Portail HAL edf
Not a member yet
11029 research outputs found
Sort by
La rivière et son réseau.: La participation numérique citoyenne, de l’alerte à la mobilisation environnementale
No full textNational audienceLa rivière et son réseau.La participation numérique citoyenne, de l’alerte à la mobilisation environnementale
Comment les machines ont pris la terre: Enquêtes sur la mécanisation de l'agriculture et ses conséquences
No full textInternational audienceL'agriculture numérique – drones, tracteurs connectés, pulvérisateurs de « précision », etc. – est aujourd'hui présentée comme une solution incontournable pour affronter les défis alimentaires et écologiques globaux. Ce projet s'inscrit dans la continuité des politiques d'équipement agricole ayant favorisé la concentration des exploitations et l'intensification des modes de production depuis les années 1950. Les machines agricoles demeurent toutefois des technologies peu débattues et peu étudiées. Quelles sont les organisations économiques et professionnelles ainsi que les politiques publiques qui, hier comme aujourd'hui, promeuvent des technologies intensives en capitaux et gourmandes en énergies fossiles ? Quelles transformations du travail agricole et quelles conséquences environnementales en résultent ? Rassemblant les contributions d'historiens et d'historiennes, de sociologues et d'anthropologues, ce livre éclaire les formes des verrouillages sociotechniques dans lesquels sont pris les agriculteurs et les agricultrices, contraignant leurs choix, augmentant leur empreinte environnementale, limitant la maîtrise de leurs outils de travail, et décourageant leurs velléités de bifurcation
Impact and modeling of topological action among sub-transmission grid units
No full textInternational audienceThe rise in renewable energy sources, storage, and flexibility means decentralizes power injection among the grid, and new congestions occur on the sub-transmission grid (60 to 150 kV, just below the extra-high voltage). It becomes pertinent to include, in EHV grid models for power flow studies, some of the sub-transmission units. However, congestions appearing on a static representation of the sub-transmission could in reality be solved with topological actions and shall not lead to curtailment. Moreover, the operation plan remains unknown when working with open data. This article analyses the impact of 1-move topological actions, and proposes a methodology to model subtransmission with its incertitude on operation plan and potential 1-move topological actions
Opinion of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) on the risks to human health associated with the proliferation of Ostreopsis spp. on the Basque coast
No full textN/AInternational audienceIn France, the presence of marine microalgae of the genus Ostreopsis has been identified repeatedly on the Mediterranean coast for several years, whereas on the French Basque coasts its presence is much more recent. In the summers of 2021 and 2022, major Ostreopsis flowering episodes were reported on the Basque coast, resulting in several hundred cases of intoxication among holidaymakers and residents. The main route of human exposure is inhalation of aerosols, although it is not yet known whether the agents responsible for poisoning are Ostreopsis cells, cell debris, known toxins produced by Ostreopsis, or other as yet unidentified compounds. Other routes of exposure (dermal contact, eye contact, ingestion of contaminated water or seafood) are also possible. Poisoning is manifested through various signs and symptoms, occurring within 48 hours of exposure (Neurosensory and neurological, respiratory, dermal and digestive). This document presents the opinion of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), established from the work of its WATER and ERCA Expert Committees. ANSES received a request from the Directorate General for Health (DGS) and the Directorate General for Food (DGAL) to update knowledge about Ostreopsis that had been reported in the Agency's opinions from 2007 and 2008 (ANSES, 2007 and 2008), and draw up specific recommendations for managing Ostreopsis proliferation on the Basque coast. The literature review conducted as part of this expert appraisal revealed that knowledge about the genus Ostreopsis (diversity, biology, ecology, toxins produced) is still too fragmentary to characterise the hazard and risk to human health. Nevertheless to help local authorities affected by Ostreopsis blooms, Agency proposes a surveillance and quality monitoring strategy based on collaboration between site managers and the regional health agencies (ARSs), applicable to sites currently subject to bathing water quality monitoring and water sports sites that meet the conditions below
Modélisation des transferts de chaleur et de masse dans une centrale photovoltaïque flottante : utilisation de la méthode des frontières immergées
No full textNational audienceLes centrales photovoltaïques flottantes présentent de nombreux avantages, notamment en termes d'optimisation de la ressource foncière, de potentiel de refroidissement des modules, et de réduction de l'évaporation. La modélisation numérique par la méthode des frontières immergées est utilisée pour simuler les transferts de chaleur et de masse dans une centrale flottante, offrant une certaine finesse dans la modélisation de la géométrie. Les résultats numériques sont confrontés à des essais en soufflerie et une application au photovoltaïque flottant présente les premiers résultats de l'impact sur le taux d'évaporation
Caractérisation expérimentale et modélisation de la dispersion atmosphérique en vent faible et en milieu bâti
No full textAtmospheric dispersion in low-wind conditions is frequently underrepresented or even overlooked in impact studies. Under these conditions, the dispersion mechanisms experience significant alterations: turbulence properties (spectrum, anisotropy) change considerably, and meandering characterized by low-frequency oscillations on the sub-mesoscale of wind direction often becomes dominant, leading to a wide range of concentration variations around the source. Developing models that integrate these processes is especially challenging due to the lack of experimental data for such scenarios, particularly in urban environment.This thesis includes both experimental and modeling components. The experimental work, carried out at SIRTA (Site Instrumental de Recherche par Télédétection Atmosphérique, situated on the campus of École Polytechnique in Palaiseau, a peri-urban area), has two parts. The first part focuses on a statistical analysis of high-frequency wind component measurements over a three-year period to investigate the characteristics of meandering and its interaction with turbulence. The second part involves conducting and analyzing measurement campaigns to acquire experimental data on the dispersion of a tracer gas (Helium) in built environments under low-wind conditions.The modeling component focuses on defining and validating a CFD modeling methodology using the open-source software Code_Saturne, adapted to these specific conditions, and relies on documented cases from the experimental campaigns, especially those featuring meandering. Three approaches of the RANS (Reynolds Averaged Navier Stokes) or URANS (Unsteady Reynolds Averaged Navier Stokes) types are examined:- a steady-state simulation with constant boundary conditions;- a pseudo-transient simulation combining multiple steady cases, conducted with different input conditions to capture the temporal variability of meteorological conditions during the release;- a fully transient simulation with variable boundary conditions.To validate these different approaches, comparisons were made between the modeling results and the measurements, covering both dynamic variables and tracer concentration.La dispersion atmosphérique en conditions de vent faible est souvent mal prise en compte voire négligée dans les études d’impact. Dans de telles conditions, les mécanismes de dispersion subissent des modifications importantes, les propriétés de la turbulence (spectre, anisotropie) sont sensiblement différentes, et le méandrement, caractérisé par des oscillations de basse fréquence à l’échelle sub-meso de la direction du vent, devient souvent prédominant, entraînant une forte variation de la concentration sur une large plage angulaire autour de la source. Le développement de modèles prenant en compte ces processus est d’autant plus difficile que l’on constate un manque de données expérimentales pour ce type de situations, notamment en milieu bâti.La thèse inclut un volet expérimental et un volet modélisation. La partie expérimentale réalisée au SIRTA (Site Instrumental de Recherche par Télédétection Atmosphérique, installé sur le campus de l’école Polytechnique à Palaiseau en milieu péri-urbain) comporte deux parties. La première est dédiée à l’analyse statistique de mesures haute fréquence des composantes du vent sur une période de trois ans pour étudier les propriétés du méandrement et son interaction avec la turbulence. La seconde consiste en la réalisation et l’analyse de campagnes de mesures pour acquérir des données expérimentales de dispersion d’un gaz traceur (Hélium) en milieu bâti et en conditions de vent faible. La partie modélisation porte sur la définition et la validation d’une méthodologie de modélisation CFD avec le code open source code_saturne adaptée à ces situations, en s’appuyant sur les cas documentés pendant les campagnes expérimentales, notamment ceux présentant du méandrement. Trois approches de type RANS (Reynolds Averaged Navier Stokes) ou URANS (Unsteady Reynolds Averaged Navier Stokes) sont étudiées :- une simulation en régime stationnaire intégrant des conditions aux limites constantes ;- une simulation pseudo-instationnaire impliquant une combinaison de cas stationnaires, réalisée avec différentes conditions d'entrée représentatives de la variation temporelle des conditions météorologiques pendant le rejet ;- une simulation en régime instationnaire avec des conditions aux limites variables. Dans le but de valider les différentes approches, des comparaisons entre les résultats de modélisation obtenus et les mesures ont été réalisées, tant pour les variables dynamiques que pour la concentration du traceur
Modélisation de la dispersion atmosphérique en conditions de vent faible en environnements complexes : application à une expérimentation d'émission de traceur sur un site industriel
No full textInternational audienceContext: Modeling atmospheric dispersion under low‐wind conditions in complex built environments is crucial for risk assessment near industrial sites. The combination of challenging atmospheric conditions, such as flow recirculation, turbulence anisotropy, plume meandering, and heterogeneous infrastructure makes accurate prediction of pollutant transport particularly difficult.Objective: This study aims to evaluate the performance of the high‐resolution ComputationalFluid Dynamics (CFD) model code_saturne (developed by EDF R&D and CEREA) under complexatmospheric and environmental conditions. The assessment is based on data from a controlledtracer release experiment conducted at an industrial site characterized by dense infrastructure andheterogeneous surface features
Multidecadal trends in CO<sub>2</sub> evasion and aquatic metabolism in a large temperate river
No full textInternational audienceRivers play a critical role in the global carbon cycle. However, the environmental and hydro-climatic factors that control the direction and magnitude of river CO2 fluxes across seasons and multidecadal periods are poorly constrained. The origin of excess river CO2 – delivered by soils, wetlands and groundwater or produced by aquatic respiration of organic matter – remains an important unknown in linking terrestrial and aquatic carbon budgets. To address these knowledge gaps, we report on a 32-year high-frequency dataset (1990–2021) from the Loire River, a large, temperate river that underwent a shift from a phytoplankton-dominated regime to a macrophyte-dominated regime around 2005. We estimated daily river-atmosphere CO2 flux (FCO2) and river net ecosystem productivity (NEP) from hourly pH, alkalinity, dissolved oxygen, water temperature and solar radiation. We demonstrate that: (i) annual FCO2 varied an order of magnitude among years (range = 200–2600 g C m2 yr−1) with a long-term decrease trend, mainly linked to decreased groundwater contribution; (ii) the mean annual contribution of internal CO2 production from net ecosystem respiration to total FCO2 was 40 %, increasing from 37±27 % in phytoplankton-dominated regime to 57±10 % in macrophyte-dominated regime; (iii) while the river predominantly acted as a CO2 source, it occasionally functioned as a CO2 sink (FCO2<0) during summer, though this sink behavior constituted a minor component (−0.6 %) of the FCO2 budget; and (iv) FCO2 exhibited strong seasonality linked to discharge, exhibiting hysteresis where FCO2 levels at equivalent discharge were 1.5 to 2 times higher during the rising limb (autumn) compared to the falling limb (spring). The magnitude of this hysteresis diminished in the later macrophyte-dominated regime, indicating a reduced seasonal control by discharge on FCO2. This study demonstrates that river FCO2 and its source are dynamic within and across years, driven by hydro-climatic variations and biological activity. Catchment-scale hydrogeological changes (including groundwater and surface water interactions) can be a more dominant driver of long-term riverine CO2 evasion than in-stream ecological regime shifts (transitions from phytoplankton-dominated to macrophyte-dominated communities), controlling the balance between internal and external CO2 production
Comparison of the environmental balances of different nuclear power cycles
No full textInternational audienceThe French National Plan for the Management of Radioactive Materials and Waste (PNGMDR) 2022-2026 asks CEA and the industrialists to assess the environmental impacts of different spent fuel reprocessing options for evolving nuclear reactor fleets. Within the new starting fleet, comprising 1650 MW EPR2 reactors, three options have been considered. A life-cycle assessment (LCA) has been performed through a model using GaBi™ software, enabling to determine the most impacting factors along the different stages of the nuclear cycles
A mixing length model for arbitrary geometry
No full textInternational audienceAbstract We present a novel phenomenological model for the mixing length used in turbulence models. It accounts for the nonlocality of the Reynolds stress tensor without introducing transport or integral equations. It has however the advantage of naturally accounting for the object's geometry while satisfying the standard symmetries of the Navier-Stokes equations. We investigate the model for the classical channel and pipe flows to characterize its main findings. We calibrate the three model parameters to recover the damping in the viscous sub-layer, the log-law of the wall, and the outer region behaviors. Our model compares favorably to friction factor measurements in the pipe flow at high Reynolds numbers and provides analytical predictions of the mixing length for several canonical flows