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Mid-to-High Frequency Energy Analysis of One-Dimensional Media Based on Second Strain Gradient Theory
No full textInternational audienceAccurate prediction of vibrational energy transmission in slender structures is essential for the analysis and design of modern mechanical systems, particularly at micro-and nano-scales and in mid-to-high frequency regimes. In this work, an energy-based vibroacoustic framework for one-dimensional viscoelastic rods and Euler-Bernoulli beams is developed using second strain gradient theory. Energy methods are especially suitable in this frequency range, where displacement-based numerical approaches become computationally inefficient and less robust, while physically relevant quantities such as energy density, energy flux, and injected power govern the system response. By incorporating higher-order strain terms, second strain gradient theory enables more accurate modeling of microstructural features and small-scale heterogeneities that are not captured by conventional continuum formulations. Analytical expressions for strain and kinetic energy densities and energy flux are derived within the SSG framework. Numerical investigations illustrate the influence of second strain gradient effects on wave propagation characteristics and vibrational energy distribution, highlighting the enhanced predictive capability of the proposed approach for mid-to-high frequency vibroacoustic analysis of one-dimensional media.</div
Reduced Thermomechanical Model of Transient Rotordynamics Resulting From Radial Rotor-Stator Contact
No full textInternational audienceThe present study focuses on the turbine transient dynamics when operating in a standalone mode. In a gas turbine engine, this state corresponds to the turbine stages being disconnected from the compressors. As a result, the rotordynamics of the turbine is governed by two opposing torques: one from aerodynamic forces, assumed constant, and the other from radial rubbing within a labyrinth seal on the turbine disc. The primary objective is to quantify the transient rotational speed and ensure it remains within the safety limits for motor integrity. Given the anticipated high levels of heat generation, it is also crucial to evaluate contact temperatures to identify regions vulnerable to melting wear. This paper presents an example in which the rotor is modeled using Timoshenko beam elements, while the stator is represented by 3D finite elements to capture the assembly details of the seal and housing components. To optimize computation time, reduction methods are applied to the stator's thermomechanical model, simplifying the contact treatment to a 2D problem. The rotorstator system is then solved in the time domain using Carpenter algorithm, which predicts a response in backward precessional motion with intermittent contact before transitioning to a dry whip regime. Frequency analysis reveals that this shift is triggered by resonance in coupled rotor-stator modes. The frictional torque ultimately reaches levels sufficient to decelerate the turbine, while also causing temperature rises above the melting point.</div
ClayPhys: Towards Toolkits that Support Making Expressive Data Physicalization
No full textInternational audienceExisting toolkits for data physicalization prioritize ease of use and adoption by novices. This is often achieved by limiting the affordances of the materials used and constraining design possibilities. The result is limited opportunities for creating expressive physicalizations. To address this limitation and to better understand how to support the creation process of expressive physicalizations, we created ClayPhys, a low-fidelity data physicalization toolkit designed to encourage making expressive data physicalizations. Our toolkit consists of clay, clay work tools, instruction and documentation handbooks, and warm-up activities that scaffold the design process. We studied the use of ClayPhys in a one-day workshop with nine expert participants. From our analysis of participants' created data physicalizations, we observed that using ClayPhys, participants could map data to different visual and physical variables, and that their designs incorporated various data interaction styles. Informed by our findings, we discuss implications for designing higher-fidelity expressive data physicalization toolkits
Quantitative and Qualitative Evaluation of IES TM-30 Indices for the Color Preference of Landscape Oil Paintings
No full textInternational audienceANSI/IES TM-30-24 Annex E provides guidelines for evaluating the color rendition performance of interior lighting, which is incorporated in the latest ANSI/IES RP-30-20 standard as a guide for museum lighting designers. However, one general guideline may not be suitable for all types of museum exhibitions. This study investigates the relationship between TM-30 indices and preference for landscape oil paintings, assesses the applicability of TM-30 color preference criteria, and examines whether the results depend on the painting color composition. Nine 3000 K lighting spectra were systematically generated with varying Rf, Rg, and best-fit ellipse rotation angles ψ on the color vector graph. Through a two-alternative-forced-choice paired comparison, the preference of 18 participants for six landscape oil paintings with various colors was evaluated. Their choices were converted to quantitative interval scores for each spectrum. Based on the statistical difference between scores, the preference criteria were adjusted by lowering Rf thresholds and dividing the most preferred level into two levels. The less-strict Rf requirement might be attributed to the lack of memory color for unfamiliar paintings. Repeated measures ANOVAs revealed that the six paintings can be classified into two groups of three paintings: a high-Rcs,h1-preferred group and a high-Rg-preferred group. Quantitative answers from participants to questionnaires provided potential methods for categorizing paintings into these groups. This study concludes with three recommendations for narrowing the selection of luminaires for landscape oil paintings: one for each group, and the adjusted preference criteria for paintings that cannot be clearly classified into either group
Sound Scattering by Shear Layers of High-Speed Isothermal and Hot Turbulent Jets
No full textInternational audienceThe scattering of sound waves by turbulent shear layers is investigated for jets with acoustic Mach numbers between 0.3 and 1.3 and temperatures equal to 1, 1.5, or 2.25 times the ambient temperature, computed by large-eddy simulations (LESs) in previous work. Sound scattering is studied by solving the two-dimensional linearized Euler equations using the LES unsteady axisymmetric flowfields as the base flow. An acoustic source radiating at Strouhal numbers between 3 and 27 is placed on the jet axis two diameters downstream of the nozzle exit. For all jets, sound scattering is mainly related to the large-scale shear-layer turbulent structures, and spectral broadening occurs, yielding components on both sides of the source frequency. These components have amplitudes increasing strongly with Mach number and slightly with jet temperature and usually form two lobes in the sound spectra. However, for a jet Mach number of 0.9, no lobes clearly emerge upstream of the source because of the leakage of upstream-propagating guided jet waves. An additional lobe associated with the initial shear-layer instability waves is also seen at low Mach numbers. Finally, for hot jets, sound scattering is caused by both the jet velocity fluctuations and the temperature fluctuations
Ice-rubber friction mechanisms across scales
No full textInternational audienceRubber-ice friction is governed by the coupled contributions of viscoelastic adhesion and interfacial heating. This work provides unique in situ / in operando insight into the friction mechanisms from the macroscopic to the molecular scale using combined experimental measurements and analytical modelling approches. Simultaneous force and real contact area imaging were used to quantify the real shear stress of SBR-silica elastomers spanning a small-strain, low-frequency shear-modulus range of 1-8 MPa (low glass transition temperature, ∼−60◦C) during pure sliding over 50 µm.s−1-1 m.s−1 and environmental temperatures down to −30◦C. The normalized real contact area exhibited a non-monotonic velocity dependence; together with a bell-shaped shear stress-velocity curve, this revealed three friction regimes: at low velocity, adhesion and viscoelastic dissipation dominated over thermal effects; near the peak, frictional heat generation increased; and at high velocity, thermally driven mechanisms, including advection-dominated heat removal, became more significant, with the possible occurrence of localized interfacial melting. No bulk melting was observed. The novelty of this work relies on bridging the scales in ice-rubber friction mechanisms. At the macroscopic scale, a simple thermal analysis of the rubber-ice sliding interface yielded a dimensionless average contact temperature that collapsed across all compounds and test conditions considered. At the molecular scale, a Chernyak-Leonov kinetics was used to describe elastomer chain attachment/detachment on ice and its temperature dependence. Successfully confronting our experimental results to this multiscale modeling lead to a predictive interfacial shear stress model that, when supplied with measured real contact area, reproduced both the magnitude and shape of the friction response
The Verification Gap in AI Accessibility: A Meta-Analysis of Architectural Paradigms and Agency Deficits
No full textInternational audienceAI-powered accessibility systems have shifted from transcription to interpretation, creating a verification paradox: blind and low-vision (BLV) users, who most rely on AI-generated narratives, lack perceptual redundancy to detect errors such as hallucinations or semantic drift, resulting in an agency deficit. Through a systematic meta-analysis of 17 empirically evaluated AI accessibility systems (2019--2025), we examine how architectural choices shape verification affordances. We introduce the Verification-Cognition Balance Index (VCBI), a composite metric quantifying trade-offs between validation rigor, user agency, complexity, and risk. Our analysis uncovers weak overall balance across the field, with transformer-based systems showing higher risk density than classical computer vision with no gain in validation rigor. Only hybrid specialized architectures—constraining AI to narrow semantic subtasks—achieve good balance in our corpus, though this finding is preliminary given the small number of such systems evaluated. We argue for a necessary paradigm shift in evaluation from system accuracy to user verifiability. Our findings suggest that for high-stakes accessibility, task-specific constrained AI outperforms general-purpose models in epistemic safety and user empowerment
A characteristic mapping method with source terms: Applications to ideal magnetohydrodynamics
No full textInternational audienceThis work introduces a generalized characteristic mapping method designed to handle non-linear advection with source terms. The semi-Lagrangian approach advances the flow map, incorporating the source term via the Duhamel integral. We derive a recursive formula for the time decomposition of the map and the source term integral, enhancing computational efficiency. Benchmark computations are presented for a test case with an exact solution and for two-dimensional ideal incompressible magnetohydrodynamics (MHD). Results demonstrate third-order accuracy in both space and time. The submap decomposition method achieves exceptionally high resolution, as illustrated by zooming into fine-scale current sheets. An error estimate is performed and suggests third order convergence in space and time, which is in agreement with the numerical results
Bilateral parking procedures
No full textWe introduce the class of bilateral parking procedures on the integer line. While cars try to park in the nearest available spot to their right in the classical case, we consider more general parking rules that allow cars to use the nearest available spot to their left. We show that for a natural subclass of local procedures, the number of corresponding parking functions of length r is always equal to . The setting can be extended to probabilistic procedures, in which the decision to park left or right is random. We finally describe how bilateral procedures can naturally be encoded by certain labeled binary forests, whose combinatorics shed light on several results from the literature