Dynamic analysis of both on and offshore wind turbines in the frequency domain
This thesis presents several developments in analysing wind turbines in the frequency domain. Previous work in the area has developed computer-based models to predict the rotationally sampled stochastic wind speed witnessed by the blades of a wind turbine. Work has also been carried out to include rudimentary capabilities to model blade, tower and drivetrain flexibilities. These are usually limited to modelling only the first mode responses in each case. This thesis describes the development of a new frequency domain model with the ability to analyse fully flexible turbines using a Finite Element analysis approach. In addition, the analysis has a number of novel features to enhance convergence and minimise numerical errors. Comparisons are made between the theoretical and measured results for a number of commercial wind turbines. Problems with land availability have recently prompted governments to investigate the possibility of siting wind turbines offshore. One type of concept sites turbines on floating platforms. It is necessary to develop models to predict how turbines influence the rigid body dynamics of the platform. Additionally the wave-induced motions of the platform influence dynamic loading in the turbines and this too should be analysed. A new frequency domain model has been advanced to calculate the forces induced through stochastic wave loading on floating platforms. A promising concept, based on a 'Tensioned Buoyant Platform (TBP)' has been investigated and the results presented. Many recent developments have been made in Frequency domain fatigue analysis. An investigation into a number of methods is discussed. Recommendations are made for the practicable use of these methods for analyising wind turbine structures.