特殊状态特殊修理的可修系统可靠性和诊断策略

本研究了特殊状态需要特殊修理的可修系统的可靠性和诊断策略。假设系统有三种运行状态：正常状态、异常状态、故障状态，有些异常状态和故障状态需要特殊的修理，系统处于哪个状态需要诊断才能知道。每当系统开始正常工作状态后，每隔一段随机时间T进行一次诊断，直到系统故障或被诊断为异常。利用概率分析和向量马尔科夫过程方法，求得了系统的可靠性指标并研究了最优诊断策略。     

具有未知扰动的广义系统的故障检测

研究具有未知扰动的随机广义系统的故障检测问题,在合理的条件下,利用状态变换从原系统中分离出一个与未知扰动解耦的降阶子系统,构造了该随机子系统稳定的滤波器,给出了输出偏差量的统计特性,在此基础上,实现了系统故障的检测．     

考虑不完全检测的冲击模型最优维修策略

针对制造系统中设备检测不完全的情形,研究基于不完全检测的冲击模型的周期检测、维修联合策略．通过定期检测获知系统的劣化状态以进行必要的预防性维修．在假设系统是退化的且有k个不同故障状态的条件下,以最小化系统运行成本为目标,以检测周期T、系统更换前故障次数Ⅳ为联合决策变量,利用更新过程理论建立了系统平均费用率C（T,N）的数学模型,并且给出最优联合策略的数值算法．最后借助数值例子演示了该模型,分析了检测水平对系统运行成本的影响．     

考虑负载共享的线性连续k-out-of-n:F系统检测策略优化

针对线性连续k-out-of-n:F系统提出定期检测策略,每隔固定周期对系统中各部件状态进行检查并以新部件更换故障部件,若系统发生故障则立即停机并更换故障部件.由于受到负载共享的影响,各工作部件故障率不仅与系统中发生故障的部件数量相关,还与其相邻部件状态有关;为此,引入损伤故障率模型描述部件故障率.基于故障序列图和更新报酬理论建立定期检测策略优化模型以最小化单位时间内的期望成本,确定最优检测周期.最后,通过算例分析验证模型的有效性.     

泊松冲击下冷贮备可修系统的可靠性分析

本文研究了一类由有限个同质部件和一个修理工组成的冷贮备可修系统在随机冲击下的可靠性问题。假设冲击以泊松过程到达。当冲击到达时,它会独立地对系统中工作的部件产生影响,而不会对冷贮备部件产生影响。每次冲击的量都服从某一确定的分布,受冲击的部件以一定的概率发生故障,其故障概率是冲击量的函数,当工作的部件发生故障时,下一个冷贮备部件立即开始工作,当所有部件故障时,系统故障,故障部件按故障顺序进行修理,修理时间服从指数分布,故障部件能被修理如新。本文显式给出了系统首次故障前平均时间、稳态可用度、稳态故障频度等可靠性指标。     

复杂可修复系统故障数据分析处理中的两个问题

马良河等．复杂可修复系统故障数据分析处理中的两个问题．数理统计与管理，１９９８，１７（３），３７～４０．本文给出了利用部件的故障数据对复杂可修复系统的可靠性状态进行分析和估计时应首先解决的两个问题：应选取合适的故障数据及应分析系统部件的固有属性对故障数据的影响。进而给出了这两个问题的解决方法及对系统性能的分析方法。最后针对飞机发动机的一组故障数据给出了计算实例。所用工具主要是假设检验和方差分析的理论     

ATM交易状态特征分析与异常检测

考虑ATM交易过程当中产生的一系列参数,如交易量、交易成功率和响应时间等,对交易状态特征进行分析并建立了异常检测模型。针对成功率与响应时间2个参数,利用聚类算法将数据点划分为正常点、疑似异常点、异常点3大类。对于疑似的异常点,再根据其时间序列周围点的分布情况确定是否确实为异常点;对于交易量参数,首先通过LOF局部离群因子对离群点进行识别,再结合交易量随时间的移动均线及标准差加以辅助筛选,得到初步的疑似异常点,进一步通过与不同天同一时刻数据进行比较,最终确定是否为异常点。根据上述模型,本文将异常情况划分为3个预警等级,并对重大故障情况进行预测。     

基于SVM极点分类的故障诊断与可靠控制

利用SVM分类技术,针对系统故障极点进行分类,利用网格搜寻法,实现对不同故障极点的分类进而实现对系统故障的检测和诊断,为了实现对系统极点变化的实时监测,给出了通过系统状态估计系统极点的新方法.在给出故障诊断的基础上,同时给出了针对相应故障的可靠控制器的设计.最后通过数例验证极点观测器对极点估计的准确性和故障诊断的准确性及可靠控制的有效性.     

具有小修和不完全预防性维修的多状态退化系统的可用度分析

研究了一种多状态退化系统,该系统由于在工作过程中逐渐退化,导致系统的效率降低.为了减少系统的失效率和退化率,系统会受到随机失效后的小修和退化到最后一个可接受工作状态时的预防性维修.在这种具有小修和不完全预防性维修的多状态退化系统模型中,假定系统能连续退化成一些离散状态,并且这些离散状态是从正常工作状态一直到完全失效状态.当系统逐渐退化到某个临界值(这里把它称作不可接受状态)时,就视系统完全失效,那么在最后一个可接受状态时系统就会得到预防性维修;当系统从任意的工作状态随机失效后就会得到小修.在这个模型中,基于它是一个连续时间的马尔可夫过程,来计算稳态可用度指标.     

有两种故障状态的两部件串联系统的预防维修策略

本文研究的是由两个部件串联组成且有两种故障状态的系统的预防维修策略, 当系统的工作时间达到T时进行预防维修, 预防维修使部件恢复到上一次故障维修后的状态。每个部件发生故障都有两种状态, 可维修和不可维修。当部件的故障为可维修故障时, 修理工对其进行故障维修, 且每次故障维修后的工作时间形成随机递减的几何过程, 每次故障后的维修时间形成随机递增的几何过程。当部件发生N次可维修故障或一次不可维修故障时进行更换。以部件进行预防维修的间隔和更换前的可维修故障次数N组成的二维策略(T, N) 为策略, 利用更新过程和几何过程理论求出了系统经长期运行单位时间内期望费用的表达式, 并给出了具体例子和数值分析。     

A model of imperfect preventive maintenance with dependent failure modes

Consider a system subject to two modes of failures: maintainable and non-maintainable. A failure rate function is related to each failure mode. Whenever the system fails, a minimal repair is performed. Preventive maintenances are performed at integer multiples of a fixed period. The system is replaced when a fixed number of preventive maintenances have been completed. The preventive maintenance is imperfect because it reduces the failure rate of the maintainable failures but does not affect the failure rate of the non-maintainable failures. The two failure modes are dependent in the following way: after each preventive maintenance, the failure rate of the maintainable failures depends on the total of non-maintainable failures since the installation of the system. The problem is to determine an optimal length between successive preventive maintenances and the optimal number of preventive maintenances before the system replacement that minimize the expected cost rate. Optimal preventive maintenance schedules are obtained for non-decreasing failure rates and numerical examples for power law models are given.     

Extended optimal inspection policies for a system in storage

A system such as missiles and spare parts of aircraft has to perform a normal operation in a severe environment at any time when it is used. However, the system is in storage for a long time from the delivery to the usage and its reliability goes down with time. Thus, a system in storage should be inspected and maintained at periodic times to hold a higher reliability than is prespecified.The following inspection model is considered: A system has three types of units, where unit 1 is maintained, unit 21 is not maintained but is replaced and unit 22 is neither maintained nor replaced. The system is overhauled if its reliability becomes lower than a prespecified probability. The number of replacements and time until overhaul are derived. Using these results, the average cost is obtained and both an optimal inspection time and an optimal replacement time to minimize it are numerically discussed.     

Optimal overhaul intervals with imperfect inspection and repair

Author for correspondence.Email:m.j.newby{at}city.ac.uk This paper is motivated by the idea of a maintenance-free operatingperiod whose objectives are to improve mission reliability andcarry out as much maintenance as possible as a second-line activity.The system may be in one of three states (good, faulty, andfailed), and expressions are developed for the average costper unit time until failure. The system is periodically inspected,the inspection being imperfect in the sense that it can resultin both false-positive and false-negative results. Simple faultscan be fixed, but a repair is imperfect, in that there is anon-zero probability of a fault remaining after a repair. Aftera fixed number of inspections, the system is overhauled. Ifthe system fails during operation, it is replaced at increasedcost. The sojourn time in each state has non-constant failurerate, and discretization and supplementary variables are usedto give a Markovian structure which allows easy computationof the average costs. Minimizing the average cost gives theoptimal number of inspections before overhauling the system.     

Linearly Coupled,Slowly Varying Oscillators: The Interaction of a Positive-Energy Mode With a Negative-Energy Mode

A linear dynamical system is considered whose normal frequencies and normal modes come into close coincidence. The case when both modes have positive energy has been discussed by Grimshaw and Allen (1979). Here the case when one mode has positive energy and the other mode has negative energy is discussed. Coupled equations are derived and solved exactly using parabolic cylinder functions. It is found that the action in both modes grows during the coupling.     

Optimally maintaining a Markovian deteriorating system with limited imperfect repairs

We consider the problem of optimally maintaining a periodically inspected system that deteriorates according to a discrete-time Markov process and has a limit on the number of repairs that can be performed before it must be replaced. After each inspection, a decision maker must decide whether to repair the system, replace it with a new one, or leave it operating until the next inspection, where each repair makes the system more susceptible to future deterioration. If the system is found to be failed at an inspection, then it must be either repaired or replaced with a new one at an additional penalty cost. The objective is to minimize the total expected discounted cost due to operation, inspection, maintenance, replacement and failure. We formulate an infinite-horizon Markov decision process model and derive key structural properties of the resulting optimal cost function that are sufficient to establish the existence of an optimal threshold-type policy with respect to the system’s deterioration level and cumulative number of repairs. We also explore the sensitivity of the optimal policy to inspection, repair and replacement costs. Numerical examples are presented to illustrate the structure and the sensitivity of the optimal policy.     

An ideal way of obtaining an optimal inspection permutation for a system with components connected in series

The problem of an inspection permutation or inspection strategy (first discussed in a research paper in 1989 and reviewed in another research paper in 1991) is revisited. The problem deals with an N‐component system whose times to failure are independent but not identically distributed random variables. Each of the failure times follows an exponential distribution. The components in the system are connected in series such that the failure of at least one component entails the failure of the system. Upon system failure, the components are inspected one after another in a hierarchical way (called an inspection permutation) until the component causing the system to fail is identified. The inspection of each component is a process that takes a non‐negligible amount of time and is performed at a cost. Once the faulty component is identified, it is repaired at a cost, and the repair process takes some time. After the repair, the system is good as new and is put back in operation. The inspection permutation that results in the maximum long run average net income per unit of time (for the undiscounted case) or maximum total discounted net income per unit of time (for the discounted case) is called the optimal inspection permutation/strategy. A way of determining an optimal inspection permutation in an easier fashion, taking advantage of the improvements in computer software, is proffered. Mathematica is used to showcase how the method works with the aid of a numerical example. Copyright © 2016 John Wiley & Sons, Ltd.     

Linearly Coupled,Slowly Varying Oscillators

A dynamical system is considered whose normal frequencies and normal modes vary slowly with time in such a way that two frequencies come into close coincidence. When this occurs the corresponding normal modes undergo a drastic change in their physical properties. Away from coincidence, each normal mode conserves its action. A multiple-time-scale asymptotic procedure is employed to derive equations which describe the mode coupling at coincidence. These equations are solved exactly using parabolic cylinder functions. It is found that in general, action is exchanged between modes at coincidence, but that except for very strong coupling the amount of action exchanged is quite small.     

Nonlinear multivariable modeling and stability analysis of vibrations in horizontal drill string

Nowadays, economical extraction of the oil and gas, and their products is an important problem. Up to now, vertical wells have been used for oil extraction but some wells exist that they cannot be reached by using the vertical drilling. Horizontal and directional drillings are some techniques to reach these wells. In this article, dynamics of the horizontal drill string is studied. According to the forces that affect the dynamics of drilling, its longitudinal vibration is analyzed. After determination of the boundary conditions and normal modes of the system with using mode summation method, displacement of the bit is obtained. Finally, dynamics of the horizontal drill string is simulated and the effect of increasing the number of modes and the mode convergence phenomenon is discussed. Through this study, while it is shown that four modes are sufficient for a reliable prediction of the stable and unstable conditions; five modes are included for the system analysis. Then, the effects of other parameters such as the mud frequency and constants of bit/rock interaction model are studied. Through the proposed parametric study, the stability of the system is investigated. Moreover, the dominant modes which cause the instability of the horizontal drilling process are determined.