Wind turbines are mainly classified into horizontal axis wind turbines (HAWTs) andudvertical axis wind turbines (VAWTs) based on different orientation of their axis ofudrotation. Ever-increasing demand for energy boosts the application of the windudturbines in the deep water. The applications of HAWTs in deep water using differentudfloating support structures have led to an increasing and versatile research due to theirudcommercial success. However, the application of the VAWTs in the offshore windudindustry also has some potential due to its economical installation and maintenance.udMore and more efforts have been invested in developing floating vertical axis windudturbines (FVAWTs), but the research on the FVAWTs is still at an early stage.udAlthough different concepts of the FVAWTs were proposed based on a combination ofuda rotor and a floater, an optimized design is still an open question. The rotor coversudstraight-blade rotor, Darrieus curved-blade type rotor and helical-blade rotor while audfloater could be a spar, semi-submersible or tension leg platform (TLP). To evaluate audFVAWT, a simulation tool is needed to perform time domain numerical simulations.udThe simulation tool should have the capability to calculate aerodynamic loads on theudrotor, hydrodynamic loads on the floater and structural dynamics of the rotor, andudinclude a controller. Based on the calculated dynamic response, a response analysis isudcarried out to better understand the response characteristics of a FVAWT as a basis foruddesign and safety criteria according to serviceability. The objective of this thesis hasudbeen the development of a coupled method for integrated dynamic analysis of theudFVAWTs and application in a systematic study of a Darrieus rotor on audsemi-submersible floating support structure.udThe aerodynamic analysis of a VAWT differs from that of a HAWT, especially whenudthe VAWT is mounted on a floater. Thus, the aerodynamics of a VAWT is firstudaddressed and a model improvement for evaluating the effect of tower tilting on theudaerodynamics of a VAWT is performed. This improved model is validated againstudexperimental data collected for an H-Darrieus wind turbine in skewed flow conditions.udBased on the assumption that the velocity component parallel to the rotor shaft isudsmall in the downstream part of the rotor, the effect of tower tilting is quantified withudrespect to power, rotor torque, thrust force and the normal force and tangential forceudcoefficients on the blades.udSecondly, a novel 5 MW FVAWT concept, based on a Darrieus rotor on audsemi-submersible support structure, is proposed. An aero-hydro-servo-elastic tooludSimo-Riflex-DMS is developed for modeling the dynamics of the FVAWT andudvalidated. This integrated dynamic model takes into account the wind inflow,udaerodynamics, hydrodynamics, structural dynamics (wind turbine, floating platformudand the mooring lines) and a generator controller. Thirdly, the response characteristics of the 5 MW FVAWT are studied based onudstatistical analysis and spectral analysis of the response. The response characteristicsudof the FVAWT under steady wind condition and those under turbulent wind conditionudare compared to investigate the effect of the turbulent wind. The advantage inudreducing the 2P effect on the FVAWT is identified by comparing with the equivalentudland-based wind turbine. Furthermore, by comparing the FVAWT with a rigidudFVAWT, the aspect of rigid versus flexible rotor is quantified, and thus the effect ofudthe modeling method of the rotor on the responses is observed. Besides the normaludoperating condition, the global motions and structural responses of the FVAWT as audfunction of azimuthal angle are studied for the parked condition. To identify the effectudof wind-wave misalignment on the platform motion, structural response and mooringudlines, the dynamic response analysis of the FVAWT in selected misaligned wind andudwave conditions are conducted.udMoreover, it is also of great interest to compare the performance of a FVAWT with audFHAWT. A comparative study of the studied FVAWT and a FHAWT with the 5 MWudNREL reference wind turbine mounted on the same semi-submersible is carried out. Audset of time domain simulations with different conditions, i.e., the decay tests, waveudonly conditions, wind only conditions and the combined wind and wave conditions,udare conducted. The dynamic responses of the FVAWT and the FHAWT, such as theudglobal motions of the floater in six DOFs, the bending moment of the bottom of theudtower and the tension at the fairleads of the mooring lines, are compared based onudstatistical results and power spectra.udLastly, a novel hydrodynamic brake installed in the FVAWT is proposed in this thesis.udThe FVAWTs with fixed-pitch blades experience large aerodynamic loads in highudwind speed condition or in stormy weather. The blades may be deformed or broken,udand the tower can collapse in more severe cases. Thus, initiating an emergencyudshutdown is one of the most important concerns for the FVAWTs. Therefore, auddynamic response analysis of the FVAWT with this installed hydrodynamic brake isudstudied for possible use in connection with emergency shutdown event. The effects ofudthe hydrodynamic brake on the platform motions and structural loads under normaludoperating conditions and during the emergency shutdown events are evaluated. Theuduse of both the hydrodynamic brake and mechanical brake is also investigated.
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