We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
A Numerical Study of Onshore Ripple Migration Using a Eulerian Two-phase Model.
- Authors
Salimi-Tarazouj, Alix; Tian-Jian Hsu; Traykovski, Peter; Zhen Cheng; Chauchat, Julien
- Abstract
A new modeling methodology for ripple dynamics driven by oscillatory flows using a Eulerian two-phase flow approach is presented in order to bridge the research gap between near-bed sediment transport via ripple migration and suspended load transport dictated by ripple induced vortices. Reynolds-averaged Eulerian two-phase equations for fluid phase and sediment phase are solved in a twodimensional vertical domain with a k-e closure for flow turbulence and particle stresses closures for shortlived collision and enduring contact. The model can resolve full profiles of sediment transport without making conventional near-bed load and suspended load assumptions. The model is validated with an oscillating tunnel experiment of orbital ripple driven by a Stokes second-order (onshore velocity skewed) oscillatory flow with a good agreement in the flow velocity and sediment concentration. Although the suspended sediment concentration far from the ripple in the dilute region was underpredicted by the present model, the model predicts an onshore ripple migration rate that is in very good agreement with the measured value. Another orbital ripple case driven by symmetric sinusoidal oscillatory flow is also conducted to contrast the effect of velocity skewness. The model is able to capture a net offshore-directed suspended load transport flux due to the asymmetric primary vortex consistent with laboratory observation. More importantly, the model can resolve the asymmetry of onshore-directed near-bed sediment flux associated with more intense boundary layer flow speed-up during onshore flow cycle and sediment avalanching near the lee ripple flank which force the onshore ripple migration. Plain Language Summary Sand ripples are common small-scale seafloor bathymetric features in wave-dominant environments. The presence of sand ripples is a major source of bottom friction of overlaying waves and currents. Migration of sand ripples is also a major form of sediment transport shaping large-scale coastal morphological evolution. As waves approach the shore, their shape evolves into sharper crests and broader troughs. This results in fast onshore velocities with a duration of less than half the wave period under the crest and slower offshore velocities under the trough with a duration longer than half the wave period. This process is quantified by a parameter referred to as velocity skewness. While field and laboratory observations reveal a clear relationship between wave orbital velocity skewness and sediment transport through a complex interplay between suspended sand transport above the ripple and ripple migration, the mechanisms driving ripple migration associated with wave orbital velocity skewness remain unclear. This study utilized a new numerical modeling tool, based on the Eulerian two-phase flow methodology, to resolve the full profile of sediment transport to bridge the gap between near-bed sand transport via ripple migration and suspended sand transport dictated by ripple induced vortices. Model results indicate that onshore ripple migration driven by onshore velocity-skewed wave orbital velocity is caused by more intense near-bed sediment flux during onshore flow cycle and sediment avalanching at lee-side of the ripple flank.
- Subjects
RIPPLES (Fluid dynamics); WHIRLWINDS; WATER waves; FLOW velocity; OCEANOGRAPHY
- Publication
Journal of Geophysical Research. Oceans, 2021, Vol 126, Issue 2, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2020JC016773