Mechanical engineer Matthew Lackner is working on the cutting edge of floating wind turbines, a technology that, according to MIT’s prestigious Technology Review, “could hold the key to exploiting” the powerful offshore winds blowing steadily off the Northeastern coast. In order to turn that “key,” Lackner has been working on clever, innovative devices such as “smart rotors” and “tuned vibration absorbers,” which reduce the severe stress placed on working parts of floating turbines and could go a long way toward making them economically feasible.
If properly engineered, such floating turbines, which can be anchored out of sight and out of mind far out to sea, could well prove the only viable alternative for wind energy in New England. “I believe the barriers to using floating turbines can be toppled by innovative engineering solutions,” observes Lackner, “and that’s what I’m trying to do.”
Floating wind turbines have many advantages over either fixed offshore turbines or onshore turbines. Not only can floating rigs harness the stronger, steadier winds that blow farther offshore, but they solve the major problem of public acceptance confronting fixed wind turbines in shallower water nearer to shore. One star-crossed project of the Cape Wind company, trying to build America’s first offshore wind farm between Cape Cod and Nantucket Island, has been stymied by negative public opinion for years.
Floating rigs could also cut costs by being assembled onshore before being towed out to sea, and then towed back to shore for maintenance. Since there is so little room in the Northeast for onshore wind farms, floating turbines could literally power the wave of the future as our only alternative. As an April 2, 2008, article in Technology Review summed up the advantages, “Advances in floating platforms could take wind farms far from coasts, reducing costs and skirting controversy.”
In the forefront of those “advances in floating platforms” is Dr. Lackner’s research for the Mechanical and Industrial Engineering Department and the UMass Wind Energy Center. He explains that “There are two main areas I’ve been focused on. One is the aerodynamics behavior of floating turbines. Basically they’re bobbing around in the water and the wind field, and this motion of the rotor makes the aerodynamics of these turbines much more complicated than a fixed rotor. The other side of that research is coming up with ways to reduce loads, or forces acting on the turbines that can damage them.”
The main barrier to overcome with floating turbines is the high cost of initial capital investment and of maintenance over time. “Just keep in mind that you pay much of the costs up front for offshore wind, but there are no fuel costs,” observes Lackner. “So the trick is to engineer your offshore turbines to bring down the cost of building and maintaining them.”
In floating turbines, significant stresses, called “fatigue loads,” are exerted on the blades and support structure by waves, wind, and ice and then passed on to the shaft, gear box, generator, and other working parts. If engineers can use innovative techniques to reduce those stresses and the vibrations they cause, they can also extend the life of the components.
“I’m looking at several ways to do that,” says Lackner. “One is smart rotor control. You help control the blades by adding aerodynamic control devices called trailing edge flaps, similar to flaps on airplanes. If a gust comes along and causes your blades to vibrate, flaps are deployed to damp down that vibration. So your components are less likely to break.”
Another technology that Lackner’s been working on responds to floating turbines bobbing in waves and wind. “I’ve been inspired by some civil engineering techniques to reduce loading from winds or earthquakes on structures such as skyscrapers and bridges,” he explains. “The term that is used is ‘structural control.’ In skyscrapers they use these spectacularly large structures that act like huge pendulums.”
One version of structural control that Lackner is studying for floating turbines is a horseshoe-shaped tube of water called a “sloshing water damper,” which, in effect, serves the purpose of an energy absorbing mass-spring-damper. Lackner explains that “The oscillation of the water sloshing back and forth in this tube stabilizes the motion of your turbine. They use this kind of device in ships to stabilize motion.”
Lackner adds that “We’ve been working with software that simulates the aerodynamics and structural dynamics of wind turbines. I added some features to simulate structural control devices. So I’ve been doing a lot of work looking into how much you can reduce loading, how to optimize the design to get the maximum benefit from these structural devices, and how to improve the overall performance.”
Lackner’s innovations couldn’t be more timely. Technology Review, which predicted that floating turbines will hold the key to harnessing wind energy in the Northeast, also predicted that the economics of the power industry are already “approaching a tipping point” that will drive rapid adoption of floating turbines.
“The technology is essentially proven," the article quoted Paul Sclavounos, a mechanical engineer and a specialist in naval architecture at MIT. "We know we can design [platforms] and spars that are not going to move in big storms. What is going to lead to this industry taking off will be the economics. We're not far from it." (February 2011)