Optimal Reliability of a Complex System

In a complex system where the redundant units cannot be reduced to a purely parallel or series configuration, the reliability is obtained by using Bayes' theorem. A mathematical model is formulated for the reliability of a system with nonlinear constraints. The system reliability is optimized based on the model and the solution is obtained by using the sequential unconstrained minimization technique (SUMT). This method is an efficient method for solving this type of problem. Two life support systems, one is the communication system of a two-man space capsule and another is a high-pressure oxygen supply system in a space capsule, have been identified to have the complex system configuration treated in this work.     

Configuration of ACK Trees for Multicast Transport Protocols

For scalable multicast transport, one of the promising approaches is to employ a control tree known as acknowledgement (ACK) tree which can be used to convey information on reliability and session status from receivers to a root sender. The existing tree configuration has focused on a ‘bottom‐up’ scheme in which ACK trees grow from leaf receivers toward a root sender. This paper proposes an alternative ‘top‐down’ configuration where an ACK tree begins at the root sender and gradually expands by including non‐tree nodes into the tree in a stepwise manner. The proposed scheme is simple and practical to implement along with multicast transport protocols. It is also employed as a tree configuration in the Enhanced Communications Transport Protocol, which has been standardized in the ITU‐T and ISO/IEC JTC1. From experimental simulations, we see that the top‐down scheme provides advantages over the existing bottom‐up one in terms of the number of control messages required for tree configuration and the number of tree levels.     

基于现场数据的地铁车辆牵引系统可靠性分析

牵引系统的可靠性对于地铁车辆的安全运行极为重要.文章结合某地铁线路的现场车辆检修记录,采用故障树法和蒙特卡洛法分析牵引系统的可靠性.首先,根据现场检修数据建立地铁牵引系统的故障树模型,并对所建立的故障树模型进行定性、定量分析.其次,运用蒙特卡洛法对地铁牵引系统进行可靠性仿真.最后,确定了牵引系统的薄弱环节和各部件的重要...     

Reliability of augmented tree networks under pin-out constraints

The binary tree network provides a cost-efficient topology for parallel computers. However, its poor reliability makes it unattractive for applications that demand high reliability. This has motivated consideration of several augmented tree networks, but these networks offer increased reliability at the expense of increased node fanout. This paper studies 2 augmented tree networks that achieve high reliability with low node fanout. Exact reliabilities of both networks are computed in O(log(number of leaves)) time by deriving a system of recurrences that exploit their recursive construction. These structures are considerably more reliable than the single tree. Moreover, reliability is sensitive to the actual inter-leaf augmentation scheme-even a minor change has a noticeable impact on reliability. Two other measures of reliability, mean time-to-failure and mission time are estimated. A closed-form approximate expression for reliability of one of these networks is obtained; it agrees quite well with the exact value     

计算机辅助生成控制系统故障树

有关故障树生成方法的研究已经成为故障树分析研究中的一个重要分支，故障树的完善程度将直接影响系统可靠性的定性分析和定量计算。因此，故障树及故障树自动生成方法的开发研究具有非常现实和极其广泛的应用价值。本文分析了已有的控制系统故障树生成方法特点，提出一种计算机辅助故障树生成方法。通过系统元件的逻辑关系对所建立的元件故障模式数据库的搜索生成系统的故障树。该方法给出了元件故障模式的建立、元件问的关联方法、控制回路模板的建立方法以及故障树自动生成算法。最后，结合一个复杂系统故障树的生成验证了该方法的可行性和有效性。     

A System Reliability Model with Classes of Failures

This paper presents an approach to system reliability involving s-dependence of the workload as well as the system configuration. Four classes of failures are described and then incorporated into the workload model. Mean time to failure and the system reliability are the functions of parameters estimated by monitoring a real system. The model allows multiple classes of users and priority requests to be represented. The model is validated using measurement data collected in an IBM installation.     

Modeling inefficiencies in a reliability system using stochastic frontier regression

For some reliability systems, it is possible to have the system reliability smaller than the reliability obtained using the configuration of the components. This may be due to the inefficiency of the system. By inefficiency, we mean any tendency or attribute that will bring down the performance of the system from the level the configuration is capable of or expected to provide or designed for. This sets a maximum limit (or frontier) for the performance of the system. Therefore, deviation of the observed level from this limit would then be an indicator of the inefficiency. In this paper, we have made an attempt to model inefficiencies in the working of a reliability system, and to define an inefficiency index. The paper discusses the practical estimation of the coefficient of inefficiency in the system performance. The stochastic frontier regression methods are used to estimate the inefficiency. The validity of the methodology has been assessed for an exponential model, using a limited simulation study. The inefficiency indices proposed in this paper are simple, as they must be to be useful to engineers. We found that the suggested indices & their estimation procedures work well.     

高可靠性光电平台嵌入式系统设计

提高航空光电侦察系统在复杂环境下运行的稳定性和可靠性,设计了基于(windowsembedded studio,WES)的光电侦察平台嵌入式系统。本系统结合以PIII处理器为核心的硬件平台,利用WES(Enhanced Write Filker)开发环境,采用中间件技术,设计可见光CCD图像采集传输组件、分布式数据通信组件和板卡驱动组件;利用(Enhanced Write Filter)技术,集成稳定可靠的分布式客户环境;最后采用NHPP数学模型,分析系统的稳定性与可靠性。实验结果表明,在相同的硬件配置下,基于WES设计的航空光电侦察平台嵌入式系统,系统可靠性和稳定性达到94%以上。并且有效缩短了系统启动时间,系统灵活性强,对硬件资源要求低,易于移植和维护升级。     

A reliability model for real-time rule-based expert systems

This paper uses two modeling tools to analyze the reliability of real-time expert systems: (1) a stochastic Petri net (SPN) for computing the conditional response time distribution given that a fixed number of expert system match-select-act cycles are executed, and (2) a simulation search tree for computing the distribution of expert system match-select-act cycles for formulating a control strategy in response to external events. By modeling the intrinsic match-select-act cycle of expert systems and associating rewards rates with markings of the SPN, the response time distribution for the expert system to reach a decision can be computed as a function of design parameters, thereby facilitating the assessment of reliability of expert systems in the presence of real-time constraints. The utility of the reliability model is illustrated with an expert system characterized by a set of design conditions under a real-time constraint. This reliability model allows the system designers to: (1) experiment with a range of selected parameter values; and (2) observe their effects on system reliability     

SS/FDMA router for flexible satellite communications networks

The subchannel switched frequency-division multiple-access (SS/FDMA) system improve the routing flexibility of transponder banks in channelized multibeam satellites. This system can efficiently be utilised to construct a VSAT (very small aperture terminal) network and/or a business satellite communications network using small aperture terminals. The authors address the application of the SS/FDMA system to such networks. A proof-of-concept (POC) model of SS/FDMA onboard equipment called the SS/FDMA router is described in terms of its configuration and measured electrical performance. Results of transmission experiments using the POC model as well as computer simulations are presented. In addition, a redundant SS/FDMA router configuration is proposed, and its reliability is calculated for a 15-year satellite mission time. Finally, estimated values of volume, mass, and DC power consumption of the redundant SS/FDMA router are presented     

Constructing fault trees for advanced process control systems $application to cascade control loops

A systematic approach to construct fault trees for advanced process control systems is presented in this paper. For illustration purpose, the proposed method is explained with a specific feedback scheme, i.e., the cascade control strategy. The digraph configuration of a standard system is first described and analyzed in detail. On the basis of a series of qualitative simulation studies, all failure mechanisms can be identified and summarized with a set of generalized fault-tree structures. The fault trees produced with the conventional digraph-based techniques are shown to be not as comprehensive as the ones constructed with the proposed approach. To demonstrate the correctness of our analysis, the successful application of the proposed structures to a heat exchange process is presented. In addition, the resulting fault tree is compared with one obtained from a single-loop feedback control system and the trade-off between the two in system reliability and control performance is assessed accordingly.     

A new methodology to handle Boolean models with loops

It is often convenient, in reliability analyses, to describe the system under study by means of a set of Boolean equations. Fault trees can be seen as hierarchical sets of Boolean equations. In some cases, the model contains loops, because the system embeds at least two components whose states depend on one another. Reliability networks are a typical example of looped models. Classical fault tree assessment methods fail to assess this kind of model. This paper proposes a logical framework to clarify the meaning of looped sets of Boolean equations; and a binary decision diagrams based method is proposed to assess them. This approach is illustrated with experimental results on a benchmark of reliability networks.     

On the Efficacy of R-on-M Redundancy

A redundant configuration consisting of m identical elements and r universal spare elements is postulated. Each of the spares in this ``r-on-m' configuration can substitute for any one of the m elements required for the system to be operational. The system reliability attainable with this configuration is examined as a function of r and m, simple bounds are derived, and a method is presented for determining the optimum values for r and m as a function of the relative complexity of the associated switch. It is shown that an r-on-m configuration can provide an extremely efficient means for obtaining significant improvement in reliability, and is often nearly as effective as a parallel configuration involving m times as many spares.     

Case study: reliability of the INEL-Site Power System

Recent power outages at the EG&G Idaho National Engineering Laboratory (INEL) prompted some customers to call for major modifications to the power system. The reliability of the INEL-Site Power System (a loop configuration) was analyzed to understand the true performance of the system and the dominant causes of outages. This was done using fault-tree modeling along with the IRRAS-PC computer code. Twenty-nine years of site-specific data were obtained from logbooks maintained by the INEL-Site Power System dispatch office. A detailed model was developed and validated against outage history for the site. The fault-tree analysis identified several major contributors to the outage frequency. It is shown that the fault-tree analysis technique provides a flexible and useful method for quantifying the system unreliability and identifying the major contributions to it. The model accurately describes the overall, INEL-Site Power System (INEL-SPS) performance and can easily be used to quantify the anticipated change in reliability due to potential modifications in the system     

Modeling and maximizing burn-in effectiveness

System burn-in can get rid of many residual defects left from component and subsystem burn-in since incompatibility exists not only among components but also among different subsystems and at the system level. Even if system, subsystem, and component burn-in are performed, the system reliability often does not achieve the requirement. In this case, redundancy is a good way to increase system reliability when improving component reliability is expensive. This paper proposes a nonlinear model to: estimate the optimal burn-in times for all levels, and determine the optimal amount of redundancy for each subsystem. For illustration, a bridge system configuration is considered; however, the model can be easily applied to other system configurations. Since there are few studies on system, subsystem, and component incompatibility, reasonable values are assigned for the compatibility factors at each level     

LD泵浦Nd:AG无水冷固体激光器可靠性分析

针对军用激光器的可靠性要求,用故障树分析法(FTA法)建立了LD泵浦Nd:YAG无水冷固体激光器的故障树模型,用下行法求出最小割集,计算了激光器的可靠度和平均无故障工作时间(MTBF),分析了激光器各部件的重要度。对激光器可靠性薄弱环节,提出了控制系统结构、增加重要子系统冗余的措施,以求较大程度地提高激光器的可靠性。理论计算与激光器实际工作符合较好。     

Reliability analysis and comparison of several structures

In this study, we consider the redundant structure with the function of swithover processing which is assumed to cause the increase of the failure rate of the system. A single component system and a simple redundant system are compared in terms of the four reliability measures such as the reliability function, the MTBF, the failure rate and the mean residual life (MRL). We find the relations of the MTBF, the failure rate, and the MRL between two systems. We also consider a quad configuration system and a parallel string configuration system and evaluate the four reliability measures for two systems. As a numerical example, the total system down of an ATM switching system is considered.     

Build better diagnostic decision trees

Enhancing the ability to perform diagnostics on a system that has failed can significantly impact maintenance and repair costs. A good diagnostic tool enables a user to analyze a failed system and identify the failed components. While the field of diagnostics is not a modern one, the way in which system diagnostics are performed is continuously changing. The automatic diagnosis based on reliability analysis (ADORA) methodology utilizes reliability information developed during the design phase to build a diagnostic map. Previous work on ADORA demonstrated how a diagnostics procedure can be performed on a system that has been analyzed using a static reliability model, particularly a fault tree (Assaf and Dugan, 2003). In this article, we extend the ADORA methodology to utilize reliability analysis of dynamic fault trees (DFTs), which are reliability models that capture sequences and combinations of component failures that induce system failure. DFTs are particularly well suited for analyzing computer-based systems.As an example the common rail fuel injection system is discussed.     

Stochastic programming models for general redundancy-optimization problems

This paper provides a unified modeling idea for both parallel and standby redundancy optimization problems. A spectrum of redundancy stochastic programming models is constructed to maximize the mean system-lifetime, /spl alpha/-system lifetime, or system reliability. To solve these models, a hybrid intelligent algorithm is presented. Some numerical examples illustrate the effectiveness of the proposed algorithm. This paper considers both parallel redundant systems and standby redundant systems whose components are connected with each other in a logical configuration with a known system structure function. Three types of system performance-expected system lifetime, /spl alpha/-system lifetime and system reliability-are introduced. A stochastic simulation is designed to estimate these system performances. In order to model general redundant systems, a spectrum of redundancy stochastic programming models is established. Stochastic simulation, NN and GA are integrated to produce a hybrid intelligent algorithm for solving the proposed models. Finally, the effectiveness of the hybrid intelligent algorithm is illustrated by some numerical examples.     

Parametric Representation of Probability in Two Dimensions?A New Approach in System Reliability Evaluation

The evaluation of system reliability becomes very diffilcult when the number of components in a system is large or the system configuration is complex. This note presents a straightforward method for system reliability evaluation. Probability is treated as a point in a Cartesian frame and formulas are derived to evaluate the reliability of series, parallel, series-parallel, and bridge networks. The values obtained by the classical method agree closely with those obtained by this parametric method.