Frequency-domain Method for Global Dynamic Response Analysis of a Semi-submersible Floating Wind Turbine
MetadataShow full item record
- Institutt for marin teknikk 
The wind energy market is increasing. Developing offshore wind turbines has several advantages. Conventional time-domain methods in global dynamic response analysis are time-consuming. Inspired by this, the frequency-domain method in global dynamic response analysis has been studied in this Master thesis project for a semi-submersible floating wind turbine, modified WindFloat concept. A linear dynamic model in frequency-domain has been established for the floating wind turbine, under a certain environmental condition. The model is developed by defining the constraint relationship between a linearized wind turbine model and a simplified model of the semi-submersible floater. To validate the linear dynamic model, fully coupled time-domain simulations have been run for the same design in a simulation tool - SIMA workbench. Turbulent wind fields generated from a turbulent-wind simulator TurbSim have been used as environmental inputs in the time-domain simulations, while rotor-average wind speed spectrum has been computed and applied in the linear dynamic model. Spectrum analyses have been performed on the results obtained from different methods by considering wave-only, wind-only and combined wind and wave conditions respectively. The comparison results indicate that the developed linear dynamic model is able to give reasonable estimates in general, though an underestimation is observed when aerodynamic loads have been taken into account, which might be due to the linearization and simplification performed.