Chaos In Course Keeping For Ships And Its Robust Control

Ship is a complex and dynamic system which is multi-variable coupled and nonlinear with large delay and large inertia.Changes of speed and loading have influence on model parameters.And navigation environment disturbances such as high-frequency of bow by wave,can also be converted into the perturbation of model parameters and structure for ships essentially.For these factors,chaos motion is prone to occur in course keeping control for ships.Chaos motion,which plays a destructive role in course keeping,will cause ships to deviate from course or be out of control. Therefore,determining whether chaos merges and be controlled or not in the process of ship motion has theoretical and practical significance on the research of course keeping.Firstly,the paper introduces the definition,characteristics of chaos and some typical chaos equations with phase diagrams,studies the road leading to chaos and methods for identifying chaos,also lists the generalized mathematical model for course keeping control system of ships.Then,because the model is similar to forced Duffing equation,from Holmes's methodology on Duffing equation,the paper makes use of theory of differential dynamical system,bifurcation and chaos to study course keeping control.Chaos phenomenon is verified,that is,the system has Lyapunov exponent greater than 0,fractal dimension and continuous power spectrum.Finally,this thesis designs nonlinear controller applying to control chaos in course keeping for ships:exact feedback linearization theory is utilized to cancel the nonlinear terms of generalized model of ship,and then add a linear controller,which is designed by closed-loop gain shaping algorithm.The method has advantages of simple design procedure and obvious physical sense.In this thesis,the Simulink toolbox of Matlab is used to simulate control results. And the paper lists time curves of yaw rate and heading angle by adding white noise and±10%model perturbation.The simulation results show that the nonlinear controller which has strong robustness,can control chaos with satisfactory course-keeping performance.