A Markov chain based study on the availability of ship systems of a naval vessel

Abstract

During the early stages of ship design exploration, design freedom is abundant but problem knowledge is scarce and most costs are already committed. This amounts to an incentive to look at the influences of the requirements on a design, to better understand how a concept is defined. This thesis investigates the operational architecture concerning how systems are used (often in a temporal fashion). A way to quantify the operational architecture is with operability, which describes the ability of a ship to perform its mission. This thesis identified the system performance consisting of availability and vulnerability part of operability as its main topic. Markov theory was selected to assess the availability of systems in order to maximize the operability of a naval vessel. Transition rates of systems are a key element of Markov theory but are hard to obtain during Early Stage Ship Design. A network-theory-based approach allocated nonquantifiable focus points to each system to determine their importance within a network. These were then linked to transition rates, which are required for a Markov chain to calculate the availability of a system. Four case studies were performed to test the model: several configurations were compared, two different focus points approaches were used, different ranges of rates were applied, and systems were added or subtracted. The model proved to behave according to educated guesses beforehand but also gave new insights in connections between nodes. The eigenvector centrality approach used to allocate focus points was found to be better than the combined connectivity approach. The scale of the ranges of rates should not result in very high values for system availability since they do not provide data which makes comparisons between network configurations possible. Very low values of system availability were deemed too far off from real-life values. This thesis paves the road towards a total assessment of operability. It has focused on the availability of systems, and delivered a method to make preliminary decisions for systems design in the early stages.