Availability of a repairable retrial system with warm standby components

In this paper, we study a repairable K-out-of-(M+W) retrial system with M identical primary components, W standby components and one repair facility. The time-to-failure and time-to-repair of the primary and standby components are assumed to be exponential and general distributions, respectively. The failed components are immediately for repair if the server is idle, otherwise the failed machines would enter an orbit. It is assumed that the retrial times are exponentially distributed. We present a recursive method using the supplementary variable technique and treating the supplementary variable as the remaining repair time to obtain the steady-state probabilities of down components at arbitrary epoch. Then, a unified and efficient algorithm is developed to compute the steady-state availability. The method is illustrated analytically for the exponential repair time distribution. Sensitivity analysis of the steady-state availability with respect to system parameters for a variety of repair time distributions is also investigated.     

基于中间件的可修复分布式系统可靠性分析

中间件是大型分布式系统的核心,可以为系统应用程序提供双机热备、双网冗余服务.针对分布式冗余系统可靠性问题,利用马尔可夫模型对可修复分布式冗余系统进行可靠性分析.按照优先恢复应用程序功能的修复策略,由系统状态转移关系建立系统状态转移图,进而得出了系统可靠度的计算方法.仿真结果表明,应用程序故障对系统可靠性的影响大于网络故障,提高修复优先级较高模块的维修率可有效增加系统的可靠度.     

连接函数下部件相依可修系统的可靠性分析

将Copula函数应用到部件相依可修系统的可靠性分析中,刻画出两相依部件组成的串联系统的寿命分布,实现单部件可修系统的虚拟化;利用增加变量法将虚拟单部件可修系统转化为马尔可夫可修系统,计算出系统的可靠性指标。通过算例验证了所讨论思路的有效性。     

Reliability and sensitivity analysis of a repairable system with imperfect coverage under service pressure condition

This paper investigates reliability and sensitivity analysis of a repairable system with imperfect coverage under service pressure condition. Failure times and repair times of failed units are assumed to be exponentially distributed. As a unit fails, it may be immediately detected, located and replaced with a coverage probability c by a standby if one is available. When the repairmen are under the pressure of a long queue, the repairmen may increase the repair rate to reduce the queue length. We derive the explicit expressions for reliability function and mean time to system failure (MTTF). Various cases are analyzed to study the effects of different parameters on the system reliability and MTTF. We also accomplish sensitivity analysis and relative sensitivity analysis of the reliability characteristics with respect to system parameters.     

基于Markov模型的可维修双机热备系统可靠性分析

为了综合考虑维修性、故障检测率及共因失效对双机热备系统可靠性的影响,利用马尔可夫模型对可维修双机热备系统进行可靠性分析.由系统状态转移关系建立双机热备系统的状态转移图,由于备用单元发生不可测失效时不能及时对其进行维修,提出在状态转移图中增加一个状态来区分此种降级工作状态.根据状态转移图得到系统状态转移方程并借助Matlab对其进行求解,得到故障检测率、失效率、维修率与共因失效因子为不同取值时的系统状态概率图.分析结果表明,维修率对可维修双机热备系统达到平稳状态所需时间贡献较大,系统工作状态概率值与故障状态概率值则由故障率与修复率的比值、故障检测率及共因失效等因素共同决定.     

藏文排序优先级算法研究

为了顺利实现藏文词语的排序算法,在藏文构件元素识别算法的基础上,该文通过建立藏文规则函数和定义藏文构件的优先级,提出了基于笛卡尔积数学模型的现代藏文音节的优先级算法。该方法既遵循藏文构词原则,又符合语法规则,同时为藏文词语排序算法提供了新的研究思路。最后该文用藏文“”系的所有满足语法规则的词语对本算法进行测试,结果表明该算法符合现代藏文词典的排序要求,且排序效率更好。     

State probability of a series-parallel repairable system with two-types of failure states

This paper presents a method for the analysis of a series-parallel safety-critical system where the system states can be distinguished into failure-safe and failure-dangerous. The method incorporates the Markov chain and universal generating function technique. In the model considered, both periodic inspection and repair (perfect and imperfect) of system elements are taken into account. The system state distributions and the overall system safety function are derived, based on the developed model. The proposed method is applicable to complex systems for analysing state distributions and it is also useful in decision-making such as determining the optimal proof-test interval or repair resource allocation. An illustrative example is given.     

Optimal replacement policy for a two-dissimilar-component cold standby system with different repair actions

In this paper, a cold standby repairable system consisting of two dissimilar components and one repairman is studied. When failures occur, the repair of both component 1 and component 2 are not ‘as good as new’. The consecutive operating times of component 1 after repair constitute a decreasing geometric process, while the repair times of component 1 are independent and identically distributed. For component 2, its failure is rectified by minimal repair, and the repair time is negligible. Component 1 has priority in use when both components are good. The replacement policy N is based on the failure number of component 1. Under policy N, we derive the explicit expression of the long-run average cost rate C(N) as well as the average number of repairs of component 2 before the system replaced. The optimal replacement policy N*, which minimises the long-run average cost rate C(N), is obtained theoretically. If the failure rate r(t) of component 2 is increasing, the existence and uniqueness of the optimal policy N* is also proved. Finally, a numerical example is given to validate the developed theoretical model. Some sensitivity analyses are provided to show the influence of some parameters, such as the costs for replacement and repair, and the parameters of the lifetime and repair time distributions of both components, to the optimal replacement policy N* and corresponding average cost rate C(N*).     

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。     

Sliding mode control of a discrete system

Conventional sliding mode control designed on the basis of a continuous system is known to be robust to the plant uncertainties. A realized digital system, however, not only yields chattering, but also may become unstable by a long sampling interval. This paper presents a stable discrete sliding mode control insensitive to the choice of sampling interval and not yielding chattering. The control system is designed on the basis of a discrete Lyapunov function and a sufficient condition of the control gain to make the system stable is given. Contrary to the continuous case, the derived switching plane of the control law is different from the sliding mode, and in its neighborhood, the control law is given by the linear state feedback. Simulations show the effectiveness of the proposed method.     

Reliability analysis of a system with combined time reserve

A semi-Markov model of a system with combined time reserve and a discrete-continuous phase space of states is considered. Basic reliability characteristics of this system are found.Translated from Kibernetika i Sistemnyi Analiz, No. 5, pp. 141–149, September–October 2004.     

Reliability of a large series-parallel system in variable operating conditions

In this paper, a semi-Markov model of system operation processes is proposed and its selected parameters are determined. A series-parallel multi-state system is considered, and its reliability and risk characteristics found. Subsequently, a joint model of system operation process and system multi-state reliability and risk is constructed. Moreover, the asymptotic approach to reliability and risk evaluation of a multi-state series-parallel system in its operation process is applied to a port grain transportation system.     

嵌入式系统硬件可靠性Copula方法建模与分析

嵌入式系统硬件的可靠性是十分重要的,它直接关系到嵌入式系统的质量和寿命。为了对嵌入式系统的硬件可靠性进行分析,利用Copula方法从硬件角度和层面对其进行研究。首先从嵌入式系统硬件的组成层面对其进行抽象定义;然后从组成嵌入式系统硬件的每个功能模块出发,对每个功能模块从软硬件综合角度进行可靠性建模,同时利用Copula函数建立了嵌入式系统硬件的可靠性模型;最后对嵌入式系统硬件可靠性模型的参数进行估计,给出具体的嵌入式系统硬件可靠性计算实例,并将所建立的模型与其他类型的Copula函数进行比较。通过实例化分析和验证结果表明,得到的嵌入式系统硬件Copula函数模型是切实可行的。     

智能PID算法在远程液位控制系统中的应用

本文介绍了利用可编程序控制器(PLC)实现的远程液位自动控制系统，详细论述了智能PID算法的控制规则，给出了由PLC完成其控制策略的硬件配置和软件实现方法。     

易用的操作系统安全模型的设计和实现

提出并实现了一种应用于PC操作系统的安全模型USPM,在保证足够安全性同时具有兼容性好、无需专门配置即可使用的特点。模型使系统能够在被黑客攻击成功的情况下保证机密文件不丢失、关键文件完整性不被破坏。USPM模型通过限制那些与远程系统进行数据交换的进程的活动来保证系统的安全性,同时通过设置一些例外规则部分的允许特定进程的访问活动来提高系统的易用性,达到在安全性和易用性间的平衡。测试表明,USPM具有较好的安全性,较低的开销和很好的易用性、兼容性。     

基于Netflow的网络安全态势感知系统研究*

综述了网络安全态势感知系统的国内外研究现状;介绍了Netflow基本原理及其数据格式;提出了基于Netflow的网络安全态势感知系统结构;重点研究了实现本系统相关的关键技术.经试验表明,该方法合理可行.     

边失效情形下一类供应链系统的可靠性分析

以基于最大覆盖选址模型的供应链系统为对象,研究了边设施失效对其可靠性的影响。建立了以系统效率最大或最小化为目标的确定性边失效和随机性边失效两种情形下的优化模型,由此给出了解决这类可靠性分析问题的一般方法。实例求解结果表明模型合理,有一定推广和应用价值。     

面向网络安全资源池的智能服务链系统设计与分析

传统网络安全架构通过将流量引导经过硬件形式的网络安全功能设备来保障网络安全,该架构由形式固定的硬件组成,导致网络安全区域部署形式单一,可扩展性较差,在面对网络安全事件时无法灵活地做出调整,难以满足未来网络的安全需求。面向网络安全资源池的智能服务链系统基于软件定义网络与网络功能虚拟化技术,能够有效解决上述问题。基于网络功能虚拟化技术新增虚拟形式的网络安全功能网元,结合已有的硬件网元构建虚实结合的网络安全资源池,并基于软件定义网络技术实现对连接网元的交换设备的灵活控制,从而构建可动态调节的网络安全服务链;基于安全日志检测与安全规则专家库实现对网络安全事件的检测与生成对应的响应方案,从而能够在面对网络安全事件时通过集中式控制的方式实现服务链的动态智能调节;对服务链的部署过程进行数学建模并设计了一种启发式的服务链优化编排算法,实现服务链的优化部署。通过搭建原型系统并进行实验,结果表明,所设计系统能够在面对安全事件时在秒级时间内完成安全事件的检测,并能够在分钟级时间内完成对安全服务链的自动调整,所设计的服务链优化部署算法能够将服务链对虚拟安全资源池中资源的占用降低65%。所设计系统有望运用于园区...     

基于BHO技术的网页安全检测系统的研究

针对日益严峻的网页安全现状和传统的网页检测系统不能满足现代网络的安全需求的情况,在详细介绍了微软浏览器帮助对象(browser help objects,BHO)技术的工作原理的基础上,提出了一个具有自主学习能力的网页安全检测系统模型.该系统通过微软BHO技术开发的插件采集网页的行为模式数据,进而通过类关联规则建立起网页访问分类器,最终实现对访问网页的安全检测与实时监控.实验结果表明,该系统可以有效地辨别恶意网页.