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Imbalance Term in the TKE Budget over Waves
No full textInternational audienceIn an attempt to reconciliate air-sea momentum flux estimates derived from open sea observations, from large eddy simulation output fields, and from wind-wave tank measurements, a series of dedicated experiments were conducted in the wind-wave tank of the Large Air-Sea Facility of Marseille, France. The turbulent friction velocity, upon which the momentum flux depends, was estimated from wind measurements by applying four classical methods including the eddy-covariance method and the inertial-dissipation method. The collected data were used to investigate some characteristics of the waveinfluenced boundary layer that were predicted by previous simulations, and to quantify a wave-dependent term of the turbulent kinetic energy equation, the so-called imbalance term ϕ imb . Our results show that the turbulent stress decreases toward lower heights where the effect of waves is large, as in the simulations, and that ϕ imb is in the range 0.3 to 0.7, which is comparable to the value found with open sea data (0.4). These preliminary results have to be confirmed with wave-following probes, because the estimated eddy-covariance flux slightly varied with height, thus it could not be strictly considered to be equal to a constant total flux
Modelling the hydrodynamic response of a floating offshore wind turbine – a comparative study
No full textInternational audienc
Projections of streamflow intermittence under climate change in European drying river networks
No full textInternational audienceAbstract. Climate and land use changes, as well as human water use and flow alteration, are causing worldwide shifts in river flow dynamics. During the last decades, low flows, flow intermittence, and drying have increased in many regions of the world, including Europe. This trend is projected to continue and amplify in the future, resulting in more frequent and intense hydrological droughts. However, due to a lack of data and studies on temporary rivers in the past, little is known about the processes governing the development of flow intermittence and drying, their timing and frequency, or their long-term evolution under climate change. Moreover, understanding the impact of climate change on the drying up of rivers is crucial to assess the impact of climate change on aquatic ecosystems, including the biodiversity and functional integrity of freshwater systems. This study is one of the first to present future projections of drying in intermittent river networks and to analyse future changes in the drying patterns at a high spatial and temporal resolution. Flow intermittence projections were produced using a hybrid hydrological model forced with climate projection data from 1985 until 2100 under three climate scenarios in six European drying river networks. The studied watershed areas are situated in different biogeographic regions, located in Spain, France, Croatia, Hungary, Czechia, and Finland, and their areas range from 150 to 350 km2. Additionally, flow intermittence indicators were developed and calculated to assess (1) changes in the characteristics of the drying spells at the reach scale and (2) changes in the spatial extent of drying in the river network at various time intervals. The results for all three climate scenarios show that drying patterns are projected to increase and expand in time and space, despite differences in the amplitude of changes. Temporally, in addition to the average frequency of drying events, the duration increases over the year. Seasonal changes are expected to result in an earlier onset and longer persistence of drying throughout the year. Summer drying maxima are likely to shift to earlier in the spring, with extended drying periods or additional maxima occurring in autumn and extending into the winter season in some regions. A trend analysis of extreme events shows that the extreme dry spells observed in recent years could become regular by the end of the century. Additionally, we observe transitions from perennial to intermittent reaches in the future
Développement d’une méthode numérique performante pour la résolution d’un modèle diphasique homogène partiellement déséquilibré en milieu poreux hétérogène
No full textEDF has developed the thermo-hydraulic code THYC-coeur to simulate water flow in the cores of PWRs (Pressurized Water Reactors) and to evaluate the Departure from Nucleate Boiling Ratio (DNBR), an indicator of the margin to the boiling crisis that could threaten core integrity. THYC-coeur mainly solves steady-state problems using finite volume schemes. Although each computation is fast (about 10 seconds for an industrial configuration), the very large number of required simulations (several million) makes code acceleration necessary, which is the main goal of this thesis.The drift-flux models are first presented and analyzed. Several analytical solutions are then constructed. To more easily study certain numerical phenomena, a simplified prototype called ThermoTorch has been developed. After verifying the global numerical scheme in both steady-state and transient regimes, an acceleration method using initialization from neural networks was tested.EDF a développé le code thermo-hydraulique THYC-cœur pour simuler l’écoulement d’eau dans le cœur des Réacteurs à Eau Pressurisée (REP) et évaluer le Rapport de Flux Thermique Critique (RFTC), indicateur de la marge à la crise d’ébullition pouvant menacer l’intégrité du cœur. THYC-cœur résout principalement des problèmes stationnaires via des schémas volumes finis. Bien que le calcul soit rapide (10 s pour une configuration industrielle), le grand nombre de simulations requises (plusieurs millions) rend nécessaire une accélération du code, objectif de cette thèse. Les modèles drift-flux sont d’abord présentés et analysés. Plusieurs solutions analytiques sont ensuite construites. Afin d’étudier plus facilement certains phénomènes numériques, un prototype simplifié, appelé ThermoTorch est développé. Après une vérification en stationnaire et en instationnaire du schéma numérique global, une méthode d’accélération utilisant une initialisation issue de réseaux de neurones a été testée
Évolution de l’hydrologie de surface en France par niveau de réchauffement
No full textCe rapport est une des synthèses des résultats obtenus pour la recharge potentielle des aquifères et les débits. Un rapport spécifique aux évolutions des niveaux piézométriques complète l’analyse réalisée ici. Ce document fait suite aux rapports sur les impacts climatiques examinés par niveau de réchauffement publiés par Météo France. Les analyses réalisées portent sur les recharges annuelles, les débits annuels et saisonniers, le régime hydrologique décrit par les variations des douze débits mensuels moyens, et deux caractéristiques des extrêmes : un débit d’étiage et un débit de crue. L’ensemble résume leurs évolutions au travers de cartes et de tableaux de synthèse. Les réponses à trois grands types d’évolution climatique possibles pour une France à +4°C illustrent les incertitudes
Can Households Drive the Energy Transition?
No full textTo accelerate the energy renovation of buildings necessary to achieve carbon neutrality by 2050, the French government has launched an energy renovation plan for buildings. This plan allocates funds across various subsidy and aid mechanisms for housing renovation. What is the impact of these investment subsidies for energy retrofit on such investment and on the consumption and savings of a homeowner household that is not in fuel poverty? How much subsidy is needed to make homes energy efficient? To answer these questions, we develop a two-period, two-goods model that incorporates "essential baskets", i.e., baskets of goods (with a "minimum energy" level and an "essential composite good"). Investment subsidy for energy retrofit is effective if it is targeted and, this targeting should not be based solely on income. Indeed, we highlight non-monetary side effects as one of the key parameters of policy effectiveness. To be effective and as inexpensive as possible for public authorities, subsidies must depend not only on household income, but also on the cost of the work and therefore on the condition of the housing before the work is carried out. For illustrative purposes, we estimate and calibrate the parameters of the model with data from French households that only use electricity as an energy source for their homes. We determine the subsidies that encourage households to renovate their homes to make them more energy efficient
Understanding Turbulent Systems : Progress in Particle Dynamics Modeling
No full textInternational audienceThis open access book provides a thorough introduction to modeling turbulent, dispersed, two-phase flows. It explains the physical phenomena and governing laws at play, followed by a clear and systematic overview of the statistical tools used to develop simplified or coarse-grained models.With a pedagogical approach, the book uses practical examples to explain complex physical processes and stochastic methods, making it accessible to readers familiar with basic courses in statistical physics and applied mathematics. It also highlights emerging research areas and unexplored challenges in the field.Designed as a self-contained resource, this book is ideal for graduate students and junior researchers in various branches of physics. At the same time, it serves as a valuable reference for experts seeking deeper insights into turbulent, dispersed, two-phase flows
Removing Behavioral Barriers to Energy Renovation: A Discrete Choice Experiment
No full textThrough a discrete choice experiment conducted among French homeowners, we determine whether easing financial constraints through two financing programmes (third-party financing and Energy Efficient Mortgages) leads to an increase in the adoption rate of energy-efficient renovations. We examine whether the introduction of a contractual mechanism that intrinsically promotes trust between the parties (one-stop-shop) can increase the adoption rate.Among other things, our study reveals certain preferences among households with regard to financing energy-efficient home renovations and assesses certain cognitive biases. We find that both financing programmes increase the probability of choosing an energy renovation over the opt-out option. Nevertheless, participants exposed to the mortgage programme have a preference for the status quo (not renovating), unlike those exposed to third-party financing.With the latter financing programme, the effectiveness of the work seems guaranteed, unlike with the mortgage. This explains why the group offered the energy-efficient mortgage is more inclined to choose renovation scenarios that include an administrative facilitator, highlighting the importance of procedural support and risk transfer in the decision-making process.</p
Simulation de la fissuration par champ de phase: Analyse technique de l'initiation et la propagation de fissure
No full textInternational audienceThis study examines numerical biases in phase-field fracture simulations. More specifically, it investigates the influence of meshing on crack path trajectories in phase-field fracture simulations. A reference problembasedonaPureSheartestwithaneccentricinitialcrackisusedtoevaluatetheimpactofspatial discretization on predicted crack trajectories. Phase-field simulations are compared to a reference solution from Linear Elastic Fracture Mechanics, towards which they theoretically converge. Results show that structured meshes introduce artificial anisotropy that forces the crack to follow a mesh-dependent trajectory. Conversely, unstructured meshes enable a more accurate prediction of the expected exponential trajectory. Indeed, the disordered nature of the mesh significantly reduces the artificial anisotropy effects induced by discretization. These observations highlight the importance of mesh selection in crack propagation simulations. Practical recommendations are finally proposed to minimize numerical biases in phase-field simulations.Cette étude propose d’étudier les bias numériques dans les simulations de la fissuration par champ de phase. Plus spécifiquement, elle examine l’influence du maillage sur la trajectoire de fissure. Un problème de référence basé sur un essai de Pure Shear avec fissure initiale excentrée est utilisé pour évaluer l’impact de la discrétisation spatiale sur la trajectoire de fissure prédite. Les simulations par champ de phase sont comparées à une solution de référence issue de la mécanique linéaire élastique de la rupture, vers laquelle elles convergent théoriquement. Les résultats montrent que les maillages structurés introduisent une anisotropie artificielle qui contraint la fissure à suivre une trajectoire dépendante du maillage. En revanche, les maillages non structurés permettent une prédiction plus fidèle de la trajectoire exponentielle attendue. En effet, le caractère désordonné du maillage réduit les effets d’anisotropie artificiels induits par la discrétisation. Ces observations mettent en évidence l’importance du choix du maillage dans les simulations de propagation de fissures. Des recommandations pratiques sont f inalement proposées pour minimiser les biais numériques dans les simulations par champ de phase
Étude du devenir environnemental des polymères anti-tartre par couplage d'une approche de modélisation numérique et expérimentale
No full textThe semi-closed cooling circuits of nuclear power plants are susceptible to mineral scaling and fouling, particularly within condenser systems and cooling towers. To mitigate calcium carbonate deposits, treatment strategies often involve acid dosing and organic scale inhibitors like sodium polyacrylate (NaPA). While effective in preventing scaling, these polymers are discharged into water bodies in dissolved and adsorbed forms, raising environmental concerns due to their affinity for suspended solids, potentially leading to accumulation in riverine ecosystems.To assess the environmental impact of sodium polyacrylate discharges, two aspects must be addressed. First, understanding the polymer’s physicochemical behavior, particularly its adsorption dynamics on mineral surfaces in varying water conditions, is essential. Second, a modeling framework is needed to simulate its fate and transport in dynamic riverine environments. Despite its industrial use, gaps remain in the literature regarding its adsorption kinetics, long-term behavior, and potential ecotoxicological effects.This thesis addresses these gaps through a multidisciplinary approach that integrates laboratory experiments with mathematical modeling. In the experimental component, batch studies characterized the adsorption kinetics and equilibrium behavior of sodium polyacrylate on sediments like kaolin and calcite found in the Seine River. The influence of key environmental variables, pH, temperature, salinity, and sediment type was investigated, leading to the calibration of a zero-dimensional (0D) adsorption kinetics submodel.In the modeling component, both numerical (1D/2D) and analytical (1D) approaches simulated the transport and adsorption of sodium polyacrylate in riverine systems. A two-dimensional numerical model was developed to solve the coupled equations governing solute dynamics, sediment transport, and polymer interactions, incorporating processes like advection and deposition. Analytical solutions provided rapid evaluation tools for predicting polymer transport under idealized conditions.Results indicate that while sodium polyacrylate poses limited short-term risk to aquatic organisms, its long-term accumulation in riverbed sediments may present greater risks to bottom organisms, especially under conditions promoting strong adsorption. Sensitivity analyses highlight the influence of seasonal flow variations, sediment composition, and polymer concentration at discharge points.By integrating experimental findings with modeling, this study offers valuable tools for predicting and assessing environmental risks associated with polymer discharges in aquatic systems.Les circuits de refroidissement semi-fermés des centrales nucléaires sont sujets à l’entartrage minéral et à l’encrassement, notamment dans les systèmes de condenseurs et les tours de refroidissement. Pour limiter les dépôts de carbonate de calcium, les traitements reposent souvent sur l’utilisation d’acide et d’inhibiteurs de tartre organiques, comme le polyacrylate de sodium (NaPA). Bien qu’efficace pour prévenir l’entartrage, ce polymère est rejeté dans les milieux aquatiques, sous forme dissoute ou adsorbée, soulevant des questions sur son impact environnemental en raison de sa forte affinité pour les matières en suspension. Pour évaluer correctement l’impact environnemental des rejets de NaPA, deux aspects sont essentiels. Premièrement, une compréhension approfondie du comportement physico-chimique du polymère et de sa dynamique d’adsorption sur les surfaces minérales est nécessaire. Deuxièmement, un cadre de modélisation est requis pour simuler son transport dans des environnements fluviaux dynamiques. Malgré son usage industriel, des lacunes subsistent concernant sa cinétique d’adsorption et ses effets écotoxicologiques. Cette thèse aborde ces lacunes avec une approche multidisciplinaire intégrant des expériences de laboratoire et de la modélisation mathématique. Dans la composante expérimentale, des études en batch ont caractérisé la cinétique d’adsorption du NaPA sur des sédiments tels que le kaolin et la calcite, présents dans la Seine. L’influence de variables environnementales (pH, température, salinité) a été examinée, permettant de calibrer un sous-modèle de cinétique d’adsorption (modèle 0D).Dans la modélisation, des approches numériques (1D/2D) et analytiques (1D) ont été utilisées pour simuler le transport et l’adsorption du NaPA. Un modèle numérique bidimensionnel a été développé pour résoudre les équations décrivant la dynamique des solutés et les interactions sédiment–polymère, intégrant les processus d’advection et de dépôt. Des solutions analytiques ont été établies pour évaluer rapidement le transport du polymère. Les résultats montrent que le NaPA présente un risque à court terme limité pour les organismes aquatiques, mais son accumulation à long terme dans le lit de la rivière pourrait représenter un risque accru pour les organismes du fond, surtout dans des conditions favorisant une forte adsorption. Les analyses de sensibilité soulignent l’importance des variations saisonnières de débit et de la composition minéralogique des sédiments. En combinant résultats expérimentaux et modélisation, cette étude fournit des outils précieux pour évaluer les risques associés aux rejets de polymères dans les environnements aquatiques