scholarly journals A Numerical Study of Sheet Flow Driven by Skewed-Asymmetric Shoaling Waves Using SedWaveFoam

2021 ◽  
Vol 9 (9) ◽  
pp. 936
Author(s):  
Yeulwoo Kim ◽  
Ryan S. Mieras ◽  
Dylan Anderson ◽  
Timu Gallien
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Sediment Transport ◽  
Transport Rate ◽  
Phase Lag ◽  
Bed Shear Stress ◽  
Sheet Flow ◽  
Sediment Transport Rate ◽  
Wave Conditions ◽  
The Impact

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.

scholarly journals PREDICTION OF SEDIMENT TRANSPORT DUE TO IRREGULAR WAVE MOTION

2012 ◽  
Vol 4 (2) ◽  
Author(s):  
Taufiqur Rachman ◽  
Suntoyo Suntoyo
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Transport Rate ◽  
Irregular Waves ◽  
Bottom Shear Stress ◽  
Coastal Morphology ◽  
New Approach ◽  
Irregular Wave ◽  
Sediment Transport Rate ◽  
Rough Bed

<p>In general, waves in coastal environments are irregular and have a random shape with a height and period that was not constant. The accuracy of sediment transport rate prediction is the most important stages in the study of morphology and coastal marine environments. In addition, the predictive model of coastal morphology is more efficient to use the bottom shear stress calculation approach for practical purposes rather than a more complex approach to the modeling of two phases. In this paper, the calculation of sediment transport was based on the bottom shear stress modelling purposed with data validation from the experimental results in the turbulent bottom boundary layer over rough bed under irregular waves. The new approach to estimate the bottom shear stress was based on combining velocity and acceleration terms. Furthermore, a new approach of the bottom shear stress was applied to formulate the sheet flow sediment transport rate for irregular waves by using the experimental data from Dibadjnia and Watanabe (1998) and the empirical formula was found.</p> <p>Keywords: sediment transport, bottom shear stress, irregular waves</p>

Steady streaming and sediment transport at the bottom of sea waves

2012 ◽  
Vol 697 ◽  
pp. 115-149 ◽  
Author(s):  
Paolo Blondeaux ◽  
Giovanna Vittori ◽  
Antonello Bruschi ◽  
Francesco Lalli ◽  
Valeria Pesarino
Keyword(s):  
Boundary Layer ◽  
Sediment Transport ◽  
Empirical Relationship ◽  
Sediment Concentration ◽  
Sediment Flux ◽  
Transport Rate ◽  
Sea Waves ◽  
Steady Streaming ◽  
Sediment Transport Rate ◽  
Advection Diffusion Equation

AbstractThe flow and sediment transport in the boundary layer at the sea bottom due to the passage of surface waves are determined by considering small values of the wave steepness and of the ratio between the thickness of the boundary layer and the local water depth. Both the velocity field and the sediment transport rate are determined up to the second order of approximation thus evaluating both the steady streaming and the net (wave-averaged) flux of sediment induced by nonlinear effects. The flow regime is assumed to be turbulent and a two-equation turbulence model is used to close the problem. The bed load is evaluated by means of an empirical relationship as function of the bed shear stress. The suspended load is determined by computing the sediment flux, once the sediment concentration is determined by solving an appropriate advection–diffusion equation. The decay of the wave amplitude, which is due to the energy dissipation taking place in the boundary layer, is taken into account. The steady streaming and the sediment transport rate at the bottom of sea waves turn out to be different from those which are observed in a wave tunnel (U-tube), because of the dependence on the streamwise coordinate of the former flow. In particular, in the range of the parameters presently investigated, the sediment transport rate at the bottom of sea waves is found to be always onshore directed while, in a water tunnel (U-tube), the sediment transport rate can be onshore or offshore directed.

scholarly journals PREDICTION OF SEDIMENT TRANSPORT DUE TO IRREGULAR WAVE MOTION

2012 ◽  
Vol 4 (2) ◽  
Author(s):  
Taufiqur Rachman ◽  
Suntoyo Suntoyo
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Transport Rate ◽  
Irregular Waves ◽  
Bottom Shear Stress ◽  
Coastal Morphology ◽  
New Approach ◽  
Irregular Wave ◽  
Sediment Transport Rate ◽  
Rough Bed

In general, waves in coastal environments are irregular and have a random shape with a height and period that was not constant. The accuracy of sediment transport rate prediction is the most important stages in the study of morphology and coastal marine environments. In addition, the predictive model of coastal morphology is more efficient to use the bottom shear stress calculation approach for practical purposes rather than a more complex approach to the modeling of two phases. In this paper, the calculation of sediment transport was based on the bottom shear stress modelling purposed with data validation from the experimental results in the turbulent bottom boundary layer over rough bed under irregular waves. The new approach to estimate the bottom shear stress was based on combining velocity and acceleration terms. Furthermore, a new approach of the bottom shear stress was applied to formulate the sheet flow sediment transport rate for irregular waves by using the experimental data from Dibadjnia and Watanabe (1998) and the empirical formula was found. Keywords: sediment transport, bottom shear stress, irregular waves

scholarly journals Mean flow structure and velocity–bed shear stress maxima phase difference in smooth wall, transitionally turbulent oscillatory boundary layers: direct numerical simulations

2021 ◽  
Vol 928 ◽  
Author(s):  
Dimitrios K. Fytanidis ◽  
Marcelo H. García ◽  
Paul F. Fischer
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Numerical Simulations ◽  
Phase Difference ◽  
Free Stream ◽  
Direct Numerical Simulations ◽  
Stream Velocity ◽  
Phase Lag ◽  
Bed Shear Stress ◽  
Oscillatory Boundary Layer

Direct numerical simulations of oscillatory boundary-layer flows in the transitional regime were performed to explain discrepancies in the literature regarding the phase difference ${\rm \Delta} \phi$ between the bed-shear stress and free-stream velocity maxima. Recent experimental observations in smooth bed oscillatory boundary-layer (OBL) flows, showed a significant change in the widely used ${\rm \Delta} \phi$ diagram (Mier et al., J. Fluid Mech., vol. 922, 2021, A29). However, the limitations of the point-wise measurement technique did not allow us to associate this finding with the turbulent kinetic energy budget and to detect the approach to a ‘near-equilibrium’ condition, defined in a narrow sense herein. Direct numerical simulation results suggest that a phase lag occurs as the result of a delayed and incomplete transition of OBL flows to a stage that mimics the fully turbulent regime. Data from the literature were also used to support the presence of the phase lag and propose a new ${\rm \Delta} \phi$ diagram. Simulations performed for ${\textit {Re}}_{\delta }=671$ confirmed the sensitivity in the development of self-sustained turbulence on the background disturbances ( $\textit{Re}_{\delta}=U_{o}\delta/\nu$ , where $\delta=[2\nu/\omega]^{1/2}$ is the Stokes' length, $U_{o}$ is the maximum free stream velocity of the oscillation, $\nu$ is the kinematic viscosity and $\omega=2{\rm \pi}/T$ is the angular velocity based on the period of the oscillation T). Variations of the mean velocity slope and intersect values for oscillatory flows are also explained in terms of the proximity to near-equilibrium conditions. Relaminarization and transition effects can significantly delay the development of OBL flows, resulting in an incomplete transition. The shape and defect factors are examined as diagnostic parameters for conditions that allow the formation of a logarithmic profile with the universal von Kármán constant and intersect. These findings are of relevance for environmental fluid mechanics and coastal morphodynamics/engineering applications.

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