Influence of Nonlinear Irregular Waves on the Fatigue Loads of an Offshore Wind Turbine

Conference paper (2012)
Department
Aerodynamics and Wind Energy (Aerospace Engineering) (TU Delft)
Copyright: © 2012 van der Meulen, M.B.; Ashuri, T.; van Bussel, G.J.W.; Molenaar, D.P.
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Published Date

14-11-2012

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Source:

The Science of Making Torque from Wind; 4th scientific conference, Oldenburg (Germany), 9-12 Oct, 2012

Faculty

Aerospace Engineering

Department

Aerodynamics and Wind Energy

Abstract

In order to make offshore wind power a cost effective solution that can compete with the traditional fossil energy sources, cost reductions on the expensive offshore support structures are required. One way to achieve this, is to reduce the uncertainty in wave load calculations by using a more advanced model for wave kinematics. As offshore wind turbines are generally sited in shallow water, nonlinear effects which results in steeper waves with higher velocities and accelerations are common. Whereas extreme waves are modeled with higher-order nonlinear regular wave models, fatigue loads are calculated from kinematics obtained by a low-fidelity linear irregular wave model. In this paper, a second-order wave model that is employed to simulate the dynamic response due to nonlinear irregular waves on a full set of IEC-standard load cases. This method is computationally efficient, which is particularly useful for design optimization studies. It is shown that by using this method for a 25 m deep site in the German Bight, equivalent fatigue loads increase by 7.5 % compared to the traditional linear wave model. The effect of nonlinear waves on fatigue is most prevalent in the foundation and tower parts near the sea surface. Furthermore, it is found that the increase in fatigue damage accumulation is most prevalent in wind-wave misaligned load cases, in which aerodynamic damping is absent.