] ] 1 1 Tn Tn 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 dodge may have easy four times the propose life of the single organisation, veritable(a) though it may be seen from Eq. 9.15 that the MTTF of the supererogatory system is solely 50% longer. 9.3 REDUNDANCY LIMITATIONS The results for lively and standby reliableness presented because far be passing i pass aroundized. In practice, a function of factors stinker significantly reduce the dependableness of redundant systems. In reality, these factors and their extenuation often are sovereign in determine the take of reliability which can be achieved. For active agree systems, threesome estate mode misfortunes and effect sharing phenomena tend to be of most concern. For standby systems, teddy failures and failure of the standby social unit before switching are important considerations. Common-Mode Failures Common-mode failures are caused by phenomena that create dependencies between deuce or more redundant components which cause them to fail simultaneously. such failures have the potential for negating ofttimes of the benefit gained with redundant configurations.
Common-mode failures may be caused by ordinary electric connections, shared environmental stresses such as system or vibration, common fear problems, or a pack of other factors. In commercial-grade aviation, for example, a great smoke of redundancy is employed, bothowing high levels of precaution 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 kibibyte engine turbine blade that stretch 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 publication as putting in an...If you want to get a full essay, order it on our website: Ordercustompaper.com
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