Optimisation of sliding mode controllers for marine applications : a study of methods and implementation issues
The optimisation of Sliding Mode controllers for marine vehicle guidance is presented in this thesis. This study is concerned with two optimisation methods which are based on natural processes. The first is Simulated Annealing which involves processes analogous to those involved in the cooling process in metallurgy. The second involves Genetic Algorithms which are based on the evolutionary process of species and genetics. These methods are evaluated through studying their application to the optimisation of controller parameters for particular marine vessels. Their performance is measured through simulation studies during the optimisation process. Existing literature in the fields of the two optimisation techniques, Sliding Mode control and marine control is surveyed. The theory of Simulated Annealing is presented in terms of the optimisation process and its convergence properties through Markov Chain analysis. A novel variation of this method, Segmented Simulated Annealing, is also outlined and evaluated in terms of its improved convergence properties. The theory of Genetic Algorithms is presented in terms of its process and convergence properties using Markov Chains and the Schema Theorem. The derivation of a decoupled Sliding Mode control theory is described and its well known stability robust properties are ensured by the choice of an appropriate set of design criteria. The elimination of the chattering phenomenon is achieved by soft switching which ensures performance robustness. The application of Sliding Mode controllers for governing the motion of three marine vehicles and their subsequent optimisation is presented. The first is the simulation of a linear mathematical representation of a military submarine. The second is the simulation of a non-linear mathematical representation of a super tanker. The third is an actual scale model of a supply ship which enables evaluation of the optimised controllers in a laboratory water basin facility.