FROM THE NEST | FALL 2024 | 31 PARETO/GETTY IMAGES As renewable energy becomes more popular, wind has been a common source of power. While many wind turbines harvest energy on land, the potential for the United States to harvest even more energy from wind lies offshore. Because wind speeds are the highest off both the East and West Coasts, offshore wind turbines can produce higher energy yields compared to what is collected in the North Sea near northern Europe. Yet, turbines in shallow waters, such as those in the North Sea, present fewer obstacles. They can be mounted on fixed-bottom platforms, held to the sea floor by a rigid structure such as a monopile or foundation. The offshore turbines now operating in the U.S., located in the relatively shallow waters over the continental shelf near New England, are fixed-bottom turbines. However, two-thirds of the U.S.’s offshore wind resources are in water deeper than about 60 meters. Engineers have adopted floating offshore platforms to create floating structures that harvest both wind energy and energy from wave action. These platforms originated with oil and gas drilling and are held in place by lines anchored to the ocean floor. Unlike oil and gas platforms, however, ones for wind turbines must be adjusted for a taller, unbalanced load. Muhannad Suleiman, professor of civil and environmental engineering and deputy director of the Advanced Technology for Large Structural Systems (ATLSS) Center, and his co-investigators are working to solve the problems this configuration presents. NSF Award Suleiman; James Ricles, Bruce G. Johnston Professor of Structural Engineering and director of the ATLSS Center; Richard Sause, professor of structural engineering; and Keith Moored, associate professor of mechanical engineering and mechanics, received a $1 million award from the National Science Foundation for a three-year project to study the mechanical interactions and control of floating turbines. Winds that load the turbines can be quite strong and push the turbine blades and the platform. Waves add to the force against the platform and pull on the mooring lines. Extreme weather, such as a hurricane or major storm, can exacerbate these forces. Suleiman’s team is trying to combine wind and wave energy generation to make these floating offshore platforms more efficient and resilient. Next Steps There are four steps to achieve this goal. The first, led by Moored and Sause, is reducing the platform’s motions to improve the structure’s resilience. Second, Sause will lead evaluations of how reducing platform motion can change mooring line fatigue responses. He will study innovations such as ballast placement and damper systems. Third, Suleiman and Moored will lead an investigation of animal-inspired solutions such as oscillating hydrofoils inspired by marine life. Rough-surfaced anchors, inspired by snakeskin, will also be analyzed for their ability to increase friction between the foundation and surrounding soil. Fourth, Ricles will lead real-time hybrid simulations based on data from the other three steps. This will allow the team to observe how the forces on the turbine, platform and mooring lines might act under extreme circumstances. Suleiman said this is important because most of the time, these subsystems are treated separately. For example, a structural engineer will look at the loads on the tower and a mechanical engineer will study the aero and hydrodynamic loads, but there are few ways to study the entire system as a single operating unit. Bringing all the parts together not only mimics the real interactions of these subsystems, but also allows for a greater understanding and the maximization of their operation and energy output.—Christine Bucher From left, National Science Foundation award recipients Muhannad Suleiman, James Ricles, Richard Sause and Keith Moored. RESEARCH $1 Million Awarded to Offshore Wind Turbine Research The National Science Foundation (NSF) award is for a three-year study of the mechanical interactions and control of floating turbines.
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