Assessing Asymmetric Fault-Tolerant Software

The most popular forms of fault tolerance against design faults use "asymmetric" architectures in which a "primary" part performs the computation and a "secondary" part is in charge of detecting errors and performing some kind of error processing and recovery. In contrast, the most studied forms of software fault tolerance are "symmetric" ones, e.g. N-version programming. The latter are often controversial, the former are not. We discuss how to assess the dependability gains achieved by these methods. Substantial difficulties have been shown to exist for symmetric schemes, but we show that the same difficulties affect asymmetric schemes. Indeed, the latter present somewhat subtler problems. In both cases, to predict the dependability of the fault-tolerant system it is not enough to know the dependability of the individual components. We extend to asymmetric architectures the style of probabilistic modeling that has been useful for describing the dependability of "symmetric" architectures, to highlight factors that complicate the assessment. In the light of these models, we finally discuss fault injection approaches to estimating coverage factors. We highlight the limits of what can be predicted and some useful research directions towards clarifying and extending the range of situations in which estimates of coverage of fault tolerance mechanisms can be trusted

Computer trading and systemic risk: a nuclear perspective

Financial markets have evolved to become complex adaptive systems highly reliant on the communication speeds and processing power afforded by digital systems. Their failure could cause severe disruption to the provision of financial services and possibly the wider economy. In this study we consider whether a perspective from the nuclear industry can provide additional insights

Reliability Analysis of Correlated Competitive and Dependent Components Considering Random Isolation Times

Funding Information: Funding Statement: This work was supported by the National Natural Science Foundation of China (NSFC) (Grant No. 62172058) and the Hunan Provincial Natural Science Foundation of China (Grant Nos. 2022JJ10052, 2022JJ30624). Publisher Copyright: © 2023 Tech Science Press. All rights reserved.Peer reviewedPublisher PD

Preliminary Interdependency Analysis: An Approach to Support Critical Infrastructure Risk Assessment

We present a methodology, Preliminary Interdependency Analysis (PIA), for analysing interdependencies between critical infrastructure (CI). Consisting of two phases – qualitative analysis followed by quantitative analysis – an application of PIA progresses from a relatively quick elicitation of CI-interdependencies to the building of representative CI models, and the subsequent estimation of any resilience, risk or criticality measures an assessor might be interested in. By design, stages in the methodology are both flexible and iterative, resulting in interacting CI models that are scalable and may vary significantly in complexity and fidelity, depending on the needs and requirements of an assessor. For model parameterisation, one relies on a combination of field data, sensitivity analysis and expert judgement. Facilitated by dedicated software tool support, we illustrate PIA by applying it to a complex case-study of interacting Power (distribution and transmission) and Telecommunications networks in the Rome area. A number of studies are carried out, including: 1) an investigation of how “strength of dependence” between the CIs’ components affects various measures of risk and uncertainty, 2) for resource allocation, an exploration of different, but related, notions of CI component importance, and 3) highlighting the impact of model fidelity on the estimated risk of cascades

Ship machinery and equipment inspection tool development for risk control and decision making

Concerning the successful business competence, strategic planning should be enhanced considering assets availability by involving maintenance and reliability operational aspects. The INCASS (Inspection Capabilities for Enhanced Ship Safety) FP7 EU funded research project aims to tackle the issue of ship inspection, identification of high-risk ships, providing access to information related to ship surveys and incorporate enhanced and harmonized cooperation of maritime stakeholders in order to avoid ship accidents, promote maritime safety and protect the environment. The current research consists of machinery and equipment specifications and stakeholders’ data requirements. Focusing on the methodology perspective, a Machinery Risk Analysis (MRA) model is introduced. All progress and methodology development takes place in Java programm ing language. Overall, the outcomes of this study demonstrate the reliability performance of marine machinery components. Future development include dynamic failure rate variation through time, probabilistic model’s sensitivity analysis and components’ and systems’ interdependencies in a user-friendly Graphical User Interface (GUI) design

System reliability analyses and optimal maintenance planning of corroding pipelines

The failure of corroding pipeline joints may induce severe consequences. However, maintenance is expensive due to the cost of excavating and repairing a single joint and typically a significant number of joints that need repair. It is central to develop an optimal cost-effective maintenance strategy that balances cost and safety. A key component of the strategy is the reliability based condition evaluation of pipeline joints. The focus of the research reported in this thesis is therefore developing efficient reliability assessment methods for pipeline individual joints, and developing an optimal maintenance framework for the entire pipeline system. First, efficient system reliability methods relying on the first-order reliability method (FORM) and important sampling (IS) are developed for the assessment of the time-dependent probabilities of small leak and burst failure of pipeline joints containing multiple corrosion defects. In addition, a novel method is developed within the FORM to obtain the design points efficiently. An improved equivalent component approach for evaluating multi-normal integrals is also developed to improve the efficiency of the FORM for system reliability analysis. In addition, a multi-objective optimization-based maintenance framework for corroding pipeline systems is formulated optimizing three objectives, i.e. the conditioned probabilities of burst and small leak, respectively, and repair cost. An improved genetic algorithm with a pre-training population is utilized to investigate the optimal Pareto front. The benefits of this framework enable decision makers to access a series of non-dominated optimal repairing solutions with respect to multiple conflicting objectives

Reliability and Condition-Based Maintenance Analysis of Deteriorating Systems Subject to Generalized Mixed Shock Model

For successful commercialization of evolving devices (e.g., micro-electro-mechanical systems, and biomedical devices), there must be new research focusing on reliability models and analysis tools that can assist manufacturing and maintenance of these devices. These advanced systems may experience multiple failure processes that compete against each other. Two major failure processes are identified to be deteriorating or degradation processes (e.g., wear, fatigue, erosion, corrosion) and random shocks. When these failure processes are dependent, it is a challenging problem to predict reliability of complex systems. This research aims to develop reliability models by exploring new aspects of dependency between competing risks of degradation-based and shock-based failure considering a generalized mixed shock model, and to develop new and effective condition-based maintenance policies based on the developed reliability models. In this research, different aspects of dependency are explored to accurately estimate the reliability of complex systems. When the degradation rate is accelerated as a result of withstanding a particular shock pattern, we develop reliability models with a changing degradation rate for four different shock patterns. When the hard failure threshold reduces due to changes in degradation, we investigate reliability models considering the dependence of the hard failure threshold on the degradation level for two different scenarios. More generally, when the degradation rate and the hard failure threshold can simultaneously transition multiple times, we propose a rich reliability model for a new generalized mixed shock model that is a combination of extreme shock model, δ-shock model and run shock model. This general assumption reflects complex behaviors associated with modern systems and structures that experience multiple sources of external shocks. Based on the developed reliability models, we introduce new condition-based maintenance strategies by including various maintenance actions (e.g., corrective replacement, preventive replacement, and imperfect repair) to minimize the expected long-run average maintenance cost rate. The decisions for maintenance actions are made based on the health condition of systems that can be observed through periodic inspection. The reliability and maintenance models developed in this research can provide timely and effective tools for decision-makers in manufacturing to economically optimize operational decisions for improving reliability, quality and productivity.Industrial Engineering, Department o

On the Queueing Behavior of Random Codes over a Gilbert-Elliot Erasure Channel

This paper considers the queueing performance of a system that transmits coded data over a time-varying erasure channel. In our model, the queue length and channel state together form a Markov chain that depends on the system parameters. This gives a framework that allows a rigorous analysis of the queue as a function of the code rate. Most prior work in this area either ignores block-length (e.g., fluid models) or assumes error-free communication using finite codes. This work enables one to determine when such assumptions provide good, or bad, approximations of true behavior. Moreover, it offers a new approach to optimize parameters and evaluate performance. This can be valuable for delay-sensitive systems that employ short block lengths.Comment: 5 pages, 4 figures, conferenc