Reliability evaluation of systems with critical human error

This paper presents four mathematical models to evaluate reliability of redundant systems with critical human error. Equations for system reliability, state probabilities and mean time to failure are developed. System reliability and mean time to failure plots are shown.     

Reliability and availability analysis of on surface transit systems

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.     

Renewal Theoretic Aspects of Two-Unit Redundant Systems

This expository paper discusses four two-unit redundant systems: 1) parallel redundancy; 2) standby redundancy; 3) standby redundancy with priority; 4) standby redundancy with noninstantaneous switchover. In models 1), 2), and 3) the switchover time is instantaneous. The integral equation of renewal theory is applied by using the concept of a cycle. Applying the integral equation of renewal theory and the cycle, we obtain systematically for each model the Laplace-Stieltjes transform of the distribution of the time to first failure and its mean.     

A method to evaluate reliability of systems with critical and non-critical human errors

This paper presents a newly developed method to perform reliability analysis of redundant systems with critical and non-critical human errors. The method is demonstrated using k-out-of-n units, parallel and series-parallel configurations. Time dependent analyses are developed for exponentially and Rayleigh distributed failure times. System reliability and mean time to failure formulas are presented.     

Reliability modeling of on-surface transit systems with human errors

This paper presents two newly developed Markov models representing on-surface transportation systems subject to hardware failures and human errors. 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.     

Reliability and availability analysis of transit systems

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.     

Stochastic models for evaluating probability of system failure due to human error

This paper presents four mathematical models of redundant systems with human error. Laplace transforms of the state probability equations are developed. Mean time to failure (MTTF) formulas are developed.     

软件可靠性及维修性评估工具（SRMET2.0）

软件可靠性及维修性评估工具（ＳＲＭＥＴ２．０）是由航天软件评测中心于１９９８年研制开发的。ＳＲＭＥＴ２．０包含了七个软件可靠性评估模型和四个软件维修性评估模型，不仅可处理完全的可靠性数据，也可处理不完全的可靠性数据。     

Comparison of mean time to first failure and mean up time

Two unit standby redundant repairable system, parallel systems and series systems are studied. The time between failures and the repair time are assumed exponentially distributed. Expressions for mean time to first failure (MTTFF) and mean up time (MUT) have been obtained. Comparisons have been made between MTTFF and MUT and the difference illustrated by numerical examples for different systems.     

Bounds on System Lifetime

Bounds are given for moments of the time to failure of systems composed of independent components. Improved bounds on the mean and on the reliability for series and parallel systems are obtained for systems composed of independent components with increasing hazard rate and increasing hazard rate average.     

Reliability analysis of networks with human errors: A block diagram approach

This paper presents an approach for performing reliability analysis of bridge and parallel-series networks with critical and non-critical human errors. Reliability and mean time to failure formulas are developed for exponential and Rayleigh distributed failure times. Selective plots are shown for demonstrating the effect of human errors on system reliability and mean time to failure. Equations for estimating a number of units in series, parallel, series-parallel and parallel-series networks are presented.     

Reliability optimization models for embedded systems with multiple applications

Summary and Conclusions-This paper presents four models for optimizing the reliability of embedded systems considering both software and hardware reliability under cost constraints, and one model to optimize system cost under multiple reliability constraints. Previously, most optimization models have been developed for hardware-only or software-only systems by assuming the hardware, if any, has perfect reliability. In addition, they assume that failures for each hardware or software unit are statistically independent. In other words, none of the existing optimization models were developed for embedded systems (hardware and software) with failure dependencies. For our work, each of our models is suitable for a distinct set of conditions or situations. The first four models maximize reliability while meeting cost constraints, and the fifth model minimizes system cost under multiple reliability constraints. This is the first time that optimization of these kinds of models has been performed on this type of system. We demonstrate and validate our models for an embedded system with multiple applications sharing multiple resources. We use a Simulated Annealing optimization algorithm to demonstrate our system reliability optimization techniques for distributed systems, because of its flexibility for various problem types with various constraints. It is efficient, and provides satisfactory optimization results while meeting difficult-to-satisfy constraints.     

Measures of testability for automatic diagnostic systems

Evaluation models of automatic diagnostic systems are investigated taking into consideration their imperfections such as failure to diagnose, incorrect isolation, false alarms, and inability to duplicate. Three measures of effectiveness are developed that enable the decision-maker to assess accurately the real capability of the diagnostic system and to evaluate and compare the performances of alternative automatic diagnostic systems based on their mean life-cycle cost. Analytic procedures for using these measures are developed, and an example is presented. It is concluded that the capability and performance of automatic diagnostic systems can be assessed using three measures of effectiveness; false removal, failure to diagnose, and false alarm correction. The three measures can be used to predict the mean life-cycle cost of automatic diagnostic systems, including the mean cost of imperfections of such systems     

Mean time to failure formulas for standard reliability networks with erlangian distributed component failure times

This paper presents newly developed mean time to failure formulas for reliability networks such as series, parallel, k-out-of-n, series-parallel, parallel-series and a bridge with special case Erlangian distributed component failure times.     

Comparative redundancy, an alternative to triple modular redundant system design

A new scheme for implementing highly reliable digital systems is proposed. The method has a circuitry overhead which is comparable to that of the triple modular redundancy (TMR) scheme, although it is shown to have a reliability, and more importantly a mean time to failure, improvement well beyond that expected from the standard TMR systems. The reliability and mean time to failure are both developed from a discrete state, continuous time, Markov model of the new system. The results for the reliability and mean time to failure characteristics for this new design of system, termed comparative redundancy, are compared to both TMR and a single unit.     

Reliability measures for two-unit systems with a dependent structure for failure and repair times

This paper deals with reliability measures for two-unit systems with a repair facility assuming that the failure times and the repair time follow a trivariate exponential distribution of Marshall and Olkin, J. Amer. Statist. Assoc., 1967, 62, 30–44. The case where the system down-time is observed, is also discussed. The system reliability and system mean-time before failure are evaluated for standby and parallel systems. When the down-time is observed the system availability, steady-state availability and the system mean down-time are evaluated for standby, parallel and series systems.     

Reliability Analysis of Systems Comprised of Units with Arbitrary Repair-Time Distributions

This work demonstrates the feasibility of reliability modeling of systems with repair capability using a semi-Markov process. A two-unit system with exponential failure times but general repair times is studied. Formulas for state-transition probabilities, waiting-time distribution functions, and mean time in each state are developed. These quantities are expressed in terms of the Laplace transform of repair time distribution functions. Once these quantities are known, mean time to system failure and system availability, as well as other system parameters, can be found using matrix manipulations. In addition, time-dependent results may be obtained. A numerical example varying the parameter in a repair-time law is presented. The formulas developed can be extended to larger systems with repair capability for only one unit at a time and exponential failure times.     

Stochastic modeling of aggregates and products of variable failurerates

This paper develops an unconventional but powerful approach to analyzing the observed and/or estimated failure rates of complex systems that operate in series and/or in parallel under varying operational and environmental conditions. Consequently such failure rates can be construed as time series which are complex in the sense that they are aggregates and/or products of two or more time series. Hence special time-series techniques are required for their analysis. Some of the results recently developed apply to the analysis of such time series. These results can also be used for the analysis of the reliability decay (growth) processes, actual failure times, times between failures, and interactions between failure times and maintenance times of complex systems     

Reliability and availability analysis of a system with warm standby and common cause failures

This paper presents reliability and availability analyses of a two unit parallel system with warm standby and common-cause failures. The standby and switching mechanisms are subject to failure. The failed system repair times are assumed to be arbitrarily distributed. Expressions for Laplace transforms of system state probabilities, steady state system availability, system reliability, and mean time to failure are developed.     

Expected Value and Variance of Failure Time in Redundant Systems

Formulas are derived for the mean value and the variance of the distribution of time to system failure for parallel redundant and m out of n systems. A novel approach is used in the derivation which requires only elementary calculus and no explicit integration of specific functions. For the general case component failure times are assumed to be statistically independent and exponentially distributed. In addition, a special case of statistical dependence is treated.