Research On The Integrated Rudder/fin Roll Stabilization And Its Control Methods

The ship sailing in the seaway rolls under the actions of waves.Rolling can make passengers uncomfortable,disturb the work of crew,influence the working of equipments on board,make cargoes damaged and lost,and reduce the applicable range of ship.Severe rollings even cause accident,which threatens the safety of ship.Roll stabilization of ship is significant to ensure the performance and safty of the ship,and extend the application range of the ship.In this paper,the integrated rudder/fin roll stabilization is studied to enhance the roll stabilization performance of the ship.To reduce rolling,ships require high performance in stabilization usually equipped with roll stabilization devices.Fin stabilizers are installed on the bilges of ship.Fin stabilizer is compact,reliable and efficient,which makes it the most commonly adopted for roll reduction.Rudder is mainly used to control the heading of ship.For the hydrodynamic force acting on the rudder produces both yaw moment and roll moment,the deflection of rudder not only causes yaw motion but also causes roll motion.The control of heading and rolling can be sapareated in frequency,as a reault,the rudder can be used to reduce rolling and control heading simultaneously.There are interactions between the control effects of rudder and fins.In some cases,the force produced by rudder under the control of autopilot couples with the force from waves,the roll of ship will be enlarged and the stailization performance of the fin stabilizer will be reduced.If the control effect of rudder to roll can be made use of,and the rudder works in coordination with fins,the roll stabilization performance will be enhanced.This paper focuses on the study of the principle and application of the integrated rudder/fin stabilization.Former studies are collected and studied,based on which the mathematical model of integrated rudder/fin stabiliztion is established,the problems to be dealed with are analyzed.Novel control methods are proposed,which are adopted with other control methods to improve the proformance of the integrated rudder/fin satblization.Scale model experiment is carried in order to verify the feasibility of integrated rudder/fin control adopted on the targed ship.The main results of this paper are as follows:Integrated rudder/fin control enhances the roll stabilization performance with rudder based on the roll stabilization of fin stabilizer.Therefore a good rudder roll stabilization is very important to the problem.According to the control requirements of the rudder roll stabilization,the MPC controller with disturbance compensation mechanism is proposed to achieve the rudder roll stabilization.The MPC can deal with MIMO control problems and achieve multi-objective optimization with state and input constraints.The disturbance compensation method should be carried out based on existing controllers to improve the control performance.It lumps the model mismatch and external disturbance according to the nominal model,and compensates the influence of the lumped disturbance by adding feedfowrd component in the control commands.The method can enhance the disturbance rejection performance and makes the controller robust to model uncertainty.Based on the rudder roll stabilization control method,the distributed MPC with disturbance compensation mechanism is proposed according to the control requirements of the integrated rudder/fin control.For the control requirements of rudder and fins are different and the dynamics of rudder and fins are different,the rudder and fins will not show their full capabilities while being controlled in the same MPC controller.The distributed MPC controls subsystems with different MPC controllers,and make them work in coordination by communications.In this paper,MPC controllers with different prediction times and control parameters are designed for rudder and fins,the rudder command is transmitted to the fin controller to make fins work in coordination with rudder.An extended state observer based on high order sliding mode differentiator is adopted to estimate the lumped disturbance.The lumped disturbance is adopted in the prediction of ship actions by the MPC controllers,to achieve the disturbance feed-forward compensation.The influences of actuator saturation to rudder roll stabilization and integrated rudder/fin control are studied in this paper.The model recovery anti-windup compensator is designed to reduce influences.Saturation limits actions of actuators,introduces nonlinearity to the model of controlled plant and makes the controller ineffective,which can induce severe deterioration in control performance.The model recovery anti-windup compensator recovers the model of the controlled plant from the viewpoint of the controller while actuators saturate,which makes the controller more effective and makes the constrained plant works like the unconstrained plant as much as possible.