STRUCTURAL CONTROL OF EDGEWISE VIBRATIONS IN LARGE WIND TURBINE BLADES

Wind is now a major source of renewable energy, and will be a key solution for pressing issues such as global warming and the increasing global need for energy. The current trend in wind turbine technology is towards larger rotors with longer blades in order to capture more energy. A consequence of turbine upscaling, however, is increased flexibility and more susceptibility to external loads, especially in the blades. These slender elements experience two primary modes of vibration, flapwise and edgewise. Though the flapwise mode is highly damped, the edgewise mode has negligible damping and may lead to aeroelastic stability problems, increased structural fatigue and decreased reliability. Therefore, strategies and technologies for load shedding and mitigation of undesirable structural vibration in wind turbine blades are critical. Many researchers have investigated solutions to overcome this challenge by implementing various control methodologies, with structural control methods being one such approach. This thesis investigates the application of passive structural controllers, namely tuned mass-spring-dampers (TMDs), to reduce blade loads. While TMDs have been extensively studied for other purposes, research remains relatively limited on their application to wind turbines, particularly for the improvement of blade performance in the edgewise direction. The TMD design for blade installation is based on well-established structural control techniques. The performance and tradeoffs of the proposed design are investigated by calculating lifetime fatigue damage, percentiles and maxima. Optimistic results are obtained when TMDs are mounted in the blades of a modern wind turbine, reducing edgewise loads and displacements primarily at high wind speeds.