in a facility like this," said Siegel.

"However, beyond the technical difficulties, we were able to run tests that confirm the wave generation capabilities of our wave energy converter, which is a crucial step in being able to cancel waves. We gathered detailed force and moment data for these runs, which will aid us in controlling a cluster of wave energy converters.

The data also lines up well with our previous results from the small scale tests and simulations, and make these 1:10 tests an important milestone in the development of this technology."

After the fixes, the converter went back underwater for more testing. The team went deeper than originally planned and, with some realignments, found success. They removed unwanted harmonics and prove the fundamental theory correct on the largest scale to date.

Siegel's team is not the first to try to conquer the engineering difficulties of harnessing energy from ocean waves. To date, survivability and efficiency have prevented other approaches to wave energy technology from being successful.

"Nothing has survived in the open ocean for more than six months at a time, and other design concepts out there right now are not efficient," he said.

The team has addressed the converter's survivability through several adaptations, the most important of which comes from designing the converter to be part of a free-floating submerged platform.

This places the converter away from the surface hazards created by major storms on the ocean's surface, which have killed other organizations' attempts to demonstrate competing wave energy technologies.

Efficiency boils down to how much electricity can be harnessed by each platform and how that translates to the price the consumer has to pay in their electric bill. Through feedback flow control, Siegel's converter constantly adjusts the two blades to their optimal angles, maximizing the amount of energy possible to turn the blades and generate electricity.

In previous tests at the Air Force Academy, the research team harnessed 99 percent of the power of a simulated ocean wave with the ocean wave converter and transfer that wave's force into electrical energy, effectively canceling out the wave in the process. Essentially, there's a wave going in, but no wave going out.

This is a significant step forward from the nearest comparable power source, wind turbines. Current wind turbine technology can only harness 59 percent of the power potential within its area of effect.

The center has one of the world's largest wave tank facilities, which will allow the test of a larger wave energy converter and eventually permit testing of three wave energy converters simultaneously.

After the tests, members of Atargis went to England for a wave energy conference. After the conference, the team returned to Colorado to analyze the data they obtained, determine the long-term fixes for the waterproofing issues and prepare for the next test. The Atargis team is scheduled to return to the Offshore Technology Research Center in early 2012 to test the use of multiple wave energy converters working at once.

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