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Wind turbine noise modeling including aeroacoustic sources and propagation effects: comparison against field measurements
No full textInternational audienceThe study of wind turbine noise and its impact is of growing importance with the increase in the demand for green and clean energy. As it is known that wind turbine noise can be a cause of annoyance in the vicinity of wind farms it is beneficial to predict with certain accuracy the generated noise in the design phase itself. A crucial step is the validation of prediction models against field measurements (in-situ). This article presents a wind turbine noise prediction model that combines Amiet’s theory to calculate trailing edge noise and turbulence interaction noise in free field with a wide-angle parabolic equation valid in moving media to account for the long-range acoustic propagation effects. The model considers the wind turbine as an extended noise source and the rotation effects (such as the convective amplification and Doppler effect) are taken into account. The predicted noise levels are compared to those obtained from a measurement campaign where acoustic, meteorological and ground impedance data have been recorded simultaneously. First, the sound source model is validated close to the wind turbines for different wind speeds and directions. Then, noise predictions are compared to SPL measurements at various distances from the sound source, between 350 and 1300 meters
Eddy-current asymptotics of the Maxwell PMCHWT formulation: the multi-body case
No full textInternational audienceA low-frequency, high-conductivity asymptotic approximation of the Maxwell transmision problem for configurations with highly-conducting, moderately conducting and non-conducting bodies, motivated by eddy current testing applications, is proposed and validated
Marchands de canon ou partenaires des armées ? Repenser les fondements de la politique industrielle de défense
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Les stratégies de tarification des pièces détachées aéronautiques en service après-vente
No full textPricing strategies are one of the most effective levers for maximizing margins in the industry. However, they are often little known and poorly mastered by these companies. The purpose of this doctoral thesis is to empirically analyse present and potential pricing strategies in the aeronautical spare parts market. The first chapter of the thesis is dedicated to the apprehension of the literature on income maximization strategies using price leverage and their limits. As there are gaps in this particular field, this thesis aims to expose the characteristics of the aeronautical spare parts market and to establish the range of possibilities in terms of pricing strategies.The second chapter deals with the analysis of the purchasing determinants of aeronautical spare parts. It has been demonstrated that the purchasing mechanisms are different according to the interactions between the agents and according to the type of competition present. In addition, price and markup levels maximizing margins were found by the econometrics analysis of sales.The last chapter gives external validation to the results obtained by verifying them by survey and by proposing an extension to areas such as the consequences of the 737 MAX and Covid-19 crises as well as future developments in this market. Finally, operational precautions resulting from all the research work are necessary.Les stratégies de tarification sont un des leviers les plus efficaces pour maximiser les marges dans l’industrie. Pourtant, elles sont souvent peu connues et mal maitrisées par ces entreprises. L’objet de cette thèse de doctorat est d’analyser empiriquement les stratégies de tarification présentes et potentielles sur le marché des pièces détachées aéronautiques. Le premier chapitre de la thèse est dédié à l’appréhension de la littérature portant sur les stratégies de maximisation du revenu en utilisant le levier prix, et leurs limites. Celle-ci étant lacunaire dans ce domaine particulier, cette thèse a vocation à exposer les caractéristiques du marché des pièces détachées aéronautiques et d’établir le champ des possibles en matière de stratégie de tarification.Le deuxième chapitre porte sur l’analyse des déterminants d’achat des pièces détachées aéronautiques. Il a été démontré que les mécanismes d’achat sont différents selon les interactions entre les agents et selon les types de concurrence en présence. De plus, des niveaux de prix et de majoration maximisant les marges ont été trouvés par l’analyse économétrique des ventes.Le dernier chapitre donne une validation externe aux résultats obtenus en les vérifiant par enquête et en proposant une extension à des domaines comme les conséquences des crises du 737 MAX et de la Covid-19 ainsi que les évolutions futures de ce marché. Enfin des préconisations opérationnelles issues de l’ensemble des travaux de recherche sont formulées
High-Energy Solitonic Source of High Harmonics
No full textInternational audienceWe report on high harmonics generation in zinc oxide thin-films driven by an all-solid fiber-based architecture. The laser delivers 41 nJ 70 fs solitonic pulses at 1764 nm and drives harmonics generation up to H7
An investigation of the appearance of lustering on HMPE fiber ropes
No full textInternational audienceThe low friction coefficient of HMPE fibers may be a disadvantage for some applications such as winches but it can also be used to develop new technology. Recently this specific property was used in the design of innovative pulleys for sailboats. The contact is then between a low friction metallic ring and a HMPE fiber rope loop. During service, a specific phenomenon appears at the contact area on the HMPE fibers called lustering due to its visual aspect. It is also observed in eye splice contact zones during tensile testing. In the present work, an investigation was made to understand and explain the appearance of the lustering of the fibers. Based on examination of different hypotheses, mechanical tests and a range of microstructural observations, the conclusion is that the appearance of the lustering phenomenon is the result of compaction of the filaments of the HMPE rope loop
The upper bound of low cycle fatigue life of pseudoelastic polycrystalline NiTi shape memory alloys
No full textInternational audienceAbstract The coupling between transformation-induced plasticity (TRIP) and low cycle fatigue of pseudoelastic shape memory alloys (SMAs) is investigated and an upper bound of low cycle fatigue life is found. Through combined in-situ infrared and digital image correlation observations on NiTi sheets, we reveal that the low cycle fatigue of SMAs is governed by the transformation band fronts with the highest temperature where TRIP is maximized. The local state at the band front is in fact determined by a coupling effect of the applied loads and thermal conditions, the former driving the transformation with heat release while the latter determining the heat transfer efficiency. This coupling leads the fatigue lives to distribute along a series of isotherms. As the coupling tends to be infinitesimal, local TRIP is limited to a minimum level, thus resulting in an upper bound of low cycle fatigue life. This agrees well with the experiments
Titanium-catalysed transformations of alkynes into complex molecular architectures
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ELI Gammatron Beamline: A Dawn of Ultrafast Hard X-ray Science
No full textInternational audienceThe realization of compact X-ray sources is one of the most intriguing applications of laser-plasma based electron acceleration. These sources based on the oscillation of short micron-sized bunches of relativistic electrons provide femtosecond X-ray pulses that are collimated, bright, and partially coherent. The state-of-the-art laser plasma X-ray sources can provide photon flux of over 1011 photons/shot. The photon flux can further be enhanced with the availability of high repetition rate, high-power lasers, providing capacities complementary to the large scale facilities such as synchrotrons and X-ray free-electron lasers. Even though the optimization of such sources has been underway for the last two decades, their applications in material and biological sciences are still emerging, which entail the necessity of a user-oriented X-ray beamlines. Based on this concept, a high-power-laser-based user-oriented X-ray source is being developed at ELI Beamlines. This article reports on the ELI Gammatron beamline and presents an overview of the research accessible with the ultrashort hard X-ray pulses at the ELI Gammatron beamline