Study On Environmental Loads And Coupled Motion Response Of Floating Offshore Wind Turbine System

The offshore wind resources have many advantages that the wind speed is high andstable dominant direction, and high energy gain. Currently, due to waters depth is veryshallow in the installation site, wind turbines are supported by fixed infrastructure in theoffshore wind farms which have been built in the world. But offshore wind resource energy inshallow water is relatively small and the development area are limited, so floating offshorewind farm in deep water become a new development direction of offshore wind farms, andfloating offshore wind turbine(FOWT) has become an international research focus. Therefore,as the research object of floating offshore wind turbine, based on aerodynamic, hydrodynamictheory, environment loads of FOWT and coupling motion are studied by the combination oftheoretical analysis, numerical simulation and model test. It has important theoretical andpractical significance for deeply master coupled characteristic, the phenomena and laws offloating offshore wind turbine, and for provide theoretical methods and design techniques fordeveloping reliable platform concept design.In aerodynamic performance research of wind turbine, firstly, the aerodynamicperformance of the horizontal axis variable-pitch wind turbine are summarized.turbulencecharacteristics of offshore wind farm is described based on wind spectral, turbulent wind ofoffshore wind farm is simulated by means of harmonic synthesis method. Steady and unsteadyaerodynamic performances of horizontal axis wind turbine are calculated by blade elementtheory and dynamic stall, dynamic wake model. Variable-speed and variable-pitch process ofwind turbine are simulated by PID control technology. Finally, numerical calculation programof steady and unsteady aerodynamic performance (including power, load, and otherparameters) for a horizontal axis variable pitch wind turbine are developed by combinationsof the above three methods. The simulation agrees well with the result calculated by Bladedsoftware of a5MW horizontal-axis offshore wind turbine designed by National RenewableEnergy Laboratory.In SPAR hydrodynamic performance research, wave loads of SPAR platform arepredicted by use of Full Slender Formulation. Considering the influence of SPAR nonlinearwave loads, in each time step, wave loads are based on SPAR instantaneous position. Nonlinear motion equations of FOWT system are established in time domain. Finally,dynamic response of SPAR platform is developed in time-domain. The wave loads anddynamic response of SPAR are predicted by means of my codes under regular and irregularwave.In coupled research of wind turbine-platform-mooring system, the main research and theresults are as follows:1) Firstly, the effects on the horizontal axis wind turbine from platform motion areillustrated. The influence laws on Power and other parameters from platform are analyzed.Then variation laws of platform motion response caused by aerodynamic damping ofhorizontal axis wind turbine are analyzed.2) Mooring system loads are simulated by means of horizontal and vertical nonlinearspring. The spring stiffness is obtained by static analysis of the mooring system. Thenaerodynamic performance prediction program of wind turbine, hydrodynamic performanceprediction program of the platform and mooring system simulation method are integrated,coupled program of wind turbine-platform-mooring system are developed in time domain.3) By use of the coupling program, coupling characteristic of windturbine-platform-mooring system is investigated and coupling characteristics of power, loadand platform motion response parameter are analyzed under random sea conditions.In hydrodynamic model test, hydrodynamic model test of5MW SPAR FOWT isdesigned. Hydrodynamic performance model test scheme of FOWT is established and modeltest method of hydrodynamic performance is mastered. Test results agree with results bynumerical simulation. In the test, heave motion response measured value of model withoutheave plate and model with it are compared. heave plate decreased heave and pitch motionresponse. Then free decay damping results of model with heave plate are applied to thenumerical calculation.