Impact of model uncertainties on the fatigue reliability of offshore wind turbines

The impact of environmental load uncertainties on the spatial fatigue reliability of offshore wind turbine foundations is discussed and exemplified. Design procedures are utilizing overall or partial safety factors to include different model- and statistical uncertainties. Uncertainties in the final design are related to decisions taken during the design process, such as; load models, analysis methods and statistical descriptions. Furthermore, to benefit from more elaborate methods, strategies to account for reduced uncertainties by increased knowledge must be adopted. This is especially important for the offshore wind energy industry, where the aim is to produce renewable energy at a competitive cost level. The challenges and consequences of using a detailed design basis are exemplified and discussed through structural reliability analyses. Epistemic load effect uncertainties related to the foundation fatigue will be presented for a detailed wind directional model, wind-wave misalignment, and a second order wave load model. It will be shown that all of these represent important uncertainties to consider during the fatigue design of an offshore wind farm.