Study On Characteristics Of Coupled Motions Of Floating Tidal Current Energy Carrier And Sea Turbine

Under the background of resource depletion and environmental degradation, ocean renewable energy has attracted the world's attention. Tidal current energy, as a kind of ocean energy, has become a new hot point. For the advantage of low cost, easy installation and maintenance, is applied widely. Floating tidal current energy converter is moored in the sea and is affected by wind, wave and current. What's more, the periodical rotation and vibration would bring extra excitation. The converter would be effected by some excitation sources of different frequency so that complex motions is generated. In the previous analysis, the contribution of tidal current turbine is always altered by a constant additional damping and a constant external force, which can reflect the change of motion amplitude but cannot describe the motions precisely. In this paper, the author considered the periodical change of wave force and self-excitation of tidal current turbine to solve its influence on tidal current energy converter.First, the theoretical models of each parts of the moored floating tidal current energy converter system. For the turbine, CFD method is applied to solve the hydrodynamic performance of the tidal current turbine with forced oscillation and periodic hydrodynamic parameter and excitation are fitted. For the floater, then radiation and diffraction problem of a vertical cylinder in the wave are derived. A vertical cylinder is used as the carrier of the tidal current energy converter. For the mooring system, cables and anchors are designed and the system is simplified as an equivalent stiffness matrix to discuss the average displacement of the converter in working condition.In frequency domain, Fourier series is expanded to derive the semi-analytical solution of nonlinear motion equation and the equation is decoupled to self-excitation motions and wave-induced motions. By programing, self-excitation response and coupled motion response of surge and pitch in regular wave are solved and amplitude of motions of different frequency in working condition and stopped condition are compared. And how tidal current turbine with different rotating velocity impacts the motions is explored.Last, for the floating tidal current energy converter, motion equation of indirect time domain method is derived, numerical solution of retardation function is given and program of time domain motion equation is developed. For tidal current turbine with different rotation velocity, time series of surge and pitch motions in regular wave is simulated and the motion regularity in the initial state and steady state are analyzed. According to Jonswap Spectrum,irregular wave is simulated,time series of motions is solved in irregular wave,extremum of horizontal motions are analyzed and whether the blade tip is moving out of the water is judged to insure the safety of the converter.