THE SCOUR EFFECTS ON THE SERVICEABILITY LIMIT STATE OF OFFSHORE WIND TURBINES ON MONOPILE FOUNDATIONS UNDER LATERAL LOADING

Abstract

Offshore wind turbines have been increasingly developed worldwide in recent years to harness wind energy in coastal regions. The monopile is the most widely used foundation for offshore wind turbines, based on the met-ocean conditions for their installation. This research primarily examines how scour affects the serviceability limit state of a monopile, particularly in terms of the lateral response of a monopile foundation under monotonic loading conditions, as well as the natural frequency of an offshore wind turbine (OWT) on a monopile foundation during free vibration analysis. The study aims to investigate the effect of varying scour depths with respect to scour types and lateral loads on the structural behaviour of the monopile foundation by considering a series of finite element simulations. The aim is to determine whether the results indicate a significant influence of scour depth on the lateral response of the monopile foundation, including increased displacement and reduced stiffness associated with different scour depths and types. This research also investigates the scour effects on the natural frequency of the OWT on the serviceability limit state of offshore wind turbines. It considers the natural frequency to assess structural safety under lateral loading by employing free vibration analysis. This analysis focuses on avoiding the turbine striking and resonance for the safety and operational conditions. It also explains the mechanics of scour in terms of the process of scour generation around a monopile in offshore wind structures and its types of global and local scours, respectively. By considering the safety of offshore wind structures, it is important to determine which type of scour can impact the serviceability limit state of the monopile. Referring to the site data assessment conducted in the Gulf of Khambhat in the Gujarat region, as documented in the FOWIND report by the Indian government for the development of offshore wind energy. Whether it's general or local scour, the generated scour is impossible to eradicate using the methods that provide protection techniques. In order to counteract the problem, this investigation will improve the old conventional methods by considering critical failure conditions in different scour depths corresponding to scour types.