Subramanyam N. Rayapati

Reliability analysis of non-maintained parallel systems subject to hardware failure and human error

Abstract This paper presents four newly developed Markov models to evaluate reliability and mean time to failure of non-maintained parallel systems with hardware failure and human error. The first three models represent two-unit, three-unit and four-unit non-maintained parallel systems, respectively, whereas the fourth model generalises the analysis to a non-maintained n-unit parallel system. System state probability equations and mean time to failure expressions are developed for all four models.

Reliability evaluation of human operators under stress

Abstract This paper presents five newly developed models to predict reliability of human operators performing time continous tasks under stress. Laplace transforms of state probability equations and operator reliability are developed. Mean time to human error (MTTHE) expressions are obtained. In addition specific plots are shown for selective models.

Reliability and availability analysis of on surface transit systems

Abstract This paper presents four Markov models pertaining to repairable and non-repairable on surface transit systems. The expressions for state probabilities, system reliability, mean time to failure (MTTF) and steady state availability are developed. System reliability, MTTF and steady state availability plots for various assumed values of system parameters are shown.

A method to evaluate reliability of three-state device networks

Abstract This paper presents a newly developed probability tree procedure to evaluate reliability of three-state device networks. Reliability networks containing four and five independent and non-identical units are studied with the aid of probability tree approach. Independent unit network configurations such as series, parallel, series-parallel, parallel-series and bridge are analyzed. Expressions for system reliability, open mode and short mode failure probabilities are developed.

Human error modelling of parallel and standby redundant systems

Four newly developed probabilistic models representing two unit parallel and standby redundant systems with human errors are presented. The supplementary variables method is used to develop the system availability expressions for all four models. In the case of Models II and IV, a general formula for the system steady-state availability is developed when the failed system repair times are erlangian distributed. System reliability, mean time to failure and variance of time to failure formulae are developed for Models I and III. Specific plots are shown to demonstrate the impact of human error on system reliability, availability and mean time to failure.

A complex system reliability evaluation method

This paper presents a newly developed method to evaluate reliability of complex systems composed of independent three-state devices. The method is demonstrated with the aid of a hypothetical example of a complex system. In addition, the impact of unit (i.e. three-state device) open and short mode failure probabilities on bridge network reliability is shown.

Common-cause failure and human error modelling of redundant systems with partially energized standby units

This paper presents two newly developed probabilistic models representing reduntant systems with common-cause failures, human errors and partially energized standby units. System reliability, steady-state availability, mean time to failure and variance of time to failure formulas are developed. Several plots and tablesdemonstrating the effect of varying human errors and common-cause failures on system reliability, mean time to failure, state probabilities and availability are presented.

Stochastic behaviour of man-machine systems operating under different weather conditions

Abstract This paper presents some comments on ‘Stochastic behaviour of man-machine systems operating under different weather condition’ [1]. In addition, reliability analysis of one of the models given in [2] is performed. State probability, human operator reliability, mean time to human error (MTTHE) and probability of human error plots are shown.

Stochastic analysis of two-unit outdoor electric power systems in changing weather

Abstract This paper presents two newly developed Markov models representing electric power systems operating in changing environment. Model I deals with a non-repairable two unit system operating in alternating environments (i.e., normal and stormy weather). Model II represents a repairable two unit system operating in changing weather. Laplace transforms of state probability equations are developed for Model I. Similarly, state probability equations are obtained for Model II. Plots pertaining to ‘probability of the system being in any one of the up states’ are shown.

Reliability and availability analysis of transit systems

Abstract This paper presents three newly developed Markov models representing on-surface transit systems. Transit system reliability, steady-state availability, mean time to failure (MTTF) and variance of time to failure formulas are developed. Selective plots are shown for each model. These plots clearly exhibit the impact of various parameters on transit system reliability, steady-state availability, and MTTF.