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Modeling a novel laser-driven electron accelerator concept: Particle-In-Cell simulations at the exascale
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Proving the Stability of the Rolling Navigation
No full textInternational audienceIn this paper, we propose to study the stability of a navigation method that allows a robot to move in an unstructured environment without compass by measuring a scalar function ϕ which only depends on the position. The principle is to ask the robot to roll along an isovalue of ϕ . Using an interval method, we prove the stability of our closed loop system in the special case where ϕ is linear
Propagation effects in the synthesis of wind turbine aerodynamic noise
No full textInternational audienceThe sound field radiated by a wind turbine changes significantly with propagation distance, depending on the meteorological conditions and on the type of ground. In this article, we present a wind turbine noise synthesis model which is based on theoretical source and propagation models. The source model is based on Amietâ’s theory for the prediction of the trailing edge noise and the turbulent inflow noise. The trailing edge noise uses the wall pressure spectrum calculated with Leeâ’s model for the suction side and Goodyâ’s model for the pressure side. The Kolmogorov spectrum is used for the prediction of the turbulent inflow noise. To account for the propagation effects associated with atmospheric refraction and ground reflection, a wide angle parabolic equation in inhomogeneous moving medium is considered. The scattering due to the turbulence in the atmosphere is accounted for using the Harmonoise model. The synthesis method is based on the moving monopole model to accurately predict the amplitude modulations at the receiver, and uses cross-fading between overlapping grains to obtain the time signals from the frequency-domain prediction model. Finally, audio signals are provided for a few test cases to emphasize various propagation phenomena associated with wind turbine noise
Etude de la capacité portante des fondations sur inclusions rigides
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Theoretical Investigation of the Mechanism of the Hock Rearrangement with InCl3 as Catalyst
No full textInternational audienceThe Hock rearrangement is an acid catalyzed reaction involving organic hydroperoxides and resulting in an oxidative cleavage of adjacent C−C bonds. It has significant industrial applications, like the production of phenol (cumene process), but it remains scarcely used in organic synthesis. In addition, its detailed mechanism has never been studied. Thus, we report herein a theoretical study of the Hock rearrangement, using InCl 3 as a Lewis acid catalyst. The aim of this work was to fully understand the mechanism of this fundamental reaction, and to rationalize the influence of the substrate electronic properties on the reaction outcome. Furthermore, the structure of the active indium(III) catalyst interacting with the peroxide substrate was investigated, revealing the co‐existence of several energetically close reaction pathways. The coordinated monomeric form of the Lewis acid emerges as the most active catalyst compared to dimeric species. However, we show that In 2 Cl 6 species coordinated to the substrate are central in this catalytic cycle, primarily serving as a reservoir of active monomeric species
Approche géométrique de l'inversion du transfert radiatif par petits fonds
No full textInternational audienceThis paper proposes an alternative to the conventional formulation of the inversion of the radiative transfer model, by separating the estimation of the water column parameters from the estimation of the background spectrum. To do this, a geometric representation of the inversion problem is introduced. It allows the estimation to be broken down into two successive optimization problems. This approach opens up the possibility of fully exploiting the diversity of the types of background observedCet article propose une alternative à la formulation classique du problème d'inversion du modèle de transfert radiatif, en dissociant l'estimation des paramètres de la colonne d'eau de l'estimation du spectre du fond. Pour ce faire, une représentation géométrique du problème d'inversion est introduite. Elle permet de décomposer l'estimation en deux problèmes d'optimisation successifs. Cette approche ouvre la possibilité d'exploiter pleinement toute la diversité des types de fond observés
Pressure analysis in nonlinear waves by revisiting the breaking wave onset
No full textInternational audienceBreaking waves are numerically simulated by solving the two dimensional nonlinear free surface boundary conditions in potential theory. Onset of breaking wave is determined for two configurations: A focused wave in intermediate depth and a dambreaking flow leading to a soliton. Two criteria are identified: first, a kinematic criterion follows from the ratio of the horizontal velocity at the crest to the phase velocity; second, a dynamic criterion is formulated in terms of the vertical pressure gradient. Thresholds of these criteria are proposed in the literature. For the two configurations studied here, it is shown that these thresholds are not universal but they are reasonable estimates of the onset of breaking wave. To facilitate this study, the Hessian matrix of the pressure is analyzed. It is shown that there exists a continuous curve that links the crest of the wave to the sea bottom. This line follows from the colinearity of the pressure gradient and one of the two eigenvectors of the Hessian matrix. The analysis of the pressure, its gradient and its second derivatives along this line gives more insights into the definition of the thresholds associated to the onset of breaking wave
In-situ monitoring of changes in ultrastructure and mechanical properties of flax cell walls during controlled heat treatment
No full textIssu de : https://doi.org/10.2139/ssrn.4404621International audiencePlant fibres are increasingly used as reinforcements, especially in thermoplastic composites. Understanding the impact of temperature on the properties of these fibres is an important issue for the manufacturing of high-performance materials with minimal defects. In this work, the structural evolution and mechanical behaviour of flax fibre cell walls were dynamically monitored by temperature-controlled X-ray diffraction and nanoindentation from 25 to 230 °C; detailed biochemical analysis was also conducted on fibre samples after each heating step. With increasing temperature up to 230 °C, a decrease in the local mechanical performance of the flax cell walls, of about −72 % for the indentation modulus and −35 % for the hardness, was measured. This was associated with a decrease in the packing of the cellulose crystal lattice (increase in d-spacing d200), as well as significant mass losses measured by thermogravimetric analysis and changes in the biochemical composition, i.e. non-cellulosic polysaccharides attributed to the middle lamellae but also to the cell walls. This work, which proposes for the first time an in-situ investigation of the dynamic temperature evolution of the flax cell wall properties, highlights the reversible behaviour of their crystalline structure (i.e. cellulose) and local mechanical properties after cooling to room temperature, even after exposure to high temperatures
Stability and Bifurcation in non linear mechanics
No full textInternational audienceAnalysis of stability and bifurcation is studied in non linear mechanics with mechanisms of dissipation : plasticity, damage, fracture. With introduction of a set of internal variables, this framework allows a systematic description of the material behaviour via two potentials : the free energy and the potential of dissipation. For standard generalized materials internal state evolution is governed by a variational inequality depending on the mechanism of dissipation. This inequality is obtained through energetic considerations in an unified description based upon energy and driving forces associated to internal variable evolution. This formulation provides criterion for existence and uniqueness of the system evolution. Examples are presented for plasticity, fracture and for damaged material
Engineering Students' Perceptions Towards Promoting Sustainability
No full textInternational audienceEngineers should play a major role in making progress towards achieving the Sustainable Development Goals (SDGs). Consequently, Engineering Education has an important responsibility for preparing engineering students to the future challenges by promoting sustainable development (SD) and implementing sustainability development education. The purpose of this study was to gauge engineering students' knowledge and perceptions whether they believe their institution is successfully promoting sustainability. It also aimed to have a better understanding to what extent the university has strategically incorporated sustainability into their faculty. We have conducted a quantitative online survey with the participation of 253 engineering students from different majors at Bachelors and Masters levels. SPSS was used to analyze and study the variations and parallels amongst the majors and to confirm the accuracy of the data. The study revealed that, despite various active sustainability development university initiatives, the engineering students' perception is that their university is not effectively promoting the principles of SD