Reliability and Availability Simulation Software

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Reliability Simulation Software

Computer programs such as AvSim+ employ Monte Carlo Simulation Methods to estimate system and sub-system parameters such as unavailability, number of expected failures, production capacity, costs etc. The process involves synthesising system performance over a given number of simulation runs. Each simulation run in effect emulates how the system might perform in real life based on the input data provided by the user. The input data can be divided into two categories – a failure logic diagram and quantitative failure and maintenance parameters. The logic diagram (either a fault tree or a reliability block diagram in the case of AvSim+) informs the computer program how component failures interact to cause system failures. The failure and maintenance parameters inform the program how often components are likely to fail and how quickly they will be restored to service. By performing many simulation runs the computer program can build up a statistical picture of the system performance by recording the results of each run.

Monte Carlo simulation must emulate the chance variations that will effect system performance in real life. To do this the computer program must generate random numbers which form a uniform distribution.

As an example of how reliability simulation works consider the following example. Suppose we wish to determine the unreliability of a complex system over a period of 1 year. A simulation model of the system could be developed which emulates the random failures and repair times of the components in the system. The model might be run over the system lifetime of 1 year 1000 times and each time a component fails the model determines whether the system has failed. If the system does not survive on 65 of the lifetime simulations then the system unreliability, F(1), could be estimated as:

F(1) = 65/1000 = 0.065

Simulation methods are generally employed in reliability studies when deterministic methods are incapable of modelling strong dependencies between failures. In addition simulation can readily handle the reliability behaviour of repairable components with non-constant failure or repair rates.

For more information on reliability simulation software and its integration with other reliability methods visit Isograph’s web site at

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Reliability and availability simulation software