Les Cahiers de RECITS n°12 - 2025: Aux sources de la démocratie technique : la créativité technique

International audienceLe concept de démocratie s’enracine sur diverses périodes et relève de multiples origines géographiques (Athènes, Moyen-Orient, Chine…), autrement dit « la » démocratie est beaucoup plus ancienne, et probablement beaucoup plus multiforme, que ce qu’on imagine. En effet, très souvent, « la » démocratie est considérée comme une réalité unique et universelle or cette dernière s’avère plurielle, loin d’être pensée de la même façon selon les femmes ou les hommes, selon les générations, dans un même milieu. et c’est même cette diversité qui la structure, et qui, en un mot, lui permet de jouer un rôle fondamental dans la société. Quant à « la » technique, elle reste également omniprésente dans les activités de l’espèce humaine, et cela au moins depuis des dizaines de millénaires. Très rapidement, de premiers groupes humains conçoivent et reconçoivent leurs outils issus de cheminements techniques plus diversifiés que ce qu’on imagine habituellement. C’est dire si la variété mais également la trajectoire de ces choix techniques demeurent sur le temps long, inhérentes de l’espèce humaine… et ne relèvent en rien d’une exclusivité du contemporain !La session du XIVe congrès de la Société Française d’Histoire des Sciences et des Techniques qui s’est tenue à Bordeaux en avril 2023 visait à approfondir la connaissance des conditions favorisant la créativité technique et à identifier des moments où le monde de la technique est « interpelé » voire « percuté » par le concept de démocratie technique. C’est une certitude, il n’existe pas d’universalité, ni de solutions techniques à l’échelle planétaire, et c’est bien cette quête de la diversité, de cheminements singuliers, d’acceptation de logiques disruptives qui permettra d’asseoir un peu plus les fondements d’une véritable démocratie technique. N’est-ce pas là, le meilleur héritage que nous pourrons transmettre aux générations à venir

Prise en compte des enjeux de pollution lumineuse sur les sites d’entreprises

International audienceThe gradual use of artificial light at night by human beings is causing light pollution, which has an impact on ecosystems and biodiversity. However, it is difficult to quantify and control, and there are still gaps in our knowledge of its impact. This article presents a methodological framework for taking account of light pollution issues on company sites, while including the safety requirements of industry. First, it proposes a macroscopic analysis to identify their lighting context in order to target priority sites, where the issues relating to lighting and biodiversity will be characterised in greater detail. The aim is then to identify conflicts so that they can be better integrated into the development of a differentiated lighting management plan, with a view to restoring dark infrastructures.L’utilisation progressive par l’être humain de la lumière artificielle nocturne engendre une pollution lumineuse qui impacte les écosystèmes et la biodiversité. Cependant, elle est difficile à quantifier et à contrôler, et des lacunes de connaissances sur ses impacts persistent. Cet article présente un cadre méthodologique qui permet, en intégrant les requis de sécurité des industriels, de prendre en compte les enjeux de pollution lumineuse sur des sites d’entreprises. Il propose tout d’abord une analyse macroscopique afin d’identifier le contexte lumineux de ces sites pour cibler des sites prioritaires. Ces derniers feront ensuite l’objet d’une étude approfondie portant sur les interactions entre éclairage et biodiversité. L’objectif est alors d’identifier les conflits entre les deux enjeux pour mieux les intégrer dans l’élaboration d’un plan de gestion différenciée de l’éclairage, dans une optique de restauration des trames noires

Small Water Impoundments Have Local and Longitudinal Impacts on Carbon Cycling Along a River Network

International audienceDamming may be one of the most significant anthropogenic modifications fragmenting river networks. Damming alters the transport and processing of coarse particulate organic matter (OM), hence influencing carbon (C) cycling, including the production and emission of carbon dioxide (CO 2 ) and methane (CH 4 ). Most studies assessing the impact of dams tend to focus on large impoundments, although small impoundments (< 15 m high) are likely to have notable local‐ and river continuum‐scale effects by fragmenting the river network. We aimed to determine if and how small impoundments affect OM stocks, leaf litter decomposition, and gaseous C emissions to the atmosphere. We monitored 21 sites across an impounded river network in central France over three seasons. We measured in situ diffusive CO 2 and CH 4 fluxes, as well as leaf litter decomposition rates, OM stocks, and OM transport. Two small impoundments and the river reaches immediately upstream and downstream had varying patterns of C emissions, with CO 2 and CH 4 fluxes highest immediately downstream of one impoundment and high seasonal variability in fluxes at the other impoundment. Small impoundments impacted the expected river continuum pattern of OM stocks, but not leaf litter decomposition nor CO 2 emissions. In sum, small impoundments can have contrasting local impacts and combined river continuum‐scale effects on C cycling. Our study highlights the importance of considering both the local‐ and river continuum‐scales when examining river C dynamics and how they are influenced by anthropogenic impacts

Analysis of the interior transmission problem in an unbounded locally perturbed periodic strip

International audienceWe analyze the interior transmission problem in a locally perturbed infinite periodic domain, considering the case where the perturbation intersects the periodic background. An equivalent formulation as coupled quasiperiodic problems is obtained by applying the Floquet-Bloch transform. We perform a discretization with respect to the Floquet-Bloch variable and prove the well-posedness of the semi-discretized problem. We then establish some a priori estimates under regularity assumptions that allow us to prove the convergence of the discrete sequence to the solution of the problem.</div

Optimized Schwarz Methods in Time for Discrete Transport Control

We investigate optimized Schwarz domain decomposition methods in time for the control of the 1D transport equation. In the case of an internal control over the whole domain, the optimization problem can be transformed into a system of two coupled PDEs. We then apply the time-domain decomposition (without overlap) strategy on this PDE system as well as on its discretized counterpart. Under Fourier analysis, we analyse three different iterations: the fixed point iteration, the relaxed iteration and the preconditioned GMRES method. For each case, we propose parameters for the transmission conditions that lead to fast convergence of the method. We illustrate our results by numerical examples

SPH modelling of water flow inside a porous medium using a Riemann based formulation

International audienceSimulating granular flows has been a major concern for thepast decades, with various environmental applications such asavalanches, landslides and scour near fluvial, coastal and off-shore constructions. These phenomena involve a porous matrixundergoing large deformations and characterized by a complexbehaviour. Thanks to its ability to handle large deformationsof the medium, SPH appears as a particularly advantageousmethod to deal with these problems. Various SPH schemesalready exist to model the granular medium behaviour, suchas the ones developed by Feng et al. [1], Bui and Nguyen [2](elastoplastic approach) or Gha¨ıtanellis [3] (elasto-viscoplasticapproach). However, to the authors’ knowledge, none of thesepapers show in their results what the water flow looks like insidethe porous structure while it deforms. Consequently, the presentwork aims at presenting a model to simulate the deformationof a granular medium as well as its infiltration by water. Theporous structure is unsaturated and is considered as a continuousmedium. Infiltrated water flows according to Darcy’s or Darcy-Forchheimer’s laws. Two different sets of particles are used forthis purpose, one for the water phase and an other one forthe porous structure, as done by Shimizu et al [4]. Riemann-based schemes have never been used yet for such purpose,though it proved to give accurate results for both fluid [6]and solid mechanics [7]. As a consequence, a new approachis proposed here by applying Riemann-based formulations onboth fluid and solid media. For the moment, the proposedmodel is not yet finished developing and only simulations withundeformable porous matrix are available for the writing of thisabstract. Results with moving, deformable porous matrix will bepresented during the conference

Prise en compte du "facteur humain" dans les études de dangers de barrages d'EDF

International audienceSince the early days of the industrial era, human performance and human error have played a key role in industrial processes. The way people are trained, the way they work, the way they organize themselves and their working conditions have progressed just as much as the various technologies and the perception of human issues. The world of dams is no exception to these changes. In hazard studies (EDD for the French Etudes de Dangers), inappropriate human actions can constitute initiating events (EI for the French Evènement Initiateur) to the central dreaded event (ERC for the French Evènement Redouté Central). This may be the case, for example, of an untimely valve opening, leading to dangerous phenomena, or of valve non-openings contributing to the attainment of a vulnerability or danger rating. In first-generation SDEs, these initiating events were referred to as “human error”, and the analysis focused on identifying possible errors that could have been committed by the responder. This reductionist approach focuses on the individual as the source of error, ignores social and organizational parameters, and overlooks the fact that, while human beings can make mistakes, they are also capable of overcoming situations in certain configurations. In second-generation ESDs, hazards involving the human factor are referred to as “Socio-Organizational and Human initiating event” (EI SOH). To rate the probability of occurrence of these initiating events, EDF has devised a specific method for dams. This method, known as “ECHO” (Evaluation et Cotation des dimensions Humaines et Organisationnelles) is conceptually inspired by James Reason's work on organizational accidents, and practically by Erik Hollnagel's CREAM method, which postulates that the failure of an action depends on the conditions under which it is carried out. This paper begins with an overview of the history of taking the human factor into account, followed by the genesis of the ECHO method and its main methodological principles (in particular, the 9 dimensions observed in the field and the approach used to propose a rating for SOH hazards). Lastly, future areas for improvement are discussed.&gt;Depuis l'origine de l'aire industrielle, la prise en compte de la performance et de l'erreur humaine dans les processus industriels a fortement évolué. La manière d'être formé, de travailler, de s'organiser ainsi que les conditions de travail ont progressé tout autant que les différentes technologies et que la perception des enjeux humains. L'univers des barrages n'échappe pas à ces évolutions. Dans les études de dangers (EDD), les actions humaines inappropriées peuvent constituer des évènements initiateurs (EI) à l'évènement redouté central (ERC). Cela peut être, par exemple, le cas d'une ouverture intempestive de vanne, induisant des phénomènes dangereux ou bien des non-ouvertures de vanne contribuant à l'atteinte d'une cote de vulnérabilité ou de danger. Dans les EDD de première génération, ces évènements initiateurs étaient appelés « Erreur humaine » et l'analyse se focalisait sur la recherche des possibilités d'erreurs pouvant être commises par l'intervenant. Cette approche réductrice focalise sur l'individu comme source d'erreur, ne tient pas compte des paramètres sociaux organisationnels et oublie que si l'homme est capable de commettre des erreurs, il est aussi capable de rattraper des situations dans certaines configurations. Dans les EDD de deuxième génération, les EI impliquant le facteur humain sont appelés « Evènement Socio-Organisationnel et Humain » (EI SOH). Pour parvenir à coter la probabilité d'occurrence de ces évènements initiateurs EDF a conçu une méthode spécifique aux barrages. Cette méthode, baptisée « ECHO » (Evaluation et Cotation des dimensions Humaines et Organisationnelles) s'inspire, sur le plan conceptuel, des travaux de James Reason sur les accidents organisationnels et sur le plan pratique, des travaux d'Erik Hollnagel avec la méthode CREAM qui postule que la défaillance de l'action dépend des conditions dans lesquelles elle est réalisée. Cette communication présente tout d'abord un historique de la prise en compte du facteur humain, puis la genèse de la méthode ECHO, ses grands principes méthodologiques (en particulier les 9 dimensions qui sont observées sur le terrain et l'approche qui permet de proposer une cotation des EI SOH). Enfin, les axes d'amélioration future sont discutés

Machine-Learning assisted characterization of defects in FeNiCr alloys induced by displacement cascades

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Asymptotic approaches for dealing with distorted crack geometries

A growing, albeit not predominant, way to contribute to the climate transition in the field of fracturemechanics is to refine predictions from damage tolerance approaches used to assess the durability andreliability of sensitive components such as those found in railway, aeronautics, aerospace or nuclearindustries. If it can be certified that the reduced safety margins remain acceptable, the intervals betweenmaintenance operations could be extended, and the replacement of defective parts delayed, therebyreducing the environmental footprint.The aim of Damage Tolerance Approaches is to ensure that the existence of unavoidable defects does notcompromise safety. This involves considering the most unfavorable case of brittle fracture and determiningthe propagation of a preexisting crack under cyclic loading until the Griffith energy fracture thresholdis reached. Currently, this is done using simplified, smoothed-out crack geometries, relying either ontabulated values or Finite Element Methods. Since meshing of the entire structure is required, the lattercurrently struggles to accurately account for the small-scale tortuosity of the crack geometry.This paper aims to show that asymptotic approaches are efficient alternatives to address this challenge.Various aspects of these approaches, along with selected applications, will be reviewed. In addition tosupporting the reduction of safety margins, these approaches also help to ensure that small geometricalperturbations do not lead to unexpected catastrophic failure. Asymptotic methods aim to provide analyticalformulas for the variation of stress intensity factors caused by small-scale crack shape perturbations.Several applications are presented including crack shape evolution, the influence of heterogeneities, andpropagation in general mixed-mode I+II+III condition

Two unsteady solutions of a homogeneous equilibrium model in a porous medium

International audienceWe present in this note two reference one-dimensional unsteady solutions of a HEM model, considering possible heat source terms, and focusing on a steady porous medium. The model is recalled first, then details on exact solutions are provided. Several Equations Of State are discussed