Keywords: gyroscopic effect, wind turbine, structural response, rotation of the rotor, inertia moment, nonlinear transient analysis.

This paper deals with the simulation of the structural response of a whole wind turbine model under stochastic wind load including the rotating rotor. It reveals the exact influence of the gyroscopic effect on the responses and reactions of a wind turbine tower. The investigation is based on a prototype erected in the real world and the external wind load is generated from a simulation of a realistic time variant wind field. In the first step, the gyroscopic effect is implemented using a simple rotor model. Compared to the analytical result, ANSYS performs a gyroscopic effect very well for beam elements and even better for mass elements. The generation of the wind turbine model is carried out with the objective of both accuracy and simplicity. A beam model of the tower is used after comparing its dynamical properties with those of a detailed tower model. The rotor blades are represented by an eccentric mass with rotary inertia to avoid convergence problems. In order to reveal the influence of the rotation, three different models are considered in the analysis. In the first model the total mass of the nacelle and the rotor is positioned directly on top of the tower, while in the second one the eccentricities are considered, too. Then in the third model the rotor rotates with a constant speed to include the gyroscopic effect. Because of the geometrical nonlinearity of a large rotation, the nonlinear transient analysis is applied using an implicit Newmark-type time integration scheme. The structural response and reactions of the wind turbine tower are observed in both spatial distribution and time histories for different models. The tower stress state is examined using the Von Mises criteria. From a comparison of the results, it can be found that attention should be paid to the eccentricity of the rotor and the nacelle because the stress state on the tower top changes considerably due to the moment caused by the eccentric mass. With the rotation of the rotor included, the gyroscopic torque is generated, inducing a small torsion of the tower, which influences the vibration of the structure as well. However, the gyroscopic torque is very small compared to the bending moment caused by the wind load. From an increase of less than 5% of the maximum equivalent stress during the rotating state, the paper draws the conclusion that the gyroscopic effect of the rotor, while it is subjected to the tower bending vibration, can be ignored in the dynamic studies of a wind turbine structure.

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