Dependability Modelling and Sensitivity Analysis of Scheduled Maintenance Systems

In this paper we present a new modelling approach for dependability evaluation and sensitivity analysis of Scheduled Maintenance Systems, based on a Deterministic and Stochastic Petri Net approach. The DSPN approach offers significant advantages in terms of easiness and clearness of modelling with respect to the existing Markov chain based tools, drastically limiting the amount of user-assistance needed to define the model. At the same time, these improved modelling capabilities do not result in additional computational costs. Indeed, the evaluation of the DSPN model of SMS is supported by an efficient and fully automatable analytical solution technique for the time-dependent marking occupation probabilities. Moreover, the existence of such explicit analytical solution allows to obtain the sensitivity functions of the dependability measures with respect to the variation of the parameter values. These sensitivity functions can be conveniently employed to analytically evaluate the effects that parameter variations have on the measures of interest.