Controllability Properties and Time Minimal Geodesics for Attitude Control With a Single Torque

In this article, we analyze the time-minimal geodesics for the controlledEuler-Poinsot dynamics describing the evolution of the orientationof a rigid spacecraft controlled with a single bounded torque. Wediscuss in detail the two underlying control problems of first thecontrol of the angular velocity of the satellite and second the controlof the attitude, our aim being to describe in fine new closed loopoptimal controls based on the so-called abnormal geodesics which canbe computed thanks to Pontryagin's maximum principle. The angularvelocity of the abnormal geodesics are branches of a cubic which canbe parameterized by P-Weierstrass functionsand they lead to define mechanical gates (or strokes for swimmers)to control the attitude generalizing the stationary rotations of theuncontrolled case. They correspond to representation of attitude transfersdepending upon the internal geometry of the spacecraft and abnormalangular velocities geodesics. In fine, the study will allow to satisfythe constraints in the NiceCube mission that is bounded torqueand time maneuver

Influence of Hydrogen Content on the Ductile Rupture of Advanced High-Strength Steels

International audienceAdvanced high-strength steels exhibit sensitivity to diffusible hydrogen content, mainly observed during tensile testing. Although the initial yield stress and ultimate tensile strength are not significantly affected, ductility decreases with increasing hydrogen content. This sensitivity to diffusible hydrogen depends on strain rate and stress concentrations. This study examines the influence of diffusible hydrogen content on the ductile fracture of DP780GI steel, in the form of 1 mm thick sheets. Samples were prepared with specific geometries, with notches and holes, to study different mechanical states, and fracture tests were performed to evaluate ductility as a function of hydrogen content and stress triaxiality. The local strain rate was around 1 × 10−4 s−1, which is lower than the value used in industrial applications, to enhance the hydrogen sensitivity. A hydrogen charging process was used, including zinc coating removal, electrochemical loading, and electrolytic deposition of a zinc layer to prevent hydrogen desorption. The hydrogen content was measured by thermal desorption analysis after the mechanical testing. It is observed that the maximum local elongation decreases with increasing hydrogen content, with a noticeable effect above 0.25 ppm. Cracks form in areas of maximum effective deformation, and their location varies depending on the geometry of the sample and the hydrogen content. The evolution of the maximum effective strain before fracture shows a significant decrease in ductility with increasing hydrogen content, regardless of the mechanical state

Support, absolute continuity and harmonic moments of fixed points of the multivariate smoothing transform

International audienceConsider the multivariate smoothing transform fixed-point equation: Z=∑i=1NAiZi in law, where N ≥ 0 is a random integer, (Ai)i ≥ 1 are d × d random nonnegative matrices, (Zi)i ≥ 1 is a sequence of independent R+d-valued random variables, independent of (N,A1,A2,…), each Zi having the same law as Z. For each fixed point, under suitable conditions, we describe its support, establish its absolute continuity, and prove the existence of its harmonic moments. The absolute continuity of Rd-valued fixed point in the not necessarily homogeneous case is also considere

Automated Testing and Calibration of Sheet Metal Models

International audienceThe efficient development of high-quality sheet metal components increasingly depends on predictive numerical simulations conducted prior to forming operations. Achieving such accuracy requires precise calibration of constitutive material models that represent the complex mechanical behaviour of metals. Mechanical testing provides the essential data for calibration, revealing material anisotropy, strain hardening, and ductile fracture. However, traditional characterisation approaches are often labor-intensive, time-consuming, and prone to operator variability. Within the phenomenological framework, numerous tests are typically required to capture the full material response, including repeats for statistical reliability, leading to high costs, extended lead times, and data management challenges. To address these limitations, this study introduces an automated mechanical testing platform designed to rapidly acquire experimental data useful for material models. Robotic automation enables fully automated test sequences, ensuring high repeatability and reducing manual intervention. When combined with automated model calibration, this approach provides a direct link between the physical material (metallic sheet) and its virtual mechanical representation

Assessing Collaborative Writing Through NLP: A Case Study on Monomodal Text Co-construction

International audienc

Digital twin-based enhancement of vibration measurements for gearbox monitoring under data scarcity

International audienc

Revue sur les stockage d'énergie thermique horizontal enterré à faible profondeur (HUTES)

International audienceUnderground thermal energy storage (UTES) are widely recognised as one of the most promising technologies for building applications due to their high energy efficiency and low operating costs. In recent years, horizontal underground thermal energy storage (HUTES) have gained recognition as effective solutions for storing intermittent renewable energy. In these systems, heat exchangers play a crucial role as heat-conducting media, with a predominantly horizontal distribution. Many notable studies have been conducted in recent years. However, most existing reviews have focused on vertical UTES, addressing their design, performance and applications, as well as horizontal ground heat exchangers integrated into geothermal heat pump systems, named as Horizontal Ground source Heat Pump. A systematic synthesis analysing the thermodynamic performance of HUTES, enabling the use of energy from renewable resources, is therefore essential. This review aims to summarise the experimental benches and analytical and numerical models of shallow HUTES with linear, spring and spiral loops, as well as their advantages and disadvantages. Evaluations and comparisons between different configurations of HUTES are presented. Particular attention is paid to the various internal and external factors influencing the thermal properties of HUTES: geometric parameters, thermophysical properties of different materials, operating and climatic conditions. Finally, conclusions are drawn on the choices to be made in order to develop the most efficient HUTES. Finally, this review offers suggestions for future developments and recommendations for research directions related to HUTES, providing avenues for further research.Le stockage souterrain d'énergie thermique (UTES) est largement reconnu comme l'une des technologies les plus prometteuses pour les applications dans le bâtiment en raison de son rendement énergétique élevé et de ses faibles coûts d'exploitation. Ces dernières années, le stockage souterrain horizontal d'énergie thermique (HUTES) s'est imposé comme une solution efficace pour stocker l'énergie renouvelable intermittente. Dans ces systèmes, les échangeurs de chaleur jouent un rôle crucial en tant que moyens de conduction thermique, avec une distribution principalement horizontale. De nombreuses études notables ont été menées ces dernières années. Cependant, la plupart des analyses existantes se sont concentrées sur les UTES verticaux, abordant leur conception, leurs performances et leurs applications, ainsi que sur les échangeurs de chaleur horizontaux intégrés dans les systèmes de pompes à chaleur géothermiques, appelés « pompes à chaleur géothermiques horizontales ». Une synthèse systématique analysant les performances thermodynamiques des HUTES, permettant l'utilisation d'énergie provenant de ressources renouvelables, est donc essentielle. Cette revue vise à résumer les bancs d'essai expérimentaux et les modèles analytiques et numériques des HUTES peu profonds avec des boucles linéaires, à ressort et en spirale, ainsi que leurs avantages et leurs inconvénients. Des évaluations et des comparaisons entre différentes configurations de HUTES sont présentées. Une attention particulière est accordée aux différents facteurs internes et externes qui influencent les propriétés thermiques des HUTES : paramètres géométriques, propriétés thermophysiques des différents matériaux, conditions d'exploitation et climatiques. Enfin, des conclusions sont tirées sur les choix à faire afin de développer les HUTES les plus efficaces. Enfin, cette étude propose des suggestions pour les développements futurs et des recommandations pour les orientations de recherche liées aux HUTES, ouvrant ainsi la voie à de nouvelles recherches

La vigne et l’herbe : alimentation et environnement végétal au château de Thouars au XVe siècle

Au XVe siècle, l'image des sires de La Trémoïlle, réputés amateurs de viande, masque une réalité plus nuancée : l'alimentation aristocratique repose avant tout sur le pain et le vin, produits de vastes redevances céréalières et viticoles. Les comptes de Thouars révèlent une consommation végétale bien plus large qu'il n'y paraît : légumes modestement présents, souvent issus de l'autoproduction, mais fruits variés, consommés frais ou secs selon les saisons, parfois valorisés pour leurs vertus symboliques et médicinales. Le végétal intervient aussi dans l'hygiène et la pharmacopée, témoignant de l'influence des savoirs médicaux savants. Autour du château, jardins, vergers, vignes et cultures céréalières structurent un paysage intensément exploité, complété par les ressources forestières. Si la viande domine dans les représentations culturelles de l'aristocratie, les sources comptables mettent en évidence le rôle essentiel et multiforme des productions végétales dans l'économie, la santé et la vie quotidienne seigneuriale

Acceleration of implicit schemes for large systems of delay differential equations

International audienceThe objective is to accelerate numerical implicit schemes for solving large linear or nonlinear delay differential equations. These schemes require solving large linear or nonlinear systems at each integration step, making effective initial guesses critical for rapid convergence. For nonlinear problems, an inexact Newton method is used, whose efficiency depends heavily on the quality of these initial guesses. To generate them, line search or trust-region algorithms are employed -each involving the solution of large linear systems. These linear systems are solved using a Krylov subspace method. Initial guesses are constructed via a Petrov-Galerkin process applied to low-dimensional approximation subspaces derived from previous steps. Error estimates are provided, linking the accuracy of the initial guesses to the timestep size, the scheme's order, and the subspace dimension. Numerical experiments show speedups of up to two orders of magnitude over standard predictor-based methods, when those converge