Publications

2009

• Quantification des flux sédimentaires dans la rade de Brest et ses abords
  
  • Lepesqueur Jérémy
  • Chapalain Georges
  • Guillou Nicolas
  • Villaret Catherine
  , 2009. La dynamique sédimentaire dans l’environnement semi-fermé de la rade de Brest et ses abords est étudiée. Outre la marée dominante, sont pris en compte les apports fluviatiles et les transferts verticaux à travers les fonds hétérogènes où se côtoient dépôts gravelo-sableux, sables, sables coquilliers et substrats biogènes (maërl, crépidules) à teneurs en pélites variables. L’étude vise à établir le bilan des flux sédimentaires, y compris ceux piégés dans la rade et échangés avec la mer d’Iroise au travers du goulet. L’étude s’appuie sur la modélisation numérique à l’aide de la chaîne TELEMAC associée à des observations in situ à des fins de « forçage » et à de validation de la modélisation. A chacune des strates biosédimentaires cartographiées par Michel Glémarec & Christian Hily (Contrat de baie de la rade de Brest, 1994) est associé un type de sédiments de nature (non cohésive, cohésive) et granularité données. L’impact sur l’hydrodynamique d’un coefficient de frottement de fond ainsi variable spatialement est examiné en confrontant des prédictions et des mesures de courant. La dynamique des différents types de sédiments de fond est calculée.
• Simulation of the turbidity maximum in the Seine estuary with a two-phase flow model
  
  • Chauchat Julien
  • Guillou Sylvain
  • Barbry Nathaly
  • Nguyen Kim Dan
  Comptes Rendus. Géoscience, Académie des sciences (Paris), 2009, 341 (7), pp.505-512. This article presents numerical simulations for the turbidity maximum (TM) in the Seine estuary using a 2-D vertical width-integrated two-phase flow model. The results are in rather good agreement with observations in a natural environment. The displacement of the TM is reproduced and a concentrated particles layer is observed on the numerical results. These results highlight the interest of this innovative approach for sediment transport simulations in estuary: no erosion or deposition laws are imposed (10.1016/j.crte.2009.04.002)
  DOI : 10.1016/j.crte.2009.04.002
• A two-phase numerical model for suspended-sediment transport in estuaries
  
  • Nguyen Kim Dan
  • Guillou Sylvain
  • Chauchat Julien
  • Barbry Nathaly
  Advances in Water Resources, Elsevier, 2009, 32 (8), pp.1187-1196. This paper presents a full 2-D X/Z numerical model for sediment transport in open channels and estuaries using a two-phase (fluid–solid particle) approach. The physical concept and the mathematical background of the model are given and test-cases have been carried out to validate the proposed model. In order to illustrate its feasibility for a real estuary, the model has been applied to simulate the suspended-sediment transport and the formation of turbidity maximum in the Seine estuary. The numerical results show that the main characteristics of estuarine hydro-sediment dynamics in the Seine estuary are in fact reproduced by the proposed model. A qualitative agreement between the numerical results and the actual observations has been obtained and is presented in this paper. (10.1016/j.advwatres.2009.04.001)
  DOI : 10.1016/j.advwatres.2009.04.001
• A double-layer Boussinesq-type model for highly nonlinear and dispersive waves
  
  • Chazel Florent
  • Benoit Michel
  • Ern Alexandre
  • Piperno Serge
  , 2009. We derive and analyze in the framework of the mild-slope approximation a new double-layer Boussinesq-type model which is linearly and nonlinearly accurate up to deep water. Assuming the flow to be irrotational, we formulate the problem in terms of the velocity potential thereby lowering the number of unknowns. The model derivation combines two approaches, namely the method proposed by Agnon et al. (Agnon et al. 1999, J. Fluid Mech., 399 pp. 319-333) and enhanced by Madsen et al. (Madsen et al. 2003, Proc. R. Soc. Lond. A, 459 pp. 1075-1104) which consists in constructing infinite-series Taylor solutions to the Laplace equation, to truncate them at a finite order and to use Padé approximants, and the double-layer approach of Lynett & Liu (Lynett & Liu 2004, Proc. R. Soc. Lond. A, 460 pp. 2637-2669) allowing to lower the order of derivatives. We formulate the model in terms of a static Dirichlet-Neumann operator translated from the free surface to the still-water level, and we derive an approximate inverse of this operator that can be built once and for all. The final model consists of only four equations both in one and two horizontal dimensions, and includes only second-order derivatives, which is a major improvement in comparison with so-called high-order Boussinesq models. A linear analysis of the model is performed and its properties are optimized using a free parameter determining the position of the interface between the two layers. Excellent dispersion and shoaling properties are obtained, allowing the model to be applied up to deep water. Finally, numerical simulations are performed to quantify the nonlinear behaviour of the model, and the results exhibit a nonlinear range of validity reaching deep water areas.
• On the Korteweg-de Vries approximation for uneven bottoms
  
  • Chazel Florent
  European Journal of Mechanics - B/Fluids, Elsevier, 2009, 28 (2), pp.pp. 234-252. In this paper we focus on the water waves problem for uneven bottoms on a two-dimensionnal domain. Starting from the symmetric Boussinesq systems derived in [Chazel, Influence of topography on long water waves, 2007], we recover the uncoupled Korteweg-de Vries (KdV) approximation justified by Schneider and Wayne for flat bottoms, and by Iguchi in the context of bottoms tending to zero at infinity at a substantial rate. The goal of this paper is to investigate the validity of this approximation for more general bathymetries. We exhibit two kinds of topography for which this approximation diverges from the Boussinesq solutions. A topographically modified KdV approximation is then proposed to deal with such bathymetries. Finally, all the models involved are numerically computed and compared. (10.1016/j.euromechflu.2008.10.003)
  DOI : 10.1016/j.euromechflu.2008.10.003
• A multilayer Saint-Venant system with mass exchanges for Shallow Water flows. Derivation and numerical validation
  
  • Audusse Emmanuel
  • Bristeau Marie-Odile
  • Perthame Benoît
  • Sainte-Marie Jacques
  ESAIM: Mathematical Modelling and Numerical Analysis, Société de Mathématiques Appliquées et Industrielles (SMAI) / EDP, 2009, 45, pp.169-200. The standard multilayer Saint-Venant system consists in introducing fluid layers that are advected by the interfacial velocities. As a consequence there is no mass exchanges between these layers and each layer is described by its height and its average velocity. Here we introduce another multilayer system with mass exchanges between the neighborhing layers where the unknowns are a total height of water and an average velocity per layer. We derive it from Navier-Stokes system with an hydrostatic pressure and prove energy and hyperbolicity properties of the model. We also give a kinetic interpretation leading to effective numerical schemes with positivity and energy properties. Numerical tests show the versatility of the approach and its ability to compute recirculation cases with wind forcing. (10.1051/m2an/2010036)
  DOI : 10.1051/m2an/2010036
• Equilibrium shoreline response: Observations and modeling
  
  • Yates Marissa L.
  • Guza R. T
  • O 'Reilly W C
  Journal of Geophysical Research, American Geophysical Union, 2009, 114 (C9), pp.9014 - 9014. [1] Shoreline location and incident wave energy, observed for almost 5 years at Torrey Pines beach, show seasonal fluctuations characteristic of southern California beaches. The shoreline location, defined as the cross-shore position of the mean sea level contour, retreats by almost 40 m in response to energetic winter waves and gradually recovers during low-energy summer waves. Hourly estimates of incident wave energy and weekly to monthly surveys of the shoreline location are used to develop and calibrate an equilibrium-type shoreline change model. By hypothesis, the shoreline change rate depends on both the wave energy and the wave energy disequilibrium with the shoreline location. Using calibrated values of four model free parameters, observed and modeled shoreline location are well correlated at Torrey Pines and two additional survey sites. Model free parameters can be estimated with as little as 2 years of monthly observations or with about 5 years of ideally timed, biannual observations. Wave energy time series used to calibrate and test the model must resolve individual storms, and model performance is substantially degraded by using weekly to monthly averaged wave energy. Variations of free parameter values between sites may be associated with variations in sand grain size, sediment availability, and other factors. The model successfully reproduces shoreline location for time periods not used in tuning and can be used to predict beach response to past or hypothetical future wave climates. However, the model will fail when neglected geologic factors are important (e.g., underlying bedrock limits erosion or sand availability limits accretion). (10.1029/2009JC005359)
  DOI : 10.1029/2009JC005359
• Multiscale in time and stability analysis of operator split solution procedures applied to thermomechanical problems
  
  • Kassiotis Christophe
  • Colliat Jean-Baptiste
  • Ibrahimbegovic Adnan
  • Matthies Hermann G.
  Engineering Computations, Emerald, 2009, 26 (1/2), pp.205-223. Purpose - The purpose of this paper is to study the partitioned solution procedure for thermomechanical coupling, where each sub-problem is solved by a separate time integration scheme. Design/methodology/approach - In particular, the solution which guarantees that the coupling condition will preserve the stability of computations for the coupled problem is studied. The consideration is further generalized for the case where each sub-problem will possess its particular time scale which requires different time step to be selected for each sub-problem. Findings - Several numerical simulations are presented to illustrate very satisfying performance of the proposed solution procedure and confirm the theoretical speed-up of computations which follow from the adequate choice of the time step for each sub-problem. Originality/value - The paper confirms that one can make the most appropriate selection of the time step and carry out the separate computations for each sub-problem, and then enforce the coupling which will preserve the stability of computations with such an operator split procedure. (10.1108/02644400910924870)
  DOI : 10.1108/02644400910924870