Key Technologies For Active Heave Compensation System In Offshore Crane

Ship motions in sea wave negatively influences many offshore engineering operations,especially lifting operations in offshore crane,including oil-drilling technology in drill-ships,building and maintaining installations,and the launching and recovering operations of Remotely Operated Vehicles.It is necessary to apply heave compensation system to assure the security and reliability of offshore operations.The contained technologies in active heave compensation system in offshore crane are researched in this paper,and the main aspects studied are as follows:(1)Considering the influence of vessel's heave,roll and pitch on the heave motion of offshore crane's tip,motion transformation in heave compensation system is presented.Building the required coordinates and deriving the transformation matrix.The choosed method of motion transformation is based on the principle of inertial measurement sensor which is used to measure the attitude of ship.Wherever the sensor is installed on the vessel's deck,the heave velocity of offshore crane's tip can be obtained by motion transformation and the measured information from sensor.(2)The heave velocity of sensor is obtained by the heave motion estimation research.The constituent of acceleration signal is analyzed,and filtering to dispose pulse disturbance and to make signal smooth are applied.To remove the trend term caused by the bias of acceleration in the process of integration,three methods of heave motion estimation methods,which are based on least square method,adaptive filtering technology and frequency domain filtering,are researched.(3)Aiming at the response lag of compensation in heave compensation system,motion prediction algorithm is researched.The motion frequencies and corresponding amplitudes and phases of offshore crane's tip can be obtained by the FFT of the heave velocity and peak detection algorithm.The equation of state can be built by using extracted motion parameters,and Kalman filtering algorithm is introduced to correct these parameters,then the corrected parameters are used to predict the heave motion of offshore crane's tip.(4)The active heave compensation experimental system is built to do experimental verification.When three methods of heave motion estimation are realized in the experimental system,the available method can be determined by comparing the results from experimental system,and then the heave velocity of offshore crane's tip can be computed by motion transformation.The heave velocity can be compensation input signal to do compensation experiments to obtain compensation efficiency.The motion prediction algorithm is realized in the experimental system,and the influence factors in motion prediction are analyzed by comparing the experimental results,and then let the predicted velocity as compensation input signal to do compensation experiments to obtain compensation efficiency.The efficiencies before and after applying motion prediction algorithm are compared to validate the feasibility and necessity of motion prediction algorithm.