Melville, Bruce WShamseldin, Asaad YGuan, DaweiYao, Zishun2025-03-262025-03-262025https://hdl.handle.net/2292/71718Offshore wind turbines usually experience large numbers of lateral cyclic vibrations induced by winds and waves in their service life. The local scour process and vibrations will likely occur simultaneously in the field, threatening the stability of the monopile foundation of Offshore Wind Turbines (OWTs). However, traditional studies mainly focus on local scour around static monopile foundations. The local scour mechanism around monopile foundations subjected to cyclic lateral vibration remains unclear. To address this research gap, the study reported herein was undertaken. The study is an experimental investigation of motions of sand particles around vibrating monopile foundations and subsequent examination of the local scour mechanism under different hydrodynamic conditions. Firstly, a sandbox experimental system was developed to analyse the characteristics of sand motion under cyclic lateral vibration, considering factors such as backfilling sand and saturated conditions. Subsequent experiments focused on the local scour process under current-only and combined wave-current conditions. In current-only conditions, the local scour development characteristics and equilibrium scour depth in different flow intensities are analysed. Additionally, the influence of vibration direction on the local scour is investigated. Lastly, the local scour mechanism around monopile foundations subjected to cyclic lateral vibration under combined wave-current conditions is investigated. The coupling effects of vibration, waves, and currents on local scour process and equilibrium scour depth around the foundation are studied. To quantify the hydrodynamic intensity induced by waves and currents, considering the influence of sediment grain size, a new dimensionless parameter named the undisturbed friction velocity-based Froude number (Fr*) is proposed. Furthermore, equations for predicting equilibrium scour depth around vibrating monopile foundations under current-only and combined wave-current conditions are proposed. In summary, this thesis represents a pioneering effort to systematically investigate the interaction between piles and soil, as well as the local scour mechanism around monopile foundations subjected to cyclic lateral vibration under complex environmental conditions. The findings significantly enhance our understanding of the local scour issues surrounding monopile foundations for OWTs and hold promise for improving foundation design and enhancing scour protection measures in offshore engineering practices.Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htmThesisCopyright: The authorAttribution-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nd/4.0/