Publications

2016

• Dynamique de plages sableuses enclavées à la pointe Bretagne
  
  • Quilfen Victor
  , 2016. La thèse a pour objectif l'étude des plages sableuses enclavées, i.e. contraintes aux extrémités par des caps rocheux, soumises aux vagues et à un cycle de marée morte-eau vive-eau. Une double approche complémentaire liant études numériques et observations et mesures in situ sur un site-atelier a été retenue. Deux modèles déterministes basés sur les différents processus physiques (hydrodynamiques, hydro-sédimentaires et morphodynamiques) en jeu dans la zone littorale et moyennés sur la verticale (2DH) on été sélectionnés. Le code XBeach (Roelvink et al., 2009) utilise un maillage aux différences finies et intègre certaines spécificités tels qu'un modèle de propagation d'un rouleau d'écume ("roller"), un modèle de génération d'ondes longues et un modèle de développement d'un contre-courant de retour "undertow". Le code TELEMAC (Hervouet, 2007) utilise un maillage aux éléments finis. Pour le site-atelier, les plages enclavées adjacentes de La Palue et de Lostmarc'h en Presqu'île de Crozon (Finistère) ont été choisies pour leur bathymétrie complexe (présence de chenaux de baïne et d'un saillant) et leur géométrie complexe (caps rocheux de longueurs diverses, îlot). Une année d'observations et de mesures in situ (levés topographiques, pose de courantomètres ADV) a été entreprise entre le mois de septembre 2014 et le mois de septembre 2015, par diverses conditions météorologiques.Dans un premier temps, la dynamique globale des plages enclavées, représentées schématiquement par une échancrure rectangulaire, a été appréhendée. En particulier, la genèse d'une barre de déferlement en zone subtidale sous l'influence des dimensions de l'échancrure rocheuse, d'un cycle de marée morte-eau vive-eau et de houles énergétiques a été illustrée à travers plusieurs séries de simulations numériques à l'aide du code XBeach.Dans un deuxième temps, la modélisation hydrodynamique des courants sur les plages de La Palue et de Lostmarc'h a été effectuée, avec l'objectif d'étudier l'influence des caractéristiques des houles (hauteur, période et direction) et de celles de l'échancrure rocheuse (longueur des caps, espacement des caps, inclinaison des pointes) sur la prédiction des courants. Une ouverture sur la modélisation aux éléments finis (TELEMAC) en comparaison à celle aux différences finies (XBeach) a été présentée. Le code XBeach a été validé sur le plan hydrodynamique grâce aux mesures in situ d'une campagne de terrain réalisée en janvier 2015. Une étude numérique hydro-sédimentaire sur une lunaison complète (du 01 septembre 2015 au 29 septembre 2015) a alors été entreprise à l'aide du code XBeach, afin d'étudier l'intensité et la direction des flux sédimentaires instantanés et résiduels au gré des différents climats de houle et de marée, et selon les différents secteurs typologiques des plages de La Palue et de Lotsmarc'h. Cela a permis de mettre en évidence les particularités de la dynamique des plages enclavées par rapport aux plages ouvertes "quasi-infinies", tels que le phénomène de "contournement de cap", mais aussi les similitudes. Les résultats du code XBeach, pour différentes configurations du modèle, ont par ailleurs été comparés aux levés topographiques réalisés au cours du mois de septembre 2015.Dans un troisième temps, après une analyse statistique approfondie des climats de houle au large des plages de La Palue et de Lostmarc'h sur une période de 7 ans, l'impact morphodynamique de tempêtes extrêmes (houles décennale et cinquentennale) conjugué à celui de la hausse du niveau marin induit par le changement climatique, a été estimé sous la forme d'une étude numérique à l'aide du code XBeach sur un profil transversal au sud de la plage de La Palue (10.70675/d9efb90dzf20dz4079zb0d3z3ab393fb3b22)
  DOI : 10.70675/d9efb90dzf20dz4079zb0d3z3ab393fb3b22
• Nonlinear and dispersive numerical modeling of nearshore waves
  
  • Raoult Cécile
  , 2016. In this work, a potential flow model based on the Euler-Zakharov equations was developed with the objective of simulating the propagation of irregular and multidirectional sea states from deep water conditions to the coast over variable bathymetry. A highly accurate representation of nonlinear and dispersive effects for bidimensional (2DH) nearshore and coastal domains on the order of kilometers is targeted.The preexisting 1DH version of the model, resolving the Laplace Boundary Value problem using a combination of high-order finite difference schemes in the horizontal direction and a spectral approach in the vertical direction, was improved and validated. The generation of incident waves through the implementation of specific Dirichlet and Neumann boundary conditions was studied in detail. In practice, these conditions were used in combination witha relaxation zone to improve the stability of the model.The linear dispersion relation of the model was derived analytically for the flat bottom case. Its analysis showed that the accuracy of the representation of dispersive effects improves significantly by increasing the vertical resolution (i.e. the maximum degree of the Chebyshev polynomial basis used to project the potential in the vertical). A convergence study conducted for moderate to highly nonlinear solitary waves confirmed the exponential convergence in the vertical dimension owing to the spectral approach, and the algebraic convergence in time and in space (horizontal dimension) with orders of about 4 (or higher) in agreement with the numerical schemes used.The capability of the model to represent nonlinear effects induced by variable bathymetry, such as the transfer of energy between harmonic components, as well as the accurate representation of dispersive properties, were demonstrated with comparisons to several experimental data sets. A visco-potential flow formulation was also implemented to take into account viscous effects induced by bulk viscosity and bottom friction. This formulation was validated inthe limit of small viscosity for mild slope bathymetries.To represent 2DH wave fields in complex nearshore domains, the model was extended using an unstructured discretization (scattered nodes) in the horizontal plane. The horizontal derivatives were estimated using the RBF-FD (Radial Basis Function - Finite Difference) method, while the spectral approach in the vertical remained unchanged. A series of sensitivity tests were conducted to evaluate numerically the robustness of the RBF-FD method, including a comparison of a variety of RBFs with or without shape factors and augmented polynomials. The 2DH version of the model was used to simulate two wave basin experiments, validating the approach and demonstrating the applicability of this method for 3D wave propagation, including nonlinear effects. As an initial attempt to improve the computational efficiency ofthe model for running simulations of large spatial domains, the code was adapted to use a parallelized direct linear solver (10.70675/a722e814zb01az4d5dz84bbz8873ab8f66a5)
  DOI : 10.70675/a722e814zb01az4d5dz84bbz8873ab8f66a5
• An application of the Reduced-Basis Method for Darcy flows
  
  • Sanchez Riad
  • Boyaval Sébastien
  • Enchéry Guillaume
  • Tran Quang Huy
  , 2016.
• Predicting the flow in the floodplains with evolving land occupations during extreme flood events (FlowRes ANR project)
  
  • Proust Sébastien
  • Berni Céline
  • Boudou Martin
  • Chiaverini Antoine
  • Dupuis Victor
  • Faure Jean-Baptiste
  • Paquier André
  • Lang Michel
  • Guillen Ludena Sebastian
  • Lopez Diego
  • Mignot Emmanuel
  • Riviere Nicolas
  • Chagot Loic
  • Rouzes Maxime
  • Moulin Frédéric
  • Goutal Nicole
  • Oukacine Marina
  • Peltier Yann
  • Ferreira Rui M.L.
  • Brito Moisés
  • Alves Elsa
  • Gymnopoulos Miltiadis
  • Leal Joao
  • Mathurin Bastien
  • Soarez Frazao Sandra
  • Bousmar Didier
  • Fernandes Joao
  • Eiff Olivier
  , 2016, pp.12 p.. Flood hazards (flow depth and velocity) must be accurately assessed in high-risk areas during extreme flood events. However, the prediction of the very high flows is not an easy task due to the lack of field data and to the strong link between flow resistance and the land occupation of the floodplain. Confinement and inhomogeneity in lateral and longitudinal directions of hydraulic roughness strongly vary with return period T. The physical processes are complex, some still largely unexplored, and the assumptions linked to numerical modelling cannot be validated without field data. The FlowRes project (2015-2018), funded by the French National Research Agency (ANR), aims at improving the flood hazard assessment in floodplains in: 1) investigating in laboratory the hydrodynamic structure associated with extreme flood flows for various land occupations and flow discharge magnitudes; 2) assessing if the existing numerical modelling practices used for T ~ 100 years are still valid for extreme events with T > 1000 years, relying on the experimental
• Ensemble-based algorithm for error reduction in hydraulics in the context of flood forecasting
  
  • Barthélémy Sébastien
  • Ricci Sophie
  • Le Pape Etienne
  • Rochoux Mélanie
  • Thual Olivier
  • Goutal Nicole
  • Habert Johan
  • Piacentini Andrea
  • Jonville Gabriel
  • Zaoui Fabrice
  • Gouin Philippe
  , 2016, 7, pp.18022. Over the last few years, a collaborative work between CERFACS, LNHE (EDF R&D), SCHAPI and CE-REMA resulted in the implementation of a Data Assimilation (DA) method on top of MASCARET in the framework of real-time forecasting. This prototype was based on a simplified Kalman filter where the description of the background error covariances is prescribed based on off-line climatology constant over time. This approach showed promising results on the Adour and Marne catchments as it improves the forecast skills of the hydraulic model using water level and discharge in-situ observations. An ensemble-based DA algorithm has recently been implemented to improve the modelling of the background error covariance matrix used to distribute the correction to the water level and discharge states when observations are assimilated from observation points to the entire state. It was demonstrated that the flow dependent description of the background error covariances with the EnKF algorithm leads to a more realistic correction of the hydraulic state with significant impact of the hydraulic network characteristics. (10.1051/e3sconf/20160718022)
  DOI : 10.1051/e3sconf/20160718022
• 3D numerical modelling of dune formation and dynamics in inland waterways
  
  • Goll Annalena
  , 2016. In this work the possibilities of direct modelling of large scale bed forms in waterways are highlighted and analysed. It is motivated by the fact that in river modelling, uncertainties in predicting water depth and bed movement can often be attributed to bed forms. Those bed forms are the dominating factor for bed load transport in many river stretches, which need to be maintained by the responsible waterways authorities.Hydrodynamic and morphodynamic experiments have been conducted at the Federal Waterways Engineering and Research Institute of Germany (BAW). High-resolution measurements have been performed over fixed, naturally formed three-dimensional sand dunes, which are at equilibrium with the surrounding flow field.Using these measured data sets, the hydrodynamic model is calibrated to simulate the complex flow situation over a train of several three-dimensional dunes. Simulation results show that it is possible to reproduce the measured turbulent flow field in the wake of the fixed dunes and that the measured and simulated water levels agree for the chosen configuration. Vertical and horizontal mesh resolution, friction coefficient, small scale bed forms and turbulence modelling are identified as most sensitive parameters during the calibration.The second part of this thesis focuses on morphodynamic simulations of the same experimental flume but with a mobile bed. High resolution measured bottom scans of the dune forms, developing over time, are available for comparison. Dune height and length, as well as the distribution moments, skewness and kurtosis are used to compare the dimensions of the dunes and also their shape and spatial distribution.Bed load transport formulation, skewness and kurtosis formulae, boundary conditions and the consideration of sub-grid scale roughness elements are the parameters which influence the quality of the results the most. A particular focus during the study is the inclusion of turbulent fluctuations in bed shear stress calculation. A new, total bed shear stress calculation is proposed, which incorporates mean flow velocities and turbulent kinetic energy provided by the turbulence model. With this approach, the numerical model is able to reproduce both qualitatively and quantitatively the measured mean bed forms dimensions and the shape moments of the physical dunes. It proves to be the only way to also produce the right distribution moment (kurtosis) of the dune field.Finally, the model is applied to project scale and tested on a stretch of the riverElbe, Germany. High resolution morphodynamic simulations coupled to 3D-hydrodynamics are conducted over several days for the chosen river stretch which is 4km in length. The dune forms preserve form and shape parameters and the dune speed agrees with the measured one. The simulations show promising results concerning the possibility of operational use of the model in the future. Local problems and statements, e.g. maintenance strategies such as changes in flow cross section, groynes and revetments, are possible tasks that can be examined (10.70675/75cc7f21z6eb0z4b37zb5b5zfe535b21e55d)
  DOI : 10.70675/75cc7f21z6eb0z4b37zb5b5zfe535b21e55d
• Towards the simulation of submerged bottom structures with vertical walls using Telemac-3D
  
  • Wang Pengze
  • Joly Antoine
  • Leroy Agnès
  , 2016. In the Telemac-Mascaret community, there is an increasing need for Telemac-3D to handle unstructured 3D meshes. One of the main target applications is the simulation of submerged structures in the flow. With this aim in view, a first step is to modify the code so that it can account for vertical structures on the bed. This is done while maintaining the advantages of the layered 3D meshes currently used in Telemac-3D, since a full destructuration would imply more complex neighbour searches, data access and would require major changes in the algorithms. The proposed approach will be presented in this article, including a description of the necessary developments, comparisons of CPU time before and after the changes, and a qualitative test case.
• Unsteady open boundaries for SPH using semi-analytical conditions and Riemann solver in 2D
  
  • Ferrand Martin
  • Joly Antoine
  • Kassiotis Christophe D
  • Violeau Damien
  • Leroy Agnès D
  • Morel François-Xavier
  • Rogers Benedict D
  , 2016. Due to the Lagrangian nature of SPH, treating inlet/outlet boundaries (that are intrinsically Eulerian) is a challenging issue. An extension to the Unified Semi-Analytical boundary conditions is presented to deal with unsteady open boundaries in confined and free-surface flows. The presented method uses Riemann invariants to calculate flow properties near the open boundaries, thus allowing the possibility to treat complex shapes. Furthermore, details are presented for a parallel implementation of this method, including particle creation and deletion , updating properties of vertices and segments, and additional constraints on the time step. Simple validation cases are then displayed to illustrate the performance of the proposed method as well as the ability to deal with complex problems such as generation of water waves and free outlets.
• A new approach of monitoring and physically-based modelling to investigate urban wash-off process on a road catchment near Paris
  
  • Hong Yi
  • Bonhomme Céline
  • Le Minh-Hoang
  • Chebbo Ghassan
  Water Research, IWA Publishing/Elsevier, 2016, 102, pp.96 - 108. Nowadays, the increasing use of vehicles is causing contaminated stormwater runoff to drain from roads. The detailed understanding of urban wash-off processes is essential for addressing urban management issues. However, existing modelling approaches are rarely applied for these objectives due to the lack of realistic input data, unsuitability of physical descriptions, and inadequate documentation of model testing. In this context, we implement a method of coupling monitoring surveys with the physically-based FullSWOF (Full Shallow Water equations for Overland Flow) model (Delestre et al., 2014) and the process-based H-R (Hairsine-Rose) model (Hairsine and Rose, 1992a, 1992b) to evaluate urban wash-off process on a road catchment near Paris (Le Perreux sur Marne, Val de Marne, France, 2661 m2). This work is the first time that such an approach is applied for road wash-off modelling in the context of urban stormwater runoff. On-site experimental measurements have shown that only the finest particles of the road dry stocks could be transferred to the sewer inlet during rainfall events, and most Polycyclic Aromatic Hydrocarbons (PAHs) are found in the particulate phase. Simulations over different rainfall events represent promising results in reproducing the various dynamics of water flows and sediment transports at the road catchment scale. Elementary Effects method is applied for sensitivity analysis. It is confirmed that settling velocity (Vs) and initial dry stocks (S) are the most influential parameters in both overall and higher order effects. Furthermore, flow-driven detachment seems to be insignificant in our case study, while raindrop-driven detachment is shown to be the major force for detaching sediment from the studied urban surface. Finally, a multiple sediment classification regarding the Particle Size Distribution (PSD) can be suggested for improving the model performance for future studies. (10.1016/j.watres.2016.06.027)
  DOI : 10.1016/j.watres.2016.06.027
• Evolution of Surge Levels Inside Harbour Basins: The Case of Le Havre Harbour
  
  • Laborie Vanessya
  • Sergent Philippe
  • Hissel François
  , 2016, pp.145-155. (10.1007/978-981-287-615-7_10)
  DOI : 10.1007/978-981-287-615-7_10
• Validation of a fully nonlinear and dispersive wave model with laboratory non-breaking experiments
  
  • Raoult Cécile
  • Benoit Michel
  • Yates Marissa L.
  Coastal Engineering, Elsevier, 2016, 114, pp.194 - 207. With the objective of modeling coastal wave dynamics taking into account nonlinear and dispersive effects, a highly accurate nonlinear potential flow model was developed. The model is based on the time evolution of two surface quantities: the free surface position and the free surface velocity potential. A spectral approach is used to resolve vertically the velocity potential in the domain, by decomposing the potential using an orthogonal basis of Cheby-shev polynomials. With this approach, a wide range of relative water depths can be simulated, as demonstrated here with the propagation of nonlinear regular waves over a flat bottom with kh = 2π and 4π (where k is the wave number and h the water depth). The model is then validated by comparing the simulation results to experimental data for four non-breaking wave test cases: (1) nonlinear dynamics of a wave train generated by a piston-type wavemaker in constant water depth, (2) shoaling of a regular wave train on beach with constant slope up to the breaking point, (3) propagation of regular waves over a submerged bar, and (4) propagation of nonlinear irregular waves over a barred beach. The test cases show the ability of the model to reproduce well nonlinear wave interactions and the dynamics of higher-order bound and free harmonics. The simulation results agree well with the experimental data, confirming the model's ability to simulate accurately nonlinear and dispersive effects for non-breaking waves. (10.1016/j.coastaleng.2016.04.003)
  DOI : 10.1016/j.coastaleng.2016.04.003
• Johnson-Segalman – Saint-Venant equations for viscoelastic shallow flows in the elastic limit
  
  • Boyaval Sébastien
  , 2017. The shallow-water equations of Saint-Venant, often used to model the long-wave dynamics of free-surface flows driven by inertia and hydrostatic pressure, can be generalized to account for the elongational rheology of non-Newtonian fluids too. We consider here the 4 × 4 shallow-water equations generalized to viscoelastic fluids using the Johnson-Segalman model in the elastic limit (i.e. at infinitely-large Deborah number, when source terms vanish). The system of nonlinear first-order equations is hyperbolic when the slip parameter is small ζ ≤ 1/2 (ζ = 1 is the corotational case and ζ = 0 the upper-convected Maxwell case). Moreover, it is naturally endowed with a mathematical entropy (a physical free-energy). When ζ ≤ 1/2 and for any initial data excluding vacuum, we construct here, when elasticity G > 0 is non-zero, the unique solution to the Riemann problem under Lax admissibility conditions. The standard Saint-Venant case is recovered when G → 0 for small data.
• Numerical study on river bar response to spatial variations of channel width
  
  • Tassi Pablo
  • Duró Gonzalo
  • Crosato Alessandra
  Advances in Water Resources, Elsevier, 2016, 93, pp.21 - 38. (10.1016/j.advwatres.2015.10.003)
  DOI : 10.1016/j.advwatres.2015.10.003
• Modelling river bank erosion using a 2D depth-averaged numerical model of flow and non-cohesive, non-uniform sediment transport
  
  • Tassi Pablo
  • El Kadi Abderrezzak Kamal
  • Die Moran Andres
  • Ata Riadh
  • Hervouet Jean-Michel
  Advances in Water Resources, Elsevier, 2016, 93, pp.75 - 88. (10.1016/j.advwatres.2015.11.004)
  DOI : 10.1016/j.advwatres.2015.11.004
• Improved numerical modeling of morphodynamics of rivers with steep banks
  
  • Tassi Pablo
  • Langendoen Eddy
  • Mendoza Alejandro
  • Abad Jorge
  • Wang Dongchen
  • Ata Riadh
  • El Kadi Abderrezzak Kamal
  • Hervouet Jean-Michel
  Advances in Water Resources, Elsevier, 2016, 93, pp.4 - 14. (10.1016/j.advwatres.2015.04.002)
  DOI : 10.1016/j.advwatres.2015.04.002
• Applying Riemann solvers to open boundaries in free surface and confined flows
  
  • Joly Antoine
  • Violeau Damien
  • Leroy Agnès D
  • Ferrand Martin
  , 2016. Due to the Lagrangian nature of SPH, dealing with open boundaries (which are intrinsically Eulerian) is a challenging issue. This issue has recently been addressed in the Unified Semi-Analytical Boundaries framework [1], where it has been shown how to properly deal with mass fluxes at the open boundaries. However imposing both velocities and pressures on the open boundaries will over-constrain the problem, and in most cases only one of these quantities will be known. Therefore, Riemann Solvers can be used to calculate and prescribe compatible fields at the open boundaries. These compatible fields allow therefore complex boundary conditions to be imposed.
• Nouveaux schémas de convection pour les écoulements à surface libre
  
  • Pavan Sara
  , 2016. Cette thèse a pour objectif la construction de schémas d’ordre élevé et peu diffusifs pour le transport d’un scalaire dans les écoulements à surface libre, en deux ou trois dimensions. On souhaite en particulier obtenir des schémas robustes, qui gardent au niveau discret les propriétés mathématiques de l’équation de transport avec une faible diffusion numérique, et les utiliser sur des cas industriels. Dans ce travail deux méthodes numériques sont envisagées : une méthode aux volumes finis (VF) et une méthode aux résidus distribués (RD). Dans les deux cas, l’équation de transport est résolue avec une approche découplée, qui est la solution la plus avantageuse en termes de précision et de coûts de calcul. Pour ce qui concerne la méthode aux volumes finis, les équations de Saint-Venant couplées à l’équation du transport sont d’abord résolues avec un schéma dit vertex-centred où le flux numérique est approximé avec un solveur de Riemann appelé Harten-Lax-Van Leer-Contact [135]. A partir de cette approche, une formulation découplée est proposée. Cette dernière permet de résoudre l’équation du transport avec un pas de temps plus grand que celui de la formulation couplée. Cette idée a été d’abord proposée pour d’autres schémas dans [13]. Pour augmenter l’ordre de précision en espace, la technique MUSCL [89] est utilisée en combinaison avec l’approche découplée. Finalement, la problématique des zones sèches est abordée. Dans le cas de la méthode aux résidus distribués, les équations de Saint-Venant sont résolues avec une méthode éléments finis, et la méthode RD est utilisée seulement pour discrétiser l’équation du transport, en focalisant l’attention sur les problèmes non stationnaires. L’équation de continuité du fluide discrétisée est employée pour garantir la conservation de la masse et le principe du maximum. Pour obtenir des schémas d’ordre deux dans les problèmes non stationnaires, un schéma prédicteur-correcteur [112] est utilisé, en l’adaptant au cas de concentration moyennée sur la verticale. Une version d’ordre 1 mais peu diffusive, est aussi présentée dans ce travail. De plus, un schéma localement implicite, complètement nouveau, est aussi formulé pour pouvoir traiter le problème des bancs découvrant. Les deux techniques sont validées d’abord sur des cas simples, pour évaluer l’ordre de précision des schémas et ensuite sur des cas plus complexes pour vérifier aussi les autres propriétés numériques. Les résultats montrent que les nouveaux schémas sont à la fois précis et conservatifs, tout en gardant la monotonie comme le prévoient les démonstrations. Un cas d’application industriel est aussi présenté en conclusion. Le schéma prédicteur-correcteur RD est adapté aussi au cas 3D, sans aucun problème théorique nouveau, par rapport au cas 2D. Les propriétés de base des schémas sont validées sur des cas test préliminaires (10.70675/fcd6a156z0e6cz4e0czbe71ze68525cebc34)
  DOI : 10.70675/fcd6a156z0e6cz4e0czbe71ze68525cebc34
• Smoothed particle hydrodynamics (SPH) for free-surface flows: past, present and future
  
  • Violeau Damien
  • Rogers Benedict D.
  Journal of Hydraulic Research, Taylor & Francis, 2016, 54 (1), pp.1 - 26. (10.1080/00221686.2015.1119209)
  DOI : 10.1080/00221686.2015.1119209
• Parallel SOR methods with a parabolic-diffusion acceleration technique for solving an unstructured-grid Poisson equation on 3D arbitrary geometries
  
  • Zapata M. A. Uh
  • Pham van Bang Damien
  • Nguyen K. D.
  International Journal of Computational Fluid Dynamics, Taylor & Francis, 2016, 30 (5), pp.370-385. (10.1080/10618562.2016.1234045)
  DOI : 10.1080/10618562.2016.1234045
• Finite element modelling of local scour below a pipeline under steady currents
  
  • Zhao Lanhao
  • Guo Bowen
  • Bai Xin
  • Zhang Wei
  • Li Tongchun
  • Williams J. J. R.
  International Journal of Computational Fluid Dynamics, Taylor & Francis, 2016, 30 (1), pp.1-6. (10.1080/10618562.2016.1142076)
  DOI : 10.1080/10618562.2016.1142076
• Unified derivation of thin-layer reduced models for shallow free-surface gravity flows of viscous fluids
  
  • Bouchut François
  • Boyaval Sébastien
  European Journal of Mechanics - B/Fluids, Elsevier, 2016, 55 (1), pp.116-131. We propose a unified framework to derive thin-layer reduced models for some shallow free-surface flows driven by gravity. It applies to incompressible homogeneous fluids whose momentum evolves according to Navier-Stokes equations, with stress satisfying a rheology of viscous type (i.e. the standard Newtonian law with a constant viscosity, but also non-Newtonian laws generalized to purely viscous fluids and to viscoelastic fluids as well). For a given rheology, we derive various thin-layer reduced models for flows on a rugous topography slowly varying around an inclined plane. This is achieved thanks to a coherent simplification procedure, which is formal but based on a mathematically clear consistency requirement between scaling assumptions and the approximation errors in the differential equations. The various thin-layer reduced models are obtained depending on flow regime assumptions (either fast/inertial or slow/viscous). As far as we know, it is the first time that the various thin-layer reduced models investigated here are derived within the same mathematical framework. Furthermore, we obtain new reduced models in the case of viscoelastic non-Newtonian fluids, which extends [Bouchut & Boyaval, M3AS (23) 8, 2013]. (10.1016/j.euromechflu.2015.09.003)
  DOI : 10.1016/j.euromechflu.2015.09.003
• First-order uncertainty analysis using Algorithmic Differentiation of morphodynamic models
  
  • Villaret Catherine
  • Kopmann Rebekka
  • Wyncoll David
  • Riehme Jan
  • Merkel Uwe
  • Naumann Uwe
  Computers & Geosciences, Elsevier, 2016, 90, pp.144-151. We present here an efficient first-order second moment method using Algorithmic Differentiation (FOSM/AD) which can be applied to quantify uncertainty/sensitivities in morphodynamic models. Changes with respect to variable flow and sediment input parameters are estimated with machine accuracy using the technique of Algorithmic Differentiation (AD). This method is particularly attractive for process-based morphodynamic models like the Telemac-2D/Sisyphe model considering the large number of input parameters and CPU time associated to each simulation. The FOSM/AD method is applied to identify the relevant processes in a trench migration experiment (van Rijn, 1987). A Tangent Linear Model (TLM) of the Telemac-2D/Sisyphe morphodynamic model (release 6.2) was generated using the AD-enabled NAG Fortran compiler. One single run of the TLM is required per variable input parameter and results are then combined to calculate the total uncertainty. The limits of the FOSM/AD method have been assessed by comparison with Monte Carlo (MC) simulations. Similar results were obtained assuming small standard deviation of the variable input parameters. Both settling velocity and grain size have been identified as the most sensitive input parameters and the uncertainty as measured by the standard deviation of the calculated bed evolution increases with time. (10.1016/j.cageo.2015.10.012)
  DOI : 10.1016/j.cageo.2015.10.012
• Différentiation algorithmique appliquée à la calibration optimale d'un modèle hydraulique à surface libre
  
  • Demangeon Félix
  • Goeury Cédric
  • Zaoui Fabrice
  • Goutal Nicole
  • Pascual Valérie
  • Hascoët Laurent
  La Houille Blanche - Revue internationale de l'eau, EDP Sciences, 2016 (4), pp.57-65. (10.1051/lhb/2016040)
  DOI : 10.1051/lhb/2016040
• Assessing flood forecast uncertainty with fuzzy arithmetic
  
  • de Bruyn Bertrand
  • Fayet Laurence
  • Laborie Vanessya
  E3S Web of Conferences, EDP Sciences, 2016, 7, pp.18002. Providing forecasts for flow rates and water levels during floods have to be associated with uncertainty estimates. The forecast sources of uncertainty are plural. For hydrological forecasts (rainfall-runoff) performed using a deterministic hydrological model with basic physics, two main sources can be identified. The first obvious source is the forcing data: rainfall forecast data are supplied in real time by meteorological forecasting services to the Flood Forecasting Service within a range between a lowest and a highest predicted discharge. These two values define an uncertainty interval for the rainfall variable provided on a given watershed. The second source of uncertainty is related to the complexity of the modeled system (the catchment impacted by the hydro-meteorological phenomenon), the number of variables that may describe the problem and their spatial and time variability. The model simplifies the system by reducing the number of variables to a few parameters. Thus it contains an intrinsic uncertainty. This model uncertainty is assessed by comparing simulated and observed rates for a large number of hydro-meteorological events. We propose a method based on fuzzy arithmetic to estimate the possible range of flow rates (and levels) of water making a forecast based on possible rainfalls provided by forcing and uncertainty model. The model uncertainty is here expressed as a range of possible values. Both rainfall and model uncertainties are combined with fuzzy arithmetic. This method allows to evaluate the prediction uncertainty range. (10.1051/e3sconf/20160718002)
  DOI : 10.1051/e3sconf/20160718002
• Construction of the Numerical Wave Databases Anemoc-2 on the Mediterranean Sea and the Atlantic Ocean Through Hindcast Simulations Over the Period 1979-2010
  
  • Tiberi-Wadier Anne-Laure
  • Laugel Amélie
  • Benoit Michel
  , 2016, pp.127--143. no abstract (10.1007/978-981-287-615-7_9)
  DOI : 10.1007/978-981-287-615-7_9