Sanjay R. Arwade, a professor in the Civil and Environmental Engineering Department and Associate Director of the Wind Energy Center at UMass Amherst, was quoted as an expert on the construction of support structures for offshore wind turbines in an article in a fall edition of Eos, the online magazine of the American Geophysical Union.
The Eos article was titled “Ocean Terrain and the Engineering Challenges for Offshore Wind Farms” and was written by science writer Katherine Kornei. The theme of the article was that deep coastal seabeds, glacial erratics, and other geophysical hurdles stand in the way of offshore wind-farm proliferation; therefore, researchers, engineers, and organizations are adapting and inventing ways to harness the breeze.
Kornei asked Arwade to comment on some of the issues surrounding foundational support structures that depend on the terrain of the seafloor. As Arwade noted, in addition to keeping an eye out for boulders, developers must also survey the properties of the seafloor itself, such as its slope and composition.
Arwade explained that most offshore wind turbines are rigidly connected to the seafloor via a foundation, the design of which is determined by local conditions. Common designs include: a so-called monopile, which is a single, long, hollow, steel tube sunk into the seafloor; a jacket foundation, meaning a three- or four-legged structure affixed to the seafloor; and a gravity base that involves a large mass, typically a block of concrete, resting on the seafloor.
Careful surveying is therefore necessary to evaluate a potential site, said Arwade. “A site investigation [to discover what the geology and geotechnical properties are] allows the design engineers to do their job.”
Arwade observed that the marine environment also brings with it many other fundamental challenges. Installing and maintaining wind turbines at sea require ships, specialized equipment, and professional divers. Also, he added, waves impart stress on turbine foundations, and storms—such as nor’easters and hurricanes—can produce powerful waves that batter structures.
According to Arwade, at some point the economic benefit of building a fixed-bottom wind farm off the coast plummets: “As the water depth gets beyond 50 meters or so, building a fixed-bottom support structure becomes borderline uneconomical or completely uneconomical.”
One focus of Arwade’s research concerns effects in the structural systems related to wind-turbine analysis and reliability.
According to Arwade, “Wind-turbine research has concentrated largely on the energy producing turbine itself, yet construction of the support structure can contribute up to 25 percent of the total life-cycle cost of an offshore turbine. I am working with collaborators on new methods for multi-physics, probabilistic simulation of offshore wind-turbine support structures to allow designers to use quantitative risk-based approaches to design of such structures.”