系统可靠性预计与分配集成系统的设计与实现

文章对系统可靠性框图建模、可靠性预计、可靠性分配的过程及相互关系进行了分析,在此基础上给出了系统可靠性预计与分配集成系统的体系结构及系统的各主要模块的功能设计,介绍了系统的实现技术,同时提出了可靠性框图模型的数据结构。     

Optimal testing resource allocation during module testing considering cost, testing effort and reliability

Software reliability is one of the most important quality attributes of commercial software. During software testing, software reliability growth models (SRGMs) are commonly used to describe the phenomenon of failure occurrence and/or fault removal which consequently enhancements software reliability. Large software systems are developed by integrating a number of relatively small and independent modules, which are tested independently during module testing phase. The amount of testing resource available is limited which is desired to be consumed judiciously so as to optimize the testing process. In this paper we formulate a resource allocation problem of minimizing the cost of software testing under available amount of testing resource, given a reliability constraint. We use a flexible SRGM considering testing effort which, depending upon the values of parameters, can describe either exponential or S-shaped failure pattern of software modules. A systematic and sequential Algorithm is proposed to solve the optimization problem formulated. Numerical examples are given to illustrate the formulation and solution procedures. Sensitivity analysis is performed to examine the behavior of some parameters of SRGM with most significant influence.     

网络结构的软件系统可靠性分配方法

针对网络结构的软件系统,通过构造软件系统的ANP结构,结合用户和程序员的观点,对超矩阵的构造进行了改进,提出基于改进型ANP的模块重要度评估方法。以软件实用性最大化为目标函数、以可靠性下限和开发费用为约束条件,建立了可靠性分配模型。并以某工厂实力信息管理系统为例,对算法进行了验证。     

基于子系统综合因子的软件可靠性分配方法

针对拥有多个分配在不同配置硬件环境上的软件子系统的综合软件系统,介绍了一种基于各子系统综合因子的软件可靠性分配方法。综合因子的确定涉及到子系统利用率等诸多因素,它的数值可以是软件详细规划时计算给出,从而对整个系统进行可靠性预分配,也可以在实际开发扣测试进程中动态地确定,从而不断地重新修正分配数值。给出详细的实例运算过程,并与传统方法进行了比较。     

On a generalized k-out-of-n system and its reliability

A consecutive-k-out-of-n system is a system with n components arranged either linearly or circularly, which fails if and only if at least k consecutive components fail. An (n,?f,?k) system further requires that the total number of failed components is less than f for the system to be working. Here we consider a more general system consisting of N modules with the ith module-composed of n _i components in parallel; the system fails if and only if there exist at least f failed components or at least k consecutive failed modules. In this paper, some formulae for the reliability of such a generalized k-out-of-n system are derived for both the linear and the circular cases. The recursive formulae established here can be easily computed. Many existing results are also shown to be special cases of the results obtained in this paper. Furthermore, we investigate some component importance properties.     

Statistical tolerance analysis of a hyperstatic mechanism,using system reliability methods

The quality level of a mechanism can be evaluated a posteriori after several months by following the number of warranty returns. However, it is more interesting to evaluate a predicted quality level in the design stage: this is one of the aims of statistical tolerance analysis. A possible method consists of computing the defect probability (P_D) expressed in ppm. It represents the probability that a functional requirement will not be satisfied in mass production. For assembly reasons, many hyperstatic mechanisms require gaps, which their functional requirements depend on. The defect probability assessment of such mechanisms is not straightforward, and requires advanced numerical methods. This problem particularly interests the VALEO W.S. company, which experiences problems with an assembly containing gaps. This paper proposes an innovative methodology to formulate and compute the defect probability of hyperstatic mechanisms with gaps in two steps. First, a complex feasibility problem is converted into a simpler problem. Then the defect probability is efficiently computed thanks to system reliability methods and the m-dimensional multivariate normal distribution Φ_m. Finally, a sensitivity analysis is provided to improve the original design. The whole approach is illustrated with an industrial case study, but can be adapted to other similar problems.     

Cost-oriented task allocation and hardware redundancy policies in heterogeneous distributed computing systems considering software reliability

Task allocation policy and hardware redundancy policy for distributed computing system (DCS) are of great importance as they affect many system characteristics such as system cost, system reliability and performance. In recent years, abundant research has been carried out on the optimal task allocation and/or hardware redundancy problem, most of which took a reliability-oriented approach, i.e., the optimization criterion was system reliability maximization. Nevertheless, besides system reliability, other system characteristics such as system cost may be of great concern to management. In this paper, we take a cost-oriented approach to the optimal task allocation and hardware redundancy problem for DCS, which addresses both system cost and system reliability issues. A system cost model which could reflect the impact of system unreliability on system cost is developed, and by minimizing the total system cost, a satisfactory level of system reliability could be reached simultaneously. In the reliability modeling and analysis of DCS, we take both hardware reliability and software reliability into account. Two numerical examples are given to illustrate the formulation and solution procedures, in which genetic algorithm is used. Results show that based on the developed system cost model, appropriate decision-makings on task allocation and hardware redundancy policies for DCS could be made, and the result obtained seems to be a fairly good trade-off between system cost and system reliability.     

计算机通信与控制系统运行可靠性的提升对策探究

随着信息技术的发展,计算机通信技术与控制技术的应用空前广泛.计算机通信技术的可靠性日趋重要.本文分析计算机通信技术与控制技术的可靠性理论,探讨目前计算机控制技术和通信技术存在的问题并提出建议.     

一种求解软件可靠性分配的近似算法

在考虑开发成本约束的基础上,通过建立一种开发成本-可靠度-满意度三者平衡的软件可靠性分配和优化模型,将对软件可靠性最优分配问题转化为对模糊非线性规划问题的求解,从而为软件可靠性分配的最优化问题提供了一种新方法。为获得具有实际意义的数值解,提出一种沿着加权梯度方向进行变异的特殊遗传算法。最后结合实例,证明了该方法的有效性和合理性。     

Evaluating the reliability of the software of a switching system with a multi-variable model

In recent years reliability growth models have gained a dominant role in the evaluation of the reliability of software products. However, their application to the quality assurance process of the software of a highly complex system such as a telecommunications switching system often shows that it is then possible to get accurate results only when some months of operation have elapsed. It is then impossible to give an answer to the typical questions which arise during the quality assurance phase: ‘Is the software ready for release? How long will it take before it is ready?’. This paper describes a multi-variable (MV) model which was developed to overcome the above limitation by providing a better model of the quality assurance process. A case study is presented, and a comparison is made between the results obtained by applying existing reliability growth models and the MV-model to it. Besides attaining surprising accuracy in its predictions and in measuring the reliability of the product, the MV-model also tries to tackle a different kind of question: ‘How is it possible to improve the effectiveness of testing?’.     

航天载荷应用软件可靠性参数的分析与确立

航天载荷应用软件可靠性研究是开展航天载荷系统可靠性工程的重要组成部分.而软件可靠性参数的分析与确立是进行软件可靠性研究的前提.首先定义并解释了航天载荷应用软件可靠性,其次对航天载荷系统中常用的软件可靠性参数进行了计算与分析,最后依据软件可靠性参数选取的原则提出了一个航天载荷应用软件可靠性参数集.该参数集在开展航天载荷软件可靠性工程中具有一定的参考价值,也是进行航天载荷软件可靠性设计与分析的前提.     

Geometrically nonlinear finite element reliability analysis of structural systems. I: theory

This article reviews the theory of finite element reliability analysis of geometrically nonlinear elastic structures (GNS) based on the total lagrangian formulation. It also provides computer implementation developments and establishes the basis of understanding of the applications presented in the second part of this investigation. Because of the slenderness of GNS, the structural responses are nonlinear even if the strains are within the elastic range. For this reason, the nonlinear relationships between strains and displacements should be considered. Since the failure surface is nonlinear, this study reviews the evaluation of structural reliability of GNS by using both first-order and second-order reliability methods. To evaluate the structural reliability, the linkage of system reliability analysis program RELSYS with the finite element analysis program (FEAP) is presented. The computer code RELSYS–FEAP is readily applicable to the evaluation of system reliability of GNS.     

Geometrically nonlinear finite element reliability analysis of structural systems. II: applications

This is the second part of an investigation on finite element reliability analysis of geometrically nonlinear elastic structures (GNS). This study concentrates on applications. The linkage code RELSYS-FEAP presented in the companion paper is used for finding both component and system reliabilities of GNS. Structural reliabilities are evaluated for both geometrically linear and nonlinear elastic behaviors. Two geometrically nonlinear applications are presented, including a truss and a suspended structure. The stress and displacement reliabilities of the truss are computed considering both geometrically linear and nonlinear elastic behaviors. The system reliability of a geometrically nonlinear suspended structure is evaluated. The structure is modeled as a series of parallel subsystems according to three system failure criteria. The effects of correlation between loads, correlation between resistances, and material behavior (brittle or ductile) are evaluated and discussed. Finally, displacement reliability indices of the suspended structure are computed.     

Architectural reliability analysis of framework-intensive applications: A web service case study

A novel methodology for modeling the reliability and performance of web services (WSs) is presented. To present the methodology, an experimental environment is developed in house, where WSs are treated as atomic entities but the underlying middleware is partitioned into layers. WSs are deployed in JBoss AS. Web service requests are generated to a remote middleware on which JBoss runs, and important performance parameters under various configurations are collected. In addition, a modularized simulation model in Petri net is developed from the architecture of the middleware and run-time behavior of the WSs. The results show that (1) the simulation model provides for measuring the performance and reliability of WSs under different loads and conditions that may be of great interest to WS designers and the professionals involved; (2) configuration parameters have substantial impact on the overall performance; (3) the simulation model provides a basis for aggregating the modules (layers), nullifying modules, or to include additional aspects of the WS architecture; and (4) the model is beneficial to predict the performance of WSs for those cases that are difficult to replicate in a field study.     

航天真空热试验测控平台可靠性保障技术探讨

由于航天测控系统在软件可靠性、可用性、易维护性等方面要求严格,从软件可靠性测试框架、可靠性模型、故障检测技术、高可用数据库等几方面进行分析,结合避错、排错、容错技术的研究现状,在通用的三层结构模型的基础上,进一步融合设备层,提出分布式四层架构模型。以航天真空热试验测控平台为例,采用自底向上的方法,从设备控制层、高可用数据库层、负载均衡集群层到展现层分别介绍该模型在测控平台中关于提高系统可靠性的设计。     

Fuzzy Bayesian reliability and availability analysis of production systems

To have effective production planning and control, it is necessary to calculate the reliability and availability of a production system as a whole. Considering only machine reliability in the calculations would most likely result unmet due dates. In this study, a new modelling approach for determining the reliability and availability of a production system is proposed by considering all the components of the system and their hierarchy in the system structure. Components of a production system are defined as production processes; components of the processes are defined as sub-processes. In this hierarchical structure we could model all kinds of failures such as material and supply, management and personnel, and machine and equipment. In the analysis, a fuzzy Bayesian method is used to quantify the uncertainties in the production environment. The suggested modelling approach is illustrated on an example. In the example, also a separate reliability and availability analysis is conducted which only considered machine failures, and the results of both analyses are compared.     

Design of a fault tolerant control system incorporating reliability analysis and dynamic behaviour constraints

In highly automated aerospace and industrial systems where maintenance and repair cannot be carried out immediately, it is crucial to design control systems capable of ensuring desired performance when taking into account the occurrence of faults/failures on a plant/process; such a control technique is referred to as fault tolerant control (FTC). The control system processing such fault tolerance capability is referred to as a fault tolerant control system (FTCS). The objective of FTC is to maintain system stability and current performance of the system close to the desired performance in the presence of system component and/or instrument faults; in certain circumstances a reduced performance may be acceptable. Various control design methods have been developed in the literature with the target to modify or accommodate baseline controllers which were originally designed for systems operating under fault-free conditions. The main objective of this article is to develop a novel FTCS design method, which incorporates both reliability and dynamic performance of the faulty system in the design of a FTCS. Once a fault has been detected and isolated, the reconfiguration strategy proposed in this article will find possible structures of the faulty system that best preserve pre-specified performances based on on-line calculated system reliability and associated costs. The new reconfigured controller gains will also be synthesised and finally the optimal structure that has the ‘best’ control performance with the highest reliability will be chosen for control reconfiguration. The effectiveness of this work is illustrated by a heating system benchmark used in a European project entitled intelligent Fault Tolerant Control in Integrated Systems (IFATIS EU-IST-2001-32122).     

Software quality analysis by combining multiple projects and learners

When building software quality models, the approach often consists of training data mining learners on a single fit dataset. Typically, this fit dataset contains software metrics collected during a past release of the software project that we want to predict the quality of. In order to improve the predictive accuracy of such quality models, it is common practice to combine the predictive results of multiple learners to take advantage of their respective biases. Although multi-learner classifiers have been proven to be successful in some cases, the improvement is not always significant because the information in the fit dataset sometimes can be insufficient. We present an innovative method to build software quality models using majority voting to combine the predictions of multiple learners induced on multiple training datasets. To our knowledge, no previous study in software quality has attempted to take advantage of multiple software project data repositories which are generally spread across the organization. In a large scale empirical study involving seven real-world datasets and seventeen learners, we show that, on average, combining the predictions of one learner trained on multiple datasets significantly improves the predictive performance compared to one learner induced on a single fit dataset. We also demonstrate empirically that combining multiple learners trained on a single training dataset does not significantly improve the average predictive accuracy compared to the use of a single learner induced on a single fit dataset.

Simulation-based analysis of middleware service impact on system reliability: Experiment on Java application server

Being a popular runtime infrastructure in the era of Internet, middleware provides more and more services to support the development, deployment and management of distributed systems. At the same time, the reliability of middleware services has a significant impact on the overall reliability of the system. Different services have different impacts and different service fault-tolerance solutions have different costs and risks. Therefore, the identification of the services that greatly affect the whole system reliability is the major obstacle to achieving reliable middleware-based systems. In this paper, we present an analytical framework to automatically reason and quantify such impacts when deploying the target system. In this framework, faults are represented by exceptions in modern programming languages; service failures are simulated by software fault injection; reliability impacts are measured by scenarios. This framework is demonstrated on multiple JEE application servers, including JBoss, JonAS and PKUAS. The experiments on two JEE blueprint applications, namely JPS and ECperf, show the feasibility, the applicability and the usability of this framework.     

Modeling and analysis of the effects of QoS and reliability on pricing, profitability, and risk management in multiperiod grid-computing networks

In this paper we develop a network equilibrium model for optimal pricing and resource allocation in Computational Grid Network. We consider a general network economy model with Grid Resource Providers, Grid Resource Brokers and Grid Users. The proposed framework allows for the modeling and theoretical analysis of Computational Grid Markets that considers a non-cooperative behavior of decision-makers in the same tier of the grid computing network (such as, for example, Grid Resource Providers) as well as cooperative behavior between tiers (between Resource Providers and Grid Brokers). We introduce risk management into the decision making process by analyzing the decision-marker's reliability and quality of service (QoS) requirement. We analyze resource allocation patterns as well as equilibrium price based on demand, supply, and cost structure of the grid computing market network. We specifically answer the following questions with several numerical examples: How do system reliability levels affect the QoS levels of the service providers and brokers under competition? How do system reliability levels affect the profits of resource providers and brokers in a competitive market? How do system reliability levels influence the pricing of the services in a competitive environment? How do users' service request types, QoS requirements, and timing concerns affect users' behaviors, costs and risks in equilibrium? How does the market mechanism allocate resources to satisfy the demands of users? We find that for users who request same services certain timing flexibility can not only reduce the costs but also lower the risks. The results indicated that the value of QoS can be efficiently priced based on the heterogeneous service demands.