A multi-objective multi-state degraded system to optimize maintenance/repair costs and system availability

In this study, a multi-state degraded system is studied, where status of system is continuously degrading over time. as time progresses, system may either deteriorate gradually and go to lower performance state, or it may fail suddenly. if the system fails, some repairs are carried out to restore the system to the previous state. when the inspections reveal that the system has reached its last acceptable state, a pm is carried out to restore the system to the higher performance states. the goal is to find the optimal pm level, so that the mean availability of the system is maximized and the total cost of the system is minimized. in this regard, markov process is employed to represent different states of system. an integrated optimization approach is also suggested based on the desirability function of statistical approach. the suggested aggregation method is robust to the potential dependency between the total cost and the mean availability. it also ensures that both objective functions fall in decision-maker's acceptable region. in order to show the efficiency of the proposed approach, a numerical example is presented and analyzed.