Extreme loading of wind turbine is treated in general deterministically without taking into account the variability of the external conditions. This is prescribed in the design codes. Furthermore, for offshore wind turbines the combination of wind and wave load estimated with the deterministic method can be conservative. In this paper a rational approach to quantify the variability of extreme loads of an offshore wind turbine is presented and a new approach to the simulation of the extreme gusts with constrained simulations is proposed. For the extreme wave, the constrained method has been developed for assessment of extreme loads for offshore structures. The constrained simulation of extreme wind gust is developed for wind energy applications. The results from simulations with deterministic and stochastic external conditions are compared. It shows that the application of probabilistic approach can reduce the conservatism in the deterministic design.
Fatigue loads are regarded as the design driver for the design of wind turbines. The fatigue loads are determined with stochastic wind fields, in contrast to the analysis of extreme loads, which is carried out with deterministic wind signals. For the future generation of wind turbines with flexible design and increased size, the extreme load can become a more important issue. Moreover, the presence of wave loading adds more dimensions to the analysis of the extreme loads. The simple addition of extreme loads caused by wind and wave gives a higher estimate of the real extreme, because the probability of simultaneous occurrence of extreme wind and wave is relatively small. Conventional analysis of extreme loads for offshore structures can be applied to an offshore wine energy converter (OWEC), however, there are fundamental differences in their response characteristics.
