Abstract
Quantification of cross-shore sediment transport is one of most intriguing challenges in shoreline and coastal geomorphology. During the past decades, several key mechanisms associated with onshore/offshore sediment transport have been identified, such as wave skewness/asymmetry, progressive wave streaming and undertow current. However, applying these mechanisms to the migration of wave formed bedforms (ripples) is not straightforward. For example, recent field observations off Fire Island, NY showed that ripples migrated onshore even during periods of offshore directed wave skewness, which is contradictory to the prediction of empirical sediment transport formulations. The physical processes driving ripple vortex formation, ejection and boundary layer streaming associated with rippled bed can further complicate the bedload/suspended load sediment transport over ripples. To fully understand these mechanisms, a comprehensive model that can resolve the ripple dynamics and interactions between free surface wave and rippled bed is examined.
Highlights
Quantification of cross-shore sediment transport is one of most intriguing challenges in shoreline and coastal geomorphology
The waves in the FS case are sinusoidal waves with an amplitude of a = 0.31 m, a wave period of T = 5 s, and a water depth of h = 4 m, the nearbed wave orbital velocity is about u/ = 0.39 m/s
The same flow condition and numerical domain are applied to the oscillating water tunnel (OWT) case, except a smooth-wall top boundary is used to avoid free surfaces
Summary
Quantification of cross-shore sediment transport is one of most intriguing challenges in shoreline and coastal geomorphology. MODELING APPROACH As a first step, a volume-of-fluid solver interFoam in the OpenFOAM framework is used to understand the hydrodynamics, such as the effect of ripple vortexes and boundary layer streaming. To examine the effects of free-stream vertical velocities, which are absent in the oscillating water tunnel (OWT), two comparative cases with free surface ( ‘FS’) and without free surface (‘OWT’) were carried out.
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