Synthèse de revêtements de nickel à haute porosité par projection de suspension par plasma HF et contribution à la compréhension des phénomènes impliqués

Depuis leurs premières applications par la NASA dans les années 60, les procédés aux plasmas thermiques se sont de plus en plus orientés vers la fabrication de matériaux spécialisés et à haute valeur ajoutée, comme les nano-poudres, les produits sphéroïdisés et les céramiques. La projection de suspension par plasma est l'une des techniques les plus récentes dans ce domaine et elle permet de traiter thermiquement une grande variété de réactifs et de réaliser des revêtements dont les propriétés physico-chimiques dépendent des produits de départ, des phénomènes en vol (lors du traitement thermique) ainsi que des phénomènes liés à la formation du revêtement projeté. Ce travail s'intéresse à la projection de suspensions de nickel dans un réacteur de projection par plasma inductif afin de vérifier et d'estimer la relation qui existe entre des paramètres opératoires choisis et une propriété physique des produits finis: la porosité. Cette étude consiste à réaliser des dépôts de nickel sur un substrat choisi et à observer la morphologie du revêtement métallique obtenu. La revue bibliographique des travaux réalisés dans les mêmes laboratoires a permis de mettre en exergue les principaux paramètres affectant la qualité du revêtement. Des tests préliminaires séparés ont été réalisés pour choisir la composition de la suspension et les paramètres d'atomisation optimaux avant de les intégrer au procédé de revêtement en question. Les échantillons fabriqués sont analysés par traitement d'images obtenues par microscopie à balayage d'électrons ainsi que par une méthode d'immersion. Une approche combinatoire permettra d'évaluer l'effet de la combinaison de certains réactifs et de post-traitements sur la porosité des revêtements de nickel obtenus. Les résultats obtenus montrent que les paramètres tels que la puissance utilisée et la méthode de refroidissement affectent les propriétés du revêtement et les porosités obtenues pour les conditions opératoires choisies varient entre 10% et 50%

Steroid Use in Idiopathic Sudden Sensorineural Hearing Loss: What is the Evidence?

Idiopathic sudden sensorineural hearing loss is a disease of unknown etiology. Controversy in the literature argues whether the condition should be treated by steroid therapy. In this case study, a Medline literature search was completed to find out if there is any evidence to support its use in this condition

De-risking Libyan giant oilfields for subsurface net zero transition

Fossil fuel production and consumption are central to global CO2 emissions and the geological storage of CO2 is among the promising solutions to achieve the global Net Zero targets. As the largest crude oil holder in Africa, Libya is one of the main hydrocarbon suppliers in the North Africa region. However, the fossil fuel dependency for economic and energy needs put the country in real challenge in keeping up the global trends toward low-carbon transition. This research aims to explore options for Libya to transition its subsurface resources for net zero applications, with particular focus on CO2 storage potential. The objectives are to (a) examine geological suitability of the giant oilfields for CO2 storage and estimate CO2 storage capacity. (b) conduct fault stability analysis to ensure CO2 storage security

Modeling rare events under uncertainties

The development of the oil and gas industry is accompanied by high risks that increase the potential for major accidents. Improving safety through implementing safety measures maintains the risk within an acceptable level and helps to prevent the occurrence of accidents. Identifying and treating uncertainty is the main challenge in performing risk analysis. This uncertainty reflects the lack of information about the accident scenario and its potential causes, as well as the absence of a modeling technique used to model accident scenarios. In most situations, there are either few or no data available to perform risk analysis. Gathering the required data from other relevant sources is one of the solutions to overcome this challenge. In the presented work, the first part of the developed methodology considers Hierarchical Bayesian Analysis (HBA) as a robust technique for an event’s frequency estimation using data collected from several sources. Results demonstrate the power of HBA in treating the uncertainty within the gathered data and providing the appropriate estimation of an event’s frequency. The estimated event’s frequency is then integrated into Bowtie (BT) analysis, one of the modeling techniques, in order to predict the occurrence of a major accident. Due to their limitations, the standard modeling techniques are unable to capture the variation of risks as changes take place in the system. Therefore, their results involve a degree of uncertainty, considered as model uncertainty. In the second part of the presented study, the developed methodology has been improved by integrating HBA and Bayesian Network (BN) into one framework to cope with data and model uncertainties simultaneously. HBA handles the uncertainty within the multi-source data, while BN is used to model the accident scenario in order to treat model uncertainty. Using HBA along with BN provides more accurate estimations and better handling of uncertainties

Fuel consumption prediction methodology for early stages of naval ship design

Thesis (S.M. in Mechanical Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M. in Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 72).In recent years, fuel consumption has increased in importance as a design parameter in Navy ships. Economical fuel consumption is important not only for operating cost measures but also for ship endurance tankage requirements. Minimizing fuel consumption has many benefits for both naval and commercial ships. This thesis work will suggest a new comprehensive approach to early-stage ship design to determine fuel consumption for the whole system. A hull must be designed to work harmoniously with an optimized propulsor and propulsion plant to ensure best performance and to comply with imposed design requirements. Thus, this work will address three main aspects of the fuel consumption equation: -- Ship's resistance is calculated using a computational fluid dynamics simulation of the vessel in calm water at various speeds up to maximum speed. -- Propeller performance is based on propeller curves for the chosen propulsor. -- Efficiencies of the drive train and electrical production and distribution system are calculated for all operating conditions. Note that for an electric-drive ship, the non-propulsion electrical loads must be included in the calculations. These three major components of the ship efficiency equation are assessed for each speed and battle condition of the mission profile. In addition, the corresponding operating conditions for each piece of machinery will be specified to estimate the total fuel consumption and tankage required. In this thesis work, I will suggest a design methodology to determine hull resistance and total power for a given ship with a specified operational profile. The total power for the operational profile will be translated to fuel consumption, thus producing annual fuel consumption requirements and recommended tankage to support the operational needs.by Eran Gheriani.S.M.in Naval Architecture and Marine EngineeringS.M.in Mechanical Engineerin

Uncertainty handling in fault tree based risk assessment: State of the art and future perspectives

YesRisk assessment methods have been widely used in various industries, and they play a significant role in improving the safety performance of systems. However, the outcomes of risk assessment approaches are subject to uncertainty and ambiguity due to the complexity and variability of system behaviour, scarcity of quantitative data about different system parameters, and human involvement in the analysis, operation, and decision-making processes. The implications for improving system safety are slowly being recognised; however, research on uncertainty handling during both qualitative and quantitative risk assessment procedures is a growing field. This paper presents a review of the state of the art in this field, focusing on uncertainty handling in fault tree analysis (FTA) based risk assessment. Theoretical contributions, aleatory uncertainty, epistemic uncertainty, and integration of both epistemic and aleatory uncertainty handling in the scientific and technical literature are carefully reviewed. The emphasis is on highlighting how assessors can handle uncertainty based on the available evidence as an input to FTA