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Accueil > Actualités > Séminaires > Séminaires 2018

Mardi 24 avril 2018 à 11h00 en salle K118

Tian-Jian Hsu, Center for Applied Coastal Research (CACR), Civil & Environmental Engineering, University of Delaware, Newark, DE, USA

Titre/Title : On wave-driven sediment transport – some insights revealed by a two-phase flow modeling approach

Contact : Julien Chauchat (équipe MEIGE)

Résumé/Abstract : A two-phase Eulerian or Euler-Lagrangian modeling framework for sediment transport has been developed through a collaborative effort between CACR, University of Delaware (Hsu’s group) and LEGI, Grenoble-INP (Chauchat’s group). With the backbone based on a Eulerian two-phase model, called SedFoam, developed with OpenFOAM, this modeling framework has been applied to various sediment transport applications. This talk focuses on several findings related to sand transport under waves. The premise of wave-driven sediment transport assumes that the instantaneous transport rate is completely in phase with wave-induced streamwise velocity above the wave boundary layer. However, laboratory and field observations indicate that such quasi-steady approach is limited in the surf zone, for example, when the wave shape becomes asymmetric near and after breaking, or when sand grain size is fine (d50 <0.15 mm). Moreover, under realistic surface waves, progressive wave streaming and wave-breaking turbulence can further enhance sediment transport, and it is not clear how they should be parameterized. When extending SedFoam into a large-eddy simulation model for sand transport under waves, we demonstrate that SedFoam can reproduce the observed sediment burst events during flow reversal and enhanced sheet flow layer thickness unique for fine sand. By combining SedFoam with a surface wave solver InterFoam/Waves2Foam, we study how the onshore sediment transport due to streaming current is amplified by a wave-stirring mechanism. By coupling SedFoam with a Discrete Element Model (DEM) called LIGGGHTS, we study the grain size grading effect (armoring and exposure) on wave-induced sediment transport. Preliminary results suggest that for sand transport driven by velocity-skewed waves typically encountered in the surf zone, grading effect enhances onshore transport by as large as 60%, and the enhancement is proportional to wave intensity and skewness.