## 1 Introduction

In order to evaluate wind turbine power train dynamics and associated loads, an exhaustive experimental measurement campaign was performed on a GE 1.5XLE wind turbine (developed by GE Wind Energy GmbH, Salzbergen/Germany), which was equipped with a GPV 455 gearbox (developed by Bosch Rexroth AG, Witten/Germany). All measurements were performed in the framework of the European UpWind project, a research program that was funded under the EU's Sixth Framework Programme.[1]

The experimental measurements revealed a three-dimensional character of wind turbine power train loads and dynamics. In particular, periodic, rotor speed-dependent gearbox orbital paths were identified.

In order to reproduce the measured experimental data by numerical simulation, a high-fidelity aerodynamic-mechanical wind turbine model of the GE wind turbine was developed.

When the highly discretized aeroelastic wind turbine model was complemented by defects such as power train misalignments and individual blade pitch errors, a good match of experimental data and corresponding numerical results was obtained.

The design and sizing of wind turbine power trains require non-linear dynamic load computations[2-4] and fatigue methods that account for all dynamic effects.[5-7] If power trains are subjected to dynamic loading, which induce misalignments, static or linear dynamic analysis methods[8] might miss stress cycles, which are relevant for the dimensioning. It is stipulated that specific combinations of axial, radial and bending loading of power trains can lead to very high stresses at the contact surfaces of bearing and gear components, even if torsional loads are moderate.[8-11]

Various topics will be dealt with. First, a brief introduction to computational approaches for dynamic analysis of wind turbines is presented. Next, the setup of the sensors for measurement of dynamic power train loads, deformations and orbital paths is explained. Afterwards, power train transients obtained by coupled aerodynamic-mechanical simulation are assessed by comparison with experimental measurements. The comparisons include deformations of the main bearing, torque arm couplings, gearbox orbital paths and load transients of the high-speed shaft (HSS) of the gearbox. Comparisons of experimentally measured and computed transients are performed in time and frequency domains. Consequences for system defects and the resulting impact on the fatigue load spectrum of wind turbine components are presented.