Research On The Path Keeping And Path Following For A Ship Sailing In Restricted Waters

Restricted waters refer to the water areas,which is restricted by water depth and channel bank or where exists obstacles such as bridge piers,other berthed/navigating ships and so on.The hydrodynamics and motion behaviors of a ship sailing in restricted waters has the following characteristics:1)A ship sailing along the channel bank is affected by ship-bank interactions,and a bank suction force and a bow-out moment acting on the ship make it lose its ability to maintain straight-line navigation and even cause it collide with the bank;2)Since the traffic density is large,the distance among ships is small,the ships are easily affected by ship-ship interactions and even collide each other;3)A ship sailing in restricted waters has low speed and poor steering ability,which makes it easily affected by the external environmental disturbances,especially the wind;4)When a ship sailing along the channel bank in shallow water,its hydrodynamic force is affected by the varying water depth and ship-bank interactions,resulting in uncertainties of the force and ship motion.In order to ensure the safe navigation of a ship sailing in restricted waters,a reasonable control of ship motion is necessary;while the above mentioned characteristics make the motion control difficult due to the model uncertainties and external environmental disturbances,and the poor steering ability makes the control problem even more difficult and complicated.Therefore,study of the motion control for a ship sailing in restricted waters is very important and has practical reference values.In this thesis,the path keeping and path following control of a ship sailing in restricted waters is studied.In the path keeping,a path keeping controller is designed to make the ship return to and maintain the original path under ship-ship interactions.In the path following,a path following controller is designed to make the ship starting from any initial positions follow the desired path independent of time.First,the path keeping problem under ship-ship interactions is studied;then,the path following problem under wind effect is studied,a state feedback controller and an output feedback controller are designed respectively;at last,the path following problem in shallow water with varying depth is studied.The details are as follows:In the first part(Chapter 3),a path keeping controller is designed based on the input-output feedback dynamic compensation linearization method.In the path keeping problem,both the lateral position and the yaw angle need to be considered,while only one control input(the rudder angle)is available,thus this is an underactuated control problem.To solve this problem,a new output is defined by combining linearly the lateral position and the yaw angle;the input-output feedback linearization method is adopted according to the newly defined output,and a fourth order single-input multiple-output nonlinear system is transformed into a second order single-input single-output linear system.By reasonably selecting the linear coefficient in the newly defined outputs,the stability of the system's internal dynamics is guaranteed.To solve the model uncertainties and external disturbances existing in the second order system,the extended state observer is adopted to estimate the unknown term in real time,and the estimation is substituted in the input-output feedback linearization method to obtain the path keeping controller for a ship sailing in restricted waters,which can make the ship return to the original path in spite of ship-ship interactions and model uncertainties.Theoretical analysis and simulation experiments have validated the proposed path keeping control strategy.In the second part(Chapter 4),a path following controller is designed based on the optimal robust H?guaranteed cost control under wind effect.For a ship sailing in restricted waters,the model parameters vary with ship-bank distance;by regarding the lateral position as a time varying parameter with bounded norm,the ship motion model can be constructed as a linear uncertain system with the varying parameter.The integral of the error between the ship's lateral position and the desired value is extended to the original linear uncertain system;a robust H_?guaranteed cost controller is designed according to the guaranteed cost control and the robust H_?technique,which is robust to model uncertainties and external disturbances.According to the Schur complement lemma,the problem of solving the robust H_?guaranteed cost control turns to solve the convex optimization problems with linear matrix inequalities.Theoretical analysis and simulation experiments are carried out to validate the proposed path following control strategy.In the third part(Chapter 5),an output feedback path following controller for a ship sailing in restricted waters is designed based on the updated-gain high-gain state observer.The high-gain state observer can fast reconstruct system states,and is robust to model uncertainties and process disturbances.However,it is sensitive to measurement noises in the steady state.To solve this problem,the updated gain is adopted to obtain the updated-gain high gain state observer.In this way,not only the advantages of the high gain state observer are preserved,but also the influence of measurement noise on the system is suppressed.The state estimation is substituted into the state feedback controller designed in the second part,and the output feedback controller based on state observer is obtained.Theoretical analysis and simulation experiments are carried out to validate the proposed control strategy.In the fourth part(Chapter 6),a path following controller for a ship sailing along the channel bank in water of varying depth is designed based on the modified LOS guidance law and the adaptive sliding mode control technology.In the shallow water with varying water depth,the ship-bank interactions vary with water depth,which gives rise to time varying drift angle.To solve this problem,a high-gain extended state observer(HGESO)is designed to estimate the time varying drift angle,and the estimated value is substituted into the LOS guidance law to obtain the HGESO based LOS guidance law.Furthermore,to deal with the unknown model parameters and the external disturbances in the yaw control system,the adaptive technique and the sliding model control technology are adopted to design the yaw tracking control system.Combining the guidance system and the control system to obtain the path following control system,the ship sailing along the channel bank in varying-depth water can follow the desired path without steady-state error.Based on Lyapunov theorem and cascade system theory,the stability of the closed-loop control system is analyzed and verified.Simulation comparisons are carried out to validate the effectiveness of the proposed control strategy.In this thesis,the path keeping and path following problem for a ship sailing in restricted waters are studied,and corresponding control strategies are designed for the specific problems.Through theoretical analysis and simulation experiments,the stability and performance of the closed-loop system under each control strategy are validated,which provides a theoretical basis and practical reference for the path keeping and path following of a ship sailing in restricted waters.