Preventive replacement is applied to improve the device availability or increase the profit per unit time of the maintenance system.
In this paper, we study age-replacement model of technical object for n-state system model. The criteria function applied in this
paper describe profit per unit time or coefficient of availability. The probability distribution of a unit‘s failure time is assumed to be
known, and preventive replacement strategy will be used over very long period of time. We investigate the problem of maximization
of profit per unit time and coefficient availability for increasing the failure rate function of the lifetime and for a wider class of lifetime. The purpose of this paper is to obtain conditions under which the profit per unit time approaches a maximum. In this paper
we shows that the criteria function (profit per unit time or coefficient availability) can be expressed using the matrix calculation
method. Finally, a numerical example to evaluate an optimal replacement age is presented.
The paper presents a mathematical model of the system of repairs and preventive replacements by age of city buses. The mathematical model was developed using the theory of semi-Markov processes. In the model developed, four types of city bus renewal processes are considered and three types of corrective repairs and preventive replacement. Corrective repairs are considered in two types: minimal repairs (repairs carried out by the Technical Service units) and perfect repairs (repairs carried out at the stations of the Service Station). The models of restoration systems that use semi-Markov processes in which minimal repairs, perfect repairs, and preventive replacements by age, have been examined in the literature to a limited extent. The system under consideration is analysed from the point of view of two criteria: profit per time unit and availability of city buses to carry out the assigned transport tasks. Conditions of criterion functions’ extremum (maximum) existence were formulated for the adopted assumptions. The considerations presented in the paper are illustrated by exemplary results of calculations.
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