A Method for Predicting System Downtime

A system whose components, upon failure, are repaired or replaced is considered. Only two system states, the ``operating' state and the ``failed' state, are distinguished. The system is by defined a reliability network and by the failure rate and repair rate of each component. The time to failure and the time to repair of the components are assumed to be exponentially distributed. A criterion of system worth is the random variable ``downtime,' denoted by D(t), which is defined as the time the system is down during the time interval (0, t). The following questions are answered: 1) What is the distribution function of D(t)? 2) What are the mean and the variance of D(t)? 3) What is the asymptotic behavior of D(t) for large values of t? 4) How can one make approximate probability statements about D(t)? It is shown that the beta distribution is a suitable approximation for the conditional distribution of D(t)/t, given that at least one failure has occurred, and that for t greater than 20 mean failure times the distribution of D(t) is practically normal.     

A 2-Dissimilar-Unit Redundant System With Repair And Preventive Maintenance

This paper presents the stochastic behaviour of a 2-dissimilar--unit cold-standby redundant system with repair and preventive maintenance. The Laplace-Stieltjes transform of (i) The first-passage time distribution to system failure, (ii) The expected number of system failures during (0, t], (iii) The probability that the system fails at time t, are all derived by using unique modifications of a Markov renewal process. Three examples are given.     

Approximation Formulas for Reliability with Repair

A system consists of n-identical parallel subsystems, each having an exponential distribution of times to failure and an exponential distribution of times to repair. The system reliability with repair is the probability of no more than q out of n subsystems being simultaneously in a failed state during time t. Under conditions frequently met in practice, system reliability with repair R(t) can be approximated by: R(t) ? exp [?t/Tm] where Tm is the mean time for the system to pass for the first time from zero to (q + 1) simultaneous subsystem failures. Exact and approximate methods of calculating Tm are developed. A detailed error analysis is presented showing the limitations of using Tm to calculate system reliability with repair.     

A Generalized Reliability Function for Systems of Parallel Components

In systems of parallel components, the system reliability function Rp(t) is usually defined as the probability that not all the parallel components fail in a time interval t, given that all the components are operating at the beginning of the interval. This definition implies that if there is one component which operates throughout the whole interval in question, then the system reliability is perfect. Consider the system S which always requires M > 1 components to do its job. It is obvious that the system is not reliable if there are only k, 1 ? k < M, components working in the time interval t. The conventional reliability function Rp(t) is then insufficient for studying the reliability of the system S. A generalized reliability function Rr,n(t) is presented in this paper, and it is shown that the conventional reliability function Rp(t) is a special case of the generalized reliability function Rr,n(t). The practical application of this generalized reliability function is also discussed.     

Cost-benefit analysis of a one out of n : G system with repair and preventive maintenance

This paper deals with the cost-benefit analysis of a 1 out of n:G system. The system consists of n identical units. Initially, one unit is placed in operation and the remaining (n−1) in cold standby. The operating unit is taken off when it either fails or is due for preventive maintenance (PM). A standby, if available, takes its place. If no standby is available when an operating unit is taken off, the system goes down. There is only one server who attends to all repair and PM actions on a first-come-first-served basis. Under suitable assumptions, the expressions are obtained for the mean up-time of the system in [0,t), the mean time the server spends on repair in [0,t) and the mean time the server spends on PM in [0,t). Under the assumption that revenue is earned and repair and PM costs are incurred linearly with time, an expression for the expected net revenue in [0,t) is obtained. The special case of age replacement is taken up and the steady-state expected net revenue per unit time is computed for various values of the system parameters.     

激光二极管寿命测试方法研究

文中介绍了半导体激光二极管(LD) 寿命测试的理论依据,给出了寿命测试的数学模 型,并据此设计了LD 高温加速寿命自动测试系统。系统通过采集恒流工作LD 的平均输出光功率随时间变化的信息,绘制LD 的老化曲线,即恒流条件下的P - t 曲线,或通过采集恒功工作LD 的工作电流随时间变化的信息,即恒功条件下的I - t 曲线,然后推断LD 正常条件下的使用寿命。     

实虚部关联的量子噪声和抽运噪声对单模激光光强关联函数的影响

采用抽运噪声和实虚部之间关联的量子噪声驱动的单模激光损失模型，运用线性化近似方法计算了反映激光动力学性质的光强关联函数C(t)和光强相对涨落C(0)，讨沦了光强关联函数随时间t的演化，分析了量子噪声实虚部间关联系数λq，抽运噪声强度P和量子噪声强度Q对光强关联函数C(t)随时间t演化过程的影响。发现C(t)随时间t的演化是单调衰减过程，但噪声强度的减小和量子噪声实虚部间关联的减弱会使演化曲线整体下移，说明噪声强度和量子噪声实虚部间的关联对C(t)随时间t的演化过程有较大的影响。当时间t增加时，C(t)与量子噪声实虚部间关联系数λq的关系曲线出现了一个极值和三个极值两种不同的情况。最后分析了线性化近似方法适用的条件。     

Excess Time, a Measure of System Repairability

The performance of systems subject to failure and repair cycles can be described by a variety of stochastic processes. Downtime is a measure of system worth which is commonly found in the reliability literature. Another measure, excess time, has been proposed in a recent paper. Both downtime and excess time are measures of the accumulated time during which the system has been inoperative. The parameter t of excess time counts only productive units of time. Thus B(t) is the excess of unproductive time over productive time. The properties and applications of excess time are reviewed and summarized.     

Correlation Entering New Fields with Real-Time Signal Analysis

Correlation analysis is a convenient technique for deyrtmining the spectral characteristics of a signal or the similarity of two different signals. One point of a correlation function is the long-term average of the product of two functions of time. The complete function is generated when the delay between the two time functions is varied. For example, if one voltage V1(t) and another voltage V2(t ? r), where r represents a finite and variable delay, are continuously multiplied together and the product fed into a low-pass filter, then the filter's output closely approximates the true mathematical correlation function. If V2; is identical to V1; in every respect except for the delay r, the result is the autocorrelation function. If V1; and V2; are totally different functions, then the result is the cross-correlation function. The outputs in both cases are functions of the delay time r. Mathematically for autocorrelation begin{equation*}C_{11}(r) = lim_{Trightarrowinfty}frac{1}{2T}int^T_{-T}V_1(t)V_1(t - r) dtend{equation*} for cross correlation begin{equation*} C_{12}(r) = lim_{Trightarrowinfty}frac{1}{2T}int^T_{-T}V_1(t)V_2(t - r) dt end{equation*} An instrument, therefore, that does this integrating process will show whether correlation exists between two signals and, if so, when maximum correlation takes place. In practice, the averaging process indicated in the above equations is performed only for a time longer than the longest period in signals f1(t) and f2(t). Autocorrelation is useful for the detection of an unknown periodic signal in the presence of noise or to measure some particular band of signal or noise frequencies.     

一种高效的基于BC图的t/k-诊断算法

为了提高系统级故障诊断中的诊断度,人们以牺牲很小一部分结点不能正确诊断为代价,提出了t/k-故障诊断策略.BC图是包括了超立方体和多种变形立方体的一类图.对于结点总数为N的BC图,本文提出了一个O(N log2N)的t/k-故障诊断算法.目前尚未有相关t/k-故障诊断算法的文章发表,但与著名的悲观一步t-故障诊断算法(t/k-故障诊断算法在k=1时的情况)的O(N2.5)相比较,在时间复杂度上本文算法是高效的.     

基于增量二维主成分分析的非线性转子系统故障诊断方法

针对智能故障诊断实际应用中存在的故障样本难 以大量获取、面对新增故障类别需要 一个完整的再训练周期的实时性等问题,提出一种采用增量二维主成分分析(incremental t wo-dimensional principal component analysis,I2DPCA)对非线性裂纹转子系统进行故 障 诊断的方法。首先构建水平支撑的非线性裂纹转子系统模型及其动力学方程,分别探究不同 裂纹深度和质量偏心参数时系统振动响应的变化特征。其次将时域振动信号归一化为图像样 本,由I2DPCA算法提取具有高判别力的低维故障特征。在上述处理基础上,使用k-最近邻( k-nearest neighbor,KNN)分类算法进行识别率的计算。数值仿真及相关实验的研究结果 表 明,基于I2DPCA算法的故障诊断方法可以在高速区域及小样本情形下有效地区分不同故障状 况的信号,为裂纹转子系统的早期故障诊断提供了新的检测策略。     

Analyses of Two Different 1-Server Systems

In this paper, the availability and the reliability of two 1-server systems with redundancy have been obtained. System 1 consists of n subsystems in series; each subsystem consists of two redundant i.i.d. components in `parallel' (cold standby) and one server. The times to failure of the components are exponentially distributed; their repair time distributions are arbitrary and different. System 2 consists of n dissimilar units and one server. The times to failure of the units are arbitrarily distributed; the repair rates are constant but all different. Explicit expressions for the Laplace transform of the mean down-time of the system in (0, t) and for the mean time to system failure have been obtained. A few particular cases are discussed.     

基于高非线性光纤中四波混频效应的全光取样系统

为了克服高比特率光信号实时取样时所面临的高速模数转换(ADC)限制,构建了一套基于高非线性光纤(HNLF)中四波混频效应的全光等效取样系统。全光取样系统主要包括取样脉冲信号产生、全光取样门和信号处理3部分,其中全光取样门为本系统的核心部分。取样脉冲和信号共同注入到HNLF中,基于四波混频效应实现全光取样。实验中,分别以10Gb/s、40Gb/s非归零OOK信号进行了取样实验验证。实验结果表明该取样系统可以实现高速光信号的取样过程。本文取样系统结构简单,且不受光信号速率的限制,可应用于更高速率的信号测量。     

Dependability metrics to assess safety-critical systems

Metrics are commonly used in engineering as measures of the performance of a system for a given attribute. For instance, in the assessment of fault tolerant systems, metrics such as the reliability, R(t) and the Mean Time To Failure (MTTF) are well-accepted as a means to quantify the fault tolerant attributes of a system with an associated failure rate, /spl lambda/. Unfortunately, there does not seem to be a consensus on comparable metrics to use in the assessment of safety-critical systems. The objective of this paper is to develop two metrics that can be used in the assessment of safety-critical systems, the steady-state safety, S/sub ss/, and the Mean Time To Unsafe Failure (MTTUF). S/sub ss/ represents the evaluation of the safety as a function of time, in the limiting case as time approaches infinity. The MTTUF represents the average or mean time that a system will operate safely before a failure that produces an unsafe system state. A 3-state Markov model is used to model a safety-critical system with the transition rates computed as a function of the system coverage C/sub sys/, and the hazard rate /spl lambda/(t). Also, /spl lambda/(t) is defined by the Weibull distribution, primarily because it allows one to easily represent the scenarios where the failure rate is increasing, decreasing, and constant. The results of the paper demonstrate that conservative estimates for lower bounds for both S/sub ss/ & the MTTUF result when C/sub sys/ is assumed to be a constant regardless of the behavior of /spl lambda/(t). The derived results are then used to evaluate three example systems.     

Parametric reliability-prediction based on small samples

Reliability prediction is considered for systems that fail due to graceful degradation of operational efficiency to below an acceptable level. The efficiency is represented by a stochastic process, X(t), either scalar or vector. The system reliability with regard to such failures is parametric. It is measured by the probability, R(τ), that X(t) is within the acceptable limits during the time period, [0,τ]. To predict parametric reliability, a procedure is proposed to determine the lower confidence bound at confidence-level, q, for R(τ). Measurement results for small N, e.g., 3-5, of X(t) at times, 0⩽t₁⩽t₂⩽…i ⩽τ are taken as initial data along with stated assumptions on the nature of X(t) variations. The small-sample feasibility is due to the prior selection of the failure-model (on the basis of the system-analogue observation) while the test results are used to estimate the model parameters