Dynamic behavior of monopile supported offshore wind turbine system

Abstract

Monopiles are designed such that the natural frequency of offshore wind turbine structure shall be kept away from rotor excitation frequency to avoid resonance. Tower-monopile system responses, such as rotation is essential design parameter to ensure safety. The output of the turbine can be enhanced with larger rotors and installed at higher water depth. However, dynamic characteristics of tower-foundation system alters significantly due to change in water depth, hub height, overall mass, wind and wave load characteristics. This paper critically assesses the dynamic characteristics of tower-monopile system considering feasible variation of rotor speed, tower height and wind speed. It is observed that soft-stiff is a suitable design approach. Decrease in Rotor Nacelle Assembly (RNA) mass is found to be most effective in design than that of the reduction in tower height. The effect of thickness of tower and monopile is insignificant in design of OWT structure. � 2015 Taylor & Francis Group, London.