An accurate stress or strain history at fatigue critical locations is often needed for a fatigue assessment. Unfortunately it is not feasible to install strain gauges as these fatigue hotspots. This contribution compares two techniques to obtain a reliable stress history at any location of the turbine structure, one is based on modal decomposition and expansion, the other is based on a Kalman filter. Both techniques will be validated and compared using data from an offshore wind turbine monitored by OWI-lab. The monitored turbine is instrumented with strain gauges at the interface between transition piece and tower and accelerometers at multiple levels. The installed strain gauges allow to validate the proposed techniques with respect to the reality.
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