Non-repairable Units Research Articles

Choosing a consumption strategy for a population of units based on reliability

Managers and decision makers are often faced with difficult decisions balancing multiple competing objectives when selecting between several strategies for how to use the units in their inventory or stockpile. This paper considers how to define different metrics which appropriately summarize the objectives of a good strategy, how to consider what impact unanticipated changes in the future might have, and how to combine several criteria into a decision when no global winner is likely. This process is discussed in the context of maximizing the reliability of a population of single-use non-repairable units, such as missiles or batteries, which are being consumed (used and removed from the population) as they age over time.

Reliability analysis of a two-unit general parallel system with warm standbys

Abstract A parallel ( 2 , n - 2 ) -system is investigated here where two units start their operation simultaneously and any one of them is replaced instantaneously upon its failure by one of the ( n - 2 ) warm standbys. We assume availability of n non-identical, non-repairable units. The unit-lifetimes in full operational mode and in partial operational mode have general distribution functions G i and H i ( i = 1 , … , n ) respectively. The system reliability is evaluated by recursive relations.

A two-unit general parallel system with ( n − 2) cold standbys—Analytic and simulation approach

A parallel (2, n − 2)-system is investigated here where two units start their operation simultaneously and any one of them is replaced instantaneously upon its failure by one of the ( n − 2) cold standbys. We assume availability of n non-identical, non-repairable units for replacement or support. The system reliability is evaluated by recursive relations with unit-lifetimes T i ( i = 1, … , n) that have a general joint distribution function F( t). On the basis of the derived expression, simulation techniques have been developed for the evaluation of the system reliability and the mean time to failure, useful when dealing with large systems or correlated unit-lifetimes and less mathematically manageable distributions. Simulation results are presented for various lifetime distributions and comparisons are made with derived analytic results for some special distributions and moderate values of n.

Scheduling starting times for an active redundant system with non-identical lifetimes

Here we examine an active redundant system with scheduled starting times of the units. We assume availability of n non-identical, non-repairable units for replacement or support. The original unit starts its operation at time s 1 = 0 and each one of the ( n − 1) standbys starts its operation at scheduled time s i ( i = 2, …, n) and works in parallel with those already introduced and not failed before s i . The system is up at times s i ( i = 2, …, n), if and only if, there is at least one unit in operation. Thus, the system has the possibility to work with up to n units, in parallel structure. Unit-lifetimes T i ( i = 1, …, n) are independent with cdf F i , respectively. The system has to operate without inspection for a fixed period of time c and it stops functioning when all available units fail before c. The probability that the system is functioning for the required period of time c depends on the distribution of the unit-lifetimes and on the scheduling of the starting times s i . The reliability of the system is evaluated via a recursive relation as a function of the starting times s i ( i = 2, …, n). Maximizing with respect to the starting times we get the optimal ones. Analytical results are presented for some special distributions and moderate values of n.

A two-unit parallel system supported by (n − 2) standbys with general and non-identical lifetimes

This paper examines a functioning policy of a parallel system. We assume availability of n non-identical, non-repairable units for replacement or support. Two units start their operation simultaneously at times , and any one of them is replaced instantaneously upon its failure by one of the ( n − 2) standby units at random starting times Si ( ). Thus, with probability one, the system is functioning with two units up till the failure of the ( n − 1)th unit. Unit lifetimes Ti have a general joint distribution function F( t ). The system has to operate for a fixed period of time, c, and it stops functioning when all available units fail before c. The probability that the system is functioning for the required period of time c depends on the distribution of the unit lifetimes. The reliability of the system is evaluated by recursive relations. Independent unit lifetimes are considered as special cases.

Using Spice Circuit Simulation Program in Reliability Analysis of Redundant Systems with Non-Repairable Units and Common-Cause Failures

The effectiveness of Simulation Program with Integrated Circuit Emphasis (SPICE) in calculating probabilities, reliability, steady-state availability and mean-time to failure of redundant systems with non-repairable units and common-cause failures described by Markov models is demonstrated. General equations and procedure for constructing the equivalent circuit forNparallel units are presented. Results obtained, forN=1,2,3, using SPICE are compared with previously published results obtained using the Laplace transform method. Full SPICE listings are included.

Common-cause failure analysis of a redundant system with non-repairable units

Abstract This paper presents a newly developed generalized expression for mean time to failure, MTTF, of a non-repairable identical unit parallel system with warm standby and common-cause failures. Also presented is a modified version of this formula that takes into account the repairability of the warm standby and/or switching mechanism. Generalized expressions for system reliability and variance of time to failure are presented along with some tables and plots of system reliability and MTTF.