Comparison of Integrated and Sequential Design Approaches for Fatigue Analysis of a Jacket Offshore Wind Turbine Structure

Abstract

One of the most important criteria in the design of fixed offshore wind turbine structures is fatigue resistance. There is an unabated need for research in order to improve and optimize current design methods. There are mainly two approaches for structural analysis available in the offshore industry: the Integrated Design Approach (IDA) and the Sequential Design Approach (SDA). Within the IDA, the entire wind turbine, consisting of the jacket structure including tower and the rotor nacelle assembly (RNA), is considered as a unique system exposed to wind- and wave-induced loads in an aero-hydro-elastic solver. In SDA, the jacket structure is converted into a superelement and implemented into an aero-elastic solver, where it is expanded by an RNA in order to obtain the wind-induced interface loads. The obtained interface loads are used for further analysis in a more advanced offshore code, where the wave-induced loads are simulated. The fatigue damage of the relevant K-joint in the support structure is afterwards compared to the one obtained in terms of IDA. Apart from the judgement about advantages and disadvantages of both approaches, this work benefits from confirming the reliability and applicability of both approaches.