A Study on Vibration Isolation in a Wind Turbine Subjected to Wind and Seismic Loading

Abstract

The primary loading on wind turbines is in the lateral direction and is of a stochastic nature, due to wind and seismic forces. As turbines grow larger, they experience proportionally larger lateral forces. Large forces require larger section sizes and overall weight of the turbine. The objective of this study is to investigate the use of vibration isolation as a structural control measure to minimize the overall wind and seismic forces transmitted to the turbine. Passive control systems such as tuned mass dampers have previously been proposed to mitigate response to wind loading but have not generally been evaluated under seismic loading. This thesis discusses the potential use of a non-linear vibration isolator just below the wind turbine nacelle to decrease the structural response of the turbine under wind and seismic loading. The structural idealization of the wind turbine structure and the applied loading are presented. The force-displacement properties of the vibration isolator are discussed and the equations of motion are modified to include the isolator. A finite element model is created which includes wind and seismic loading and incorporates a vibration isolator. Simulations are performed to determine a number of key structural response variables without the vibration isolator, and with a vibration isolator having varied force-displacement properties. The changes in those key response variables are presented and discussed. It is concluded that vibration isolation is a viable method for reducing structural response of wind turbines. Some practical concerns and areas of future research are discussed.