Simulation numérique par la méthode des éléments spectraux des vibrations induites par relâcher tourbillonnaire

RÉSUMÉ Les vibrations induites par relâcher tourbillonnaire (Vortex-induced VIbrations, VIV) sont un phénomène d’interaction fluide-structure où un corps immergé dans un fluide se met à vibrer selon une ou plusieurs directions à cause des lâchers de tourbillons engendrés par l’écoulement à sa paroi. Dans certaines conditions, ce couplage entre les mouvements du fluide et du corps peut induire des vibrations importantes sur ce dernier et l’endommager par fatigue. Ce projet de recherche vise à simuler ce phénomène avec un cylindre dans un écoulement tridimensionnel à faible nombre de Reynolds Re < 300, pour le cas extrême où le cylindre a une inertie négligeable face à celle du fluide et peut vibrer à la fois transversalement et dans la direction de l’écoulement. L’étude s’inscrit dans la lignée des travaux réalisés à l’École Polytechnique de Montréal pour des cas de figure comparables avec des écoulements bidimensionnels. Les simulations sont réalisées avec un code d’éléments spectraux en développement, la première étape de ce projet vise à le rendre fonctionnel et à l’adapter pour résoudre des problèmes d’interaction fluide-structure dans un second temps. Le projet se décompose donc en deux parties, la première moitié de l’étude se concentre sur la vérification, la validation et l’optimisation du code. Un schéma implicite fortement couplé est implémenté pour résoudre le couplage étudié dans le référentiel relatif au cylindre. La seconde partie du projet est tournée vers la simulation du phénomène des VIV et son analyse détaillée, un ensemble de simulations bidimensionnelles permet de valider le modèle avant le passage à la troisième dimension très coûteuse en ressources.----------ABSTRACT Vortex-induced vibrations (VIV) are a fluid-structure interaction phenomenon where an immersed body vibrates due to the vortex shedding generated by the flow along its walls. Under certain conditions, the coupling between the motion of the body and the flow may induce important vibrations and damage it by fatigue. The objective of this research project is to simulate the VIV phenomenon for a zero mass cylinder with two degrees of freedom, in a three-dimensional flow at low Reynolds number (Re < 300). This work follows previous VIV studies in two-dimensional laminar flows performed by researchers at Polytechnique Montréal. The numerical study is carried out with an in-house code based on the spectral element method. Before any VIV simulations, the first step of the project is to adapt this code to solve fluid-structure coupling problems. This study is therefore divided in two parts, the first half focuses on verification, validation and optimization of the code. An implicit strongly coupled scheme is implemented to solve the specific VIV coupling. The second part is dedicated to the simulation of the VIV phenomenon and its detailed analysis. Two-dimensional cases are simulated to validate the numerical model before the final three-dimensional study

MAORY for ELT: preliminary design overview

MAORY is one of the approved instruments for the European Extremely Large Telescope. It is an adaptive optics module, enabling high-angular resolution observations in the near infrared by real-time compensation of the wavefront distortions due to atmospheric turbulence and other disturbances such as wind action on the telescope. An overview of the instrument design is given in this paper

Active tectonics of the Alps-Dinarides junction : quantitative morphology, fault kinematics and implications for the Adria microplate geodynamics

Au Nord-Est de la microplaque Adriatique la jonction Alpes-Dinarides représente une région clé pour comprendre les interactions entre la microplaque et l’Europe stable. Alors que la tectonique active de la partie alpine de cette zone est relativement bien contrainte, peu de données sont disponibles quant aux déformations actives contrôlées par la rotation de la microplaque à travers les Dinarides. Par une approche morpho-tectonique (étude de terrain combinée à l’analyse d’images aériennes et satellitaires, de cartes topographiques et modèles numériques de terrain haute résolution) nous avons cartographié en détails les failles actives des Dinarides septentrionales et de la partie orientale des Alpes du Sud. Sur la base de cette cartographie et des données géologiques une quarantaine de décalages tectoniques cumulés allant de quelques mètres à plusieurs kilomètres a été identifiée. A l’aide de datations 36Cl de marqueurs morphologiques affectés par les failles combinées aux chronologies existantes les vitesses de déformation actuelles ont ensuite été estimées. L’évolution des déformations depuis le Pliocène a pu être contrainte dans les Dinarides mettant en évidence une initiation des failles au début du Pliocène et un changement cinématique important autour du Pléistocène moyen. Les vitesses obtenues, notamment environ 3mm/an de mouvement dextre le long des Dinarides, ont finalement été confrontées aux modèles existants ce qui a conduit à proposer un modèle cinématique décrivant l’accommodation de la rotation de l’Adriatique par le mouvement relatif de blocs lithosphériques rigides et qui permet d’expliquer les déformations actives observées aux frontières de ces blocs.At the northeastern corner of the Adria microplate the Alps-Dinarides junction represents a key region to understand the interactions between the microplate and the stable Europe. While the active tectonics of the alpine part of the area is relatively well-known, few data allow characterizing the present-day deformations controlled by the microplate rotation across the Dinarides. Using a morpho-tectonic approach (field study combined to the analysis of aerial and satellite images, topographical maps and high-resolution digital elevation models) we mapped in details the active faults in the Northern Dinarides and the eastern part of the Southern Alps. Based on this mapping and geologic data forty tectonic cumulative displacements ranging from few meters to several kilometers have been identified. By determining the 36Cl exposure ages of faulted geomorphic markers and comparing it to existing chronologies the present-day rates of deformation have then been assessed. The evolution of the deformations since the Pliocene could also have been constrained revealing an Early Pliocene age for the onset of strike-slip faulting and a major kinematic change during the Middle Pleistocene. Finally the yielded faults slip-rates, especially about 3 mm/yr of right-lateral motion across the Dinarides, have been compared to existing models. That allowed proposing a kinematic model describing the Adria rotation accommodation through the relative motion of rigid lithospheric blocks and explaining the observed active deformations at their boundaries

The Mojave Section of the San Andreas Fault (California), 2: Pleistocene Records of Near‐Field Transpression Illuminate the Atypical Evolution of the Restraining “Big Bend”

Abstract With an obliquity of ∼30° relative to plate motion direction, the ∼300‐km‐long Big Bend of the San Andreas Fault is one of the world's largest restraining bends. The 5–6 Ma (∼160 km of total displacement) longevity of this mechanically inefficient structure and the lack of evidence for associated widespread uplift both challenge existing models of transpression and bend evolution. We focus on the structurally simplest section of the Big Bend (the Mojave section of the San Andreas: MSAF) to characterize the pattern of near‐field (<5 km from the San Andreas trace) uplift over two different timescales. The topography of vertically deformed alluvial surfaces is used to demonstrate that near‐field uplift along the least oblique segment of the MSAF has been significant over the last ∼40 ka (∼1–2 mm/yr), and driven by slip on two oppositely dipping blind reverse faults. Topographic and structural analyses of the MSAF near‐field are conducted at the scale of the entire fault to show that, at least on the NE side of the MSAF, these blind structures coincide with the front of a fault‐parallel bedrock ridge with clear characteristics of a young transpressive ridge. Structural, sedimentary, and geomorphic arguments converge to suggest that these blind structures were activated ∼315 ka ago and record a Mid‐Pleistocene kinematic reorganization of the MSAF fault‐zone. This reorganization is tentatively interpreted as a shift in the mode of accommodation of the transpressive component of plate motion, in turn driven by the strike‐slip advection of crustal strength gradients along the Big Bend

Télémédecine et neurologie (à propos de l'expérience du réseau des urgences neurologiques (Raids-UN/FC))

BESANCON-BU Médecine pharmacie (250562102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Reply to Comment by Poli et al. on “Fragmentation of the Adriatic Promontory: New Chronological Constraints From Neogene Shortening Rates Across the Southern Alps (NE Italy)”

International audienc

The Mojave Section of the San Andreas Fault (California): 1. Shaping the Terrace Stratigraphy of Little Rock Creek Through the Competition Between Rapid Strike‐Slip Faulting and Lateral Stream Erosion Over the Last 40 k.y.

Abstract To determine the post‐40 ka slip‐rate along the Mojave section of the San Andreas Fault (MSAF) we re‐analyze the sedimentary record preserved where Little Rock (LR) Creek flows across the fault. At this location, interaction between the northeast‐flowing stream and right‐lateral fault has resulted in the abandonment and preservation of 11 strath terraces and one paleo‐floodplain in the downstream trailing corner of the river, two of which are also preserved upstream to provide cross‐fault matches. A new model of fault‐induced river deflection, together with standard terrace riser restoration, yields strike‐slip displacements of 1,140 ± 160 m for the older terrace and 360 ± 70 m for the younger one. When combined with new 10Be dating and reinterpretation of prior measurements the displaced terraces yield right‐lateral slip‐rates of 27.7+6.9/−3.5 and 26.8+3.4/−3.0 mm/yr over the last 23 k.y. and last 40 k.y., where uncertainties are at 95% credible intervals. These new rate determinations are consistent with independent late Holocene estimates, indicating that the long‐term rate of strain accumulation along the MSAF is relatively fast and does not vary significantly when averaged over timescales of 15–20 k.y. Using our new model of stream deflection, we find that the fluvial sequence was emplaced in two distinct periods, each characterized by a temporally stable but markedly different deflected river geometry. Each period coincides with a distinct stage of erosive power along LR Creek determined from independent paleoclimate proxies. Importantly, application of the new river‐deflection model allows strike‐slip displacements to be determined in the absence of upstream piercing points

Membrane characterisation from the support to the skin layer: Application to silicon carbide (SiC) membranes

SiC membranes are used in many industrial fields with high performances and good retention efficiency in the filtration of loaded liquids such as wastewater, oil or wine. Technologies allow to characterise membrane’s surface but few allow the characterisation of its depth. This paper proposes the combination of results obtained by the usual techniques of porous materials and by 3D X-ray tomography characterisation. A morphological analysis of solid and porous phase is carried out on the total thickness of the membrane. Combination of results on all layers is relevant for the study of SiC membranes, showing not only the SiC surface properties but also the 3D description of the porous material (i.e. support, layer and skin). The definition of essential parameters to define the efficiency of a filtration such as hydrophobicity, porosity and tortuosity allows to justify the use and superior performance of SiC membranes for the filtration of loaded liquids

Green pharmaceutical chemistry: solvent regeneration using pervaporation

International audienc

Solvent Regeneration in Complex Mixture Using Pervaporation

International audienceThis study aims to demonstrate the efficiency of dichloromethane (DCM) regeneration from a methanolic effluent by a combination of distillation and membrane pervaporation process. The presence of an azeotrope (MeOH/DCM/water) makes the regeneration of DCM via distillation alone impossible. A process simulation using ProSim software was carried out in order to evaluate the behavior of the azeotropic mixture. Two secondary treatments aiming to purify the DCM contained in the azeotrope were investigated. The first is the washing of the azeotrope with water. ProSim software was used to target the optimal conditions for washing before the experimental test. Residual water was recovered in the organic phase, meaning that the quality specifications for DCM were not reached. The second process studied for DCM purification was a pervaporation step. The feasibility of this had been proven at laboratory scale. The recovered DCM had the quality of a new solvent, and the whole process (distillation + pervaporation) reached a global DCM regeneration yield of 71.8% before optimization. This yield was limited by the distillation of methylal (also called dimethoxymethane) present in the methanolic effluent at the end of the distillation of the azeotrope, a compound retained by the pervaporation membrane. The pervaporation was performed on a hydrophilic Hybsi membrane letting methanol and water pass through and retaining the DCM (membrane surface = 0.15 m(2)). Optimization and scaling up were then carried out with a semi-industrial pervaporation pilot (membrane surface = 1.05 m(2)) which enabled the industrial scale-up. In order to facilitate the steering of the process and to ensure continuous and efficient monitoring of the regeneration operation, online monitoring by near-infrared probe (NIR) had been implemented allowing the composition of the mixture to be determined with an accuracy of +/- 0.05% on each compound. Finally, an assessment had been conducted of the regeneration pathways for methanol recovery at the bottom of the distillation column, for maximizing the regeneration of methanolic effluents by separating heavy compounds and methylal from methanol