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. Since traditional wind turbine design codes reduce the drive train to just a few degrees of freedom, considerable research effort is spent in advanced modelling and simulation techniques to gain more insights in the dynamics at hand. This work focusses on the gearbox modal behaviour assessment by means of three more complex modelling techniques of varying complexity: the purely torsional-, rigid six degree of freedom with discrete flexibility and flexible multibody technique. Both simulation and experimental results are discussed. Typical mode categories for traditional wind turbine gearboxes are defined. Moreover the challenge of the definition of an accurate approach to condense finite element models for representing the flexible components in the flexible multibody models is overcome. Furthermore the interaction between the structural modes of the planet carrier and planetary ring flexibility with the overall gearbox modes is investigated, resulting in the definition of two new mode categories: the planet carrier modes and planetary ring modes.