Availability Models of Maintained Systems

The concept of availability includes reliability as well as preventive and corrective maintenance. An availability model which includes both aspects of this problem is proposed in this paper. The model includes the following decision variables: 1. failure rates and repair rates of individual units 2. the time period for perfect-preventive maintenance for a given mission time 3. the optimal failure and repair rates as a function of design costs, corrective and preventive maintenance costs. The objective is to minimize the design and operating costs where the availability requirements are satisfied. An example is solved for a system with n subsystems in series where two units in parallel comprise each subsystem. The general approach is applicable to solving other complex availability problems.