Hydrodynamic Performance Of Submersible Platform And Heaving Wave Energy Converters Hybrid System

Wave energy is becoming a hot research spot due to its merits such as wide distribution and high energy flux density.However,the high cost hinders the development of wave energy technology.Presently,Integration of wave energy converters and other offshore equipment is a relatively effective developmental method to reduce the cost.This thesis proposes a novel hybrid system consisting of heaving wave energy converters and a submersible platform,applying wave energy as power supplement for daily use on the platform.First,this thesis establishes a coupled dynamic model of heaving absorbers and fixed platform under regular waves based on the linear potential flow theory and uses the model to design and optimize the layout of the hybrid system.The operation location is North Sea in Europe.Numerical searching is used to find the optimal power take-off damping for a range of incident period.This paper studies the influence of the device size on the power generation performance of the hybrid system,the interaction between the devices and between the device and the platform.Based on this,this paper establishes a multi-degree-of-freedom constrained coupled dynamic model of the hybrid system in the frequency domain,and controls the motion amplitude of the platform through the equivalent stiffness matrix of the catenary mooring;this model is used to study the effect of the PTO selection method on the energy characteristics of the integrated system,the influence of the movement characteristics,the influence of the existence of devices on the movement and mooring of the platform,and the influence of the movement of the platform on the power generation performance of the hybrid system.Subsequently,the linear wave superposition method and the indirect time domain method were used to establish a time-domain multi-degree-of-freedom constrained coupled dynamic model of the hybrid system under irregular waves,and the correctness of the model establishment was verified by comparing the target spectrum with the calculated spectrum.The total power generation of the integrated system under the optimal PTO damping and the performance of the hybrid system under regular waves are compared.Finally,the wave period corresponding to the maximum total power generation of the hybrid system in the irregular wave is given to study the motion response of each part of the hybrid system and the time history of the power output.Results show that a fatter float has a greater annual total power generation,and its cost per unit mass changes not obviously.Therefore,in order to make the power generation performance of the entire integrated system good,a fatter float is more suitable.When the PTO damping is optimal for all the incident periods,the power generation of the hybrid system is greater,but the movement of the platform in all directions in regular waves in the frequency domain is greatly increased,especially the pitch direction,which leads to a decrease in the safety of the platform.When the PTO damping is fixed,the power generation of the system is slightly reduced,but the safety of the platform is improved;The frequency domain results of the integrated system in irregular waves obtained by the linear combination method are in good agreement with the time domain results.Therefore,the frequency domain results can be used to quickly and efficiently optimize the PTO damping,improving the overall power generation performance of the hybrid system.