Laboratoire d'Hydraulique Saint-Venant

We propose an approach to vision-based robot control, called 2 1/2 D visual servoing, which avoids the respective drawbacks of classical position-based and image-based visual servoing. Contrary to the position-based visual servoing, our scheme does not need any geometric three-dimensional model of the object. Furthermore and contrary to image-based visual servoing, our approach ensures the convergence of the control law in the whole task space. 2 1/2 D visual servoing is based on the estimation of the partial camera displacement from the current to the desired camera poses at each iteration of the control law. Visual features and data extracted from the partial displacement allow us to design a decoupled control law controlling the six camera DOFs. The robustness of our visual servoing scheme with respect to camera calibration errors is also analyzed: the necessary and sufficient conditions for local asymptotic stability are easily obtained. Then, due to the simple structure of the system, sufficient conditions for global asymptotic stability are established. Finally, experimental results with an eye-in-hand robotic system confirm the improvement in the stability and convergence domain of the 2 1/2 D visual servoing with respect to classical position-based and image-based visual servoing.

Organic chemicals can contribute to local and regional losses of freshwater biodiversity and ecosystem services. However, their overall relevance regarding larger spatial scales remains unknown. Here, we present, to our knowledge, the first risk assessment of organic chemicals on the continental scale comprising 4,000 European monitoring sites. Organic chemicals were likely to exert acute lethal and chronic long-term effects on sensitive fish, invertebrate, or algae species in 14% and 42% of the sites, respectively. Of the 223 chemicals monitored, pesticides, tributyltin, polycyclic aromatic hydrocarbons, and brominated flame retardants were the major contributors to the chemical risk. Their presence was related to agricultural and urban areas in the upstream catchment. The risk of potential acute lethal and chronic long-term effects increased with the number of ecotoxicologically relevant chemicals analyzed at each site. As most monitoring programs considered in this study only included a subset of these chemicals, our assessment likely underestimates the actual risk. Increasing chemical risk was associated with deterioration in the quality status of fish and invertebrate communities. Our results clearly indicate that chemical pollution is a large-scale environmental problem and requires far-reaching, holistic mitigation measures to preserve and restore ecosystem health.

Microorganisms are vital in mediating the earth’s biogeochemical cycles; yet, despite our rapidly increasing ability to explore complex environmental microbial communities, the relationship between microbial community structure and ecosystem processes remains poorly understood. Here, we address a fundamental and unanswered question in microbial ecology: ‘When do we need to understand microbial community structure to accurately predict function?’ We present a statistical analysis investigating the value of environmental data and microbial community structure independently and in combination for explaining rates of carbon and nitrogen cycling processes within 82 global datasets. Environmental variables were the strongest predictors of process rates but left 44% of variation unexplained on average, suggesting the potential for microbial data to increase model accuracy. Although only 29% of our datasets were significantly improved by adding information on microbial community structure, we observed improvement in models of processes mediated by narrow phylogenetic guilds via functional gene data, and conversely, improvement in models of facultative microbial processes via community diversity metrics. Our results also suggest that microbial diversity can strengthen predictions of respiration rates beyond microbial biomass parameters, as 53% of models were improved by incorporating both sets of predictors compared to 35% by microbial biomass alone. Our analysis represents the first comprehensive analysis of research examining links between microbial community structure and ecosystem function. Taken together, our results indicate that a greater understanding of microbial communities informed by ecological principles may enhance our ability to predict ecosystem process rates relative to assessments based on environmental variables and microbial physiology.

This paper assesses some recent trends in the novel numerical meshless method smoothed particle hydrodynamics, with particular focus on its potential use in modelling free-surface flows. Due to its Lagrangian nature, smoothed particle hydrodynamics (SPH) appears to be effective in solving diverse fluid-dynamic problems with highly nonlinear deformation such as wave breaking and impact, multi-phase mixing processes, jet impact, sloshing, flooding and tsunami inundation, and fluid–structure interactions. The paper considers the key areas of rapid progress and development, including the numerical formulations, SPH operators, remedies to problems within the classical formulations, novel methodologies to improve the stability and robustness of the method, boundary conditions, multi-fluid approaches, particle adaptivity, and hardware acceleration. The key ongoing challenges in SPH that must be addressed by academic research and industrial users are identified and discussed. Finally, a roadmap is proposed for the future developments.

An accurate study of a floating offshore wind turbine (FOWT) system requires interdisciplinary knowledge about wind turbine aerodynamics, floating platform hydrodynamics and mooring line dynamics, as well as interaction between these discipline areas. Computational Fluid Dynamics (CFD) provides a new means of analysing a fully coupled fluid-structure interaction (FSI) system in a detailed manner. In this paper, a numerical tool based on the open source CFD toolbox OpenFOAM for application to FOWTs will be described. Various benchmark cases are first modelled to demonstrate the capability of the tool. The OC4 DeepCWind semi-submersible FOWT model is then investigated under different operating conditions.

Abstract The Surface Water and Ocean Topography (SWOT) satellite mission planned for launch in 2020 will map river elevations and inundated area globally for rivers >100 m wide. In advance of this launch, we here evaluated the possibility of estimating discharge in ungauged rivers using synthetic, daily “remote sensing” measurements derived from hydraulic models corrupted with minimal observational errors. Five discharge algorithms were evaluated, as well as the median of the five, for 19 rivers spanning a range of hydraulic and geomorphic conditions. Reliance upon a priori information, and thus applicability to truly ungauged reaches, varied among algorithms: one algorithm employed only global limits on velocity and depth, while the other algorithms relied on globally available prior estimates of discharge. We found at least one algorithm able to estimate instantaneous discharge to within 35% relative root‐mean‐squared error (RRMSE) on 14/16 nonbraided rivers despite out‐of‐bank flows, multichannel planforms, and backwater effects. Moreover, we found RRMSE was often dominated by bias; the median standard deviation of relative residuals across the 16 nonbraided rivers was only 12.5%. SWOT discharge algorithm progress is therefore encouraging, yet future efforts should consider incorporating ancillary data or multialgorithm synergy to improve results.

Abstract Currents effects on waves have led to many developments in numerical wave modeling over the past two decades, from numerical choices to parameterizations. The performance of numerical models in conditions with strong currents is reviewed here, and observed strong effects of opposed currents and modulations of wave heights by tidal currents in several typical situations are interpreted. For current variations on small scales, the rapid steepening of the waves enhances wave breaking. Using different parameterizations with a dissipation rate proportional to some measure of the wave steepness to the fourth power, the results are very different, none being fully satisfactory, which points to the need for more measurements and further refinements of parameterizations. For larger-scale current variations, the observed modifications of the sea state are mostly explained by refraction of waves over currents and relative wind effects, that is, the wind speed relevant for wave generation is the speed in the frame of reference moving with the near-surface current. It is shown that introducing currents in wave models can reduce the errors on significant wave heights by more than 30% in some macrotidal environments, such as the coast of Brittany, in France. This large impact of currents is not confined to the locations where the currents are strongest, but also downwave from strong current gradients.

While global sea level has risen by 20 cm since the mid-19th century, the role of this process in present-day and past shoreline mobility is still debated. In this paper, we review previous studies that explored the relations between sea-level rise and shoreline changes over the last few decades. Existing methods can be classified into two groups: (1) approaches based on the analysis of trends and variability in shoreline change observations, which investigate whether a correlation with the temporal or spatial patterns sea level changes can be established; and (2) approaches based on the comparison of shoreline observations with a coastal model outcome, which attempt to evaluate the contribution of sea-level rise to shoreline mobility using coastal evolution modeling tools. The existing applications of these methods face two common difficulties: first, shoreline data are often lacking or insufficiently resolved temporally to capture the dynamics of coastlines; and second, relative sea level along the coast is generally only known in a limited number of areas where tide gauges are available. These two challenges can be met, owing to the increasing amount of shoreline change observations and complementary geodetic techniques. The wide range of different interpretations regarding the role of sea-level rise in recent shoreline changes highlights the necessity to conduct specific studies that rely on local observations and models applicable in the local geomorphological context.

The presence of specific benzodiazepine binding sites in the hearts of dogs and human beings was demonstrated in vivo by a noninvasive method, positron emission tomography (PET). An antagonist of the peripheral-type benzodiazepine binding site, PK 11195, was labeled with carbon-11, a short-lived positron emitter. When injected at high specific activity, 11C-PK 11195 was concentrated in the myocardium. As increasing amounts of unlabeled PK 11195 were added to the radioactive ligand, the myocardial ligand concentration was proportional to myocardial regional perfusion up to quantities of 40 nmol/kg body weight. Above 40 nmol/kg the ligand concentration reached a maximum value (6000 pmol/cm3), which could be considered as the total number of binding sites per unit heart volume. The specificity of 11C-PK 11195 binding to canine heart was demonstrated from a study on the inhibition of binding for radioligand by an excess of several agonists or antagonists of benzodiazepine receptor. The distribution and specificity of 11C-PK 11195 was similar in dogs and in human beings. PET thus opens the way to the investigation of the peripheral-type benzodiazepine receptor in a clinical situation, since it has recently been shown that this receptor could be coupled to the calcium channel in the heart.

Abstract. Assessing coastal vulnerability to climate change at regional scales is now mandatory in France since the adoption of recent laws to support adaptation to climate change. However, there is presently no commonly recognised method to assess accurately how sea level rise will modify coastal processes in the coming decades. Therefore, many assessments of the physical component of coastal vulnerability are presently based on a combined use of data (e.g. digital elevation models, historical shoreline and coastal geomorphology datasets), simple models and expert opinion. In this study, we assess the applicability and usefulness of a multi-criteria decision-mapping method (the analytical hierarchy process, AHP) to map physical coastal vulnerability to erosion and flooding in a structured way. We apply the method in two regions of France: the coastal zones of Languedoc-Roussillon (north-western Mediterranean, France) and the island of La Réunion (south-western Indian Ocean), notably using the regional geological maps. As expected, the results show not only the greater vulnerability of sand spits, estuaries and low-lying areas near to coastal lagoons in both regions, but also that of a thin strip of erodible cliffs exposed to waves in La Réunion. Despite gaps in knowledge and data, the method is found to provide a flexible and transportable framework to represent and aggregate existing knowledge and to support long-term coastal zone planning through the integration of such studies into existing adaptation schemes.

Experiments have been performed in the Shallow Water Wave Basin of DHI (Hørsholm, Denmark), on large arrays of up to 25 heaving point absorber type Wave Energy Converters (WECs), for a range of geometric layout configurations and wave conditions. WEC response and modifications of the wave field are measured to provide data for understanding WEC array interactions and to evaluate array interaction numerical models. Each WEC consists of a buoy with a diameter of 0.315 m and power take-off (PTO) is modeled by realizing friction based energy dissipation through damping of the WEC’s motion. Wave gauges are located within and around the WEC array. Wave conditions studied include regular, polychromatic, long- and short-crested irregular waves. A rectilinear arrangement of WEC support structures is employed such that several array configurations can be studied. In this paper, the experimental arrangement and the obtained database are presented. Also, results for wave height attenuation downwave a rectilinear array of 25 heaving WECs are presented, for the case of irregular waves. Up to 16.3% and 18.1% (long-crested) and 11.2% and 18.1% (short-crested waves) reduction in significant wave height is observed downwave the WEC array, for the radiated wave field only and for the combination of incident-diffracted-radiated (perturbed) wave field, respectively. Using spectra at different locations within and around the array, the wave field modifications are presented and discussed.

Abstract. The evaluation of the probability of occurrence of extreme natural events is important for the protection of urban areas, industrial facilities and others. Traditionally, the extreme value theory (EVT) offers a valid theoretical framework on this topic. In an over-threshold modelling (OTM) approach, Pickands' theorem, (Pickands, 1975) states that, for a sample composed by independent and identically distributed (i.i.d.) values, the distribution of the data exceeding a given threshold converges through a generalized Pareto distribution (GPD). Following this theoretical result, the analysis of realizations of environmental variables exceeding a threshold spread widely in the literature. However, applying this theorem to an auto-correlated time series logically involves two successive and complementary steps: the first one is required to build a sample of i.i.d. values from the available information, as required by the EVT; the second to set the threshold for the optimal convergence toward the GPD. In the past, the same threshold was often employed both for sampling observations and for meeting the hypothesis of extreme value convergence. This confusion can lead to an erroneous understanding of methodologies and tools available in the literature. This paper aims at clarifying the conceptual framework involved in threshold selection, reviewing the available methods for the application of both steps and illustrating it with a double threshold approach.

Abstract Modern offshore wind turbines are susceptible to blade deformation because of their increased size and the recent trend of installing these turbines on floating platforms in deep sea. In this paper, an aeroelastic analysis tool for floating offshore wind turbines is presented by coupling a high‐fidelity computational fluid dynamics (CFD) solver with a general purpose multibody dynamics code, which is capable of modelling flexible bodies based on the nonlinear beam theory. With the tool developed, we demonstrated its applications to the NREL 5 MW offshore wind turbine with aeroelastic blades. The impacts of blade flexibility and platform‐induced surge motion on wind turbine aerodynamics and structural responses are studied and illustrated by the CFD results of the flow field, force, and wake structure. Results are compared with data obtained from the engineering tool FAST v8.

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Abstract A field study was carried out to investigate the development of alternate bars in a secondary channel of the Loire River (France) as a function of discharge variations. We combined frequent bathymetric surveys, scour chains and stratigraphical analysis of deposits with measurements and modelling of flow dynamics. The channel exhibited migrating bars, non‐migrating bars and superimposed dunes. Possible mechanisms of bar initiation were found to be chutes associated with changes of bank direction and instability resulting from interactions between existing bars during the fall in water level after floods. We propose that the reworking of bar sediments during low flows (high width‐to‐depth ratio β ), reinforced by high values of the Shields mobility parameter, can explain the formation or re‐generation of new alternate migrating bars during a subsequent flood. The migration pattern of the bars was found to be cyclic and to depend mainly on (i) channel layout and (ii) the dynamics of superimposed dunes with heights and lengths depending on location and discharge value. For instance, the hysteresis affecting the steepness of dunes influences the flow resistance of the dunes as well as the celerity of migrating bars during flood events. We compare the findings from the field with results from theoretical studies on alternate bars. This gives insight in the phenomena occurring in the complex setting of real rivers, but it also sheds light on the extent to which bar theories based on idealized cases can predict those phenomena. Copyright © 2014 John Wiley & Sons, Ltd.

Policy must address drivers, not just symptoms, of subsidence.

Abstract. Since the turn of the 21st century, image-based velocimetry techniques have become an increasingly popular approach for determining open-channel flow in a range of hydrological settings across Europe and beyond. Simultaneously, a range of large-scale image velocimetry algorithms have been developed that are equipped with differing image pre-processing and analytical capabilities. Yet in operational hydrometry, these techniques are utilised by few competent authorities. Therefore, imagery collected for image velocimetry analysis (along with reference data) is required both to enable inter-comparisons between these differing approaches and to test their overall efficacy. Through benchmarking exercises, it will be possible to assess which approaches are best suited for a range of fluvial settings, and to focus future software developments. Here we collate and describe datasets acquired from seven countries across Europe and North America, consisting of videos that have been subjected to a range of pre-processing and image velocimetry analyses (Perks et al., 2020, https://doi.org/10.4121/uuid:014d56f7-06dd-49ad-a48c-2282ab10428e). Reference data are available for 12 of the 13 case studies presented, enabling these data to be used for reference and accuracy assessment.

BACKGROUND: Nucleoside and ritonavir (RTV) toxicities have led to increased interest in nucleoside reverse transcriptase inhibitors (NRTIs) and RTV-sparing antiretroviral regimens. SPARTAN was a multicenter, randomized, open-label, noncomparative pilot study evaluating the efficacy, safety, and resistance profile of an investigational NRTI- and RTV-sparing regimen (experimental atazanavir [ATV] dose 300 mg bid + raltegravir [RAL] 400 mg bid [ATV+RAL]). The reference regimen consisted of ATV 300 mg/RTV 100 mg qd + tenofovir (TDF) 300 mg/emtricitabine (FTC) 200 mg qd (ATV/r+TDF/FTC). METHODS: Treatment-naïve HIV-infected patients with HIV-RNA ≥5,000 copies/mL were randomized 2:1 to receive twice-daily ATV+RAL (n=63) or once-daily ATV/r+TDF/FTC (n=31). Efficacy at 24 weeks was determined by confirmed virologic response (CVR; HIV-RNA <50 copies/mL) with noncom-pleters counted as failures based on all treated subjects. RESULTS: The proportion of patients with CVR HIV RNA <50 copies/mL at week 24 was 74.6% (47/63) in the ATV+RAL arm and 63.3% (19/30) in the ATV/r+TDF/FTC arm. Systemic exposure to ATV in the ATV+RAL regimen was higher than historically observed with ATV/r+TDF/ FTC. Incidence of Grade 4 hyperbilirubinemia was higher on ATV+RAL (20.6%; 13/63) than on ATV/r+TDF/FTC (0%). The criteria for resistance testing (virologic failure [VF]: HIV-RNA ≥400 copies/mL) was met in 6/63 patients on ATV+RAL, and 1/30 on ATV/r+TDF/FTC; 4 VFs on ATV+RAL developed RAL resistance. CONCLUSIONS: ATV+RAL, an experimental NRTI- and RTV-sparing regimen, achieved virologic suppression rates comparable to current standards of care for treatment-naïve patients. The overall profile did not appear optimal for further clinical development given its development of resistance to RAL and higher rates of hyperbilirubinemia with twice-daily ATV compared with ATV/RTV.

Abstract Few studies have examined the three‐dimensional flow structure and bed morphology within elongate loops of large meandering channels. The present study focuses on the spatial patterns of three‐dimensional flow structure and bed morphology within two elongate meander loops and examines how differences in outer bank roughness influence near‐bank flow characteristics. Three‐dimensional velocities were measured during two different events—a near‐bankfull flow and an overbank event. Detailed data on channel bathymetry and bed form geometry were obtained during a near‐bankfull event. Flow structure within the loops is characterized by strong topographic steering by the point bar, by the development of helical motion associated with flow curvature, and by acceleration of flow where bedrock is exposed along the outer bank. Near‐bank velocities during the overbank event are less than those for the near‐bankfull flow, highlighting the strong influence of the point bar on redistribution of mass and momentum of the flow at subbankfull stages. Multiple outer bank pools are evident within the elongate meander loop with low outer bank roughness, but are not present in the loop with high outer bank roughness, which may reflect the influence of abundant large woody debris on near‐bank velocity characteristics. The positions of pools within both loops can be linked to spatial variations in planform curvature. The findings indicate that flow structure and bed morphology in these large elongate loops is similar to that in small elongate loops, but differs somewhat from flow structure and bed morphology reported for experimental elongate loops.

Yates, M.L.; Le Cozannet, G.; Garcin, M.; Salai, E., and Walker, P., 2013. Multidecadal atoll shoreline change on Manihi and Manuae, French Polynesia.As interest in the impact of sea-level rise on atoll islands increases, this study contributes to the growing database of observations of shoreline changes on South Pacific Islands, where few observations are currently available. Historical aerial photographs and recent satellite images were used to evaluate multidecadal surface area and shoreline changes on two atolls in French Polynesia: Manihi and Manuae. During the 40- to 50-year study period, atoll island surface area primarily increased or remained stable on Manihi and decreased on Manuae. Distinct ocean and lagoon shoreline changes were observed in different geographical regions of each atoll. On Manihi, ocean shoreline accretion rates were larger on the NW rim than the SE rim. On Manuae, atoll islands on the NE rim were eroding on the lagoon side and accreting on the ocean side, whereas islands on the SE rim showed the opposite trend. Sea-level rise is often thought to cause atoll erosion, but in this study, lagoon and ocean shorelines both eroded and accreted over a period when sea-level rise rates were greater than the global mean. Surface area changes related directly to anthropogenic activities were identified on only two of the 47 atoll islands. After completing a classification of the incident wave field, it was hypothesized that waves have an important role in controlling the shoreline change variability. Additional field surveys and in situ observations are needed to validate this hypothesis and to understand better island response to changing forcing factors.Une analyse de la mobilité du trait de côte au cours des cinquantaines dernières années a été réalisée sur deux atolls de Polynésie Franaise (Pacifique Sud): Manihi (Nord-ouest de l'archipel des Tuamotus) et Manuae (Est de l'archipel des îles de la Société). La mobilité de la limite de végétation permanente a été extraite de photographies aériennes anciennes de 1955 ou 1961 et d'images satellites à haute résolution acquises dans les années 2000. Cette analyse a nécessité le géoréférencement des photographies aériennes puis la digitalisation des limites successives de la végétation permanente. La ligne de végétation permanente a été utilisée comme marqueur des mouvements de basse fréquence du trait de côte (i.e., échelles de temps pluri-décennales). En effet, elle demeure aisément identifiable aussi bien sur les images anciennes que récentes tout en s'émancipant des variations à haute fréquence (marée, surcote etc.) et des difficultés de pointage de certains marqueurs sur les photographies anciennes. Les incertitudes liées au géoréférencement et à la digitalisation du trait de côte ont été évaluées et conduisent à ne considérer que des mouvements supérieurs à 5m sur la durée considérée. Dans de trés nombreux îlots (motu), des changements de plus grande ampleur sont observés et sont de fait sont considérés comme significatifs. Ils indiquent une tendance générale à l'érosion à Manuae et à l'accrétion à Manihi. Cependant, au sein d'un même atoll, nous observons une grande variabilité des évolutions des limites de végétation des motu : ainsi, la plupart des motu sont en accrétion côté lagon et côté océan à Manihi, toutefois, certains sont en érosion côté océan, côté lagon ou bien des deux côtés. Dans ces deux atolls peu anthropisés, les aménagements ne modifient la ligne de rivage que dans deux des 47 motu étudiés (quarante-et-un à Manihi, six à Manuae). Selon Becker et al. (2012), l'élévation du niveau marin, dans cette partie du Pacifique, a été supérieure à la moyenne globale depuis 60 ans. Des études antérieures suggèrent que l'élévation du niveau marin induit une érosion des îlots notamment sur leur face océanique. Ces effets n'apparaissent pas dominants dans les deux atolls étudiés. Au contraire, la tendance d'évolution du trait de côte obsevée n'est pas hom