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Article Citation - WoS: 20Citation - Scopus: 20On Optimal Age Replacement Policy for a Class of Coherent Systems(Elsevier, 2020) Eryilmaz, Serkan; Eryılmaz, Serkan; Pekalp, Mustafa Hilmi; Eryılmaz, Serkan; Industrial Engineering; Industrial EngineeringAccording to the well-known age replacement policy, the system is replaced preventively at time t or correctively at system failure, whichever occurs first. For a coherent system consisting of components having common failure time distribution which has increasing failure rate, we present necessary conditions for the existence of the unique optimal value which minimizes the mean cost rate. The conditions are mainly based on the signature which only depends on the system's structure. The results are illustrated for linear and circular consecutive type systems. (C) 2020 Elsevier B.V. All rights reserved.Article Citation - WoS: 45Citation - Scopus: 48Age-Based Preventive Maintenance for Coherent Systems With Applications To Consecutive-k-out-of-n< and Related Systems(Elsevier Sci Ltd, 2020) Eryilmaz, SerkanThis article presents a signature-based representation for the expected cost rate of age-based preventive maintenance policy for a binary coherent system consisting of independent exponential components, and then specializes the method to consecutive k-out-of-n system and its generalizations. According to the age-based preventive maintenance policy, the system is replaced at failure or before failure. For an arbitrary coherent system, the number of failed components at replacement time is a random variable. Thus, the expected cost per unit of time involves the mean number of failed components at replacement time. This mean is represented in terms of signature. Extensive numerical and graphical examples are presented for m-consecutive k-out-of-n:F and consecuthre-k-within-m-out-of-n:F systems.Article Citation - WoS: 19Citation - Scopus: 21Revisiting Discrete Time Age Replacement Policy for Phase-Type Lifetime Distributions(Elsevier, 2021) Eryilmaz, SerkanFor a system (or unit) whose lifetime is measured by the number cycles, according to the discrete time age replacement policy, it is replaced preventively after n cycles or correctively at failure, whichever oc-curs first. In this paper, discrete time age replacement policy is revisited when the lifetime of the system is modeled by a discrete phase-type distribution. In particular, the necessary conditions for the unique and finite replacement cycle which minimizes the expected cost per unit of time are obtained. The nec-essary conditions are mainly based on the behavior of the hazard rate. The results are illustrated for some special discrete phase-type lifetime distributions. Computational results are also presented for the optimal replacement cycle under specific real life setups. (c) 2021 Elsevier B.V. All rights reserved.Article Citation - WoS: 14Citation - Scopus: 15Age Based Preventive Replacement Policy for Discrete Time Coherent Systems With Independent and Identical Components(Elsevier Sci Ltd, 2023) Eryilmaz, SerkanThe paper is concerned with an age based preventive replacement policy for an arbitrary coherent system that consists of components that are independent and have common discrete lifetime distribution. The system having an arbitrary structure is replaced preventively after a specific number of cycles or correctively at its failure time. The necessary conditions for the unique and finite replacement cycle that minimize the expected cost per unit of time are obtained. The policy is studied for some particular system models including the well-known k-out-of -n structure. The findings of the paper extend the results in the literature from single unit and parallel systems to an arbitrary coherent system. Numerical results are presented for particular discrete component lifetime distributions.Article Citation - WoS: 10Citation - Scopus: 14Optimal Age Replacement Policy for Discrete Time Parallel Systems(Springer, 2023) Eryilmaz, Serkan; Tank, FatihIn the case of discrete age replacement policy, a system whose lifetime is measured by the number cycles is replaced preventively after a specific number of cycles or correctively at failure, whichever occurs first. Under the discrete setup, the policy has been mostly considered for single unit systems. In this paper, a discrete time age replacement policy is studied for a parallel system that consists of components having discretely distributed lifetimes. In particular, the necessary conditions for the unique and finite replacement cycle that minimize the expected cost rate are obtained. The theoretical results are illustrated with numerical examples to observe the effect of the cost values and the mean lifetime of the components on the optimal replacement cycle.
