Includes vita. / Title from PDF of title page. / Document formatted into pages; contains 155 pages. / Thesis (Ph.D.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: This dissertation research attempts to explore efficient algorithms and engineering methodologies of analyzing the overall reliability and availability of networks integrated with software failures and hardware failures. Node failures, link failures, and software failures are concurrently and dynamically considered in networks with complex topologies. MORIN (MOdeling Reliability for Integrated Networks) method is proposed and discussed as an approach for analyzing reliability of integrated networks. A Simplified Availability Modeling Tool (SAMOT) is developed and introduced to evaluate and analyze the availability of networks consisting of software and hardware component systems with architectural redundancy. / ABSTRACT: In this dissertation, relevant research efforts in analyzing network reliability and availability are reviewed and discussed, experimental data results of proposed MORIN methodology and SAMOT application are provided, and recommendations for future researches in the network reliability study are summarized as well. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Prescriptively, the requirement of fire safety protection systems for distribution substations is not provided in the compliance document for fire safety to the New Zealand Building Code. Therefore, the New Zealand Fire Service (NZFS) has proposed a list of fire safety protection requirements for distribution substations in a letter, dated 10th July 2002. A review by Nyman [1], has considered the fire safety requirements proposed by the NZFS and discussed the issues with a number of fire engineers over the last three years. Nyman concerned that one of the requirements regarding the four hour fire separation between the distribution substation and the interior spaces of the building may not be necessary when considering the risk exposure to the building occupants in different situations, such as the involvement of the sprinkler systems and the use of transformers with a lower fire hazard. Fire resistance rating (FRR) typically means the time duration for which passive fire protection system, such as fire barriers, fire walls and other fire rated building elements, can maintain its integrity, insulation and stability in a standard fire endurance test. Based on the literature review and discussions with industry experts, it is found that failure of the passive fire protection system in a real fire exposure could potentially occur earlier than the time indicated by the fire resistance rating derived from the standard test depending on the characteristics of the actual fire (heat release rate, fire load density and fire location) and the characteristics of the fire compartment (its geometric, ventilation conditions, opening definition, building services and equipment). Hence, it is known that a higher level of fire safety, such as 4 hour fire rated construction and use of sprinkler system, may significantly improve the fire risk to health of safety of occupants in the building; however, they could never eliminate the risk. This report presents a fire engineering Quantitative Risk Assessment (QRA) on a transformer fire initiating in a distribution substation inside a high-rise residential and commercial mixeduse building. It compares the fire safety protection requirements for distribution substations from the NZFS to other relevant documents worldwide: the regulatory standards in New Zealand, Australia and United States of America, as well as the non-regulatory guidelines from other stakeholders, such as electrical engineering organisation, insurance companies and electricity providers. This report also examines the characteristics of historical data for transformer fires in distribution substations both in New Zealand and United States of America buildings. Reliability of active fire safety protection systems, such as smoke detection systems and sprinkler systems is reviewed in this research. Based on the data analysis results, a fire risk estimate is determined using an Event Tree Analysis (ETA) for a total of 14 scenarios with different fire safety designs and transformer types for a distribution substation in a high-rise residential and commercial mixed-use building. In Scenario 1 to 10 scenarios, different combinations of fire safety systems are evaluated with the same type of transformer, Flammable liquid (mineral oil) insulated transformer. In Scenario 11 to Scenario 14, two particular fire safety designs are selected as a baseline for the analysis of transformer types. Two types of transformer with a low fire hazard are used to replace the flammable liquid (mineral oil) insulated transformer in a distribution substation. These are less flammable liquid (silicone oil) insulated transformers and dry type (dry air) transformers. The entire fire risk estimate is determined using the software package @Risk4.5. The results from the event tree analysis are used in the cost-benefit analysis. The cost-benefit ratios are measured based on the reduced fire risk exposures to the building occupants, with respect to the investment costs of the alternative cases, from its respective base case. The outcomes of the assessment show that the proposed four hour fire separation between the distribution substations and the interior spaces of the building, when no sprinkler systems are provided, is not considered to be the most cost-effective alternative to the life safety of occupants, where the cost-benefit ratio of this scenario is ranked fifth. The most cost-effective alternative is found to be the scenario with 30 minute fire separation and sprinkler system installed. In addition to the findings, replacing a flammable liquid insulated transformer with a less flammable liquid insulated transformer or a dry type transformer is generally considered to be economical alternatives. From the QRA analysis, it is concluded that 3 hour fire separation is considered to be appropriate for distribution substations, containing a flammable liquid insulated transformer and associated equipment, in non-sprinklered buildings. The fire ratings of the separation construction can be reduced to 30 minute FRR if sprinkler system is installed. This conclusion is also in agreement with the requirements of the National Fire Protection Association (NFPA).

Les notions de robustesse structurale sont intégrées dans les codes de conception européens suite à l'effondrement partiel et progressif de la tour Ronan Point de Canning Town à Londres (Angleterre, 16.05.1968). Le cadre réglementaire des Eurocodes définit la robustesse comme l'aptitude d'une structure à résister à des événements accidentels dits identifiés (incendies, explosions, chocs) ou non identifiés (conséquences d'une erreur humaine, attentats) sans présenter de dégâts disproportionnés par rapport à la cause d'origine. Cette définition incite les ingénieurs à inclure dans les procédures de conception les notions de dommage initial (défaillance locale) et de dommage disproportionné (défaillance globale). L'objectif de ces travaux de thèse est de développer un outil de simulation de la robustesse de structures lorsque des incertitudes de sollicitations (évènement accidentel) et / ou une faute de dimensionnement (conception ou de réalisation) interfèrent avec les dimensionnements réglementaires. La robustesse est évaluée à travers un indice compris entre 0 (structure peu robuste) et 1 (structure très robuste) et calculé à partir des probabilités de défaillance initiale et globale. Cette thèse propose une méthodologie reposant sur la recherche d’arbres complets d'évènements illustrant l'ensemble des cheminements potentiels d'une défaillance initiale localisée jusqu'à la ruine globale. L'approche développée s'applique aux structures hyperstatiques, dans lesquelles la rupture d'un ou plusieurs éléments n'entraine pas systématiquement la ruine de l'ensemble de la structure. En effet, les éléments non endommagés restants peuvent être en mesure de supporter les chargements externes par une redistribution des efforts internes.La procédure est illustrée dans les cas de structures unidimensionnelles hyperstatiques de poutres bi-encastrées et d'un portique référencé dans les normes et classiquement étudié dans la littérature. Le mode local de défaillance de nos simulations est la formation d'une rotule (fragile ou plastique) lorsque le moment sollicitant appliqué atteint la valeur du moment résistant d'une section droite. Deux types de lois probabilistes, Gaussiennes et Log-normales, sont testées par l'approche développée et par des simulations Monte-Carlo. Les variables aléatoires choisies peuvent être indépendantes ou corrélées. Nous présentons les résultats sous forme d’arbres d'évènements comportant l'ensemble des branches exclusives, sans intersection entre branches issues d’un même nœud. Cette spécificité permet de calculer des indices caractérisant la robustesse de la structure selon chaque scénario.L'analyse de l’arbre des évènements et des indices de robustesse permet de mettre en évidence les fragilités potentielles pouvant engendrer une défaillance généralisée d'une structure vis-à-vis d’accidents ou d’actes de malveillance. La méthode développée fournit un outil de simulation et de diagnostic efficace, tant en phase de conception qu'en phase de réhabilitation, permettant d'envisager le renforcement de bâtis existants ou futurs et d'assurer la sécurité des personnes et des ouvrages environnants. / Localized initial failures in constructions can sometimes be followed by disproportionate damage (collapse) spreading to the whole or the major part of a building. Since the partial and progressive collapse of the Ronnan Point tower (London, $1968$) caused by a gas explosion, the concept of robustness has been introduced in standards. Structural robustness is defined as the ability of a structure to withstand unforeseen events causing local damage like fire, explosion or impact, without suffering disproportionate collapse. This definition encourages engineers to include the concepts of initial damage (local failure) and disproportionate damage (global failure) in design procedures. The main objective of this PhD work is to develop a simulation tool in order to highlight the potential weakness in a structure when uncertain sollicitations (accidental events) and/or dimensional fault (design or realization) interfere with the standard predictions. The robustness is evaluated by an index varying from 0 (non-robust structure) to 1 (very robust structure) and is calculated from the initial and global failure probabilities. The proposed methodology is based on an event tree analysis summurizing all the distinct potential scenarios, from the initial damage to the collapse of the structure. The developed approach is applied to statically indeterminate unidimensional structures like beams and frame. The redundancy's consequence is that the break of one or several cross sections will not necessarily lead to the collapse of the whole system: the redistribution of the internal efforts allows the remaining undamaged parts of the structure to support the external (applied) loading. The methodology is illustrated by some examples of clamped-clamped beam and frame, loaded with punctual forces. The cross sections are supposed to have an elastic behaviour until the formation of plastic hinges (local failure). Two types of probabilistic laws, Gaussian and Log-normal, are tested by the developed approach and by Monte-Carlo simulations. The chosen random variables can be either independent or correlated. The resulting complete event tree contains all the exclusive paths from an localised damage to the global failure, without intersection between branches stemming from the same node. This specific property allows to evaluate the robustness indexes of the structure with the ratio between the local and global probabilities, according to each scenario. The analysis of the event tree and of the robustness indexes allows to highlight the potential brittleness which could cause a generalized collapse of the structure with respect to accidents or malicious acts. The developed methodology provides an effective tool of simulation and diagnostic, both in the design phase and in the rehabilitation one, useful to the reinforcement of existing or future buildings and to ensure the safety of people and surrounding structures.

This thesis focuses on the theoretical description of risk management options related to information technologies and describes methods used to risk analysis. Described methods are fault tree analysis, event tree analysis, FMEA, HAZOP and Markovov analysis. Practical part includes proposal and implementation of program that visualizes decision trees and determines probability of each tree item.

No description available.

For railways, risk analysis is carried out to identify hazardous situations and their consequences. Until recently, classical methods such as Fault Tree Analysis (FTA) and Event Tree Analysis (ETA) were applied in modelling the linear and logically deterministic aspects of railway risks, safety and reliability. However, it has been proven that modern railway systems are rather complex, involving multi-dependencies between system variables and uncertainties about these dependencies. For train derailment accidents, for instance, high train speed is a common cause of failure; slip and failure of brake applications are disjoint events; failure dependency exists between the train protection and warning system and driver errors; driver errors are time dependent and there is functional uncertainty in derailment conditions. Failing to incorporate these aspects of a complex system leads to wrong estimations of the risks and safety, and, consequently, to wrong management decisions. Furthermore, a complex railway system integrates various technologies and is operated in an environment where the behaviour and failure modes of the system are difficult to model using probabilistic techniques. Modelling and quantification of the railway risk and safety problems that involve dependencies and uncertainties such as mentioned above are complex tasks. Importance measures are useful in the ranking of components, which are significant with respect to the risk, safety and reliability of a railway system. The computation of importance measures using FTA has limitation for complex railways. ALARP (As Low as Reasonably Possible) risk acceptance criteria are widely accepted as ’\'best practice’’ in the railways. According to the ALARP approach, a tolerable region exists between the regions of intolerable and negligible risks. In the tolerable region, risk is undertaken only if a benefit is desired. In this case, one needs to have additional criteria to identify the socio-economic benefits of adopting a safety measure for railway facilities. The Life Quality Index (LQI) is a rational way of establishing a relation between the financial resources utilized to improve the safety of an engineering system and the potential fatalities that can be avoided by safety improvement. This thesis shows the application of the LQI approach to quantifying the social benefits of a number of safety management plans for a railway facility. We apply Bayesian Networks and influence diagrams, which are extensions of Bayesian Networks, to model and assess the life safety risks associated with railways. Bayesian Networks are directed acyclic probabilistic graphical models that handle the joint distribution of random variables in a compact and flexible way. In influence diagrams, problems of probabilistic inference and decision making – based on utility functions – can be combined and optimized, especially, for systems with many dependencies and uncertainties. The optimal decision, which maximizes the total benefits to society, is obtained. In this thesis, the application of Bayesian Networks to the railway industry is investigated for the purpose of improving modelling and the analysis of risk, safety and reliability in railways. One example application and two real world applications are presented to show the usefulness and suitability of the Bayesian Networks for the quantitative risk assessment and risk-based decision support in reference to railways.

The thesis deals with project management body of knowledge with focus on a risk management. It explained the importance of risk management in software developing projects. Risk management cycle and used methodology is described. The core unit of second part is requirements analysis for risk management support system, description of the application via UML and implementation of application which was created in development environment NetBeans IDE 6.5 in Java language. Conclusion of my thesis contains a short summary and possible way of extension.

No description available.

One of the objectives of this study is to develop a methodology, together with a set of software programs that evaluate, in a power system, the risks of catastrophic failures caused by hidden failures in the hardware or software components of the protection system. The disturbance propagation mechanism is revealed by the analysis of the 1977 New York Blackout. The step-by-step process of estimating the relay hidden failure probability is presented. A Dynamic Event Tree for the risk-based analysis of system catastrophic failures is proposed. A reduced 179-bus WSCC sample system is studied and the simulation results obtained from California sub-system are analyzed. System weak links are identified in the case study. The issues relating to the load and generation uncertainties for the risk assessment of system vulnerabilities are addressed. A prototype system - the Hidden Failure Monitoring and Control System (HFMCS) - is proposed to mitigate the risk of power system catastrophic failures. Three main functional modules - Hidden Failure Monitoring, Hidden Failure Control and Misoperation Tracking Database - and their designs are presented. Hidden Failure Monitoring provides the basis that allows further control actions to be initiated. Hidden Failure Control is realized by using Adaptive Dependability/Security Protection, which can effectively stop possible relay involvement from triggering or propagating disturbance under stressed system conditions. As an integrated part of the HFMCS, a Misoperation Tracking Database is proposed to track the performance of automatic station equipment, hence providing automatic management of misoperation records for hidden failure analysis. / Ph. D.

This thesis deals with the matter of risk managament in IT projects. It explains the importance of risk management in such projects and shows different ways and methods of managing and analyzing the risks. After explaining the basic concepts and the various phases of risk management the text focuses on two methods of risk analysis - the fault tree analysis of event tree analysis. Use of both methods is explained for both quantitative and qualitative analyses. The second half of the work includes the design of an application for the support of risk analysis employing the methods of fault tree analysis and event tree analysis. This is followed by a description of the implementation of the proposed system in a web environment using jQuery, Nette Framework and Dibi.