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Mode Competition Phenomena and Impact of the Initial Conditions in Nonlinear Vibrations Leading to Railway Curve Squeal
No full textInternational audienceCurve squeal is a highly disturbing tonal noise produced by railway vehicles on tight curves, primarily attributed to lateral sliding at the wheel-rail interface. An essential step to estimate curve squeal noise levels is to determine the nonlinear self-sustained vibrations, for which time integration is a commonly used method. However, although it is known that the initial conditions affect the solutions obtained with time integration, their impact on the limit cycles is often overlooked. This study investigates this aspect for a curve squeal model based on falling friction and a modal reduction of the wheel and provides some insights on the mode competition phenomena and the nature of the final limit cycles obtained. The paper first details the curve squeal model, stability analysis, as well as the initial condition derivation, and then discusses the time integration and limit cycle results in both time and frequency domains. The results reveal two primary families of limit cycles that can be obtained for both types of initial conditions. The cases where stationary vibrations result in a quasi-periodic regime converge to a unique limit cycle which displays three fundamental frequencies corresponding to specific wheel modes, plus harmonic interactions among them
Comparison of surface layers responses under heavy truck loadings on new and rehabilitated pavement with different interface bond conditions
No full textInternational audienceThe integrity and functionality of road pavements are vital for ensuring safe and efficient transportation networks. However, surface layers are prone to various forms of deterioration. This study investigates the responses of two pavement structures—one newly constructed and one rehabilitated—under traffic loading, through experimental tests conducted on an accelerated pavement testing facility and numerical simulations using the Viscoroute©2.0 software. Focus is placed on surface layer behaviour, with an emphasis on understanding the behaviour of interfaces between the asphalt layers. The findings show that the new pavement structure exhibits good bonding and continuous strain distribution, while the rehabilitated pavement structure exhibits partial sliding at the interface and strain discontinuity. For the new pavement structure, the strains are well predicted using a bonded interface, while for the rehabilitated pavement structure, the strains are predicted using a thin elastic interface layer with a low elastic modulus
Comportement de fatigue des sols traités à la chaux et/ou aux liants hydrauliques
No full textInternational audienceLes ouvrages en sols traités sont traditionnellement utilisés pour renforcer les couches de forme des infrastructures linéaires de transport comme les routes, les autoroutes et les lignes ferroviaires à grande vitesse. Récemment, l’usage du traitement s’est diversifié, pour les ouvrages hydrauliques comme les digues. Ces nouvelles utilisations soulèvent de nouveaux défis pour la durabilité de ce type de matériaux et d’ouvrages pouvant être exposés à des charges cycliques mécaniques. La compréhension du phénomène de fatigue devient ainsi un enjeu crucial pour garantir la stabilité de ces constructions pendant toute leur durée de vie. Afin de mieux appréhender le phénomène, une base de données a été créée en compilant des résultats expérimentaux de laboratoire disponibles dans la littérature. Elle comprend environ 430 essais étudiant le comportement en fatigue d’éprouvettes de sol traité à la chaux et/ou aux liants hydrauliques routiers. Le type de sol, les paramètres d’état, le temps, les conditions de cure, les conditions d’essais ainsi que les résultats sont synthétisés afin de pouvoir mener une analyse croisée sur un nombre important d’essais. En particulier, l’impact du temps de cure est étudié afin de déterminer son effet sur le comportement en fatigue des matériaux
Cédric Quertier, Guerres et richesses d’une nation. Les Florentins à Pise au xive siècle
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Evaluation of the feasibility of 3D-printed Ti-6Al-4V assembled bone plates
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La formation du sujet entrepreneur dans une agence de design thinking
No full textInternational audienceS’inscrivant dans les recherches récentes sur les identités et subjectivités des professionnels de la création, cette recherche examine le processus de performativité du sujet entrepreneur chez les travailleurs créatifs, intégrés au sein d’une organisation. Elle s’appuie sur le cadre théorique de la performativité de Butler et sur une ethnographie réalisée auprès des designers d’une agence de design thinking. Les résultats préliminaires révèlent que les designers se doivent d’être polyvalents et d’avoir l’esprit « team leader », résonnant avec les dimensions d’autonomie et de responsabilité des discours entrepreneuriaux. Ces prescriptions se retrouvent dans le contenu du travail, au travers de pratiques collaboratives (jeu, cadrage, illustration, rythme) impliquant de nombreux outils et processus organisationnels. La réalisation de ces pratiques peut être source de tensions (stress, frustration, épuisement) et diffère entre les designers. Certains d’entre eux incarnent le sujet entrepreneur avec succès, tandis que d’autres en sont exclus ou adoptent une posture plus ambiguë (détachement, résistance)
An agent-based modeling of rescue operations for the evaluation of short-range flash flood forecasts
No full textInternational audienceThis paper presents the application of an agent based model to evaluate how short-range flood forecasts may improve the emergency management of a severe flash-flood event. The considered flood hit several inhabited areas in the Aude River basin, south-eastern France, in October 2018. Particularly, the capacity to trigger timely rescue operations at the right places is evaluated and compared, depending on the input information used in the emergency decision process: from rainfall observations up to flash flood impacts forecasts at the river reach scale. To achieve this evaluation, the field operations of firemen rescue teams are simulated in an agent-based model, which provides a detailed description of the complexity of the emergency situation: location and timing of flood damages, limited number of rescue teams, traveling times, decisions taken under uncertainty about the future evolution of the event. The flash flood impacts forecasts involved in the decisions are obtained using (i) three different short range (0-6h) quantitative precipitation forecast (QPF) products or a naive zero future rainfall scenario, (ii) a distributed hydrological model and (iii) a simple impacts model evaluating the number of flooded buildings. The presented results confirm that the efficiency of the rescue operations is generally improved when using QPFs as input of the decision chain, due to the increased anticipation. But they also illustrate how this added value can be highly altered by the combined effects of forecast uncertainties (false alarms) and limited available rescue means. In a fictive situation where rescue means are extremely limited, using a zero future rainfall scenario proves to be almost as efficient as using QPFs
No time like the future? Towards a generative, prospective and possibilities‐focussed ‘futures social psychology’
No full textInternational audienceAnticipating, considering and incorporating possible futures are central components of human social life. Our social actions, beliefs, values and interactions are all oriented towards, or away from, various future outcomes. Yet despite this, social psychology is yet to harness its unique contribution to our understanding of the future, not addressing the challenges that many other disciplines are confronting in this emerging discipline. In this editorial, we introduce our special issue on ‘futures social psychology’, and in doing so, we provide a starting point for scholars interested in furthering research in this area. We outline previous important discipline‐specific and methodological contributions, connecting social psychological perspectives to the wider academic and practitioner landscape. We outline how our eleven special issue contributions advance discussion, theorizing and research methodology on topics such as sustainability, collective group continuity, prefigurative politics, AI sentience and degrowth policies. Finally, we encourage social psychologists of all topic and methodological persuasions to adopt a generative, prospective and possibilities‐focussed approach to their work, to ensure that social psychology as a discipline can effectively meet the challenges of the future and maximize its impact
Transient Slip Rates as a Key Control on Laboratory-and Natural-Earthquake Nucleation
No full textInternational audienceThe transition from slow, stable slip to rapid seismic rupture is a key yet incompletely understood phase of earthquake development. Using laboratory experiments designed to reproduce earthquake-like fault behavior, we document a wide spectrum of nucleation processes preceding dynamic rupture. In our experiments, the onset of nucleation follows a small foreshock, and the slip velocity resulting from this foreshock controls both the duration and width of the nucleation phase. This relationship, observed in the lab and mirrored in data extracted from natural earthquakes, suggests that the pace of early slip is a fundamental parameter governing rupture growth. These results are consistent with a novel framework that couples rate-and-state friction to a fracture energy that evolves with rupture speed, emphasizing two controlling factors: a characteristic slip impulse and the level of overstress. Interestingly, while foreshocks often mark the start of nucleation, we also find that under certain parameter ranges, small slip transients can transition directly into full rupture without a discrete foreshock. Our findings provide new constraints for linking precursory slip and foreshock activity to earthquake nucleation physics, providing estimates of the state evolution slip distance for the nucleation phase of real earthquakes
From foreshock to mainshock: transient slip velocity sets nucleation time
No full textInternational audienceUnderstanding how fault slip transitions from slow, stable motion to fast, dynamic rupture is critical for improving earthquake models, yet the governing physical conditions remain uncertain. We present results from controlled laboratory experiments that simulate earthquake-like ruptures. These experiments capture a broad range of nucleation behaviors, including precursory slip and foreshock activity. We observe a consistent relationship between the characteristics of early slip events and the subsequent rupture dynamics. Specifically, transient slip rates following a foreshock predict both the duration and extent of the nucleation phase; this trend is reflected not just in the laboratory data but also along certain natural faults. Preliminary analysis suggests that these behaviors align with theoretical models incorporating velocity-dependent fracture energy and rate-and-state friction. Our findings point toward a set of parameters that may help distinguish when early slip evolves into a full rupture. This work is ongoing and contributes to a broader effort to connect lab-based rupture processes with observations from natural earthquakes