A two non-identical three-state units redundant system with common-cause failures and one standby unit

This paper presents a mathematical model for predicting a two non-identical three-state active units redundant system with common-cause failures and one standby unit. The units may fail in either of two mutually exclusive failure modes or by the occurrence of common-cause failures. System is only repaired when all the units fail (including the standby unit). The failure rates of units are constant and system repair times are arbitrarily distributed. Laplace transforms of the state probabilities are derived.     

Cost analysis of a two-unit standby system with delayed replacement and better utilization of units

This paper develops the model for a system, having two identical units—one operative and the other cold standby. Each unit of the system has three modes—normal, partial failure and total failure. The replacement time of a failed unit by a standby unit is not negligible but is a random variable. System fails when both the units fail totally. Failure time distributions of units are exponential, whereas repair time distributions are arbitrary. Several reliability characteristics of interest to system designers and operations managers have been evaluated using the theory of regeneration point technique.     

Reliability analysis of a system with a mixture of warm and cold standby

A single-server two-unit standby system with two modes of each unit—normal and total failure—is considered. The standby units are repeatedly interconverted after a random time from warm to cold and cold to warm. Upon failure of the operative unit, the standby unit, if it is warm, starts to operate instantaneously; otherwise, the system goes down until the cold standby starts to operate. System failure occurs when both units fail totally. Identifying the system at suitable regenerative epochs, the integral equations are set up and the expressions for reliability and mean time to system failure (MTSF) are obtained. The graphical behaviour of MTSF is also studied in a particular case.     

Two-unit cold-standby redundant system subject to random checking, corrective maintenance and system replacement with repairable and non-repairable types of failure

We consider a system comprising two identical units. Initially one unit operates and the other remains as a cold standby. At random intervals, checking is done to ascertain the need of Corrective Maintenance (CM). In case CM has to be carried out, the standby unit starts operating. While the unit is operative, it may fail. Failures are of two types, repairable and non-repairable. When the system fails with non-repairable failure of both the units, it is replaced. Several reliability characteristics of interest to system designers as well as to operations managers have been evaluated.     

Comparison of two stochastic models for two-unit series system with cold standbys

Reliability characteristics are compared for two stochastic models of a system that has two non-identical units, arranged in series, each unit with its identical cold standby. The same set of assumptions is used for both models, except that in model 2 both of the standby units replace the failed operative unit instantaneously whereas in model 1 an operative failed unit is replaced by its corresponding standby unit (i.e. only one unit is replaced in this case). A single repair facility is available to repair the failed unit. Failure and repair time distributions are assumed to be negative exponential.     

The effect of preventive maintenance on a two-dissimilar unit standby system

A system which consists of two dissimilar units, one as a main unit the other as a standby, is considered, taking account of repair and preventive maintenance (PM). The standby unit cannot fail and the switch is perfect. The Laplace transform (LT) of the survivor function of the time to the first system failure (TFSF) and the mean are derived. Finally, a theorem about the effect of maintenance is proved.     

System characteristic and cost analysis of a two unit standby system with spare units

This paper deals with the stochastic analysis of a standby system having two main units and two spare units.A spare unit is only used for operation when both main units fail and if it fails,it is replaced by the new one until the repair of the failed main unit is completed. The system fails when the last spare unit fails while one main unit is under repair and the other has failed. Using renewal theoretical arguments, certain characteristics of the system are derived and using them the cost of the system is calculated. Particular cases of the model are also considered.     

Analysis of a repairable redundant system with delayed replacement

The paper deals with a redundant system with two types of spare units—a warm standby unit for instantaneous replacement at the time of failure of the active unit and a cold standby (stock) unit which can be replaced after a random amount of time. Failure time distributions of operative and standby units are exponential whereas all repair times follow arbitrary distributions. The system has been studied in detail by applying the results from the theory of semi-Markov process and mean-time-to-system-failure, steady-state availability, expected number of visits to a state, second moment of time in an up-state and expected profit of the system have been obtained.     

Cost-benefit analysis of a single server three-unit redundant system with inspection, delayed replacement and two types of repair

This paper deals with a redundant system with two types of spare units—a warm standby unit for instantaneous replacement at the time of failure of the active unit and a cold standby (stock) unit which can be replaced after a random amount of time. The type of the failure of operative or warm standby unit is detected by inspection only. The service facility plays the triple role of replacement, inspection and repair of a unit. Failure time distributions of operative and warm standby units are negative exponential whereas the distributions of replacement time, inspection time and repair times are arbitrary. The system has been studied by using regenerative points.     

Availability of Some Repairable Computer Systems

A mathematical model is established for the availability of a modularly redundant repairable system which consists of many active units and one standby; coverage is considered. The hazard rates for an active unit and for the standby unit are different and are assumed to be constant. Repair time distributions are general. Availability for the system, mean system up-time, and mean system down-time are derived.     

Stochastic analysis of a two unit cold standby system with preparation time for repair

This paper deals with the cost-benefit analysis of a two unit cold standby system in which the cold standby unit replaces the failed operative unit after a random amount of time. Inspection is required to decide whether it needs type I or type II repair. Failure, repair, replacement and inspection time distributions are arbitrarily distributed. A repair man is not always available with the system, but is called for repair whenever the operative unit fails.     

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 redundant system with non-instantaneous switchover and “preparation time” for the repair facility

This paper discusses two models of two-unit standby redundant systems in which the switchover time is a random variable and the repair facility is not available for a random time immediately after each repair completion. In model I the probability distributions of the life time of the online unit and switchover time are general while all the other distributions are exponential. Model II is a cold standby system in which the probability distributions of the “preparation time” of the repair facility is exponential and all the other distributions are general. Using the regeneration point technique the availability functions of the two systems are determined. Several special cases are also discussed.     

Cost analysis of a two-unit chargeable standby system with interchangeable units and two types of failure

This paper studies the analysis of a stochastic model related to a two-unit chargeable standby system with interchangeable units (identical), i.e. the operative and standby units are interchanged at random epochs. The system can fail either due to power fluctuations or due to the operator's inefficiency. Failure time distributions are negative exponential while the distributions of repair times and time to interchange (of units) are arbitrary. Using a regenerative point technique, we have obtained various reliability characteristics to carry out the cost-benefit analysis.     

Stochastic analysis of a two unit standby system with two switching devices and sliding preventive maintenance

A two unit standby (cold) system with two switches and sliding preventive maintenance policy is analysed. One switch is used to put the standby unit into operation, while the other is used to shift a failed unit into the repair facility. Switches may be found to fail at the time of need. P.M. of an on-line unit is performed while the other unit is in standby. Using regenerative point technique in Markov renewal process theory several reliability characteristics of interest to system designers and operations managers are obtained.     

Two models for two-dissimilar-unit standby redundant system with three types of repair facilities and perfect or imperfect switch

This paper deals with two models for two-dissimilar-unit cold standby redundant systems under the assumption that each unit works in three different modes—normal, partial failure and total failure. In model I, the switch is perfect but it is imperfect in model II. The failure and repair times are assumed to have different arbitrary distributions.Explicit expressions for the mean time to system failure and the availability analysis are obtained in each model. A computer program is shown for comparison between the two models.     

Availability of Priority Standby Redundant Systems

A priority standby system consisting of two repairable units is considered. One unit, the priority unit, is always in service except when it is failed. The standby unit is in service only for the duration of repair of the priority unit. Expressions are derived for the availability of such a system for both preemptive and nonpreemptive repair. The results assume reasonably general failure-time and repair-time distributions of the priority and standby units. The preemptive priority results are relatively insensitive to the form of the distributions.     

Reliability analysis of a system with preventive maintenance, inspection and two types of repair

This paper considers a two-unit (identical) parallel system with facilities of preventive maintenance, inspection and two types of repair, type I and type II. These two types of repair facilities have a considerable difference in their costs. Both the units of the system can fail simultaneously due to some common-cause or they can fail one by one. The time of failure of a unit and system, the commencement of maintenance and inspection are assumed to be constant while repair and maintenance times are arbitrarily distributed. Various measures of system effectiveness are evaluated using regenerative point technique.     

Cost analysis of a two unit priority standby system with imperfect switch and arbitrary distributions

This paper deals with cost analysis of a single server two-unit (one priority and the other ordinary) cold standby system with two modes—normal and total failure. A switch is used to operate the standby unit (ordinary) and it works successfully with known probability p( = 1 ? q). Priority unit gets preference both for operation and repair. Failure and repair time distributions are arbitrary. System fails when switch or both the units fail totally. The system is observed at suitable regenerative epochs in order to obtain reliability characteristics of interest to system designers and operations managers. Explicit results for the exponential time distributions have been obtained in particular cases.     

Availability of a complex system having shelf-life of the components and common-cause failures

In this paper, a complex system comprised of two types of component is considered. Type I consists of N components connected in series, whereas type II consists of components connected in standby redundancy. It is assumed that a standby component may also fail in its shelf-life. Further, the system experiences two modes of failure—the first due to change in performance characteristics and the second due to a common cause. The availability of such a system is investigated using supplementary variable techniques and Laplace transforms. Finally, a number of interesting particular cases are discussed.