| This paper presents an analysis on floating offshore wind turbine according to thedevelopment demand in China. In the transitional water areas between shallow anddeep water, where depths are50-80m, traditional Spar platform are not suitablebecause of the large displacement or deep draft. To develop offshore wind energy atthese water depths, a new design of floating platform for a wind turbine is proposed.A turbine-tower-platform-mooring line coupled numerical model is set up for thisnew floating platform for wind turbine, with the hydro-and aero-dynamic loads actedon, including second-order wave force. The numerical simulation tool for the coupleddynamic response prediction is developed. To study the importance of thesecond-order difference-frequency wave force on the responses of the floatingplatform,1st-and2nd-order numerical models are developed. The simulationcapability of the numerical tool is validated through comparisons.Applying this simulation tool, this paper carries out the coupled aero-hydrodynamic analysis in the time domain of this new floating platform. According to theoperational environments of offshore wind turbines, the simulation of the6-DOFglobal rigid-body motion responses under working and survival conditions areperformed by both1st-and2nd-order numerical models. The motion behavior of theplatform in different loading scenarios is studied, with emphasis on the effects ofsecond-order difference-frequency wave force. Through the comparisons of theresponse time series, spectra and the mooring tensions between different models, it isfound that the second-order wave forces influence the results significantly. Therefore,neglecting it may affect the operational and surviving safety. In addition, theaerodynamic force in the working condition dominates the motion responses, so theeffect of second-order force is less significant than that in the survival condition.The loading on the floating offshore wind turbine is complicated due to thecombined wind and wave forces. The incident angel of the environment forces mayaffect the dynamic response of the wind turbine system. To study the motion responseof the wind turbine in different incident directions, five simulations with differentangels are performed and the results in working and survival conditions are compared. The control system of wind turbine can adjust the blade pitch to keep the ratedpower of the generation. When the blade pitch control fails, the blade pitch imbalancewill happen. This is one of the main causes of the torque excitation of the shaft. Thispaper simulates this accidental condition and compares the6-DOF response timeseries and spectra with those in normal condition. It is shown that the blade pitchimbalance influences the responses of the wind turbine system significantly,especially the side-to-side motions, which are related to roll, sway and yaw.Meanwhile, the transient responses in these motions are observed. When the bladepitch control malfunctions, the excitations occur in roll and yaw at the rotor1p and2pfrequencies. Accordingly, the tower-base side-side shear force changes greatly. |
PDF Full Text Request