The world of computers experienced an explosive period of growth toward the end of the 20th century with the widespread availability of the Internet and the development of the World Wide Web. As people began using computer networks for everything from research and communication to banking and commerce, network failures became a greater concern because of the potential to interrupt critical applications. Fault tolerance systems were developed to detect and correct network failures within minutes and eventually within seconds of the failure, but time-critical applications such as military communications, video conferencing, and Web-based sales require better response time than any previous systems could provide. The goal of this thesis was the development and implementation of a Network Fault Tolerance (NFT) system that can detect and recover from failures of network interface cards, network cables, switches, and routers in much less than one second from the time of failure. The problem was divided into two parts: fault tolerance within a single local area network (LAN), and fault tolerance across many local area networks. The first part involves the network interface cards, network cables, and switches within a LAN, which the second part involves the routers that connect LANs into larger internetworks. Both parts of the NFT solution were implemented on Windows NT 4.0 PC's connected by a switched Fast Ethernet network. The NFT system was found to correct system failures within 300 milliseconds of the failure.

A detecção de falhas em uma plataforma distribuída é um componente essencial para uma grande quantidade de estratégias de tolerância a falhas, como a restauração do estado das aplicações distribuídas através de checkpointing e message logging. Porém, esta detecção frequentemente depende da comunicação confiável entre os nós de processamento e os módulos de detecção de falhas. Em grades computacionais hierárquicas com limitações de conectividade, a comunicação direta entre nós e módulos de detecção é muitas vezes impossível. Outro fator que dificulta a detecção de falhas em grades computacionais é a localização geograficamente esparsa entre as instituições e os recursos computacionais disponíveis na grade e a consequente utilização de redes de longa distância para os conectar. Esta dissertação apresenta uma arquitetura para a detecção de falhas em plataformas distribuídas otimizada para o funcionamento em grades computacionais hierárquicas, levando suas limitações e requisitos em consideração. A arquitetura, denominada GFDA (Grid Fault Detection Architecture), é estruturada em módulos de detecção das falhas que afetam nós computacionais disponibilizados na grade, módulos de detecção de falhas das aplicações distribuídas, e módulos de coleção, processamento e encaminhamento das notificações de falha e recuperação emitidas pelos módulos de detecção. Detalhes da implementação e da verificação do funcionamento correto da arquitetura são apresentados, bem como resultados obtidos através da execução de componentes da arquitetura em um cluster de computadores simulado através de máquinas virtuais. São propostas técnicas para a otimização da qualidade de serviço de detecção de falhas. Os resultados obtidos com a utilização destas técnicas são comparados com resultados obtidos com abordagens tradicionais. Observa-se que as técnicas implementadas na arquitetura GFDA para o processamento de notificações de falha e recuperação e a introdução de redundância nas mensagens trocadas entre os módulos de detecção de falhas traz resultados positivos em condições adversas de conectividade. Conclui-se que a arquitetura GFDA contribui para o estabelecimento de uma solução viável para a detecção de falhas em uma grade computacional hierárquica em que há restrições de conectividade entre os nós computacionais. / In distributed platforms, fault detection is an essential requirement to a wide range of fault tolerance techniques, such as restoring the state of distributed applications with checkpointing and message logging. However, fault detection often depends on reliable communication between the processing nodes and detection fault modules. Direct communication between the nodes and detection modules is often impossible in hierarchical grid computing platforms. The physical distance between the institutions and resources available on the grid, and thus the requirement of long distance networks connecting them, is another factor that makes direct fault detection in computer grids a challenge. This thesis presents a fault detection architecture for distributed platforms, optimized for usage in hierarchical grids and thus taking into account its restrictions and requirements. The architecture, named GFDA (Grid Fault Detection Architecture), is structured as fault detection modules for faults that affect the computing nodes available on the grid, detection modules for faults that affect the distributed applications, and modules that perform the collection, processing and forwarding of the fault and recovery notifications generated by the detection modules. This thesis presents implementation details, an evaluation of the correctness of the designed architecture, and results obtained through the deployment of parts of the architecture in a simulated cluster that uses virtual machines to simulate computing nodes. Techniques to optimize the quality of the detection fault service are proposed. The results obtained through the usage of such techniques are compared to the results obtained through traditional approaches. Positive results were extracted even under adverse connectivity conditions by using techniques such as the processing of fault and recovery notifications and the introduction of redundant information in the messages exchanged between the detection modules. It is concluded that the GFDA architecture contributes to the establishment of a viable solution for fault detection in a hierarchical grid computing platform that presents connectivity restrictions between the nodes.

Geologic storage of anthropogenic carbon dioxide (CO2) by injection into underground porous sandstone reservoirs has been proposed as a method for the reduction of anthropogenic greenhouse gas emissions. Upwards migration and leakage of injected fluids along natural fault and fracture networks is a key risk factor for potential injection locations. We examine exposed natural analogs to evaluate the impacts of faulting and fracturing on reservoir and top-seal pairs and to evaluate evidence for paleomigration of fluids along the fault zone. We examine the Iron Wash fault, a 25-km long normal fault which cuts Jurassic sedimentary rocks and has throws that range from 20-120 m, to examine how a fault may affect seal integrity. Field mapping, kinematic analysis, petrographic analysis, characterization of the fault zone facies and fault architecture, analysis of altered and mineralized rocks in and around the fault zone, and modeling of fault seal capacity was conducted to provide an understanding of the Iron Wash fault zone. Field data and observations were combined with well log and borehole data to produce three types of models for the Iron Wash fault: 1) geometric model of the fault in the subsurface, 2) predictive models of fault zone behavior and fault seal analysis, and 3) predictive geomechanical models of the response of the fault zone to an imposed stress field and increasing the effective stress on the fault. We conclude that the Iron Wash fault zone has low sealing capacity and will likely not behave as a seal for fluids against the fault zone due primarily to modest throw on the fault and high frequency of fractures associated with the fault zone. Analysis of fluid alteration and mineralization around the fault zone indicates that the fault zone was conduit for paleo-fluids. We conclude that the fault is not likely to develop a sealing membrane and therefore will most likely fail as a seal to fluids moving through the reservoirs modeled here. Modeling results indicate that a reduction in the effective normal stress on fault surfaces may induce failure of faults resulting in earthquakes or increased hydraulic conductivity of fractures.

<p>The focus of this work is on faults, and the main issue is statistical analysis and stochastic modeling of faults and fault patterns in petroleum reservoirs. The thesis consists of Part I-V and Appendix A-C. The units can be read independently. Part III is written for a geophysical audience, and the topic of this part is fault and fracture size-frequency distributions. The remaining parts are written for a statistical audience, but can also be read by people with an interest in quantitative geology. The topic of Part I and II is statistical model choice for fault size distributions, with a samling algorithm for estimating Bayes factor. Part IV describes work on spatial modeling of fault geometry, and Part V is a short note on line partitioning. Part I, II and III constitute the main part of the thesis. The appendices are conference abstracts and papers based on Part I and IV.</p> / Paper III: reprinted with kind permission of the American Geophysical Union. An edited version of this paper was published by AGU. Copyright [2000] American Geophysical Union

The Inner Piedmont (IP) is the Neoacadian migmatitic orogenic core of the southern Appalachians, exhibiting the widest area of high-grade metamorphism; regional upper amphibolite facies with isolated pods of granulite grade metamorphism. Peak P-T conditions in central GA reached 4.0-7.6 kbars and 630-715 ̊ C. The Brindle Creek fault (BCf) separates high-grade metasedimentary rocks of the eastern Tugaloo terrane (Tt) and Cat Square terrane (CSt). The Tt consists of the Neoproterozoic to early Paleozoic(?) Tallulah Falls Formation, Chauga River Formation, and the Mid-Ordovician Poor Mountain Formation, intruded by Early to Middle Ordovician granitoids. The CSt consists of Siluro-Devonian metasedimentary rocks, such as sillimanite-schist, biotite gneiss, amphibolite, and minor calc-silicate, intruded by Acadian-Neoacadian plutons. Original termination of the CSt was mapped by the USGS just south of Athens, GA, against the central Piedmont suture; however, new evidence from aeromagnetic anomalies and detailed geologic mapping revealed that the CSt and BCf extend into central GA. The BCf truncates a suite of curved magnetic anomalies on the aeromagnetic map. The curved anomalies that truncate against the linear feature may represent the Neoacadian deflection of the IP southwestward along the crustally weak Brevard fault zone. Another prominent lineament was identified southeast of the BCf; detailed geologic mapping revealed an additional thrust sheet in the CSt. Mesozoic brittle reactivation of the late Paleozoic dextral Towaliga fault was also identified striking NE-SW through the field area. Multiple episodes of movement were observed in outcrop and at the micro-scale, defined by crosscutting fracture sets. Low temperature quartz mylonite (350-450 ̊ C) may signify continued shearing of the IP into the late Alleghanian orogeny. A felsic plutonic suite extends the length of the field area, consisting of three distinct granitoids: (1) an older biotite-rich megacrystic granite with megacrysts of K-feldspar; (2) a weakly foliated medium to coarse grained inequigranular granodiorite; and (3) a younger non-foliated fine-grained granodiorite. Analysis revealed that granitoids from central GA are similar texturally and petrographically with granitoids from NC’s CSt. Further whole-rock geochemical analysis revealed that these rocks share similar REE, trace element, and tectonic discriminate patterns. The most important point garnered from the trace element and REE patterns in spider diagrams, such as similarities in peaks and troughs, is that they must share either a common parent, process, or contaminant.

The focus of this work is on faults, and the main issue is statistical analysis and stochastic modeling of faults and fault patterns in petroleum reservoirs. The thesis consists of Part I-V and Appendix A-C. The units can be read independently. Part III is written for a geophysical audience, and the topic of this part is fault and fracture size-frequency distributions. The remaining parts are written for a statistical audience, but can also be read by people with an interest in quantitative geology. The topic of Part I and II is statistical model choice for fault size distributions, with a samling algorithm for estimating Bayes factor. Part IV describes work on spatial modeling of fault geometry, and Part V is a short note on line partitioning. Part I, II and III constitute the main part of the thesis. The appendices are conference abstracts and papers based on Part I and IV. / Paper III: reprinted with kind permission of the American Geophysical Union. An edited version of this paper was published by AGU. Copyright [2000] American Geophysical Union

The emergence of complex and autonomous systems, such as modern aircraft, unmanned aerial vehicles (UAVs) and automated industrial processes is driving the development and implementation of new control technologies aimed at accommodating incipient failures to maintain system operation during an emergency. The motivation for this research began in the area of avionics and flight control systems for the purpose to improve aircraft safety. A prognostics health management (PHM) based fault-tolerant control architecture can increase safety and reliability by detecting and accommodating impending failures thereby minimizing the occurrence of unexpected, costly and possibly life-threatening mission failures; reduce unnecessary maintenance actions; and extend system availability / reliability. Recent developments in failure prognosis and fault tolerant control (FTC) provide a basis for a prognosis based reconfigurable control framework. Key work in this area considers: (1) long-term lifetime predictions as a design constraint using optimal control; (2) the use of model predictive control to retrofit existing controllers with real-time fault detection and diagnosis routines; (3) hybrid hierarchical approaches to FTC taking advantage of control reconfiguration at multiple levels, or layers, enabling the possibility of set-point reconfiguration, system restructuring and path / mission re-planning. Combining these control elements in a hierarchical structure allows for the development of a comprehensive framework for prognosis based FTC. First, the PHM-based reconfigurable controls framework presented in this thesis is given as one approach to a much larger hierarchical control scheme. This begins with a brief overview of a much broader three-tier hierarchical control architecture defined as having three layers: supervisory, intermediate, and low-level. The supervisory layer manages high-level objectives. The intermediate layer redistributes component loads among multiple sub-systems. The low-level layer reconfigures the set-points used by the local production controller thereby trading-off system performance for an increase in remaining useful life (RUL). Next, a low-level reconfigurable controller is defined as a time-varying multi-objective criterion function and appropriate constraints to determine optimal set-point reconfiguration. A set of necessary conditions are established to ensure the stability and boundedness of the composite system. In addition, the error bounds corresponding to long-term state-space prediction are examined. From these error bounds, the point estimate and corresponding uncertainty boundaries for the RUL estimate can be obtained. Also, the computational efficiency of the controller is examined by using the number of average floating point operations per iteration as a standard metric of comparison. Finally, results are obtained for an avionics grade triplex-redundant electro-mechanical actuator with a specific fault mode; insulation breakdown between winding turns in a brushless DC motor is used as a test case for the fault-mode. A prognostic model is developed relating motor operating conditions to RUL. Standard metrics for determining the feasibility of RUL reconfiguration are defined and used to study the performance of the reconfigured system; more specifically, the effects of the prediction horizon, model uncertainty, operating conditions and load disturbance on the RUL during reconfiguration are simulated using MATLAB and Simulink. Contributions of this work include defining a control architecture, proving stability and boundedness, deriving the control algorithm and demonstrating feasibility with an example.

The Inner Piedmont (IP) is the Neoacadian migmatitic orogenic core of the southern Appalachians, exhibiting the widest area of high-grade metamorphism; regional upper amphibolite facies with isolated pods of granulite grade metamorphism. Peak P-T conditions in central GA reached 4.0-7.6 kbars and 630-715 ̊ C. The Brindle Creek fault (BCf) separates high-grade metasedimentary rocks of the eastern Tugaloo terrane (Tt) and Cat Square terrane (CSt). The Tt consists of the Neoproterozoic to early Paleozoic(?) Tallulah Falls Formation, Chauga River Formation, and the Mid-Ordovician Poor Mountain Formation, intruded by Early to Middle Ordovician granitoids. The CSt consists of Siluro-Devonian metasedimentary rocks, such as sillimanite-schist, biotite gneiss, amphibolite, and minor calc-silicate, intruded by Acadian-Neoacadian plutons. Original termination of the CSt was mapped by the USGS just south of Athens, GA, against the central Piedmont suture; however, new evidence from aeromagnetic anomalies and detailed geologic mapping revealed that the CSt and BCf extend into central GA. The BCf truncates a suite of curved magnetic anomalies on the aeromagnetic map. The curved anomalies that truncate against the linear feature may represent the Neoacadian deflection of the IP southwestward along the crustally weak Brevard fault zone. Another prominent lineament was identified southeast of the BCf; detailed geologic mapping revealed an additional thrust sheet in the CSt. Mesozoic brittle reactivation of the late Paleozoic dextral Towaliga fault was also identified striking NE-SW through the field area. Multiple episodes of movement were observed in outcrop and at the micro-scale, defined by crosscutting fracture sets. Low temperature quartz mylonite (350-450 ̊ C) may signify continued shearing of the IP into the late Alleghanian orogeny.A felsic plutonic suite extends the length of the field area, consisting of three distinct granitoids: (1) an older biotite-rich megacrystic granite with megacrysts of K-feldspar; (2) a weakly foliated medium to coarse grained inequigranular granodiorite; and (3) a younger non-foliated fine-grained granodiorite. Analysis revealed that granitoids from central GA are similar texturally and petrographically with granitoids from NC’s CSt. Further whole-rock geochemical analysis revealed that these rocks share similar REE, trace element, and tectonic discriminate patterns. The most important point garnered from the trace element and REE patterns in spider diagrams, such as similarities in peaks and troughs, is that they must share either a common parent, process, or contaminant.

The focus of this research is on identification, location, interruption, characterization and overall management of faults in conventional AC distribution systems as well as isolated MVDC power systems. The primary focus in AC distributions systems is on identifying and locating underground cable faults using voltage and current waveforms as the input data. Cable failure process is gradual and is characterized by a series of single-phase sub-cycle incipient faults with high arc voltage. They often go undetected and eventually result in a permanent fault in the same phase. In order to locate such incipient cable faults, a robust yet practical algorithm is developed taking into account the fault arc voltage. The algorithm is implemented in the time-domain and utilizes power quality monitor data to estimate the distance to the fault in terms of the line impedance. It can be applied to locate both sub-cycle as well as permanent faults. The proposed algorithm is evaluated and proved out using field data collected from utility distribution circuits. Furthermore, this algorithm is extended to locate evolving faults on overhead distribution lines. Evolving faults are faults beginning in one phase of a distribution circuit and spreading to another phase after a few cycles. The algorithm is divided into two parts, namely, the single line-to-ground portion of the fault and the line-to-line-to-ground portion of the fault. For the single line-to-ground portion of the fault, the distance to the fault is estimated in terms of the loop or self-reactance between the monitor and the fault. On the other hand, for the line-to-line-to-ground and line-to-line portion of the fault the distance is estimated in terms of the positive-sequence reactance. The secondary focus of fault management in AC distribution systems is on identifying fault cause employing voltage and current waveform data as well as meteorological information. As the first step, unique characteristics of cable faults are examined along with methods to identify such faults with suitable accuracy. These characteristics are also used to distinguish underground cable faults from other overhead distribution line faults. The overhead line faults include tree contact, animal contact and lightning induced faults. Waveform signature analysis, wavelet transforms and arc voltages during the fault event are used for fault cause identification and classification. A statistical based classification methodology to identify fault cause is developed by utilizing promising characteristics. Unlike the AC system infrastructure which is already in place, the DC system considered in this document is that of a notional electric ship. The nature of DC current, with the absence of a current zero as well as the presence of power electronic devices influencing the current behavior, makes interrupting DC fault currents challenging. As a part of this research an innovative DC fault interruption scheme is proposed for rectifier- fed MVDC systems. A fault at the terminals of a phase-controlled rectifier results in a high magnitude current impulse caused by the filter capacitor discharging into the fault resistance. It is proposed to use a series inductor to limit the magnitude of this current impulse. The addition of the inductor results in an underdamped series RLC circuit at the output terminals of the rectifier which causes the fault current to oscillate about zero. Furthermore, it is proposed to utilize a conventional AC circuit breaker to interrupt this fault current by exploiting the zero crossings resulting from the oscillations. Using the proposed scheme for the example case, the peak fault current magnitude as well as the interruption time is significantly reduced. / text

This dissertation addresses fault detection and isolation (FDI) for nonlinear systems based on models using two different approaches. The first approach detects and isolates single and multiple faults, particularly when there are restrictions in measuring process variables. The FDI model-based method is based on nonlinear state estimators, in which the estimates are calculated under high filtering, and a high fidelity residuals model, obtained from the difference between measurements and estimates. In the second approach, a robust fault detection and isolation (RFDI) system, that handles both parameter estimation and parameters with uncertainties, is proposed in which complex models can be simplified with nonlinear functions so that they can be formulated as differential algebraic equations (DAE). In utilizing this framework, faults are identified by performing a statistical analysis. Finally, comparisons with existing data-driven approaches show that the proposed model-based methods are capable of distinguishing a fault from the diverse array of possible faults, a common occurrence in complex processes. / text