Study On Hydrodynamic And Energy Conversion Characteristics Of A Moonpool Buoy Wave Energy Converter

As the global energy demand increases and the environmental problems aggravates,the new renewable energy technologies have developed,the ocean renewable energy has become hotspot for domestic and foreign scholars,especial the ocean wave energy.The oscillating float wave energy converter,which is simple structure,high conversion efficiency and easy to array,has great potential for research and development.In the thesis,Moonpool Buoy Wave Energy Converter(MBWEC)is taken as the research object.Based on the potential flow theory,a semianalytical solution introducted viscous dissipation is developed,in addition,theoretical analysis,numerical calculation and model test are completed,which lays the foundation for the the hydrodynamic calculation of double floating body.Firstly,the basin of MBWEC was divided,and then the diffraction and radiation problems of MBWEC under linear wave conditions are studied by using the eigenfunction expansionmatching method.The hydrodynamic coefficients such as wave load,additional mass and radiation damping acting on the device were obtained,and the influence of moonpool measure on the hydrodynamic characteristics of MBWEC is analyzed.The motion response and capture width ratio of MBWEC in frequency domain are obtained by constructing the double resonance coupled motion equation.The influence of the moonpool measure and the damping coefficient of PTO(Power take-off)on the dynamic characteristics and the efficiency of wave energy conversion was analyzed.The damping coefficient is taken as a variable and derivatives to obtain the optimal damping coefficient and its capture width ratio,optimizing the regarding Damping system.Secondly,through the impulse response function method,the frequency-domain analytical expression is transformed into the time-domain semi analytical expression.At the same time,based on the nonlinear damping system,the time-domain motion motion equations of double float are constructed,and the motion response and time domain transient capture width ratio are solved by the fourth-order runge-kutta method,in order to consider the viscous effect,viscous dissipation term in the potential flow theory is introduced,finally obtain relatively accurate correction coefficient of viscous dissipation;Based on the theory of irregular waves,ISSC wave spectrum was selected to study the time-domain motion characteristics of MBWEC under irregular waves.Then,using the viscous CFD method based on RANS equation,the motion characteristics and conversion power of MBWEC were numerically simulated by Star-CCM+software,and the analytical results of the potential flow with viscous dissipation are compared and verified with the computational results of CFD method,proving that the potential flow theory could consider the rationality of viscous effect with the dissipation method.Finally,the experimental model design of MBWEC and the pool test of dynamic characteristics were carried out to further analyze and study the motion characteristics and energy conversion of MBWEC.The experiment is divided into a single float experiment with no moon pool and a float experiment with moon pool.The effects of PTO damping coefficient,wave height,wave period and lunar pool platform device on MBWEC's wave energy conversion characteristics were studied experimentally,and the theoretical calculation results were compared with the test results of the pool to find the appropriate viscous dissipation coefficient,which laid a foundation for the practical application of the dissipative potential flow method.