Operational Modal Analysis of Wind Turbines: Onshore and Offshore Floating

The exploration of the wind energy is of vital importance to overcome the dependence on fossil fuels. Therefore, this should be done not only at onshore or offshore sites with shallow waters, but also in deep waters, where floating solutions are needed. Considering the diversity of dynamic loads applied to wind turbines (rotor harmonics, wind and waves), the experimental estimation of modal properties during operation is of extreme relevance to identify possible resonances with impact on fatigue consumption and to detect anomalies from the tracking of the modal parameters over time. However, the application of Operational Modal Analysis (OMA) techniques to time-series recorded in wind turbines faces a significant number of difficulties, as many of its assumptions are more severely violated than in conventional civil engineering structures. Still, in the present paper, it is demonstrated that with adequate data processing tools, good results can be achieved. The paper reports the results obtained in onshore case studies using diverse types of sensors and also in a floating offshore wind turbine. The additional challenges observed in floating structures are described and solutions to circumvent them proposed.