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Unsupervised machine-learning pipeline for data-driven defect detection and characterisation: Application to displacement cascades
No full textInternational audienc
A harmonic balance normal form parametrisation for single mode reduction of nonlinear vibrating systems
No full textInternational audienceThis paper introduces a model-order reduction technique for lightly damped nonlinear vibrating systems. By combining calculation details that are specific to the harmonic balance method, the asymptotic numerical method, and the normal form style parametrisation for invariant manifolds, a complete procedure that can cope with single-mode reduction is detailed. Introducing harmonic decomposition in the process allows for a different treatment of the temporal information of the solution, which comes with advantages as compared to normal form expansions based on polynomial expansions. The computation proceeds with two nested loops on both the harmonics and the polynomial degree expansion. A decisive advantage of the procedure is its ability to compute a new expansion from a known solution, which allows the derivation of amplitudedependent piecewise reduced order models (ROMs), together with an integrated procedure that can switch from the invariant manifolds computation attached to either fixed points or limit cycles. Once the validity limit of a first expansion is met, the procedure can restart from a point where convergence is reached and produce a new ROM. This feature has the potential to overcome the well-known limitations of asymptotic expansions associated with the parametrisation method for invariant manifolds, and is derived here only for conservative systems. The whole analysis also clearly establishes the links existing between the normal form approach and computations based on the harmonic balance combined with the asymptotic numerical method. Examples of increasing complexity, starting from a Duffing equation, a two-degree-of-freedom system and a finite element beam model, are analysed, and comparisons with existing techniques are provided
Experimental and numerical study of microwave heating in sand columns: Water saturation effects on temperature profiles and heat transfer mechanisms
No full textInternational audienceSubsurface heating finds applications in soil remediation and enhanced resource recovery, with microwave heating offering advantages over conventional methods (conductive heating, hot vapor injection). However, the transition from laboratory-scale studies conducted in microwave ovens to in situ applications using embedded antennas in relevant environments remains poorly studied. This study investigates microwave heating mechanisms of a 2.45 GHz coaxial antenna in sand across varying water saturation levels.Results reveal that the reported advantages of microwave heating-rapid and homogeneous temperature rise-require a critical water content. For near-dry sand (<5% water saturation), temperature increased but exhibited steep, non-constant radial gradients. Conversely, at higher saturation levels (14% and 22%), temperature profiles rapidly developed near-constant, reduced gradients. Despite these differences, modeling indicates that thermal conduction, rather than direct absorption, remains the dominant heat transfer mechanism across all tests. Furthermore, the study identifies a significant discrepancy between nominal power and actual absorbed power, highlighting a low conversion efficiency. These results suggest that while microwave heating is effective for moderately saturated soils, further optimization of power and heat delivery is essential to promote its applicability to thermal desorption of polluted soil
Prévisibilité des étiages et évaluation des chaines de prévisions
No full textRapport du WP5 du projet ANR CIPRHE
Assimilation de données pour la prévision des débits d’étiage
No full textWithin the framework of WP3 of the ANR CIPRHES project, data assimilation techniques have been developed and/or evaluated at spatial scales ranging from watershed to the entire country of France. General conclusions common to all of these studies emerge. The first is that assimilating observed streamflows improves the simulation of river flows for historical periods. It appears to have a modest but present effect on low flow forecasts. The results from these studies show a very short persistence of the assimilation contribution in forecasting (less than 10 days). Moreover, the results demonstrate a real interest in terms of operational scores (e.g., anticipating the onset of drought periods). Finally, assimilating groundwater table levels does not seem to improve either the simulation of river flows for historical periods or future river flow forecasts.As a perspective, it is necessary to increase the number of assimilated observation points, either to improve the contribution of assimilation itself, or to enhance the method in order to improve its robustness in more varied hydrological contexts. Finally, the modalities for which a transition to operational use in the PREMHYCE platform could be considered in the future still need to be defined.Dans le cadre du WP3 du projet ANR CIPRHES, des techniques d’assimilation ont été développées et/ou évaluées à des échelles spatiales allant du bassin versant jusqu’à la France entière. Il en ressort des conclusions générales communes à l’ensemble de ces travaux. La première est que l’assimilation des débits observés permet d’améliorer la simulation des débits en périodes historiques. Elle semble avoir un effet modeste mais néanmoins présent sur la prévision des débits d’étiage. Les résultats issus de ces travaux montrent une persistance très courte de l’apport de l’assimilation en prévision (inférieure à 10 jours). De plus, les résultats montre un réel intérêt au regard de scores plus opérationnels (exemple : anticiper le démarrage des périodes de sécheresse). Enfin, l’assimilation des niveaux de nappe ne semble pas apporter d’amélioration ni sur la simulation des débits en période historique, ni sur la prévision future des débits.En perspectives de ces travaux, il est nécessaire d’augmenter le nombre de points d’observation assimilés, soit pour améliorer l’apport de l’assimilation en elle-même, soit pour améliorer la méthode pour qu’elle soit robuste dans des contextes hydrologiques plus variés. Enfin, il reste à définir les modalités pour lesquelles un passage en opérationnel dans la plate-forme PREMHYCE pourrait être envisagé dans le futur
Mean Field Control of Thermostatically Controlled Loads as Piecewise Deterministic Markov Processes
No full textInternational audienceThis paper presents a mean-field control approach for Piecewise Deterministic Markov Processes (PDMPs), specifically designed for controlling a large number of agents. By modeling the interactions of a large number of agents through an aggregate cost function, the proposed method mitigates the high dimensionality of the problem by focusing on a representative agent. The contribution of this work is the application of a PDMP-based mean-field control framework to the coordination of a large population of Thermostatically Controlled Loads (TCLs). Adapting this framework to TCLs requires incorporating a quality-of-service constraint ensuring that each agent's temperature remains within a specified comfort range. To achieve this, an additional jump intensity is introduced so that agents are very likely to switch between heating and cooling modes when they reach the boundaries of their temperature range. This extension to TCLs is demonstrated through Water Heaters (WHs) control, with a decentralized algorithm based on a dual formulation and stochastic gradient descent. The numerical results obtained illustrate this approach on two examples (signal tracking and taking into account energy price)
Virtual Design of Masonry Triplet Shear Tests using Digital Image Correlation
No full textInternational audienceNumerous studies highlight the diverse opportunities offered by multi-view image correlation techniques. For example, in masonry structures, these techniques enable the propagation of cracks to be quantified in joints and blocks. However, many parameters must be considered to transition from measurements to identifying physical parameters. Consequently, it is difficult to know a priori whether the planned experiment will enable for a precise identification of the model parameters to be calibrated. A good practice, detailed in this article, involves designing the experiment through virtual tests. The first step involves positioning the cameras in a virtual setup using Blender by combining near-field and far-field cameras for multiview purposes. Once a numerical model has been selected for nonlinear simulations, the second step involves examining the influence of geometric parameters to optimize the specimen response with respect to the quantities of interest. Last, virtual tests are conducted in Blender to simulate experiments under conditions close to reality. Based on the force data produced by the numerical simulations and the displacement fields measured from images generated during virtual tests, the proposed method enables for sensitivity analyses and uncertainty quantifications to ensure that the model parameters can be calibrated prior to the actual experimental campaign
Assessment of Indium‐Free Transparent Conductive Oxide Back Contacts for High‐Efficiency Ultra‐Thin Cu (In,Ga)Se 2 Solar Cells Down to 250 nm
No full textInternational audienceABSTRACT This work examines the feasibility and performance impact of replacing the usual molybdenum back contact with indium‐free transparent conductive oxides (TCOs) like fluorine‐doped tin oxide (SnO 2 :F) and aluminum‐doped zinc oxide (ZnO:Al) for ultra‐thin Cu (In,Ga)Se 2 (CIGS) solar cells (250–450 nm). Motivated by indium scarcity and cost reduction, these TCOs are evaluated for their figure of merit, stability under Se atmosphere, Na diffusion permeability, and band alignment with CIGS absorbers. Using simulations, prototype fabrication, and comprehensive characterizations, the compatibility of these TCOs with CIGS absorbers is assessed. Solar cells with thicknesses of 450 and 250 nm are fabricated. Their performance was compared under both rear and front illumination, as well as with the use of reflectors. A record efficiency of 8.6% with front illumination is achieved for a 250‐nm CIGS absorber using a gold back reflector with SnO 2 :F, single‐step CIGS deposition, and no heavy alkalines doping. The best rear‐illuminated efficiencies are obtained with ZnO:Al back contacts, reaching 6% for a 250‐nm CIGS, with only a 9% loss in J sc compared to front illumination, confirming a lower surface recombination rate at the ZnO:Al/CIGS interface compared to Mo/CIGS or SnO 2 :F/CIGS interfaces
Eaux, ville et santé : constats, enjeux et solutions
No full textEditorialInternational audienceQu’entend-on par l’eau dans la ville ? Quelle importance pour notre santé ? Dans un environnement urbain toujours plus dense et imperméable, une urbanisation croissante et dans un contexte de changement climatique, l’eau reste indispensable à la vie, son importance pour la santé et le bien-être est indiscutable. L’eau doit être considérée sous toutes ses formes : souterraines, superficielles, pluviales, potables, usées, etc., ainsi que dans tous ses usages et ses bienfaits. Elle est en effet source [...
