Discrete-particle model for bedload transport: application
to the equilibrium beach profile problem
Calantoni, J., and Drake, T.G., 1999, Discrete-particle model
for bedload transport: application to the equilbrium beach profile
problem: International Association of Hydraulic Research Symposium
on River, Coastal and Estuarine Morphodynamics, 6-10 Sept. 1999,
Genoa, Italy
Discrete-particle computer simulations
of bedload sediment transport over a plane sloping bed provide
an interesting comparison with predictions of energetics-based
models for an equilibrium beach slope. In the model, time-varying
pressure gradients similar to those induced by the passage of
surface gravity waves drive the coupled motion of discrete particles
and fluid. Fluid, particle-contact and body forces on the individual
spherical particles are integrated at small time steps to provide
positions, velocities and rotations of each particle in the assemblage
Particles have quartz density and a distribution of diameters
about a mean of 1.1 mm. The fluid is crudely modeled as a series
of parallel slabs, and momentum is transferred between slabs using
a mixing-length model. Simulated transport rates are typically
within 20 percent of rates from physical experiments conducted
in an oscillatory flow tunnel by other workers using quartz sand
having the same distribution of sizes (King, 1991). Simulations
used three waveforms having a maximum near-bed fluid velocity
of 1 m/s and differing degrees of asymmetry. For all waveforms
simulated to date, bedload transport rates are a linear function
of the tangent of the bed slope, but only for slopes up to about
7 degrees. At higher slopes the transport is nonlinear, in contradiction
to predictions of energetics-based models.
Supported
by the Coastal Dynamics Program of the Office of Naval Research.