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Development of a New Laboratory Earthquake Setup Featuring a Paraffin oil-based Gel as Analogue Material
No full textInternational audienc
Mechanical and thermal contributions to the damage suffered by an aeronautical structure subjected to an intense and sudden electrical discharge
No full textInternational audienceLightweight aeronautical structures and power generation structures such as wind turbines are fitted with protection systems designed and certified to withstand severe climatic events such as lightning strikes. During these events, high currents flow through the protection, but are likely to induce effects in the depth of the supporting composite structure and reach or even perforate pressurised tanks. By studying the damage suffered by a structure with different levels of protection, one could predict the damage that could occur in unprotected areas in the event of a partial discharge from power supply cables of future-generation aircraft or power station equipment. However, analysing the damage while the current is being delivered is very difficult and necessarily indirect via remote observations. In order to gain a better understanding of the contribution of mechanical and thermal loading resulting from the electrical source of a high current delivered in a few microseconds, by analysing similarities in the damage generated by a lightning, we carried out test campaigns and simulated laser shocks (mechanical) and electron beam shocks (thermomechanical) and compared them with lightning strike damage. The instrumented experimental environment that has been set up will be used to analyse the sources of damage that can be observed on the digital twin of these experiments. The results presented here are experimental results and corresponding simulations (digital twin) of laser impact tests on composite aeronautical laminates with or without lightning strike protection. The use of numerical simulation makes it possible to validate some hypotheses about the damage behaviour of the CFRP composite laminates tested, compared with traditional quasi-static characterisations. Through comparisons with experiments, the simulation also enables to determine dynamic interface failure thresholds and the tracing of the mechanical contribution of a lightning strike or high current discharge
Transformations systémiques et coopération. Coopérer pour (se) former, (se) professionnaliser, (s’) engager au service de transformations socio-écologiques dans le maritime
No full textInternational audienceCette journée d’étude clôt le projet de formation et de recherche action collaborative HOLI-D Blue (2021-2024) dédié à l’accompagnement des transformations socio-écologiques (TSE) dans les domaines maritimes par la formation et la professionnalisation des étudiant·es, futurs professionnel·les des métiers de la mer et du littoral. En liant expérimentation et recherche, HOLI-D Blue a confirmé la nécessité d’opérer des transformations systémiques à tous les niveaux des curricula de l’enseignement supérieur pour y parvenir. HOLI-D Blue mène en ce sens une réflexion scientifique afférent à la formation des adultes appréhendable comme un écosystème complexe. Pour autant, les relations et interrelations entre les différents éléments de cet écosystème sont encore peu questionnées alors même qu’elles constituent un des leviers clés pour la TSE. Cette journée d’étude propose alors d’interroger ce que peuvent être des coopérations et leurs modalités au service de la TSE, au sein d’écosystèmes de formation
Predicting the impact of wind turbine noise: general overview and results of the PIBE project
No full textInternational audiencePIBE (Prévoir l’Impact du Bruit des Éoliennes – Predicting the impact of wind-turbine noise) is a research project funded by ANR (French National Research Agency) which main objectives are to better understand the noise levels created by wind-turbines and assess noise-reduction solutions. One topic of this project focuses on the propagation of uncertainty. Code_TYMPAN™ is an open-source software for calculating industrial noise in the environment. Its open architecture, implemented by a Python API, allows advanced users to build and solve models programmatically. This open architecture made possible the implementation of a parametrical computational tool (OCP – Outil de Calcul Paramétrique). This tool generates input data, launches the calculations with Code_TYMPAN™, generates and post-processes output data. Thus, sensitivity analysis and propagation of uncertainty were performed on an industrial test case. This development demonstrates the feasability of introducing uncertainties in acoustic engineering studies
Computation of Green's functions for the acoustic scattering by an elastic structure excited by a turbulent flow in water
No full textInternational audienceTo model the hydrodynamic noise produced by an elastic ship hull or propeller excited by a turbulent boundary layer, we need an efficient method to compute the acoustic scattering by an elastic body surrounded by a fluid. In 3D, Boundary Element Methods (BEM) are used to reduce the computational costs, for both the fluid and the elastic body. A natural way to compute the boundary integral representation (BIR) of the sound pressure is to use formulations based on the free space acoustic and elastic Green's functions. However, since the turbulent flow along the elastic body is known only statistically, the use of these Green's functions would be too expensive. A remedy is to compute a Green's function adapted to the physical problem, thus satisfying the transmission conditions of the fluid-structure problem. This so-called "tailored Green's function" is determined by solving a coupled acoustic-elastic problem with the BEM, and leads to a simplified BIR of the sound pressure compatible with a stochastic source term. We first validate the computation of the tailored Green's function over a classic spherical geometry. Then we compare the scattering of multiple quadrupoles by elastic or rigid NACA0012 profiles
Stick to your Role! Stability of Personal Values Expressed in Large Language Models
No full textInternational audienceStandard Large Language Models (LLMs) evaluation contains many different queries from similar minimal contexts (e.g. multiple choice questions). Conclusions from such evaluations are little informative about models' behavior in different new contexts (e.g. in deployment). We argue that context-dependence should be studied as a property of LLMs. We study the stability of value expression over different contexts (conversation topics): Rank-order stability on the population (interpersonal) level, and Ipsative stability on the individual (intrapersonal). We observe consistent trends - Mixtral, Mistral, Qwen, and GPT-3.5 model families being more stable than LLaMa-2 and Phi - over those two types of stability, two different simulated populations, and even on a downstream behavioral task. Overall, LLMs exhibit low Rank-Order stability, highlighting the need for future research on role-playing LLMs, as well as on context-dependence in general. This paper provides a foundational step in that direction, and is the first study of value stability in LLMs
Non-linear fluid-structure interaction of a semi-rigid jib with forestay modeling
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Optimising hydrofoils using automated multi-fidelity surrogate models
No full textInternational audienceLifting hydrofoils are gaining importance, since they drastically reduce the wetted surface area of a ship, thus decreasing resistance. To attain efficient hydrofoils, the geometries can be obtained from an automated optimization process. However, hydrofoil simulations are computationally demanding, since fine meshes are needed to accurately capture the pressure field and the boundary layer on the hydrofoil. Simulation-based optimization can therefore be very expensive.Surrogate models, trained by a limited number of simulations, can reduce the cost for optimization by performing simulations where these are more informative. Furthermore, if an efficient low-fidelity solver is available, multi-fidelity framework can provide a further reduction in required simulations, by combining the accuracy of a few high-fidelity with an exploration of many low-fidelity computations.We propose a hydrofoil optimization procedure based on two simulation codes, a hydrofoil potential flow solver for low-fidelity and a RANS solver for high(er)-fidelity simulations. The RANS solver uses adaptive grid refinement to attain high accuracy with a limited computational budget. Two different multi-fidelity frameworks are compared for a realistic hydrofoil: only RANS based and potential-RANS based. The efficiency for different combinations of fidelity levels is investigated
Bandwidth Spreading With Range Cell Migration in FMCW Automotive Radar
No full textInternational audienceHigh range and speed resolutions provided by FMCW automotive radars are prone to range cell migration in high speed scenarios. The range and Doppler information are smeared through multiple frequency bins in fast an slow-time dimensions, resulting in biased estimations and worsened separation performance. In this paper, the FMCW signal model with inter-pulse range cell migration is derived, the induced bandwidth spreading is illustrated and quantified with simulations. Windowing is shown to mitigate this spreading
Anisotropy of coherent phonon in Bismuth crystal
No full textInternational audienceIn this article, we investigate the coherent A 1 g phonon mode in bismuth crystal using transient reflectivity measurements, focusing on two distinct crystallographic orientations: one with the principal axis ((1 1 1)-direction in the trigonal cell representation) perpendicular to the sample surface, and the other with the principal axis parallel to the surface. Our results demonstrate significant variations in the amplitude, frequency, and lifetime of the coherent phonon mode between these two orientations, even when identical pumping and probing conditions are applied. We attribute these differences to the anisotropy of the electron effective mass, which influences electron mobility and, in turn, affects the phonon dynamics in bismuth