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Assessing Abnormal Proximal Junctional Angles in Adult Spinal Deformity
No full textInternational audienceStudy design: Multicentric retrospective study of prospectively collected data.Objective: Based on normative data from a cohort of asymptomatic volunteers, this study sought to determine the rate of abnormal values of proximal junctional angles (PJA) in adult spinal deformity (ASD) surgery patients, and compare it with PJK rate. Summary of BackgroundData: Proximal junctional kyphosis (PJK) definition does not take the vertebral level into account. Methods: This study included 721 healthy volunteers and 824 ASD surgery patients with 2year postoperative follow-up. Normative values for each disc and vertebral body between T1 and T12 were analyzed, then normative values for PJA at each thoracic level were defined in the volunteer cohort as the mean±2 standard deviations. PJA abnormal values at the upper instrumented vertebra (UIV) were compared with Glattes' and Lovecchio's definitions for PJK in the ASD population at two years.</div
Science Arts & Métiers (SAM) is an open access repository that collects the work of Arts et Métiers Institute of Technology researchers and makes it freely available over the web where possible
No full textInternational audienceThe present paper analyzes separately the effect of the features of the typical AM defects on the fatigue resistance of Ti-6Al-4V alloy. To do so, different defect population in terms of sizes and morphologies were obtained by varying the L-PBF process parameters. The distance of these defects with respect to the surface was also controlled. A uniaxial fatigue testing campaign (R = −1) has then been conducted. The results have showed great influence of the nature of the defect population on the fatigue strength of Ti-6Al-4V alloy, for the case of surface crack initiation. The results have also allowed to quantify the criticality of internal defects with respect to their sizes and showed that the defect morphology has no influence on the fatigue strength for the case of internal crack initiation
Linking lacunarity to inertial particle clustering: Applications in solar photovoltaics
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Embedding Mo 2 O 2 S 2 ‐Bis(thiosemicarbazone) Complexes Into Polyurethane Matrices: Synthesis and Characterization
No full textInternational audience[Mo V 2 O 2 S 2 ] 2+ ‐based thiosemicarbazone complexes are an interesting family of molecules, which can display various biological properties. However, in order to develop applications, it is necessary to shape this type of complex, in polymer matrices for example. In this article, we report the synthesis of a series of 16 composite materials corresponding to the incorporation of [(Mo 2 O 2 S 2 ) n (L 1–6 ) n ] ( n = 1, 2) bis‐thiosemicarbazones complexes in a polyurethane matrix. These composites are described as [Mo V 2 O 2 S 2 ] 2+ –thiosemicarbazone‐based polyurethanes and denoted PU‐[(Mo 2 O 2 S 2 ) n (L 1–6 ) n ] ( n = 1, 2). Various [(Mo 2 O 2 S 2 ) n (L 1–6 ) n ]–bis‐thiosemicarbazone complexes were used including di‐ or tetranuclear structures with different numbers of uncoordinated amino and hydroxyl groups and alkyl substituents on the ligands L i ( i = 1–6). The composite materials obtained are studied in depth by SEM–EDX, FT‐IR, NMR, TGA, and DSC to understand the organization of polymer chains and complexes within the materials and to highlight certain changes in physical properties induced by the nature of the complexes. The complexes are homogeneously distributed within the polymer matrices and the embedding of these complexes seems to be mainly due to hydrogen bonding networks. Nevertheless, these H‐bond networks are strong enough to provoke modification of the physical properties of the polymers in terms of thermal stability or flexibility
Thermohydraulic assessment of mixing behaviors and entropy generation using pseudoplastic fluids in short microfluidic devices
No full textInternational audienceThermal mixing fluids in chaotic microdevices have significant importance in many potential applications and have enormous utility in thermal engineering processes. In microfluidic devices, The Two-Layer with Crossing Channels Micromixer (TLCCM) emphasized its efficiency in thermally homogenizing Newtonian fluids, which inspired us to investigate its performance using pseudoplastic fluids. A numerical comparative investigation has been carried out to evaluate the thermal mixing performances of pseudoplastic fluids in laminar steady flows using four chaotic microdevices: TLCCM, L, OH and OX. Quantitative validation of pseudoplastic fluids within a complex geometry, subject to constant heat flux, has been done. Navier-Stokes, the mass conservation, energy and species transport equations have been solved numerically employing CFD code. The pseudoplastic fluids consist of carboxymethyl cellulose solutions, which are characterized using the power-law model, the flow behavior index ranging from 0.75 to 1 and the generalized Reynolds number ranging from 0.2 to 70. To quantify the thermal mixing efficiency, the effects of the fluid behavior index, the generalized Reynolds number, on the thermal mixing degree for the proposed micromixers are presented, where high thermal mixing degrees have been obtained which evolve between 0.9 and 0.99. The entropy generation due to heat transfers and fluid pressure drops has been introduced versus the generalized Reynolds numbers for different fluid behavior indexes. The Bejan number values evolve close to 1. The probability density function PDF (%) at the TLCCM micromixer exit is localized in a narrow range that refers to the ideal temperature value for mixing, which is 315 Kelvin, whatever the fluid behavior index value
A FFT-based mesoscale continuum dislocation mechanics with defect energy: Applications to composites and polycrystals
No full textInternational audienceA crystal plasticity elastoviscoplastic FFT (fast Fourier transform) formulation with a mesoscale continuum field dislocation mechanics model is presented, which incorporates a defect energy density that depends on GND densities and an associated material length scale. This allows to thermodynamically derive internal length scale dependent intra-crystalline backstress and Peach-Koehler force acting on GND densities. The model considers GND density evolution through a filtered numerical spectral approach, which is coupled with stress equilibrium through the elastoviscoplastic FFT algorithm. The discrete Fourier transform (DFT) method together with finite difference (FD) schemes is applied to solve both the backstress tensor and the Fourier-Green operator. Numerical results are first reported for two-phase laminate composites with plastic single crystal channels and elastic precipitates for shear loadings. Channel size effects are simulated and analyzed on the overall and local hardening behaviors during monotonous loadings. In addition, the evolutions of GND densities and the role of their associated backstress on size effects are examined during reversible shear loading. In a second part, the role of the defect energy internal length scale on polycrystal's hardening during tension-compression is discussed. The results are compared to those obtained using FFT-based continuum field dislocation mechanics without defect energy
Instabilités et émergence de structures cohérentes dans l'écoulement de canal plan turbulent
No full textTurbulent flows are characterised by a marvellous phenomenology combining chaos and order, fluctuations on multiple scales and recurrent patterns named coherent structures. The aim of this thesis is to elucidate certain physical processes involving coherent structures in the turbulent channel flow. Different numerical techniques are implemented towards this aim, with a common ground: investigate how coherent structures become unstable and, eventually, generate new coherent structures on different scales. This investigation is divided in three parts.In the first part, the generation of extreme dissipation events is considered. Nonlinear optimal perturbations are computed with respect to a fully turbulent snapshot and the dynamics induced by these perturbations is analysed and compared to the dynamics of naturally occurring extreme events, establishing a connection between the two. Interestingly, the nonlinear optimal perturbation works towards a destabilisation of near-wall streaks, suggesting that an instability of streaks is a possible cause of extreme events.In the second part, the instability of streaks is adressed more directly but in a different direction. A linear stability analysis is performed on an array of periodic streaks in order to show that these structures undergo sub-harmonic or detuned instabilities with unstable modes characterized by large wavelengths (several times larger than the streaks wavelength). These instabilities are related to the large-scale motions (LSMs) observed in experiments and direct numerical simulations of high-Reynolds number flows.In the third part, the large-scale linear instability of streaks is revisited at low Reynolds number in order to capture the wavelengths and the critical Reynolds number of the instability leading to laminar-turbulent patterns. The thesis concludes with the development of a nonlinear model for laminar-turbulent pattern formation. Ideas, limitations and possible directions to improve this model are tested and discussed.Les écoulements turbulents se caractérisent par une phénoménologie remarquable combinant chaos et ordre, fluctuations à de multiples échelles et motifs récurrents appelés structures cohérentes. L'objectif de cette thèse est d’élucider certains processus physiques impliquant des structures cohérentes dans l’écoulement turbulent de canal plan. Différentes techniques numériques sont mises en œuvre dans ce but, avec un fil conducteur commun : étudier comment les structures cohérentes deviennent instables et, finalement, engendrent de nouvelles structures cohérentes à d’autres échelles. Cette étude est divisée en trois parties.Dans la première partie, la génération d’événements extrêmes de dissipation est examinée. Des perturbations optimales non linéaires sont calculées par rapport à un champ instantané pleinement turbulent, et la dynamique induite par ces perturbations est analysée et comparée à celle des événements extrêmes se produisant naturellement, établissant ainsi un lien entre les deux. Fait intéressant, la perturbation optimale non linéaire agit vers une déstabilisation des stries proches de la paroi, ce qui suggère qu’une instabilité de ces stries pourrait être à l’origine des événements extrêmes.Dans la deuxième partie, l’instabilité des stries est abordée plus directement, mais sous un angle différent. Une analyse de stabilité linéaire est effectuée sur un réseau périodique de stries afin de montrer que ces structures subissent des instabilités sous-harmoniques ou désaccordées, caractérisées par des modes instables de grande longueur d’onde (plusieurs fois supérieure à celle des stries). Ces instabilités sont reliées aux mouvements de grande échelle (Large-Scale Motions, LSMs) observés dans les expériences et les simulations numériques directes d’écoulements à nombre de Reynolds élevé.Dans la troisième partie, l’instabilité linéaire à grande échelle des stries est réexaminée à faible nombre de Reynolds afin de déterminer les longueurs d’onde et le nombre de Reynolds critique de l’instabilité menant à la formation de motifs laminaires-turbulents. La thèse se conclut par le développement d’un modèle non linéaire de formation des motifs laminaires-turbulents. Les idées, les limitations et les pistes d’amélioration de ce modèle sont testées et discutées
Predictive Modeling of EMC Disturbances in a Current-Mode Controlled AC/DC Buck Driver for LED Lighting
No full textInternational audienceThis paper addresses the significant conducted electromagnetic noise (EMC) generated by compact, currentmode controlled (CMC) AC/DC Buck drivers used in LED lighting. The study's main objective is to establish a robust analytical model to accurately predict the EMC noise spectrum across the switching frequency range without requiring timeconsuming physical measurements. The modeling methodology focuses on identifying the primary noise generation mechanisms (Common-Mode and Differential-Mode) linked to high dV/dt and dI/dt transitions of the power switches. Crucially, the model integrates key parasitic elements (e.g., loop inductances and inter-winding capacitances) often ignored, which are essential for accurate noise prediction. The proposed approach involves (1) developing a noise source model, (2) characterizing coupling paths via LISN and line impedance modeling, and (3) simulating the final noise spectrum. Validation against laboratory measurements (CISPR 15 compliant) demonstrates a high correlation with the predicted values. This predictive model offers engineers a powerful tool for designing optimized EMC filters a priori, thereby substantially reducing design iterations and accelerating the development of compliant, high-density power electronics solutions.</div
IdeAM: A Serious Game to Foster Creativity in Additive Manufacturing
No full textInternational audienceThis study investigates the potential of serious games (SG) to enhance creativity in additive manufacturing (AM). While AM offers unique opportunities to explore complex designs, traditional manufacturing methods often limit designers’ creativity due to cognitive biases formed by years of using conventional processes. This research aims to introduce IdeAM, a SG designed to foster creativity in AM and help overcome these cognitive constraints.The IdeAM game was developed using the DICE framework (Define, Imagine, Create, Evaluate) with iterative feedback from both users and experts. The game immerses participants in creative scenarios through its content, rules, and aesthetic, encouraging the exploration of AM’s 4 key complexities as defined by Gibson: shape, hierarchical, functional, and material complexities.To evaluate its effectiveness, participants were divided into focus and control groups. The performance was assessed based on 3 aspects: creative solution generation, AM technical potential use, and participant experience. The results show that IdeAM significantly improved participants' creativity and their ability to explore AM’s technical potential. Additionally, participants reported higher motivation and engagement compared to the control group.The originality of this work lies in its novel integration of creativity in AM into a serious game, an area that has received limited attention in existing literature. The impact of this study extends to future SG initiatives in AM, with implications for both educational and industrial applications
REDUCED ORDER MODELING (ROM) EQUIPPED WITH RANDOM FOREST FOR STRUCTURAL DYNAMICS ANALYSIS
No full textInternational audienceThis work introduces a novel minimally intrusive Proper Orthogonal Decomposition (POD)-based method for parametric dynamic structural analysis, addressing computational challenges posed by varying material properties such as Young's modulus or thickness. By leveraging two machine learning models-one predicting the mass matrix and the other the stiffness matrix for a given set of parameters-the approach significantly reduces computational demands while ensuring high accuracy. Validated through 65 case studies across different parameter sets, the methodology demonstrated stable and accurate displacement predictions, with most cases achieving errors within 1-2%. Larger discrepancies observed for the lowest thickness, caused by high oscillations in the dynamic modes' coefficient, were effectively mitigated using Savitzky-Golay filtering. These results underline the method's capability to provide parameter-specific reliability and computational efficiency, positioning it as a promising solution for real-time digital twin applications in dynamic structural analysis