Extended block replacement policy of a system subject to shocks

A generalization of the block replacement (BR) policy is proposed and analyzed for a system subject to shocks. Under such a policy, an operating system is preventively replaced by new ones at times i/spl middot/T (i=1,2,3,...) independently of its failure history. If the system fails in: (a) ((i-1)/spl middot/T, (i-1)/spl middot/T+T/sub 0/), it is either replaced by a new one or minimally repaired; or (b) ((i-1)/spl middot/T+T/sub 0/, i/spl middot/T), it is either minimally repaired or remains inactive until the next planned replacement. The choice of these two actions is based on some mechanism (modeled as random) which depends on the number of shocks since the latest replacement. The average cost rate is obtained using the results of renewal reward theory. The model with two variables is transformed into a model with one variable and the optimum policy is discussed. Various special cases are considered. The results extend many of the well-known results for BR policies.