Abstract
Offshore Wind Power will be part of net zero solution and they are currently being installed/commissioned and planned in seismic areas. Offshore Wind Turbine (OWT) infrastructures (turbines, sub-stations, and sub-sea cables) in seismic countries are exposed to earthquake-related effects (such as strong shaking, ground slope movement, soil liquefaction, tsunamis) apart from the usual extreme offshore weather (such as hurricanes, typhoons, extreme waves etc.). Design and analysis procedures of offshore wind turbines were initially based on offshore Oil and Gas Industry (i.e., American Petroleum Institute standards) and the inadequacies were realised which led to research and development and standards/guidelines such as DNV (Det Norske Veritas) and Bureau Veritas. This research initially identifies the research gaps in these codes of practices with a focus on the performance criteria for offshore wind turbines in seismic areas. To this effect, the main contribution of this research is to aid design of monopiles in seismic zones through modifications of the so called “10-step methodology”. This is carried out by adding 7 additional steps which includes Site Response Analysis (SRA), Soil Structure Interaction (SSI) modelling in seismic regions using physics-based p-y curves for liquefiable soils. State of the art open-source software OpenSees and DeepSoil are employed to obtain the seismic loads which provides appropriate outputs during SRA. Furthermore, SAP2000 is used to evaluate the strucutral performance of OWTs during seismic events. The proposed 17 step method is validated using the only available field case record (referred to as nearshore Kamisu Wind Farm) of OWT performance during Earthquake and Tsunami during the 2011 Great East Japan earthquake. The results showed a good overall performance prediction of the offshore turbines. Extensive parametric studies were carried out based on the proposed methodology such as dimension variation of the pile, consideration of different sizes of turbines, damping ratio variations, different types of soil profiles and liquefiable zone. In this thesis the study is expanded on the other sites such as the Chang-Bin wind farm in Taiwan with respect to Chi-Chi 1999 earthquake. It is envisaged that the proposed method is helpful towards the design of bottom-fixed offshore wind turbines in seismic regions. The use of other energy sources in a conceptual level is studied, a scoring matrix is proposed to assist the consideration of other energy sources in addition to offshore wind turbines. These systems include, deep geothermal systems (in seismic regions), hydrogen energy, ocean thermal energy, ocean current energy, tidal current energy, and wave energy. By addressing the challenges specific to such regions, the research contributes to the safe and efficient expansion of the offshore wind industry, fostering sustainable energy production on a global scale.