CNRS Saint-Venant Hydraulics Laboratory

Paris, France

CNRS Saint-Venant Hydraulics Laboratory

Paris, France
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Onyutha C.,Muni University | Willems P.,CNRS Saint-Venant Hydraulics Laboratory
International Journal of Climatology | Year: 2017

In this study, spatio-temporal variability in daily rainfall extremes based on 0.5°×0.5° gridded data over the Nile basin was analysed using the quantile perturbation method. The co-occurrence of the extreme rainfall variability with the variation in the large-scale ocean-atmosphere conditions was also investigated. Based on a 15-year moving window, it was found that the extreme rainfall shows oscillatory behaviour over multi-decadal time scales. The latitudinal difference in the multi-decadal extreme rainfall oscillations divides the study area into the Northern, Central, and Southern regions. The variability in the extreme rainfall of the Central region is dominantly driven by the variation in the sea surface temperatures of the Atlantic and Pacific Oceans. For the Southern region, extreme rainfall variability is linked to the anomalies in the sea level pressure of the North Atlantic Ocean and the variation in the sea surface temperature of the Indian Ocean. The variation in the extreme rainfall of the Northern region corresponds to the anomalies in sea surface temperatures of the Indian and Atlantic Oceans as well as from the Pacific Ocean. © 2017 Royal Meteorological Society.

Van Mechelen C.,Nature and Landscape | Van Meerbeek K.,Nature and Landscape | Willems P.,CNRS Saint-Venant Hydraulics Laboratory | Hermy M.,Nature and Landscape
Landscape and Urban Planning | Year: 2014

Green roofs are efficient tools to improve life quality in densely populated areas. The contribution to the reduction of stormwater runoff and the heat-island effect may even augment with climate change. In this study, impacts of climatic changes on vegetation drought stress and stormwater retention of two green roof types (one with sedum-moss vegetation, one with grass-herbs vegetation) and a standard bitumen roof were assessed using a water balance model (GreenRoof). A case study of the Flemish region in Belgium was done, but the study can be representative for temperate maritime climates worldwide. Local weather data for the 2050s were generated with the LARS-WG weather generator based on climate scenarios from two multi-model ensembles of respectively 15 global and 9 regional climate models. Under the projected differences in precipitation and evaporating power of the atmosphere, runoff was expected to decrease in summer and to increase in winter on all roof types. Grass-herb green roofs could reduce runoff more than sedum-moss green roofs, but were more sensitive to increased drought stress. Both green roof types were shown to remain a valid option for runoff reduction in urban areas as compared to bitumen roofs, mainly in summer. The benefit of green roofs can increase under climatic changes but increased vegetation stress urges reconsideration of green roof design and vegetation choice to obtain an optimal runoff reduction and vegetation survival. © 2013 Elsevier B.V.

Camenen B.,IRSTEA | van Bang D.P.,CNRS Saint-Venant Hydraulics Laboratory
Continental Shelf Research | Year: 2011

This paper deals with the sedimentation of highly concentrated sediment suspensions (cohesive as well as non-cohesive) and the beginning of the consolidation of cohesive sediments. Based on a comparison of existing empirical formulas and experimental data, the particle Reynolds number was shown to be of importance for the behaviour of particularly non-cohesive sediments. In addition it plays a role in determining whether one or two interfaces develop during the sedimentation phase. In the case of cohesive sediments, the estimation of the gelling concentration, although difficult, seems to be fundamental. Some suggestions on the estimation of the permeability coefficient and total settling function are then given in order to improve the modelling of the sedimentation and consolidation behaviour for concentrations close to the gelling concentration. © 2010 Elsevier Ltd.

Goutal N.,Électricité de France | Sainte-Marie J.,CNRS Saint-Venant Hydraulics Laboratory | Sainte-Marie J.,French Institute for Research in Computer Science and Automation
International Journal for Numerical Methods in Fluids | Year: 2011

The classical Saint-Venant system is well suited for the modeling of dam breaks, hydraulic jumps, reservoir emptying, flooding etc. For many applications, the extension of the Saint-Venant system to the case of non-rectangular channels is necessary and this section-averaged Saint-Venant system exhibits additional source terms. The main difficulty of these equations consists of the discretization of these source terms. In this paper we propose a kinetic interpretation for the section averaged Saint-Venant system and derive an associated numerical scheme. The numerical scheme-2nd order in space and time-preserves the positivity of the water height, and is well-balanced. Numerical results including comparisons with analytic and experimental test problems illustrate the accuracy and the robustness of the numerical algorithm. © 2010 John Wiley & Sons, Ltd.

Chapelle D.,French Institute for Research in Computer Science and Automation | Gerbeau J.-F.,French Institute for Research in Computer Science and Automation | Sainte-Marie J.,French Institute for Research in Computer Science and Automation | Sainte-Marie J.,CNRS Saint-Venant Hydraulics Laboratory | Vignon-Clementel I.E.,French Institute for Research in Computer Science and Automation
Computational Mechanics | Year: 2010

This paper is motivated by the modeling of blood flows through the beating myocardium, namely cardiac perfusion. As in other works, perfusion is modeled here as a flow through a poroelastic medium. The main contribution of this study is the derivation of a general poroelastic model valid for a nearly incompressible medium which experiences finite deformations. A numerical procedure is proposed to iteratively solve the porous flow and the nonlinear poroviscoelastic problems. Three-dimensional numerical experiments are presented to illustrate the model. The first test cases consist of typical poroelastic configurations: swelling and complete drainage. Finally, a simulation of cardiac perfusion is presented in an idealized left ventricle embedded with active fibers. Results show the complex temporal and spatial interactions of the muscle and blood, reproducing several key phenomena observed in cardiac perfusion. © 2009 Springer-Verlag.

Audusse E.,University of Paris 13 | Audusse E.,French Institute for Research in Computer Science and Automation | Bristeau M.-O.,French Institute for Research in Computer Science and Automation | Pelanti M.,French Institute for Research in Computer Science and Automation | And 3 more authors.
Journal of Computational Physics | Year: 2011

We present a multilayer Saint-Venant system for the numerical simulation of free surface density-stratified flows over variable topography. The proposed model formally approximates the hydrostatic Navier-Stokes equations with a density that varies depending on the spatial and temporal distribution of a transported quantity such as temperature or salinity. The derivation of the multilayer model is obtained by a Galerkin-type vertical discretization of the Navier-Stokes system with piecewise constant basis functions. In contrast with classical multilayer models in the literature that assume immiscible fluids, we allow here for mass exchange between layers. We show that the multilayer system admits a kinetic interpretation, and we use this result to formulate a robust finite volume scheme for its numerical approximation. Several numerical experiments are presented, including simulations of wind-driven stratified flows. © 2011 Elsevier Inc.

Levy F.,University Paris Diderot | Levy F.,CNRS Saint-Venant Hydraulics Laboratory | Jaupart C.,University Paris Diderot
Geophysical Journal International | Year: 2012

We investigate how subduction may be triggered by continental crust extension at a continental margin. The large topography contrast between continental and oceanic domains drives the spreading of continental crust over oceanic basement. Subduction requires the oceanic plate to get submerged in mantle, so that negative buoyancy forces may take over and drive further descent. This is promoted by two mechanisms. Loading by continental crust bends the oceanic plate downwards. Extension in the continental domain induces crustal thinning, which acts to raise mantle above the oceanic plate. In this model, the width of the continental region undergoing extension is an important control parameter. The main physical controls are illustrated by laboratory experiments and simple theory for elastic flexure coupled to viscous crustal spreading. Three governing dimensionless parameters are identified. One involves the poorly constrained oceanic plate buoyancy. We find that the oceanic plate can be thrust to depths larger than 40km even if it is buoyant, enabling metamorphic reactions and density increase in the oceanic crust. Another parameter is the ratio between the width of the continental extension region and the flexural parameter for the oceanic plate. Initiating subduction is easier if the continent thins over a short lateral distance or if the oceanic plate is strong. The third important parameter is the ratio of oceanic plate thickness to initial continental crust thickness, such that a weak plate and a thick crust do not favour subduction. Thus, the change from a passive to an active margin depends on the local characteristics of the continental crust and is not determined solely by the age and properties of the oceanic lithosphere. It is shown that the spreading of continental crust induces uplift of the margin as the adjacent seafloor subsides. Evidence for the emplacement of continental crust over oceanic basement at passive margins is reviewed. © 2012 The Authors Geophysical Journal International © 2012 RAS.

Bristeau M.-O.,French Institute for Research in Computer Science and Automation | Goutal N.,CNRS Saint-Venant Hydraulics Laboratory | Goutal N.,Électricité de France | Sainte-Marie J.,French Institute for Research in Computer Science and Automation | Sainte-Marie J.,CNRS Saint-Venant Hydraulics Laboratory
Computers and Fluids | Year: 2011

For geophysical flows, the Saint-Venant system is often a good approximation of the Navier-Stokes equations and so it is widely used for the simulations of shallow water flows and gravity waves. But the Saint-Venant system fails to represent the non-hydrostatic effects such as those associated for example with dispersive waves. To overcome this limitation, we propose an extended version of the Saint-Venant system and an associated finite volume scheme for the numerical simulations. The proposed model has several interesting properties e.g. it admits an energy balance and it preserves the dynamics of solitary waves. Several numerical results are given and especially comparisons between simulations and experimental measurements. © 2011 Elsevier Ltd.

Brigode P.,Électricité de France | Brigode P.,CNRS Transfers and Interactions in Hydrosystems and Soils | Bernardara P.,Électricité de France | Bernardara P.,CNRS Saint-Venant Hydraulics Laboratory | And 4 more authors.
International Journal of Climatology | Year: 2013

Classifications of atmospheric circulation patterns are useful tools to improve the description of the climate of a given region and the analysis of meteorological situations. In particular, weather pattern (WP) classifications could be used to improve the description of spatial heavy rainfall. Here, a bottom-up approach, previously used to build WP classification in France, is applied for the definition of a WP classification useful for the description of Austrian heavy rainfall. The optimal spatial extent and the optimal position of the geopotential fields to be taken into account for a WP classification is studied. The proposed WP classification is shown to be coherent with the general knowledge on synoptic situations responsible for heavy rainfall over Austria. Moreover, the classification has good performances in terms of heavy rainfall spatial description compared to 152 COST 733 classifications defined in the same region. In particular, we show that the choice of spatial extent of the geopotential fields, their position and their characteristics is relevant for capturing physical information on synoptic situations responsible for heavy rainfall and that it can improve WP classification performances. © 2012 Royal Meteorological Society.

Kumcu S.Y.,University of Konya | Kokpinar M.A.,CNRS Saint-Venant Hydraulics Laboratory
World Environmental and Water Resources Congress 2013: Showcasing the Future - Proceedings of the 2013 Congress | Year: 2013

Circular dropshafts, commonly used in urban storm water systems for energy dissipation and flow control, are characterized by significant flow aeration. In the laboratory, a series of experiments were performed in a circular dropshaft having two identical horizontal inflow and outflow circular channels having diameters of d=0.12 m, and a circular drop chamber having diameter of D=0.358 m for observing flow patterns and measuring air bubble entrainment flow parameters. Experimental observations showed distinct flow regimes associated with nappe impact in the shaft pool, in the outflow channel, or in the opposite shaft wall. New detailed air-water flow measurements were conducted in a circular dropshaft with using double-tip fiber optical probe. Measurements of void fractions, bubble frequencies, and bubble sizes were conducted for different flow conditions of the circular inflow channel. In the shaft pool, the results obtained from measurements demonstrated the complexity of different air entrainment mechanisms. © 2013 American Society of Civil Engineers.

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