HAL - Université de Franche-Comté
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Evaluating Robustness of Deep Reinforcement Learning for Autonomous Surface Vehicle Control in Field Tests
No full textInternational audienceDespite significant advancements in Deep Reinforcement Learning (DRL) for Autonomous Surface Vehicles (ASVs), their robustness in real-world conditions, particularly under external disturbances, remains insufficiently explored. In this paper, we evaluate the resilience of a DRL-based agent designed to capture floating waste under various perturbations. We train the agent using domain randomization and evaluate its performance in real-world field tests, assessing its ability to handle unexpected disturbances such as asymmetric drag and an off-center payload. We assess the agent's performance under these perturbations in both simulation and real-world experiments, quantifying performance degradation and benchmarking it against an MPC baseline. Results indicate that the DRL agent performs reliably despite significant disturbances. Along with the open-source release of our implementation, we provide insights into effective training strategies, real-world challenges, and practical considerations for deploying DRLbased ASV controllers
Moisture effects on the transverse compressive behaviour of single flax fibres
No full textInternational audienceStudying the effects of moisture on the mechanical behaviour of single flax fibres, particularly in the transverse direction, is of key importance for the reliable use of biobased composites exposed to varying humidity levels. In this study, the apparent transverse Young’s modulus evolution of single flax fibres is recorded through repeated compressive load/unload cycles conducted at three Relative Humidity (RH) levels— 40 %, 60 %, and 80 %. No significant changes in the apparent Young’s modulus, determined from the unloading, were observed during transverse compression cycling or under increasing humidity conditions. The absence of apparent softening with the rise in RH is attributed to the expression of two antagonistic mechanisms: wall softening due to plasticization and structural stiffening linked to fibre compaction. Intriguingly, a noteworthy transverse stiffening is recorded at 40 % RH following the humidification and drying of the fibre. This outcome is ascribed to a hornification phenomenon
Grid hollow octet truss lattices that are stable at low relative density
No full textInternational audienceStretching-dominated lattice materials are renowned for their lightweight nature and exceptional mechanical properties. These materials, however, have historically struggled with scalability towards low relative densities at which they often exhibit unstable oscillation behavior. Here, we propose a viable solution to this issue by integrating hollow truss elements and a grid distribution into the conventional octet truss lattice. The proposed grid hollow octet truss lattices demonstrate significant improvement over the conventional octet truss lattice, with stiffness and specific energy absorption capacities respectively 25.8% and 98% larger. To quantitatively assess the stability of low relative density metamaterials, three metrics are proposed and validated. The effect on the mechanical properties of the octet lattice of the ratio of inner to outer radius and of the grid number are comprehensively investigated numerically. Numerical simulations indicate that larger geometrical parameters and grid numbers significantly enhance the stability of the octet lattice. Consequently, the proposed lattices exhibit comparable energy absorption capacity as smooth shell lattices at equivalent relative density but demonstrate a more stable nonlinear response, maintaining nearly constant stress levels at a relative density of 0.1. Experimental validation supports these findings, highlighting potential for applications to load bearing and energy absorption
Friction anisotropy dependence on morphology of GLAD W films
No full textInternational audienceScratch tests on tungsten GLAD films examined friction anisotropy at various deposition angles (), normal forces (), and scratching directions (). A linear model of the coefficient of friction () revealed four behavior groups, ranging from isotropic ( = 0°and 30°) to orthotropic ( 60°). Intermediate angles (40° 60°) showed slight non-centrosymmetric anisotropy. Post-scratch analysis linked these behaviors to film morphology. A transition from dense to columnar structures, with columns elongated perpendicular to the atom flux, influenced plasticity. Less deformation occurred along scratching directions ( = 90°/270°) due to column chaining, resulting in higher friction. A mechanical model highlighted how morphology-driven plasticity variations explain the anisotropic behavior
Experimental study of the influence of the vents on the thermal performance of a Trombe wall
No full textInternational audienceThis article presents an experimental study of a Trombe wall made of cellular concrete, associated with different vent configurations. The experiments were conducted in the laboratory using a Trombe wall connected to an adjacent room, under conditions of an intermediate season. The measurements focus on temperature and heat flux measured in various areas of the facility. Five configurations are compared: one with the vents fully open, three with reduced vent surface areas and different positions, and one with the vents fully closed. The impact of the number and position of the vents on the thermal behavior and efficiency of the Trombe wall is measured and analyzed. The results indicate that only the configuration with the vents fully closed exhibits a very different thermal behavior compared to the other configurations. In this configuration, the insulating properties of cellular concrete result in a minimal temperature increase in the room, making it an appropriate solution for maintaining occupant comfort even during summer conditions. Configurations with partially closed vents show generally similar behavior, except when there are significant reductions in vent surface. To effectively limit convective transfer with partial vent closure, a substantial reduction in vent surface (at least 60%) is required
Architected acoustic metamaterials : an integrated design perspective
No full textInternational audienceThe review focuses on architected acoustic metamaterials to manipulate airborne sound waves, with only limited discussions on elastic metamaterials related to solid media. We review the design of acoustic metamaterials and the physical mechanisms underpinning their performance and related manufacturing methodologies, while also examining potential issues and challenges affecting the use of metamaterials in acoustics. The complexities of several metamaterial architectures are discussed. A new classification system is proposed to distinguish metamaterial configurations based on the typology of the channels inside the acoustic meta-atom. Several types of acoustic metamaterials architectures, such as perforated and micro-perforated panels, acoustic foams, resonators, various geometrical paths, and piezoelectric patches, are also discussed. The fundamental acoustic mechanisms of these classes of metamaterials are identified and commented on. The paper also describes the main measurement techniques used for acoustic metamaterials and the physical quantities evaluated, providing a guide to characterize and assess their performance. The fundamental challenges of the current metamaterials designs are discussed, with a focus on the complex synergy between architectural patterns of acoustic metamaterials and their thickness. We clarify the distinction between acoustic and elastic metamaterials, emphasizing the design and applications of materials that manipulate sound waves in fluid media. The paper also offers further comments about the need for practical design tools to allow the use of acoustic metamaterials in real-world applications
An efficient modeling methodology of piezoaeroviscoelastic systems for vibration-based energy harvesting and subsonic flutter suppression
No full textInternational audienceIn the open literature the flutter suppression and vibration-based energy harvesting using, respectively, viscoelastic materials and piezoelectric transducers have been studied by several authors. However, most of the available archives are limited to supersonic flight conditions and, furthermore, few papers have investigated the consequence of using the concept of piezoaeroviscoelasticity on the subsonic flutter suppression and electrical power generation, which motivates this contribution. Thus, the focus is placed on the mathematical modeling and numerical investigations of a two degrees of freedom typical wing section subjected to an unsteady airflow containing discrete viscoelastic mounts and attached to a resistive piezo-shunted circuit. In the modeling of the piezoaeroviscoelastic problem, the complex modulus approach combined with the concept of shift factor and reduced frequency has been retained to represent the frequency- and temperature-dependent behavior of the viscoelastic substructure. To model the unsteady aerodynamic loadings acting on the typical section, it was assumed the well-known linearized thin airfoil theory. Numerical simulations were performed for some design parameters and subsonic flight conditions to demonstrate the main features and capabilities of the proposed modeling methodology and the possibility of increasing the dynamic stability and power generation of the piezoaeroviscoelastic airfoil. In addition, a parametric study has been performed with the aim of evaluating the degree of influence of operating temperature and resistance on the stability and power generation
Invalidité et indemnisation des pertes de gains professionnels futurs : quelle articulation ?
No full textInternational audienceObservations sur Civ. 2, 3 avril 2025, n° 23-19.227L'impossibilité de retrouver un emploi ne peut se déduire du seul classement en invalidité de 2e catégorie par la caisse de sécurité sociale, lequel ne suffit donc pas à justifier l'indemnisation d'une perte totale des gains professionnels futurs
