CFD Simulation Of Hydrodynamic Characteristics Of Oscillating-Buoy Wave Energy Converters

The wave energy is a huge amount of marine renewable energy,the utilization of wave energy can greatly ease the energy pressure,as the main wave energy utilization device,the hydrodynamic and energy absorption performance of the wave energy converter have been researched extensively,but some problems still exist,such as the nonlinear problems of the buoy and wave,the PTO nonlinear problem,the energy absorption with multi-degree of freedom.In this paper,the typical oscillating buoy wave energy device is the study object,the combination way of the theoretical analysis and numerical simulation is used to establish the dynamics model of the buoy in the wave energy device,the motion?load?energy absorption characteristics?free surface deformation and flow field of the buoy were researched,it can provide a theoretical method and design basis for the safe work and efficient operation of the device.In this paper,the wave energy device development situation at home and abroad was introduced,the progress of theoretical and experimental research methods was described,and the basic theory of CFD method was presented,the CFD method of buoy motions was established,through the simulation of the linear and nonlinear wave flow field,the accuracy of wave made by the numerical water tank was verified;through the simulation of cylindrical and conical buoy heave,and the comparison with the foreign authoritative datas and experimental datas,the accuracy of buoy motions simulated by the numerical wave tank was verified.Using this method,the time-domain nonlinear problems on the water on the buoy in the linear waves,the nonlinear waves attacked and free surface deformation were simulated successfully.As for the hydrodynamic performance of the buoy,the hydrodynamic and the energy absorption performance of the typical cylindrical buoys with flat and hemispherical bottoms and the cylindrical and conical buoys with the open hole were discussed.Aim at the cylindrical and conical buoys with the open hole,the free oscillation and damping oscillation mechanical models were used,the buoy motion mechanism was explained from the curves of the motion,load and flow field under the two mechanical models,the moon pool phenomenon and flow details were shown by flow field.The capture width ratio was introduced to measure the energy absorption rate of the buoy.On the basis of the single buoy,the heave hydrodynamic performance of typical mooring two-buoys wave energy device was researched,two kinds of structure models were proposed,and the motion equations were set up.By changing the control parameters of the PTO damping coefficient and anchor elasticity coefficient,the advantages and disadvantages of two kinds of mechanical models were elaborated,for a specific model,the natural period was changed to study the heave hydrodynamic performance by controlling the overall draft,the masses of the buoy and column,anchor elasticity coefficient.Using CFD,the nonlinear PTO was simulated in the two-buoys wave energy device,the concept of combined control mode was proposed,which can maintain a high capture width ratio in the larger damping coefficient band.For two degrees of freedom point absorber wave energy device,the heave and pitch hydrodynamic performance were studied,as a reference,the hydrodynamic performance of single heave and pitch degree of freedom were studied,finding out the heave and pitch natural period and the optimal PTO damping coefficients.Typical work conditions were selected,the buoy motions with the heave and pitch degree of freedom were simulated,the differences between two degrees of freedom and single degree of freedom were explained from the motion,load and energy absorption,and the energy loss in the two kinds of motion modes was discussed from the flow field.