Implementation of Ground Input Motion and Dynamic Soil-Structure Interaction into Openfast for the Seismic Analysis of Offshore Wind Turbines

Abstract

The development of offshore wind energy is expected to contribute significantly to the decarbonization of the electrical energy production sector, and the number of offshore wind farms is growing fast due to the maturity of the technology, the reduction in costs, and the increase in size and power of the turbines. Floating offshore wind is developing fast, but offshore wind turbines (OWTs) founded to the sea floor are still the dominant technology, with different types of support structures (monopiles, jackets, tripods) depending on the sea depth and the conditions of the location. The dynamic properties of these support structures are a key factor in the design of the system from a civil engineering point of view, and the distinctive features of OWTs (including the nature of the loads and the variable geometry of the system due to the rotation of the blades and the continuous actions of the control system) suggest that specific tools, able to adequately model the different subsystems, should be used in structural and seismic analyses. For this reason, input ground motion and dynamic soil-structure interaction capabilities have been implemented in OpenFAST, an open-source nonlinear aero–hydro–servo–elastic code for the simulation of wind turbines, in which the environmental loads and the response of all the main elements are taken into account through specific models and modules. This paper presents the equations of motion and the specific procedure followed to implement input ground motion and soil-structure interaction into the SubDyn module, and presents validation results to illustrate the applicability of the approach.