Analytical Solution Of Hydrodynamic Force And Energy Conversion For Axisymmetric Heave-buoy Wave Power Devices

Wave energy is a kind of marine renewable energy with wide distribution and huge reserves.Development and utilization of wave energy can relieve the pressure of fossil energy demand and environmental pollution.The key technology to realize the efficient conversion of wave energy is to improve the hydrodynamic configuration and the matching characteristics of the power take-off(PTO)mechanism.Though they have been widely studied in this area,there are many basic problems have not been solved very well,such as configuration of capture device,accurate analysis of hydrodynamic performance,nonlinear effect of PTO,scheme of array layout and energy conversion laws and analytic techniques etc.This paper takes the typical oscillating-buoy wave energy device as the research object.In the framework of potential flow theory,the vibration model of the floater on the wave surface is established.The analytical solutions to the movement,load and energy conversion of the device are developed.The hydrodynamic and energy conversion characteristics as well as their change regulations of the oscillating-buoy wave energy devices with different configurations are studied.It can provide theoretical method and calculation basis for the design of efficient wave energy device.Based upon the review of the theoretical research status of hydrodynamics and wave energy conversion characteristics of the oscillating-buoy wave power devices,the vibration models of single,coaxial-twin and multi-body-array wave energy devices are established.The mechanism of energy conversion is expounded combining the basic principles of single and multi-degree of freedom system.Based upon the linear potential flow theory,the analytical expressions for the optimal energy absorption of a coaxial double body device are derived basis on the derivation of the analytical formula for the optimal energy of the single unit.According to the single-body oscillating-buoy wave power device,based upon the classical analytical method combining the linear wave theory and Eigen-function expansion matching,a Composite Eigen-Series Solution(CESS)based Boundary Approximation Method(BAM)is put forward to solve the hydrodynamic problems of a revolving body.The hydrodynamic semi-analytical solutions of the variable cross-section single cylindrical oscillating-buoy wave energy device are obtained.Based upon the BAM,the motion and energy conversion characteristics of the device are studied from two aspects of the shape and dimensions of the absorber and PTO damping.The influence laws of the floater's dimensions on the resonant frequency of the absorber and the optimal PTO damping are discussed.It is found in the study that the optimal PTO damping of a single cylinder in the resonant state has the over damping phenomenon,which results in the failure of the vibration system.This paper puts forward the method of over damping correction,and studies the effectiveness of the optimal PTO damping and the over damping correction.The energy conversion characteristics of the absorber with the bottom configuration of the cylinder,the cone,the hemisphere and the parabolic with optimal PTO damping are discussed from two aspects of draught and displacement.According to the coaxial dual oscillating-buoy wave power device,while maintaining the same absorber and the PTO damping is optimal,based upon the classical analytical method,the analytic solutions to hydrodynamic forces and energy conversion for two kinds of coaxial-dual wave power devices with their supporter damping plate and moon-pool paddock respectively.The change regulations of motion and energy conversion characteristics of the first kind of device considering optimal PTO damping and variable draught and radius of the damping plate are discussed.In this paper,the variation regulations of the motion and energy transformation of the inner absorber with the parameters such as the supporter's configurations and dimensions are studied in detail.Based upon the linear wave theory based classical analytical method and multi-parameter control variable method,considering the main impact factors such as the absorbers array layouts,separated distance between the absorbers and incidence wave angles,the analytical solution to the hydrodynamic forces and the numerical solution to the wave energy conversion of the single oscillating buoys array are studied and presented.The variation regulations of absorber's motion and wave energy conversion with these parameters are obtained.Based upon the analysis of the main impact factors of the wave energy conversion,the influences of different array layouts on the wave energy conversion of the single-body oscillating buoy array are discussed.