考虑维修优先权的多状态温贮备系统可靠性模型

针对工程应用中装备维修和保养两类活动具备不同优先级这一问题,考虑单一维修台可进行维修和保养两类工作,其中维修具有优先权.以多状态温贮备系统为研究对象,采用可近似拟合任意分布的Phase-type(PH)分布构建一种描述能力更强的系统可靠性模型,得出系统稳态可用度、系统故障率、平均故障间隔时间等一系列可靠性指标的解析表达式.最后利用算例验证PH分布的适用性,演示系统可靠性函数随时间的变化趋势,并讨论维修台工作速率对系统故障率、稳态可用度、维修台忙期稳态概率和平均故障间隔时间的影响.算例结果表明,所提模型具有较广泛的应用价值.     

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.     

离散时间单重休假冷储备系统的可靠性分析

利用离散向量Markov过程方法研究了离散时间单重休假两同型部件冷储备可修系统。在部件寿命服从几何分布,修理时间和修理工休假时间服从一般离散型概率分布的假定下,引入修理时间和休假时间尾概率,求得了系统的稳态可用度、稳态故障频度、待修概率、修理工空闲概率和休假概率,以及首次故障前平均时间等可靠性指标。     

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.     

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.     

全寿命周期下退化的大规模系统预防性维修策略优化

单元退化情形下,考虑全寿命周期的大规模系统可靠性设计与预防性维修策略的综合优化问题将变得更为复杂.针对单元失效服从威布尔分布的情形,考虑多单元联合的预防性维修模式,构建可靠性约束下大规模系统全寿命周期成本优化模型.单元数量众多带来的组合规模指数增长问题将导致非线性择优困难,利用遗传算法编程快速求解全局最优解,包括设计阶段的单元可靠性和使用阶段的系统预防性维修周期.最后通过典型算例分析验证模型与算法的正确性和有效性,探究维修改善因子、单元可靠性和预防性维修周期等决策变量间的相互关系.研究成果有助于简化系统工程师的可靠性工程设计过程,具有一定的理论和应用价值.     

双贮备系统冷/温/热贮备模型的优化选择研究

对运行设备安装双贮备设备是实现系统高可靠性的有效方法.在双贮备系统冷/温/热三种贮备模型中,选择哪种贮备模型对系统性能指标和经济指标均有重要影响,因此对如何选择双贮备系统的贮备模型从而使系统性能最优或经济效益最大的问题进行研究具有现实意义.而现有研究成果很少涉及双贮备系统贮备模型的优化选择问题.为此,本文创新性地提出一种确定双贮备系统最优贮备模型的选择方法.分别建立系统冷/温/热贮备模型,分析每个模型的系统状态及系统半Markov核函数,利用Markov更新方程、Laplace变换以及Laplace-Stieltjes变换技术推导系统稳态可用度、稳态平均维修次数、维修人员稳态忙期概率以及冷贮备模型的平均激活时间,并从经济角度给出系统单位时间内的净收益函数.最后分别以性能指标和经济指标作为研究目标,通过模型对比分析给出不同条件下的系统贮备模型的优化选择算法,并对每个研究目标下的优化选择算法进行实例计算.计算结果表明以不同性能指标和不同费用作为参考得出的最优贮备模型不尽相同,从而验证了所提方法能够有效地确定不同衡量标准下的系统最优贮备模型.     

一种冗余调度的可靠网格计算模型

为了解决动态、不稳定的网格环境下的可靠计算问题,提出一种基于冗余调度的可靠网格计算模型.首先给出计算网格系统可靠性的定义,并基于系统可靠性定义给出了冗余调度的可靠网格计算模型,设计了冗余调度算法,模拟实验结果证明了提出的模型可以提高计算网格任务调度的可靠性.为了使提出的模型更好应用于实际网格计算环境,给出基于概率的冗余度优化公式,将该公式引入到冗余调度模型,可以获得优化的调度冗余度,不仅可以提高任务调度系统的可靠性,而且能提高资源的利用率.     

基于多元Copula函数的冗余系统可靠性模型研究

在传统k/n表决冗余系统的基础上考虑了系统中部件单元的权重输出形成权重表决系统，该系统中的部件单元寿命变量间具有相依性。运用统计学领域中的多元Copula函数理论刻画各部件单元之间的相关性，基于容斥原理推导出多种部件类型的权重表决系统可靠性模型。结合具体算例，选定典型的Copula函数以及部件独立状态计算系统可靠度，并分析了部件间相关程度对系统可靠度的实际影响，为考虑部件间相依关系的冗余系统可靠度计算提供了参考。     

存在故障相关及不完备检测的主辅并联系统可靠性建模与维修策略

主辅部件并联普遍存在于机电系统中, 部件间存在故障相关性等因素使得针对系统的可靠性建模和维修策略优化尤为困难. 本文以部件间存在I类和III类故障相关性及因检测系统的不完备引起主部件累积损伤速率分布改变的主辅并联系统为对象, 通过对系统退化过程的分析建立其可靠性模型. 依据所建模型和观测的辅助部件的故障次数及系统的运行时间, 建立(T, N)预防性更换策略优化模型. 通过案例分析检测系统的完备性、累积损伤速率等参数对系统可靠性及预防性维修策略的影响.     

Profit function analysis of system with mixture of warm and cold standby

This paper deals with the profit function analysis of a single-server two-unit standby system with two modes of each unit normal (N) and total failure (F). Regarding the standby unit, an interconversion is made repeatedly after a random length of time from warm to cold and cold to warm. Upon failure of the operative unit, the standby unit, if it is warm, starts the operation instantaneously; otherwise the system goes down until the cold standby starts operation. System failure occurs when both units fail totally. Identifying the system at suitable regenerative instants, integral equations are set up and explicit expressions of interest to system designers are obtained to carry out the profit function analysis. The results of two particular cases are also derived.     

On a batch arrival Poisson queue with a random setup time and vacation period

The single server queue with vacation has been extended to include several types of extensions and generalisations, to which attention has been paid by several researchers (e.g. see Doshi, B. T., Single server queues with vacations — a servey. Queueing Systems, 1986, 1, 29–66; Takagi, H., Queueing Analysis: A Foundation of Performance evaluation, Vol. 1, Vacation and Priority systems, Part. 1. North Holland, Amsterdam, 1991; Medhi, J., Extensions and generalizations of the classical single server queueing system with Poisson input. J. Ass. Sci. Soc., 1994, 36, 35–41, etc.). The interest in such types of queues have been further enhanced in resent years because of their theoretical structures as well as their application in many real life situations such as computer, telecommunication, airline scheduling as well as production/inventory systems. This paper concerns the model building of such a production/inventory system, where machine undergoes extra operation (such as machine repair, preventive maintenance, gearing up machinery, etc.) before the processing of raw material is to be started. To be realistic, we also assume that raw materials arrive in batch. This production system can be formulated as an M^x/M/1 queues with a setup time. Further, from the utility point of view of idle time this model can also be formulated as a case of multiple vacation model, where vacation begins at the end of each busy period. Besides, the production/inventory systems, such a model is generally fitted to airline scheduling problems also. In this paper an attempt has been made to study the steady state behavior of such an M^x/M/1 queueing system with a view to provide some system performance measures, which lead to remarkable simplification when solving other similar types of queueing models.This paper deals with the steady state behaviour of a single server batch arrival Poisson queue with a random setup time and a vacation period. The service of the first customer in each busy period is preceded by a random setup period, on completion of which service starts. As soon as the system becomes empty the server goes on vacation for a random length of time. On return from vacation, if he finds customer(s) waiting, the server starts servicing the first customer in the queue. Otherwise it takes another vacation and so on. We study the steady state behaviour of the queue size distribution at random (stationary) point of time as well as at departure point of time and try to show that departure point queue size distribution can be decomposed into three independent random variables, one of which is the queue size of the standard M^x/M/1 queue. The interpretation of the other two random variables will also be provided. Further, we derive analytically explicit expressions for the system state (number of customers in the system) probabilities and provide their appropriate interpretations. Also, we derive some system performance measures. Finally, we develop a procedure to find mean waiting time of an arbitrary customer.     

双向链路下IEEE 802.16e中节能类型Ⅲ的性能分析

为了有效地节省移动终端(mobile station,MS)的能量消耗,延长无线城域网中MS的生命期,综合考虑了IEEE 802.16e节能类型III的双向链路,将上行链路抽象为一个服务台,下行链路抽象为另一个服务台,将休眠状态和侦听状态抽象为休假期,建立了一个两服务台同步休假的多重休假排队系统。应用半马尔可夫过程方法,导出了排队系统的稳态分布。给出了IEEE 802.16e节能类型III中上/下链路数据帧的平均延时和能量节省率等性能指标的表达式,并通过数值例子定量刻画了系统参数对系统性能的影响。     

A tandem queue with general bulk service and servers' “vacation”

This paper analyses two queueing models consisting of two units I and II connected in series, separated by a finite buffer of size N. In both models, unit I has only one exponential server capable of serving customers one at a time and unit II consist of c parallel exponential servers, each of them serving customers in groups according to general bulk service rules. When the queue length in front of unit II is less than the minimum of batch size, the free servers take a vacation. On return from vacation, if the queue length is less than the minimum, they leave for another vacation in the first model, whereas in the second model they wait in the system until they get the minimum number of customers and then start servicing. The steady-state probability vector of the number of customers waiting and receiving service in unit I and waiting in the buffer is obtained for both the models, using the modified matrix geometric method. Numerical results are also presented.     

Stationary distributions and optimal control of queues with batch Markovian arrival process under multiple adaptive vacations

We consider an infinite-buffer single server queue with batch Markovian arrival process (BMAP) and exhaustive service discipline under multiple adaptive vacation policy. That is, the server serves until system emptied and after that server takes a random maximum number H different vacations until either he finds at least one customer in queue or the server have exhaustively taken all the vacations. The maximum number H of vacations taken by the server is a discrete random variable. We obtain queue-length distributions at various epochs such as, service completion/vacation termination, pre-arrival, arbitrary, post-departure and pre-service. The proposed analysis is based on the use of matrix-analytic procedure to obtain queue-length distribution at a post-departure epoch. Later we use supplementary variable method and simple algebraic manipulations to obtain the queue-length distribution at other epochs using queue-length distribution at post-departure epoch. Some important performance measures, like mean queue lengths and mean waiting times have been obtained. Several other vacation queueing models can be obtained as a special case of our model, e.g., single-, multiple-vacation model and queues with exceptional first vacation time. Finally, the total expected cost function per unit time is considered to determine a locally optimal multiple adaptive vacation policy at a minimum cost.