scholarly journals A MODEL OF BEACH PROFILE EVOLUTION INCLUDING WAVE-UNDERTOW INTERACTION

2012 ◽  
Vol 1 (33) ◽  
pp. 16
Author(s):  
Chi Zhang ◽  
Jinhai Zheng ◽  
Titi Sui ◽  
Zeki Demirbilek ◽  
Lihwa Lin
Keyword(s):  
Sediment Transport ◽  
Flow Model ◽  
Transport Model ◽  
Wave Model ◽  
Empirical Method ◽  
Momentum Balance ◽  
Gradient Term ◽  
Beach Profile ◽  
Laboratory Observation ◽  
Sandbar Migration

A numerical model of beach profile evolution is developed to study the onshore and offshore sandbar migration under different wave conditions. The integrated model consists of wave model, roller model, flow model, sediment transport model and bed evolution model. In particular, the interaction between waves and wave-induced undertow current is considered in the flow model. This is achieved by adding a mean pressure gradient term into the firs-order momentum balance equation of flow. A simple empirical method is also introduced to describe the variation in eddy viscosity during one wave cycle. A preliminary application of the present model shows good agreements of both onshore and offshore sandbar migration phenomenon with the laboratory observation. It is found that the offshore sandbar migration is dominated by undertow while wave affects the transport rate. For the onshore sandbar migration, although sediment transport is mainly driven by wave and the undertow is weak, the transport pattern is considerably modified by undertow. It is shown that the combined effects of wave and undertow are important in beach profile evolution.

A RANS numerical model for cross-shore beach profile evolution

2020 ◽  
Author(s):  
Julio Garcia-Maribona ◽  
Javier L. Lara ◽  
Maria Maza ◽  
Iñigo J. Losada
Keyword(s):  
Sediment Transport ◽  
Numerical Model ◽  
Transport Model ◽  
Numerical Models ◽  
Computational Cost ◽  
Physical Modelling ◽  
Computational Effort ◽  
Beach Profile ◽  
Time Step ◽  
Wave Conditions

<p>The evolution of the cross-shore beach profile is tightly related to the evolution of the coastline in both small and large time scales. Bathymetry changes in extreme maritime events can also have important effects on coastal infrastructures such as geotechnical failures of foundations or the modification of the incident wave conditions towards a more unfavourable situation.</p><p>The available strategies to study the evolution of beach profiles can be classified in analytical, physical and numerical modelling. Analytical solutions are fast, but too simplistic for many applications. Physical modelling provides trustworthy results and can be applied to a wide variety of configurations, however, they are costly and time-consuming compared to analytical strategies. Finally,  numerical approaches offer different balances between cost and precision depending on the particular model.</p><p>Some numerical models provide greater precision in the beach profile evolution, but incurring in a prohibitive computational cost for many applications. In contrast, the less expensive ones assume simplifications which do not allow to correctly reproduce significant phenomena of the near-shore hydrodynamics such as wave breaking or undertow currents, neither to predict important features of the beach profile like breaker bars.</p><p>In this work, a new numerical model is developed to reproduce the main features of the beach profile and hydrodynamics while maintaining an affordable computational cost. In addition, it is intended to reduce to the minimum the number of coefficients that the user has to provide to make the model more predictive.</p><p>The model consists of two main modules. Firstly, the already existing 2D RANS numerical model IH2VOF is used to compute the hydrodynamics. Secondly, the sediment transport model modifies the bathymetry according to the obtained hydrodynamics. The new bathymetry is then considered in the hydrodynamic model to account for it in the next time step.</p><p>The sediment transport module considers bedload and suspended transports separately. The former is obtained with empirical formulae. In the later,the distribution of sediment concentration in the domain is obtained by solving an advective-diffusive transport equation. Then, the sedimentation and erosion rates are obtained along the seabed.<br>Once these contributions are calculated, a sediment balance is performed in every seabed segment to determine the variation in its level.</p><p>With the previously described strategy, the resulting model is able to predict not only the seabed changes due to different wave conditions, but also the influence of this new bathymetry in the hydrodynamics, capturing features such as the generation of a breaker bar, displacement of the breaking point or variation of the run-up over the beach profile. To validate the model, the numerical results are compared to experimental data.</p><p>An important novelty of the present model is the computational effort required to perform the simulations, which is significantly smaller than the one associated to existing models able to reproduce the same phenomena.</p>

scholarly journals Modeling Bed Evolution Using Weakly Coupled Phase-Resolving Wave Model and Wave-Averaged Sediment Transport Model

2016 ◽  
Vol 58 (3) ◽  
pp. 1650011-1-1650011-50 ◽  
Author(s):  
Francesco Gallerano ◽  
Giovanni Cannata ◽  
Oriana De Gaudenzi ◽  
Simone Scarpone
Keyword(s):  
Sediment Transport ◽  
Transport Model ◽  
Wave Model ◽  
Sediment Transport Model ◽  
Weakly Coupled ◽  
Bed Evolution

scholarly journals A NUMERICAL MODEL FOR DUNE DYNAMICS

1980 ◽  
Vol 1 (17) ◽  
pp. 95
Author(s):  
J. Sundermann ◽  
H.-J. Vollmers ◽  
W. Puls
Keyword(s):  
Sediment Transport ◽  
Path Length ◽  
Erosion Rate ◽  
Flow Model ◽  
Transport Model ◽  
Shear Velocity ◽  
Mean Flow ◽  
Sediment Transport Model ◽  
The Mean ◽  
Bed Material

A numerical sediment transport model is formulated that serves especially for the simulation of bedform mechanics. The model is based on the idea that sediment transport is determined by the erosion rate and the path length of bed material. Formulas for the erosion rate and the path length are derived from physical considerations and from measurements; they depend mainly on the local values of the shear velocity and the mean flow velocity near the bed. The behaviour of detached sediment is simulated by a Monte Carlo procedure, which is based on the mean flow velocities and the eddy viscosity. All flow properties that are needed for the sediment transport model are computed by a numerical flow model that includes two turbulence equations. Results of the flow model and the sediment transport model are compared with measured data.

scholarly journals MEASUREMENT AND MODELING OF THE INFLUENCE OF GRAIN SIZE AND PRESSURE GRADIENTS ON SWASH ZONE SEDIMENT TRANSPORT

2012 ◽  
Vol 1 (33) ◽  
pp. 58
Author(s):  
Ilya Khairanis Othman ◽  
Tom E. Baldock ◽  
David P. Callaghan
Keyword(s):  
Grain Size ◽  
Sediment Transport ◽  
Pressure Gradient ◽  
Transport Model ◽  
Fine Sand ◽  
Coarse Sand ◽  
P Value ◽  
Gradient Term ◽  
Swash Zone ◽  
Transport Calculation

The paper examines the dependency between sediment transport rate, q, and grain size, D, (i.e. q∝Dp) in the swash zone. Experiments were performed using a dam break flow as a proxy for swash overtopping on a mobile sediment beach. The magnitude and nature of the dependency (i.e. p value) is inferred for different flow parameters; the initial dam depth (or initial bore height), do, the integrated depth averaged velocity, ∫u3 dt, and against the predicted transport, qp using the Meyer-Peter Muller (MPM) transport model. Experiments were performed over both upward sloping beds and a horizontal bed. The data show that negative dependencies (p0) are obtained for ∫u3 dt. This indicates that a given do and qp transport less sediment as grain size increases, whereas transport increases with grain size for a given ∫u3 dt. The p value is expected to be narrow ranged, 0.5≤ p≤-0.5. A discernible difference observed between the measured and predicted transport on horizontal and sloping beds suggests different modes of transport. The incorporation of a pressure gradient correction, dp/dx, using the surface water slope (i.e. piezometric head), in the transport calculation greatly improved the transport predictions on the horizontal bed, where dp/dx is positive. On average, the incorporation of a pressure gradient term into the MPM formulation reduces qp in the uprush by 4% (fine sand) to 18% (coarse sand) and increases qp over a horizontal bed by 1% (fine sand) to two orders of magnitude (coarse sand). The measured transport for fine and coarse sand are better predicted using MPM and MPM+dp/dx respectively. Poor predictions are obtained using Nielsen (2002) because the pressure gradient in the uprush is of opposite sign to that inferred from velocity data in that paper. It is suggested that future swash sediment transport models should incorporate the grain size effect, partly through the pressure gradient, although the dp/dx influence is small for fine sands because of the grain size scaling contained in the stress term.

Sign in / Sign up

Export Citation Format

Share Document