Abstract
SedWaveFoam, an OpenFOAM-based two-phase model that concurrently resolves the free surface wave field, and the bottom boundary layer is used to investigate sediment transport throughout the entire water column. The numerical model was validated with large-scale wave flume data for sheet flow driven by shoaling skewed-asymmetric waves with two different grain sizes. Newly obtained model results were combined with previous nonbreaking and near-breaking wave cases to develop parameterization methods for time-dependent bed shear stress and sediment transport rate under various sediment sizes and wave conditions. Gonzalez-Rodriguez and Madsen (GRM07) and quasi-steady approaches were compared for intra-wave bed shear stress. The results show that in strongly asymmetric flows, considering the separated boundary layer development processes at each half wave-cycle (i.e., GRM07) is essential to accurately estimating bed shear stress and highlights the impact of phase-lag effects on sediment transport rates. The quasi-steady approach underpredicts (∼60%) sediment transport rates, especially for fine grains under large velocity asymmetry. A modified phase-lag parameter, incorporating velocity asymmetry, sediment stirring, and settling processes is proposed to extend the Meyer-Peter and Mueller type power law formula. The extended formula accurately estimated the enhanced net onshore sediment transport rate observed under skewed-asymmetric wave conditions.
Highlights
IntroductionSandbar evolution is known to be affected by the point of wave breaking [1], infragravity waves [2], and longshore currents [3]
This study investigated the phase-lag effects on time-dependent sediment transport rates under skewed-asymmetric surface waves using the new numerical modeling strategy
The analysis presented here represents a first step toward integrating enhanced onshore sediment transport mechanisms due to the phase-lag effect by modifying the quasisteady approach based on two-phase flow numerical model results and experimental data of [41,42,72]
Summary
Sandbar evolution is known to be affected by the point of wave breaking [1], infragravity waves [2], and longshore currents [3]. Energetic storms drive rapid offshore sandbar migration [4], whereas onshore-directed sandbar recovery is expected during quiescent periods [5]. Thornton et al [6] showed that energetics-based sediment transport models, e.g., [7], were unsatisfactory for sandbar migration predictions, especially under mild wave conditions. Nearshore morphological evolution is closely connected to cross-shore sandbar migration, e.g., [8,9]. Improved understanding of onshore and offshore sediment fluxes driven by waves and currents needs to be achieved to advance parameterizations for physical processes by including additional physics [12]
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