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Accueil > Actualités > Doctorats > Doctorats 2015

Vendredi 11 décembre 2015, soutenance de thèse de Raphaël MAURIN - 14h00, Amphithéâtre K118, site Bergès

Investigation of granular behavior in bedload transport using an Eulerian-Lagrangian model

Membres du jury

  • Kimberly HILL, Associate Professor, University of Minnesota, Rapporteur
  • Hervé CAPART, Professor, National Taiwan University, Rapporteur
  • Alexandre VALANCE, Directeur de Recherche, CNRS, Institut de Physique de Rennes, Examinateur
  • Philippe CLAUDIN, Directeur de Recherche, CNRS, ESPCI, Examinateur
  • Éric BARTHÉLÉMY, Professeur des Universités, LEGI, Grenoble INP, Examinateur
  • Philippe FREY, Chercheur HDR, IRSTEA Grenoble, Directeur de thèse
  • Julien CHAUCHAT, Maître de Conférence, LEGI, Grenoble INP, Co-encadrant de thèse
  • Bruno CHAREYRE, Maître de Conférence, 3SR, Grenoble INP, Co-encadrant de thèse

Résumé

Turbulent bedload transport represents the main contribution to the riverbed morphological evolution, and associates the non-trivial collective granular behavior with a turbulent fluid flow. Therefore, its description is both a scientific challenge and a societal issue. The present numerical approach focuses on the granular phase characterization, and considers idealized steady uniform bedload transport, with monodisperse spherical beads and a unidirectional fluid flow. This simplified configuration allows to study the underlying physical mechanisms.

A minimal coupled numerical model is proposed, associating a three-dimensional discrete element method with a one-dimensional volume-averaged fluid momentum balance resolution. The model is compared with classical experimental results of dimensionless sediment transport rate as a function of the Shields number. The comparison is extended to granular depth profiles of existing quasi-2D bedload transport experiments. The validated model is further employed to analyze the granular depth structure in bedload transport. Varying the channel inclination angle and the specific density, it is shown that the classical Shields number and dimensionless sediment transport rate formulations do not take appropriately into account the effects of these two parameters. Analyzing the solid depth profiles and the continuous two-phase flow equations, a rescaling of the Shields number is proposed and is shown to make all the data collapse onto a master curve. In addition, the bedload transport granular rheology is characterized by computing locally the stress tensor as a function of the depth. The obtained results are analyzed in the framework of the μ(I) rheology. It allows to draw a picture of the different granular regime in bedload transport, and challenges the existing granular rheology.