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Optimal Allocation of Active Spares in Series Systems and Comparison of Component and System Redundancies

Part of: Operations research and management science Distribution theory - Probability Special processes

Published online by Cambridge University Press:  14 July 2016

Neeraj Misra ,
Ishwari D. Dhariyal  and
Nitin Gupta
Neeraj Misra*
Affiliation:
Indian Institute of Technology Kanpur
Ishwari D. Dhariyal*
Affiliation:
Indian Institute of Technology Kanpur
Nitin Gupta*
Affiliation:
Indian Institute of Technology Kanpur
*
∗Postal address: Department of Mathematics and Statistics, Indian Institute of Technology Kanpur, Kanpur, 208016, India.
∗∗Email address: guptan@iitk.ac.in
∗Postal address: Department of Mathematics and Statistics, Indian Institute of Technology Kanpur, Kanpur, 208016, India.
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Abstract

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We consider the problem of allocating k active spares to n components of a series system in order to optimize its lifetime. Under the hypotheses that lifetimes of n components are identically distributed with distribution function F(⋅), lifetimes of k spares are identically distributed with distribution function G(⋅), lifetimes of components and spares are independently distributed, and that ln(G(x))/ln(F(x)) is increasing in x, we show that the strategy of balanced allocation of spares optimizes the failure rate function of the system. Furthermore, under the hypotheses that lifetimes of n components are stochastically ordered, lifetimes of k spares are identically distributed, and that lifetimes of components and spares are independently distributed, we show that the strategy of balanced allocation of spares is superior to the strategy of allocating a larger number of components to stronger components. For coherent systems consisting of n identical components with n identical redundant (spare) components, we compare strategies of component and system redundancies under the criteria of reversed failure rate and likelihood ratio orderings. When spares and original components do not necessarily match in their life distributions, we provide a sufficient condition, on the structure of the coherent system, for the strategy of component redundancy to be superior to the strategy of system redundancy under reversed failure rate ordering. As a consequence, we show that, for r-out-of-n systems, the strategy of component redundancy is superior to the strategy of system redundancy under the criterion of reversed failure rate ordering. When spares and original components match in their life distributions, we provide a necessary and sufficient condition, on the structure of the coherent system, for the strategy of component redundancy to be superior to the strategy of system redundancy under the likelihood ratio ordering. As a consequence, we show that, for r-out-of-n systems, with spares and original components matching in their life distributions, the strategy of component redundancy is superior to the strategy of system redundancy under the likelihood ratio ordering.

Keywords

Active redundancysystem redundancycomponent redundancycoherent systemstochastic orderingSchur concaveSchur convex

MSC classification

Secondary: 90B25: Reliability, availability, maintenance, inspection 60E15: Inequalities; stochastic orderings 60K10: Applications (reliability, demand theory, etc.)
Type
Research Article
Information
Journal of Applied Probability , Volume 46 , Issue 1 , March 2009 , pp. 19 - 34
Copyright
Copyright © Applied Probability Trust 2009 

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