Multibody modelling of varying complexity for modal behaviour analysis of Wind Turbine Gearboxes

In the currently booming market of wind turbines, a clear focus is put on the design of reliable and cost-effective subsystems, such as the gearbox. A requirement for reliable gearbox design calculations is sufficient insight in the dynamics of the entire wind turbine drive train. To ensure this, considerable research effort is spent in advanced modelling and simulation techniques. This work investigates the modal behaviour of wind turbine gearboxes by means of three multibody modelling techniques of varying complexity: the purely torsional-, rigid six degree of freedom with discrete flexibility- and flexible multibody technique. Beased on experimental validation shortcomings of the first techniques are shown. Moreover limitations of the second technique are indicated. Furthermore the flexible multibody technique is suggested as most accurate. In addition the importance of accurate coupling structures to link the flexible components to the multibodymodel is proven and the influence of planet carrier and planetary ring flexibility shown, whereas findings are compared to literature. In this regard two new mode categories are defined: the planet carrier modes and planetary ring modes