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La convergence technologique : le cas du véhicule autonome électrique
No full textInternational audienc
Modal analysis of an iced offshore composite wind turbine blade
No full textInternational audienceIn the far north, low temperatures and atmospheric icing are a major danger for the safe operation of wind turbines. It can cause several problems in fatigue loads, the balance of the rotor and aerodynamics. With the aim of improving the rigidity of the wind turbine blade, composite materials are currently being used. A numerical work aims to evaluate the effect of ice on composite blades and to determine the most adequate material under icing conditions. Different ice thicknesses are considered in the lower part of the blade. In this paper, modal analysis is performed to obtain the natural frequencies and corresponding mode shapes of the structure. This analysis is elaborated using the finite element method (FEM) computer program through ABAQUS software. The results have laid that the natural frequencies of the blade varied according to the material and thickness of ice and that there is no resonance phenomenon
Efficient jib-mainsail fluid-structure interaction modelling based on an extended lifting-line theory ⇓validations with semi-rigid sails experiments
No full textInternational audienceThe present work takes place in the framework of the “Jib Sea” project. The main purpose of the project is to develop a new sail design made of articulated composite panels, for large merchant ships. The French laboratory “ENSTA Bretagne, IRDL” is involved in this industrial project to provide its expertise on fluid-structure interactions modelling. A fast and robust approach to model fluid-structure interactions for yacht sails is presented. Specifically, interaction effects between the jib and the mainsail are taken into account in the flow model presented. This is achieved using the lifting-line theory combined with a discrete vortex method, involving distributions of lumped-vortex elements along sail sections. The flow model is coupled with a structural finite element software, using shell elements for the modelling of sail membranes, beam stringers for battens modelling and a quasi-static resolution based on a dynamic backward Euler scheme. Numerical comparisons with experiments are conducted on a 50 m2 composite mainsail prototype and a conventional jib, built and hoisted on an onshore balestron rig. Measurements, such as strain gauges or cable tensions, are synchronized with a wind sensor. These data collected together enable both global and local numerical-experimental comparisons for forces and moments, providing a validation of the proposed fluid-structure interactions modelling of yacht sails. A good matching between experimental and numerical modelling is observed on local comparisons. Indeed, relative differences are all less than 25% for TWA ∈ [−20; 20] and TWS < 10 kn. Global comparison results exhibit validations with experiments for |TWA < 10 deg and TWS < 10 kn, where numerical-experimental relative differences are less than 10%
Exact bounded-error continuous-time linear state estimator
No full textInternational audienceThis paper proposes an interval-based method for estimating the state of a linear continuous-time dynamical system. In this work, we assume that the measurements are provided at discrete times and that all errors are bounded. Interval analysis is used to propagate the interval uncertainties continuously over time. The resulting method is guaranteed to never lose any feasible solution and provides an optimal polygonal enclosure of the state trajectory. A reproducible example illustrates the principle of the method
Complex-scaling method for the complex plasmonic resonances of planar subwavelength particles with corners
No full textInternational audienceA subwavelength metallic particle supports localized surface plasmons for some negative permittivity values, which are eigenvalues of the self-adjoint quasi-static plasmonic eigenvalue problem (PEP). This work investigates the existence of complex plasmonic resonances for a 2D particle whose boundary is smooth except for one straight corner. These resonances are defined using the multivalued nature of some solutions of the corner dispersion relations and they are shown to be eigenvalues of a PEP that is complex-scaled at the corner, the finite element discretization of which yields a linear generalized eigenvalue problem. Numerical results show that the complex scaling deforms the essential spectrum (associated with the corner) so as to unveil both embedded plasmonic eigenvalues and complex plasmonic resonances. The later are analogous to complex scattering resonances with the local behavior at the corner playing the role of the behavior at infinity. These results corroborate the study of Li and Shipman (J. Integral Equ. Appl. 31(4), 2019), which proved the existence of embedded plasmonic eigenvalues and discussed the construction of particles that exhibit complex plasmonic resonances
Questioning causality on sex, gender and COVID-19, and identifying bias in large-scale data-driven analyses: the Bias Priority Recommendations and Bias Catalog for Pandemics
No full textThe COVID-19 pandemic has spurred a large amount of observational studies reporting linkages between the risk of developing severe COVID-19 or dying from it, and sex and gender. By reviewing a large body of related literature and conducting a fine grained analysis based on sex-disaggregated data of 61 countries spanning 5 continents, we discover several confounding factors that could possibly explain the supposed male vulnerability to COVID-19. We thus highlight the challenge of making causal claims based on available data, given the lack of statistical significance and potential existence of biases. Informed by our findings on potential variables acting as confounders, we contribute a broad overview on the issues bias, explainability and fairness entail in data-driven analyses. Thus, we outline a set of discriminatory policy consequences that could, based on such results, lead to unintended discrimination. To raise awareness on the dimensionality of such foreseen impacts, we have compiled an encyclopedia-like reference guide, the Bias Catalog for Pandemics (BCP), to provide definitions and emphasize realistic examples of bias in general, and within the COVID-19 pandemic context. These are categorized within a division of bias families and a 2-level priority scale, together with preventive steps. In addition, we facilitate the Bias Priority Recommendations on how to best use and apply this catalog, and provide guidelines in order to address real world research questions. The objective is to anticipate and avoid disparate impact and discrimination, by considering causality, explainability, bias and techniques to mitigate the latter. With these, we hope to 1) contribute to designing and conducting fair and equitable data-driven studies and research; and 2) interpret and draw meaningful and actionable conclusions from these
Gas-dynamic density downramp injection in a beam-driven plasma wakefield accelerator
No full textInternational audienceWe present the experimental demonstration of density downramp injection at a gas-dynamic shock in a beam-driven plasma accelerator. The ultrashort driver electron beam with a peak-current exceeding 10 kA allows operation in the blowout regime and enables injection of electron witness bunches at gentle density ramps, i.e., longer than the plasma wavelength, which nurtures prospects for ultralow bunch emittance. By precision control over the position of injection we show that these bunches can be energy-tuned in acceleration gradients of near 120 GV m−1
Theory of femtosecond strong field ion excitation and subsequent lasing in N2+
No full textInternational audienceDelayed cavity-free forward lasing at the wavelengths of 391 and 428 nm was observed in recent experiments in air or pure nitrogen pumped with an intense femtosecond laser pulse at wavelength of 800 nm. The mechanism responsible for the lasing is highly controversial. In this article we propose a model explaining the delayed lasing, which contains two parts: (i) ionization of neutral nitrogen molecules and subsequent excitation of nitrogen ions in a strong pump laser pulse, and (ii) coherent emission of excited ions due to the presence of long-lived polarizations maintained by a weak laser post-pulse and coupling simultaneously ground state X 2 Σ + g to states A 2 Π u and B 2 Σ + u of singly ionized nitrogen molecules N + 2. Two regimes of signal amplification are identified: a signal of a few picosecond duration at low gas pressures and a short (sub-picosecond) signal at high gas pressures. The theoretical model compares favorably with results obtained by different experimental groups
Ground target finding mechanism for unmanned aerial vehicles to secure crop field data
No full textInternational audienceUnmanned aerial vehicles (UAVs) are being used in many military and civil applications while their use along wireless sensors is emerging abruptly as it upgrades the network in terms of reliability, lifetime, and connectivity. The system performance and throughput can be further enhanced if the UAVs in use are capable to locate ground sensor nodes as a means to address them smartly. In typically localization, the direction of arrival of incoming signals from a target node is measured by using a uniformed linear array (ULA) of antennas having signal processing capabilities. However, adding numerous antennas (transmitter receivers set) on a UAV is an extra burden which ultimately effects its speed, flight time, agility, and payload capacity. Considering the issue, a typical ULA antenna system is modeled by using virtual phased array (VPA) antenna. In the proposed VPA, a single antenna installed on a moving UAV will achieve the desire results. The well-known multiple signal classification algorithm is modified to adapt this virtual antenna system. Four extra modules including calibrator, virtual antenna, rectifier, and adjustment are added in classical multiple signal classification algorithm to make it enable to work with single antenna. The proposed system mitigates the existing challenges of physical ULA and improves system throughput. Furthermore, due to its virtualness, VPA can adjust the number of antenna elements and interelement spacing, which adds multifrequency support and adaptive precision mechanism. A simulation model is developed in MATLAB to verify the performance of the VPA where the proposed system is evaluated against different scenarios with a varying number of parameters. It is found that VPA gives the same resolution and precision as a physical ULA antenna but it is more flexible, user-friendly, cost-effective, reliable, and most importantly, does not affect the UAV characteristics
An open access dataset for developing automated detectors of Antarctic baleen whale sounds and performance evaluation of two commonly used detectors
No full textInternational audienceSince 2001, hundreds of thousands of hours of underwater acoustic recordings have been made throughout the Southern Ocean south of 60° S. Detailed analysis of the occurrence of marine mammal sounds in these circumpolar recordings could provide novel insights into their ecology, but manual inspection of the entirety of all recordings would be prohibitively time consuming and expensive. Automated signal processing methods have now developed to the point that they can be applied to these data in a cost-effective manner. However training and evaluating the efficacy of these automated signal processing methods still requires a representative annotated library of sounds to identify the true presence and absence of different sound types. This work presents such a library of annotated recordings for the purpose of training and evaluating automated detectors of Antarctic blue and fin whale calls. Creation of the library has focused on the annotation of a representative sample of recordings to ensure that automated algorithms can be developed and tested across a broad range of instruments, locations, environmental conditions, and years. To demonstrate the utility of the library, we characterise the performance of two automated detection algorithms that have been commonly used to detect stereotyped calls of blue and fin whales. The availability of this library will facilitate development of improved detectors for the acoustic presence of Southern Ocean blue and fin whales. It can also be expanded upon to facilitate standardization of subsequent analysis of spatiotemporal trends in call-density of these circumpolar species