Structural analysis of a wind turbine and its drive train using the fl exible multibody simulation technique J. Peeters1, D. Vandepitte2, P. Sas2 1 Hansen Transmissions International, Leonardo da Vincilaan 1, B-2650 Edegem, Belgium e-mail: jpeeters 2 K.U.Leuven, Department of Mechanical Engineering, Celestijnenlaan 300 B, B-3001, Heverlee, Belgium Abstract This article demonstrates the application of a generic methodology, based on the fl exible multibody simulation technique, for the dynamic analysis of a wind turbine and its drive train, including a gearbox. The analysis of the complete wind turbine is limited up to 10 Hz, whereas the study of the drive train includes frequencies up to 1500 Hz. Both studies include a normal modes analysis. The analysis of the drive train includes additionally a response calculation for an excitation from the meshing gears, a Campbell analysis for the identifi cation of possible resonance behaviour and a simulation of a transient load case, which occurs as a sudden torque variation caused by a disturbance in the electrical grid. 1Introduction Duringthelastdecades, theinterestforusingrenewableenergysourcesforelectricitygenerationincreased1. One of its results is a boom in the wind turbine industry since ten years. Figure 1 shows how the global in- stalled wind power capacity reached 59.3 GW at the end of 2005, of which about 20% had been installed in 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 the load levels and variations on all components in their machines. Peeters 3 gives an overview of the existing traditional simulation codes. He concludes that the concept of the structural model of a wind turbine in all these codes is more or less similar and that the behaviour of the complete drive train (from rotor hub to gener- ator) is typically represented by only one degree of freedom (DOF). This DOF represents the rotation of the generator and, consequently, the torsion in the drive train. Peeters describes additionally the consequences of using this limited structural model for the simulation of drive train loads. The output of the traditional simulations lacks insight in the dynamic behaviour of the internal drive train components. De Vries 4 also raises the lack of insight in local loads and stresses in a drive train and the insuffi cient understanding of the design loads. He relates furthermore a series of gearbox failures in wind turbines to these consequences of simulating with a limited structural model. More insight can be gained from a more detailed simulation approach. Peeters 3 presents a generic methodology for this, which is based on three multibody system (MBS) modelling approaches. 3665 MW Figure 1: The evolution of the global cumulative installed wind power capacity from 1995 to 2005 2. The fi rst approach is limited to the analysis of torsional vibrations only. The second technique offers a more realistic representation of the bearings and the gears in the drive train and its generic implementation can be used for both helical and spur gears in parallel and planetary gear stages. The third method is the extension to a fl exible MBS analysis, which yields information about the elastic deformation of the drive train components in addition to their large overall rigid-body motion. The implementation of the different models was done in LMS DADS Revision 9.6 5 (DADS). This article presents an application of the second and third technique for the analysis of a drive train in a wind turbine. This example includes: a normal modes analysis for the determination of eigenmodes and eigenfrequencies (1) of the wind turbine and (2) in the drive train a response calculation for an excitation from the meshing gears a Campbell analysis for the identifi cation of possible resonance behaviour a simulation of a transient load case 2Drive train layout and model implementation Figure 2 shows the wind turbine for the present application. It is a generic example of which the results are representative for a modern wind turbine with a gearbox. The drive train has one main bearing integrated in the gearbox carrying the wind turbine rotor. The generator is a doubly fed induction generator (DFIG) and the gearbox design is a combination of two planetary stages with one high speed parallel stage. The wind turbine rotor is connected to the planet carrier of the fi rst planetary stage. This stage has spur gears and its ring wheel is fi xed in the gearbox housing. This housing is assumed to be rigid as well as its connection to the bed plate. This latter frame supports also the generator and rests on the yaw bearing, which connects the complete nacelle with the tower. The second gear stage in the gearbox is a helical planetary