On the modelling, analysis and optimization of system reliability

This thesis is concerned with techniques for the improvement of system reliability. It is directed towards the problem of optimum system design of maintained and unmaintained systems from a reliability view point.For unmaintained systems the application of standbys as a means of increasing system reliability is considered. A model that takes account of three different modes of switch malfunction is developed and from the model explicit reliability expressions are derived. Making use of these explicit expressions the performance of standbys in digital systems is studied and the optimum system design problem of standby systems is formulated.For maintained systems a mathematical model is developed to study the effects of imperfect maintenance and from the model conditions under which preventive maintenance is beneficial are derived. A new maintenance model which includes a repair limit policy is developed and the problem of optimum design of maintained systems is formulated as a non-linear constraint optimization problem. Different methods for solving this type of problem are discussed and a post-optimality analysis of reliability problems is also given.Finally problems associated with a system whose failure/repair process is non-Markovian are discussed and an analysis technique presented.