A load sharing system reliability model with managed component degradation

Motivated by an industrial problem affecting a water utility, we develop a model for a load sharing system where an operator dispatches work load to components in a manner that manages their degradation. We assume degradation is the dominant failure type, and that the system will not be subject to sudden failure due to a shock. By deriving the time to degradation failure of the system, estimates of system probability of failure are generated, and optimal designs can be obtained to minimize the long run average cost of a future system. The model can be used to support asset maintenance and design decisions. Our model is developed under a common set of core assumptions. That is, the operator allocates work to balance the level of the degradation condition of all components to achieve system performance. A system is assumed to be replaced when the cumulative work load reaches some random threshold. We adopt cumulative work load as the measure of total usage because it represents the primary cause of component degradation. We model the cumulative work load of the system as a monotone increasing and stationary stochastic process. The cumulative work load to degradation failure of a component is assumed to be inverse Gaussian distributed. An example, informed by an industry problem, is presented to illustrate the application of the model under different operating scenarios

Reliability modeling and preventive maintenance of load-sharing systems with degrading components

This article presents certain new approaches to the reliability modeling of systems subject to shared loads. It is assumed that components in the system degrade continuously through an additive impact under load. The reliability assessment of such systems is often complicated by the fact that both the arriving load and the failure of components influence the degradation of the surviving components in a complex manner. The proposed approaches seek to ease this problem, by first deriving the time to prior failures and the arrival of random loads and then determining the number of failed components. Two separate models capable of analyzing system reliability as well as arriving at system maintenance and design decisions are proposed. The first considers a constant load and the other a cumulative load. A numerical example is presented to illustrate the effectiveness of the proposed models

A New Method for Reliability Calculation of the Active Systems with Time-Dependent Failure Rates based on Weibull Distribution

Due to the high sensitivity in applying of electronic and mechanical equipment, creating any conditions to increase the reliability of a system is always one of the important issues for system designers. Hence, making academic models much closer to the real word applications is very attractive. In the most studies in the reliability area, it is assumed that the failure rates of the system components are constant and have exponential distributions. This distribution and its attractive memory less property provide simple mathematical relationships in order to obtain the system reliability. But in real word problems, considering time-dependent failure rates is more realistic to model processes. It means that, the system components do not fail with a constant rate during the time horizon; but this failure rate changes over the time. One of the most useful statistical distributions in order to model the time-dependent failure rates is the Weibull distribution. This distribution is not a memory less one, so it was impossible to apply simple and explicit mathematical relationships as the same as exponential distributions for the reliability of a system. Therefore, researchers in this field have used simulation technique in these circumstances which is not an exact method to get near-optimum solutions. In this paper, for the first time, it is tried to obtain a mathematical equation to calculate the reliability function of a system with time-dependent components based on Weibull distribution. Also, in order to validate the proposed method, the results compared with exact solution that exists in literature

Envelhecimento e rejuvenescimento de software: 20 anos (19952014) - panorama e desafios

Although software aging and rejuvenation is a young research held, in its first 20 years a lot of knowledge has been produced. Nowadays, important scientific journals and conferences include SAR-related topics in their scope of interest. This fast growing and wide range of dissemination venues pose a challenge to researchers to keep tracking of the new findings and trends in this area. In this work, we collected and analyzed SAR research data to detect trends, patterns, and thematic gaps, in order to provide a comprehensive view of this research held over its hrst 20 years. Adopted the systematic mapping approach to answer research questions such as: How the main topics investigated in SAR have evolved over time? Which are the most investigated aging effects? Which rejuvenation techniques and strategies are more frequently used?CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorDissertação (Mestrado)Embora o envelhecimento e rejuvenescimento de software seja um campo de pesquisa novo, em seus primeiros 20 anos muito conhecimento foi produzido. Hoje em dia, revistas e conferências científicas importantes incluem temas relacionados a SAR no seu âmbito de interesse. Este crescimento rápido e a grande variedade de locais de disseminação representam um desafio para os pesquisadores para manter o acompanhamento das novas descobertas e tendências nesta área. Neste trabalho, foram coletados e analisados dados de pesquisa em SAR para detectar tendências, padrões e lacunas temáticas, a hm de proporcionar uma visão abrangente deste campo de pesquisa em seus primeiros 20 anos. Adotou-se a abordagem de mapeamento sistemático para responder a perguntas de pesquisa, tais como: Como os principais temas investigados em SAR têm evoluído ao longo do tempo? Quais são os efeitos do envelhecimento mais investigados? Quais técnicas e estratégias de rejuvenescimento são mais frequentemente usadas

Some extensions to reliability modeling and optimization of networked systems

Ph.DDOCTOR OF PHILOSOPH

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen