Publications

2024

• Où on reparle du pump erosion test pour préciser ses spécificités
  
  • Cadet Simon
  • Larrarte Frédérique
  • Mbolamana Jules Tinot
  • Gomit Guillaume
  • Jarny Sébastien
  • Nicolas Xavier
  • Chevalier Christophe
  , 2024. Un prototype de terrain dédié à la mesure de l'érodabilité de sédiments fins a été développé. Cet appareil, nommé PumpET, pour Pump Erosion Test, a été conçu de manière empirique pour être un matériel de terrain « low cost », aisément transportable et reproductible. Il a été présenté lors des 18èmes Journées de l'Hydrodynamique. Des tests sur le terrain ont permis de valider le concept. Dans le même temps, diverses pistes d'amélioration ont été envisagées. Mais avant toute modification du prototype, nous avons choisi de préciser ses potentialités par, d'une part, des essais en conditions contrôlées et, d'autre part, des simulations numériques impliquant des étudiants de Master 2. Nous présenterons les démarches suivies, les résultats et surtout les implications vers des modifications plus ou moins substantielles de ce prototype.
• Experimental study of unsteady flows in urbanised areas
  
  • Beteille Elisa
  , 2024. The failure of hydraulic structures can result in the propagation of flood waves across large domains containing rural and urban areas. Such events would cause rapid flooding with complex flows, leading to catastrophic consequences for downstream populations and facilities, and devastating natural environments and ecosystems. Unfortunately, climate change is expected to increase the probability of extreme weather events, and the rise of intense rainfall presents new challenges for managing hydraulic dams. Additionally, the rapid expansion of urban areas increases communities’ vulnerability to flooding.Therefore, it is crucial to accurately describe these complex phenomena and predict their evolution using numerical models. The validation and calibration of these models are performed using data from laboratory studies, as there are scarce observations and measurements from real-case event. Furthermore, the highly transient nature of these phenomena poses challenges for current metrology, contributing to a lack of precise and comprehensive data on these phenomenons within the scientific community.To advance our understanding of the physical processes involves and validate numerical models, an experimental setup was developed at the EDF Lab Chatou in France. This setup enables the study of dam-break wave propagation through a series of obstacles representing idealised urban areas. The objective is to characterise the flow dynamics and analyse how various urban parameters, such as building spacing and number of streets, influence the flood process. Wave sensors measure water levels upstream, within, and downstream of the urban area. Additionally, a high-speed camera positioned above the flow performs Large-Scale Particle Image Velocimetry (LSPIV) measurements to calculate the instantaneous velocity field of the free surface. Moreover, the interaction between the wave and obstacles is documented using a high-speed camera along the channel and the water elevation in this area is calculated using image analysis measurements. Finally, the global impact of the urban forms on the flow is analysed through energy head calculations downstream of them.Simultaneously, detailed numerical simulations of the observed flows are conducted using the open-source Computational Fluid Dynamics (CFD) solver code_saturne. The initial validation of the model is carried out on simple urban configurations, identifying areas for improvement. Finally, simulations of a selected number of urban forms are performed to extend the experimental dataset. Previously measured punctual tendencies of the energy head are confirmed through profile analysis, and head loss coefficients related to the studied urban parameters are extracted.Overall, the thesis results contribute to a new dataset on unsteady flows in urbanised areas, enhancing understanding of these complex phenomena and supporting the validation of numerical models. Moreover, with improved knowledge of these phenomena, communities can develop safer urban planning strategies and optimise the design of industrial safety measures. A novel method to assess the influence of various urban parameters on the flow using the spatially averaged energy head is proposed. This method could support the calibration of simplified numerical models to account for the effects of urban areas on large-scale flood studies. This work aims to protect both property and people within a changing environmental and societal context.
• Observation morphodynamique à long terme pour l'étude des évènements extrêmes dans l'évolution et la projection morphologiques des côtes
  
  • Suanez Serge
  • Stéphan Pierre
  • Hénaff Alain
  • Letortu Pauline
  • Rouan Mathias
  • David Laurence
  • Pierson Julie
  • Floc'H France
  • Bertin Stéphane
  • Le Dantec Nicolas
  • Jaud Marion
  • Ammann Jérôme
  • Augereau Emmanuel
  • Prunier Christophe
  • Delacourt Christophe
  • Dodet Guillaume
  • Accensi Mickaël
  • Ardhuin Fabrice
  • André Gaël
  • Leballeur Laurent
  • Yates Marissa L.
  , 2024. Depuis plus de 20 ans, des suivis topomorphologiques sont réalisés sur plusieurs sites littoraux de Bretagne caractérisés par des morphologies très variées comme des systèmes de plage/dune, des cordons de galets, ou des falaises rocheuses. Ces observations ont été facilitées par le développement et la généralisation de techniques de mesures pertinentes dès les années 2000 (GPS, TLS, drone, LiDAR, imageries satellitaires, etc.). Pour chacune de ces morphologies, le choix d’un indicateur permettant d’enregistrer les changements morphologiques liés à la variation des conditions météo-marines (évènements extrêmes vs temps calme) est observé à des fréquences mensuelle à annuelle. La compilation de ces données permet de proposer un inventaire des évènements extrêmes ayant eu un impact significatif sur la morphologie des côtes en terme d’érosion et/ou de submersion au cours des deux dernières décennies. Ces données permettent également d’estimer les périodes de retour de ces épisodes morphogènes et/ou de faire des projections à plus ou moins long terme de l’évolution du littoral, notamment pour l’érosion.
• Numerical modelling of marine dunes in a shallow shelf sea in an offshore wind farm context
  
  • Durand Noémie
  , 2024. Marine dunes, also known as sand waves, are large sedimentary bedforms found on the seabed of shallow shelf seas. They migrate under the combined influence of tidal currents, winds, and waves, moving at rates of up to tens of metres per year. This dynamic behaviour is relevant to human activities, such as renewable energy projects. However, the morphology and dynamics of dunes in open marine environments are not well understood. Most modelling research to date has relied on two-dimensional vertical representations, ignoring lateral variations along the dune crests. Previous studies have largely used simplified hydrometeorological forcing, such as representative tidal currents and winds.The present research aims to extend our knowledge of marine dune dynamics and modelling over time and space scales ranging from days to years and metres to kilometres. It also seeks to advance our understanding of the interactions between marine dunes and offshore wind farm (OWF) foundations. To achieve this, we have developed a three-dimensional (3D) coastal area model using the openTELEMAC system for an application offshore Dunkirk, France. The area, proposed site for a 600 MW offshore wind project, is characterised by large marine dunes.Extensive site-specific surveys have been conducted, providing data to characterise the meteorological forcing, hydrodynamics, sedimentology, and morphodynamics of the area. The region is influenced by strong tidal flows, with near-bed currents up to 0.9 m/s, and winds predominantly from the southwest and, to a lesser extent, from the north. The seabed is mainly composed of reasonably well sorted gravelly sands with median grain sizes between 240 µm and 450 µm. There is little evidence of spatial or seasonal trends in the sediment data. The surveys document the evolution of large marine dunes with heights between 2 m and 3 m, travelling at a net rate of approximately 30 m/year.Our 3D numerical model, validated with the in situ data, was shown to accurately simulate hydrodynamics and dune dynamics. Simplifying assumptions excluded wave effects and focused on bedload transport. Two sediment transport predictors were evaluated in detail: the Soulsby and van Rijn predictor (SvR97), which was noted for its robustness and suitability for long-term modelling, and the Soulsby and Damgaard predictor (SD05), which accurately reflected the morphology of the dune but produced instabilities in the long term. Therefore, the SvR97 predictor was used in our research.To determine the contribution of wind-induced currents compared to tide-induced currents to the dynamics of large marine dunes, a 4-month period was simulated, with and without meteorological effects included in the numerical model. The results show that the migration of marine dunes is closely related to the amplitude and direction of the residual flow, which are influenced by wind conditions. Therefore, meteorological forcing is necessary to accurately represent seabed changes over time. Although deviations in wind direction from the prevailing pattern have the potential to temporarily reverse the general migration trend, they are too sporadic to fundamentally alter the sediment dynamics in the study area.To understand the impact of OWF foundations on the dynamics of large marine dunes, exploratory scenarios with a single monopile were run for a period of 2 years. These scenarios were later extended to a realistic scenario consisting of 46 wind turbines within the proposed Dunkirk OWF footprint. Our results show that monopiles significantly affect their environment, causing dunes to converge towards them along the tidal flow axis, which we linked to the ‘wake effect’. This effect accelerates dune propagation, highlighting the need for careful siting of wind turbines to mitigate impacts on dune fields. These findings bridge the gap between studies at the OWF level and those at the monopile level.
• Effect of shoaling length on rogue wave occurrence
  
  • Zhang Jie
  • Mendes Saulo
  • Benoit Michel
  • Kasparian Jérôme
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2024, 997, pp.A69. The impact of shoaling on linear water waves is well known, but it has only been recently found to significantly amplify both the intensity and frequency of rogue waves in nonlinear irregular wave trains atop coastal shoals. At least qualitatively, this effect has been partially attributed to the ‘rapid’ nature of the shoaling process, i.e. shoaling occurs over a distance far shorter than that required for waves to modulate themselves and adapt to the reduced water depth. Through a theoretical model and highly accurate nonlinear simulations, we disentangle the respective effects of the length and angle of a shoal's slope. We investigate the effects of the shoaling process rapidness on the evolution of key statistical and spectral sea-state parameters. We let the wave field evolve over a slope with constant angle in all cases while we vary the slope length. Our results indicate that the non-equilibrium dynamics is not affected by the slope length, because further extending the slope length does not influence the magnitude of the statistical and spectral measures as long as the non-equilibrium dynamics dominates the wave evolution. Thus, the shoaling effect on rogue waves is deduced to be mainly driven by the slope magnitude rather than the slope length. (10.1017/jfm.2024.687)
  DOI : 10.1017/jfm.2024.687
• Étude hydrodynamique des courses de natation en eau libre
  
  • Bolon Baptiste
  , 2024. Ce travail présente une étude physique des courses de natation en eau libre. Deux grands sujets sont abordés. D'abord, nous étudions les interactions entre nageurs (drafting), dans des configurations de nage à 2 athlètes et en peloton. Grâce à des mesures expérimentales et des calculs numériques, nous sommes capable d'évaluer l'impact de la position relative des nageurs sur la force de traînée qu'ils subissent. Ces résultats nous permettent de proposer une trajectoire optimale de dépassement. Ensuite, nous nous intéressons à l'impact des courants de la Seine sur la stratégie à mener lors de la course des Jeux Olympiques de Paris. Nos travaux montrent qu'il existe une trajectoire optimale le long du parcours, qui permet, en profitant des courants favorables et en évitant les courants les plus défavorables, de minimiser le temps de course d'un nageur. De même, il existe aussi une stratégie optimale de dépense énergétique qui permet à un nageur de minimiser son temps de course.
• A review of TELEMAC-2D numerical schemes for modelling two-dimensional free surface flows
  
  • Moussaddak Abdessamad
  • Decoene Astrid
  • Goeury Cédric
  • Ponçot Angélique
  • Taddei Tommaso
  , 2024. We 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.
• Kinematics of nonlinear waves over variable bathymetry. Part II: Statistical distributions of orbital velocities and accelerations in irregular long-crested seas
  
  • Zhang Jie
  • Ma Yuxiang
  • Benoit Michel
  Coastal Engineering, Elsevier, 2024, 193, pp.104589. In coastal areas, variable bottom effects significantly enhance wave nonlinearity and complicate wave propagation. It is of practical interest to characterize the nonlinear effect on the statistics of free surface displacements and particle kinematics. In this work, we take advantage of a fully nonlinear potential flow model to investigate the statistics of unidirectional irregular waves propagating over an uneven bottom. By confronting the simulated results with existing experimental results (free surface elevation and horizontal velocity beneath the mean sea level) in the temporal, spectral, and statistical domains, we show the high fidelity of the model in predicting the nonlinear irregular wave kinematics. As the relative importance of low-frequency harmonics becomes lower for acceleration, the model performance in predicting the measured horizontal acceleration is even better than that for the measured horizontal velocity. The empirical statistical distributions of velocity and acceleration in both horizontal and vertical directions are compared with both the normal (Gaussian) and the log-normal (LN) distributions. The latter requires skewness as an input in addition to the mean and standard deviation of the signal. We notice that, unlike the free surface displacement generally of positive skewness, the signal of velocities and accelerations are sometimes characterized by negative skewness. In such cases, the negative LN distribution should be adopted. Although the LN distribution has rarely been used for short-term statistics of wave elevation and kinematics, the detailed comparisons presented here demonstrate very good performance for all kinematic variables. In particular, in the area following a rapid reduction of water depth, where the sea-state is out-of-equilibrium, the heavy tails in the distributions are well reproduced by the LN model, indicating some generality and merits of this model. (10.1016/j.coastaleng.2024.104589)
  DOI : 10.1016/j.coastaleng.2024.104589
• Kinematics of nonlinear waves over variable bathymetry. Part I: Numerical modelling, verification and validation
  
  • Benoit Michel
  • Zhang Jie
  • Ma Yuxiang
  Coastal Engineering, Elsevier, 2024, 193, pp.104577. Fluid 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. (10.1016/j.coastaleng.2024.104577)
  DOI : 10.1016/j.coastaleng.2024.104577
• Experimental analysis on the influence of urban forms on unsteady urban flooding
  
  • Beteille Elisa
  • Boyaval Sébastien
  • Larrarte Frédérique
  • Demay Eric
  , 2025. Unsteady urban flooding, such as dam-break waves, poses catastrophic risks to downstream populations and results in severe damage. To assess and mitigate these risks, it is essential to forecast the influence of urban forms on flooding severity. In this paper, datasets are provided from reduced-scale physical experiments of transient flow through idealized suburban districts. The experiments are conducted in a rectangular horizontal open channel, where flow conditions are achieved by rapidly opening a gate holding a volume of water. To evaluate the impact of urban forms on flow behavior, we investigated two urban parameters; the number and width of streets in the main direction of the flow. The experiments provide complete water hydrographs for thirteen urban forms. Conductive and acoustic gauges are positioned at different locations to track the wavefront and water depth variation. The results illustrate the impact of the two studied urban parameters on flow variables and provide valuable validation data for computational urban planning models.
• Wave–structure interaction by a two–way coupling between a fully nonlinear potential flow model and a Navier–Stokes solver
  
  • Landesman Paul
  • Harris Jeffrey
  • Peyrard Christophe
  • Benoit Michel
  Ocean Engineering, Elsevier, 2024, 308, pp.118209. A two-way domain decomposition coupling procedure between a fully nonlinear potential flow model and a Navier–Stokes solver capturing the free surface with a Volume of Fluid method is used to study wave–structure interaction applied to offshore wind turbines. Away from the structure, the large-scale inviscid wave field is modeled by the potential code. Wave generation and absorption in this 3D hybrid model take place in the outer potential domain. The codes exchange data in the region around their common boundaries. Through the two-way coupling, waves propagate in and out of the viscous subdomain, making the hybrid algorithm suitable to study wave diffraction on marine structures, while keeping the viscous subdomain small. Each code uses its own mesh and time step. Subdomains are overlapping, therefore continuity conditions on velocity and free surface have to be verified on two distinct coupling surfaces at any time. Parallel implementation with communications between the models relying on the Message Passing Interface library allows calculations on large spatial and temporal scales. The coupling algorithm is first tested for regular nonlinear waves and then applied to simulate wave loads exerted on a vertical monopile in 3D. Attention is paid to the high-order components of the horizontal force. (10.1016/j.oceaneng.2024.118209)
  DOI : 10.1016/j.oceaneng.2024.118209
• Spatial and temporal analysis of the sand dynamics in alpine rivers for 3D numerical modelling
  
  • Weit A
  • Camenen B
  • Dramais G
  • Bel C
  • Jodeau M
  • Langlais S
  • Lauters F
  , 2024. Hydraulic structures can impact the sediment continuity of the river and can create a sediment imbalance downstream of dams according to the different sediment classes (silt, sand, gravel). For operators, one important issue is the presence of sand (d>63 μm), which can lead to exploitation difficulties, issues for flushing or emptying operations as well as to ecological, in-dustrial or safety issues. It was recognized that the percentage of sand particles that is transported by suspension compared to bedload transport can often prevail. However, today it is still a real challenge to evaluate the spatial and temporal variability of these sand concentrations in gravel-bed rivers since sand dynamics are generally supply limited. Using 3D hydro-sedimentary modelling could help to better understand processes of sand transport in rivers. In this article, we will present results from experimental monitoring that will then be used for 3D numerical modelling (TELEMAC 3D + Gaia) on engineered rivers in the Northern French Alps.
• Hydrodynamic Modelling of Seine Bay and Estuary in Moderate and Extreme Conditions: With a Focus on Johanna Storm
  
  • Shafiei Hassan
  • Huybrechts Nicolas
  • Laborie Vanessya
  • Turki Imen
  • Salameh Edward
  • Laignel Benoît B.
  , 2024, 1, pp.79-102. Seine estuary experiences large tidal ranges (e.g., around 7 m during spring tide) and a long high-tide slack time (roughly three hours). As an embayed estuary located in the English Channel, its dynamics is highly affected by the tidal transformation and mass/momentum exchanges between the English Channel and Seine Bay. However, these mechanisms are not well studied yet. In this investigation, a Telemac2D hydrodynamic model of Seine Bay and Estuary (abbreviated as SBE in this paper) is developed and calibrated for both moderate and extreme conditions. First, the main parameters affecting the tidal dynamics of SBE are identified. Then, the model is enhanced to correct the simulation of tidal propagation in Seine Bay in moderate conditions, thereby reproducing the length and shape of the high-tide slack in the Seine estuary as observed by the in-situ measurements. The enhancement procedure is further confirmed by applying it to another marine-boundary-condition type (i.e., time series of total water level as well as harmonic constituents). Moreover, the results in the bay are validated using remotely-sensed, altimetry data. Then, the model is adapted to simulate the storm-surge events in SBE, focusing on the Johanna storm which caused considerable damage and casualties in March 2008. The calibrated model is used to investigate the tidal dynamics as well as the effects of meteorlogical forces in SBE and can be a useful tool to further study the hydro-eco-morphology of the SBE. This work aims at providing a reliable map of surface water evolution throughout the SBE in stormy conditions. The model will be used in the Cal/Val phase of the SWOT (Surface Water and Ocean Topography) mission to calibrate and validate the SWOT simulator. (10.1007/978-981-97-4072-7_6)
  DOI : 10.1007/978-981-97-4072-7_6
• Un exemple de partage de l’espace : les loisirs nautiques sur la Loire
  
  • Larrarte Frédérique
  • Kerhervé Yvon
  • Toutain Nicolas
  • Jan Hubert
  , 2024. Plus long fleuve de France, la Loire acquiert, à Nantes, un caractère maritime qui a forgé une bonne partie de son histoire et de son développement économique depuis des siècles. Avec un trafic de 30 millions de tonnes de trafic par an, Nantes Saint-Nazaire Port est le 4e grand port maritime français et 28 500 emplois sont générés par l'activité portuaire (selon une étude Insee 2022 sur données 2018). Au-delà de cet aspect économique, la Loire peut être représentée comme l’épine dorsale de l’agglomération nantaise dont les 24 communes se répartissent sur ses 2 rives. Bien connue en termes de génie civil pour ses ouvrages d’art comme le pont de Cheviré ou des éléments du patrimoine maritime comme le canal maritime de la Basse Loire (dit canal de la Martinière), l’agglomération est aussi le lieu de vie de plus de 650000 habitants. Et leurs loisirs regardent souvent vers l’eau ! Dans cette communication, nous présenterons comment les associations sportives se sont structurées en un Collectif des Association Nautiques de l’agglomération nantaise pour permettre que la navigation de loisir, quasi absente sur la Loire il y a 30 ans, reprenne sa place, au même titre que les autres activités, sur la Loire et son affluent l’Erdre, en permettant aux habitants de découvrir leur ville à partir de l’eau, en mode déplacement doux. (10.5150/jngcgc.2024.077)
  DOI : 10.5150/jngcgc.2024.077
• Physics of sport: Olympic swimming
  
  • Carmigniani Rémi Arthur
  , 2024. This manuscript reviews the main research subjects I have been conducting on “Physics of Sport” and particularly on Olympic swimming since I was appointed as a researcher at École des Ponts in the Laboratoire d’Hydraulique Saint-Venant in 2018. This work started with the launch of Sciences2024 research project, dedicated to solving problems identified with athletes to support them in their quest for medals at the Paris 2024 Olympic and Paralympic Games. It is funded by the ANR project NePTUNE and the Fondation Groupe EDF. Thisthesispresents4axesofresearchonOlympicswimming: thestudyofwaterresistance, the modeling of the velocity–stroke rate and coordination relationships, the measurement and modeling of starts and turns trajectories, and the prediction of racing conditions in open water. All this work is being conducted with the aim of benefitting the French athletes as they prepare for the Paris 2024 Olympic and Paralympic Games. This work is multi-disciplinary (artificial intelligence, computer vision, bio-mechanics, physiology, fluid mechanics, etc.), with a key discipline: physics. The first step is to observe, then understand and model, proposing the most basic and minimal law possible. This approach makes it possible to highlight important laws of sport, such as the speed-frequency relationship in paddle sports. While it’s true that athletes haven’t necessarily waited for physicists to help them perform, I hope that this work will enable us to better understand the mechanisms that have enabled the best (French) athletes to get close to their optimal performance, so that we can transfer it to future generations. The thesis is written in English so that it can be widely shared, and to provide an overview of the work carried out since 2018 for the Paris Games.
• Les espaces bleus de Nantes Métropole : quand les loisirs nautiques retrouvent la Loire.
  
  • Larrarte Frédérique
  • Kerhervé Yvon
  • Toutain Nicolas
  • Jan Hubert
  , 2024. Beaudelaire disait « Homme libre toujours tu chériras la mer », Renaud chante quant à lui « C’est pas l’homme qui prend la mer, c’est la mer qui prend l’homme ». Et comment, dans la ville natale de Jules Verne qui , rappelons le, a aussi bien écrit l’Ile à Hélice que 20000 lieues sous les mers, ignorer tout l’imaginaire lié à la mer. Le dossier de presse de l’exposition Objectif mer, : l’océan filmé (Musée National de la Marine, Paris, décembre 2023-mai 2024) indique d’ailleurs que « Aujourd’hui, peut-être avec plus de puissance qu’auparavant - effets spéciaux numériques oblige -, la mer est toujours au cinéma ….. Elle symbolise aussi la liberté, le départ vers l’inconnu et les aventures, de même que la fragilité de la Nature et du genre humain, tout en apparaissant impitoyable dans sa masse aveugle et sauvage. ». Ces propos font écho à ceux de Kalaora (Kalaora et Lacroix, 2022) qui dit que « cet espace ouvre vers une part d’aventure et d’incertain parce qu’il incite à larguer les amarres, et à accepter le flottement de la consciences et l’imprévisibilité de la destination finale ». Akoun (1999), cité par Brulé-Josso (2012), indique que « Depuis plus de cent cinquante ans, en mer, l’enthousiasme propre au « mythe » de la « modernité » est exprimé avec force et constance par les amateurs de voile se sentant « libres » de parcourir « les derniers espaces de liberté ». D’après Guigueno ( 2007), « la Coupe de l’America fait partie des spectacles proposés dans un port qui est aussi l’archétype de la métropole moderne ». Mais par ailleurs « La voile sportive n’est pas une pratique populaire. ». Mais toute la voile n’est pas « sportive », Brulé-Josso (2012) rappelle que « Aujourd’hui, il est très communément dit et écrit que la « plaisance moderne » est née à cette période et que le Centre nautique des Glénans est l’institution qui a contribué à cet avènement. Pour ses fondateurs, l’héritage culturel revendiqué est celui des pêcheurs. ». Ceci nous amène à nous intéresser aux activités nautiques autres que la « voile sportive ». Dans cette communication, nous présenterons comment des associations se sont structurée en un Collectif des Association Nautiques de l’agglomération nantaise pour permettre que la navigation loisir, quasi absente sur la Loire il y a 30 ans, prenne sa place, au même titre que les autres modes de transports loisir sur la Loire et son affluent l’Erdre, en permettant aux habitants de découvrir leur ville à partir de l’eau, en mode déplacement doux. Nous mettrons en particulier l’accent sur la pratique du voile-aviron dont les supports sont parfois inspirés de bateaux utilisés pour la pêche comme les yoles de Ness inspirés de bateaux des îles Shetland.
• Predicting water quality in urban rivers: Linking high frequency monitoring and spatial rainfall
  
  • Guillot - Le Goff Arthur
  • Cartier Yoann
  • Carmigniani Rémi Arthur
  • Malardé Damien
  • Saad Mohamed
  • Dubois Philippe
  • Einfalt Thomas
  • Brigitte Vinçon-Leite
  , 2024.
• About the structural stability of Maxwell fluids: convergence toward elastodynamics
  
  • Boyaval Sébastien
  , 2024, 35, pp.271-280. Maxwell's models for viscoelastic flows are famous for their potential to unify elastic motions of solids with viscous motions of liquids in the continuum mechanics perspective. But rigorous proofs are lacking. The present note is a contribution toward well-defined viscoelastic flows proved to encompass both solid and (liquid) fluid regimes. In a first part, we consider the structural stability of particular viscoelastic flows: 1D shear waves solutions to damped wave equations. We show the convergence toward purely elastic 1D shear waves solutions to standard wave equations, as the relaxation time λ and the viscosity µ grow unboundedly λ ≡ µ/G → ∞ in Maxwell's constitutive equation λ τ +τ = 2 µD(u) for the stress τ of viscoelastic fluids with velocity u. In a second part, we consider the structural stability of general multi-dimensional viscoelastic flows. To that aim, we embed Maxwell’s constitutive equation in a symmetric-hyperbolic system of PDEs which we proposed in our previous publication [ESAIM:M2AN 55 (2021) 807-831] so as to define multi-dimensional viscoelastic flows unequivocally. Next, we show the continuous dependence of multi-dimensional viscoelastic flows on λ ≡ μ/ G using the relative-entropy tool developped for symmetric-hyperbolic systems after C. M. Dafermos. It implies convergence of the viscoelastic flows defined in [ESAIM:M2AN 55 (2021) 807-831] toward compressible neo-Hookean elastodynamics when λ → ∞. (10.1007/978-3-031-55264-9_23)
  DOI : 10.1007/978-3-031-55264-9_23
• Re-analysis of extreme sea state events modelling using a data-driven technique
  
  • Goeury Cédric
  • Thierry Fouquet
  • Tristan Bagnis
  • Michel Benoit
  • Maria Teles
  , 2024. With the objective of better answering marine and coastal engineering needs, sea state databases are created by hindcast simulations over long periods. The wave hindcast ANEMOC-3 database, built using the spectral model TOMAWAC for wave generation and propagation and the hydrodynamic circulation model TELEMAC-2D for tidal water levels and currents calculation, covers a period of 45 years from 1979 to 2023. During the calibration of the database, the numerical results must be consistent with past observational data (in situ or satellite measurements). Among other things, this process relies on calibration to determine “empirical adequacy” (Oreskes et al., 1994). In particular, the calibration aims at simulating a series of reference events by adjusting some uncertain physically-based model parameters until the agreement with available data reaches a satisfactory level. The objective of this work is to implement an efficient calibration algorithm, capable of processing measurements optimally, and of estimating the partially known parameters in the numerical model.
• Reduced Basis method for finite volume simulations of parabolic PDEs applied to porous media flows
  
  • Tarhini Jana
  • Boyaval Sébastien
  • Enchéry Guillaume
  • Tran Quang Huy
  , 2024. Numerical simulations are a highly valuable tool to evaluate the impact of the uncertainties of various modelparameters, and to optimize e.g. injection-production scenarios in the context of underground storage (of CO2typically). Finite volume approximations of Darcy’s parabolic model for flows in porous media are typically run many times, for many values of parameters like permeability and porosity, at costly computational efforts. We study the relevance of reduced basis methods as a way to lower the overall simulation cost of finite volume approximations to Darcy’s parabolic model for flows in porous media for different values of the parameters such as permeability. In the context of underground gas storage (of CO2 typically) in saline aquifers, our aim is to evaluate quickly, for many parameter values, the flux along some interior boundaries near the well injection area—regarded as a quantity of interest—. To this end, we construct reduced bases by a standard POD-Greedy algorithm. Our POD-Greedy algorithm uses a new goal-oriented error estimator designed from a discrete space- time energy norm independent of the parameter. We provide some numerical experiments that validate the efficiency of the proposed estimator.
• Fluorescence spectroscopy for tracking microbiological contamination in urban waterbodies
  
  • Angelotti de Ponte Rodrigues Natália
  • Carmigniani Rémi
  • Guillot-Le Goff Arthur
  • Lucas Françoise S
  • Therial Claire
  • Naloufi Manel
  • Janne Aurélie
  • Piccioni Francesco
  • Saad Mohamed
  • Dubois Philippe
  • Vinçon-Leite Brigitte
  Frontiers in Water, Frontiers, 2024, 6. Dissolved organic matter (DOM) plays a crucial role in freshwater ecosystem function. Monitoring of DOM in aquatic environments can be achieved by using fluorescence spectroscopy. Particularly, DOM fluorescence can constitute a signature of microbiological contamination with a potential for high frequency monitoring. However, limited data are available regarding urban waterbodies. This study considers fluorescence data from field campaigns conducted in the Paris metropolitan region: two watercourses (La Villette basin and the river Marne), two stormwater network outlets (SO), and a wastewater treatment plant effluent (WWTP-O). The objectives of the study were to characterize the major fluorescence components in the studied sites, to investigate the impact of local rainfall in such components and to identify a potential fluorescence signature of local microbiological contamination. The components of a PARAFAC model (C1-C7), corresponding to a couple of excitation (ex) and emission (em) wavelengths, and the fluorescence indices HIX and BIX were used for DOM characterization. In parallel, fecal indicator bacteria (FIB) were measured in selected samples. The PARAFAC protein-like components, C6 (ex/em of 280/352 nm) and C7 (ex/em of 305/340 nm), were identified as markers of microbial contamination in the studied sites. In the La Villette basin, where samplings covered a period of more than 2 years, which also included similar numbers of wet and dry weather samples, the protein-like components were significantly higher in wet weather in comparison to dry weather. A positive relationship was obtained between C6 and FIB. In urban rivers, the high frequency monitoring of C6 levels would support the fecal contamination detection in rivers. In addition, it could help targeting specific field campaigns to collect comprehensive dataset of microbiological contamination episodes. (10.3389/frwa.2024.1358483)
  DOI : 10.3389/frwa.2024.1358483
• Fluorescence spectroscopy for tracking microbiological contamination in urban waterbodies
  
  • Angelotti de Ponte Rodrigues Natália
  • Carmigniani Rémi
  • Guillot-Le Goff Arthur
  • Lucas Françoise
  • Therial Claire
  • Naloufi Manel
  • Janne Aurélie
  • Piccioni Francesco
  • Saad Mohamed
  • Dubois Philippe
  • Vinçon-Leite Brigitte
  Frontiers in Water, Frontiers, 2024, 6. Dissolved organic matter (DOM) plays a crucial role in freshwater ecosystem function. Monitoring of DOM in aquatic environments can be achieved by using fluorescence spectroscopy. Particularly, DOM fluorescence can constitute a signature of microbiological contamination with a potential for high frequency monitoring. However, limited data are available regarding urban waterbodies. This study considers fluorescence data from field campaigns conducted in the Paris metropolitan region: two watercourses (La Villette basin and the river Marne), two stormwater network outlets (SO), and a wastewater treatment plant effluent (WWTP-O). The objectives of the study were to characterize the major fluorescence components in the studied sites, to investigate the impact of local rainfall in such components and to identify a potential fluorescence signature of local microbiological contamination. The components of a PARAFAC model (C1-C7), corresponding to a couple of excitation (ex) and emission (em) wavelengths, and the fluorescence indices HIX and BIX were used for DOM characterization. In parallel, fecal indicator bacteria (FIB) were measured in selected samples. The PARAFAC protein-like components, C6 (ex/em of 280/352 nm) and C7 (ex/em of 305/340 nm), were identified as markers of microbial contamination in the studied sites. In the La Villette basin, where samplings covered a period of more than 2 years, which also included similar numbers of wet and dry weather samples, the protein-like components were significantly higher in wet weather in comparison to dry weather. A positive relationship was obtained between C6 and FIB. In urban rivers, the high frequency monitoring of C6 levels would support the fecal contamination detection in rivers. In addition, it could help targeting specific field campaigns to collect comprehensive dataset of microbiological contamination episodes. (10.3389/frwa.2024.1358483)
  DOI : 10.3389/frwa.2024.1358483
• A viscoelastic flow model of maxwell-type with a symmetric-hyperbolic formulation
  
  • Boyaval Sébastien
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2024, 351 (S1), pp.251-259. Maxwell models for viscoelastic flows are famous for their potential to unify elastic motions of solids with viscous motions of liquids in the continuum mechanics perspective. But the usual Maxwell models allow one to define well motions mostly for one-dimensional flows only. To define unequivocal multi-dimensional viscoelastic flows (as solutions to well-posed initial-value problems) we advocated in [ESAIM:M2AN 55 (2021) 807-831] an upper-convected Maxwell model for compressible flows with a symmetrichyperbolic formulation. Here, that model is derived again, with new details. (10.5802/crmeca.165)
  DOI : 10.5802/crmeca.165
• Assessment of two non-invasive techniques for measuring turbulent benthic fluxes in a shallow lake
  
  • Breton Felipe
  • Calabro-Souza Guilherme
  • Lorke Andreas
  • Dubois Philippe
  • Jodeau Magali
  • Moilleron Régis
  • Vinçon-Leite Brigitte
  • Jan Jiří
  • Borovec Jakub
  • Lemaire Bruno J.
  Environmental Pollution, Elsevier, 2024, 351, pp.124032. Benthic fluxes refer to the exchange rates of nutrients and other compounds between the water column and the sediment bed in aquatic ecosystems. Their quantification contributes to our understanding of aquatic ecosystem functioning. Near-bed hydrodynamics plays an important role at the sediment-water interface, especially in shallow lakes, but it is poorly considered by traditional measuring techniques of flux quantification, such as sediment incubations. Thus, alternative sampling techniques are needed to characterize key benthic fluxes under in-situ hydrodynamic conditions. This study aimed to evaluate the performance of two promising methods: relaxed eddy accumulation (REA) and mass transfer coefficient (MTC). We applied them in a hyper-eutrophic shallow lake to measure the fluxes of ammonium, phosphate, iron, and manganese ions. For the first time, REA revealed hourly nutrient flux variations, indicating a strong lake biogeochemical dynamics at short time-scales. Daily average fluxes are of similar orders of magnitude for REA and MTC for ammonium (24 and 42 mmol m2 d-1), manganese (1.0 and 0.8), and iron (0.8 and 0.7) ions. They are one order of magnitude higher than fluxes estimated from sediment incubations, due to the difficulty in reproducing in-situ oxygen and hydrodynamic conditions in the laboratory. Although the accuracy of both techniques needs to be improved, the results revealed their potential: REA follows the short-term biogeochemical dynamics of sediments, while MTC could be widely used for lake monitoring because of its simpler implementation. (10.1016/j.envpol.2024.124032)
  DOI : 10.1016/j.envpol.2024.124032
• PREFACE for THESIS-2019 Special Issue of the EJMFLU
  
  • Dias Frédéric
  • Dan Nguyen Kim
  • Hsu Tian-Jian
  • Guillou Sylvain S
  European Journal of Mechanics - B/Fluids, Elsevier, 2024. (10.1016/j.euromechflu.2024.03.006)
  DOI : 10.1016/j.euromechflu.2024.03.006