Validation du code NS3IFS et comparaison avec des données expérimentales pour des écoulements autour de tabliers de ponts

Dans ce rapport, nous nous intéressons aux effets du vent autour de profils de pont élémentaires. En régime laminaire, plusieurs études ont déjà été effectuées ou sont en cours [19, 1]. Elles ont permis de reproduire quelques caractéristiques globales comme les coefficients aéroélastiques. Cependant, la présence de l'obstacle génère de la turbulence dont l'effet sur le champ de pression qui se développe autour du profil est mal connu. L'objectif est ici de tester et valider les modèles de turbulence mis au point par N. Devaux [6] dans les cas statiques. Les données disponibles fournies par le CSTB de Nantes portent sur les champs de pression autour de trois maquettes : rectangle mince ou épais, viaduc de Millau. L'étude est focalisée sur l'utilisation du modèle k-ε dont on donne une description complète. Des tests de sensibilité sont effectués avant de procéder aux simulations proprement dites. Globalement, les résultats sont assez encourageants. Même si le modèle k-ε présente quelques déficiences dans les zones de recirculation, il reproduit qualitativement et quantitativement les observations expérimentales

Impact of a flood event on the biogeochemical behaviour of a mesotrophic alpine lake: Lake Bourget (Savoy)

International audienceA flood event which occurred during the onset of thermal stratification and of algal growth (March 1996) was studied in mesotrophic Lake Bourget (France). Both physical and biogeochemical processes occurring during this episode were assessed. The dominant effect was a decrease of nutrient concentrations along the river-lake ecotone. This phenomenon seemed mainly linked to biological factors: stimulation of the spring algal and bacterial growth. After the flood, the algae aggregated with allochthonous particles brought by the river and were rapidly eliminated by sedimentation. The effect of this early spring flood, seemed spatially restricted and rather neutral as regards lake water quality. In the lake region crossed by the river plume, the overall effect after the flood was a decrease of P available for the phytoplankton. In the open water, the P concentration was probably not modified by the load supplied by the flood

Impact of a flood event on the biogeochemical behaviour of a mesotrophic alpine lake: Lake Bourget (Savoy)

International audienceA flood event which occurred during the onset of thermal stratification and of algal growth (March 1996) was studied in mesotrophic Lake Bourget (France). Both physical and biogeochemical processes occurring during this episode were assessed. The dominant effect was a decrease of nutrient concentrations along the river-lake ecotone. This phenomenon seemed mainly linked to biological factors: stimulation of the spring algal and bacterial growth. After the flood, the algae aggregated with allochthonous particles brought by the river and were rapidly eliminated by sedimentation. The effect of this early spring flood, seemed spatially restricted and rather neutral as regards lake water quality. In the lake region crossed by the river plume, the overall effect after the flood was a decrease of P available for the phytoplankton. In the open water, the P concentration was probably not modified by the load supplied by the flood

How to evaluate nature-based solutions performance for microclimate, water and soil management issues – Available tools and methods from Nature4Cities European project results

International audienceIn the context of climate change, Nature-Based Solutions (NBSs), a recently developed concept, are increasingly considered as part of the adaptation strategies of the cities. Studies using expert models and methods (EMM) receive a great deal of scientific attention. Considering EMM increasing use, this study aims to perform an analysis of the reported evaluation results, reflecting the capability of the EMM to accurately tackle urban challenges identified within the EU Nature4Cities project. Then, we propose a set of indicators and recommendations about sixteen EMM to be used by funders, researchers and practitioners when evaluating the performance of NBSs. The coupling of the different components (climate, water and soil) is not a simple matter. The analysis relies on the definition of the range of the reported metrics and on the investigation of the relationship between the various indices, applied for the EMM evaluation. Secondly, the study assesses the existing EMM, indicating the potential of NBSs: (i) to reduce urban heat island, (ii) to limit surface warming, (iii) to increase the thermal comfort of people, (iv) to limit the overheating and runoff of surfaces due to impervious areas, (v) to increase water retention during stormy episodes, (vi) to improve storm water quality at the outlet of the sustainable urban drainage systems, (vii) to promote the filtration and epuration of storm water runoff in soil and (viii) to be a support for vegetation. The analysis reveals that EMM can be considered as helpful tools for urban microclimate, urban soil and water management analysis, provided their limitations and characteristics are taken into account by the user when choosing tools and interpreting results (e.g. application scale). With regard to the performance of NBSs, the most commonly used indicators clearly depend on the scale of the project

Advances and challenges in CFD modelling of crop climate interaction in greenhouses, Advances in innovation technology of protected horticulture

International audienc

Advances and challenges in CFD modelling of crop climate interaction in greenhouses, Advances in innovation technology of protected horticulture

International audienc

A contribution to the study of thermal and hydrodynamical behaviour of lake Bourget: density currents and internal waves

National audienceUnderstanding the ecological evolution of a lake requires a good knowledge of the main physical processes which occur there. The thesis analyses two mechanisms closely associated with the hydrodynamic and thermal behaviour of lake Bourget (France) the density currents, which are driven by the river inflows, and the internal waves, which are generated by wind events. Two approaches have been carried out : field surveys (wind data, temperatures and currents in the lake have been collected) on the one hand, and mathematical modelling on the other hand. Both for density currents and internal waves, the mathematical approaches have been validated for academic cases simplified geometry, thermal stratification with two layers. At the environmental scale, numerical results are in good agreement with most of the observations. Following this study, a coupling with anecological model will be implemented