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 Turbines to harness tidal energy

Geoffrey CowlesTidal energy turbines harness the power of the tides in much the same way that wind turbines harness the power of the wind. Still a relatively new "green" energy source, tidal energy holds great promise.

But it's not yet clear what the most efficient turbine design would be for real ocean conditions—or what impact the turbines would have on the marine environment.

The National Science Foundation has awarded $300,000 to Prof. Geoffrey Cowles of SMAST and co-investigator Prof. Luigi Martinelli of Princeton University, in cooperation with Ocean Renewable Power Company, to assess both the performance of tidal energy turbines and their interactions with the immediate marine environment.

The promise of tidal energy

"The most recent estimate of the harvestable tidal resource in the United States is 65,000 GWh or the equivalent of approximately 10 large power plants," said Cowles.

"While tidal energy is likely to play a small role in the overall U.S. renewable energy portfolio, it has the potential to be important in places where it is concentrated, which include the northeast and northwest U.S. coasts and Alaska."

Improving turbine design, analyzing environmental impact

Compared with other renewable energy sources, tidal power offers a key advantage: it's highly predictable and experiences only small fluctuations on timescales longer than a day.

To accomplish that, Cowles and Martinelli propose linking two computer models that will "talk" to each other: one to simulate the operation of the turbine itself, and the other to represent the dynamics of the surrounding waters and their interaction with the turbine.

Cowles explained that the turbine design uses realistic flow conditions provided by a larger-scale ocean model. The turbine then supplies information to the oceanographic model about changes in momentum and turbulence associated with the energy extraction.

"These are incorporated in the ocean model to evaluate the impact of the devices on the marine environment," he said.

The researchers will apply a novel technique that can improve efficiency by automatically changing the shape of the simulated turbine.

"We'll be using design techniques that were developed primarily for aerospace applications, and are quite powerful," Cowles said.

"In the initial stages of the design process, engineers can design the turbine's geometry—its shape and properties. But as the changes become more subtle, complex computations must guide the turbine’s design."

This two-way multi-model approach enables us to include environmental impact as part of the overall design process.  

Cowles noted that the computational requirements associated with this level of detailed accuracy can be quite large.

"Our computations will be run at national supercomputing centers as well as on the UMass Dartmouth cluster currently housed in the Carney Library, which was purchased with funds from the National Science Foundation, the Air Force Office of Scientific Research, and UMass Dartmouth."

Opportunity for student research

The project will support a Ph.D. student at UMass Dartmouth as well as one at Princeton University. The students will be conducting the bulk of the research, both the technical and exploratory components.

"The students will gain from having to get their hands dirty in the coding, instead of using commercial software," Cowles said, "They’ll gain general experience in high performance computing and computational modeling, in addition to designing their research programs."

The SMAST students I've been fortunate to work with are quite passionate about their work. The achievement they seek is to make an impact on the field through the contributions of their research.

Transition to a research mindset

The opportunity to work on the development of the FVCOM ocean model, under the guidance of Prof. Changsheng Chen, brought Cowles to UMass Dartmouth.

"My contributions led to the further work on the model development," he said. "I enjoy the challenges of computing ocean flows very much and was very pleased and fortunate to be offered a tenure-track faculty position in the Dept. of Fisheries Oceanography.

"I've had to transition from an engineering background with a faster-better-more efficient mindset to working at the fringe of the natural sciences, where research tends to be guided by a hypothesis-driven approach. My mentors within the fisheries department at SMAST are very focused on developing future scientists, and I’ve learned a lot from them."

Cowles has also been able to work with "other computationally-focused faculty" at UMass Dartmouth's  Center for Scientific Computing and Visualization Research (SCVR), which was formally established last year.

"One of the key tenets of the Center is that computational simulation is an integral part of the path to discovery and knowledge and is widely accepted as the third pillar of science, along with observation and theory," Cowles said. "My own work and discoveries are made 'in silico,' that is, via computer simulation."

Combining two interests: ships and scientific computing

Cowles took a "fairly circuitous route" toward his career as a professor at SMAST.

"I've been interested in ships from a young age. Then a fluid mechanics course my senior year at Cornell turned me on to scientific computing."

His class was asked to "write what would be a very simplistic flow solver by today's standards. But after seeing how a bit of FORTRAN could generate useful and beautiful information, I was hooked."

Cowles pursued a Ph.D. that combined his interests, working on computational techniques to resolve the fluid forces on a ship. He subsequently worked with an America's Cup syndicate performing hydrodynamic simulations in support of their design process.