James F. Manwell, director of the Wind Energy Center and professor of mechanical and industrial engineering at the University of Massachusetts Amherst, was the primary author of a section of a wind-energy paper just published inthe journal Science. The article also generated the theme – the Grand Vision for Wind Energy – of the NAWEA/WindTech 2019 conference taking place at UMass Amherst Oct. 14-16.
The Science article is part of the rollout for the conference. Manwell was the primary author of the offshore portions of the section “Second grand challenge: aerodynamics, structural dynamics, and offshore wind hydrodynamics of enlarged wind turbines.”
As Manwell and his co-authors explain, an operating wind turbine might appear to be very still except for the rotation of the blades, yet the entire system is constantly in motion because of forces and movements exerted in all directions.
The researchers say numerical wind turbine simulation capabilities that incorporate up-to-date knowledge of wind turbine physics, including coupling aerodynamics, structural dynamics, controls engineering, and even hydrodynamics for offshore applications, have empowered the wind industry to design machines that produce efficient power for many years.
One result, they say, is that wind turbines have grown to become the largest dynamic machines in the world. They are massive structures that must operate continuously for 20 years or more under constant complex loading. Blades approach 80 meters long, and towers are expanding well above 100 meters for maximum tip heights often going beyond 200 meters, equivalent to a building more than 60 stories high.
To put these dimensions in context, they say, three of the largest passenger aircraft on the planet can easily fit within the swept area of one wind turbine rotor.
However, the researchers say, the industry is seeking even larger turbines that access higher wind speeds aloft and provide economies of scale, thus reducing manufacturing, installation and operating costs.
As turbines continue to mushroom in size, there are research questions around offshore wind turbine dynamics involving their interaction with the atmosphere, wakes and other sources of complex forces upon the rotors. These questions, as the authors note, include the aeroelastic behavior of very large and flexible machines and additional dynamics associated with deployment offshore in extreme weather conditions.
The authors say that offshore installations require the combined modeling of aerodynamics with the hydrodynamic forces from waves and currents. Particularly relevant for these offshore applications are extreme weather conditions such as hurricanes or tropical cyclones. The authors explain that the uncertainty of offshore turbines is amplified if the entire rotor is rocking into and out of its own wake, as could happen on a floating substructure.
The authors say new materials and manufacturing methods are a major part of supporting the development of offshore wind turbines. Understanding the dynamics will help establish the design requirements, but materials and manufacturing breakthroughs must be developed to produce low-cost and reliable machine designs. There is still a critical need to improve materials performance for particularly difficult environmental conditions and operational loads, according to the researchers.
According to the authors, another challenge related to materials science and engineering for wind energy is the need for turbines to be mass produced inexpensively and be able to be recycled readily.
This paper was based on a larger report released in April.