Study On The Motion And Energy Characteristics Of Coaxial Two-body Wave Energy Converter

The two-body heaving wave energy converters absorb wave energy by making use of the relative motion between buoy and float.It has the advantages of the reliable principle,simple structure,flexible application,and high efficiency.Although the concept of this kind of device is widely accepted,it still lacks of the deep research on the theoretical mechanism and general characteristics,especially the laws of the relative motion and interaction between the floaters.Aiming at the above problems,this paper takes coaxial two-body wave energy converter as the research object,and uses theoretical analysis,numerical simulation and model test to analyze its dynamics and kinematics,and then makes a comprehensive and systematic discussion on the optimization of its energy capture.Firstly,the research background and significance of this paper are described from three aspects:the characteristics and value of wave energy demand in the world and the development of wave energy devices.The kinematics and dynamics analysis of the two-body heave wave energy converter is introduced from three aspects of theoretical analysis,numerical simulation and model test.Therefore,the coaxial two-body wave energy converter device is determined as the research object,and the motion response and energy characteristics are studied by combining theoretical analysis,numerical simulation and model test.In chapter 2,the hydrodynamic characteristics of coaxial two-body wave energy converter device are studied.Based on the theory of potential flow,the analytical solutions of diffraction and radiation in waves are derived in detail,and the analytical expressions of wave excitation force and radiation force are obtained.Based on this,the hydrodynamic characteristics of coaxial two-body wave energy converters are analyzed,and the variation rules of additional mass,damping coefficient and wave excitation force under different float-buoy draft ratio and float-buoy diameter ratio are analyzed.In chapter 3,the viscous correction method for the relative hydrodynamic dynamics of the vertical dOF of the coaxial two-body wave energy converter is studied.First introduced with viscous CFD calculation methods of modeling and solving,and then through the model calculation,the existence of the viscous effect is analyzed,and from the catamaran relative motion amplitude response,relative motion phase and relative motion power conversion efficiency from three aspects,analyzes the viscous effect for motion and energy characteristics,the influence of catamaran device and find out the characteristics of the viscous effect.Based on the above characteristics,a viscous calculation method based on free attenuation motion is proposed,and the key influencing factors in the calculation process are analyzed.The viscous correction formula of coaxial two-body wave energy converter is fitted.In chapter 4,the motion response and energy conversion characteristics of coaxial two-body wave energy converters are studied.Firstly,the paper introduces the various structures calculated in this chapter,including the damped plate-type floating body,streamlined floating body and float structures with different bottom shapes and diameters.The CFD modeling and calculation method is the same as that in Chapter 3,and the new structure model is verified.Taking wave parameters and PTO damping values as the key parameters,the influence of wave parameters on the motion response and energy conversion characteristics of coaxial two-body wave energy converter was analyzed,and the optimal energy acquisition analysis was carried out.The energy conversion characteristics of two-body wave energy converter with different structures are analyzed and compared.In chapter 5,pool tests are carried out on two kinds of coaxial two-body wave energy converter.The mechanical characteristics and wave energy conversion characteristics of the system are further studied,and the feasibility of the concept and the correctness of the theory are verified.The operation characteristics of the device under irregular wave conditions are analyzed emphatically.In chapter 6,the characteristics of coaxial two-body wave energy converters array are studied.A square array composed of four devices is taken as the research object,and the energy capture characteristics of the array are analyzed by taking device spacing and wave incidence direction as parameters.The performance of each device in the array is analyzed.The operation characteristics of the array under irregular wave conditions are analyzed emphatically.