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oai:www.repository.cam.ac.uk:1810/3895772025-09-24T01:42:25Zcom_1810_213729com_1810_256065col_1810_219485

The Seismic Response of Offshore Wind Turbines Supported by Monopiles and Alternative Foundations in Liquefiable Soils https://doi.org/10.17863/CAM.121409 Español-Espinel, Carlos 0000000215823742 Madabhushi, SP Gopal Haigh, Stuart The Asia-Pacific (APAC) economies generate over half of the offshore wind power in the world, yet a significant portion of their offshore wind farms is likely to face catastrophic earthquakerelated phenomena during their operational life. Among these, liquefaction of saturated sands forming the seabed is possibly the most probable and detrimental to offshore wind turbines (OWTs). Monopiles have emerged as the preferred foundation type for offshore wind turbines in most APAC countries. These foundations were initially designed based on the experience acquired from Europe, in regions that are not seismically active. However, earthquake-induced liquefaction introduces challenges that these foundations were not originally intended to address. In view of this, the present thesis has been developed in two phases. The initial phase has focused on the study of the seismic response of monopiles in liquefiable soils using both, centrifuge, and numerical modelling. The experimental setup designed for centrifuge testing aimed to reproduce a monopile supported OWT subjected to the combined action of earthquake induced liquefaction, dynamic loading, and operational loading from wind and waves. In particular, this part of the thesis explores the development of excess pore pressure around monopiles during earthquakes. In fact, significant differences have been observed between the excess pore pressure accumulated in the far field and that in the soil adjacent to and inside the monopile. Such variations are associated with the amount of stress transferred from the static and dynamic moments acting on the monopile to the surrounding soil. These stresses impact the effective stress in the soil surrounding the monopile, and consequently, its overall behaviour, including settlement and rotation. In general, the observed earthquake induced rotation experienced by the monopiles tested in this thesis, largely exceeds the Serviceability Limit State (SLS) design requirements of a maximum turbine tilt of 0.5° (DNV-ST-0126, 2021; DNV-RP-0585, 2021). However, the amount of average settlement and rotation experienced by monopiles may be affected by several factors. Among these, the monopile diameter, the magnitude of the operational loading, and the density of the sand layers in which the monopile is installed have been studied. Excessive rotation may result in increased fatigue loading on the turbine blades, leading to decreased performance and operational lifespan of the OWT. University of Cambridge 2025-01-29 Thesis Doctoral Doctor of Philosophy (PhD) eng EPSRC iCASE 20000012 https://www.repository.cam.ac.uk/handle/1810/389577 https://www.repository.cam.ac.uk/bitstreams/a8cac85e-3723-47ad-86ab-2d0078f04075/download 7db2763cebfd44d387074c038c99267d https://www.repository.cam.ac.uk/bitstreams/7fc01b6d-26b9-431f-89e1-cfe5c0a1c4e2/download 87eda9de84448d1f82354d60eee3eb5f http://purl.org/NET/rdflicense/allrightsreserved Offshore Wind Earthquake Engineering Dynamic Centrifuge Modelling Earthquake-induced Liquefaction Finite Element Modelling