Characterizing fatigue damage by waves and wind using experimental data of a 6 MW monopile offshore wind turbine

The worldwide rapid deployment of offshore wind turbines (OWTs) to combat climate change highlights the pressing need to ensure their structural reliability and longevity. Operating in harsh marine environments, these critical infrastructures require continuous monitoring to maintain reliable power generation and assess their fatigue-induced degradation. Capturing the complex relationship between damage accumulation and environmental and operational conditions remains a significant challenge due to lack of large-scale experimental data. Fatigue is a dominant degradation mechanism for OWTs, thus characterizing its relationship to environmental conditions is critical to ensuring the longevity of these renewable power sources. This study presents fatigue analysis of an instrumented 6 MW offshore wind turbine with a monopile foundation located in the U.S. east-coast waters, leveraging continuous monitoring data over the span of a year. The turbine is equipped with strain gauges, accelerometers, and a supervisory control and data acquisition (SCADA) system measuring the turbine operational conditions. Wave measurements are taken from a nearby wave buoy to characterize the sea state. This paper aims to (i) conduct a fatigue analysis of the turbine, using rainflow cycle counting and the linear damage accumulation method, to establish a fatigue correlation between the two instrumented elevations, and (ii) explore the relationship between fatigue damage accumulation and environmental and operational drivers, including wind-wave alignments and misalignments. The results revealed that the most severely damaging wind-wave scenarios were infrequent, whereas cumulative damage for the monitoring period was governed by repeated, moderate environmental conditions, resulting in incremental damage over time.