Component Maintenance Strategies and Risk Analysis for Random Shock Effects Considering Maintenance Costs

Maintenance can improve a system’s reliability in a long operation period or when a component has failed. The reliability modeling method that uses the stochastic process degradation model to describe the system degradation process has been widely used. However, the existing reliability models established using stochastic processes only consider the internal degradation process, and do not fully consider the impact of external random shocks on their reliability modeling. Furthermore, the existing theory of importance does not consider the actual factors of maintenance cost. In this paper, based on the reliability modeling of random processes, the degradation rate under the influence of random shocks is introduced into the time scale function to solve the impact of random shocks on product reliability, and two cost importance measures are proposed to guide the maintenance selection of the components under limited resources in the system.Finally, a subsystem of an aircraft hydraulic system is analyzed to verify the proposed method’s performance

Rotating biological contactors for wastewater treatment - A review

Rotating biological contactors (RBCs) for wastewater treatment began in the 1970s. Removal of organic matter has been targeted within organic loading rates of up to 120 g m−2 d−1 with an optimum at around 15 g m−2 d−1 for combined BOD and ammonia removal. Full nitrification is achievable under appropriate process conditions with oxidation rates of up to 6 g m−2 d−1 reported for municipal wastewater. The RBC process has been adapted for denitrification with reported removal rates of up to 14 g m−2 d−1 with nitrogen rich wastewaters. Different media types can be used to improve organic/nitrogen loading rates through selecting for different bacterial groups. The RBC has been applied with only limited success for enhanced biological phosphorus removal and attained up to 70% total phosphorus removal. Compared to other biofilm processes, RBCs had 35% lower energy costs than trickling filters but higher demand than wetland systems. However, the land footprint for the same treatment is lower than these alternatives. The RBC process has been used for removal of priority pollutants such as pharmaceuticals and personal care products. The RBC system has been shown to eliminate 99% of faecal coliforms and the majority of other wastewater pathogens. Novel RBC reactors include systems for energy generation such as algae, methane production and microbial fuel cells for direct current generation. Issues such as scale up remain challenging for the future application of RBC technology and topics such as phosphorus removal and denitrification still require further research. High volumetric removal rate, solids retention, low footprint, hydraulic residence times are characteristics of RBCs. The RBC is therefore an ideal candidate for hybrid processes for upgrading works maximising efficiency of existing infrastructure and minimising energy consumption for nutrient removal. This review will provide a link between disciplines and discuss recent developments in RBC research and comparison of recent process designs are provided (Section 2). The microbial features of the RBC biofilm are highlighted (Section 3) and topics such as biological nitrogen removal and priority pollutant remediation are discussed (Sections 4 and 5). Developments in kinetics and modelling are highlighted (Section 6) and future research themes are mentioned

Importance Measure-Based Maintenance Strategy Considering Maintenance Costs

Maintenance is an important way to ensure the best performance of repairable systems. This paper considers how to reduce system maintenance cost while ensuring consistent system performance. Due to budget constraints, preventive maintenance (PM) can be done on only some of the system components. Also, different selections of components to be maintained can have markedly different effects on system performance. On the basis of the above issues, this paper proposes an importance-based maintenance priority (IBMP) model to guide the selection of PM components. Then the model is extended to find the degree of correlation between two components to be maintained and a joint importance-based maintenance priority (JIBMP) model to guide the selection of opportunistic maintenance (OM) components is proposed. Also, optimization strategies under various conditions are proposed. Finally, a case of 2H2E architecture is used to demonstrate the proposed method. The results show that generators in the 2E layout have the highest maintenance priority, which further explains the difference in the importance of each component in PM

Beam-Material Interaction

Th is paper is motivated by the growing importance of better understanding of the phenomena and consequences of high- intensity energetic particle beam interactions with accelerator, generic target , and detector components. It reviews the principal physical processes of fast-particle interactions with matter, effects in materials under irradiation, materials response, related to component lifetime and performance, simulation techniques, and methods of mitigating the impact of radiation on the components and envir onment in challenging current and future applicationComment: 28 pages, contribution to the 2014 Joint International Accelerator School: Beam Loss and Accelerator Protection, Newport Beach, CA, USA , 5-14 Nov 201

Reliability Analysis of Electrotechnical Devices

This is a book on the practical approaches of reliability to electrotechnical devices and systems. It includes the electromagnetic effect, radiation effect, environmental effect, and the impact of the manufacturing process on electronic materials, devices, and boards

A performance-based warranty for products subject to competing hard and soft failures

This article studies a performance-based warranty for products subject to competing hard and soft failures. The two failure modes are competing in the sense that either one, on a "whichever-comes-first" basis, can cause the product to fail. A performance-based warranty not only covers the repair or replacement of any defect, but also guarantees the minimum performance level throughout the warranty period. In this article, we propose three compensation policies—that is, free replacement, penalty, and full refund, when a product's performance fails to meet the guaranteed level. The expected warranty servicing costs for the three policies are derived, based on the competing risks concept. A warranty design problem is further formulated to simultaneously determine the optimal product price, warranty length, and performance guarantee level so as to maximize the manufacturer's total profit. Numerical studies are conducted to demonstrate and compare the three performance-based compensation policies. It is shown that the full refund policy always leads to the lowest total profit, whereas neither of the other two policies can dominate each other in all scenarios. In particular, the free replacement policy results in a higher total profit than the penalty policy when the replacement cost is low, the penalty cost coefficient is high, and/or the product reliability is high

Extreme climate shock and locust infestation impacts in Ethiopia : farm-level agent-based simulation of adaptation and policy options

Extreme climate shocks have been a daunting problem for smallholder farmers in Ethiopia for a decade. In recent years, locust invasions in many parts of the country have become another livelihood challenge to the subsistence farming population who already lives in dire livelihood situations. These two compounding shocks can lead to total crop failure at the early crop development stage or any crop growth stage. They are creating a massive economic upheaval in rainfed-dependent countries particularly affecting the well-being of resource-poor subsistence farmers. To reduce the effect of recurring shocks, especially climate risks, farmers have been implementing different risk management strategies. In addition to farmer autonomous adaptation practices, the government has been supporting farmer climate adaptation efforts by designing different policy interventions. In locust-hit areas, government and non-governmental organizations have designed and implemented different locust relief programs aimed at reducing associated welfare losses. Whether farmers can adapt to the effects of climate shocks or not by autonomous adaptation and/or with policy support is an empirical policy question. Moreover, as there are no studies of locust impacts and locust relief programs evaluation, the degree of locust livelihood devastation and the roles of locust relief policy interventions in minimizing the effect of locust shock are policy concerns. To address these important and key empirical questions, this thesis applied a farm-level agent-based simulation model. MPMAS, a modeling framework developed at the University of Hohenheim for agent-based simulations, was applied to capture inseparable production and consumption decisions of subsistence farming households in the Central Rift Valley of Ethiopia. The modeling framework uses a whole-farm mathematical programming modeling approach to represent complex dynamics of farm household decisions where a set of constraints and their complex relationships are considered. This simulation model enables scenario-based policy analysis by comparing different climate, locust, and policy scenarios which is hardly possible using statistical and other reduced forms of econometrics models. Through establishing scenarios, the model helps to disentangle the pathways through which external shocks may affect the well-being of smallholder farmers. MPMAS has been extensively applied for policy simulations in different countries including Ethiopia. This thesis extends previous MPMAS applications in Ethiopia by including new features for Central Rift Valley (MPMAS_CRV). MPMAS_CRV was parameterized from the CIMMYT household survey augmented with CSA datasets and own field research. Smallholder farmers ex-ante considerations of risk management strategies for possible climate shock are explicitly captured in MPMAS_CRV to assess their role in climate adaptation and welfare improvements. As part of enhancing the adaptive capacity of farm households to recurring climate shocks, the effect of policy interventions such as better access to credit services and improved agricultural technology are quantified by establishing climate and policy scenarios. Similarly, the thesis quantified the impact of locust invasions on household welfare outcomes and their response to locust relief interventions including food or cash transfers complemented with inputs and livestock provisions. Locust simulation is one of the novelties of this research as it is the first study to explicitly capture the welfare effects of the desert locust and assess the roles of locust relief programs through the application of MPMAS. To enable climate and locust shock effects quantification and associated policy interventions, different simulation experiments were designed comprised of climate and locust shock frequencies and policy scenarios. The simulation experiments and analysis were performed using the computational resources of bwForCluster within the bwHPC infrastructure in the state of Baden-Württemberg, Germany. Before using MPMAS_CRV for policy simulations, its reliability was validated using land use, livestock holding, and amount of crop sales by comparing simulated against observed survey values. The validation results suggest that MPMAS_CRV can represent and reflect real-world conditions so that it is reliable to use for impact quantification and policy simulations. In addition to empirical validation, the thesis conducted a global uncertainty analysis to check the robustness of the simulation results under different parameter variations and combinations to minimize erroneous policy formulations. Uncertainty analysis results show that the model converges rapidly at 50 repetitions which implies that these model repetitions are enough to cover the model uncertainty space. In terms of extreme climate impacts and adaptations, the simulation results suggest that climate shocks affect the welfare of agents adversely to the extent that they face temporary food shortages, loss of discretionary income, and depletion of livestock assets. The welfare losses are similar for both with and without ex-ante measure scenarios which indicates that farm agents cannot adapt to extreme shocks by employing autonomous adaptations. After the shocks are over, the simulation results reveal that agents cannot recover income and livestock losses immediately even when they consider ex-ante measures in the planning for possible risks. This suggests that for resource-poor farm agents, income and assets recovery takes a longer period after perturbation which can lead to a long-term livelihood crisis and a poverty trap. But, according to the simulation results in this thesis, agents can recover from food shortage immediately after the shocks are over, as meeting minimum food requirements are an absolute priority for agents (which is also true with real-world subsistence smallholder farmers) over other competing goals. Credit and technology policy simulation analysis further depict that welfare losses are partly compensated compared to without policies. Welfare losses of agents are better compensated when credit and technology are used jointly than when they are implemented separately. Similarly, technology policy intervention is better in compensating welfare losses compared to credit policy. Though policy interventions have compensational effects in minimizing the losses, they cannot completely offset the negative effects of extreme climate shocks even when implemented jointly. Disaggregation of simulation results by resource endowments suggests that agents with higher baseline income (without policy) and farm size appeared to be relatively less affected by shocks, and benefit from policy interventions the most. Locust simulation results also suggest that locust shock leads to agent livelihood crisis and makes slower recovery of income and livestock assets rebuild without any relief intervention programs. Simulation of different locust relief policy interventions reveals that combined relief policy interventions appear to be superior in compensating welfare losses compared to individual relief interventions. When food or cash transfer is combined with inputs and assets the welfare losses are considerably reduced compared to the individual policy intervention. When asset recuperation is combined with other relief programs, livestock losses are substantially reduced which signifies the importance of asset support in building an asset base which has long-term benefits. Strengthening early warning systems by including seasonal weather forecasting has paramount importance to prevent the crisis of desert locust plague.Extreme Klimaschocks sind für Kleinbauern in Äthiopien seit einem Jahrzehnt ein beängstigendes Problem. In den letzten Jahren sind Heuschreckeninvasionen in vielen Teilen des Landes zu einer weiteren Herausforderung für die Existenzgrundlage der ohnehin schon unter schwierigen Bedingungen lebenden Subsistenzbauern geworden. Diese beiden sich gegenseitig verstärkenden Schocks können zu totalen Ernteausfällen in der frühen Entwicklungsphase der Ernte oder in jeder Wachstumsphase führen. Sie führen zu massiven wirtschaftlichen Umwälzungen in Ländern, die vom Regen abhängig sind, und beeinträchtigen insbesondere das Wohlergehen der ressourcenarmen Subsistenzbauern. Um die Auswirkungen wiederkehrender Schocks, insbesondere von Klimarisiken, zu verringern, haben die Landwirte verschiedene Risikomanagementstrategien eingeführt. Zusätzlich zu den autonomen Anpassungspraktiken der Landwirte hat die Regierung die Bemühungen der Landwirte zur Klimaanpassung durch verschiedene politische Maßnahmen unterstützt. In Gebieten, die von Heuschrecken heimgesucht wurden, haben Regierung und Nichtregierungsorganisationen verschiedene Programme zur Bekämpfung der Heuschrecken entwickelt und umgesetzt, um die damit verbundenen Wohlfahrtsverluste zu verringern. Ob sich Landwirte durch autonome Anpassung und/oder mit politischer Unterstützung an die Auswirkungen von Klimaschocks anpassen können oder nicht, ist eine empirische politische Frage. Da es keine Studien über die Auswirkungen von Heuschrecken und die Bewertung von Heuschreckenhilfsprogrammen gibt, sind das Ausmaß der Zerstörung der Lebensgrundlagen durch Heuschrecken und die Rolle der Heuschreckenhilfsmaßnahmen bei der Minimierung der Auswirkungen des Heuschreckenschocks von politischem Interesse. Um diese wichtigen und zentralen empirischen Fragen zu beantworten, wurde in dieser Arbeit ein agentenbasiertes Simulationsmodell auf Betriebsebene eingesetzt. MPMAS, ein an der Universität Hohenheim entwickelter Modellierungsrahmen für agentenbasierte Simulationen, wurde angewandt, um die untrennbaren Produktions- und Verbrauchsentscheidungen von Subsistenzbauernhaushalten im zentralen Rift Valley in Äthiopien zu erfassen. Der Modellierungsrahmen verwendet einen mathematischen Programmierungsansatz für den gesamten Betrieb, um die komplexe Dynamik der Entscheidungen der bäuerlichen Haushalte darzustellen, wobei eine Reihe von Beschränkungen und deren komplexe Beziehungen berücksichtigt werden. Dieses Simulationsmodell ermöglicht eine szenariobasierte Politikanalyse durch den Vergleich verschiedener Klima-, Heuschrecken- und Politikszenarien, was mit statistischen und anderen reduzierten Formen ökonometrischer Modelle kaum möglich ist. Durch die Erstellung von Szenarien hilft das Modell, die Wege zu entschlüsseln, über die sich externe Schocks auf das Wohlergehen von Kleinbauern auswirken können. MPMAS wurde in verschiedenen Ländern, darunter auch in Äthiopien, ausgiebig für Politiksimulationen eingesetzt. Diese Arbeit erweitert frühere MPMAS-Anwendungen in Äthiopien durch neue Funktionen für das zentrale Rift Valley (MPMAS_CRV). MPMAS_CRV wurde anhand der CIMMYT-Haushaltsbefragung parametrisiert und mit CSA-Datensätzen und eigener Feldforschung ergänzt. Ex-ante-Überlegungen von Kleinbauern zu Risikomanagementstrategien für mögliche Klimaschocks werden in MPMAS_CRV explizit erfasst, um ihre Rolle bei der Klimaanpassung und der Verbesserung des Wohlstands zu bewerten. Um die Anpassungsfähigkeit der landwirtschaftlichen Haushalte an wiederkehrende Klimaschocks zu verbessern, werden die Auswirkungen politischer Maßnahmen, wie z. B. ein besserer Zugang zu Krediten und verbesserter landwirtschaftlicher Technologie, durch die Erstellung von Klima- und Politikszenarien quantifiziert. In ähnlicher Weise wurden in dieser Arbeit die Auswirkungen von Heuschreckeninvasionen auf das Wohlergehen der Haushalte und ihre Reaktion auf Heuschreckenhilfsmaßnahmen wie Nahrungsmittel- oder Geldtransfers, ergänzt durch Betriebsmittel und Viehhaltung, quantifiziert. Die Heuschrecken-Simulation ist eine der Neuerungen dieser Studie, da sie die erste ist, die explizit die Auswirkungen der Wüstenheuschrecken auf das Wohlergehen der Haushalte erfasst und die Rolle von Heuschrecken-Hilfsprogrammen durch die Anwendung von MPMAS bewertet. Um die Auswirkungen von Klima- und Heuschreckenschocks zu quantifizieren und damit verbundene politische Interventionen zu ermöglichen, wurden verschiedene Simulationsexperimente entworfen, die Klima- und Heuschreckenschockhäufigkeiten und politische Szenarien umfassen. Die Simulationsexperimente und Analysen wurden mit den Rechenressourcen des bwForCluster innerhalb der bwHPC-Infrastruktur des Landes Baden-Württemberg durchgeführt. Vor der Verwendung von MPMAS_CRV für Politiksimulationen wurde seine Zuverlässigkeit anhand der Landnutzung, des Viehbestands und des Umfangs der Ernteverkäufe durch Vergleich der simulierten mit den beobachteten Erhebungswerten validiert. Die Validierungsergebnisse deuten darauf hin, dass MPMAS_CRV reale Bedingungen darstellen und widerspiegeln kann, so dass es zuverlässig für die Quantifizierung von Auswirkungen und für Politiksimulationen verwendet werden kann. Zusätzlich zur empirischen Validierung wurde in dieser Arbeit eine globale Unsicherheitsanalyse durchgeführt, um die Robustheit der Simulationsergebnisse unter verschiedenen Parametervariationen und -kombinationen zu überprüfen und fehlerhafte Politikformulierungen zu minimieren. Die Ergebnisse der Unsicherheitsanalyse zeigen, dass das Modell bei 50 Wiederholungen schnell konvergiert, was bedeutet, dass diese Modellwiederholungen ausreichen, um den Raum der Modellunsicherheit abzudecken. In Bezug auf extreme Klimaauswirkungen und Anpassungen deuten die Simulationsergebnisse darauf hin, dass Klimaschocks das Wohlergehen der Landwirte insofern beeinträchtigen, als sie mit vorübergehender Nahrungsmittelknappheit, dem Verlust von verfügbarem Einkommen und der Erschöpfung des Viehbestands konfrontiert sind. Die Wohlfahrtsverluste sind sowohl für Szenarien mit als auch ohne Ex-ante-Maßnahmen ähnlich, was darauf hindeutet, dass sich die landwirtschaftlichen Akteure nicht durch autonome Anpassungen an extreme Schocks anpassen können. Nach den Schocks zeigen die Simulationsergebnisse, dass die Landwirte die Einkommens- und Viehbestandsverluste nicht sofort ausgleichen können, selbst wenn sie bei der Planung möglicher Risiken Ex-ante-Maßnahmen berücksichtigen. Dies deutet darauf hin, dass es bei ressourcenarmen Landwirten länger dauert, bis sich Einkommen und Vermögen nach einer Störung erholen, was zu einer langfristigen Existenzkrise und einer Armutsfalle führen kann. Den Simulationsergebnissen in dieser Arbeit zufolge können sich die Agenten jedoch unmittelbar nach dem Ende der Schocks von der Nahrungsmittelknappheit erholen, da die Deckung des Mindestbedarfs an Nahrungsmitteln für die Agenten absolute Priorität vor anderen konkurrierenden Zielen hat (was auch für Subsistenz-Kleinbauern in der realen Welt gilt). Die Simulationsanalyse der Kredit- und Technologiepolitik zeigt außerdem, dass Wohlfahrtsverluste im Vergleich zu einer Politik ohne sie teilweise kompensiert werden. Die Wohlfahrtsverluste der Akteure werden besser ausgeglichen, wenn Kredit und Technologie gemeinsam eingesetzt werden, als wenn sie getrennt eingesetzt werden. In ähnlicher Weise kompensiert die Technologiepolitik Wohlfahrtsverluste besser als die Kreditpolitik. Obwohl politische Interventionen kompensatorische Effekte haben, indem sie die Verluste minimieren, können sie die negativen Auswirkungen extremer Klimaschocks nicht vollständig ausgleichen, selbst wenn sie gemeinsam eingesetzt werden. Eine Disaggregation der Simulationsergebnisse nach Ressourcenausstattung legt nahe, dass Agenten mit einem höheren Grundeinkommen (ohne Politik) und einer höheren Betriebsgröße relativ weniger von Schocks betroffen zu sein scheinen und am meisten von politischen Maßnahmen profitieren. Die Ergebnisse der Heuschrecken-Simulationen deuten auch darauf hin, dass der Heuschreckenschock zu einer Existenzkrise führt und eine langsamere Erholung des Einkommens und des Viehbestands ohne jegliche Hilfsprogramme bewirkt. Die Simulation verschiedener Heuschreckenhilfsmaßnahmen zeigt, dass kombinierte Hilfsmaßnahmen im Vergleich zu einzelnen Hilfsmaßnahmen die Wohlfahrtsverluste besser auszugleichen scheinen. Wenn Nahrungsmittel- oder Geldtransfers mit Betriebsmitteln und Vermögenswerten kombiniert werden, sind die Wohlfahrtsverluste im Vergleich zu den einzelnen Maßnahmen erheblich geringer. Wenn die Rückgewinnung von Vermögenswerten mit anderen Hilfsprogrammen kombiniert wird, werden die Verluste beim Viehbestand erheblich reduziert, was auf die Bedeutung der Unterstützung von Vermögenswerten für den Aufbau einer Vermögensbasis hinweist, die langfristig von Nutzen ist. Die Stärkung der Frühwarnsysteme durch Einbeziehung saisonaler Wettervorhersagen ist von größter Bedeutung, um die Krise der Wüstenheuschreckenplage zu verhindern

Recent Advancements in Modeling and Simulation of Entry Systems at NASA

This paper describes recent development of modeling and simulation technologies for entry systems in support of NASA's exploration missions. Mission-tailored research and development in modeling of entry systems occurs across the Agency (e.g., within the Orion and Mars 2020 Programs), however the aim of this paper is to discuss the broad, cross-mission research conducted by NASA's Entry Systems Modeling (ESM) Project, which serves as the Agency's only concerted effort toward advancing entry systems across a range of technical disciplines. Technology development in ESM is organized and prioritized from a system-level perspective, resulting in four broad technical areas of investment: (1) Predictive material modeling, (2) Shock layer kinetics and radiation, (3) Computational and experimental aerosciences, and (4) Guidance, navigation, and control. Investments in thermal protection material modeling are geared toward high-fidelity, predictive models capable of handling complex structures, with an eye toward optimizing design performance and quantifying thermal protection system reliability. New computational tools have been developed to characterize material properties and behavior at the microstructural level, and experimental techniques (molecular beam scattering, micro-computed tomography, among others) have been developed to measure material kinetics, morphology, and other parameters needed to inform and validate detailed simulations. Advancements have also been made in macrostructural simulation capability to enable 3-D system-scale calculations of material response with complex topological features, including differential recession of tile gaps. Research and development in the area of shock layer kinetics has focused on air and CO2-based atmospheres. Capacity and capability of the NASA Ames Electric Arc Shock Tube (EAST) have been expanded in recent years and analysis of resulting data has led to several improvements in kinetic models, while simultaneously reducing uncertainties associated with radiative heat transfer predictions. First-principles calculations of fundamental kinetic, thermodynamic, and transport data, along with state-specific models for non-equilibrium flow regimes, have also yielded new insights and have the potential to vastly improve model fidelity. Aerosciences is a very broad area of interest in entry systems, yet a number of important challenges are being addressed: Coupled fluid-structure simulations of parachute inflation and dynamics; Experimental and computational studies of vehicle dynamics; Multi-phase flow with dust particles to simulate entry environments at Mars during dust storms; Studies of roughness-induced heating augmentation relevant to tiled and woven thermal protection systems; and Advanced numerical methods to optimize computational analyses for desired accuracy versus cost. Guidance and control in the context of entry systems has focused on development of methods for multi-axis control (i.e. pitch and yaw, rather than bank angle alone) of spacecraft during entry and descent. With precision landing requirements driven by Mars human exploration goals, recent efforts have yielded 6-DOF models of multi-axis control with propulsive descent of both inflatable and rigid ellipsled-like architectures

ICASE

This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in the areas of (1) applied and numerical mathematics, including numerical analysis and algorithm development; (2) theoretical and computational research in fluid mechanics in selected areas of interest, including acoustics and combustion; (3) experimental research in transition and turbulence and aerodynamics involving Langley facilities and scientists; and (4) computer science