Fatigue assessment of offshore wind turbines

  • Abdolmajid Moghtadaei

Student thesis: Doctoral ThesisDoctor of Philosophy


Offshore wind turbines are complex marine structures that are exposed to stochastic dynamic environmental actions such as wind and waves which result in high cycle fatigue conditions. The accuracy of estimated residual life for such structures is directly linked to the various numerical modelling approach. An accurate action is therefore required to ensure a reliable fatigue life estimation and hence the structural safety of all components affecting the modelling technique and analysis set-up under different environmental conditions.

In order to have an idea of the performance of different numerical modelling, a monopile wind turbine case study is selected that is located in the North Sea at a water depth of 30 m. Firstly, a scaled prototype of the monopile is tested in the wave tank of Queen’s University Belfast and the same case created in OpenFoam for the Computational Fluid Dynamics study of hydrodynamic loads. Seven different load cases are selected and generated both in the wave tank and numerical model. The wave characteristics are selected in the regions that the body is slender relative to wavelength. The water depth is considered as intermediated water depth and wave regions are in the non-linear region as described by Stoke’s Second Order or higher.

In this study, the objective is to perform a code-to-code fatigue life sensitivity analysis under operational and non-operational conditions using time-domain coupled aero-hydro-servo simulations. The comparison is performed for a reference 5-MW floating wind turbine configuration (OC4 semi-submersible) using OpenFAST developed in NREL and an FE structural dynamic model (FlexCom) developed in Wood Plc. The accumulated damage in the tower base, tower top is calculated and the effects of various modelling factors, including wind and wave simulation by considering 50%, 65%, 75% and 85% percentile of wave height and wave period in the fatigue damage occurrence are examined.

Thesis is embargoed until 31 December 2025.
Date of AwardDec 2022
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorMadjid Karimirad (Supervisor), Trevor Whittaker (Supervisor) & Charles Young (Supervisor)


  • Offshore Wind Turbine
  • Floating offshore wind turbine
  • Fatigue assessment
  • Finite Element Analysis
  • Computational Fluid Dynamics
  • numerical modelling
  • Aero-hydro-servo-elastic
  • Coupled simulations

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