The effects of surge motion of the floating platform on hydrodynamics performance of horizontal-axis tidal current turbine

Under practical operation conditions, hydrodynamic characteristics of floating horizontal-axis turbine are affected by the wave-induced motion response of the floating platform for the turbine system. In this thesis, CFX software is adopted to analyze the hydrodynamic performance of the turbine in constant inflow with the turbine being forced vibrating and to study how the hydrodynamic performance of the turbine is influenced by surge frequency, surge amplitude and speed ratio. Based on the simulation data from CFX, axial damping coefficient can be obtained by least square fitting the time-varying axial force curves of surging turbine. The simulation results demonstrate that compared with turbine only rotating in constant inflow, shaft loads and energy utilization ratio of the surging turbine experience oscillations respectively; the oscillation amplitudes of these two parameters have a positive correlation with the frequency and amplitude of the surge and speed ratio; the frequency and amplitude of the surge have little impact on axial damping coefficient but this coefficient is positively proportioned to the rotational speed of the turbine. The results of this study can provide data to study motion response of floating platform for floating tidal current turbine system and control design of the output electricity.