Periodical Pm Policies For A Two‐unit System With Failure Rate Interaction

In this thesis, two periodical preventive maintenance (PM) models for atwo-unit system subject to failure rate interaction between units arepresented.For a two-unit system, without failure interaction between units, thefailure rates of units also increase with age by ageing process respectively.Considering the failure rate interaction, unit1’s failure rate of is affected byunit2through an adjustment factor which is a non-decreasing function ofunit2’s cumulative failure number. The adjustment factor varies with time.In model1, preventive maintenances that unit1is replaced areperformed every fixed time T as well as the two-unit system is all replacedat the Nth preventive maintenance. Each unit fails during periods betweensuccessive PM, a minimal repair is performed. To derive the long-runexpected cost per unit time by introducing relative costs as a criterion ofoptimality in order to determine an optimal interval between successive PMand the optimal number of PM before the system replacement that minimizethe expected cost rate.In model2, maintenance policy is periodical imperfect preventivemaintenance. An improvement factor model is constructed to describe theeffect of maintenance on machine, considering the maintenance cost, systemage, study effect of maintenance activities. Based on the model1, to derivethe expected cost per unit time under reliability constrain.Finally, two numerical examples are given to illustrate two models,respectively, using Matlab program to find out the optimal solution andpresenting the sensitivity analysis for major parameters.