Offshore wind turbine foundation monitoring, extrapolating fatigue measurements from fleetleaders to the entire wind farm

The present contribution is part of the ongoing development of a fatigue assessment strategy driven purely on in-situ measurements on operational wind turbines. The primary objective is to estimate the remaining life time of existing wind farms and individual turbines by instrumenting part of the farm with a load monitoring setup. This load monitoring setup allows to measure interface loads and local stress histories. This contribution will discuss how these load measurements can be translated into a remaining life time assessment of the instrumented turbine. However, different conditions at the wind farm, such as turbulence, differences in water depth and foundation design will cause different turbines to fatigue at different rates.
In this paper we will use the load measurements on two oshore wind turbines in the Northwind offshore wind farm to perform a remaining useful lifetime analysis. By calculating the damage equivalent loads (DELs) on the turbines the fatigue progression is quantified for every 10
minute interval. These ten-minute allows to analyse the eect of site and environmental conditions of fatigue progression. The setup of two instrumented wind turbines also allows to use measurements on one turbine to predict consumed life time on the other turbine.