Geometry and Migration of Sand Ripple under Oscillatory Flow using SedFoam
Abstract
The sea bed is covered by sedimentary structures with a large range of sizes and different shapes. One of the small structures are ripples, which strongly influence turbulence intensity near the bed. Hence, they play a key role in determining sediment transport and hydrodynamic dissipation. Understanding the geometry and migration of such ripples driven by a range of wave forcing is the main objective of the present study. As a first step, an Eulerian two-phase model, SedFoam, is utilized to study ripple dynamics under oscillatory flow. SedFoam is able to resolve the full profile of sediment transport without the priori assumption of bedload and suspended load and it has been extensively validated for sheet flows. The carrier fluid phase was solved by Reynolds-averaged mass and momentum equations which are coupled with the continuum particle phase with drag force, pressure gradient force and turbulent suspension force. The fluid Reynolds stress is model by a k-ɛ turbulence model that includes the effect of sediment on damping the flow turbulence. Inter-granular particle stresses are modeled by a closure based on the Kinetic theory of granular flows. Model verification was performed using Nielsen empirical formulae for a range of mobility number in the orbital ripple regime. Using a Stokes wave (R = 0.63), the ripple migration velocity is calculated and compared with empirical formulae. A good agreement between the empirical formulae and the model results obtained for ripple height and the length . The magnitude and direction of transport fluxes between the near-bed load and suspended load are analyzed. By decreasing the sediment size and keeping the same wave excursion length, the model is further used to investigate the transition between orbital and an-orbital regimes and the transition to sheet flows.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP53B..24S
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGY