SPH modeling of the vertical flow structure and turbulence in the swash

Abstract

The vertical structure of swash-zone flows and turbulence, which is critical to sediment transport and flooding due to over-topping of dunes, will be examined using a Smoothed Particle Hydrodynamics model (DualSPHysics) evaluated with field observations obtained near La Jolla, CA in fall 2003. The mesh-free model is based on the Lagrangian description of fluid particle motion, and is capable of tracking free surfaces with discontinuities, moving boundaries, and large deformations; such as those in plunging waves and hydraulic jumps that occur when a swash backwash collides with the following uprush. The model is initialized with a flat sea surface and the measured beach profile and is forced at the offshore boundary with waves observed in 5 m water depth. The model is used to simulate the cross-shore and vertical structure of wave orbital motions, turbulence, and time-mean flows across the surf zone to the swash zone over 10 min periods. Model simulations are compared with field observations of waves and mean flows collected near the bed in 2.5, 1.5, and 1.0 m water depths and at 5 locations in the swash zone. Offshore significant waves heights ranged from 0.5 m to 1.5 m and cross-shore velocities in the surf and swash were up to 0.8 in/s. Model-data comparisons will be presented, the dependence of simulations on free parameters such as smoothing length, distance between particles, and artificial viscosity will be described, and the simulated flows and turbulence will be discussed.