Abstract Summary
The interest in improving our understanding on the seismic response of the support structures of large Offshore Wind Turbines (OWTs) is gradually increasing due to the present commitment to the replacement of fossil fuels with renewable energies, and the consequent expansion of offshore wind farms in the world. In this line, this paper explores and compares the seismic responses of the support structures of three different reference OWT of increasing power and size: the NREL 5 MW RWT, the IEA Wind 10 MW RWT and the IEA Wind 15 MW RWT, all of them on monopiles. The seismic response of these OWTs is studied considering three different working conditions (parked, operating and producing electrical power, or during an emergency shutdown due to the arrival of an earthquake), and the structural response under the arrival of different earthquakes is compared to that of the structures submitted only to the different environmental loads. From the point of view of the structural model, the responses computed using a simplified fixed-base model are compared with those computed using a model in which the flexibility of the foundation is included using a simplified lumped parameter model (LPM) that allows to introduce the dynamic properties of the soil-foundation system and, especially, its capacity to dissipate energy back into the soil. In this regard, the needed impedance and kinematic interaction functions are computed using an advanced Boundary Element – Finite Element (BEM-FEM) model in which the pipe pile is modelled using FEM shell structural elements, and the unbounded layered soil is modelled using the BEM. Then, the structural response of the system is evaluated using OpenFAST, adapted to include the LPM to model the soil-foundation system at the base of the structure, and to include the possibility of considering the seismic signal as filtered Foundation Input Motions. The influence of aspects such as Soil-Structure Interaction, rated power, operating mode, direction of shaking or time of arrival of the seismic signals are summarized and discussed. This study was supported by the Consejería de Economía, Conocimiento y Empleo (Agencia Canaria de la Investigación, Innovación y Sociedad de la Información) of the Gobierno de Canarias and FEDER through research project ProID2020010025, and by the Ministerio de Ciencia e Innovación and the Agencia Estatal de Investigación of Spain, and FEDER, through research project PID2020-120102RBI00 (MCIN/AEI/10.13039/ 501100011033).
