Granular Matter最新文献

Particle Tracking Velocimetry (PTV) is a Lagrange-based flow visualization technique that tracks the motion of multiple particles or granules simultaneously. With the widespread application of three-dimensional (3D) particle imaging systems, 3D PTV algorithms have attracted considerable interest, whereas many 3D algorithms are developed from the corresponding 2D algorithms; moreover, compared with 3D algorithms, 2D algorithms are more suitable for real-time flow monitoring in industry. This paper proposes a 2D PTV algorithm based on the Voronoi diagram (VD) that is optimized by the minimum enclosing ellipse (MEE); then a re-matching process based on a homemade method called Quasi-Parallel Correction (QPC) is developed to correct the abnormal results produced by PTV at large inter-frame particle displacement. This PTV is thereby named MQ-PTV. MQ-PTV is then employed for reconstructing a granular flow made of dense polypropylene particles along a declined chute, an aeolian sand flow over sand bed, the migration of a barchans swarm and the motion of stars, thus confirming its practicability in a wide variety of particle motion reconstruction.

Investigations into the various properties of granular matter composed of particles with defined shapes have gained increasing attention. Additive manufacturing, with its freedom of shape and rapid prototyping capabilities, has significantly contributed to these studies. However, this technique may introduce defects in the manufactured particles, which can significantly affect the properties of granular materials. The extent of these defects on particles of different shapes is investigated here. Particles of various shapes (cube, octahedron, quatropod, stellated octahedron, tetrahedron, and tetrapod) were manufactured and subsequently imaged using micro-Computed Tomography. The surface roughness, solidity, and convexity of the particles were quantified. Discrete element simulations of granular bed porosity, utilizing both idealized and real particle shapes, were conducted with different surface mesh resolutions and frictional parameters. A clear influence of the manufacturing process on the packing properties of 3D printed particles was identified. This influence is not uniform across all shapes and is directly correlated with the particle convexity. For numerical simulations, a shape-dependent correction of particle density and surface characteristics are imperative for each shape under consideration, despite the fact that the particles were manufactured using the same technique and material.

Graphic abstract

Existing image analysis algorithms cannot achieve consistency with human visual classification results when classifying particles based on angular levels. To address this issue, this paper proposes an image analysis method based on triangle side ratio to quantify particle angularity, referred to as a TSR method. The proposed method utilizes a primary parameter, Mean Angularity, to assess the mean angularity level, and employs three auxiliary parameters to offer insights into the Sharpest Angularity, the Flat Proportion, and the Number of Angularity. When quantifying the angularity, the method further provides the count of convex angles. Each parameter can reflect different characteristic information of the angularity. When using the mean angularity level to order particles, the TSR method achieves the same results as visual classification, and furthermore introduces a range of values for the main parameter corresponding to the different angularity levels. The TSR method is simpler and more stable, since the particle parameters can be calculated directly without contour smoothing, and consistent results are achieved for different shapes with the same degree of angular sharpness. The results of the study on lunar soil, volcanic rock, mechanism stone, and stream stone, show that the TSR method can objectively and comprehensively analyze and quantify the particle angularity.

Graphic abstract

We present an experimental investigation on the flow and clogging of bi-disperse mixtures of coarse and fine grains of different densities passing through small orifices. We vary the density ratio (coarse/fine) from 1.87 down to 0.79 by using amaranth seeds, glass and ceramic beads of similar size as the fine species in combination with 2.0 mm glass beads as the coarse grains. We analyzed the effect of the density ratio on the effective flow rate of the coarse species, the segregation during flow and the clogging for a range of orifice diameters. As in previous studies, the flow of the coarse grains is facilitated by the fine species, which prevents clogging. We show that the effective flow rate of the coarse species is virtually independent of the density ratio. These results suggest that in practical applications with the goal of clogging reduction, the density of the fine species used to ease the flow is not a relevant parameter and can be selected based on practical or economic constraints.

Graphic abstract

Schematic diagram of the flow of large grains through a small orifice when they are diluted in a mixture with fine grains

The fluidized bed bioreactor is an economical and efficient method for wastewater treatment. In the fluidized bed bioreactor, fluidized particles carrying microorganisms consume the organic pollutants in wastewater. The collision and friction between carrier particles in the fluidized bed can affect the efficiency of wastewater treatment. Therefore, understanding the hydrodynamics of fluidized bed bioreactors is crucial. In this study, the particle collision velocity depending on particle volume fraction and granular temperature, as well as considering the influence of particle surface roughness and elasticity through the critical Stokes number, a dynamic restitution coefficient model for wet rough particles is developed to provide a more accurate description of the collision behavior between wet rough particles. The model is incorporated into the kinetic theory of rough spheres to perform numerical simulations on the hydrodynamic characteristics of a three-dimensional liquid-solid tapered fluidized bed using the two-fluid model. The simulation results exhibit better agreement with experimental data by Wu et al. compared to prior studies. Furthermore, sensitivity analyses are conducted on drag force, virtual mass force, and lift force. It is observed that the Koch-Hill drag model predicts the bed expansion heights closest to the measured results. Additionally, the impacts of static bed height and particle density on the fluidized bed hydrodynamics are investigated. Simulation results indicate that an increase in static bed height initially leads to an increase and then a decrease in particle collision velocity. Within the current study scope, particle collision velocity exhibits a monotonic increase with increasing particle density.

Granular materials belong to the class of complex materials within which rich properties can emerge on large scales despite a simple physics operating on the microscopic scale. Most notable is the dissipative behaviour of such materials mainly through non-linear frictional interactions between the grains which go out of equilibrium. A whole variety of intriguing features thus emerges in the form of bifurcation modes in either patterning or un-jamming. This complexity of granular materials is mainly due to the geometrical disorder that exists in the granular structure. Diverse configurations of grain collections confer to the assembly the capacity to deform and adapt itself against different loading conditions. Whereas the incidence of frictional properties in the macroscopic plastic behavior has been well described for long, the role of topological reorganizations that occur remains much more elusive. This paper attempts to shed a new light on this issue by developing ideas following the configurational entropy concept within a proper statistical framework. As such, it is shown that contact opening and closing mechanisms can give rise to a so-called configurational dissipation which can explain the irreversible topological evolutions that granular materials undergo in the absence of frictional interactions.

Graphical Abstract

The response of dry sand to rapid penetration by a rigid projectile is investigated through a series of high-speed penetration experiments. A ballistic range is used to vertically launch cylindrical projectiles and a scaled version of a 155 mm M107 projectile at impact velocities of approximately 200 m/s into sand targets. A photon Doppler velocimeter is used to track projectiles from impact to rest in the soil target. Data collected from the experiments include the evolution of the cavity crown along with displacement, velocity, and acceleration time history. Analysis of the results reveal that the soil bulk density has a major role in penetration resistance at high relative densities. The role of bulk density diminishes at lower relative densities. Furthermore, the shape of the projectile nose has limited influence on the penetration response, due to the formation of a kernel of crushed sand at high velocities. The crushed sand kernel, known as the false nose, has a curved surface, and it can be approximated as a cone with a 60° apex angle. Only projectiles with a nose sharper than this value affect penetration resistance, while blunter noses effectively behave as 60° cones due to the formation of the false nose. A phenomenological equation of penetration resistance comprising inertial and frictional bearing resistance is used to describe the penetration response and predict the depth of burial (DoB) of the projectile in the soil target with reasonable accuracy.

Graphical Abstract

Laboratory made granular–granular impact craters have been used as model analogues of planetary impact craters. These kind of craters have been observed and studied using profilometry techniques that allow to retrieve important morphologic features from the impacted surface. In this work, we propose to use a Time-of-Flight camera (Microsoft Kinect One) for the acquisition of depth data. We show comparisons between the typically used technique and the analysis derived from the Time-of-Flight data. We also release craterslab, a Python library developed to automate most of the tasks from the process of studying impact craters produced by granular projectiles hitting on the surface of granular targets. The library is able to acquire, identify, and measure morphological features of impacted surfaces through the reconstruction of 3D topographic maps. Our results show that using a Time-of-Flight camera and automating the data processing with a software library for the systematic study of impact craters can produce very accurate results while reducing the time spent on different stages of the process.

Graphical abstract

Three-dimensional representation of the lunar crater Werner by craterslab as a tool for morphometric analysis of natural and laboratory impact craters.