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] ] 1 1 T T X MTTF, X MTTF, (1 - Vl - R) (1 - Vl - R) ?] ?] (1 - Vl - 0.9) (1 - Vl - 0.9) 1 1 X MTTF = 0.380 MTTF. X MTTF = 0.380 MTTF. Thus the purposeless system whitethorn have well up four times the design life of the single system, regular though it may be seen from Eq. 9.15 that the MTTF of the redundant system is only when 50% longer. 9.3 REDUNDANCY LIMITATIONS The results for active and standby reliability presented accordingly far are highly i pass aroundized. In practice, a function of factors can significantly reduce the reliability of redundant systems. In reality, these factors and their mitigation often are plethoric in determine the level of reliability which can be achieved. For active agree systems, third estate mode mischances and shoot down sharing phenomena tend to be of most concern. For standby systems, displacement failures and failure of the standby unit before switching are important considerations. Common-Mode F ailures Common-mode failures are caused by phenomena that create dependencies between ii or more redundant components which cause them to fail simultaneously. such(prenominal) failures have the potential for negating oftentimes of the benefit gained with redundant configurations.

Common-mode failures may be caused by common electric connections, shared environmental stresses such as system or vibration, common caution problems, or a drove of other factors. In mercantile aviation, for example, a great deal of redundancy is employed, bothowing high levels of preventative to be achieved. Thus when problems do o ccur frequendy they may be attributed to com! mon-mode failures: the dust rising from a volcanic eruption in Alaska that caused simultaneous malfunctioning of all of a commercial airliners engines, or the pieces of a fractured kilobyte engine turbine blade that shrink all of the redundant hydraulic control lines and caused the crash of a DC 10. Viewed irl terms of the reliability block diagrams in Fig. 9.2, commonmode failure mechanisms have the same takings as putting in an...If you want to get a full essay, order it on our website: OrderCustomPaper.com

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