ABSTRACT
As can been seen from Figure 1, the flapwise and total bending moments at the blade root reach their maximum at the rated current speed and then decrease rapidly as the pitch angle increases to keep the power constant. It can also be seen that at the peak the difference between these two moments is insignificant. However, the pitch control does not react instantly to high frequency fluctuations of the current speed due to turbulence. The current speed fluctuations may cause much larger bending moments at the blade root than the peak values in Figure 1. To take this into account, a random variable ΔU representing fluctuations of the tidal current speed around its average value is introduced. Since it is clear that from a physical point of view the magnitude of ΔU should be limited, the latter is modelled by a beta random variable defined on (−0.3Ur, 0.3Ur) with a zero mean, where Ur = rated current speed.
