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On the behavior of a granular soil deposit subjected to horizontal vibration: A discrete element modeling
No full textInternational audienceThis paper presents an analysis of the behavior of a non-cohesive granular material deposit excited at its base by a horizontal harmonic vibration. The analysis is carried out numerically by means of a 2D discrete element model. The performed simulations highlighted some aspects of vibration behavior in non-cohesive deposits, such as the shape of the vertical profile of the displacement, notably in the case of large displacements. The analysis particularly focused on the amplification of the movement at the free surface of the deposit, as well as its dependence on some parameters such as the excitation frequency and the excitation amplitude of the deposit confinement. The obtained results showed that the behavior of the deposit following the change in the excitation frequency is similar to the case of an elastic deposit excited by a harmonic displacement at the base, i.e. the Dynamic Amplification Factor (DAF) initially increases with the frequency increase, it reaches a peak of resonance then it decreases. The resonance frequency estimated from this analysis is close to the fundamental frequency for low excitation amplitudes, but becomes smaller as the excitation amplitude increases. On the other hand, for a fixed frequency, increasing the amplitude of the excitation induces greater amplification. It has been shown that this increase results from the degradation of the shear modulus due to the increase in the level of involved shear strain. Therefore, unlike elastic deposits, for non-cohesive granular deposits, increasing strain leads to a degradation of the shear modulus, resulting in a downward shift of the resonance frequency and can induce a significant increase in amplification. The confinement of the deposit is achieved by increasing the gravitational acceleration; it has been shown that increased confinement makes the deposit stiffer, and therefore reduces the amplification of the introduced movement
Mixture-of-experts for handwriting trajectory reconstruction from IMU sensors
No full textInternational audienceThe use of digital pens for online handwriting trajectory reconstruction is a prevalent method for human-computer interaction. In this study, we focus on a digital pen equipped with sensors where we aim at reconstructing the online handwriting trajectory. This pen enables writing on any surface and preserving the digital trace of handwriting. This type of pen could be used as an aid to learning to write in classroom.In this paper, we propose a new approach learning to finely reconstruct the touching trajectories while precisely analyzing the hovering part in order to position the next touching trace correctly. This relies on a Mixture-Of-Experts (MOE) approach. The first expert is dedicated for the pencil touch, and is named touching expert model. The second one is dedicated for the hovering pen trajectory, and is named hovering expert model. We improve on the learning of each of these experts based on additional context or specific examples. In addition we introduce a novel public benchmark dataset, to enable future research and comparisons in the field of handwriting reconstruction. The results demonstrates a significant enhancement compared to its primary competitorsL'utilisation de stylos numériques pour la reconstruction en ligne de la trajectoire de l'écriture est une méthode répandue pour l'interaction homme-machine. Dans cette étude, nous nous concentrons sur un stylo numérique équipé de capteurs afin de reconstruire la trajectoire de l'écriture en ligne. Ce stylo permet d'écrire sur n'importe quelle surface et de préserver la trace numérique de l'écriture. Ce type de stylo pourrait être utilisé comme aide à l'apprentissage de l'écriture en classe.Dans cet article, nous proposons une nouvelle approche apprenant à reconstruire finement les trajectoires d'effleurement tout en analysant précisément la partie en vol stationnaire afin de positionner correctement la trace d'effleurement suivante. Cette approche repose sur un mélange d'experts (MOE). Le premier expert est dédié au toucher du crayon, et est nommé modèle expert du toucher. Le second est dédié à la trajectoire du stylo en vol stationnaire, et est nommé modèle expert en vol stationnaire. Nous améliorons l'apprentissage de chacun de ces experts en fonction d'un contexte supplémentaire ou d'exemples spécifiques. En outre, nous introduisons un nouvel ensemble de données de référence publiques, pour permettre des recherches et des comparaisons futures dans le domaine de la reconstruction de l'écriture manuscrite. Les résultats démontrent une amélioration significative par rapport à ses principaux concurrent
Buckling of Simply Supported Bi-Periodic Elastic Columns
No full textInternational audienceIn this paper, the buckling of a simply supported stepped periodic column is studied using an analytical method. The column is composed of biperiodic cells of stepped Euler–Bernoulli continuous segments. The deflection solution in each cell can be expressed from the resolution of a fourth-order differential equation. After expressing the continuity conditions between each cell, it is possible to relate the solution of each cell with respect to its neighbors. The differential eigenvalue problem of the bi-periodic structure is converted into a linear difference eigenvalue problem associated to the coefficients of the expressed solution in each cell. A transcendental equation for the buckling load of the continuous biperiodic column is obtained from the resolution of the discrete linear difference eigenvalue problem. This transcendental equation is valid whatever the number [Formula: see text] of bi-periodic cells, with [Formula: see text] larger than 2. This general expression is corroborated with the buckling values obtained using a direct method for few cells ([Formula: see text] and [Formula: see text] for instance). The behavior of the stability limit for large [Formula: see text] values is also specifically studied. It is shown that the bi-periodic column asymptotically converges toward a homogenized Euler–Bernoulli column with equivalent stiffness calibrated from Reuss’s averaging method. More refined beam models are also derived using asymptotic arguments. The buckling load converges toward the one of a gradient beam model for sufficiently large number [Formula: see text] of cells, which can be equivalently derived from a second-order homogenized beam theory. The convergence of this second-order homogenized beam model toward the equivalent homogenized Euler–Bernoulli column (obtained from Reuss’s averaging method) is from below, as also reported for the exact solution of the biperiodic continuous column. A comparison is also carried out for large values of [Formula: see text] with a nonlocal Euler–Bernoulli model, which has the same order of accuracy as obtained from the gradient beam model (second-order homogenized beam model)
On the Use of Graphs for Satellite Image Time Series: A comprehensive review
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Absence de doute sérieux sur la légalité d'un arrêté municipal ordonnant le couvre-feu des mineurs de seize ans
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Transcender le traumatisme pour travailler la résilience des populations : l’exemple de la mémoire de la tempête Xynthia 15 ans après
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WAXD investigations on the effect of loading history on strain-induced crystallization for a fully formulated filled natural rubber
No full textInternational audienceModelling crystallization under stretch is a key topic for fatigue design of rubber-like antivibration parts. Nevertheless, most of the academic studies consider unfilled natural rubber while the industrial materials are fully formulated compounds filled with carbon blacks and exhibit a highly dissipative visco-elastic behavior. This behavior is very useful for antivibration systems but complicates the characterization and modelling of the phase change, as the addition of fillers and additives brings in numerous additional dissipation sources and intricates the time effects on the thermomechanical response and on crystallization. In this study, we use well resolved WAXD synchrotron measurements to perform in situ measurements under various mechanical protocols. The objective is to characterize the evolution of the triplet {strain, stress, crystallinity index}, and their derivatives, for various time and mechanical solicitations. First, classic load/unload tension tests over a range of strain rates leading to non-equilibrium cases are achieved, to serve as a reference database on the compound studied. Then, a multi-relaxation cyclic test combining static and monotonic steps is applied in order to describe the crystallization state and kinetics around a relaxed state (sometimes called "equilibrium hysteresis"). The results provide a precious database to identify or challenge the existing thermodynamic models, for conditions seldom met in the literature: fully formulated material and various mechanical loading time histories
Pour des Schémas Directeurs Immobiliers et Energétiques transformatifs au sein du secteur public. Retour sur l’évaluation des SDIE accompagnés par l’ADEME
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Quand la Constitution tremble. Causes et conséquences d'une instabilité politique sans précédent sous la Ve République (conférence-débat, Vannes)
No full textOrganisation d'une conférence-déba
Downstream tidal turbine transient local blade loading characterization
No full textInternational audienceFlow perturbations carried in the wake of an upstream turbine can have a significant impact on the local and transient loads observed on the downstream one. To get a better understanding of the effect of unsteady asymmetric flow on the load felt by a downstream turbine and develop a method to extract local and transient blade loading from CFD results, fully transient simulations designed to study this effect were performed with a RANS k-ω SST turbulence model using ANSYS-CFX. A horizontal axis tidal turbine (HATT) was used for the study. Three configurations were considered: the downstream turbine aligned with the upstream one, the downstream turbine offset by 0.5D and finally offset by 1D, with D being the diameter of the turbine. A 10D clearance between both turbines was used. Results show that when fully in-line, the downstream turbine sees reduction in power coefficient by almost 70 %, with a temporal variation of this coefficient having a relative amplitude of more than 30 %. Furthermore, the blades see localized loading varying by a factor of up to 2 during their rotation and the changes in the load amplitude applied at the same location are varying by more than 13 %. Blade load and flapwise bending moment display significant amplitude variations for the 0D and 0.5D offsets, with values 8 and 12 times higher to what is observed for the 1D offset