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Negative refraction of water waves by hyperbolic metamaterials
No full textInternational audienceWe study the propagation of water waves in a three-dimensional device alternating open canals and resonant canals with subwavelength resonances. The dispersion of water waves in such a medium is obtained by analysing the full three-dimensional problem and combining Bloch–Floquet analysis with an asymptotic technique. We obtain the closed forms of the dispersions for resonant canals containing one or two resonators, which depend on only two functions associated with symmetric and antisymmetric modes, and on a geometric parameter analogous to the hopping parameter in topological systems. The analysis of the complete band structure reveals frequency ranges alternating between elliptical and hyperbolic dispersions; in particular, the hyperbolic regime gives rise to a negative effective water depth with a consequent negative refraction. Throughout the course of our study, our theoretical results are validated by comparison with numerical calculations of the full three-dimensional problem
Caractérisation et modélisation de la fatigue et de la durabilité de ligne d’ancrages en polyamide pour les éoliennes offshore flottantes
No full textPolyamide 6 fibre ropes are of interest for floating offshore wind turbines mooring lines thanks to their low stiffness, good tensile strength and high strain to failure (20%). The complex visco-elasto-plastic behaviour of polyamide 6 ropes is not fully understood. The development of a reliable model for the mechanical behaviour of polyamide 6 fibres is essential for permanent mooring applications. This study proposes to validate and improve a 1D constitutive law composed of four springratchet and dashpot elements, that aims at completely describing the complex behavior of polyamide 6 fibre elements. The mooring lines will be under tension during all their service life and submitted to cyclic loading due to the waves and the movements of the plateform. Hence, they should show durability in terms of creep and fatigue life. Two experimental studies, respectively on long term creep behaviour and fatigue durability, are presented in this study. Also, to extend our understanding of the dissipation and degradation mechanisms in fatigue, the developement of a behaviour law based on the mesoscopic scale of a rope and its implementation in finite element analysis are presented. The final 3D model should allow a better understanding of the non linear behaviour and help to assess the dissipated energy due to the internal friction between components.Grâce à une résistance équivalente à celle du polyester, et à une élongation à rupture plus importante (20%), les lignes en polyamide 6 se distinguent pour l’ancrage de flotteurs d’éoliennes offshore en eaux peu profondes (< 200 m). Un premier verrou réside dans la complexité de leur comportement mécanique non linéaire. Cette étude propose de valider et d’améliorer un modèle de comportement 1D composé de quatre éléments ressort-rochet-amortisseur qui permet une description précise du comportement d’une ligne en polyamide 6. Cette loi permettrait un premier dimensionnement des lignes d’ancrage. Ces lignes seront sous tension pendant toute leur durée de vie en service. Elles seront soumises àdes sollicitations cycliques dues à la houle et aux mouvements de la plateforme. Un second verrou réside donc dans leur durabilité en fluage et en fatigue. Deux études expérimentales dédiées respectivement, à leur comportement en fluage long terme et à leur durée de vie en fatigue, sont donc présentées. Afin d’améliorer la compréhension des mécanismes de dégradation et de dissipation en fatigue, le développement d’une loi de comportement basée sur l’échelle mésoscopique d’un cordage et son implémentation dans un logiciel d’éléments finis sont présentés. Le modèle 3D final doit permettre une meilleure analyse du comportement non linéaire et, notamment, des phénomènes de dissipation dus aux frictions internes entre composants
From Pathological Bifurcations to Meaningful Planetary Change Agents
No full textInternational audienceThis chapter discusses and analyzes the phenomenon of pathological bifurcation among French engineering students. Pathological bifurcation occurs when sustainable development succeeds in inspiring student activism, but that passion expresses itself destructively. The chapter answers two questions. First, we interrogate whether pathological bifurcation is a product of lacunae with current SD education practices. Having answered affirmatively, we reflect on how to treat this diagnosis. Our suggestion is that if SDG related curricular innovations are desirable, so too is an extensive grounding in the traditional teachings of what we call planetary humanities. These are lessons drawn from around planet inculcating the very traditional moral art of controlling one's passions in such a way as to best foster collective flourishing.T
Caractérisation précise de la réponse acoustique du fond marin pour l’amélioration de l’identification des fonds
No full textEchosounders are commonly used in hydrography to measure bathymetry; they can also provide seabed reflectivity information based on the measurement of the seafloor acoustic response. The aim of the PhD is to provide a detailed description of the seafloor acoustic response metrology based on both theoretical and practical states of the art. Empirical methods to compute the backscattering strength, developed in operations by users, softwares or echosounder manufacturers, are confronted to theoretical statements from literature. The link between the two domains is made using a stochastic model based on the bathymetric processing of singlebeam and multibeam echosounders (respectively SBES and MBES). From this model, an accurate definition of the seafloor acoustic response is proposed and estimators of the backscattering strength are derived. The best estimator is then identified by comparing their bias, variances, and speeds of convergence. Finally, a measure of the accuracy of backscattering strength acquisitions with SBES or MBES is proposed, based on the uncertainty of the measurements. This uncertainty can be used as an a priori information about the quality of a planned survey, or as an a posteriori indication of precision of the seafloor response measurements.Les échosondeurs sont aujourd’hui largement utilisés en hydrographie pour mesurer la bathymétrie ; ils fournissent une information de réflectivité du fond à partir de la mesure de la réponse acoustique du fond marin. L’objectif de cette thèse est de proposer une description détaillée de la métrologie de la réponse acoustique des fonds fondée sur les états de l’art théoriques et opérationnels. Les méthodes empiriques pour calculer l’index de rétrodiffusion, développées en opération par les utilisateurs, logiciels, ou les fabricants d’échosondeurs, sont confrontées aux considérations de la littérature. Le lien entre les deux domaines est fait en utilisant un modèle stochastique se basant sur le traitement bathymétrique des sondeurs mono- et multi-faisceaux. À partir de ce modèle, une définition précise de la réponse acoustique du fond marin est proposée et des estimateurs de l’index de rétrodiffusion sont calculés. Le meilleur estimateur est ensuite identifié par comparaison des biais, variances et rapidité de convergence. Enfin, une mesure de la précision de l’acquisition des index de rétrodiffusion avec des sondeurs mono- et multifaisceaux est proposée, basée sur l’incertitude de la mesure. Cette incertitude peut être utilisée en tant qu’information a priori sur la qualité d’un levé planifié, ou comme une indication a posteriori sur la précision de la mesure de la réponse du fond marin
Bioglider: an integrated glider solution for enhancing environmental knowledge
No full textInternational audienceThis paper presents a technological solution for the observation and monitoring of the marine ecosystem. Three complementary devices, one optic imaging and one scientific acoustic instrument as well as one acoustic communication modem, have been integrated on glider platforms, providing qualitative and quantitative zooplankton and fish ecology observations, which are especially relevant in Nordic and Arctic polar regions. This 'Bioglider' solution has been tested on two available gliders. Another essential platform component for ocean observing are subsurface mooring lines which can complement glider observations in terms of temporal scales. Most of the time, they cannot have surface expressions in these regions because of sea-ice cover or harsh sea conditions, prohibiting real time data delivery. Underwater acoustic communication can allow the glider to serve as a data messenger, retrieving data from the moorings, complementing its measuring capacities. The Bioglider data transmission protocol and the Hydro-Acoustic Link Simulator were successfully tested in different test scenarios. We also developed a MIMO (Multi-input Multi-output) acoustic platform and obtained theoretical results about equalizing structures to face the harsh multipath acoustic underwater propagation. These developments address the challenges posed by sea-ice cover, harsh sea conditions, and maritime traffic, ensuring near real-time data delivery and enabling comprehensive observations of the marine environment. The Bioglider sensor solution and Bioglider data transmission solution have been implemented or designed for the existing and commercially available gliders and are validated by first promising results from an operational, technological and scientific point of view
Hybrid Navigation Acceptability and Safety
No full textInternational audienceAutonomous vessels have emerged as a prominent and accepted solution, particularly in the naval defence sector. However, achieving full autonomy for marine vessels demands the development of robust and reliable control and guidance systems that can handle various encounters with manned and unmanned vessels while operating effectively under diverse weather and sea conditions. A significant challenge in this pursuit is ensuring the autonomous vessels' compliance with the International Regulations for Preventing Collisions at Sea (COLREGs). These regulations present a formidable hurdle for the human-level understanding by autonomous systems as they were originally designed from common navigation practices created since the mid-19th century. Their ambiguous language assumes experienced sailors' interpretation and execution, and therefore demands a high-level (cognitive) understanding of language and agent intentions. These capabilities surpass the current state-of-the-art in intelligent systems. This position paper highlights the critical requirements for a trustworthy control and guidance system, exploring the complexity of adapting COLREGs for safe vessel-on-vessel encounters considering autonomous maritime technology competing and/or cooperating with manned vessels
Colla-Config: A stakeholders preferences-based approach for product lines collaborative configuration
No full textInternational audienceDuring collaborative configuration of software product lines (SPL), multiple stakeholders contribute together in building a single product specification. Conflicting situations can arise during the configuration process due to contradictions between some/all stakeholders’ configuration choices. Detecting and resolving such situation rise two major challenges: choosing which choices to omit, and taking stakeholders’ preferences into account. Several SPL collaborative configuration approaches are available. However, they either do not present detailed information on the strategies for conflict resolution, or they rely on a systematic process that resolves conflicts by prioritizing configuration decisions made at earlier stage, constraining therefore some of stakeholders’ choices. The lack of flexibility may hinder conflict resolution as choices taken at earlier stages overlay those at later phases. To mitigate these limitations, we propose a new collaborative configuration approach (Colla-Config) that provides a preference-based conflict resolution method within a free-order configuration process; each stakeholder expresses his/her preferences through a set of substitution rules, and freely makes his/her configuration decisions towards the desired product, without being constrained by the configuration decisions made by the other ones. To assess the feasibility and the usability of the proposed approach, we conducted a usability test designed following the ISO/IEC 25062:2006 Common Industry Format for usability tests. Results of the experiments provide preliminary evidence of the approach feasibility and the tool ability to properly support the SPL collaborative configuration
Wind turbine sound propagation: Comparison of a linearized Euler equations model with parabolic equation methods
No full textInternational audienceNoise generated by wind turbines is significantly impacted by its propagation in the atmosphere. Hence, for annoyance issues, an accurate prediction of sound propagation is critical to determine noise levels around wind turbines. This study presents a method to predict wind turbine sound propagation based on linearized Euler equations. We compare this approach to the parabolic equation method, which is widely used since it captures the influence of atmospheric refraction, ground reflection, and sound scattering at a low computational cost. Using the linearized Euler equations is more computationally demanding but can reproduce more physical effects as fewer assumptions are made. An additional benefit of the linearized Euler equations is that they provide a time-domain solution. To compare both approaches, we simulate sound propagation in two distinct scenarios. In the first scenario, a wind turbine is situated on flat terrain; in the second, a turbine is situated on a hilltop. The results show that both methods provide similar noise predictions in the two scenarios. We find that while some differences in the propagation results are observed in the second case, the final predictions for a broadband extended source are similar between the two methods
BIOMASS DEGRADATION PROCESSES USING A TIO2-BASED PHOTOCATALYST LEADING TO ACTIVATED BIOMASS
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Future Perspectives of Capacity Building in Engineering Education
No full textInternational audienceThis workshop aimed to encourage sharing of Capacity Building practices inEngineering Education across the SEFI community and open dialogue to shape howSEFI can support the community and their practices through the CapacityBuilding Special Interest Group. Participants also had the opportunity to discusstheir own experiences of Capacity Building, also known as pedagogical training orprofessional development, and compared and contrasted this to others’ experiences.They considered where Capacity Building has been beneficial for themselves andtheir colleagues. Participants were also asked to consider areas that will requireCapacity Building in the future, feeding into ideas for pan-European support thatSEFI might provide, including consideration of the environmental facilitators andbarriers for Capacity Building.The aim was for participants to develop an understanding of the wide variety of waysin which Capacity Building can be organised in Higher Education institutions acrossEurope, which might provide inspiration for improving current practices within theirown institutions. It was also intended for the workshop to support the building of aCommunity of Practice of educators who are involved with and/or lead CapacityBuilding activities in their own institutions or within the broader SEFI network