Availability optimisation of multi-state series-parallel systems with human failures

Nowadays, the availability of systems and tendency to commit errors has become an important issue during the design of many engineering systems. Humans play a key role in the overall availability of engineering systems because many systems are interconnected by human links to a certain degree. Obviously, if the system is multi-state, methods to achieve the availability values of the system have an important role. In this paper, a redundancy optimisation problem for multi-state systems subject to human failures is formulated to minimise the system cost. Human failures are recognised with a fault tree analysis method, the universal generating function algorithm is used to compute the system availability and the genetic algorithm to optimise the system structure. To illustrate the credibility and applicability of the model, a case study is offered and analysed. The result of the solved model is corroborated and shows the efficiency of the used methods.