Availability measures for an intermittently used repairable system

This paper obtains generalized Availability Measures, as defined by L. A. Baxter, for an intermittently used repairable system. The regenerative point technique of Markov Renewal Processes has been employed to obtain these measures. Some comments have also been made on the discrepancies that existed in the derivation of availability in the past.     

Reliability analysis of k-out-of-n systems with partially repairable multi-state components

In some environments the components might not fail fully, but can lead to degradation and the efficiency of the system may decreases. However, the degraded components can be restored back through a proper repair mechanism. In this paper, we present a model to perform reliability analysis of k-out-of-n systems assuming that components are subjected to three states such as good, degraded, and catastrophic failure. We also present expressions for reliability and mean time to failure (MTTF) of k-out-of-n systems. Simple reliability and MTTF expressions for the triple-modular redundant (TMR) system, and numerical examples are also presented in this study.     

Reliability prediction for repairable redundant systems

It is assumed that the mean time to failure and mean repair time are known for each of the subsystems of a system. The subsystems conform to the usual exponential failure (and repair) laws and their behaviors are mutually independent. The system includes redundant subsystems in active standby status. Whenever, after a system failure, repair of a failed subsystem re-establishes an adequate configuration, the system as a whole is returned to active status while repair of other failed subsystems (if any) continues. Under this set of assumptions, equations are developed which permit prediction of mean time to failure and mean down time for the system. The development differs somewhat from the use of birth-and-death equations which has been customary for similar problems in the past.     

Availability analysis of a repairable standby human-machine system

This paper presents a model representing a two units active and one unit on standby human-machine system with general failed system repair time distribution. In addition, the model takes into consideration the occurrence of common-cause failures. The method of linear ordinary differential equation is presented to obtain general expressions for system steady state availability for failed system repair time distributions such as Gamma, Weibull, lognormal, exponential, and Rayleigh. Generalized expressions for system reliability, time-dependent availability, mean time to failure, and system variance of time to failure are also presented. Selected plots are presented to demonstrate the impact of human error on system steady state availability, reliability, time-dependent availability, and mean time to failure.     

Reliability and ageing of repairable systems

This paper discusses some of the complexities of ageing repairable systems, especially those relating to computation of their reliability. In order to cope with them in a realistic manner, a discrete event simulation model using the time between successive failures of the subsystems has been proposed. The model has been used for the evaluation of improvement or deterioration of system reliability with increasing age. The effects of the design modification of one or more subsystems on the system reliability are studied by conducting simulation experiments. Live data from the operation of a fleet of trainer aircraft is used for illustration purposes; the results are presented and discussed.     

A reliability test-plan for series systems with components havingstochastic failure rates

This paper proposes a reliability test plan for a series system, by considering the parameter λ_j of the exponential distribution to be a random variable having uniform distribution over [0, &thetas;_j], j = 1, 2,..., n. Explicit expressions are obtained for the optimal values of the t_j, when the number of components in the system is 2. The general solution, albeit implicit, has also been obtained when the number of components in a given system is ⩾3. Mathematical programming is used to find the optimal solution and to illustrate it with numerical results     

Bayes credibility intervals for reliability of series systems withvery reliable components

An asymptotic expansion for the posterior Cdf of the reliability of series systems with very reliable components is obtained. This result allows us not only to calculate the Cdf easily but to estimate the magnitude of error when the infinite series expansion is truncated. Numerical results show that the asymptotic expansion converges very rapidly. Consequently, the computation of Bayes credibility intervals based on the truncated expansion is efficient and accurate     

Distribution-free analysis of repairable fault-tolerant systems

This paper presents a unified treatment of methods for distribution-free analysis of repairable fault-tolerant systems. Material from diverse sources is presented for the first time in an integrated, easily accessible unit. In addition, new results are derived which enable more detailed analysis than had carlier been possible. New, streamlined proofs based only on elementary techniques are developed, facilitating extensions of the theory to a wider range of applications.     

Availability analysis of a repairable system with common-cause failure and one standby unit

This paper investigates the mathematical model of a system consisting of two non-identical parallel redundant active units, with common-cause failure, and a cold standby unit. The failed units are repaired one at a time or are repaired together, if they fail due to common cause failure. All repair time distributions are arbitrary and different. The analysis is carried out under the assumption of having a single service facility for repair and replacement.Applying the supplementary variable technique, Laplace transforms of the various state probabilities are developed. Explicit expressions for the steady state probabilities and the steady state availability are derived.Some well known results are obtained as special cases. A numerical example is given to illustrate the effect of the repair policy on the steady state probabilities and the availability of the system.     

A new model for repairable systems with bounded failure intensity

This paper proposes a new model, called the 2-parameter Engelhardt-Bain process (2-EBP) model, to describe the failure pattern of complex repairable systems subjected to reliability deterioration with the operating time, and showing a finite bound for the intensity function. The characteristics of the 2-EBP model are discussed, and the physical meaning of its parameters is derived. The 2-EBP model can be viewed as a dynamic power law process, whose shape parameter ranges from 2 to 1 as the system age increases, converging asymptotically to the homogeneous Poisson process. Maximum likelihood estimates of model parameters & other quantities of interest, as well as a testing procedure (based on the likelihood ratio statistic) for time trend, are provided. Numerical applications are given to illustrate the 2-EBP model & the related inferential procedures, and to emphasize on the caution to use in assuming the (very often used) power law process when the presence of a finite bound for the failure intensity is conjecturable.     

Reliability modeling algorithms for a class of large repairable systems

The reliability performance of some multistate large repairable systems cannot be described by a dichotomy of success and failure but by probability and frequency distribution of several levels of performance, algorithms for reliability modeling of such systems consisting of several units, each contributing a finite amount to the total system capacity. The first algorithm describes system model building by the sequential addition of units and the second one can be used for taking off particular units from the system model. The algorithms are fast and can be easily implemented in a computer program.     

A maintenance policy for repairable systems based on opportunisticfailure-rate tolerance

An opportunistic hazard rate replacement policy for a repairable system with several types of units is presented. A unit is repaired at failure when the hazard rate falls in (0, L-u). A unit is replaced at failure when the hazard rate falls in (L-u , L). An operating unit is replaced when its hazard rate reaches L. When a unit is replaced because its hazard rate reaches L, all operating units with their hazard rates falling in (L-u, L) are replaced. The long-run mean cost rate as a function of L and u is derived. Optimal L and u are obtained to minimize the total maintenance cost rate. Application and analysis of results are demonstrated through a numerical example. The maintenance model is designed for a system with multitype units. Each type has its own increasing hazard rate. Units are repaired or replaced depending on their hazard rate at a failure or active replacement of another unit. The repair interval, replacement limit, and replacement tolerance are determined to yield the optimal total maintenance cost rate     

Computing steady-state mean time to failure for non-coherent repairable systems

Mean time to failure (MTTF) is an important reliability measure. Previous research is mainly concerned with the MTTF computation of coherent systems. In this paper, we derive equations to calculate the steady-state MTTF for noncoherent systems. Based on the equations, we extend the BDD by adding an intersection edge in each BDD node to efficiently store additional information for MTTF computation of noncoherent systems. A recursive algorithm is developed for MTTF computation using the extended BDD. To accelerate building the extended BDD, a method is proposed to avoid calculating the intersection edge for some nodes by keeping node monotonicity during the BDD construction. We show the efficiency of our algorithm by applying it to some example fault trees, real-life applications, and large fault tree benchmarks.     

A model for the integrity assessment of ageing repairable systems

The failure rate of mechanical repairable systems that deteriorate with time due to ageing can usually be visualized by a bathtub curve. This study shows that an equation that is valid in other respects for describing creep curves can easily be deduced from functional forms of the failure rate of mechanical repairable systems. Creeping pieces can be considered repairable systems that evolve under an applied load, as combining positive and negative feedback loops. More generally, this can be extended to mechanical repairable systems, the negative feedback loops corresponding to repair and overhaul operations. The equation describing creep curves reflects the ageing of mechanical repairable systems. A critical time at which the system can no longer be restored to full performance, in spite of repair and/or replacement of subparts, can then be predicted. An application example is given using published failure data corresponding to a submarine main-propulsion diesel engine. The proposed model should apply every time that mechanical system ageing is expressed by a bathtub curve     

Reliability of repairable systems with periodic modifications

In this paper, we focus on transient and steady-state behavior of repairable systems with periodic modifications by arbitrarily distributed times to failure and repair and durations between modifications. We propose an efficient method for computing the reliability characteristics on the basis of integral equations.     

Availability analysis of transit systems

This paper presents two mathematical models of repairable transit systems. State probability equations for both models are developed.     

Diagnostic-strategy selection for series systems

The selection of efficient testing strategies for repairable systems composed of components arranged in series is considered. Two cost models (for perfect and imperfect testing) represent the consequences of possible test realizations. The probability that any particular component is responsible for the failure is derived and used as a basis for the two models. The model for perfect testing is solved exactly. In the optimal perfect-test sequence the components are tested in decreasing order of the ratio of: [probability that the component is responsible for the system failure] to [component test cost]. For imperfect testing, possible diagnostic errors are included in a model for which two heuristic solution strategies are provided. The model represents the consequences of both false-positive and false-negative component-test outcomes. The heuristic strategies yield efficient test sequences. Under reasonable assumptions, the second heuristic strategy is guaranteed to locate the optimal test sequence. The model can quantitatively evaluate the benefits of test-accuracy enhancement plans. These models and algorithms provide convenient methods for selecting efficient test-sequences. This is illustrated by representative examples     

Common-cause failures and critical human errors in repairable and non-repairable systems

This paper presents a reliability analysis of a k-out-of-N:G redundant system with common-cause failures, critical human errors and r repair facilities. The system is in a failed state when common-cause failures or critical human errors occurred or k units failed. When less than k units failed, the failed units are to be repaired. If the whole system is in a failed state, it cannot be repaired. Laplace transorms of state probabilities and system reliability are derived. Various versions of mean time to failure of a system are also reported.     

Optoelectronic components for multigigabit systems

Gigabit data rates are becoming relevant for several applications areas, including computer interconnections, trunk telecommunications, and phased-array radar control. LED's, lasers, p-i-n FET's, photoconductors, and avalanche photodiodes are candidate components. Silicon NMOS, bipolar, GaAs FET, and heterojunction bipolar logic IC technologies are all appropriate and no obstacles are apparent to prevent direct modulation to ∼ 10-20 Gbit/s. Wavelength multiplexing will impact strongly in several applications enabling complex new system architectures. Increasing speed and complexity Will drive technology to higher optoelectronic integration levels.