Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session A17: Granular Flows: General |
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Chair: Manaswita Bose, Indian Institute of Technology Bombay Room: 250 A |
Sunday, November 24, 2024 8:00AM - 8:13AM |
A17.00001: Numerical experiments into particle shape effects on immersed granular column collapse Sharey D Guleria, Yuanqing Liu, Lian Shen Granular flows, driven by shear (e.g., sediment transport) or gravity (e.g., pyroclastic flows, landslides, avalanches), are significantly influenced by particle density, size, and shapes. In this study, we pander to gravity-driven granular flows, specifically channelized granular column collapse, using particle-resolved simulations via an immersedboundary method. We systematically investigate the effects of particle shape (sphere, spheroid, and their mixture) on granular column collapse. For spheroids, we vary the aspect ratio from minor to major axis radius to study the |
Sunday, November 24, 2024 8:13AM - 8:26AM |
A17.00002: Rheology and thermodynamics of a granular pile Rouslan Krechetnikov, Andrei Zelnikov From the onset of the subject, granular media have been defying the toolkit of statistical mechanics thus hindering our understanding of their thermodynamical and rheological properties. In the present work, we offer a resolution to this problem in the case of static granular media by considering a collective behavior of 2D identical balls forming a granular pile in the gravity field. Besides the uncertainty due to rough substrate on which the pile is built, we uncover another one due to ambiguities occurring in the positions of some interior balls. Both are responsible for the thermodynamic description of the granular pile. In particular, a pile is characterized by three temperatures: one is infinite, the other is negative, and the third is of higher-order. Also, considering the fields of ball displacements and the normal force deviations from the ideal isosceles triangular structure of a regular pile reveals the hyperbolic nature of the displacement field and ability of the force field to change the characteristic type from hyperbolic to elliptic. The latter property not only explains the origin of force chains and provides an adequate description of the rheology of static granular media, but turned out to be instrumental for understanding the granular media thermodynamics. |
Sunday, November 24, 2024 8:26AM - 8:39AM |
A17.00003: Flow Structures and Sorting Effects of Vibration-Driven Immersed Dense Granular Systems Yi An, Chi Wang Understanding the dynamic characteristics of vibration-driven immersed dense granular systems (VIGS) is crucial for comprehending the mechanisms in applications such as ore sorting and debris flow assessment. This work, through the combination of CFD-DEM simulations and laboratory experiments, studies the dynamic characteristics of VIGS. Using a newly developed homogenization method, a macroscopic convective structure with thermodynamic similarity is found in a system of monodisperse spherical particles with the same density, verifying the critical role of granular flow structure in VIGS. To further understand the influence of the flow structure, the quasi-two-dimensional monodisperse VIGS with different density ratio conditions was experimentally studied, and the sorting effect was analyzed. It was found that the sorting effect is closely related to the state of the flow structure. The vibration intensity, the density ratio of particles to the surrounding fluid, and the fluid viscosity jointly affect the state of the flow structure, thereby influencing the sorting effect. The granular gas state of particles has a good sorting effect but requires high vibration intensity, while the Leidenfrost state with a liquefied surface is an optimal state where vibration energy input and sorting efficiency are balanced. This study might provide data and theoretical support for the sorting needs of immersed dense particles. |
Sunday, November 24, 2024 8:39AM - 8:52AM |
A17.00004: ABSTRACT WITHDRAWN
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Sunday, November 24, 2024 8:52AM - 9:05AM |
A17.00005: Small frictional differences yield motion in opposing directions: separation of dry granular materials via horizontal dual-mode vibrations Shelly Zhang, Irwin Donis-Gonzalez, Gregory H Miller, William D Ristenpart Recent work has established that objects placed on a horizontally vibrating surface exhibit net motion in one direction if the vibration has multiple frequency modes that break temporal symmetry. Here we report that granules with small differences in friction coefficient can move in opposite directions in response to specific vibratory waveforms, yielding an extremely rapid separation. We use a shooting method numerical simulation to predict the object’s steady velocity by applying Coulomb’s friction law balanced with inertia. Given the frictional properties of the granular materials, we conduct numerical studies to predict the optimal choice of vibratory waveform that induces maximum and opposite steady velocities. We present experimental tests of separating granular materials, millimeter-scale objects, and agricultural products, and we discuss the implications for efficient separation and purification in various industrial processes. |
Sunday, November 24, 2024 9:05AM - 9:18AM |
A17.00006: Stokesian relationships for the rheology of granular flows and particle-size segregation Tianxiong Zhao, Daisuke Noto, Hugo N Ulloa, Xia Li, Tomas Trewhela Shear-induced segregation plays a critical role in various industrial and natural processes. The necessity to understand and predict particle segregation prompts our study of the basic principles underlying this phenomenon. This study aims to establish a relationship between segregation velocity and the properties of granular materials through various expressions connecting to a Stokes' settling velocity. We use the Discrete Element Method to simulate an intruder particle of varying sizes embedded in a sheared granular flow. From a comparison between theoretical trajectories and simulation results, we derive a new scaling law that offers a detailed characterization of the variables involved in segregation. Deviations between simulated and theoretical trajectories are also discussed. This study suggests an intrinsic connection between the segregation process and particle settling in fluids, leading to a Stokes-like expression for particle segregation velocity. |
Sunday, November 24, 2024 9:18AM - 9:31AM |
A17.00007: Crater formation in a cohesive granular bed by an impinging turbulent jet Alexis Lin, Ram Sudhir Sharma, Joanne Steiner, Cyprien Morize, Philippe Gondret, Alban Sauret The erosion of particles by an impinging turbulent jet is observed in various situations, such as the cleaning of a surface or during the landing of a spacecraft. Beyond the threshold of erosion, a round turbulent jet of gas normally impinging a cohesionless granular bed displays an axisymmetric crater. Here, we experimentally consider the effects of inter-particle cohesion on the craters formed beyond the erosion threshold by controlling the cohesion between the grains and the momentum of the turbulent jet. We report the morphology of the steady-state craters observed. Our experiments show that the presence of cohesion significantly alters the erosion dynamics and, as a result, the craters that form. The morphology of the craters are described by extending the framework previously developed to describe the effects of cohesion on the onset of erosion in this geometry. |
Sunday, November 24, 2024 9:31AM - 9:44AM |
A17.00008: Bouncing, piling, spreading: Impact of a dense granular jet on a rough surface Ram Sudhir Sharma, Alban Sauret Handling of granular materials often involves the formation of axisymetric sandpiles. Their growth as material is being poured, and in particular the radial extension of the grains, are an important parameter to predict. We experimentally study the continuous impact of a dense stream of grains on a rough surface. Initially, a central granular jump is observed between the incoming grains and prior grains that have been deposited. As more mass is provided, the radius of the jump is observed to reduce. Once the granular jump reaches its minimum radius, incoming grains are observed to start piling symmetrically. The presence of the pile removes the individual effects of bouncing grains that are instead pushed into the pile's apex, leading to a growing center and avalanches on the free surface as the pile spreads. We describe these different regimes and the transition between them in terms of the mass flux of the granular jet and the height over which the grains are allowed to accelerate in the air prior to impact. The range of avalanche behavior in the second regime is then characterized. This system illustrates the complexity of the transition between the grain scale and the pile scale. |
Sunday, November 24, 2024 9:44AM - 9:57AM |
A17.00009: Geometrical Neural Surrogate for Granular Systems Tony D Rosato, Vishagan Ratnaswamy, Youngjin Chung, Weiqing Gu Density relaxation is a phenomenon where bulk granular materials subjected to external time-dependent forces experience an increase in solids fraction. We report on a graphical neural surrogate of the process using training sets generated by discrete element simulations of uniform, inelastic, frictional soft spheres. Ensembles of assemblies of N particles are generated via gravity deposition into a periodic box with a rigid floor, that is subjected to a half-sinusoidal motion of amplitude a and frequency ω to mimic tapping. The complexity of the phenomenon is consequent upon a large parameter space, and the long time scale associated with microstructural rearrangements. Training sets are comprised two ensembles (Γ=aω2/g= 2.75, 3.25) consisting of the sphere positions at relaxed states for each of the 15,000 applied taps. We use geometric deep learning to forecast the evolution of the assembly microstructure by constructing 15,000 adjacency matrices (N x N) endowed with particle coordinates as added features from the contact networks for 25 realizations of each ensemble. With a 70% training set, a variational autoencoder is used to estimate a probability distribution over possible configurations in the latent space, while a decoder generates new configurations based on the previous tap and the latent space. Particle positions beyond the training set are then used to compute solids fractions and distributions of coordination number and free volume that are found to be in good agreement with the simulations. |
Sunday, November 24, 2024 9:57AM - 10:10AM |
A17.00010: Fluctuations affecting granular rheology Benjamin Alessio, Yue Meng, Ching-Yao Lai Granular flows are susceptible to environmental forcings and fluctuations which may impact their rheologies in complicated ways. Recent advances in kinetic theory have shown that collisional models can explain a range of behavior far wider than the paradigm of the past two decades would suggest. Such models can naturally include the effect of environmental forcings in the energy balance, though may be prohibitively complicated in some circumstances. Simpler empirical models have been proposed to extend the eponymous μ(I) rheology by including the effect of the granular temperature field. Though these constitute a promising first approach to predict directly the effect of induced fluctuations such as environmental forcings, they lack a fundamental basis. Based on discrete element method (DEM) simulations, we establish a direct connection between kinetic theory and these empirical models in order to determine at what point more complicated models are necessary. |
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