HAL-CEA
Not a member yet
145450 research outputs found
Sort by
TRUST: the HPC open-source CFD platform – from CPU to GPU
No full textInternational audienceSince 1993, the CEA has developed TRUST, an open-source CFD software platform designed to address a wide range of thermohydraulic problems. Initially focused on nuclear applications, the platform has progressively evolved to support incompressible single-phase flows, low-Mach-number reactive flows, and fully compressible multi-phase flows. TRUST incorporates a variety of numerical schemes and supports multiple mesh types, making it suitable for both academic and industrial applications, as well as for deployment on standard computing systems and high-performance computing (HPC) clusters. Notably, it has enabled one of the largest Direct Numerical Simulations (DNS) to date for hydrogen risk assessment, involving over 2 billion cells and more than 50,000 MPI processors. Recently, the development team has begun integrating GPU-based computing technologies–such as AmgX, rocALUTION, AMGCL and Kokkos–to develop a hybrid CPU/GPU version of the code capable of delivering high performance across diverse architectures. This article presents an overview of the TRUST platform, reviews the largest simulation performed to date with the CPU version, outlines the ongoing GPU integration strategy, and highlights selected results
ELIXIR Microbiome Community – 2025 face to face/hybrid meeting report
No full textThis document reports on the agenda, key points, and outcomes of the ELIXIR Microbiome Community's face-to-face and hybrid meeting, which took place on April 9-10, 2025, in Barcelona, Spain
Momentum and energy budgets of high-pressure subcooled boiling flows using two-fluid RANS simulations
No full textInternational audienceThis study presents the simulation of a high-pressure upward boiling flow in a vertical pipe, using the two-fluid model with Neptune_CFD standard closure laws. Radially-dependent experimental bubble diameters are enforced in the simulations, reducing the number of closure laws and helping to decouple some phenomena in the analysis. The goal of this paper is to highlight the predominant physical phenomena as a function of flow conditions and as a function of the distance to the wall, in order to help determine which model should be improved as a priority. Analysis of the momentum balance for the vapor phase shows that in the radial direction, the predominant effects are turbulent dispersion moving the vapor away from the wall, balanced by the drag and lift forces. An increase in mass flow rate or thermodynamic quality increases liquid shear rate, turbulent viscosity and turbulent dispersion. In addition, liquid enthalpy budget analysis reveals that the liquid temperature is determined by an equilibrium between the radial turbulent diffusion of wall heat, axial inertial thermal effects and an interphase exchange by condensation. Simulations predict significant evaporation near the wall, although this phenomenon has not been observed experimentally, which is a source of error in the mass and enthalpy balances. We demonstrate the improvement in predictions in the near-wall region induced by the use of a limiter to the liquid heat flux in wall Heat Flux Partitioning (HFP) model. Condensation reaches its maximum in an intermediate radial position between the center and the wall, where interfacial area and subcooling are large. This position depends on the thermodynamic quality
Évaluation des impacts environnementaux à partir d'une ACV simplifiée pour un réseau massif MIMO distribué
No full textInternational audienceCe travail évalue l'impact environnemental des réseaux multi-antennes distribués sans cellule (CF-mMIMO), une technologie envisagée pour les futures générations de télécommunications. Bien que largement reconnus pour leur efficacité énergétique à haut débit, aucune évaluation de leur impact environnemental n'a été réalisée afin de justifier de leur pertinence, notamment par rapport aux architectures co-localisées usuelles. Dans cette étude, l'empreinte environnementale est analysée à l'aide d'une analyse du cycle de vie (ACV) simplifiée et comparée à d'autres études afin de vérifier la cohérence du modèle. Les résultats obtenus indiquent que selon les configurations choisies et les performances visées, le déploiement des réseaux CF-mMIMO peut autant être une option à faible qu'à fort impact environnemental. Enfin, l'introduction d'un modèle tenant compte de la fabrication des équipements montre que l'efficacité énergétique seule n'est pas pertinente.</div
Soil Carbon Dynamics Reshaped by Ancient Carbon Quantification
No full text(IF 12;Q1)International audienceSoil is a major terrestrial carbon reservoir, and enhancing its carbon stock is a central strategy to mitigate climate change. Earth system models project a net soil carbon sink by 2100, the magnitude of which is still under debate, differing significantly between approaches. Radiocarbon-based studies often suggest a limited soil carbon accumulation capacity, but these estimates are biased by the presence of ancient, radiocarbon-free, organic carbon (aOC). This carbon no longer contributes to soil carbon dynamics and increases the average 14 C age of soil carbon because it is radiocarbon-depleted. This known radiocarbon caveat can be overcome with a better understanding of the aOC (ancient radiocarbon-free OC) distribution in the world's soils. Here we apply a mixing linear equation to 313 soils worldwide from radiocarbon databases to estimate the aOC contained in soils. The aOC contained in soils has different origins, from rock-derived to old biospheric C strongly associated with mineral particles during pedogenesis. Our findings show a mean aOC content of 2.4 mg/g ±3.2 SD with an aOC contribution up to 11% of the soil organic carbon in topsoils (0-30 cm depth), reaching 25% in subsoils (30-100 cm depth) and more than half in deep soil (> 100 cm depth). We demonstrate that the aOC content is particularly high in Andosols and Cryosols. We subtracted the aOC contributions to calculate a global mean corrected age of non-aOC carbon to 1 m depth of 290 years, contrasting sharply with previously reported values of 3100 to 4830 years. This corrected estimate aligns more closely with independent isotopic proxies ( 13 C and 36 Cl) of soil carbon dynamics. These results also reconcile empirical data with the parameterization of Earth system models
Projections of coral reef carbonate production from a global climate–coral reef coupled model
No full textInternational audienceCoral reefs are under threat due to climate change and ocean acidification. However, large uncertainties remain concerning future carbon dioxide emissions, climate change and the associated impacts on coral reefs. While most previous studies have used climate model outputs to compute future coral reef carbonate production, we use a coral reef carbonate production module embedded in a global carbonclimate model. This enables the simulation of the response of coral reefs to projected changes in physical and chemical conditions at finer temporal resolution. The use of a fastintermediate complexity model also permits the simulation of a large range of possible futures by considering different greenhouse gas concentration scenarios (Shared Socioeconomic Pathways (SSPs)) and different climate sensitivities (hence different levels of warming for a given level of acidification), as well as the possibility of corals adapting their thermal bleaching thresholds. We show that without thermal adaptation, global coral reef carbonate production decreases to less than 25 % of historical values in most scenarios over the 21st century, with limited further declines between 2100 and 2300 irrespective of the climate sensitivity. With thermal adaptation, there is far greater scenario variability in projections of reef carbonate production. Under high-emission scenarios the rate of 21st century declines is attenuated, with some global carbonate production declines delayed until the 22nd century. Under high-mitigation sce-narios, however, global coral reef carbonate production can recover in the 21st and 22nd centuries and thereafter persist at 50 %-90 % of historical values, provided that the climate sensitivity is moderate
Light-triggered quenching of the 19F-MRI signal from micelle-encapsulated PERFECTA
No full textInternational audienceWe report the development of a fluorinated micellar nanosystem whose 19F-MRI signal can be selectively dimmed by application of an external stimulus. A photo-activatable quencher unit (ferrocene) was co-encapsulated with..
Boiling flow visualization experiment scaled to divertor cooling conditions
No full textInternational audiencededicated experiment FEDORA (Fusion Experiment for Divertor Optimization Research Applications) has been constructed to visualize flow boiling at scaled fusion divertor conditions. Its main purpose is to obtain the information on local boiling parameters, needed for the development of mechanistic boiling models in Computational Fluid Dynamics (CFD) codes. Current boiling models, although grounded on realistic physical principles, still rely heavily on empirical correlations, particularly for boiling parameters such as nucleation site density, bubble departure diameter, and bubble departure frequency. Due to the harsh operating conditions in the water-cooled divertor plasma-facing components (high heat fluxes over 10 MW/m 2 , mean flow velocity of about 9 m/s), visualization of boiling in realistic cooling channels is not feasible. The proposed experiment addresses this challenge by employing a surrogate coolant, characterized by lower latent heat and saturation temperature. By analyzing key dimensionless numbers, the aim is to replicate boiling conditions to be similar to those in coolant channels of upcoming divertor designs. Distinctive features of the proposed experimental setup include visually transparent boiling channel, infra-red transparent window and a thin electrically heated foil. This setup allows simultaneous high-speed and high-resolution recording of boiling phenomena in the flow and measurement of temperature distribution on the heated surface. In this work, the design, similarity analysis and the first measurement results are presented, proving the concept of the visualization approach to understand the boiling heat transfer in divertor cooling channels
Poisson solvers for strongly stratified turbulent flows
No full text(IF 3;Q2)International audienceTurbulent mixing occurs in numerous applications and natural flows between fluids of very different density contrasts where the Boussinesq approximation no longer applies. In the low Mach number limit of arbitrary large density contrasts, called the Variable-Density approximation, the Poisson solver that determines the pressure field can be numerically very costly. Here we investigate the performances of two solvers: the Generalized Minimal Residual, GMRES, and the Bi-Conjugate Gradients STAB at order l, BICGS(l). Comparisons are made in two different frameworks: the Unstably Stratified Homogeneous Turbulence (USHT) and the Rayleigh-Taylor instability (RTI). Direct Numerical Simulations with 10243 up to 20483 points are performed. The USHT configuration serves as a challenging test lab to set the relevant optimizations for both the GMRES and BICGS(l) solvers before addressing the more realistic RTI. It appears that GMRES provides the smallest residual norm, while the BICGS(2) algorithm can be up to 25% faster and yields a comparable residual norm. Such performances are reached thanks to original optimizations of the BICGS(l) algorithm. In addition, we developed a fast Poisson solver that significantly speeds up the computations, at the expense of only a moderate loss of accuracy
Development of agropastoralism in Southwest Asia. Cross-dating of archaeological ceramics by radiocarbon and archaeomagnetic dating
No full textInternational audienceThe ERC-StG AGROCHRONO project studies the development of agropastoralism in the Indo-Iranian borderlands. The objectives are to specify the chronological, cultural, economic and environmental framework in which the first agropastoral populations in the region developed from the 7 th millennium BC onwards