Simple And Direct Nonlinear Robust Control Of Rudder/Fin Joint System

Ship roll stabilization control is one of the important research fields in ship motion control technology.Ship rudder/fin joint control system is a new roll stabilization device based on fin stabilizer and rudder roll stabilizer,which can guarantee the precision of course-keeping control and improve the effect of roll stabilization while overcoming the shortcomings of fin stabilizer and rudder roll stabilizer,thus improving ship's seaworthiness,security and comfort of crew and passenger.The thesis has made a furher study about the rudder/fin joint control system.A nonlinear mathematical model for the rudder/fin joint system has been built so as to describe the nonlinearity of ship motion.In order to effectively control rudder/fin joint system,a simple and direct nonlinear robust control algorithm based on closed-loop gain shaping algorithm and exact feedback linearization method has been presented,which is applied to the nonlinear rudder/fin joint system.Firstly,for the convenience of study on the simple and direct nonlinear robust algorithm,two nonlinear mathematical models of rudder/fin joint system have been built,considering the nonlinear characteristics of course-keeping for a given linear rudder/fin joint system.Then,according to Newton dynamical equation and based on MMG modelling method,a rudder/fin joint nonlinear mathematical model of four degrees of freedom including wind,wave and current has been built,and the calculation formulas about the parameters and hydrodynamic derivatives appearing in the model have been given in detail.In addition,the thesis points out that the deduction of the Nomoto model for ships is not very precise in the view of mathematics,and that the application range of the Nomoto model and the amendment of Nomoto model parameters for small ships and fast ships have been given.As a simplified H_∞robust control theory,the closed-loop gain shaping algorithm constructs the controller K using four parameters with engineering sense,which is a simple and direct control algorithm based on symmetric information.At present,the closed-loop gain shaping algorithm can't independently design the controller for MIMO nonlinear system,so it is combined with exact feedback linearization method and extended to MIMO nonlinear system.According to the characteristics of the exact feedback linearization method,two simple and direct nonlinear robust control algorithms for r = n and r