Integrated Fatigue Loading for Wind Turbines in Wind Farms by Combining Ambient Turbulence and Wakes

A study is presented of an offshore application of a fatigue model for wind turbines operating partly in ambient turbulence and partly wakes. In order to limit the number of aeroelelastic calculations in design verification, it is necessary to reduce the measured distribution of turbulence intensities into specific design turbulence. In this study, the observation that the fatigue loading is proportional to the turbulence is used. Thus, turbulence is used as primary design parameter, substantially describing the fatigue effects. The design turbulence is defined as the turbulence that gives an equal amount of fatigue damage as the combination of true distribution of ambient turbulence and turbulence generated from wake effects. The single most important parameter responsible for the increase in fatigue loading is very short distances between turbines.