Time Scale Analysis Based Rudder Roll Stabilization Techniques In Ship Path-Following Problem

With the development of international shipping and ocean engineering,together with the high demands of warships,the control and maneuvering ability of ships have become very im-portant nowadays.For example,ships with wide hull are very vulnerable to the large roll mo-tions,which cause the stability loss and even capsizing of the ships and goods.Thus the study of roll reduction control is quite necessary in ship control community.In recent years,more attentions have been paid in the path-following,trajectory tracking and roll reduction control,which are more complicated than the traditional course-keeping and track keeping problems.The modern ship motion control issues are big challenges for researchers,due to the huge complexity of the system nonlinearity and environmental disturbances.The difficulties include:the ship motion system is under-actuated and highly nonlinear,together with considerable sys-tem uncertainties.Many modern control laws introduced in path-following problem are difficult to use in industry.The rudder forces are too limited to give an effective control input.The so-called non-minimum phase characteristic makes it very difficult to reduce the roll motion.This thesis studies a comprehensive problem:rudder roll control（RRS）in the path-following problem using singular perturbation techniques and （?）₁adaptive control.At first,this problem is decoupled into two subproblems,a path-following control problem and a traditional RRS control problem in course-keeping situation.Then,the subproblems are combined to-gether to handle the comprehensive problem.It should be noted that these problems are current research focuses.This thesis introduces new control strategies to these problems:1.Introducing （?）₁adaptive control to the path-following problem,which obtains a accurate and robust tracking performance.2.The RRS system being decoupled into a slow course-keeping subsystem and a fast roll motion subsysetem based on singular perturbation strategy.3.Combining the （?）₁adaptive control with singular perturbation strategy to study the RRS problem in path-following problem.The ship motion models of 1-DoF,3-DoF and 4-DoF are used in this thesis to deal with different control problems.The models are of top importance in control design.The main principle of selecting a mathematical model is to make it as simple as possible when the accuracy is guaranteed.This thesis describes several techniques in simplifying the mathematical model in different situations.Besides,a brief introduction of the （?）₁adaptive control and singular perturbation theory is given.A robust path-following performance is obtained by using the （?）₁adaptive control strategy.The system uncertainty is very important in path-following problem.This system uncertainty is introduced by the environmental disturbances and the complexity of the tracking path.（?）₁adap-tive control has very fast adaption speed and relative simple form,and it has a solid background based on the （?）₁-norm theory.The guidance-based strategy is used in this thesis to decouple the whole system into a guidance subsystem and a control subsystem.In the guidance subsystem,the whole system is described in a revised Serret-Frenet frame,which transforms the original tracking problem to a regulation problem.The control subsystem considers the dynamics of system.By taking into account the desired heading rate given by the guidance subsystem,the （?）₁adaptive control subsystem gives out the rudder commands.An adaptive Nomoto model is introduced to describe the heading motion in the revised Serret-Frenet frame.All the system uncertainty is assumed to be captured by an adaptive parameterσ,which is identified by the （?）₁adaptive strategy on-line.As soon as the stable value ofσis obtained,the output of the system are usually satisfying under the adaptive control.The system uncertainties caused by the wave forces and the geometrical complexity of the path are also investigated.The time scale decomposition techniques based on singular perturbation are introduced to the RRS system.The traditional RRS system used in course-keeping problem is discussed.Different from the traditional frequency domain control laws,the RRS system is described in time domain in this thesis,where the more details of the system states can be obtained.Due to the fact that the roll motion is much faster than the motions in other DoFs,singular perturbation method is used to decouple the whole system into a slow heading motion subsystem and a fast roll motion subsystem.The coupling effects are also considered by the quasi-steady-state equi-librium（QSSE）.These coupling effects are important in some cases such as the steady turning motion.The standard procedures of singular perturbation are:describe the motion system in a singular perturbation form,calculate the QSSE,and decouple the system into two different time scale subsystems,introduce a new time scale in the fast subsystem,where the slow states are regarded as constants,design the control strategy individually in each subsystem,combine the separate control laws and give the final control input.The detailed analysis about stability and robustness is conducted in this thesis.The RRS control in path-following problem is dealt with by combining （?）₁adaptive control and singular perturbation strategy.There are two control objectives in this part:path-following performance and the roll reduction performance.The path-following performance is considered as the primary objective and the roll reduction performance as the secondary one.The path-following performance is important to the roll reduction performance,mainly due to the follow-ing facts:the wave forces and path complexity add the uncertainties to the system,a strategy should be made to allocate the rudder input bandwidth to each subsystem,enough bandwidth separation gap should be guaranteed to avoid the interference between each subsystem.Under such circumstances,the robust control performance of （?）₁adaptive control is of top importance.The simulation shows that the path-following performance is stable and robust to the large wave disturbances and complex tracking path under the （?）₁adaptive control.The rudder commands are also mild and stable,thus leaves large control bandwidth to the roll reduction subsystem.The path-following and roll reduction performances are evaluated in this thesis,which show satisfying results.Based on （?）₁adaptive control and singular perturbation strategy,this thesis introduces a new time domain analysis framework to the 4-DoF ship motion control problem.The system uncertainty,nonlinearity and geometric complexity can be simplified to some extent under such analysis framework.