Semi-active pendulum to control offshore wind turbine vibrations

Abstract

Wind energy presents itself, nowadays, as one of energy sources in fast development and implementation all over the world. The project, building and maintenance of the so called wind farm still present lots of challenges for engineers and researches. In this context, offshore wind turbine are found: wind turbines installed on ocean next to coast which, between other advantages, gets benefit of more intense and consistent wind with less turbulence in these regions. One of conceptions from this kind of wind turbine is the floating. This kind of structural system can be analyzed like a discrete model of inverted pendulum. This type structure can be vulnerable to excessive vibration caused by wind loads. One of the most used vibration control systems is the Tuned Mass Damper (TMD). It basically consist of a mass-spring-damper system attached to the main structure, the frequency of the damper is tuned to a particular frequency, with the goal of making the TMD vibrate out of phase with the main system, thus transferring the energy system to the damper. However, passive devices only work properly for the design frequency range, and wind forces are random type of excitations. In this sense, a better approach would be design a semi-active device. Semi-active control joins confidence and simplicity typical of passive systems with active control adaptability. It is characterized by not adding mechanical energy due to the structure and to have properties that can change dynamically. These devices can be viewed as controllable passive devices because despite of its changing properties of damping and/or stiffness it action on the structure is passive. This work aims to achieve better results in vibration control of offshore wind turbines proposing a semi-active controller to it, considering an inverted pendulum discrete model.