Which, expressed in mathematical form and using equation 11.15c, gives
Also, from the logic of equation 11.15a,
11.4 Network reduction teachniques
Most systems do not consist of only series chain or parallel configurations but more often a combination of both. The general principles and concepts of such networks were discussed in chapters 4 and 5 and it is therefore not intended to repeat these details at this point. Briefly, however, one method for solving these network is sequentially to reduce the network using appropriate equation for series and parallel combinations until the network is reduced to a single equivalent component. This method, known as network reduction, was described in chapter 4 and the reliability parameters of the equivalent component are the parameters of the complete system.
Consider the following numerical example to illustrate the application of the series and parallel equations derived in Sections 11.2 and 11.3 to the network reduction teachnique.
Example 11.3
Reconsider Example 4.8 and evaluate the system failure rate, average repair time and unavailability if all components are identical and have a failure rate of 0.05 f/yr and an average repair time of 20 hours.
The system in this example is shown in figure 4.7. the first reduction requires combining components 3 and 4 in parallel to give equivalent component 6. Using Equations 11.15 to 11.18 gives