Study Of Robust Control Of Rudder/Fin Joint System

Traditional ship direction keeping and rolling stabilization are referred to be two different problems. Now,multiple-input and multiple-output rudder/fin joint control system is growingly important as the delving of ship maneuvering and modern control theories. But all of the researches are based on the linear model of ship motion,no matter using optimistic control,LQG control or fuzzy control. The non-linear ship motion is neglected. The rolling and the horizontal motion of ship are coupled intensely. Meanwhile,the coupling motion is often presented as non-linear function according to experiment results and the ship is usually disturbed by sea wave when it cruises. So the motion of ship is a coupling,non-linear process with large disturbance. The paper designs a rudder/fin joint control system based on the non-linear motion model of ship,which has nice performance on attenuating the rolling as well as controlling the direction of the ship.First,ship motion equation of rearing,pitching and rolling are founded based on momentum theory and momentum torque theory,and the force and torque exert by the sea are studied,including the force of water on the ship,on the rudder and the fin,and the disturbance of the sea wave. Sea wave high,pitching force,rolling force and rearing torque simulation algorithms are put forward.Secondly,the non-linear model of ship motion was studied. The non-linear term and the term related to pitching velocity are referred to disturbance of the system to get state feedback designed mathematic model of the rudder/fin joint control system. The non-linear rudder/fin joint control system-designing problem was transformed into disturbance attenuation linear system designing problem,which uses quadratic performance as object function. The object satisfied orthogonal condition,by introducing the proper scaling matrix. After verification of the pre-condition,the controller was designed,using the resolving method of state feedback standard control problem based on Riccati inequality. The author choosed weighting matrix for different sea conditions,designed the controller and the rudder/fin joint control system.Finally,the author simulated the controller with MATLAB. According to the simulation curves and data,we could find that the controller designed using state feedback control theory has nice control performance on rearing and rolling,but the control performance on pitching is not very good. The controlling goals are reached.