Research On Semi-active Heave Compensation System In Offshore Crane

During practical work,offshore cranes are affected by wind and waves,which will produce six free movements:roll,pitch,yaw,pitch and heave.Among them,heave has the greatest negative impact on offshore cranes,which may lead to the reduction of its working efficiency and safety accidents.In this paper,taking a heavy load offshore crane as the research object,a semi-active heave compensation system is proposed.The main contents include the following aspects:(1)Summarize the national and international research results of semi-active heave compensation,and put forward a scheme of semi-active heave compensation system for offshore cranes with heavy load and high sea conditions.The system adopts hydraulic parallel structure and has two working modes:passive and semi-active.According to this scheme,the important components of the compensation system are designed and calculated.(2)The passive heave compensation system is modeled and simulated.The passive heave compensation system,wire rope and load are simplified to a spring-damping structure,in which the nonlinear friction force on the hydraulic cylinder is an important factor affecting the compensation effect.Therefore,according to the characteristics of passive compensation cylinder friction,the thickness of lubricating oil film is introduced to establish an extended LuGre friction model.The simulation results shows that the passive heave compensation system has a good compensation effect when the load and sea conditions are unchanged,but when the load and sea conditions change,the compensation efficiency decreases,so it is necessary to add active heave compensation to obtain better compensation effect and deal with the change of parameters.(3)The semi-active heave compensation system is modeled and simulated.Considering the coupling relationship between the active compensation part and the passive compensation part,the displacement and speed of the load and the pressure in the hydraulic cylinder are set as state variables,and the state equation of the semi-active heave compensation system is established.Because PID control is difficult to solve the problems of external disturbance and complicated sea conditions of semi-active heave compensation system,a disturbance observer based on extended state variables is proposed,which can estimate the external disturbance value in real time.Nonlinear cascade control is introduced,with displacement control as the outer loop and pressure control as the inner loop,and sliding mode control is used to reduce observation error.Improve the control accuracy.Through simulation analysis,it is found that this control method has good anti-interference ability and robustness.(4)In order to verify the effectiveness of the passive heave compensation system model proposed in this paper,a passive compensation experiment was carried out.A passive heave compensation device was built.During the experiment,the parameters such as gas volume,hydraulic oil pipe diameter and ship heave motion period were changed.Comparative experiments were carried out,and the conclusions were as follows:The friction force of hydraulic cylinder has great influence on the passive heave compensation system.Increasing the diameter of hydraulic oil pipe or the total volume of accumulator can improve the efficiency of passive heave compensation system.The experimental parameters are substituted into the simulation model,and it is found that the simulation results are similar to the experimental results,which verifies the correctness of the simulation model and the experimental scheme.