Combined hardware and software aspects of reliability

This paper presents the similarities and differences between hardware, software and system reliability. Relative contributions to system failures are shown for software and hardware and failure and recovery propensities are also discussed. Reliability, availability and maintainability (RAM) concepts have been broadly developed for software reliability than hardware reliability. Extending these software concepts to hardware and system reliability helps in examining the reliability of complex systems. The paper concludes with assurance techniques for defending against faults. Most of the techniques discussed originate in software reliability but apply to all aspects of a system. Also, the effects of redundancy on overall system availability are shown.     

Formal Specification and Quantitative Analysis of a Constellation of Navigation Satellites

Navigation satellites are a core component of navigation satellite‐based systems such as Global Positioning System, Global Navigation Satellite System and Galileo, which provide location and timing information for a variety of uses. Such satellites are designed for operating on orbit to perform tasks and have lifetimes of 10 years or more. Reliability, availability and maintainability analysis of systems has been indispensable in the design phase of satellites in order to achieve minimum failures or to increase mean time between failures and thus to plan maintenance strategies, optimise reliability and maximise availability. In this paper, we present formal models of both a single satellite and a navigation satellite constellation and logical specification of their reliability, availability and maintainability properties, respectively. The probabilistic model checker PRISM has been used to perform automated analysis of these quantitative properties. Copyright © 2014 John Wiley & Sons, Ltd.     

The Safe-SADT method for aiding designers to choose and improve dependable architectures for complex automated systems

Dependability evaluation is crucial to controlling the risks associated with system failure, and for this reason, it is one of the fundamental steps in automated system design. However, the dependability evaluation methods that are currently exploited are not appropriate, given the level of complexity of such industrial systems. The ineffectiveness of the existing methods led us to develop and propose the Safe-SADT (structured analysis and design technique) method. Our method allows the explicit formalization of functional interactions, the identification of the characteristic values affecting the dependability of complex systems, the quantification of the reliability, availability, maintainability, and safety (RAMS) parameters of the system's operational architecture, and the validation of that operational architecture in terms of the dependability objectives and constraints set down in the functional requirement specifications (FRS). The results presented in this paper are limited to RAM quantification.     

Reliability,Availability and Maintainability Analysis of Industrial Systems Using PSO and Fuzzy Methodology

The purpose of this paper is to present a methodology for analyzing the system performance of an industrial system by utilizing uncertain data. Although there have been tremendous advances in the art and science of system evaluation, yet it is very difficult to assess their performance with a very high accuracy or precision. For handling of these uncertainties, fuzzy set theory has been used in the analysis while their corresponding membership functions are generated by solving a nonlinear optimization problem with particle swarm optimization. For finding the critical component of the system which affects the system performance mostly, a composite measure of reliability, availability and maintainability (RAM) named as the RAM-index has been introduced which influences the effects of failure and repair rate parameters on its performance. A time varying failure and repair rate parameters are used in the analysis instead of constant rate models. Finally, the computed results are finally compared with existing methodologies. The suggested framework has been illustrated with the help of a case.     

Evaluation and assessment of reliability and availability software for securing an uninterrupted energy supply

The significance of reliability, availability and maintainability (RAM) in recent years increased due to rising energy cost and the competitive market. These issues have a considerable effect on the energy generation and potential saving as well. RAM can be assessed by implementing effective software tools generating adequate models. They also provide results visualization via a tabular and/or graphical representation. Various software tools have been selected, tested and a brief overview drawn. It has been a wide selection; however, most of the information available has been driven by marketing and sales features. This work focuses on the main features of several promising complex reliability packages and its target is a balanced assessment of their main features.     

RAMS+C informed decision-making with application to multi-objective optimization of technical specifications and maintenance using genetic algorithms

The role of technical specifications and maintenance (TSM) activities at nuclear power plants (NPP) aims to increase reliability, availability and maintainability (RAM) of Safety-Related Equipment, which, in turn, must yield to an improved level of plant safety. However, more resources (e.g. costs, task force, etc.) have to be assigned in above areas to achieve better scores in reliability, availability, maintainability and safety (RAMS). Current situation at NPP shows different programs implemented at the plant that aim to the improvement of particular TSM-related parameters where the decision-making process is based on the assessment of the impact of the change proposed on a subgroup of RAMS+C attributes.This paper briefly reviews the role of TSM and two main groups of improvement programs at NPP, which suggest the convenience of considering the approach proposed in this paper for the Integrated Multi-Criteria Decision-Making on changes to TSM-related parameters based on RAMS+C criteria as a whole, as it can be seem as a decision-making process more consistent with the role and synergic effects of TSM and the objectives and goals of current improvement programs at NPP. The case of application to the Emergency Diesel Generator system demonstrates the viability and significance of the proposed approach for the Multi-objective Optimization of TSM-related parameters using a Genetic Algorithm.     

可靠性及维修性对飞机系统效能的影响分析

通过可靠性(Reljability)、维修性(Maintainability)对可用性和可信性的定量分析，建立了由参数选择和指标确定的飞机系统效能模型，在此基础上，对效能因素可靠性及维修性进行了详细图解分析，同时为提高效能的管理工作提供了辅助手段。     

Reliability and mechanical design

A lot of results in mechanical design are obtained from a modelisation of physical reality and from a numerical solution which would lead to the evaluation of needs and resources. The goal of the reliability analysis is to evaluate the confidence which it is possible to grant to the chosen design through the calculation of a probability of failure linked to the retained scenario. Two types of analysis are proposed: the sensitivity analysis and the reliability analysis. Approximate methods are applicable to problems related to reliability, availability, maintainability and safety (RAMS)     

Reliability Target Assessment Based on Integrated Factors Method (IFM): A Real Case Study of a Sintering Plant

The success of a company depends on customer’s satisfaction: quality, price, and service. These three goals depend in particular on R.A.M.S. characteristics: reliability, availability, maintainability, and safety. In the last few years, in order to guarantee high standards of reliability and maintainability, new methodologies and techniques have been developed to estimate the R.A.M.S. targets. In particular, the reliability target represents both the starting and the ending point of R.A.M.S. analysis. The design of the reliability target of a system is a crucial aspect of reliability analysis, as it affects the performance of the system and components. This paper aims to develop a new approach called “IFM Target,” to define the reliability target for complex systems through the integrated factors method, to combine the advantages of usually used approaches, and to overcome some criticalities highlighted in a careful literature analysis. The proposed method has been applied on a sintering system. The results show the effectiveness of the proposed approach.     

Modeling system behavior for risk and reliability analysis using KBARM

With advances in technology and the growing complexity of technological systems, the job of the reliability/system analyst has become more challenging as they have to study, characterize, measure and analyze the behavior of systems with the help of various traditional analytical (mathematical and statistical) techniques, which require knowledge of the precise numerical probabilities and component functional dependencies, information which is difficult to obtain. Even if data are available they are often inaccurate and are thus subject to uncertainty, i.e. historical records can only represent the past behavior and may be unable to predict the future behavior of the equipment. To cope with such situations, the knowledge‐based approximate reasoning methodologies (KBARMs) provide necessary help. Among them, the fuzzy and grey methodologies are the most viable and effective tools for coping with imprecise, uncertain and subjective information in a consistent and logical manner. In this paper, the authors present a methodological and structured approach (which makes use of both qualitative and quantitative techniques) to model, analyze and predict the failurebehavior of two units, namely the forming and press units of a paper machine, using KBARMs. Various system parameters such as repair time, failure rate, mean time between failures, availability and expected number of failures are computed to quantify the system behavior in terms of fuzzy, crisp and defuzzified values. Furthermore, a risk ranking approach based on fuzzy and grey relational analysis is discussed to prioritize various failure causes associated with the components in failure mode and effects analysis (FMEA). Copyright © 2007 John Wiley & Sons, Ltd.     

Tradeoff Analysis for RMS of Equipment Based Operation Availability and Life Cycle Cost

Reliability, maintainability, supportability (RMS) are the important performance indexes of equipment, which affect not only the availability, but also the life cycle cost (LCC) of the equipment. First discussed is the qualitative relation between reliability and LCC and the costs which may be used to enhance the reliability. Secondly, the factors that affect the maintainability are summarized, and if maintainability is advanced, the trend of the LCC is depicted. Thirdly, the qualitative relation between th...     

Alternatives and challenges in optimizing industrial safety using genetic algorithms

Safety (S) improvement of industrial installations leans on the optimal allocation of designs that use more reliable equipment and testing and maintenance activities to assure a high level of reliability, availability and maintainability (RAM) for their safety-related systems. However, this also requires assigning a certain amount of resources (C) that are usually limited. Therefore, the decision-maker in this context faces in general a multiple-objective optimization problem (MOP) based on RAMS+C criteria where the parameters of design, testing and maintenance act as decision variables. Solutions to the MOP can be obtained by solving the problem directly, or by transforming it into several single-objective problems. A general framework for such MOP based on RAMS+C criteria is proposed in this paper. Then, problem formulation and fundamentals of two major groups of resolution alternatives are presented. Next, both alternatives are implemented in this paper using genetic algorithms (GAs), named single-objective GA and multi-objective GA, respectively, which are then used in the case of application to solve the problem of testing and maintenance optimization based on unavailability and cost criteria. The results show the capabilities and limitations of both approaches. Based on them, future challenges are identified in this field and guidelines provided for further research.     

Assessing trends in Duane plots using robust fits

The Duane plot is a simple and widely used graphical technique in the analysis of repairable systems. The fitting of a straight line to points in that graph serves to determine the behavior of the system assuming a power law process. However, the classical least squares fitting suffer from lack of robustness and it is specially heavily affected by the more remote and perhaps least interesting points. In order to solve this drawback we propose a robust fit based on Least Median of Squares (LMS) or Least Trimmed Squares (LTS) regression estimators of [1].This methodology has been applied in a project aimed to study the reliability, availability and maintainability of the aerial contact line of the Spanish railways.     

某型装备载车系统维修性人机工程设计研究

目的 某型装备载车系统为依据机动使用要求设计的特种车辆,为契合任务需要,在一定程度上提高其使用可用度,针对其维修性需求进行分析。方法 通过建立以维修性核心评价指标为中心的人机工程设计参数体系,确定“简化及模块化设计、良好的可测试性及可达性、具有完善的防差错和识别标记的设计、保证维修的安全性”等人机工程设计原则,并对常用系统建模方法,如PETRI网、IDEF、UML和eEPC等进行比较,选用事件驱动过程链(eEPC)方法进行建模。结论 通过收集统计该型装备载车系统试验及试用阶段维修性相关数据,运用eEPC的流程模型开展针对性的分析与讨论,提出对其维修性人机工程设计改进的措施与建议,实现缩短其预防性维修时间、修复性维修时间,提高应急反应速度和装备任务可靠性。     

Availability of Maintained Systems: A State-of-the-Art Survey

Availability appears to be a more appropriate measure than reliability for measuring the effectiveness of maintained systems because it includes reliability as well as maintainability. This paper is a survey and a systematic classification of the literature relevant to availability. Emphasis in this paper is centered on the current state of the art on a variety of topics related to availability. Among the topics discussed are: the definition and concepts of the availability; the probability density functions (pdf) of failure times, the pdf of repair times, system configurations, and the various approaches employed to obtain the availability models; confidence intervals of availability; effect of preventive maintenance policies on availability; availability parameters in the model; and systems optimization.     

Analytic Critical Flow Method (ACFM): A Reliability Allocation Method Based on Analytic Hierarchy Process

RAMS is an acronym for reliability, availability, maintainability and safety. These four properties concern the application of important methodologies to design and manage complex systems. In the present research, starting from the analysis of several literature reliability allocation techniques, a reliability allocation method has been implemented called analytic critical flow method (ACFM). Critical flow method is a reliability allocation method for series-parallel configurations, based on failure analysis of each unit of the system. The new approach is based on critical flow method, whose results are matched with the analytic hierarchy process multicriteria method. The result is a dynamic model that combines the advantages of the allocation method and the multicriteria approach. The need to develop the ACFM is the outcome of a careful analysis of the current military and commercial approaches. In particular, no literature method takes into account to assign a different level of significance (weight) to the different units of the system, simultaneously to the considered factors. The proposed approach has been applied and compared with other traditional methods on an aerospace prototype (series-parallel configuration), where the reliability allocation process is rigorous. The results demonstrate the effectiveness of the new approach and its ability to overcome the criticalities highlighted in literature.     

An integrated methodology for the dynamic performance and reliability evaluation of fault-tolerant systems

We propose an integrated methodology for the reliability and dynamic performance analysis of fault-tolerant systems. This methodology uses a behavioral model of the system dynamics, similar to the ones used by control engineers to design the control system, but also incorporates artifacts to model the failure behavior of each component. These artifacts include component failure modes (and associated failure rates) and how those failure modes affect the dynamic behavior of the component. The methodology bases the system evaluation on the analysis of the dynamics of the different configurations the system can reach after component failures occur. For each of the possible system configurations, a performance evaluation of its dynamic behavior is carried out to check whether its properties, e.g., accuracy, overshoot, or settling time, which are called performance metrics, meet system requirements. Markov chains are used to model the stochastic process associated with the different configurations that a system can adopt when failures occur. This methodology not only enables an integrated framework for evaluating dynamic performance and reliability of fault-tolerant systems, but also enables a method for guiding the system design process, and further optimization. To illustrate the methodology, we present a case-study of a lateral-directional flight control system for a fighter aircraft.     

Operating Environment-Based Availability Importance Measures for Mining Equipment (Case Study: Sungun Copper Mine)

When a system’s performance is inadequate, the concept of availability importance can be used to improve it. The availability of an item depends on the combined aspects of its reliability and maintainability. In a system consisting of many subsystems, the availability of some subsystems is more important to system performance than others. The availability measure determines the priority of availability across subsystems. Most researchers only consider operation time and ignore the influence of the operating environment; therefore, their estimations are not accurate enough. In contrast to previous research, we focus on the influence of the operating environment on the system/subsystem’s characteristics with a view to prioritizing them based on the importance of availability. The paper considers part of the mining fleet system of Sungun copper mine, including the wagon drill, loader, bulldozer, and dump truck subsystems. We identify an ordered list of possibilities for availability improvement and suggest changes or remedial actions for each item to either reduce its failure rate or reduce the time required to repair it.     

An artificial neural network for modeling reliability, availability and maintainability of a repairable system

The paper explores the application of artificial neural networks to model the behaviour of a complex, repairable system. A composite measure of reliability, availability and maintainability parameters has been proposed for measuring the system performance. The artificial neural network has been trained using past data of a helicopter transportation facility. It is used to simulate behaviour of the facility under various constraints. The insights obtained from results of simulation are useful in formulating strategies for optimal operation of the system.