Dynamic response of wind turbine tower assemblies

Abstract

As wind turbine towers are composed of several flexible inter-connected components, it is important that the engineer has the ability to understand the dynamic behaviour of the system, including that of its components, in order to ensure the serviceability and survivability of the structure. The object of this thesis is to investigate, both theoretically and experimentally, the free and forced vibrations of wind turbine tower assemblies, using model order reduction techniques. This approach reduces the number of degrees-of- freedom of the system rendering the dynamic analysis more computationally efficient. First, discrete, distributed parameter and finite element models are proposed in order to obtain the natural frequencies and mode shapes of the individual components of the wind turbine tower, as well as a coupled tower and blades assembly. Next, the forced vibration response of all individual and coupled assemblies is modelled in the time domain with both classical and non-classical damping. A gust response factor design methodology is also proposed using a two degree-of-freedom coupled tower and blades assembly. A physical reduced scale wind turbine tower model was then constructed, and its transfer function obtained experimentally. This model was then immersed within a turbulent wind flow created in a wind tunnel where its response was recorded. The measured response was validated using a theoretical model based on random vibration theory, using the previously measured transfer function.