Sediment transport under wave groups: Relative importance between nonlinear waveshape and nonlinear boundary layer streaming

Abstract

[1] Sediment transport under nonlinear waves in a predominately sheet flow condition is investigated using a two-phase model. Specifically, we study the relative importance between the nonlinear waveshape and nonlinear boundary layer streaming on cross-shore sand transport. Terms in the governing equations because of the nonlinear boundary layer process are included in this one-dimensional vertical (1DV) model by simplifying the two-dimensional vertical (2DV) ensemble-averaged two-phase equations with the assumption that waves propagate without changing their form. The model is first driven by measured time series of near-bed flow velocity because of a wave group during the SISTEX99 large wave flume experiment and validated with the measured sand concentration in the sheet flow layer. Additional studies are then carried out by including and excluding the nonlinear boundary layer terms. It is found that for the grain diameter (0.24 mm) and high-velocity skewness wave condition considered here, nonlinear waveshape (e.g., skewness) is the dominant mechanism causing net onshore transport and nonlinear boundary layer streaming effect only causes an additional 36% onshore transport. However, for conditions of relatively low-wave skewness and a stronger offshore directed current, nonlinear boundary layer streaming plays a more critical role in determining the net transport. Numerical experiments further suggest that the nonlinear boundary layer streaming effect becomes increasingly important for finer grain. When the numerical model is driven by measured near-bed flow velocity in a more realistic surf zone setting, model results suggest nonlinear boundary layer processes may nearly double the onshore transport purely because of nonlinear waveshape.

SedFoam-2.0: a 3-D two-phase flow numerical model for sediment transport

“…Table 3 summarizes the model coefficients. These coefficients were shown to work well for typical medium to coarse sand transport Yu et al, 2010;Cheng et al, 2017a). Furthermore, it was found that the coefficient B (see Eq.…”

“…Turbulence model Particle stress Asano (1990), Li and Sawamoto (1995), and Dong and Zhang (2002) mixing length Bagnold Jenkins and Hanes (1998) mixing length kinetic theory Revil-Baudard and Chauchat (2013) mixing length granular rheology Li et al (2008) k − L Bagnold Bakhtyar et al (2009) k − ε Bagnold , Chauchat and Guillou (2008), and Amoudry et al (2008) k − ε kinetic theory Yu et al (2010) and Cheng et al (2017a) Amoudry (2014 and Bombardelli (2009, 2010) k − ω kinetic theory Lee et al (2016) k − ε granular rheology is modeled by the fluctuation energy of the particle phase (or granular temperature). Various models were developed to model the granular temperature.…”

“…This turbulence model has been implemented mostly for compatibility with earlier works. Cheng et al (2017a) have implemented the k − ε model refined from and Yu et al (2010), in which (13) the turbulent eddy viscosity ν b t is calculated by…”

Extension ofk-ωturbulence closure to two-phase sediment transport modelling: Application to oscillatory sheet flows

“…This is one of the reasons why two-phase flow models have become widely used to investigate sediment transport under the sheet flow regime (e.g., [1][2][3][4][5]). Another important aspect of the two-phase framework for sediment transport is its ability to represent the coupled fluid sediment system continuously from within the stationary bed throughout the entire bottom boundary layer (see for example the explanatory diagrams in [6][7][8]).…”

A semianalytical model for sheet flow layer thickness with application to the swash zone

“…The effects of boundary layer streaming [Dohmen-Janssen and Hanes, 2002;Nielsen, 2006;Yu et al, 2010] and of groundwater in/exfiltration [Turner and Masselink, 1998], which affect net sediment transport, are not included in the model. For example, groundwater infiltration induces a net downward force on sediment grains (counteracting sediment mobilization) but also decreases the boundary thickness, increasing the shear stress (enhancing sediment mobilization) [Butt et al, 2001].…”