Research On Model And Control Method Of Ocean Wave Active Compensation System Based On Hybrid Mechanism

With the increasing demand for energy in countries around the world,the importance of energy for all human beings is also growing gradually.Compared with thermal power generation and hydropower generation,offshore wind power generation is characterized by environmental protection,cleanliness and pollution-free.Moreover,the coastline of China is long and the potential resources of offshore wind energy are huge.In recent years,the offshore wind power generation of China has developed rapidly and has become one of the main sources of energy in China.However,there are still some problems in the development of offshore wind energy for our country.Specifically,for example,the failure rate of offshore wind turbines is high,and offshore wind turbines need frequent repair and maintenance.Hence how to ensure that the repairmen can successfully climb the wind turbine platform under certain sea conditions is an urgent problem to be solved.Therefore,proceeding a research on ocean wave compensation has important scientific value and practical engineering significance.Firstly,according to the actual demands of offshore platform operation and maintenance,the design of the offshore ocean wave compensation system is carried out and determine the technical indicators of the system(such as motion freedom,motion parameters,structural parameters,size and weight).At the same time,the composition of the specific equipment is described.Hereafter,the four sub-systems composed of the offshore compensation platform are designed in detail,and the design work of the control system is emphasized.Secondly,the coordinate system and kinematics model of the system are established according to the mechanical structure of the ocean wave compensation system.Then,the forward kinematics analysis of the hybrid mechanism is carried out and the positive kinematics solutions of the Stewart platform is determined by comparing several positive kinematics solving methods simultaneously.The D-H method is adopted by us to analyze the positive and inverse kinematics of the 3-DOFs tandem mechanism.Therefrom,the inverse kinematics of the 9-DOFs hybrid mechanism is solved by position matching and attitude matching.Based on this,the Jacobian matrix of 9-DOFs hybrid mechanism is derived.Thirdly,the Lagrange method is adopted to derive the dynamic model of the 6-DOFs Stewart platform.The kinetic energy and potential energy of the moving platform and the driving rods are analyzed respectively,and the kinetic energy and potential energy expressions of the overall 6-DOFs Stewart platform are derived.The Newton-Euler iterative dynamics equation is used to analyze the dynamics of the 3-DOFs tandem mechanism.Among them,the joint force and torque of the rotating joint,the swing joint and the moving joint of the 3-DOFs tandem mechanism are analyzed iteratively,and then the Newton-Euler dynamic equation of the 3-DOFs tandem mechanism are obtained,which lays the foundation for the control of the ocean wave compensation system based on the hybrid mechanism.Finally,the control scheme of the system is determined on the basis of the kinematics and dynamics derivation results of the hybrid boarding system.Meantime,an inverse kinematics solution method of the hybrid boarding system based on fuzzy algorithm is proposed,which realizes the numerical integration method to obtain the inverse kinematics solutions.That is,the method can actively compensate the disturbances of the ocean wave.What is more,a fuzzy strategy is put forward to plan the variable values reasonably,which solves the uniqueness problem of inverse kinematics solution and can satisfy the requirement of variable constraints perfectly.When conducting ocean wave compensation,the Stewart parallel platform is used to compensate the wave disturbance in roll direction.Moreover,it is efficient to compensate other disturbances by adjusting the joint angles of gangway.The effectiveness and the robustness of the proposed method is demonstrated using numerical simulation when the ocean wave disturbance is added into the hybrid boarding system.