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IEEE Transactions on Reliability is the premiere technical journal for reliability and related disciplines. We strive to continue this reputation, so we continue to discover what makes journals great. We have discovered that IEEE journals work to have the qualities readers and authors would like to expect. Correctness and technical merit are important features of accepted manuscripts, with correctness rating as most important to the responding editors. Writing and solving real problems seem to be the least important features. The relative unimportance of these last two categories may be a concern, except that relative importance is not an indicator of absolute importance. However, a recent IEEE survey suggests that members place most value on more practical articles, which suggests that the relative importance of solving real problems should be high if we are to meet the needs of our members through our journals. [ABSTRACT FROM AUTHOR]

A method is proposed in this paper to determine whether a product, a component, or a system in reliability life testing has a longer lifetime than the other. We propose two indices to compare reliability. The comparison is also distribution-free; i.e., it does not require the assumption on the lifetime distributions. A comparability index that is derived by integrating the weighted difference between the reliability functions of the two groups under comparison is named the "Better or Worse" (BOW) index. The second comparability index that is derived by calculating the overlapping area under the two distributions in comparison is named "Reliability Comparability" (RC) to quantify the degree of similarity between the two distributions. These two new indices are compared with the conventional methods currently used in the IC industries. Practical applications in lifetime-type reliability comparison are also illustrated in this paper. [ABSTRACT FROM AUTHOR]

Topological optimization is an important problem in communication networks. Exact reliability optimization methods are restricted to small problems, or specialized network topologies. For larger problems, simulation-based approaches are more practical. In simulation-based optimization, one often needs to compare the reliability of a large number of similar networks. The traditional reliability estimation & rank process is the most time consuming step of most optimization algorithms. In this paper, a novel approach is proposed to directly estimate the reliability ranking of some edge relocated networks without the need to estimate their reliabilities. In the case study considered in this paper, the proposed Synchronous Construction Ranking method achieved over 30,000 times speedup over the traditional approach using the Merge Process estimation algorithm. [ABSTRACT FROM AUTHOR]

Network analysis is an important approach to model real-world systems. System reliability, and system unreliability are two related performance indices useful to measure the quality level of a supply-demand system. For a binary-state network without flow, the system unreliability is the probability that the system can not connect the source and the sink. Extending to a limited-flow network in the single-commodity case, the arc capacity is stochastic, and the system capacity (i.e. the maximum flow) is not a fixed number. The system unreliability for (d + 1), the probability that the upper bound of the system capacity equals d, can be computed in terms of upper boundary points. An upper boundary point is the maximal system state such that the system fulfills the demand. This paper concentrates on a multicommodity limited-flow network (MLFN) in which multicommodity are transmitted through unreliable nodes and arcs. Nevertheless, the system capacity is not suitable to be treated as the maximal sum of the commodity because each commodity consumes the capacity differently. We define the system capacity as a demand vector if the system fulfills at most such a demand vector. The main problem of this paper is to measure the quality level of a MLFN. We propose a new performance index, the probability that the upper bound of the system capacity equals the demand vector subject to the budget constraint, to evaluate the quality level of a MLFN. A branch-and-bound algorithm based on minimal cuts is presented to generate all upper boundary points in order to compute the performance index. The computational complexity of the proposed algorithm is analyzed. [ABSTRACT FROM AUTHOR]

This paper discusses some of the difficulties in the paper: "A BDD-based algorithm for reliability analysis of phased-mission systems" by X. Zang, H. Sun, and K. S. Trivedi. [ABSTRACT FROM AUTHOR]

Stringent in-service and operating requirements oblige marine diesel engines to possess high levels of reliability and availability. To achieve the desired reliability and availability levels, it is necessary to carry out costly maintenance activity on the cylinder liners, the wear on which is a major factor in causing diesel engine failure. This paper presents a s-based methodology that can be used to carry out a condition-based estimate of liner reliability with respect to failure through excessive wear, and to plan condition-based maintenance activity. The wear process is described through an ad hoc cumulative damage model, and the reliability of the liners is estimated on the basis of wear measures, and predictions of wear increase. The approach proposed allows reducing maintenance costs without noticeably affecting liner reliability. In fact, it gives the probability of inspecting or replacing liners only when there is a high likelihood that their wear level will exceed the wear limit before the next inspection date. The proposed model, and planning procedure have been applied to a data set consisting of wear measures of the cylinder liners of two SULZER RTA 58 engines equipping twin ships of the Grimaldi Group. [ABSTRACT FROM AUTHOR]

This paper proposes efficient methods to assess the reliability of phased-mission systems (PMS) considering both imperfect fault coverage (IPC), and common-cause failures (CCF). The IPC introduces multimode failures that must be considered in the accurate reliability analysis of PMS. Another difficulty in analysis is to allow for multiple CCF that can affect different subsets of system components, and which can occur s-dependently. Our methodology for resolving the above difficulties is to separate the consideration of both IPC and CCF from the combinatorics of the binary decision diagram-based solution, and adjust the input and output of the program to generate the reliability of PMS with LPC and CCF. According to the separation order, two equivalent approaches are developed. The applications and advantages of the approaches are illustrated through examples. PMS without IPC and/or CCF appear as special cases of the approaches. [ABSTRACT FROM AUTHOR]

Numerous stochastic models for repairable systems have been developed by assuming different time trends, and repair effects. In this paper, a new general repair model based on the repair history is presented. Unlike the existing models, the closed-form solutions of the reliability metrics can be derived analytically by solving a set of differential equations. Consequently, the confidence bounds of these metrics can be easily estimated. The proposed model, as well as the estimation approach, overcomes the drawbacks of the existing models. The practical use of the proposed model is demonstrated by a much-discussed set of data. Compared to the existing models, the new model is convenient, and provides accurate estimation results. [ABSTRACT FROM AUTHOR]

The system capacity of a deterministic flow network is the maximum flow from the source to the destination. In a single-commodity stochastic-flow network (branches all have several possible capacities, and may fail), the system reliability, the probability that the maximum flow is larger than or equal to a given demand, is an important performance index to measure the quality level of a network. In a two-commodity stochastic-flow network, different types of commodities are transmitted through the same network simultaneously, and compete for the capacities. We concentrate on the reliability problem for such a network subject to the budget constraint. This paper defines firstly the system capacity as a pattern. We propose a performance index, the probability that the system capacity is less than or equal to a given pattern subject to the budget constraint, to evaluate the system performance. A simple algorithm based on minimal cuts is proposed to generate all maximal vectors meeting the demand and budget constraints. The performance index can then be computed in terms of all such maximal vectors. [ABSTRACT FROM AUTHOR]

In this paper, we develop a generalized multi-state degraded system reliability model subject to multiple competing failure processes, including two degradation processes, and random shocks. The operating condition of the multi-state systems is characterized by a finite number of states. We also present a methodology to generate the system states when there are multi- failure processes. The model can be used not only to determine the reliability of the degraded systems In the context of multi-state functions, but also to obtain the states of the systems by calculating the system state probabilities. Several numerical examples are given to Illustrate the concepts. [ABSTRACT FROM AUTHOR]

This paper deals with a new reliability model for nonrepairable systems, the Hyperbolic. A decreasing hazard rate approaching a value greater than zero is its distinctive characteristic. Potentially, many mechanisms of failure can produce mortality laws of Hyperbolic type. The "Deterioration", "Stress-Strength", and "Shocks" failure models discussed here are such models. To make the use of the Hyperbolic model easier, the maximum likelihood estimators of its parameters are given. They can be calculated without any difficulty, and appear to be acceptable for practical technological applications. Finally, two applicative examples are given. These examples exhibit that when the mechanism of failure is one of the types discussed, the Hyperbolic model shows a better fit compared with other alternative reliability models, like Gamma, and Weibull. [ABSTRACT FROM AUTHOR]

This paper discusses contact discontinuity of electromechanical switches, and presents a model that considers the effect of vibration-induced inertial force on operational reliability. Using this model, the operational reliability of a switch with a specific contact assembly can be assessed for given vibration conditions. Under the vibration conditions, a minimum contact spring force functioning of the switch, while the magnitude of contact uncertainty determines the need of an additional force to ensure operational reliability. With reduced contact uncertainty, the operational reliability of switches approaches either 0 or 1, solely depending upon the design & operational conditions. In this model, the parameters of c', b,& σ/μ need to be determined either empirically, or experimentally before the model can be used for reliability assessment. To theoretically determine those parameters, Hertz contact with randomly distributed surface asperities needs to be considered. Finally, although this model starts from a log-normal distribution of electrical contact the approach can be applied to other distributions, such as the inverse Gaussian and Weibull distributions. [ABSTRACT FROM AUTHOR]

A powerful equation is derived for determining the probability of safe/failure states dependent on random variables, following a homogeneous Poisson process in a finite domain. The equation is generic & gives the probability of all types of relative configurations of the random variables governing reliability. The significance of the derived equation stems from the fact that the reliability problems only, or to a simple function of the relative distances between the locations of the random variables. Many intractable reliability problems can be solved easily using the derived equation which reduces complex reliability problems to problems with trivial solutions. The power of the equation is illustrated by the derivation of a number of important special cases, and numerous applications: i) determining the probability of existence of a set of minimum intervals between the locations of random variables in a finite interval, ii) determining the number density envelope of the random variables which prevents clustering within a critical distance, and iii) a closed-form relationship for determining reliability during shock loading. The new equation is at the basis of a new reliability measure which consists of a combination of a set of specified minimum free gaps before/between random variables in a finite interval, and a minimum specified probability with which they must exist. The new reliability measure is at the heart of a technology for setting quantitative reliability requirements based on minimum failure-free operating periods (MFFOP). The equation is applied to cases where failure is triggered because of clustering of two ore more demands, forces, or manufacturing/material flaws following a homogeneous Poisson process in a specified time interval/length. A number of important applications have also been considered related to the conditional case (a homogeneous Poisson process conditioned on the number of random variables in a finite interval). Solutions have been provided for common problems related to: i) collisions of demands from a given number of customers using a particular equipment for a specified time; ii) overloading of supply systems from a given number of consumers connecting independently & randomly, and iii) analysis of random failures following a homogeneous Poisson process where only the number of failures is known, but not the actual failure times. In the paper, it is demonstrated that even for a small number of random variables in a finite interval, the probability of clustering of two or more random variables is surprisingly high, and should always be accounted for in risk assessments. [ABSTRACT FROM AUTHOR]

The effect of repair of a complex system can usually be approximated by the following two types: minimal repair for which the system is restored to its functioning state with minimum effort, or perfect repair for which the system is replaced or repaired to a good-as-new state. When both types of repair are possible, an important problem is to determine the repair policy; that is, the type of repair which should be carried out after a failure. In this paper, an optimal allocation problem is studied for a monotonic failure rate repairable system under some resource constraints. In the first model, the numbers of minimal & perfect repairs are fixed, and the optimal repair policy maximizing the expected system lifetime is studied. In the second model, the total amount of repair resource is fixed, and the costs of each minimal & perfect repair are assumed to be known. The optimal allocation algorithm is derived in this case. Two numerical examples are shown to illustrate the procedures. [ABSTRACT FROM AUTHOR]

The transient behavior of a system with operational and repair times distributed following phase-type distributions is studied. These times are alternated in the evolution of the system, and they form 2 separate geometric processes. The stationary study of this system when the repair times form a renewal process has been made [3]. This paper also considers that operational times are partitioned into two well-distinguished classes successively accupied: good, and preventive. An algorithmic approach is performed to determine the transition probabilities for the Markov process which governs the system, and other performance measures beyond those in [3] are calculated in a well-structured form. The results are applied to a numerical example, and the transient quantities are compared with the ones obtained in the stationary case. The computational implementation of the mathematical expressions formulated are performed using the Matlab program. [ABSTRACT FROM AUTHOR]