Motion Of Granular Material Research Articles

Sand creep motion in slow spin-up experiment: An analog of regolith migration on asteroids.

We studied the creep motion of granular materials in a gradient potential field that is created using a slow spin-up experiment device. Natural sand confined in the acrylic box is spun up by a controlled turntable and the surface flows are captured using video-based measurements. Various spin-up accelerations were considered to understand the responses of creep motion on different accelerating paths. Convergent behaviors in the morphological change of sand surface were observed in the final steady state. To quantify the quasistatic spin-up process, we examined the net flux and the surface slope as a function of the spin rate and offset from the rotation axis. The creep motion of sand demonstrated behaviors similar to the regolith migration in numeric simulations. We have noticed the sand surface approaches criticality as the spin-up proceeding, consistent with the observation that top-shaped asteroids near limiting spin rate take on critical shapes. Comparisons to large-scale numeric simulations and analytical solutions reveal underlying similarities between the experiments and the million-year evolution of asteroid regolith under Yarkovsky-O'Keefe-Radzievskii-Paddack acceleration, which raises the possibility of studying asteroid surface processes in laboratory analog experiments.

Dynamically structured bubbling in vibrated gas-fluidized granular materials.

The dynamics of granular materials are critical to many natural and industrial processes; granular motion is often strikingly similar to flow in conventional liquids. Food, pharmaceutical, and clean energy processes utilize bubbling fluidized beds, systems in which gas is flowed upward through granular particles, suspending the particles in a liquid-like state through which gas voids or bubbles rise. Here, we demonstrate that vibrating these systems at a resonant frequency can transform the normally chaotic motion of these bubbles into a dynamically structured configuration, creating reproducible, controlled motion of particles and gas. The resonant frequency is independent of particle properties and system size, and a simple harmonic oscillator model captures this frequency. Discrete particle simulations show that bubble structuring forms because of rapid, local transitions between solid-like and fluid-like behavior in the grains induced by vibration. Existing continuum models for gas-solid flows struggle to capture these fluid-solid transitions and thus cannot predict the bubble structuring. We propose a constitutive relationship for solids stress that predicts fluid-solid transitions and hence captures the experimental structured bubbling patterns. Similar structuring has been observed by oscillating gas flow in bubbling fluidized beds. We show that vibrating bubbling fluidized beds can produce a more ordered structure, particularly as system size is increased. The scalable structure and continuum model proposed here provide the potential to address major issues with scale-up and optimal operation, which currently limit the use of bubbling fluidized beds in existing and emerging technologies.

Vibration separation of multiple mixed particle curves based on image recognition and machine learning

The motion characteristics of particulate matter are very wonderful. With the development of science and technology, the motion of granular materials has gradually become a hot topic, which has attracted the attention of many scientists and experts. The research of granular matter has gradually become specialized and systematic. With the gradual improvement of the system, a frontier research field particle physics has been formed. Under the combined action of external force and internal force, particles can reflect the properties of fluid, but in the process of flow, it will show different size separation phenomenon from the fluid. The problem of particle separation was formally introduced into the field of physics in 1987. In reality, the existence of particles is not unique. In view of this, the author makes a systematic research and Analysis on the behavior and factors of vibration.

Multibody Dynamics Versus Fluid Dynamics: Two Perspectives on the Dynamics of Granular Flows

Abstract Considering that granular material is second only to water in how often it is handled in practical applications, characterizing its dynamics represents a ubiquitous problem. However, studying the motion of granular material poses stiff computational challenges. The underlying question in this contribution is whether a continuum representation of the granular material, established in the framework of the smoothed particle hydrodynamics (SPH) method, can provide a good proxy for the fully resolved granular dynamics solution. To this end, two approaches described herein were implemented to run on graphics processing unit (GPU) cards to solve the three-dimensional (3D) dynamics of the granular material via two solution methods: a discrete one, and a continuum one. The study concentrates on the case when the granular material is packed but shows fluid-like behavior under large strains. On the one hand, we solve the Newton–Euler equations of motion to fully resolve the motion of the granular system. On the other hand, we solve the Navier–Stokes equations to describe the evolution of the granular material when treated as a homogenized continuum. To demonstrate the similarities and differences between the multibody and fluid dynamics, we consider three representative problems: (i) a compressibility test (highlighting a static case); (ii) the classical dam break problem (highlighting high transients); and (iii) the dam break simulation with an obstacle (highlighting impact). These experiments provide insights into conditions under which one can expect similar macroscale behavior from multibody and fluid dynamics systems governed by manifestly different equations of motion and solved by vastly different numerical solution methods. The models and simulation platform used are publicly available and part of an open source code called Chrono. Timing results are reported to gauge the efficiency gains associated with treating the granular material as a continuum.

Mixing and Segregation of Granular Materials in a Precessing Cylindrical Container

It is difficult to mix different kinds of granular materials. The so-called Brazil nut effect is a well-known phenomenon showing the segregation of granular materials with different density or size. Since the motion of granular materials depends on a lot of parameters such as the diameter, density, elastic coefficient, frictional coefficient, and so on, the physics of granular materials is complicated. In this study, we numerically simulate the mixing of two kinds of spherical particles with different diameters confined in a precessing cylindrical container. We change the angular velocity of the spinning container and the angle between the spin and precession axis to evaluate how they affect the mixing of the particles.

An Eulerian model for the motion of granular material with a large Stokes number in fluid flow

This study introduced a novel Euler–Euler approach for modeling granular multiphase flow. The motion of particles with a large Stokes number was investigated assuming that granular material has unilateral compressibility. Solid pressure in the momentum equations for granular multiphase flow was determined so that the unilateral incompressibility condition was satisfied. Using the continuity condition of the granular phase, the equation was rewritten in the optimal form to calculate the solid pressure. A discrete formulation of smoothed particle hydrodynamics was applied for the convective terms so that the discrete matrix was positive semidefinite for the convergence and the discretization for an unstructured mesh was allowed. Frictional stress was then determined from solid pressure and, by using the solid pressure and frictional stress, momentum equations for the granular phase were solved. The method was incorporated into ANSYS FLUENT by a UDF (user defined function). Model validation was performed through a comparison with two previous results, and efficacy of the proposed model was confirmed.

Can we develop a general theory of the dynamics of turbulent flows and the motion of granular materials?

Most flows in nature and in engineering applications are turbulent. Turbulence is not a feature of fluids but of fluid flows, and turbulent flow includes multi-scale vortices. Many turbulent flows can be observed in our daily life; however, it is very difficult to give a precise definition of turbulence. Some of the characteristics of turbulent flows can be described, such as the randomness, the diffusivity, the dissipation, and the vorticity fluctuations of turbulent flows. Granular flow is the flow of solid particles in gas or liquid phase, which has been the subject of intense activity at the leading edge of fluid mechanics, soil mechanics, rheology, and statistical physics. The relevant research is motivated by a variety of applications encountered in industrial processes. Most important question is the lack of constitutive equations. The difficulty originates from fundamental characteristics of granular matter such as negligible thermal fluctuations, highly dissipative interactions, and a lack of separation between the microscopic grain scale and the macroscopic scale of the flow. To date, no general theory for the dynamics of turbulent flows and granular flows exists. In this article, we discuss the fundamental characteristics of turbulent flows and granular flows and the relevant theories and methods, and analyze the difficulties in the research of turbulent flows and granular flows.

Influence of flight shape on discharging profiles of granular material in rotary dryer

In this work, Discrete Element Method (DEM) is used in order to calculate the motion of granular material in rotating dryers. We are particularly interested in analysing the effect of flight shape on the behaviour of spherical particles in the cross section of the dryer. We will be using two segments flights and three different profiles : a straight flight (180° between both segments), an angled flight (with an angle of 120°) and a rightangled flight (90°). The results show that the profile of the flight affects significantly the motion of the particles in the cross section of the dryer. Changing the angle between the segment’s flight, changes the flight loading and thus the material hold-up which leads to different discharging profiles of the flight. For a right angled flight, the range of the discharge angle increases leading to a more uniformized cascade pattern in time and an enlarging of the area occupied by the curtains of particles. The specific durations (discharging time, falling time) are also determined and studied as a function of the flight shape.

Horizontal flow and surface patterns in a vertically vibrated annular granular layer.

A set of experiments was carried out on the motion of granular materials in a vertically vibrated annular system with a sawtooth-shaped base. We observed the coexistence of granular flow and surface patterns such as periodic subharmonic waves and kink pairs. Different patterns can transit each other as control parameters vary. The flow varies with space and time, and oppositely directed flows can occur at different levels and different moments. The magnitude and direction of the flow depend on the parameters defining the system in a complex manner. The motion of the patterns relates to the granular flow in a different way from that in which the wave in an ordinary fluid relates to the moving fluid. A preliminary explanation is given to our experimental findings.

STATIC AND DYNAMIC CHARACTERISTICS OF TRANSPORT PROCESSES IN DISPERSE SYSTEMS

This article deals with a mathematical model that describes the static and dynamic characteristics of the process in the fluidized bed granulation and shows the change in coolant temperature and fluidized bed during the heat-mass transfer processes during the motion of granular material through relevant technological areas in the machine that gives a granular product with desired properties. The variation of temperature determines the kinetics of granulation and physico-mechanical properties of the pellets. Therefore, the proposed mathematical model can be used to create an efficient system of managing the process of formation of mineral fertilizers in the fluidized bed with liquid dehydration systems.

DEM simulation of oblique shocks in gravity-driven granular flows with wedge obstacles

Deflecting wedge obstacles are often built to divert hazardous flows away from residential areas that are in the way of harm. When a rapid avalanche flow is deflected by an obstacle, this usually causes abrupt changes in the flow thickness and velocity and exhibits characteristics like oblique shock waves in the aerodynamic system or oblique hydraulic jumps in the open channel flows. In this study, the Discrete Element Method (DEM) is employed to simulate the motion of granular materials impinging on a wedge obstacle in an adjustable inclination chute. We use chutes with four different inclined angles combined with wedge obstacles having different angles to investigate the overall flow behavior. Both the flow velocity and the flow depth are obtained by averaging the numerical simulation data, and then the granular temperature and the shock angle are calculated. The results of the DEM simulation are compared with that of the classical oblique shock theory. We find that there is good agreement between the classical oblique granular shock theoretical calculations and the DEM simulation results. Moreover, the microdynamic variables related to flow structure such as the packing density and the coordination number are also discussed in the present study.

The influence of driving conditions on flow behavior in sheared granular flows

Granular materials may behave like a solid, a liquid, or a gas, depending on the processing conditions. In this study, a two-dimensional annular shear cell was used to investigate the dynamic properties of granular flow when subject to varying driving conditions. The effects of different driving conditions on granular flow were examined by taking images of the motions of granular materials with a high-speed camera. Image processing technology and a particle tracking method were employed to measure velocity, slip velocity, local solid fraction, and granular temperature. The results show a gradual decrease in the velocity profile from the shearing boundary to the stationary wall when only the inner or outer wall rotates. The tangential velocity of granular materials is greater with only a rotating outer wall than with an inner wall rotating singly at the same velocity. The results also show that slip velocity increases in conjunction with wall velocity and decreases if the solid fraction is increased. This study also examined flow behaviors caused by rotating both walls, first in the same direction, and then in opposite directions. The results indicate that granular temperatures in a system with both walls rotating in opposite directions are higher than in a system with walls rotating in the same direction.

Numerical simulations of granular dynamics II: Particle dynamics in a shaken granular material

Surfaces of planets and small bodies of our Solar System are often covered by a layer of granular material that can range from a fine regolith to a gravel-like structure of varying depths. Therefore, the dynamics of granular materials are involved in many events occurring during planetary and small-body evolution thus contributing to their geological properties.We demonstrate that the new adaptation of the parallel N-body hard-sphere code pkdgrav has the capability to model accurately the key features of the collective motion of bidisperse granular materials in a dense regime as a result of shaking. As a stringent test of the numerical code we investigate the complex collective ordering and motion of granular material by direct comparison with laboratory experiments. We demonstrate that, as experimentally observed, the scale of the collective motion increases with increasing small-particle additive concentration.We then extend our investigations to assess how self-gravity and external gravity affect collective motion. In our reduced-gravity simulations both the gravitational conditions and the frequency of the vibrations roughly match the conditions on asteroids subjected to seismic shaking, though real regolith is likely to be much more heterogeneous and less ordered than in our idealised simulations. We also show that collective motion can occur in a granular material under a wide range of inter-particle gravity conditions and in the absence of an external gravitational field. These investigations demonstrate the great interest of being able to simulate conditions that are to relevant planetary science yet unreachable by Earth-based laboratory experiments.

Collision Analysis between Granular Materials and Elastic Plate

The method of collision analysis between granular materials and a plate is investigated numerically and experimentally. The motions of granular materials and the plate are analyzed by using the discrete element method and the finite element method, respectively. The damping characteristics of the plate are given by the Rayleigh damping. The validity of the analysis method is examined by a comparison of the experimental results. In the experimental approach, the response of an aluminum thin plate was measured when some steel balls collided with it. The contact behavior of the plate is evaluated by the displacement response and the frequency response of the plate.

Density segregation in a vertically vibrated granular bed

The dominant mechanism affecting the flow behavior of granular materials is the random motions of particles that results from the interactive collisions between particles. The velocity fluctuations induce the segregation in granular flows. The different densities of granular materials with different filling layers and packing ratios were used to investigate the segregation mechanisms in a vibrated granular bed in this study. The image processing techniques were employed to track the motion of granular materials. The fluctuating velocities of granular materials were measured under segregation in a vibrated granular bed. The segregation phenomena depend on the packing ratio and the filling layer of the stainless steel–glass mixtures. At the fewer filling layers, the heavier stainless steel beads migrate to the bottom regions with the lower granular temperature, so the granular temperature plays a significant role on density segregation. For the higher filling layers, the bulk convection motion is the main mechanism affecting segregation, so the heavier beads clump to the convection center and the clump size enlarges with the increasing packing ratio of heavier beads due to the bulk convection motion.

A roe-average algorithm for a granular-gas model with non-conservative terms

A Roe-average algorithm has been derived for a granular-gas model, proposed by Goldshtein and Shapiro [Goldshtein, Shapiro, Mechanics of collisional motion of granular materials: Part 1. General hydrodynamic equations, J. Fluid Mech. 282 (1995) 75–114], which contains non-conservative terms in the Euler-like hyperbolic governing equations apart from sink terms, which arise from inelastic collision of granules and are present only in the energy equation. The non-conservative terms introduce non-isentropic effects in acoustic-wave propagation within granular media and they also contribute to the Rankine–Hugoniot relations across a discontinuity. A Roe-average algorithm, based on the same granular-gas model, was derived in the literature [V. Kamenetsky, A. Goldshtein, M. Shapiro, D. Degani, Evolution of a shock wave in a granular gas, Phys. Fluids, 12 (2000) 3036–3049] which then required the implementation of a shock-fitting technique at a discontinuity. In the present work, Roe-averaged variables have been obtained from the Rankine–Hugoniot jump relations and the non-conservative terms have been incorporated in the numerical flux formula consistent with upwind principles associated with the granular speed of sound. Results for unsteady one-dimensional granular flows, colliding with a wall, demonstrate the capability of the proposed algorithm to capture strong shocks in addition to flow features not found in molecular gases, such as a fluidized region downstream of the shock and a compacted solid-block region adjacent to the wall.

464 粒状体ダンパの減衰メカニズムに関する研究 : 粒状体の配列と動的挙動が制振特性に与える影響

464 粒状体ダンパの減衰メカニズムに関する研究 : 粒状体の配列と動的挙動が制振特性に与える影響

Thermal and force‐chain effects in an experimental, sloping granular shear flow

AbstractForce chains figure prominently in shearing motions of granular materials, inasmuch as these chains of load‐bearing grains dominate resistance to motion. A simple scaling of the forces involved in the motion of a dry, gravity‐driven granular shear flow induced by vibrations (see, e.g., Roering et al., 2001; Roering, 2004) suggests that this shearing motion reflects a balance between the rate of production and the rate of disruption of granular force chains. The rate of production of force chains is proportional to the rate of shear. The rate of disruption is proportional to the rate of shear as force chains ‘age’ during rotation, whence they become unstable and self‐destruct. The rate of disruption is also proportional to the frequency and intensity of elastic waves, induced by acoustic vibrations, that propagate through the granular material and weaken force chains. The analysis is empirically consistent with the exponential‐like profiles of grain displacement, and the strongly nonlinear increase in grain flux with increasing surface slope, observed in experiments. Copyright © 2008 John Wiley & Sons, Ltd.

A kinetic scheme for the Savage–Hutter equations

AbstractThe Savage–Hutter (SH) equations describe the motion of granular material under the influence of friction. Based on the kinetic formulation of the SH equations, we present a kinetic scheme in one dimension, which describes the deformation of the mass profile and allows it to start and to stop. Moreover the method is able to preserve the steady states of granular masses at rest. The method is tested on several numerical examples. Copyright © 2008 John Wiley & Sons, Ltd.

Mixing of cohesive particles in a shear cell

This paper discusses two series of experiments performed in a shear cell device with six different amounts of silicone oils and using 2-mm soda lime beads as the granular materials. The first series of experiments were mixing experiments, and the developments of mixing layer thicknesses were measured. The second series of experiments had the same experimental conditions as the first series but used different combinations of colored particles. In the second series of experiments, the motions of granular materials were recorded by a high-speed camera. Using the image processing technology and particle tracking method, the positions and velocities of particles were measured. The self-diffusion coefficient could be found from the history of the particle displacements. The measured mixing layer thicknesses are compared with the calculations from a simple diffusion equation using the data of apparent self-diffusion coefficients obtained from the current measurements. The comparisons show good agreements, demonstrating that the mixing process of granular materials occur through the diffusion mechanism in this cohesive sheared flow. In addition, the apparent self-diffusion coefficient decreases with the increasing liquid volume, indicating that cohesive effect between particles reduces granular mixing.