Portail HAL edf
Not a member yet
11029 research outputs found
Sort by
A review of TELEMAC-2D numerical schemes for modelling two-dimensional free surface flows
No full textInternational audienceWe review the numerical scheme of the open-sourcesoftware TELEMAC-2D for the two-dimensional shallow waterequations for flood forecasting. The TELEMAC-MASCAREThydro-informatics system is an open-source software suite that isdesigned to model a wide range of free-surface flow phenomenain both river and maritime hydraulics. Since the start ofthe TELEMAC project in 1987, TELEMAC-MASCARET hasundergone numerous updates that have made it a widely usedtool for engineering applications in hydraulics. We provide acomprehensive discussion of the mathematical model and itsboundary conditions; we discuss the temporal discretizationwhich is based on a time-splitting approach; we present thespatial discretization based on the finite element method; finally,we describe the correction step for handling wet-dry fronts
Effect of the operating temperature on the degradation of solid oxide electrolysis cells
No full textInternational audienceThe present work aims to better understand the effect of operating temperature on the degradation of Solid Oxide Electrolysis Cells (SOECs). The studied SOECs consist of LaSr CoFeOCeGdO (LSCF-GDC) oxygen electrode, GDC diffusion barrier layer, YZrO (YSZ) electrolyte and Ni-YSZ hydrogen electrode. Durability tests are carried out at 750, 800 and 850 °C for 2000 hours at -1 A•cm , using 10/90 vol.% H/HO and dry air at the hydrogen and oxygen electrodes, respectively. The electrochemical impedance spectra measured before and after ageing reveal a strong evolution related to the hydrogen electrode, while the change in the oxygen electrode contribution remains negligible. A set of advanced characterization techniques are employed to study the cell degradation. For the hydrogen electrode, a large Ni depletion is observed after ageing, which increases with the operating temperature. The analysis of the oxygen electrode shows an elemental inter-diffusion between the LSCF-GDC/GDC/YSZ layers on the manufactured cells that seems to not evolve significantly upon operation. Moreover, the presence of SrZrO is not detected in the pristine cell and in the operated ones. Besides, only a limited LSCF decomposition is found in good agreement with the electrochemical characterizations. Hypotheses that could explain the good oxygen electrode stability are discussed
Active Learning of (small) Quantile Sets
No full textInternational audienceGiven an expensive-to-evaluate black-box function, one is often interested in retrieving the set of inputs leading to outputs with given properties within a parcimonious number of function evaluations. In this work, we consider a multivariate function with both deterministic and uncertain inputs and focus on the estimation of a "quantile set": a set of deterministic inputs leading to outputs whose probability of belonging to a critical region is bounded by a given threshold.Previous work (R. Ait Abdelmalek-Lomenech et al., Bayesian sequential design of computer experiments for quantile set inversion, to appear in Technometrics) gave satisfying results in this task, but proved to be insufficient for the estimation of sets whose size is small relatively to the whole domain of deterministic inputs. To tackle this issue, we propose a Gaussian processes-based sequential acquisition strategy in the joint space of deterministic and uncertain inputs. The provided strategy, coupled with a sequential Monte Carlo framework, allows to retrieve small quantile sets
Hybrid Modeling for In Situ Artificial Fish Spawning Ground Stabilization
No full textInternational audienceErosion generally reduces the resilience of replenished gravel in rivers. As a result, structures are sometimes added to modify the upstream flow and stabilize artificial spawning grounds. In particular, rows of boulders can be placed around the replenishment area to limit the transport of replenished gravel during flood events. This study aims to optimize the arrangement of these rows, based on field experiments as well as physical and numerical models. A combined hydro-sedimentary numerical model is calibrated and validated by comparing simulated and measured morphological evolutions in nine laboratory experiments. The results show that boulders positioned downstream of the replenishment slow down the flow above the replenishment, decreasing shear stress over the gravel. The stabilization efficiency depends on both the positioning of the boulders and the arrangement of the replenished surface. To achieve sustainable spawning, prospective scenarios using the numerical model highlight the need to limit the width of the replenishment area. Experiments demonstrated that when the replenishment area spans the entire width flume, the erosion rate is significantly higher compared to a narrower replenishment area placed close to the edges. This effect is attributed to increased flow velocities in the center of the channel, leading to increased shear stress and gravel erosion
Converting from primary to final energy and back: the controversial consequences of making electricity like any other energy resource
No full textInternational audienceSituating itself in the STS-inspired economic anthropology, this paper draws attention to the essential role played by metrics and their metrology in the constitution of ‘energy resources’ (Callon, 1998; Mallard, 1998; Copper, 2015; Neyland et al., 2017). It does so by examining two publicly held and heated discussions that took place intermittently during the years 2019 to 2021 in France. These were related, for one, to the choice of a primary versus final energy metric to express the energy performance of buildings and, for the other, to the setting of the primary energy factor of electricity. These discussions took place in the context of the reform of the French building code and of the energy label of buildings, the Energy Performance Certificate (EPC). While the EPC is traditionally expressed in primary energy, a 2019 law opened the way for a change toward final energy. In the parlance of energy accounting, ‘primary’ energy is the energy as it is ‘found in nature’ before being transformed to be use as ‘final energy’. ‘Final energy’ is the energy metric of consumption, it reflects the energy that needs to be mobilized in order to deliver an end-use service such as lighting a bulb, powering a motor or warming an electrical resistance in direct electric heating. By convention, in France at least, there is no difference between primary and final energy for oil and gas. One kWh of crude oil is equal to one kWh of heating oil despite it having been considerably transformed through refining. On the other hand, electricity which does not exist in primary form since it cannot be ‘found in nature’, is multiplied by a conversion coefficient to be expressed as primary energy. This coefficient is called the ‘primary energy factor’ (PEF) and is, by definition, conventional. It has long been set at 2.58 in France (while it was 2.1 at the European level), a calculation that was supposed to reflect the composition of the electricity production mix with the perennially complex question of the estimation of the efficiency of nuclear power plants. Expressed in final instead of primary energy, the energy performance of dwellings heated with electricity (around 30% of French dwellings) would have been automatically upgraded via the division by 2.58 of their electricity consumption. While the 2019 law had been finally discarded and the EPC remains in primary energy, the PEF has been revised to 2.3 and a carbon metric added to the EPC rating. This paper will retrace the debates and controversies surrounding these metrological reforms. In the course of those debates, arguments were held as to the triggering effect that such metrological choices would have both on the ‘infrastructures of production’ (the energy mix) and on the ‘infrastructure of consumption’ (thermal properties of buildings and heating systems), (van Vliet et al., 2015 ; Shove and Trentmann, 2019). It will thus contribute to the thinking on energy resources by emphasizing the role played by metrology and the ‘politics of calculation’ in energy policy-making (Niskanen and Rohracher, 2022). It complements sociological approaches that advocate to unpack concepts such as ‘energy’ or ‘fuels’ to account for the richness and diversity of what people do in practice and that is obscured by the use of such terms (Shove and Walker, 2014; Bridge et al., 2018). The paper shows that these aspects are carefully discussed during the conception phase of energy policy as its metrology has structuring consequences on the energy mix and on the demand-side composition. The paper points at the crucial role of metrology in constituting electricity as an homogeneous energy resource that can be compared to others but also merged with them and circulate as a stable entity from the national energy accounting system to the building stock dashboard to the commercialization of housing
Consequences of climate change in the Rhône River on the swim performance and metabolism of Alburnoides bipunctatus
No full textInternational audienceNowadays, global warming is a real issue and the first in line to be impacted by temperature increase are ectotherms. Indeed, their body temperature depends on environmental temperature, which is a factor that influences biochemical and physiological reaction rates as well as body condition. We studied two different populations of a pelagic fish, Alburnoides bipunctatus, that were caught mid-February 2024 upstream or downstream the Bugey nuclear power plant, located along the Rhône River. Indeed, as the water is warmer downstream the power plant, this river section can be regarded as a “future condition” considering global warming. So, we wondered whether downstream fish had different adaptations regarding swim performance and whole-body metabolism compared to the upstream ones. Both populations were maintained at 12°C before and during experimentation. 12 fish from each group went through a Ucrit protocol, which is the most known method to measure swimming performance in fish and can be considered as a proxy of the fish’s general fitness and well-being. This allowed the measurement of SMR, MMR and aerobic scope (AS), as well as the net cost of transport for each swimming speed.We supposed that upstream fish would be in better condition than downstream ones, but that the latter would probably have a higher metabolism as they live in a warmer environment. Our results show that upstream fish have a greater Ucrit than downstream ones, indicating that they may be in better condition. Their SMR, MMR and AS are also higher, meaning that upstream fish have a greater capacity to increase their aerobic metabolic rate above maintenance levels. However, upstream fish are smaller than downstream ones, so there is an effect of size on our results. So, even though most of the fish are juveniles, our results could be driven by the metabolic theory of ecology
Fragmentation temporelle de la demande énergétique en Europe : impact du changement climatique sur la manœuvrabilité du système énergétique
No full textInternational audienceThe energy demand in Europe is projected to be affected by climate change in the future. The heating needs are expected to decrease while the cooling needs are expected to increase.The study investigates the impact of climate change on the temporal fragmentation of heating and to a lesser extent cooling needs and its implication on the energy power system. Ten bias-corrected and downscaled simulations from CMIP6 at 25 25 km2 horizontal resolution over Europe have been used to estimate change in heating and cooling energy needs under four anthropogenic scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5), using heating degree days (HDD) and cooling degree days (CDD) as proxies. Consistent with already published literature, here updated using the last CMIP6 simulation ensemble, the results show a large decrease of HDD over Europe and an increase of CDD under all scenarios. However, the study goes one step further by showing a fragmentation of the periods of heating needs during winter in the future which can potentially lead to a fragmentation of heating energy demand. In the worst-case scenario, periods of heating needs could be separated by up to 7 days, 9 times per winter. The cooling needs in summer are expected to be more frequent and last longer compared to the present climate. The fragmentation of temperature-sensitive energy needs for heating and to a lesser extent for cooling are expected to have an operational and economical impact on the balancing of the energy system
Accelerated construction of projection-based reduced-order models via incremental approaches
No full textInternational audienceWe present an accelerated greedy strategy for training of projection-based reduced-order models for parametric steady and unsteady partial differential equations. Our approach exploits hierarchical approximate proper orthogonal decomposition to speed up the construction of the empirical test space for least-square Petrov–Galerkin formulations, a progressive construction of the empirical quadrature rule based on a warm start of the non-negative least-square algorithm, and a two-fidelity sampling strategy to reduce the number of expensive greedy iterations. We illustrate the performance of our method for two test cases: a two-dimensional compressible inviscid flow past a LS89 blade at moderate Mach number, and a three-dimensional nonlinear mechanics problem to predict the long-time structural response of the standard section of a nuclear containment building under external loading
La recharge des véhicules électriques en copropriété. Enquête sur la difficulté à faire advenir les infrastructures collectives de recharge pour véhicules électriques
No full textInternational audienceLes politiques de transition environnementale soutiennent depuis plusieurs décennies, en France, l’avènement du véhicule électrique, qui représente, depuis peu, une part conséquente des ventes de véhicules individuels. Son essor a d’abord concerné les ménages résidant en maisons individuelles, l’accès au VE pour les résidents des logements collectifs n’étant pas si aisé (lieux de stationnement non contigus aux logements, coûts d’infrastructure en amont des points de charge, et difficulté de prise de décision collective cf. Brisepierre et Pierre, 2023, en cours de publication). Cela contribue à poser la question de la diffusion du véhicule électrique en immeuble comme un problème d’équité sociale : il est crucial qu’il soit rendu accessible à tous les segments de la population.Les récents décrets de la Loi d’Orientation des Mobilités (LOM) se sont donc donnés pour objectif de favoriser la recharge dans les bâtiments collectifs. Bien plus, ils cherchent à aller plus loin que les solutions du « droit à la prise », qui permettent certes d’accéder relativement facilement à un point de charge en immeuble, mais ne facilitent pas les démarches collectives – voire les entravent. L’enjeu est de taille, puisqu’il s’agit d’imaginer des systèmes plus durables et globalement moins consommateurs à terme (en Euros et en ressources) : installer des infrastructures de recharge partagées par les résidents d’un même bâtiment. Que se passe-t-il dans les faits en 2023 ? Que dire de la mise en œuvre de cette politique visant à favoriser des projets d’infrastructures collectives en immeuble ? C’est le sujet d’une enquête qualitative menée mi-2023, qui fera l’objet de cette communication. Celle-ci mettra en avant les raisons pour lesquelles l’infrastructure individuelle de recharge, consistant à faire valoir son droit à la prise, est actuellement encore très largement dominante en France. On y soulignera des leviers de changement de cette situation, en considérant chacune des configurations sociotechniques rencontrées. Et nous y mettrons en avant les bonnes raisons et intentions de passer à une infrastructure collective de recharge pour son VE-VHR en copropriété. Enfin, nous montrerons que les consommations électriques de recharge sont, à l’heure actuelle, un impensé dans bon nombre de cas, en copropriété
High-order numerical integration on self-affine sets
No full textWe construct an interpolatory high-order cubature rule to compute integrals of smooth functions over self-affine sets with respect to an invariant measure.The main difficulty is the computation of the cubature weights, which we characterize algebraically, by exploiting a self-similarity property of the integral.We propose an -version and a -version of the cubature, present an error analysis and conduct numerical experiments