5. Modal Parameters Estimation of an Offshore Wind Turbine Using Measured Acceleration Signals from the Drive Train

Offshore Wind Turbine (OWT) is complex structure that consists of different parts (e.g. foundation, tower, drivetrain, blades, …). The last decade there is a continuous trend towards larger machines with the goal of cost reduction. Modal behavior is an important design aspect. For tackling NVH issues and validating complex simulation models it is of high interest to continuously track the vibration levels and the evolution of the modal parameters (resonance frequencies, damping ratios, mode shapes) of the fundamental modes of the turbine. Wind turbines are multi-physical machines with significant interaction between their subcomponents. This paper will exploit this and present the possibility of identifying and tracking consistently the structural vibration modes of the drivetrain of the instrumented offshore wind turbine by using signals (e.g. acceleration responses) measured on the drivetrain system. The experimental data has been obtained during a measurement campaign on an offshore wind turbine in the Belgian North Sea where the OWT was in standstill condition. The drivetrain, more specifically the gearbox, is instrumented with a dedicated measurement set-up consisting of 17 sensor channels with the aim to continuously track the vibration modes. The consistency of modal estimates made at consequent 10-min intervals is validated, and the dominant drivetrain modal behavior is identified.