修理工带休假的单部件可修系统的可靠性分析

考虑修理工带有单重休假的单部件可修系统,系统发生故障时可能因修理工的休假而得不到立即修理,因此系统可处于工作、等待修理和修理三种状态.利用全概率分解技术和拉普拉斯或拉普拉斯--司梯阶变换工具,讨论了系统的可靠度、瞬时可用度和稳态可用度,以及(O,t]时间中系统的平均故障次数和稳态故障频度,得到了关于系统的可靠度、瞬时可用度和稳态可用度,以及(O,t]时间中系统的平均故障次数和稳态故障频度等可靠性指标的重要结果.     

具有单重休假和修复不如新的两部件温贮备系统

研究了修理工单重休假且由两个不同型部件和一个修理工组成的可修型温贮备系统. 系统考虑了在工作故障和贮备 故障都不能 “修复如新”, 部件 1 是修复非新而部件 2 修复如新的条件下, 假设部件的工作寿命、贮备寿命、故障后的修理时间和贮备故障后的修理时间均服 从不同的指数分布, 修理工休假服从一般连续型分布. 运用几何过程理论、补充变量法、 拉普拉斯变换及拉普拉斯--司梯阶变换, 得到了系统的可用度、可靠度和系统首次故障前平均时间等可靠性指标. 最后, 通过数值模拟验证了结果的有效性.     

带启动时间和可修服务台的M/M/1/N工作休假排队系统

分析带有启动时间、服务台可故障的M/M/1/N单重工作休假排队系统.在该系统中,服务台在休假期间不是完全停止工作,而是处于低速服务状态.假定服务台允许出现故障且当出现故障时,服务台停止为顾客服务且立即进行修理.服务台的失效时间和修理时间均服从指数分布,且工作休假期和正规忙期具有不同的取值;同时,从关闭期到正规忙期有服从指数分布的启动时间.建立此工作休假排队系统的有限状态拟生灭过程(QBD),使用矩阵几何方法得到QBD的各稳态概率相互依赖的率阵,从而求得稳态概率向量.通过有限状态QBD的最小生成元和稳态概率向量得到系统的基本阵和协方差矩阵,求解出系统方差、系统稳态可用度、系统吞吐率、系统稳态队长、系统稳态故障频度等系统性能.数值分析体现了所提出方法的有效性和实用性,通过敏感性分析将各参数对系统性能的影响进行了初探,为此模型的实际应用提供了很好的理论依据.     

具有自重置功能的两部件温贮备可修系统的可靠性分析

该文讨论具有自重置功能的两部件温贮备可修系统.系统有两种修理策略,一是每个部件都有自重置功能,即通过自动错误检测从故障中自动恢复;二是通过修理工修理故障的部件.该文首先研究该系统稳态和瞬时可靠性指标,然后讨论了系统各参数对系统可靠性的影响.     

基于优先使用权的温贮备可修重试系统可靠性与期望成本模型

针对具有两种不同类型部件的温贮备可修系统,基于优先使用权规则,将部件的重试特性和不可靠修理设备引入系统,建立一种新的系统可靠性和成本模型.失效部件由一个不可靠修理设备维修,当正常的修理设备维修失效部件时会发生不完全故障,此时,它或以一定的概率立即被维修,或以一定的概率继续低效维修失效部件.在不完全故障下,修理设备有可能发生完全性故障,完全性故障后会立即被维修.鉴于维修环境的随机波动性,利用PH分布对修理设备的修理时间进行建模,这在一定程度上拓展了模型的适用性.通过概率讨论得到稳态下系统的一些主要性能指标,构建单位时间的总期望成本函数,并就总期望成本关于各参数的敏感性进行分析.通过数值实例展示系统参数对系统稳态性能指标和系统成本的影响,为系统可靠性设计者和决策者提供理论支撑和参考.     

考虑多维修台异步多重休假的温贮备冗余系统可靠性模型

考虑多维修台保障多个系统时维修力量存在调度与分配的情况,引入多维修台异步多重休假策略;以温贮备冗余系统为研究对象,针对以往研究利用指数分布等典型分布导致模型约束条件过于严格的问题,采用连续phase-type(PH)分布描述系统中工作部件寿命、温贮备部件寿命以及维修台休假时间和维修时间,建立通用性更好的系统可靠性解析模型,给出系统可靠度、系统稳态可用度等冗余系统可靠性指标和稳态忙期维修台数量等维修台稳态指标;利用算例验证模型适用性,演示了维修台数量、系统温贮备部件数量变化以及修理工休假速率、维修速率变化对系统各可靠性指标和维修台稳态指标的影响.算例计算结果表明,所提出的可靠性模型能够有效复现多维修台调度对冗余系统可靠性的影响,从而为维修台数量的合理安排及系统部件数量的优化配置提供理论基础和实践参考.     

带工作休假和工作故障的M/M/1/N排队系统性能分析

本文在可修M/M/1/N排队系统中引入了启动时间、工作休假和工作故障策略.在该系统中,服务台在休假期间不是完全停止工作,而是处于低速服务状态.设定服务台在任何时候均可发生故障,当故障发生时立刻进行维修.且当服务台在正规忙期出现故障时,服务台仍以较低的服务速率为顾客服务.服务台的寿命时间和修理时间均服从指数分布,且在不同...     

带启动时间和工作故障的M/M/1/N排队系统性能分析

在M/M/1/N可修排队系统中引入了工作故障和启动时间.服务台在忙期允许出现故障,且在故障期间不是完全停止服务而是以较低的服务速率为顾客服务.同时,从关闭期到正规忙期有服从指数分布的启动时间.通过分析此模型的二维连续时间Markov过程,求解出系统平稳方程,建立此系统的有限状态拟生灭过程(QBD).根据系统参数,求解出水平相依的子率阵,从而得到系统稳态概率向量的矩阵几何表示形式.在系统稳态概率向量的基础上,求解出系统吞吐率、系统稳态可用度、系统稳态队长及系统处于各个状态的概率等性能指标的解析表达式.文中的敏感性分析体现了这种方法的有效性和可用性,同时,对系统各性能受系统参数的影响进行了探索.实验表明,文中提出模型的稳定性较好,且更贴近实际服务过程,因此这种模型将被广泛应用于各种实际服务中.     

考虑通信部件的双机系统的可靠性分析

本文从容错计算机系统的工作原理出发,把典型双机系统中的通信部件与计算机分开考虑,利用马尔柯夫更新过程研究了部件修理时间服从任意分布情况下的双机系统可靠性问题,给出了有关可靠性指标的计算公式。     

考虑机理耦合的分层IFC系统恢复机制研究

基于故障机理耦合关系改进的二元决策图(BDD)模型,针对典型的带有监测设备的分层系统不完全覆盖的故障恢复机制进行研究。从部件间的故障机理耦合关系出发,研究了系统中存在的未覆盖故障对系统故障行为的影响,并提出了考虑这些影响时系统故障行为建模与分析方法。利用阶段离散型时间模型,分析了不同故障恢复机制下系统故障行为并进行了理论推导;细化阶段型时间离散模型,提出了将故障机理耦合关系、IFC故障行为以及故障恢复机制综合的建模方法。     

Multi-server machine repair model with standbys and synchronous multiple vacation

This paper investigates a machine repair problem with homogeneous machines and standbys available, in which multiple technicians are responsible for supervising these machines and operate a (R, V, K) synchronous vacation policy. With such a policy, if any V idle technicians exist in the system, these V (V < R) technicians would take a synchronous vacation. Upon returning from vacation, they would take another vacation if there is no broken machine waiting in the queue. This pattern continues until at least one failed machine arrives. It is assumed that the number of teams/groups on vacation is less than or equal to K (0 ≦ KV < R). The matrix analytical method is employed to obtain a steady-state probability and the closed-form expression of the system performance measures. Efficient approaches are performed to deal with the optimization problem of the discrete/continuous variables while maintaining the system availability at a specified acceptable level.     

云计算环境下的可修分布式系统可靠性分析方法

随着云计算技术的进一步发展,越来越多的应用系统托管在云计算平台上,这就对构成云计算平台的众多分布式系统的可靠性提出了更高的要求。传统分析方法难以在系统规模较大时对可修分布式系统做可靠性分析。为了提高服务质量以及降低因违反服务水平协议而导致的经济损失,本文基于马尔可夫模型提出一种适用于可修分布式系统的可靠性分析方法。通过简化系统的状态空间,在系统运行期间对其软硬件状态进行采样,并通过对分布式系统的失效过程和修复过程进行分析,根据给定时间内的失效概率序列、修复概率序列计算分布式系统的节点状态转移矩阵,得出该马尔可夫矩阵对应的稳态向量。根据特定分布式系统的自身特性,对该稳态向量进一步分析,得出系统最终的可靠性衡量指标。最后通过实验验证了该方法的可用性和有效性。     

Bayesian assessing for a repairable system with standby imperfect switching and reboot delay

System performance measures of a repairable system are studied from a Bayesian viewpoint with different types of priors assumed for unknown parameters, in which the system consists of two active components and one warm standby. There is a failure probability q that switches from standby state to active state. Time-to-failure of components is assumed to be an exponential distribution. The reboot time and repair time are also exponential distributions. When time-to-failure, time-to-repair and reboot time are with uncertain parameters, a Bayesian assessing is adopted to evaluate system performance measures. Monte Carlo simulation is used to derive the posterior distribution for the steady-state availability and the mean time-to-system failure. Some numerical experiments are performed to illustrate the results derived in this article.     

Optimal replacement policy for a repairable system with multiple vacations and imperfect fault coverage

The present investigation deals with the reliability analysis of a repairable system consisting of single repairman who can take multiple vacations. The system failure may occur due to two types of faults termed as major and minor. When the system has failed due to minor faults, it is perfectly recovered by the repairman. If the system failure is due to major faults, there are some recovery levels/procedures that recover the faults imperfectly with some probability. However, the system cannot be repaired in ‘as good as new’ condition. It is assumed that the repairman can perform some other tasks when either the system is idle or waiting for recovery from the faults. The life time of the system and vacation time of the repairman are assumed to be exponential distributed while the repair time follows the general distribution. By assuming the geometric process for the system working/vacation time, the supplementary variable technique and Laplace transforms approach are employed to derive the reliability indices of the system. We propose the replacement policy to maximize the expected profit after a long run time. The validity of the analytical results is justified by taking numerical illustrations.     

Cost-minimization analysis of a working vacation queue with N-policy and server breakdowns

This paper investigates the N-policy M/M/1 queueing system with working vacation and server breakdowns. As soon as the system becomes empty, the server begins a working vacation. The server works at a lower service rate rather than completely stopping service during a vacation period. The server may break down with different breakdown rates during the idle, working vacation, and normal busy periods. It is assumed that service times, vacation times, and repair times are all exponentially distributed. We analyze this queueing model as a quasi-birth–death process. Furthermore, the equilibrium condition of the system is derived for the steady state. Using the matrix-geometric method, we find the matrix-form expressions for the stationary probability distribution of the number of customers in the system and system performance measures. The expected cost function per unit time is constructed to determine the optimal values of the system decision variables, including the threshold N and mean service rates. We employ the particle swarm optimization algorithm to solve the optimization problem. Finally, numerical results are provided, and an application example is given to demonstrate the applicability of the queueing model.     

Entropy maximization and NT vacation M/G/1 model with a startup and unreliable server: comparative analysis on the first two moments of system size

We consider the control policy of an M/G/1 queueing system with a startup and unreliable server, in which the length of the vacation period is controlled either by the number of arrivals during the idle period, or by a timer. After all the customers have been served in the queue, the server immediately takes a vacation and operates an NT vacation policy: the server reactivates as soon as the number of arrivals in the queue reaches a predetermined threshold N or when the waiting time of the leading customer reaches T units. In such a variant vacation system, the steady-state probabilities cannot be obtained explicitly. Thus, the maximum entropy principle is used to derive the approximate formulas for the steady-state probability distributions of the queue length. A comparitive analysis of two approximation approaches, using the first and the second moments of system size, is studied. Both solutions are compared with the exact results under several service time distributions with specific parameter values. Our numerical investigations demonstrate that the use of the second moment of system size for the available information is, in general, sufficient to obtain more accurate estimations than that of the first moment.