Stochastic behaviour of a two-unit cold standby redundant electronic equipment under human failure

This paper presents a mathematical model to evaluate availability and M.T.T.F. of a two-unit cold standby system with three possible states of each unit; viz. good, partially failed and failed, incorporating the concept of human failure. The model has been developed for exponential failures and general repairs. Single service facility is available in each state during the operational stage of the electronic equipment. Laplace transforms of the various state probabilities have been obtained. Steady-state probabilities, steady-state availability and mean time to failure have been derived.     

Toward a deeper understanding of the availability of series-systems without aging during repairs

It is shown in detail that the steady-state availability of a series-system with no aging of components during the repair of another one can be interpreted as a conditional probability of the well-known s-independent case conditioned on allowing for at most one failed component at any time. Trivially, this conditional probability is larger than the standard probability, viz. the product of all components' probabilities. Yet it can be shown that also without this new interpretation of the formula for the availability of a series-system without aging during repairs it is exceptionally easy to prove the fact that by no aging during repairs, the availability of series-systems increases; a most plausible result.     

Improving GSM call completion by call reestablishment

Global system for mobile communications (GSM) call reestablishment service allows a mobile station to resume a call in which the radio link has been temporarily interrupted due to interference or bad signal (which is referred to as an interrupted call). This service increases end user satisfaction and network quality perception. We propose analytic models to study the performance for call reestablishment service. Our study indicates that call reestablishment can significantly reduces dropping for interrupted calls     

Availability for repairable components and series systems

The failure pattern of repairable components is often modelled by an alternating renewal process which implies that a failed component is perfectly repaired. In practice, repair is often imperfect. This paper proposes a generalized availability model for repairable components and series systems. The lifetime of a repaired component has a general distribution which can be different from that of a new component. Availability and some asymptotic quantities in these models are derived. An example illustrates the application of these models     

Reliability and availability analysis for two non-identical unit parallel systems with common cause failures and human errors

This paper presents three models with common cause failure and human error analysis of a two non-identical unit parallel system. The difference between models I and II is that, in model I the failed system is repaired back to its normal operating state whereas in model II it is not so. Similarly, the basic difference between models II and III is that, in model II it is possible for the partially failed system to be restored to its normal operating state and in model III it is not so. The system reliability, time dependent system availability, steady-state system availability and mean-time to failure are developed for the above models. The problem is discussed with a numerical example.     

Cost analysis in two-unit warm standby models with a regular repairman and patience time

The present paper deals with two-unit warm standby models having one regular and one expert repairman. It is assumed that the expert is called only if the regular repairman is not able to complete the repairs within some tolerable (patience) time. In model 1, it is assumed that the regular repairman can always do the repairs of the unit, failed from standby state. In model 2, the regular repairman sometimes may not be able to do the repairs of the above nature within some patience time and the expert is called for in case of standby failure also.The various measures of system effectiveness are calculated using semi-Markov and regenerative processes. Based on these measures a rule is developed when the services of the expert man should be utilized profitably.     

综合化航空电子系统中的热重启动设计

为解决综合化航空电子系统中冷重启动时大电流冲击导致的电子元器件加剧老化问题,以及避免冷重启动时系统中无需重启动部分正常工作被中断现象,提出将热重启动引入综合化航空电子系统设计中。结合综合化航空电子系统的控制结构和处理器的复位功能,分析了热重启动在综合化航空电子系统中实现的可行性,给出了实现热重启动的软硬件设计方法。经过实验验证,热重启动能够有效解决冷重启动方式在综合化航空电子系统的弊端。     

Stochastic behaviour of a three-state complex repairable system with three types of failures

This paper deals with the operational availability of a three-state complex repairable system consisting of n distinct units arranged in series. Single service facility is available for three types of failures of the complex system. A mathematical model for the complex system under severe restrictions has been developed for exponential failures and general repairs. Laplace transforms of various state probabilities have been evaluated and availability is then obtained by the inversion process. Few graphical illustrations are also given in the end so as to explain the practical utility of the model.     

Modeling and analyzing the effects of periodic inspection on theperformance of safety-critical systems

This paper presents a method for incorporating into Markov models of safety-critical systems, periodic inspections and repairs which occur deterministically in time. Both perfect and imperfect inspections and repairs can be modeled. Based on this new modeling technique, closed-form solutions are derived for a variety of important performance indexes including MTTF, MTTF_D, MTTF_S, average availability, and average probability of failing dangerously. The solutions are applied to an example system to illustrate how the method can be used to study the effects on performance of: (a) choices of the time-length between periodic inspections and repairs, and (b) improvements in inspection and repair techniques     

A hybrid model for weekday replacements with infant mortality failures

A hybrid availability model of a repairable system with infant mortality failures is proposed. The hybrid model can efficiently represent different types of state transitions by the use of a hierarchy of models: (1) a time-discretized component submodel, which provides a piecewise-linear failure rate during an operating interval; (2) a phased-mission model, which transforms the state probability vector according to repair activity; and (3) a combinatorial model, which is used to predict the number of working units among a collection of identical components. The modeling approach is illustrated by predicting the expected number of working components for a multiple-component system where replacement components are ordered at the end of business hours each weekday end. Replacement occurs on the next weekday morning.     

A multicomponent two-unit cold standby system with three modes

This paper investigates a mathematical model of a two-unit cold standby redundant system with three possible states of each unit—normal, partially failed and failed. Each unit has n components, each having a constant failure rate and a repair rate, an arbitrary function of the time spent. These vary from component to component. Steady-state probabilities, steady-state pointwise availability, mean time to system failure and Laplace transforms of various transient probabilities have been obtained. Several earlier results are verified as special cases.     

备件保障度评估与备件需求量模型研究

基于更新过程理论,给出了部件寿命服从不同分布(指数分布、威布尔分布、正态分布和Г分布)情况下,单不可修部件的备件保障度模型;然后给出了多不可修部件和多可修部件的备件保障度模型．通过具体算例,验证了模型的正确性;最后在备件保障度模型的基础上,给出了备件需求量模型。     

NRLA & MOD-Metric Models as Aids in Design Decisions

This paper reports partial results and extensions of a study at Clemson University from 1980 December to 1982 May. The purpose was to develop an integrated model set to aid in evaluating design alternatives on the availability and logistic support requirements of major weapon systems. The model set includes the Network Repair Level Analysis (NRLA) and MOD-Metric models. System design decisions concern the nominal reliability of components, the extent to which components are hierarchially designed, the accessibility of components, and whether the component will be repaired or discarded when it fails. System design includes the design of the logistic support system and its relation to the hardware. Design alternatives should be carefully investigated to determine the effects that each would have on ownership costs, performance, and availability. This model set was applied to the components of the air refueling boom of the KC-135A tanker aircraft. The 2-echelon, 2-indenture inventory system used at times by the US Air Force is assumed. In particular we report: 1) the effects of component reliability on spare stock levels and spare parts costs, and 2) the impact of component reliability on the level at which repair takes place. The models have similar data requirements and they yield useful conclusions. However, there are some difficulties. The spares decisions from MOD-Metric are not necessarily compatible with NRLA because the MOD-Metric analysis is far more sophisticated.     

Reliability Model with 1 or 2 Repair Channels

Two models have been considered for a complex system with two classes of components L1 and L2. L1 components are connected in series; failure of an L1 component causes failure of the system. Class L2 consists of large number of components. Failure of any one L2 component reduces the efficiency of the system. Repairs of L2 components are followed by post-repairs. In Model I, repairs and post-repairs are done by a single channel; in Model II, there are separate channels for the two. Failure and repair times are exponentially distributed. Laplace transforms of the various probability states are obtained.     

Reliability of Systems with Limited Repairs

Reliability is the probability that a system functions according to specifications over a given period of time. During this period, system specifications may allow failures and repairs to occur. This paper considers systems with specifications which limit the repair process. Such systems place a limitation on either the repair duration or the number of repairs. For example, a system controlling a real-time process may go down, be repaired, and continue proper control as long as the repair duration does not exceed a specified bound. Otherwise, the system fails. We model and analyze systems with three different types of limited repairs: 1) Bounded repair time, 2) Bounded cumulative repair time, and 3) Bounded number of repairs. Examples of such models exist in real-time process control, shock models, transaction processing, and maintenance models. For each of the three types of systems with limited repairs, we derive the distributions and the mean values of the system lifetime, the cumulative operational time, and the largest continuous operational time before a complete system failure. We also consider the execution of a task on such systems. The task is preempted upon the occurence of a failure, and is resumed or repeated after repair. The probability of completion of a task with a given work requirement in the three limited downtime scenarios is derived. We study the effect of preemptive-resume versus preemptive-repeat failures on the probability of task completion.     

Recoverable Class Loaders for a Fast Restart of Java Applications

We present recoverable class loaders to enable a fast start-up and recovery of Java applications. This is achieved by snapshooting the static state of Java applications namely the class loaders and their associated class objects, which are then recovered during subsequent restarts. Recoverable class loaders are especially useful in the context of mobile applications and mobile services. First, they allow to speed up shutdown and restart of applications for power- and resource-management reasons on resource-restricted mobile devices. Second, services can be much faster rebooted to cure software faults such as memory leaks thereby improving the availability of services. We implemented recoverable class loaders inside the JamVM and the OSGi middleware Oscar. For both cases of use—Java application restart and service recovery—we provide experimental evaluations that show a substantially reduced start-up time from up to 96%.     

直流线路雷击原因分析及防范对策

针对一起800 k V直流输电线路雷击故障跳闸,分析确定故障性质和雷击点范围,得出负极性雷电是造成直流线路故障的主要原因.由于行波保护动作,启动了控制系统的直流线路故障重启功能,使得故障控制成功后,直流系统恢复运行.根据直流线路易遭受雷击的特点,提出直流线路防止雷电绕击的应对措施.     

Computer models for AGT system operations studies

The major functions, inputs, and outputs of the seven computer models developed during the Automated Guideway Transit (AGT) System Operations Studies (SOS) project are described. The models were designed to provide tools to enable the transportation community to analyze the operation of AGT systems in the complete spectrum of deployments. Three analytic models are described: the feeder system model, which determines the cost and service characteristics of the non-AGT components of the door-to-door trip; the system cost model, which calculates annual and life cycle costs and environmental impacts; and the system availability model, which calculates the impact of failures and recovery times on passenger and vehicle delays in the network. Four simulation models are described: the discrete event simulation model, which models individual trips and vehicles on AGT networks for a wide range of management algorithms, service policies, and network configurations; the system planning model, which models vehicle and passenger flows on AGT networks; the detailed station model, which models individual vehicle and passenger movement in a station; and the detailed operational control model, which is a time step simulation that models individual or strings of vehicles on links, merges, or intersections.     

Modeling server-unreliability in closed queuing-networks

A method is presented to model server unreliability in closed queuing networks. Breakdowns and repairs of servers, assumed to be time-dependent, are modeled using virtual customers and virtual servers in the system. The problem is thus converted into a closed queue with all reliable servers and preemptive resume priority centers. Several recent preemptive priority approximations and an approximation of the one proposed are used in the analysis. This method has approximately the same computational requirements as that of mean-value analysis for a network of identical dimensions and is therefore very efficient     

Selection of a checkpoint interval in a critical-task environment

The selection of an optimal checkpointing strategy has most often been considered in the transaction processing environment where systems are allowed unlimited repairs. In this environment an optimal strategy maximizes the time spent in the normal operating state and consequently the rate of transaction processing. This paper seeks a checkpoint strategy which maximizes the probability of critical-task completion on a system with limited repairs. These systems can undergo failure and repair only until a repair time exceeds a specified threshold, at which time the system is deemed to have failed completely. For such systems, a model is derived which yields the probability of completing the critical task when each checkpoint operation has fixed cost. The optimal number of checkpoints can increase as system reliability improves. The model is extended to include a constraint which enforces timely completion of the critical task