Transport sédimentaire et morphodynamique en zone littorale

Sediment transport and morphodynamics in nearshore areas

As part of the MODLIT program, which is a laboratory qualification campaign for sandy beach morphodynamics model, an instrumental study has been conducted in the LHF multidirectional wave basin (Grenoble-INP / SOGREAH, France) . A key-point of the understanding of sandy beaches dynamics is the knowledge of the interactions between surface and groundwater hydrodynamics, in particular between swash and beach watertable, and their impact on accretion and erosion processes above the still water level. A dedicated cross-shore line of 9 relative pressure sensors has been deployed from the inner surf zone to the berm, combining buried and free sensors. Every sensors were located below the mean water level. Spectral analysis shows the low-pass filtering of pressure waves and allows to discriminate the low frequency modes. A detailed sequence of pressure field snapshots is presented to reveal the groundwater flows and highlight the role of swash overtopping in pressure gradients.

A novel set-up designed for flow visualizations and turbulence measurements in rotating high-aspect-ratio ducts has been described. The 8 m long duct was placed across a 13 m diameter turntable and the setup enabled stereoscopic Ply-measurements over a wide range of rotation numbers Ro 2 Omega 2H/U <= 0.80. Measurements of all three components of the instantaneous velocity vector were made in a plane spanning the channel from the pressure to the suction side. Together with the mean flow characteristics, the important turbulence statistics, such as all components of the Reynolds stress tensor and the spanwise component of the vorticity field, were obtained and compared to DNS results. The field measurements provided more details about the flow than earlier experimental studies of turbulent flows in rotating ducts.;The overall observation was that the Coriolis force due to the imposed system rotation damped the turbulence level along the suction side whereas an augmentation of the turbulent agitation was found at the pressure side of the rotating channel. These findings are fully consistent with data from earlier DNS studies. The same set-up can readily be used to explore the influence of rotation on internal flows with separation bubbles provoked by massive obstructions, for instance turbulent flows over a backward-facing step or in ducts with transverse ribs of various shapes. (C) 2010 Elsevier Ltd. All rights reserved.

This paper describes the CFD of incompressible air-water flows by solving Euler equations with a 2-phase flow model leading to a hyperbolic system of conservation laws solved with a finite volume discretization on unstructured grids. An artificial compressibility approach allows for a fully explicit scheme for an efficient parallel implementation. The numerical model is based on a low Mach number preconditioning and a 2nd-order Riemann solver. Applications to breaking waves on a 15% slope with and without the influence of macro-roughness are performed concerning impact and run-up processes on the beach.