Through ongoing collaboration with Dr. Joe Calantoni of the Naval Research Laboratory, We have begun to couple the 2D Navier-Stokes hydrodynamic model with the discrete particle model (DPM). The Navier-Stokes olver is described here . The majority of this work is performed by Dr. Calantoni who is one of only a handful of researchers running highly resolved models of particle transport. The particle model consists of: the Eulerian fluid phase is a one-dimensional eddy-viscosity mixing length model. The Lagrangian particle phase is a three-dimensional molecular dynamics simulation using spherical particles with the material properties of quartz to represent sand grains. The two-phase WBBL model was coupled at every simulation time step via Newton’s Third Law through fluid-particle interaction forces of buoyancy, drag and added mass. The DPM is fed with fluid velocities and pressure gradients to drive the fluid phase and particles. At present the model coupling is only one way such that the hydrodynamics do not feel the changes that the bed undergoes. This work is in its infancy, but the movie below shows the vorticity field (color) and sediment for a short time duration near the outer swash zone. We believe this type of model coupling will enable us to understand better the mechanisms driving sediment transport in the swash zone. For instance, FIGURE 1 shows particle trajectories for several particles taken from roughly the same location. It is clear from the figure that some of the particles travel more like bedload, some more like suspended load and their overall travel distances and directions can vary wildly.
Note: file is over 3 Mb so it may take a while to play.
FIGURE 1. The lines represent the average trajectory of 10 selected particles initially located in a cross-shore bin, around the start position. Particles were selected to represent the largest net cross-shore displacement. The arrows indicate the direction of the trajectory in time.
For more information on these topics see Drake and Calantoni, Journal of Geophysical Research (2001), or Calantoni and Puleo, Continental Shelf Research (In Review).
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