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3 Journal of Polish Safety and Reliability Association

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On a general standby system and its optimization

Cha J. H., Yun W. Y.

Journal of Polish Safety and Reliability Association

2009

Vol. 1

95--100

Redundancy or standby is a technique that has been widely applied to improving system reliability and availability in the stage of system design. In this paper, we consider a standby system with two units in which the first unit (unit 1) starts its operation under active state and the other unit (unit 2) is under cold standby state at the starting point. After a specified time s (switching time), the state of unit 2 is changed to warm standby state and, as soon as the operating unit 1 fails, the state of unit 2 is changed to active state. If unit 1 fails before times, the system fails. Units can fail at both active and warm standby states. A general method for modeling the standby system is adopted and, based on it, system performance measures (system reliability and mean life) are derived. We consider the problem of determining optimal switching time which maximizes the expected system life. Some numerical examples are studied.

Burn-in procedures in accelerated environment and system maintenance policies

Cha J. H.

Journal of Polish Safety and Reliability Association

2008

Vol. 1

101--107

Burn-in is a widely used engineering method which is adopted to eliminate defective items before they are shipped to customers or put into field operation. In order to shorten the burn-in process, burn-in is most often accomplished in an accelerated environment. However, there have been few probabilistic or stochastic models for the burn-in procedures in accelerated environment. In this paper, under a new stochastic model for accelerated burn-in procedure, the problems of determining both optimal accelerated burn-in time and optimal replacement policy are considered. Components are burned-in under an accelerated environment, then those surviving the burn-in procedure are put into field operation and they are maintained under a replacement policy. The properties of the optimal accelerated burn-in time and optimal replacement policy are obtained and a numerical example which illustrates the usage of obtained results will be presented.

A study on the performance measures of a system operated in random environment

Cha J. H., Mi J.

Journal of Polish Safety and Reliability Association

2007

Vol. 1

55--58

Most devices (systems) are operated under different environmental conditions. The failure process of a system not only depends on the intrinsic characteristic of the system itself but also on the external environmental conditions under which the system is being operated. In this article we study a stochastic failure model in random environment and investigate the effect of the environmental factors on the failure process of the system. Some stochastic orderings will also be briefly discussed.