Modelling Sheet-Flow Sediment Transport in Wave-Bottom Boundary Layers Using Discrete-Element Modelling

Abstract

Sediment transport in oscillatory boundary layers is a driving mechanism of coastal geomorphologic change. Most formulae for bed-load transport in near-shore regions subsume the smallest-scale physics of the phenomena by parameterizing interactions between particles. In contrast, the authors directly simulate granular physics in the wave-bottom boundary layer using a discrete-element model consisting of a three-dimensional particle phase coupled to a one-dimensional fluid phase via Newton's Third Law through forces of buoyancy, drag, and added mass. The particulate sediment phase is modeled using discrete, non-spherical particles formed to approximate natural grains by overlapping two spheres. Both the size of each sphere and the degree of overlap can be varied for these composite particles to generate a range of non-spherical grains. Simulations of particles having a range of shapes showed that the critical angle - the angle at which a grain pile will fail when tilted slowly from rest - increases from approximately 26 degrees for spherical particles to nearly 39 degrees for highly non-spherical composite particles having a dumbbell shape. Simulations of oscillatory sheet flow were conducted using composite particles with an angle of repose of approximately 33 degrees and a Corey shape factor greater than about 0.8, similar to the properties of beach sand. The results from the sheet-flow simulations with composite particles agreed more closely with laboratory measurements than similar simulations conducted using spherical particles. The findings suggest that particle shape may be an important factor for determining bed-load flux, particularly for larger bed slopes. (5 figures, 18 refs.)

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Document Details

Document Type
Technical Report
Publication Date
Jan 01, 2004
Accession Number
ADA426491

Entities

People

  • Joseph Calantoni
  • K. Todd Holland
  • Thomas G. Drake

Organizations

  • United States Naval Research Laboratory

Tags

Communities of Interest

  • Air Platforms
  • Energy and Power Technologies

DTIC Thesaurus Topics

  • Boundaries
  • Boundary Layer
  • Buoyancy
  • Composite Materials
  • Coordinate Systems
  • Equations
  • Experimental Data
  • Fluid Dynamics
  • Geometry
  • Layers
  • Measurement
  • Mechanics
  • Particles
  • Sedimentation
  • Simulations
  • Subatomic Particles
  • Three Dimensional

Readers

  • Aerosol Science/Aerosol Physics
  • Coastal and Marine Engineering/Sediment Transport/Hydraulic Engineering
  • Fluid Dynamics.