One of the key aspects of sustainable development is to reduce the greenhouse gas emissions. In order to achieve climate goals, it is expected that wind energy will increase its importance in the electricity production. Offshore wind energy is expected to triple its installed capacity between 2020 and 2025. Several countries have expressed plans to add this kind of energy to their energy matrix. Many of these countries are located in seismic active regions, such as China, Japan and the United States of America (USA).
Given that traditionally this kind of projects have been developed in non-seismic regions, there is a general lack of knowledge about how monopile offshore wind turbines (OWT) respond to seismic excitation. Two main properties of these structures play an important role on it response to seismic loads: 1) the large pile diameter embedded in the soil and 2) the nonlinear behavior during the operational stage.
The analysis of this kind of structures is commonly performed in the time domain, simulating operational and idling conditions. It is known that the soil structure interaction (SSI) is frequency dependent, and therefore, it is not a straightforward task to include this dependency in a time domain analysis. Previous research developed at Siemens Gamesa, performed in the time domain (and therefore neglecting frequency dependency of the SSI), suggests that seismic loads can become design driving.
This work focuses on estimating the influence of the frequency dependent SSI on the seismic response of monopile OWT. The analysis is performed in the frequency domain; therefore only idling states of the turbine is included, and aerodynamic damping is neglected. Furthermore, the structural components of the system (e.g. structural material, soil) are assumed to be linear.