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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 may have rise 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 exclusively 50% longer. 9.3 REDUNDANCY LIMITATIONS The results for active and standby dependability presented thus far atomic number 18 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 predominate in determine the level of reliability which can be achieved. For active agree systems, third estate mode ills and accuse sharing phenomena tend to be of most concern. For standby systems, reverse failures and failure of the standby unit before switching are important considerations. Common-Mode Failures Common-mode failures are caused by phenomena that create dependencies between both or more redundant components which cause them to fail simultaneously. such 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 upkeep problems, or a drove of other factors. In mercenary aviation, for example, a great deal of redundancy is employed, bothowing high levels of resort to be achieved. Thus when problems do occur frequendy they may be attributed to common-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 prove all of the redundant hydraulic control lines and caused the crash of a DC 10. Viewed irl terms of the reliability block diagrams i n Fig. 9.2, commonmode failure mechanisms ha! ve 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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