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Zahra Saberzadeh, Mostafa Razmkhah,
Volume 13, Issue 1 (9-2019)
Abstract
The complex systems containing of n elements are considered, each having two dependent components. The main goal of this paper is to investigate the mean residual life of such systems with some intact components at time t. Toward this end, the bivariate binomial model and also two different generalizations are described. Finally, some graphical and numerical analyses are provided for mean residual life of such systems under Farlie-Gumbel-Morgenstern model.
Mohammad Nasirifar, Mohammadreza Akhoond, Mohammadreza Zadkarami,
Volume 13, Issue 2 (2-2020)
Abstract
The parameters of reliability for the most family marginal distribution is estimated with the assumption of independence between two component stress and strength, but, unfortunately when these two component are correlated, have been less discussed. Recently, a method based on a copula function for estimating the reliability parameter is proposed under the assumption of correlation between stress and strength components. In this paper, this method is used to estimate the reliability parameter when the distribution of componets is Generalized Exponential (GE). For this purpose FGM, generalized FGM and frank copula function have been used. Then simulation is also used to demonstrate the suitability of the estimates. In the end, reliability parameter for data relative contribution of major groups in terms of age breakdown of the population of urban and rural areas in Iran in the year 1390 will be estimated.
Majid Chahkandi,
Volume 13, Issue 2 (2-2020)
Abstract
The performance of a system depends not only on its design and operation but also on the servicing and maintenance of the item during its operational lifetime. Thus, the repair and maintenance are important issues in the reliability. In this paper, a repairable k-out-of-n system is considered that starts operating at time 0. If the system fails, then it undergoes minimal repair and begins to operate again. The reliability function, hazard rate function, mean residual life function and some reliability properties of the system are obtained by using the connection between the concepts of minimal repair and record values. Some known stochastic orders are also used to compare the lifetimes and residual lifetimes of two repairable k-out-of-n systems. Finally, based on the given information about the lifetimes of k-out-of-n systems, some prediction intervals for the lifetime of the proposed repairable system are obtained.
Ali Shadrokh, Shahram Yaghoobzadeh Shahrastani,
Volume 13, Issue 2 (2-2020)
Abstract
In this study, the E-Bayesian and hierarchical Bayesian for stress-strength, when X and Y are two independent Rayleigh distributions with different parameters were estimated based on the LINEX loss function. These methods were compared with each other and with the Bayesian estimator using Monte Carlo simulation and two real data sets.
Ghobad Barmalzan, Abedin Haidari,
Volume 13, Issue 2 (2-2020)
Abstract
This paper examines the problem of stochastic comparisons of series and parallel systems with independent and heterogeneous components generalized linear failure rate. First, we consider two series system with possibly different parameters and obtain the usual stochastic order between the series systems. Next, we drive the usual stochastic order between parallel systems. We also discuss the usual stochastic order between parallel systems by using the unordered majorization and the weighted majorization order between the parameters on the Ɗп.
Jafar Ahmadi, Fatemeh Hooti,
Volume 13, Issue 2 (2-2020)
Abstract
In survival studies, frailty models are used to explain the unobserved heterogeneity hazards. In most cases, they are usually considered as the product of the function of the frailty random variable and baseline hazard rate. Which is useful for right censored data. In this paper, the frailty model is explained as the product of the frailty random variable and baseline reversed hazard rate, which can be used for left censored data. The general reversed hazard rate frailty model is introduced and the distributional properties of the proposed model and lifetime random variables are studied. Some dependency properties between lifetime random variable and frailty random variable are investigated. It is shown that some stochastic orderings preserved from frailty random variables to lifetime variables. Some theorems are used to obtain numerical results. The application of the proposed model is discussed in the analysis of left censored data. The results are used to model lung cancer data.
Reza Ahmadi,
Volume 14, Issue 1 (8-2020)
Abstract
We propose an integrated approach for decision making about repair and maintenance of deteriorating systems whose failures are detected only by inspections. Inspections at periodic times reveal the true state of the system's components and preventive and corrective maintenance actions are carried out in response to the observed system state. Assuming a threshold-type policy, the paper aims at minimizing the long-run average maintenance cost per unit time by determining appropriate inspection intervals and a maintenance threshold. Using the renewal reward theorem, the expected cost per cycle and expected cycle length emerge as solutions of equations, and a recursive scheme is devised to solve them. We demonstrate the procedure and its outperformance over specific cases when the components' lifetime conforms to a Weibull distribution. Further, a sensitivity analysis is performed to determine the impact of the model's parameters. Attention has turned to perfect repair and inspection, but the structure allows different scenarios to be explored.
Mohammad Hossein Poursaeed, Nader Asadian,
Volume 14, Issue 1 (8-2020)
Abstract
A system in discrete time periods is exposed to a sequence of shocks so that shocks occur randomly and independently in each period with a probability p. Considering k(≥1) as a critical level, we assume that the system does not fail when the number of successive shocks is less than k, the system fails with probability Ө, if the number of successive shocks is equal to k and the system completely fails as soon as the number of sequential shocks reaches k+1. Therefore, this model can be considered as a version of run shock model, in which the shocks occur in discrete periods of time, and the behavior of the system is not fixed when encountering k successive shocks. In this paper, we examine the characteristics of the system according to this model, especially the first and second-order moments of the system's lifetime, and also estimate its unknown parameters. Finally, a method is proposed to calculate the mean of the generalized geometric distribution.
Mohadaseh Khayyat, Rasool Rozegar, Ghobad Barmalzan,
Volume 14, Issue 1 (8-2020)
Abstract
The modified proportional hazard rates model, as one of the flexible families of distributions in reliability and survival analysis, and stochastic comparisons of (n-k+1) -out-of- n systems comprising this model have been introduced by Balakrishnan et al. (2018). In this paper, we consider the modified proportional hazard rates model with a discrete baseline case and investigate ageing properties and preservation of the usual stochastic order, hazard rate order and likelihood ratio order in this family of distributions.
Shahram Yaghoobzadeh,
Volume 14, Issue 1 (8-2020)
Abstract
In this study, the E-Bayesian estimation of the reliability parameter, R = P(Y < X < Z), when X, Y and Z are three independent inverse Rayleigh distribution with different parameters, were estimated based on ranked set sampling method. To assess the efficiency of the obtained estimates, we compute the average absolute bias and relative efficiency of the derived estimates and compare them with those based on the corresponding simple random sample through Monte Carlo simulations. Also, E-Bayesian estimation of R is compared with its maximum likelihood estimation in each method. Finally, three real data sets are used to analyze the estimation methods.
Ebrahim Amini Seresht, Ghobad Barmalzan,
Volume 14, Issue 2 (2-2021)
Abstract
This paper examines the problem of stochastic comparisons of k-out-of-n systems with independent multiple-outlier scale components. In this regard, we first consider a k-out-of-n system comprising multiple-outlier scale components and then, by using a permanent function, investigate the likelihood ratio order between these systems.
Elham Basiri,
Volume 14, Issue 2 (2-2021)
Abstract
When a system is used, it is often of interest to determine with what probability it will work longer than a pre-fixed time. In other words, determining the reliability of this system is of interest. On the other hand, the reliability of each system depends on the structure and reliability of its components. Therefore, in order to improve the reliability of the system, the reliability of its components should be improved. For this purpose, it is necessary to carry out maintenance operations, which will increase costs. Another way to increase the reliability of systems is to change the location of the components. In this paper, the location of system components and optimal maintenance period are determined by minimizing the costs and maximizing the reliability of a series-parallel system. Finally, a numerical example is presented to evaluate the results in the paper.
Akram Kohansal, Nafiseh Alemohammad, Fatemeh Azizzadeh,
Volume 14, Issue 2 (2-2021)
Abstract
The Bayesian estimation of the stress-strength parameter in Lomax distribution under the progressive hybrid censored sample is considered in three cases. First, assuming the stress and strength are two random variables with a common scale and different shape parameters. The Bayesian estimations of these parameters are approximated by Lindley method and the Gibbs algorithm. Second, assuming the scale parameter is known, the exact Bayes estimation of the stress-strength parameter is obtained. Third, assuming all parameters are unknown, the Bayesian estimation of the stress-strength parameter is derived via the Gibbs algorithm. Also, the maximum likelihood estimations are calculated, and the usefulness of the Bayesian estimations is confirmed, in comparison with them. Finally, the different methods are evaluated utilizing the Monte Carlo simulation and one real data set is analyzed.
Reza Zarei, ,
Volume 14, Issue 2 (2-2021)
Abstract
In this paper, the Bayesian and empirical Bayesian approaches studied in estimate the multicomponent stress–strength reliability model when the strength and stress variables have a generalized Rayleigh distribution with different shape parameters and identical scale parameter. The Bayesian, empirical Bayesian and maximum likelihood estimation of reliability function is obtained in the two cases known and unknown of scale parameter under the mean squared error loss function. Then, these estimators are compared empirically using Monte Carlo simulation and two real data sets.
Hoda Kamranfar, Javad Etminan, Majid Chahkandi,
Volume 14, Issue 2 (2-2021)
Abstract
A repairable system with two types of failures is studied. Type I failure (minor failure) is removed by a minimal repair, whereas type II failure (catastrophic failure) is modified by an unplanned replacement. The first failure of the system follows a Weibull probability distribution and two maintenance policies are considered. In the first policy, the system is replaced at time T or the first type II failure, and in the second policy, the system is replaced at the nth type I failure, the first type II failure or at time T, whichever takes place first. This paper aims to derive a general representation for the likelihood function of the proposed models. The likelihood-ratio test statistic, maximum likelihood estimators and asymptotic confidence intervals for the parameters are also found. Finally, a Monte Carlo simulation is conducted to illustrate the results.
Majid Chahkandi, Jalal Etminan, Mohammad Khanjari Sadegh,
Volume 15, Issue 1 (9-2021)
Abstract
Redundancy and reduction are two main methods for improving system reliability. In a redundancy method, system reliability can be improved by adding extra components to some original components of the system. In a reduction method, system reliability increases by reducing the failure rate at all or some components of the system. Using the concept of reliability equivalence factors, this paper investigates equivalence between the reduction and redundancy methods. A closed formula is obtained for computing the survival equivalence factor. This factor determines the amount of reduction in the failure rate of a system component(s) to reach the reliability of the same system when it is improved. The effect of component importance measure is also studied in our derivations.
Motahare Zaeamzadeh, Jafar Ahmadi, Bahareh Khatib Astaneh,
Volume 15, Issue 2 (3-2022)
Abstract
In this paper, the lifetime model based on series systems with a random number of components from the family of power series distributions has been considered. First, some basic theoretical results have been obtained, which have been used to optimize the number of components in series systems. The average lifetime of the system, the cost function, and the total time on test have been used as an objective function in optimization. The issue has been investigated in detail when the lifetimes of system components have Weibull distribution, and the number of components has geometric, logarithmic, or zero-truncated Poisson distributions. The results have been given analytically and numerically. Finally, a real data set has been used to illustrate the obtained results.
Ebrahim Amini Seresht, Ghobad Barmalzan,
Volume 15, Issue 2 (3-2022)
Abstract
This paper discusses stochastic comparisons of the parallel and series systems comprising multiple-outlier scale components. Under uncertain conditions on the baseline reversed hazard rate, hazard rate functions and scale parameters, the likelihood ratio, dispersive and mean residual life orders between parallel and series systems are established. We then apply the results for two exceptional cases of the multiple-outlier scale model: gamma and Pareto multiple-outlier components to illustrate the found results.
Ghobad Barmalzan, Ali Akbar Hosseinzadeh, Ebrahim Amini Seresht,
Volume 15, Issue 2 (3-2022)
Abstract
This paper discusses the hazard rate order of the fail-safe systems arising from two sets of independent multiple-outlier scale distributed components. Under certain conditions on scale parameters in the scale model and the submajorization order between the sample size vectors, the hazard rate ordering between the corresponding fail-safe systems from multiple-outlier scale random variables is established. Under certain conditions on the Archimedean copula and scale parameters, we also discuss the usual stochastic order of these systems with dependent components.
Ebrahim Amini-Seresht, Ghobad Barmalzan, Ebrahim Nasiroleslami,
Volume 16, Issue 1 (9-2022)
Abstract
This paper deals with some stochastic comparisons of convolution of random variables comprising scale variables. Sufficient conditions are established for these convolutions' likelihood ratio ordering and hazard rate order. The results established in this paper generalize some known results in the literature. Several examples are also presented for more illustrations.
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