Long-term modal behaviour assessment of wind turbine drivetrains

Over the last years Noise, Vibration and Harshness (NVH) problems have become important drivers in
the design of wind turbine drivetrains. The knowledge of an accurate modal model is critical to tackle
these issues. In this context, Operational Modal Analysis (OMA) is a commonly used method, as it
allows to characterize the dynamic response behaviour of machines for their most important operating
points. One of the most stringent limitations at present day is that processing vibration data classically
requires user interaction. This paper investigates an automated OMA methodology. Long-term data of an
offshore wind turbine will be processed to illustrate the developed automated algorithms. As vibration
data of rotating machines is processed, there needs to be dealt with harmonic content. To this end,
cepstral liftering and Order Based Modal Analysis (OBMA) will be used. After this pre-processing step,
a p-LSCF algorithm will be used to perform the parameter estimation. Finally, the modal estimates will
automatically be tracked to monitor their evolution in order to be able to deduce correlations between the
operating regime of the turbine and the dynamic behaviour.