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Impact of a two-dimensional steep hill on wind turbine noise propagation
No full textInternational audienceAbstract. Wind turbine noise propagation in a hilly terrain is studied through numerical simulation in different scenarios. Linearized Euler equations are solved in a moving frame that follows the wavefront, and wind turbine noise is modeled with an extended moving source. We employ large-eddy simulations to simulate the flow around the hill and the wind turbine. The sound pressure levels (SPLs) obtained for a wind turbine in front of a 2D hill and a wind turbine on a hilltop are compared to a baseline flat case. First, the source height and wind speed strongly affect sound propagation downwind. We find that topography influences the wake shape, inducing changes in the sound propagation that drastically modify the SPL downwind. Placing the turbine on the hilltop increases the average sound pressure level and amplitude modulation downwind. For the wind turbine placed upstream of a hill, a strong shielding effect is observed. But, because of the refraction by the wind gradient, levels are comparable with the baseline flat case just after the hill. Thus, considering how terrain topography alters the flow and wind turbine wake is essential to accurately predict wind turbine noise propagation
The CHIMERE chemistry-transport model v2023r1
No full textInternational audienceA new version of the CHIMERE model is presented. This version contains both computational and physico-chemical changes. The computational changes make it easy to choose the variables to be extracted as a result, including values of maximum sub-hourly concentrations. Performance tests show that the model is 1.5 to 2 times faster than the previous version for the same setup. Processes such as turbulence, transport schemes and dry deposition have been modified and updated. Optimization was also performed for the management of emissions such as anthropogenic and mineral dust. The impact of fires on wind speed, soil properties and leaf area index (LAI) was added. Pollen emissions, transport and deposition were added for birch, ragweed, olive and grass. The model is validated with a simulation covering Europe with a 60 km × 60 km resolution and the entire year of 2019. Results are compared to various measurements, and statistical scores show that the model provides better results than the previous versions
A comparison of alternative models for solving a non-linear single plant Hydro Unit Commitment problem
No full textInternational audienceA wide range of real world optimization problems involves continuous decisions and non-linearities. Each non-linear component of such problems can be modeled either linearly or non-linearly, considering or not additional integer variables. This results into different modeling choices that can drastically impact the solution time and quality. In this paper, we evaluate representative modeling alternatives, including common models from the literature as well as new models featuring less common functions. The single plant Hydro Unit Commitment problem (1-HUC) is the considered non-linear use case. Among the non-linearities of the 1-HUC, we focus on those involved in the power production, more precisely the head effect and the turbine efficiency. The power is defined as a two-dimensional non-convex and non-concave function of the water flow and head decision variables, the latter being itself a one-dimensional concave function of the turbined volume. We consider both the general problem and a common special case, assuming that the water head is fixed. Several available solvers are used for each non-linear model and the best virtual solver is retained to focus on the model capabilities rather than on the solver performance. Based on the numerical experiments, three models stand out as the most efficient in terms of computational time, solution quality and feasibility, sometimes in a counter-intuitive manner. For each of these models, a solver is highlighted as the most adequate
Disentangling top-down drivers of mortality underlying diel population dynamics of Prochlorococcus in the North Pacific Subtropical Gyre
No full textInternational audiencePhotosynthesis fuels primary production at the base of marine food webs. Yet, in many surface ocean ecosystems, diel-driven primary production is tightly coupled to daily loss. This tight coupling raises the question: which top-down drivers predominate in maintaining persistently stable picocyanobacterial populations over longer time scales? Motivated by high-frequency surface water measurements taken in the North Pacific Subtropical Gyre (NPSG), we developed multitrophic models to investigate bottom-up and top-down mechanisms underlying the balanced control of Prochlorococcus populations. We find that incorporating photosynthetic growth with viral- and predator-induced mortality is sufficient to recapitulate daily oscillations of Prochlorococcus abundances with baseline community abundances. In doing so, we infer that grazers in this environment function as the predominant top-down factor despite high standing viral particle densities. The model-data fits also reveal the ecological relevance of light-dependent viral traits and non-canonical factors to cellular loss. Finally, we leverage sensitivity analyses to demonstrate how variation in life history traits across distinct oceanic contexts, including variation in viral adsorption and grazer clearance rates, can transform the quantitative and even qualitative importance of top-down controls in shaping Prochlorococcus population dynamics
Kinematics of nonlinear waves over variable bathymetry. Part I: Numerical modelling, verification and validation
No full textInternational audienceFluid particle kinematics due to wave motion (i.e. orbital velocities and accelerations) at and beneath the free surface is involved in many coastal and ocean engineering applications, e.g. estimation of wave-induced forces on structures, sediment transport, etc. This work presents the formulations of these kinematics fields within a fully nonlinear potential flow (FNPF) approach. In this model, the velocity potential is approximated with a high-order polynomial expansion over the water column using an orthogonal basis of Chebyshev polynomials of the first kind. Using the same basis, original analytical expressions of the components of velocity and acceleration are derived in this work. The estimation of particle accelerations in the course of the simulation involves the time derivatives of the decomposition coefficients, which are computed with a high-order backward finite-difference scheme in time. The capability of the numerical model in computing the particle kinematics is first validated for regular nonlinear waves propagating over a flat bottom. The model is shown to be able to predict both the velocity and acceleration of highly nonlinear and nearly breaking waves with negligible error compared to the corresponding stream function wave solution. Then, for regular waves propagating over an uneven bottom (bar-type bottom profile), the simulated results are confronted with existing experimental data, and very good agreement is achieved up to the sixth-order harmonics for free surface elevation, velocity and acceleration
Experimental characterisation of the isosteric desorption energy of VeRCoRs concrete: Comparison of the isotherms and hygrometric methods
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Control of Staphylococcus epidermidis biofilm by surfactins of an endophytic bacterium Bacillus sp. 15 F
No full textInternational audienceThe present paper deals with the preparation and annotation of a surfactin(s) derived from a culture of the endophytic bacterium Bacillus 15F. The LC-MS analysis of the acetonitrile fraction confirmed the presence of surfactins Leu/Ile7 C15, Leu/Ile7 C14 and Leu/Ile7 C13 with [M+H]+ at m/z 1036.6895, 1022.6741 and 1008.6581, respectively. Various concentrations of the surfactin(s) (hereafter referred to as surfactin-15F) were used to reduce the adhesion of Staphylococcus epidermidis S61, which served as a model for studying antibiofilm activity on polystyrene surfaces. Incubation of Staphylococcus epidermidis S61 with 62.5 µg/ml of surfactin-15F resulted in almost complete inhibition of biofilm formation (90.3 ± 3.33%), and a significant reduction of cell viability (resazurin-based fluorescence was more than 200 times lower). The antiadhesive effect of surfactin-15F was confirmed by scanning electron microscopy. Surfactin-15F demonstrated an eradication effect against preformed biofilm, causing severe disruption of Staphylococcus epidermidis S61 biofilm structure and reducing viability. The results suggest that surfactins produced by endophytic bacteria could be an alternative to synthetic products. Surfactin-15F, used in wound dressings, demonstrated an efficient treatment of the preformed Staphylococcus epidermidis S61 biofilm, and thus having a great potential in medical applications
Sunscreen pollution is abated during the COVID-19 “Anthropause” of 2020 in two U.S. National Parks: Cape Lookout National Seashore and Kaloko-Honokōhau National Historical Park
No full textInternational audienceFrom March to June 2020, governments across the world imposed lockdowns in an attempt to reduce the transmission of COVID-19 during the early phase of the pandemic. This period of time in which human activity slowed worldwide has been coined the “Anthropause”. The goal of this study was to determine if sunscreen pollution abated during the Anthropause and to identify the severity of the pollution when tourism/recreation recovered at two coastal units of the U.S. National Park System: Kaloko-Honokōhau National Historical Park in Hawaiʻi, U.S.A. and Cape Lookout National Seashore in North Carolina, U.S.A. Active ingredients of sunscreen products were measured in water and sand samples at both locations, including oxybenzone, octinoxate, octocrylene, octisalate, homosalate, and relevant breakdown products of some of these ingredients. A risk assessment was conducted on Anthropause and post-Anthropause contaminant levels for both locations to determine if there was a threat reduction during the Anthropause, and whether tourism recovery in the post-Anthropause period served as a threat to coastal wildlife. Both national park units exhibited an almost absolute reduction in the levels of sunscreen contamination during the Anthropause period, a striking commonality considering the geographic expanse separating the parks. Once travel restrictions were lifted, a large influx of tourists ensued at both locations, resulting in a relatively sudden and dangerous increase in the levels of sunscreen chemical pollution. This study supports the argument that unmanaged tourism is a source of coastal sunscreen pollution that poses a threat to the localized continuity of species populations and biodiversity, especially to coral reefs and fisheries
The European GO-VIKING Project on Flow-Induced Vibrations: Overview and Current Status
No full textInternational audienceThe interaction between cooling fluid and solid structures (rods, tubes) in nuclear power plants may lead to flow-induced vibrations (FIV), causing material fatigue, fretting wear, and eventually loss of component integrity. This can cause further safety issues as well as substantial standstill costs due to longer or unplanned outages. With the growing computational power, the application of modern 3D numerical simulation tools for the accurate prediction of FIV phenomena is rapidly increasing. In 2022, the GO-VIKING ( G athering expertise O n V ibration I mpa K t I n N uclear power G eneration) project received a grant within the Horizon Europe research and innovation funding program. Sixteen European and two US partners started their collaboration in the field of FIV experiments and analysis. Over four years, the GO-VIKING project investigates FIV phenomena occurring in nuclear reactor cores and steam generators under single- and two-phase flow conditions. The project’s main objectives are to expand the expertise in the field of FIV through generation of new experimental and high-resolution numerical data; development, improvement, and validation of fluid-structure interaction (FSI) methods for FIV evaluation; training stakeholders in the application of these methods; and synthesizing guidelines for the prediction and assessment of FIV phenomena in nuclear reactors. This paper provides an overview of the GO-VIKING objectives, scientific program, as well as of the main scientific achievements in the first project year