An implementation of multi-support seismic input motion into openfast for the earthquake analysis of offshore wind turbines

Abstract

Nowadays offshore wind energy plays a key role in the development of renewable energies in Europe. Most of offshore wind turbines installed are fixed to the seabed, with monopiles being the most commonly used substructures in this field. However, the use of multi support substructures, such as jackets and tripods has increased considerably in recent years due to the greater depth of new wind farms locations. Dynamic behaviour and seismic risk are two factors of special importance in the design of these structures. Due to this problem, there is a need to study the seismic response of offshore wind turbines on this type of substructure. In this area, one of the most widely-used open-source advanced tool available in the literature is OpenFAST, which is a multi-physics and multi-fidelity software for the simulation of the coupled dynamic response of wind turbines in the time domain. This paper presents a formulation for the implementation of multi-support seismic input motion into OpenFAST, specifically into the SubDyn module. On the other hand, validation results for a reference offshore wind turbines on a jacket substructure are shown, conducting a number of cases with different seismic signals (translational and rotational motion) to demonstrate the correct implementation. The new mod ified code allows to analyse the accelerations and internal forces of offshore wind turbines on multisupport substructures, taking into account seismic input motion (including input rotation at each individual support) and soil-structure interaction.