No / The Internet of Things (IoT) has brought significant advancements in various domains, providing innovative and efficient solutions. However, ensuring the safe design and operation of IoT devices is crucial, as the consequences of component failure can range from system downtime to dangerous operating states. Several methods have been proposed to evaluate the failure behaviours of IoT-based systems, including Fault Tree Analysis (FTA), a methodology adopted from other safetycritical domains. This study integrated FTA and Bayesian Network (BN) models to assess IoT system reliability based on components’ reliability data and other statistical information. The integrated model achieved efficient predictive failure analysis, considering combinations of 12 basic events to quantify the overall system’s reliability. The model also enables criticality analysis, ranking basic events based on their contributions to system failure and providing a guide for design modification in order to enhance IoT safety. By comparing failure data in FTA and criticality indices obtained using the BN model, the proposed integration offers a probabilistic estimation of IoT system failure and a viable safety guide for designing IoT systems.

Small unmanned aerial vehicles (SUAVs) are plagued by alarmingly high failure rates. Because these systems are small and built at lower cost than full-scale aircraft, high quality components and redundant systems are often eschewed to keep production costs low. This thesis proposes a process to ``design in'' reliability in a cost-effective way. Fault Tree Analysis is used to evaluate a system's (un)reliability and Dempster-Shafer Theory (Evidence Theory) is used to deal with imprecise failure data. Three unique sensitivity analyses highlight the most cost-effective improvement for the system by either spending money to research a component and reduce uncertainty, swap a component for a higher quality alternative, or add redundancy to an existing component. A MATLAB$^{\circledR}$ toolbox has been developed to assist in practical design applications. Finally, a case study illustrates the proposed methods by improving the reliability of a new SUAV design: Virginia Tech's SPAARO UAV. / Master of Science

No / Fault management is one of the important management functions of a telecommunication network and mainly deals with fault monitoring and diagnosis. This paper applies reliability theories and methodologies for the fault management of an aeronautical communication system developed within the EU FP7 SANDRA project. The failure of the SANDRA terminal demonstrator is an undesirable event and the corresponding fault tree was built upon a reliability function analysis and was used to quickly monitor failures in the system. By using Monte Carlo simulations, the SANDRA demonstrator's reliability can be predicted and important components, which have major contributions to system failures, can be identified. The results can be used to improve the system reliability by adding parallel components in weak and important places.

Yes / Quantitative risk assessment (QRA) approaches systematically evaluate the likelihood, impacts, and risk of adverse events. QRA using fault tree analysis (FTA) is based on the assumptions that failure events have crisp probabilities and they are statistically independent. The crisp probabilities of the events are often absent, which leads to data uncertainty. However, the independence assumption leads to model uncertainty. Experts’ knowledge can be utilized to obtain unknown failure data; however, this process itself is subject to different issues such as imprecision, incompleteness, and lack of consensus. For this reason, to minimize the overall uncertainty in QRA, in addition to addressing the uncertainties in the knowledge, it is equally important to combine the opinions of multiple experts and update prior beliefs based on new evidence. In this article, a novel methodology is proposed for QRA by combining fuzzy set theory and evidence theory with Bayesian networks to describe the uncertainties, aggregate experts’ opinions, and update prior probabilities when new evidences become available. Additionally, sensitivity analysis is performed to identify the most critical events in the FTA. The effectiveness of the proposed approach has been demonstrated via application to a practical system. / The research of Sohag Kabir was partly funded by the DEIS project (Grant Agreement 732242).

Yes / Time, cost and risk are the main elements that effect the operating margin of the oil and gas companies due to Turnaround Maintenance (TAM). Turnaround Maintenance (TAM) is a methodology for the total shutdown of plant facilities during a pre-defined period to execute inspection actions, replacement and repairs according to Scope of Work (SoW). This paper presents a new methodology for improving TAM scheduling of oil and gas plants. The methodology includes four stages: removing Non-critical Equipment (NE) from reactive maintenance to proactive maintenance, risk-based inspection of Critical Static Equipment (CSE), risk-based failure of Critical Rotating Equipment (CRE), and application of failure distributions. The results from improving TAM scheduling is associated with decreasing duration and increasing interval between TAM leading to improved availability, reliability, operation and maintenance costs and safety risks. The paper presents findings from the TAM model application. The methodology is fairly generic in its approach and can also be adapted for implementation in other oil and gas industries that operate under similar harsh conditions.

Yes / Fault tree analysis (FTA) is a powerful technique that is widely used for evaluating system safety and reliability. It can be used to assess the effects of combinations of failures on system behaviour but is unable to capture sequence dependent dynamic behaviour. A number of extensions to fault trees have been proposed to overcome this limitation. Pandora, one such extension, introduces temporal gates and temporal laws to allow dynamic analysis of temporal fault trees (TFTs). It can be easily integrated in model-based design and analysis techniques. The quantitative evaluation of failure probability in Pandora TFTs is performed using exact probabilistic data about component failures. However, exact data can often be difficult to obtain. In this paper, we propose a method that combines expert elicitation and fuzzy set theory with Pandora TFTs to enable dynamic analysis of complex systems with limited or absent exact quantitative data. This gives Pandora the ability to perform quantitative analysis under uncertainty, which increases further its potential utility in the emerging field of model-based design and dependability analysis. The method has been demonstrated by applying it to a fault tolerant fuel distribution system of a ship, and the results are compared with the results obtained by other existing techniques.

Submitted by Jean Medeiros (jeanletras@uepb.edu.br) on 2016-04-27T13:57:00Z No. of bitstreams: 1 PDF - Élida Medeiros do Nascimento.pdf: 2966865 bytes, checksum: af4c289198c4970b2369d273cf340702 (MD5) / Made available in DSpace on 2016-04-27T13:57:00Z (GMT). No. of bitstreams: 1 PDF - Élida Medeiros do Nascimento.pdf: 2966865 bytes, checksum: af4c289198c4970b2369d273cf340702 (MD5) Previous issue date: 2015-08-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The present study seeks to identify and analyze the hazards in exploitation of ornamental stones. To reach the proposed objective, we conducted an investigation in the productive system (exploitation, beneficiation and marketing) in region of the Várzea city (PB), one of the main poles extractors and processors of quartzite of the state of Paraíba, Northeastern Brazil. The exploitation of quartzite is performed by several miners for more than 40 years and involves more than 900 workers, it’s the main source of employment and income of the city. The study allowed to describe the productive system (exploitation, beneficiation and marketing), subdividing it into stages, identify and analyze only on the exploitation, the main hazards involved in each of its stages. Thus opted for a search of hybrid character (quantitative and qualitative) with the application of two risk assessment techniques: FMEA (analysis mode and effect of failures) and the FTA (fault tree analysis). The FMEA generated as results the definition of the risks of exploitation, its classification as to the importance, as also identified its causes, consequences and proposed measures that should be adopted to mitigate them. The FTA was used to allow a clear view through a graphical representation of the possible causes of these risks, becoming a facilitator in managing the risks in mining activity. The weighting of the risks showed that dust containing high percentage of crystalline silica (44.3% -70.7% SiO2), the noise, the use of explosives, vibration, and the informality of mining activity were the risks that had the highest percentages, both for individual assessment of risks as for the characterization of the steps from exploitation. Finally, the fault trees were built, where possible qualitatively describe the main causes of fatal accidents involving workers. Since at this stage they were used dimensions suggested by completing the FMEA form and the literature review. The results obtained during the study are characterized as essential to draw up proposals, goals and strategies to manage the risks evaluated by the above methods. / O presente estudo busca identificar e analisar os perigos existentes na explotação de rochas ornamentais. Para alcance do objetivo proposto, realizou-se uma investigação no sistema produtivo (explotação, beneficiamento e comercialização) na região do município de Várzea (PB), um dos principais polos extratores e beneficiadores de quartzito do estado da Paraíba, no Nordeste do Brasil. A explotação de quartzito é realizada por vários garimpeiros há mais de 40 anos e envolve mais de 900 trabalhadores, se configurando como a principal fonte de emprego e renda do Município. O estudo nos permitiu descrever o sistema produtivo (explotação, beneficiamento e comercialização), subdividi-lo em etapas, identificar e analisar, apenas na explotação, os principais perigos envolvidos em cada uma de suas etapas. Optou-se assim por uma pesquisa de caráter híbrido (quantitativo e qualitativo) com a aplicação de duas técnicas da avaliação de risco: a FMEA (análise de modo e efeito de falhas) e a FTA (análise de árvore de falhas). A FMEA gerou como resultados a definição dos riscos da explotação, sua classificação quanto à importância, como também identificou suas causas, consequências e propôs medidas que deverão ser adotadas para mitigá-los. A FTA foi utilizada para permitir a clara visualização, através de uma representação gráfica, das possíveis causas desses riscos, tornando-se um instrumento facilitador no gerenciamento dos riscos nessa atividade extrativista. A ponderação dos riscos mostrou que as poeiras contendo alto percentual de sílica cristalina (44,3%-70,7% de SiO2), os ruídos, o uso de explosivos, as vibrações, e a informalidade da atividade extrativista foram os riscos que apresentaram os maiores percentuais, tanto para avaliação individual dos riscos quanto pela caracterização das etapas da explotação. As árvores de falhas estabelecidas possibilitaram descrever qualitativamente as principais causas dos acidentes fatais com trabalhadores, nos quais foram usadas as dimensões sugeridas pelo preenchimento do formulário FMEA e pela revisão de literatura. Os resultados obtidos durante a realização do estudo se configuram como essenciais para elaborar propostas, metas e estratégias para gerenciar os riscos avaliados através das metodologias supracitadas.

Nuclear-based hydrogen generation is a promising way to supply hydrogen for this large market in the future. This thesis focuses on one of the most promising methods, a thermochemical Cu-Cl cycle, which is currently under development by UOIT, Atomic Energy of Canada Limited (AECL) and the Argonne National Laboratory (ANL). The safety issues of the Cu-Cl cycle are addressed in this thesis. An investigation of major accident scenarios shows that potential tragedies can be avoided with effective risk analysis and safety management programs. As a powerful and systematic tool, fault tree analysis (FTA) is adapted to the particular needs of the Cu-Cl system. This thesis develops a new method that combines FTA with a reliability analysis tool, multi-state system (MSS), to improve the accuracy of FTA and also improve system reliability. / UOIT

Modern society is unquestionably heavily reliant on supply of electricity. Hence, the power system is one of the important infrastructures for future growth. However, the power system of today was designed for a stable radial flow of electricity from large power plants to the customers and not for the type of changes it is presently being exposed to, like large scale integration of electric vehicles, wind power plants, residential photovoltaic systems etc. One aspect of power system control particular exposed to these changes is the design of power system control and protection functionality. Problems occur when the flow of electricity changes from a unidirectional radial flow to a bidirectional. Such an implication requires redesign of control and protection functionality as well as introduction of new information and communication technology (ICT). To make matters worse, the closer the interaction between the power system and the ICT systems the more complex the matter becomes from a reliability perspective. This problem is inherently cyber-physical, including everything from system software to power cables and transformers, rather than the traditional reliability concern of only focusing on power system components. The contribution of this thesis is a framework for reliability analysis, utilizing system modeling concepts that supports the industrial engineering issues that follow with the imple-mentation of modern substation automation systems. The framework is based on a Bayesian probabilistic analysis engine represented by Probabilistic Relational Models (PRMs) in com-bination with an Enterprise Architecture (EA) modeling formalism. The gradual development of the framework is demonstrated through a number of application scenarios based on substation automation system configurations. This thesis is a composite thesis consisting of seven papers. Paper 1 presents the framework combining EA, PRMs and Fault Tree Analysis (FTA). Paper 2 adds primary substation equipment as part of the framework. Paper 3 presents a mapping between modeling entities from the EA framework ArchiMate and substation automation system configuration objects from the IEC 61850 standard. Paper 4 introduces object definitions and relations in coherence with EA modeling formalism suitable for the purpose of the analysis framework. Paper 5 describes an extension of the analysis framework by adding logical operators to the probabilistic analysis engine. Paper 6 presents enhanced failure rates for software components by studying failure logs and an application of the framework to a utility substation automation system. Finally, Paper 7 describes the ability to utilize domain standards for coherent modeling of functions and their interrelations and an application of the framework utilizing software-tool support. / <p>QC 20140505</p>

Reliability and safety of complex software-intensive systems are proved to be a crucial matter since most of these systems fulfil tasks, where a failure could lead to catastrophic consequences. For example, in space systems such as satellites, a failure could result in the loss of the satellite. Therefore, a certain level of reliability and safety must be assured for such systems to trust the services they provide. Standards set this level and put requirements for the analysis and assurance of these properties using documented evidence. In particular, European Cooperation for Space Standardization (ECSS) standards for space systems require Fault Tree Analysis(FTA) for identifying the causes of system failure and consequently safety hazards, as well as fault trees as evidence for the assurance of reliability and safety. In this thesis, we present a tool supported model-based approach to generate fault tree automatically from an existing system modelling and analysis toolset. CHESS is a system and dependability modelling toolset and integrates Concerto-FLA to enable the support of failure logic analysis. We proposed a model-based transformation from Concerto-FLA to fault tree model and implemented it as an Eclipse plugin in CHESS toolset. A case study is performed in the aerospace domain; more specifically we modelled Attitude Control System (ACS) and automatically generated IEC-61025-compliant fault trees. / AMASS project