Hydrodynamic Performance Of Hybrid System Combing Floating Wind Platform And Wave Energy Converters

Offshore wind and marine renewable energy have become a research hotspot due to the energy shortage,environmental pollution,and other reasons.A design concept of hybrid system combing offshore wind power and wave energy is proposed.This will save ocean space,share power generation platform and mooring system,improve power generation and power stability,and reduce power generation cost.Secondly,the floating wind platform will be protected by the reasonable arrangement of wave energy converters(WECs)to some extent,because they absorbs the wave energy near the floating wind platform and changes the local wave field.Firstly,a frequency-domain numerical model of the hybrid system combining a fixed platform and WECs is established based on the linear potential flow theory.The WECs and the platform are connected through the power take off(PTO)system.The coupling hydrodynamic coefficients are calculated using the high-order boundary element method,and the radiation damping of WECs is corrected considering the viscous effect.According to a typical sea condition,the size and layout of the cylindrical WEC are optimized.Considering the optimal PTO damping,the power generation and power volume ratio of hybrid system with different designs are studied.Then,based on Newton-Euler equation,the multi-constraint coupled motion model of floating platform,WECs and mooring system is established.The mooring force is transformed into the equivalent stiffness matrix in frequency domain based on static catenary theory.The variations of platform motion and mooring forces with the diameter and draft ratio of added wave energy float are analyzed.The variations of the total power generation of WECs after considering the motion of the platform and the corresponding reasons are also studied.Finally,based on the indirect time-domain method,the coupling model of the wind platform-WECs hybrid system is established and verified.The optimal PTO damping coefficient of the WECs based on time domain is preliminarily determined.The variation trend of dynamic response and power generation of the wind platform before and after the addition of the wave energy device,as well as the power generation performance of the WECs after considering the wind load,are compared.The results show that the viscosity has a great influence on the WEC.The larger the diameter-draft ratio,the smaller the viscous effect of the cylindrical WEC and the greater the total power generation.Considering the wind load of the superstructure of the turbine before and after the addition of the WECs,the forces on the fixed platform,the motion of the platform and the maximum mooring forces all tend to decrease in the pitch mode,especially in the range where the pitch motion of the platform is large.The added WECs reduces the the rig capsized risk degree of the floating platform caused by heavy weather.This means compared to a single platform,the security of the hybrid system combing the floating wind platform and WECs is greatly improved in the extreme condition.After adding the WECs,at the critical stage when the wind turbine reaches the rated power,the ratio of the power of the motion turbine to that of the fixed turbine decreases more slowly.Therefore,the adding WECs plays a beneficial role in the generation of the wind energy.