Modeling And Virtual Simulation Of Underactuated Surface Vessel Motion Control System

The conventional method to control planing surface vessels is indirectly achieved through the course control which is actuated by a steering nozzle. If the planar position and course is controlled directly, we need to regulate the angle and the thrust force of the steering nozzle to control the movements in three degrees of freedom synchronously. Obviously, the control system of planing surface vessels is typical underactuated system. In order to ensure the safety of the planing surface vessel, many constraints such as the angle of the steering nozzle and radius of gyration must be in consideration in the design process of ship motion controller, otherwise it will undermine the performance of the planing surface vessels, even lead to collapse of the hull and other serious consequences. The underactuated system with constraints is essence nonlinear system, and can not be stabilized by any smooth time-invariant control law. For underactuated surface vessel (USV) lacking of effective means of control, backstepping control and predictive control are proposed in this work to deal with USV system. This study is aimed to analyze the underactuated characteristics of planing surface vessels, and guarantee the safe movement.The 6-degree of freedom and kinematic nonlinear models of the USV under consideration are derived based on Lagrangian energy method and some assumptions. For the controller design, the 3-degree of freedom dynamic and kinematic nonlinear models of the USV in horizontal plane are considered. The small time local controllability of the motion control system of the USV in horizontal plane is proved.The stabilization and tracking problems of the underactuated planning vessel are considered, respectively. For the stabilization problem, two cascaded subsystems are obtained through global diffeomorphism and feedback transformation, one can be viewed as a system perturbed by the output of the other subsystem. It proved that one of the two cascaded subsystems is globally asymptotically stable if the other system is global uniformly asymptotically stable, which enable us only design a stabilizing controller for the other system. Tracking control of underactuated surface vessel has proved to be a challenging problem, inherently nonlinear, strong coupling and not amenable to linear control theory. For the nonlinear model of tracking control system, the error system of tracking control redefined in a new form is constructed after global diffeomorphism and feedback transformations. A global tracking controller is constructed with the help of direct Lyapunov function and backstepping approach.Aimed at observing the motion of the USV under a designed control method, a 3D (Three-Dimensions) virtual simulation system was proposed based on visual simulation technology and VC++ development environment. Firstly, the surface vessel's 3D model was established by using the Multigen Creator software, and optimized by using advanced modeling techniques such as texture, material and lighting. Secondly, utilized Marine module which was provided by Vega Prime, the virtual ocean scene was created to supply the environment in which the 3D model was contained and moving, which simulated the real ocean's dynamic waves and the ship wakes. Finally, the platform was built with the use of VC++, which could be used to simulate the motion of a surface vessel and assist the design of control system for the surface vessel system.Finally, the stability controller designed to the vessel was simulated in the virtual system, providing that the designed system was valid.