A New Method to Determine the Failure Frequency of a Complex System

Two key indices in system reliability evaluation are the probability that the system is failed and the frequency of system failure. Other measures such as the mean cycle time and the mean down time can be easily derived from these quantities. This paper considers the reliability evaluation of a complex maintainable system using a cut set approach. The available literature on this subject generally deals with the failure probabilities. The technique proposed by Buzacott to determine the frequency of failure has the drawback that explicit formulae for system availability must be first derived. Numerical values are then obtained by further manipulation. This approach is, therefore, not suitable for computer application. The contribution of this paper is the development of a new formula for the frequency of system failure using a cut set approach, from which the numerical values can be obtained directly. This method overcomes the drawback of Buzacott's method and is suitable for computer application. Upper and lower bounds for frequency are also given and the method is illustrated by an example.