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Le comportement inter-échelle de l'incertitude dans la turbulence Navier-Stokes tridimensionnelle
No full textInternational audienceWe derive the scale-by-scale uncertainty energy budget equation and demonstrate theoretically and computationally the presence of a self-similar equilibrium cascade of decorrelation in an inertial range of scales during the time range of power law growth of uncertainty in statistically stationary homogeneous turbulence. This cascade is predominantly inverse and driven by compressions of the reference field's relative deformation tensor and their aligments with the uncertainty velocity field. Three other subdominant cascade mechanisms are also present, two of which are forward and also dominated by compressions and one of which, the weakest and the only non-linear one of the four, is inverse. The uncertainty production and dissipation scalings which may follow from the self-similar equilibrium cascade of decorrelation lead to power law growths of the uncertainty integral scale and the average uncertainty energy which are also investigated. Compressions are not only key to chaoticity, as previously shown, but also to stochasticity.Nous dérivons l'équation du bilan énergétique de l'incertitude échelle par échelle et démontrons théoriquement et informatiquement la présence d'une cascade d'équilibre auto-similaire de décorrélation dans une gamme inertielle d'échelles pendant la période de croissance en loi de puissance de l'incertitude dans une turbulence homogène statistiquement stationnaire. Cette cascade est principalement inverse et entraînée par des compressions du tenseur de déformation relative du champ de référence et leurs alignements avec le champ de vitesse de l'incertitude. Trois autres mécanismes de cascade sous-dominants sont également présents, deux d'entre eux sont en avant et également dominés par les compressions et un autre, le plus faible et le seul non-linéaire des quatre, est inverse. Les échelles de production et de dissipation de l'incertitude qui peuvent découler de la cascade de décorrélation à l'équilibre auto-similaire conduisent à des croissances en loi de puissance de l'échelle intégrale de l'incertitude et de l'énergie moyenne de l'incertitude, qui sont également étudiées. Les compressions ne sont pas seulement la clé de la chaoticité, comme on l'a montré précédemment, mais aussi de la stochasticité
In Situ Monitoring of Retained Austenite Decomposition During Tempering of High-Strength Tool Steels
No full textInternational audienceThis study investigates the decomposition of retained austenite (RA) in tool steels for plastic molding in correlation with the alloy chemical composition and the tempering parameters. Two grades differing in their silicon content with initial mixed bainitic/martensitic microstructures were investigated using in situ synchrotron high-energy X-ray diffraction (HEXRD) during tempering in the 550 °C to 600 °C temperature range for one-hour holding time. Results indicated carbide formation during heating or isothermal holding; however, retained austenite remained untransformed up to the end of the tempering holding time in all investigated conditions for both grades. In situ HEXRD provides direct evidence of the transformation of retained austenite into fresh martensite on cooling from the tempering stage. This behavior is correlated to the evolution of carbon enrichment of retained austenite and the effect of silicon is discussed
Contrôle optimal en temps réel des flux de puissance dans les micro-réseaux électriques : formalisation sous forme de processus décisionnel markovien et résolution par méthodes à gradient de politique
No full textIn the context of the energy sector decarbonization and the need for flexibility in the European power grid, microgrids have emerged as an innovative solution for integrating intermittent renewable energy resources and addressing new consumption modes. However, real-time power flow control in these systems, formalized in the literature as a stochastic sequential decision problem, suffers from the lack of a unified modeling framework. This thesis proposes a Markov Decision Process (MDP) based formalization framework. A clear distinction is made between technological (or unfeasibility-related) constraints and constraints describing the undesirability of certain actions, thereby improving the interpretability of the results. The impact of the reward function configuration is studied for the infinite-horizon MDP formalization. The optimal policy obtained through this framework is compared, in terms of performance, to that derived from the finite-horizon MDP formalization. A constrained finite-horizon MDP is also formalized, where the constraint is not technological. Finally, several policy gradient methods are implemented and evaluated in terms of convergence speed, performance, and reliability.Dans le cadre de la décarbonation du secteur énergétique et du besoin de flexibilité du réseau électrique européen, les micro-réseaux électriques se distinguent comme une solution innovante pour intégrer des ressources énergétiques renouvelables intermittentes et répondre à de nouveaux modes de consommation. Toutefois, le contrôle en temps-réel des flux de puissance dans ces systèmes, formalisé comme un problème de décision séquentielle stochastique dans la littérature, souffre d’un manque de cadre de modélisation unifié. Cette thèse propose une formalisation basée sur les processus décisionnels markoviens (MDPs) comme cadre de modélisation. Une distinction claire est faite entre les contraintes technologiques ou contraintes de faisabilité et les contraintes décrivant la non-souhaitabilité de certaines actions, permettant ainsi une meilleure interprétabilité des résultats. L'impact de la configuration de la fonction de récompense est étudié pour la formalisation sous MDP à horizon infini et la politique optimale obtenue à travers celle-ci est comparée, en termes de performance, à celle obtenue à travers la formalisation sous MDP à horizon fini. Un MDP à horizon fini contraint est formalisé ; la contrainte n'étant pas technologique. Enfin, plusieurs méthodes de résolution à gradient de politique sont implémentées et évaluées en termes de vitesse de convergence, de performance et de fiabilité
Experimental measurement of the vorticity-strain alignment around extreme energy transfer events
No full textInternational audienceThis work experimentally explores the alignment of the vorticity vector and the strain-rate tensor eigenvectors at locations of extreme upscale and downscale energy transfer. We show that the turbulent von Karman flow displays vorticity-strain alignment behavior across a large range of Reynolds numbers, which are very similar to previous studies on homogeneous, isotropic turbulence. We observe that this behavior is amplified for the largest downscale energy transfer events, which tend to be associated with sheet-like geometries. These events are also shown to have characteristics previously associated with high flow field non-linearity and singularities. In contrast the largest upscale energy transfer events display much different structures which showcase a strong preference for vortex-compression. We then show further evidence to the argument that strain-self-amplification is the most salient feature in characterizing cascade direction. Finally, we identify possible invariant behavior for the largest energy transfer events, even at scales near the Kolmogorov scale
Are manual wheelchair rear wheel rolling resistance and friction (in)-dependent of load, tire pressure, and camber angle? An evaluation across different surfaces
No full textInternational audiencePurpose: Rolling resistance of manual wheelchair (MWC) has been widely studied, and while many studies have focused on the effects of rear-wheel configurations and surface types, few studies have comprehensively explored a broad range of surfaces and their interactions with wheel configurations. Additionally, rear wheel grip (i.e., friction) remains underexplored. Materials and methods: To assess the specific impact of rear-wheel configurations on both rolling resistance and grip, a deceleration cart with four identical wheels was developed. The rolling resistance and static friction of three tire types were tested across two loads, four camber angles, three inflation pressures, and seven surface types, including sports and everyday surfaces. Measurements were obtained using wireless inertial measurement units during deceleration tests and using a handheld dynamometer during grip tests, following an experimental design approach. Results: Statistical analysis identified surface type as the most influential factor on rolling resistance and static friction, with tire pressure and camber angle also having significant surface-dependent effects. Conclusion: The use of the deceleration cart enabled precise determination of the specific rolling resistance properties and static friction coefficients of MWC wheels, facilitating the creation of a dataset that characterizes the rolling resistance and grip properties of wheels on various surfaces
Future Planet - How the present can influence the future
No full textInternational audience"Future Planet - How the present can influence the future" is an interactive and collaborative virtual environment designed to raise awareness of environmental issues and promote sustainable choices. The project addresses critical issues such as deforestation, air pollution and clean energy and challenges users to solve them in order to create a sustainable future. Users make good or bad decisions to learn about the impact on the environment - for example, planting appropriate trees combats deforestation, while poor building decisions increase pollution. By completing tasks, such as discovering hidden seeds or collecting research papers, players unlock items that they can use to develop their future planet. Cooperation is important: one player in the present makes decisions that affect the future, while another in the future observes the effects and provides assistance. Interaction features include a gesture-based 3D user interface with a miniature earth for teleportation and unique tools for navigation and item management. By combining education, gamification and immersive elements, the project encourages users to explore sustainable behaviors and work together to create a greener, more sustainable planet
Roughness Effects on Dense-Gas Turbine Flow: Comparison of Experiments and Simulations
No full textInternational audienceThis article presents a combined numerical and experimental study of the high-subsonic organic vapor flow in a linear turbine cascade. The profile geometry is the well-documented LS59 highly loaded rotor blade and the working fluid is Novec649, a dense gas used in organic Rankine cycles. Large eddy simulations are carried out with and without the roughness introduced by the additive manufacturing process. The results for the rough blade are in fair agreement with experiments, while the smooth surface induces a change in the vortex shedding regime. A detached shedding, characterized by a long recirculation downstream of the trailing edge and a base pressure plateau, is obtained in the experiments and by discretizing the roughness in the simulation. By contrast, a transonic vortex shedding is established when the surface is smooth: intense vortices roll up immediately after the trailing edge, yielding a short bubble and a lattice of shock waves. A strong pressure drop is observed at the trailing edge, resulting in high profile losses. In both cases, the boundary layer is turbulent ahead of the separation, but its thickness is significantly greater in the rough configuration, which may be the reason for the change of regime
Redefining physiological whole-body alignment according to pelvic incidence: normative values and prediction models
No full textInternational audienceBackground context: Spinopelvic alignment assessment needs to account for pelvic incidence (PI).Purpose: This study aimed at providing normative values for commonly used parameters in whole-body alignment analysis based on PI.Design: Multicentric prospective study.Patient sample: This study included healthy volunteers with full-body biplanar radiograph in free-standing position.Outcome measures: All radiographic data were collected from 3D reconstructions: Sagittal vertical axis (SVA), T1 pelvic angle (TPA), spino-sacral angle (SSA), sagittal odontoid-hip axis angle (ODHA), pelvic parameters, sacro-femoral angle (SFA), knee flexion angle (KFA), ankle flexion angle (AA), Pelvic shift (PSh), lumbar lordosis (LL), thoracic kyphosis (TK) and cervical lordosis (CL).Methods: Population was divided into five groups according to PI. Normative values were described for each group. Linear regressions including age and PI provided prediction formulas for PT, TPA, SSA and SFA.Results: 642 subjects were included. Mean age was 37.7 ± 16.3 years (range: 18-90). Mean PI in the cohort was 49.3 ± 9.5°. LL, PT, SFA, SSA and TPA correlated with PI and age. ODHA, TK, CL and the other lower limb parameters were not associated with PI. All normative values across PI groups are provided for segmental, regional and global alignment parameters. Prediction formulas were: PT=-12.7 + 0.38*PI + 0.14*Age, TPA=-16.9 + 0.34*PI + 0.15*Age, SSA = 109.8 + 0.58*PI-0.19*Age, and SFA = 173 + 0.39*PI + 0.11*Age.Conclusions: SSA, PT, TPA and SFA must be assessed according to patient's PI. This study provides normative values for each PI group, and predictive formulas taking age and PI into account. PI cannot be used to define thoracic and cervical curvatures.Level of evidence: II
Weak trunk extensors in adult spinal deformity patients are related to sagittal malalignment and kinematic limitations
No full textInternational audienceBackground: Adult spinal deformity (ASD) is associated with muscles' degeneration that affects postural control and outcomes of an eventual corrective surgery. Evaluation of ASD is usually based on static radiographs and more recently on functional assessment. However, there has been limited exploration of muscle strength weakness in ASD. The aim was to investigate the relationship between trunk muscles' strength in ASD and its relationship with radiographic and kinematic alterations and quality-of-life decline.Methods: 28 ASD and 18 asymptomatic subjects underwent biplanar radiographs with 3D calculation of spino-pelvic and global postural parameters. 3D movement analysis of gait, sitting to standing and stair ascent, was studied allowing the calculation of head, trunk and lower limbs 3D kinematics. Participants filled out health related quality of life questionnaires. A single operator measured 4 times the strength of the trunk muscles, using a hand-held dynamometer, to assess measurements' reliability. ASD population was divided into two groups based on the strength of trunk extensors: ASD-weak extensors (N = 11 patients having trunk extensors strength0.94). On standing radiographs, the ASD-weak extensors group showed an increased positive sagittal malalignment compared to the other groups (SVA=61 mm vs ASD-normal extensors: 18 mm, controls: -4 mm, p < 0.001). This sagittal malalignment remained during movement (kinematic-SVA=223 mm vs ASD-normal extensors:178 mm, controls:138 mm, p < 0.001). Muscle strength weakness was correlated to the decline of quality-of-life scores (PCS-SF36: r = 0.48, VAS for pain: ρ=-0.39).Conclusions: This study showed that weak trunk extensors are associated with sagittal malalignment in static position, kinematic limitations during daily life activities and reduced quality of life scores. Future studies will investigate the effect of muscle strengthening on both static and dynamic alignment in ASD and their quality of life
Relationship between structure and thermal stability of fluorosilicones at high temperatures
No full textInternational audienceThe thermal stability of fluorosilicones at high temperatures has been investigated with thermogravimetric analysis (TGA) based on their chemical structure (copolymerization and crosslinking), and compounding (incorporation of silica and titanium dioxide particle fillers). This allowed the comparison of thermal degradation kinetics of model samples and commercial fluorosilicones rubbers. Increasing dimethylsiloxane content in copolymers enhances thermal stability, while the presence of vinyl groups accelerates degradation by promoting depolymerization and crosslinking reactions at an earlier stage. In model filled fluorosilicone rubbers (FSR), untreated silica particles were found to destabilize the polymer matrix in the short term, whereas commercial filled FSRs exhibited greater thermal stability due to treated silica surfaces. Additionally, commercial samples crosslinked with DCP mixed with CaCO 3 resulted in the highest thermal stability. FTIR transmission analysis of copolymer residues revealed that degradation does not favor the preferential release of any monomer (dimethylsiloxane or trifluoropropylmethylsiloxane). Elemental analysis of a model homopolymer suggested that depolymerization is the dominant degradation mechanism, but side group scissions also contribute to this process