Farm-wide interface fatigue loads estimation: A data-driven approach based on accelerometers

Fatigue has become a major consideration factor in modern offshore wind farms as optimized design codes, and a lack of lifetime reserve has made continuous fatigue life monitoring become an operational concern. In this contribution, we discuss a data-driven methodology for farm-wide tower-transition piece fatigue load estimation. We specifically debate the employment of this methodology in a real-world farm-wide setting and the implications of continuous monitoring. With reliable nacelle-installed accelerometer data at all locations, along with the customary 10-minsupervisory control and data acquisition (SCADA) statistics and three strain gauge-instrumented 'fleet-leaders', we discuss the value of two distinct approaches: use of either fleet-leader or population-based data for training a physics-guided neural net-work model with a built-in conservative bias, with the latter taking precedence. In the context of continuous monitoring, we touch on the importance of data imputa-tion, working under the assumption that if data are missing, then its fatigue loads should be modeled as under idling. With this knowledge at hand, we analyzed the errors of the trained model over a period of 9 months, with monthly accumulated errors always kept below5%. A particular focus was given to performance under high loads, where higher errors were found. The cause for this error was identified as being inherent to the use of 10-min statistics, but mitigation strategies have been identified. Finally, the farm-wide results are presented on fatigue load estimation, which allowed to identify outliers, whose behavior we correlated with the operational conditions. Finally, the continuous data-driven, population-based approachhere presented can serve as a springboard for further lifetime-based decision-making.