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This thesis focuses on the use of computer simulation for modeling risk of a multi-state repairable component. In production processes, maintenance decisions are often made based on uncertain assessment of risk, not only in the probability when a process component goes into a state of failure but also in the cost of lost production and preventive maintenance. In this thesis work, preventive maintenance of a component is modeled and simulated, in order to minimize risk (cost), as: a Markov process with multiple states and fixed transition probabilities, under the assumption that with a sufficient number of states the Markovian property is valid, a non Markov process with two possible states and non-fixed transition probabilities for a periodically decreasing reliability component, and a non Markov process with two possible states and non-fixed transition probabilities for a continuously decreasing reliability component. / Engineering Management

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Maintenance management is to design, operate, and maintain the reliability and availability of assets at a required performance level using the lowest possible cost. The standby redundancy is one of the means to achieve highly reliable system with less dependable units. As commonly used performance indicator, the reliability and availability should be precisely analysed for a repairable standby system. The reliability of a standby system is mainly studied in the framework of lifetime approach. Most existing models are developed for a two-unit standby system and a Kout- of-N system with identical units. The system units are assumed to be binary-state and the failures of system units are modelled as sudden failures. The deteriorations of units are modelled as time-dependent failure rate and are assumed to be independent. In addition, most of the existing models do not consider maintenance is carried out on the system. In reality, the deteriorations and the resultant failures in real-world systems are often interactive with each other. The systems normally experience several, often imperfect, restorations before a complete renewal. Therefore, the study of different repair policies, such as opportunistic and individual policies, in multi-unit systems need also be investigated. To address the problem, the reliability and availability models for a 2-out-of-3 cold standby system will be studied in a multi-state system reliability framework. A multistate multi-path failure mode is proposed to model the interactive deteriorations. The concept of repair matrix will be adopted to model the effect of unit level restorations on system reliability. The availabilities under individual repair policy and opportunistic repair policy will be developed.

Abstract not available: / Thesis (PhD (Systems Engineering))--University of Pretoria, 2007. / Industrial and Systems Engineering / unrestricted

The reliability of products has played a very important role for the competitiveness of enterprises. Foremost on the agricultural machinery area, where the reliability of the machinery will impact directly the production costs and profitability of farms. Agricultural tractors are complex machines with diverse systems and components interacting among themselves and establishing a dependency relationship among their performances. When these machines fail, are restored to recover their production capability. Many different techniques for reliability study have been developed based on components reliability studies, when testes under well defined conditions of bench tests to replicate well-known failure modes. Statistical distributions are used to represent the failures behavior of different kind of tests. Most of these studies, though, were developed for components that will be replaced when failed. Therefore they have to be analyzed under techniques that are suited for repairable systems. Many repairable systems have been analyzed with techniques that are only suited for non-repairable systems. This work proposes a comparison between the two techniques to analyze the differences and advantages of each one, and its applicability to the development of agricultural tractors / A confiabilidade dos produtos tem desempenhado um papel muito importante para a competitividade das empresas. Principalmente na área de máquinas agrícolas onde a confiabilidade do maquinário terá uma influência direta nos custos de produção e, conseqüentemente, na rentabilidade da mesma. Tratores agrícolas são máquinas complexas com diversos sistemas e componentes interagindo entre si e estabelecendo uma relação de dependência entre seus desempenhos. Quando estas máquinas falham, são restauradas para recuperar sua capacidade de produção. Muitas técnicas de estudo da confiabilidade têm sido desenvolvidas, baseadas em estudos de confiabilidade de componentes, quando submetidos a condições bem determinadas de solicitações, em testes de bancadas que reproduzem determinados modos de falha. Distribuições estatísticas são usadas para representar o comportamento de falhas de diversos tipos de ensaio. A maioria destes estudos, entretanto, foram desenvolvidos para componentes que irão ser substituídos quando falharem. Por isso devem ser analisados através de técnicas adequadas para sistemas reparáveis. Muitas análises de sistemas reparáveis têm sido feitas considerando técnicas desenvolvidas para sistemas não reparáveis. Este trabalho propõe uma comparação das duas técnicas para a análise das diferenças e vantagens de cada uma das técnicas e sua adequação ao desenvolvimento de tratores agrícolas. No final conseguimos concluir e comprovar a importância do conhecimento do embasamento matemático das diferentes técnicas para evitar análises de confiabilidade enganosas. A fácil disponibilidade e utilização de sofwares, permitem que engenheiros sem o devido embasamento teórico apresentado neste trabalho façam análises que levem a conclusões errôneas sobre a tendência da confiabilidade dos equipamentos analisados

It is an undisputable fact that most systems, upon consistence usage are bound to fail in the performance of their intended functions at a point in time. When this occurs, various strategies are set in place to restore them back to a satisfactory performance. This may include replacing the failed component with a new one, swapping parts, resetting adjustable parts to mention but a few. Any such system is referred to as a repairable system. There is the need to study these systems and use statistical models to predict their failing time and be able to set modalities in place to repair them at least cost to the operator. The main objective of this paper is to analyze data collected on the projectors used for teaching and learning activities in some designated rooms at the Brigham Young University (BYU) under the auspices of the Office of Information Technology (OIT) and help to detect the failure rate of such systems, predict the optimal replacement time for the parts with the view of maximizing the reliability of the systems and finally formulate a cost model that will be used to estimate the optimal cost involve in servicing a failed projector.

There are many methods for modelling the reliability of systems based on component failure data. This task becomes more complex as systems increase in size, or undertake missions that comprise multiple discrete modes of operation, or phases. Existing techniques require certain levels of expertise in the model generation and calculation processes, meaning that risk and reliability assessments of systems can often be expensive and time-consuming. This is exacerbated as system complexity increases. This thesis presents a novel method which generates reliability models for phasedmission systems, based on Petri nets, from simple input files. The process has been automated with a piece of software designed for engineers with little or no experience in the field of risk and reliability. The software can generate models for both repairable and non-repairable systems, allowing redundant components and maintenance cycles to be included in the model. Further, the software includes a simulator for the generated models. This allows a user with simple input files to perform automatic model generation and simulation with a single piece of software, yielding detailed failure data on components, phases, missions and the overall system. A system can also be simulated across multiple consecutive missions. To assess performance, the software is compared with an analytical approach and found to match within 5% in both the repairable and non-repairable cases. The software documented in this thesis could serve as an aid to engineers designing new systems to validate the reliability of the system. This would not require specialist consultants or additional software, ensuring that the analysis provides results in a timely and cost-effective manner.

Indiana University-Purdue University Indianapolis (IUPUI) / Recent years have seen a growth in research on system reliability and maintenance. Various studies in the scientific fields of reliability engineering, quality and productivity analyses, risk assessment, software reliability, and probabilistic machine learning are being undertaken in the present era. The dependency of human life on technology has made it more important to maintain such systems and maximize their potential. In this dissertation, some methodologies are presented that maximize certain measures of system reliability, explain the underlying stochastic behavior of certain systems, and prevent the risk of system failure. An overview of the dissertation is provided in Chapter 1, where we briefly discuss some useful definitions and concepts in probability theory and stochastic processes and present some mathematical results required in later chapters. Thereafter, we present the motivation and outline of each subsequent chapter. In Chapter 2, we compute the limiting average availability of a one-unit repairable system subject to repair facilities and spare units. Formulas for finding the limiting average availability of a repairable system exist only for some special cases: (1) either the lifetime or the repair-time is exponential; or (2) there is one spare unit and one repair facility. In contrast, we consider a more general setting involving several spare units and several repair facilities; and we allow arbitrary life- and repair-time distributions. Under periodic monitoring, which essentially discretizes the time variable, we compute the limiting average availability. The discretization approach closely approximates the existing results in the special cases; and demonstrates as anticipated that the limiting average availability increases with additional spare unit and/or repair facility. In Chapter 3, the system experiences two types of sporadic impact: valid shocks that cause damage instantaneously and positive interventions that induce partial healing. Whereas each shock inflicts a fixed magnitude of damage, the accumulated effect of k positive interventions nullifies the damaging effect of one shock. The system is said to be in Stage 1, when it can possibly heal, until the net count of impacts (valid shocks registered minus valid shocks nullified) reaches a threshold $m_1$. The system then enters Stage 2, where no further healing is possible. The system fails when the net count of valid shocks reaches another threshold $m_2 (> m_1)$. The inter-arrival times between successive valid shocks and those between successive positive interventions are independent and follow arbitrary distributions. Thus, we remove the restrictive assumption of an exponential distribution, often found in the literature. We find the distributions of the sojourn time in Stage 1 and the failure time of the system. Finally, we find the optimal values of the choice variables that minimize the expected maintenance cost per unit time for three different maintenance policies. In Chapter 4, the above defined Stage 1 is further subdivided into two parts: In the early part, called Stage 1A, healing happens faster than in the later stage, called Stage 1B. The system stays in Stage 1A until the net count of impacts reaches a predetermined threshold $m_A$; then the system enters Stage 1B and stays there until the net count reaches another predetermined threshold $m_1 (>m_A)$. Subsequently, the system enters Stage 2 where it can no longer heal. The system fails when the net count of valid shocks reaches another predetermined higher threshold $m_2 (> m_1)$. All other assumptions are the same as those in Chapter 3. We calculate the percentage improvement in the lifetime of the system due to the subdivision of Stage 1. Finally, we make optimal choices to minimize the expected maintenance cost per unit time for two maintenance policies. Next, we eliminate the restrictive assumption that all valid shocks and all positive interventions have equal magnitude, and the boundary threshold is a preset constant value. In Chapter 5, we study a system that experiences damaging external shocks of random magnitude at stochastic intervals, continuous degradation, and self-healing. The system fails if cumulative damage exceeds a time-dependent threshold. We develop a preventive maintenance policy to replace the system such that its lifetime is utilized prudently. Further, we consider three variations on the healing pattern: (1) shocks heal for a fixed finite duration $\tau$; (2) a fixed proportion of shocks are non-healable (that is, $\tau=0$); (3) there are two types of shocks---self healable shocks heal for a finite duration, and non-healable shocks. We implement a proposed preventive maintenance policy and compare the optimal replacement times in these new cases with those in the original case, where all shocks heal indefinitely. Finally, in Chapter 6, we present a summary of the dissertation with conclusions and future research potential.

In Tort Law, it is said that an individual mustrepair the damage he causes.  What is the extention of this maxim? Is this affirmation accurate? What is considered damage for Law?Jean-Sebastién Borghetti answers this and other questions as understood by French Law, seeking to delimit the French system of civil liability. In that sense, through this  article, the author proposes that not all affronts constitute a damage as understood by Law, and that not every damage can be repaired. / En la Responsabilidad Civil, se afirma que todoaquel que causa un perjuicio debe repararlo. ¿Cuál es el alcance de esta máxima? ¿Qué tan exacta es esta afirmación? ¿Qué es un perjuicio para el Derecho?Jean-Sebastién Borghetti responde estas y otras preguntas desde el Derecho francés, buscando delimitar el sistema francés de la responsabilidad civil. En ese sentido, a través del presente artículo, el autor propone que no todo agravio constituye un perjuicio para elDerecho, y que no todo perjuicio es reparable.