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We interpret the Taylor–Green cellular vortex model in terms of the Kolmogorov length and velocity scales, in order to study the balance between aggregation and breakup of cohesive sediment in fine-scale turbulence. One-way coupled numerical simulations, which capture the effects of cohesive, lubrication and direct contact forces on the flocculation process, reproduce the non-monotonic relationship between the equilibrium floc size and shear rate observed in previous experiments. The one-way coupled results are confirmed by select two-way coupled simulations. Intermediate shear gives rise to the largest flocs, as it promotes preferential concentration of the primary particles without generating sufficiently strong turbulent stresses to break up the emerging aggregates. We find that the optimal intermediate shear rate increases for stronger cohesion and smaller particle-to-fluid density ratios, and we propose a simple model for the equilibrium floc size that agrees well with experimental data reported in the literature.
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Two-Scale Discrete Element Modeling of Gyratory Compaction of Hot Asphalt
This paper presents a discrete element model for simulations of the compaction process of hot mixed asphalt (HMA). The model is anchored by the concept of a fine aggregate matrix (FAM), which consists of the binder and fine aggregates. In the simulation, the coarse aggregates are explicitly modeled as composite particles. Meanwhile, the FAMis considered as the thick coating of the coarse aggregates with complex constitutive laws. Interparticle interactions include influences of (1) particle properties via Hertz–Mindlin relations; and (2) FAM properties via lubrication relationships. The lubrication relationships include a variable for viscosity for which we derive normal and tangential rate-dependent forms using rheology theory of dense granular-fluid systems, verified reasonable for our systems with the discrete element simulations and experiments with FAM. We assimilate these elements into gyratory compaction simulations of HMA of different aggregate size distributions. We compare these with experiments and find that this model is capable of capturing the measured effects of grain size distribution on the overall compaction behavior of HMA. We conclude by highlighting the advantages of this discrete element model for HMA compaction problems.
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- Award ID(s):
- 2203110
- PAR ID:
- 10500032
- Publisher / Repository:
- ASCE
- Date Published:
- Journal Name:
- Journal of Engineering Mechanics
- Volume:
- 148
- Issue:
- 2
- ISSN:
- 0733-9399
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1061/(ASCE)EM.1943-7889.0002033
