Numerical and experimental evaluation of the erodibility of particle packings with surface treatments and spring reinforcements using the discrete element method
Date
2019
Authors
Peterson, Kirsten LaRhea, author
Heyliger, Paul, advisor
Bareither, Christopher, advisor
Atadero, Rebecca, committee member
Kampf, Stephanie, committee member
Journal Title
Journal ISSN
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Abstract
Chapter 4. The erodibility of homogeneous two-dimensional spherical particle packings subjected to added mass surface treatments was explored using a combination of physical flume experiments and the discrete element method (DEM). Packings composed of spherical glass particles, with and without surface treatments and angled at two different slopes, were tested experimentally and simulated numerically under surficial flow conditions. The surface treatments acted to add mass to the surface of the particle packings. Particle erosion was quantified by tracking eroded particles as a function of fluid velocity. DEM simulations and flume experiments were first performed with a layer of steel particles that served as an extreme case of surface treatment. Similar trends were observed between the simulations and experiments, whereby the number of eroded particles decreased by an average of 90% when compared to untreated cases. The results from this surface treatment suggested that if the surface treatment mass is large enough, nearly all particle erosion under surficial flow conditions can be mitigated. Additional experiments were performed with surface treatments composed of increasing application rates of wetted agricultural straw. The particle erosion rates were dominated by piecewise linear behavior as a function of eroded mass versus fluid velocity. This behavior indicated a) an initial resistance to flow based on gravity, followed by b) a surface treatment movement that induced widespread failure or erosion at a much higher rate. Dislodgement and subsequent erosion of particles occurred at higher fluid velocities (over 50% higher for the highest straw application rate) when the surface treated cases were compared to the untreated cases. Conclusions drawn from the simulation and experiment results indicated a direct correlation between added mass on the surface of a particle packing and decreased erosion under surficial flow conditions and showed that as slope increased, erosion levels increased and began at lower surficial flow fluid velocities. Chapter 5. The erodibility of three-dimensional particle packings reinforced numerically with elastic springs and subjected to overland flow conditions was explored using the discrete element method (DEM). Particle packings at three slopes, subjected to overland flow at two fluid velocities, and four reinforcement configurations resulted in a total of 24 datasets of simulation results for comparisons to be made. The three slopes were composed of the same 2400 particles with coarse sand material properties and a uniform distribution of diameters between 1.8 and 8.0 millimeters. The elastic spring reinforcements represent a potential modeling technique for root development in a soil. The spring reinforcement technique presented here is a proof-of-concept attempt to model three-dimensional slopes at up-scaled particle sizes, root stiffness, and fluid velocities. Particle displacements were tracked and compared as functions of time, reinforcement level, and slope. The results suggest linear relationships between decreased particle movement with increased percent reinforced surface particles, increased particle movement with increased slope, and decreased sediment yields with increased percent reinforced surface particles. Also, at the lower fluid velocity, particle displacements were more dependent on incremental changes in slope; whereas at the higher fluid velocity, particle displacements were not dependent on small changes in slope. Overall, the results from the simulations and experiments showed the influence of elastic spring reinforcements on particle movements and the next step of the research would be to assess the scaling effects and apply the root model to smaller particles, more indicative of where roots are expected to grow.
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Subject
mechanics
surface treatments
slope reinforcements
discrete element modeling