Causality and Temporal Dependencies in the Design of Fault Management Systems

Reasoning about causes and effects naturally arises in the engineering of safety-critical systems. A classical example is Fault Tree Analysis, a deductive technique used for system safety assessment, whereby an undesired state is reduced to the set of its immediate causes. The design of fault management systems also requires reasoning on causality relationships. In particular, a fail-operational system needs to ensure timely detection and identification of faults, i.e. recognize the occurrence of run-time faults through their observable effects on the system. Even more complex scenarios arise when multiple faults are involved and may interact in subtle ways. In this work, we propose a formal approach to fault management for complex systems. We first introduce the notions of fault tree and minimal cut sets. We then present a formal framework for the specification and analysis of diagnosability, and for the design of fault detection and identification (FDI) components. Finally, we review recent advances in fault propagation analysis, based on the Timed Failure Propagation Graphs (TFPG) formalism.Comment: In Proceedings CREST 2017, arXiv:1710.0277

Using imprecise continuous time Markov chains for assessing the reliability of power networks with common cause failure and non-immediate repair.

We explore how imprecise continuous time Markov chains can improve traditional reliability models based on precise continuous time Markov chains. Specifically, we analyse the reliability of power networks under very weak statistical assumptions, explicitly accounting for non-stationary failure and repair rates and the limited accuracy by which common cause failure rates can be estimated. Bounds on typical quantities of interest are derived, namely the expected time spent in system failure state, as well as the expected number of transitions to that state. A worked numerical example demonstrates the theoretical techniques described. Interestingly, the number of iterations required for convergence is observed to be much lower than current theoretical bounds

Juridical Side of ALARP: The Monte Bianco Tunnel

When the ALARP “as low as reasonably practicable” principle is considered in judgments, this always comprehends a proportionate cost-risk analysis of protection measures: minimum risk has to mean level of safety maximization conditional to a given equitable profit, and maximum profit given a minimum sufficient level of safety. In London Court in 1949, Lord Asquith's definition of “reasonably practicable” in its judgment “Edwards v. National Coal Board”, as well as the whole judgment, became the legal basis of a requirement for risk assessments. Since then, ALARP has been officially endorsed and safety measures implemented in governments and enterprises in order to mitigate and manage risks. The study aims to analyse the failures in the Monte Bianco tunnel’s accident – which occurred on March 24, 1999 – from a logical perspective in order to develop a higher level of safety based on past experience and that played a central role in generating the current European Directive 2004/54/EC on minimum safety requirements for tunnels. This article reveals the consequences of ignoring the value of ALARP principle. Error analysis in Forensic Engineering are discussed and Gu@larp model contribution is considered

Issues on simulation of the railway rolling stock operation process – a system and literature review

Railway traffic simulation, taking into account operation and maintenance conditions, is not a new issue in the literature. External effects in such networks (eg. level crossings) were not taken into account in studies. The used models do not take into account sufficiently the process of degradation and recovery of the network. From the technical side, currently carried out simulations are made using similar approaches and techniques as in the initial stage of research. Well-established work in this area could be the basis for evaluation of new solutions. However, the progress in simulation tools during the last years, especially in performance and programming architecture, attempt to create a modern simulation tool. In the paper were presented the main assumptions for the evaluated event-based simulation method, with application to stiff-track transportation network

Cast partials analysis using a proprietary test station

This paper discusses issues related to arch cast partials. Functional analysis of such prostheses was carried out, factoring in loads and strains to which they are exposed. Consequently, a test station was designed for measuring model prosthesis strain under dynamic load

An overview on the obsolescence of physical assets for the defence facing the challenges of industry 4.0 and the new operating environments

Libro en Open AccessThis contribution is intended to observe special features presented in physical assets for defence. Particularly, the management of defence assets has to consider not only the reliability, availability, maintainability and other factors frequently used in asset management. On the contrary, such systems should also take into account their adaptation to changing operating environments as well as their capability to changes on the technological context. This study approaches to the current real situation where, due to the diversity of conflicts in our international context, the same type of defence systems must be able to provide services under different boundary conditions in different areas of the globe. At the same time, new concepts from the Industry 4.0 provide quick changes that should be considered along the life cycle of a defence asset. As a finding or consequence, these variations in operating conditions and in technology may accelerate asset degradation by modifying its reliability, its up-to-date status and, in general terms, its end-of-life estimation, depending of course on a diversity of factors. This accelerated deterioration of the asset is often known as “obsolescence” and its implications are often evaluated (when possible), in terms of costs from different natures. The originality of this contribution is the introduction of a discussion on how a proper analysis may help to reduce errors and mistakes in the decision-making process regarding the suitability or not of repairing, replacing, or modernizing the asset or system under study. In other words, the obsolescence analysis, from a reliability and technological point of view, could be used to determine the conservation or not of a specific asset fleet, in order to understand the effects of operational and technology factors variation over the functionality and life cycle cost of physical assets for defence

Resilience - A Key Element in User-centred Services?

Population changes indicates a demographical distribution with even more elderly. The authorities emphasize the importance to stay in good health and being independent as long as possible. Still, some will need some assistance to be physical active by doing exercising and thus preventing incidents and injuries. The paper describes a project in a Norwegian local council aiming at developing a user-centred service model. The service may be characterized as a new model of public-private-voluntary partnership. The service model may be adapted to other areas and services. The work presented in this paper has been part of a more extensive research project, whose Norwegian title translates into "Be the boss of your own life". A new role to the local council is to take the responsibility as organizer, cocreator and coordinator of the services offered by different actors. Together they shall meet the individual user's needs. The research project has developed a method to develop performance indicators, and to measure and evaluate a new service model. The purpose of the method is to be a tool enhancing learning about effects both related to service user and service provider. The key performance indicators in the new model are based on theoretical knowledge and comprise the seven areas: resilience, service provision, user satisfaction, management and leadership, stimulating work conditions, coordination and improvement efforts, and efficiency improvements.acceptedVersio