Abstract
This article demonstrates the application of a generic methodology， based on the flexible multibodysimulation technique， for the dynamic nalysis of a wind turbine and its drive train， including a gearbox. Theanalysis of the complete wind turbine is limited up to 10 Hz， whereas the study of the drive train includesfrequencies up to 1500 Hz. Both studies include a normal modes analysis. The analysis of the drive trainincludes additionally a response calculation for an excitation from the meshing gears， a Campbell analysisfor the identification of possible resonance behaviour and a simulation of a transient load case， which occursas a sudden torque variation caused by a disturbance in the electrical grid.
1 Introduction
During the last decades， the interest for using renewable energy sources for electricity generation increased ［1］.One of its results is a boom in the wind turbine industry since ten years. Figure 1 shows how the global installedwind power capacity reached 59.3 GW at the end of 2005， of which about 20% had been installedin that year. This rapid growth is expected to continue in the coming years and to drive new technological improvements to further increase the capacity and reduce the cost of wind turbines.In their design calculations， the wind turbine manufacturers use dedicated software codes to simulate theload levels and variations on all components in their machines. Peeters ［3］ gives an overview of the existingtraditional simulation codes. He concludes that the concept of the structural model of a wind turbine in allthese codes is more or less similar and that the behaviour of the complete drive train （from rotor hub to generator）is typically represented by only one degree of freedom （DOF）。 This DOF represents the rotation of thegenerator and， consequently， the torsion in the drive train. Peeters describes additionally the consequencesof using this limited structural model for the simulation of drive train loads. The output of the traditionalsimulations lacks insight in the dynamic behaviour of the internal drive train components. De Vries ［4］ alsoraises the lack of insight in local loads and stresses in a drive train and the insufficient understanding of thedesign loads. He relates furthermore a series of gearbox failures in wind turbines to these consequencesof simulating with a limited structural model. More insight can be gained from a more detailed simulationapproach. Peeters ［3］ presents a generic methodology for this， which is based on three multibody system（MBS） modelling approaches.
