Brazil Nut Effect Research Articles

Methods of parallel computation applied on granular simulations

Every year, parallel computing has becoming cheaper and more accessible. As consequence, applications were spreading over all research areas. Granular materials is a promising area for parallel computing. To prove this statement we study the impact of parallel computing in simulations of the BNE (Brazil Nut Effect). This property is due the remarkable arising of an intruder confined to a granular media when vertically shaken against gravity. By means of DEM (Discrete Element Methods) simulations, we study the code performance testing different methods to improve clock time. A comparison between serial and parallel algorithms, using OpenMP® is also shown. The best improvement was obtained by optimizing the function that find contacts using Verlet’s cells.

Orbiting experiment may help decode the mysteries of rubbly asteroids

Shake a bowl of mixed nuts and the large ones rise to the surface. This size-sorting phenomenon has been dubbed “the Brazil nut effect” because these large nuts often rise to the top of the mix—or, more accurately, smaller nuts like cashews and peanuts filter down into the gaps between large nuts over time. But the effect, whose physics remain something of a mystery, is more than a barroom curiosity: To ensure consistency, the Brazil nut effect must be considered when mixing granular materials of different sizes and densities to create, for example, powdered metal alloys, pharmaceuticals, and pigments for paints (1). A shuffling of surface materials on asteroids after they're struck by meteoroids (artist's depiction)—something like the Brazil nut effect—may explain why some asteroids have a particularly rubbly surface. Image courtesy of NASA/JPL-Caltech. In recent years, astronomers have suggested the Brazil nut effect isn’t actually restricted to Earth. In fact, it might explain why the surfaces of some asteroids appear unusually riddled with boulders. Consider the asteroid 25143 Itokawa. Data gathered by Japan’s Hayabusa probe, which visited Itokawa and gathered samples in 2005, suggest that the interior of the 535-m-long asteroid is about 40% open space (2); in essence, scientists propose, it’s a pile of rubble loosely held together by gravity, possibly aided by electrostatic or other cohesive forces between individual bits. About 80% of the asteroid’s surface is rough terrain sporting boulders from a few meters to 50 m across (3). The smallest objects seen during Hayabusa’s close approaches were centimeter-sized fragments of gravel—but cameras should have been able to see things as small as 6 millimeters across, scientists estimate. So where did all of the small pieces go? Were they bounced into space during past collisions between the asteroid and other objects? [Itokawa’s gravity is estimated …

Numerical simulations of oscillation-driven regolith motion: Brazil-nut effect

Many if not most small asteroids are rubble piles covered by regolith, and small perturbations may be enough to disturb their surfaces in complex ways due to microgravity. Experiments to study low-gravity regolith dynamics are challenging, and properly validated numerical simulations can provide valuable insights. In this paper, we investigate numerically size segregation among regolith grains, which is likely to occur after repeated shaking events. In particular, we are interested in the so-called Brazil-nut effect (BNE), i.e. the migration of a large intruder towards the top of a vertically shaken granular system. We go a step forward in simulating this effect by implementing horizontal periodic boundary conditions (PBC) in the N-body code pkdgrav, with the aim of making the simulations more representative of the expected asteroid environment. We study the influence of PBC on the BNE in Earth gravity and compare them with a walled case. We also investigate the influence of static and rolling friction on the BNE. With walls, we observe the well-known convection mechanism driving the BNE. However, we find that a different mechanism, consisting of void filling, is responsible for the BNE with PBC, and we discuss its relevance in light of previous studies. By running simulations in 10−4g, we show that this void-filling mechanism remains relevant in a low-gravity environment. However, we find that depending on the gravity level, the void-filling mechanism is differently influenced by the friction properties of particles. We speculate that this is likely due to a change in the granular flow time-scales.

Predicting the Motion of an Intruder in a Vertically Vibrated 2D-Granular-Bed using Contact Points Approximation

<p class="TTPAbstract">In this study, 2-dimensional Brazil nut effect experiments were setup. An intruder moves from its initial position at the middle-bottom of a container to its final position at the top of the granular bed. To predict the motion of the intruder, the number of contact points for each grain around the intruder was counted manually for grains in the first layer until the third layer. The average numbers of contact points from grains in each of 8 directions respected to the center of the intruder were calculated to determine the direction of total force acting on the intruder by grains in the first layer, in the first two-layers, and in the first three-layers.The result will be more acceptable using the data of two or three layers of grains in predicting intruder movement.</p>

Predicting the Motion of an Intruder in a Vertically Vibrated 2D-Granular-Bed using Contact Points Approximation

<p class="TTPAbstract">In this study, 2-dimensional Brazil nut effect experiments were setup. An intruder moves from its initial position at the middle-bottom of a container to its final position at the top of the granular bed. To predict the motion of the intruder, the number of contact points for each grain around the intruder was counted manually for grains in the first layer until the third layer. The average numbers of contact points from grains in each of 8 directions respected to the center of the intruder were calculated to determine the direction of total force acting on the intruder by grains in the first layer, in the first two-layers, and in the first three-layers.The result will be more acceptable using the data of two or three layers of grains in predicting intruder movement.</p>

The evolution of potential energy and contactopy two dimension granular materials in the case of compaction inhibited Brazil-nut effect

Compaction inhibit Brazil nut effect experiment by using acrylic material as bed and intruder has peformed. There are five diameter of granular bed (cm): 0.68, 0.53, 0.47, 0.42, and 0.375 and single intruder with diameter 2.4 cm used in this experiment. Vibration taken under r = 3 and frequency (Hz): 14, 15, 16, 17, 18, and 19. Discontinue vibration technique is used in this experiment. Vibrating system is done around one second then stop for a moment before next vibration. This technique used to make easier the process photo taken in each second. These photos then processed to gain contactopy and height of system. Based on the data, contactopy of all system observed are increasing. The average of contactopy without intruder system toward ratio of granular bed diameter and the width of shaking place giving logarithmic equation . This equation show the value of contactopy without intruder system under certain ratio of granular bed diameter and the width of shaking place. Potential energy change for both system without intruder and with intruder are decreasing as the height system is decreasing. These result show that compaction inhibit Brazil nut effect phenomena still obey the minimum energy principle (MEP). The whole results of this research confirm that increasing contactopy and decreasing potential energy not only valid for Brazil nut effect, but also for compaction inhibit Brazil nut effect phenomenon.

Experimental study of granular convection in (real) two- dimension Brazil-nut effect

Brazil-nut Effect (BNE) experiment in (real) two-dimension is conducted. Container, bed particles, and intruder are made from the same material, i.e. 2 mm thickness acrylic plate. Dimensionless acceleration r and vibration frequency f are in the range of 2-4 and 13-17 Hz, respectively. It is observed that rise time Trise decreases with the increase of Γ similar to reported by others, but there is a range of f and Γ, where Trise increases with the increase of Γ due to occurrence of Leidenfrost effect, which reduces convection flow of granular particles.

The spherical Brazil Nut Effect and its significance to asteroids

Many asteroids are likely rubble-piles that are a collection of smaller objects held together by gravity and possibly cohesion. These asteroids are seismically shaken by impacts, which leads to excitation of their constituent particles. As a result it has been suggested that their surfaces and sub-surface interiors may be governed by a size sorting mechanism known as the Brazil Nut Effect. We study the behavior of a model asteroid that is a spherical, self-gravitating aggregate with a binary size-distribution of particles under the action of applied seismic shaking. We find that above a seismic threshold, larger particles rise to the surface when friction is present, in agreement with previous studies that focussed on cylindrical and rectangular box configurations. Unlike previous works we also find that size sorting takes place even with zero friction, though the presence of friction does aid the sorting process above the seismic threshold. Additionally we find that while strong size sorting can take place near the surface, the innermost regions remain unsorted under even the most vigorous shaking.

Recycling oriented vertical vibratory separation of copper and polypropylene particles

Vibration has been employed in various engineering processes for material handling. The famous Brazil nut effect, large particles tend to rise to the top under vibration, initiates various research about vibration induced particle segregation. Particle size and density are two determining factors for their behavior under vibration. Previous research in University of Nottingham proves vertical vibratory separation to be a promising environmental friendly mechanical separation method for recycling metallic fraction from shredded Waste Electric and Electronic Equipment (WEEE) stream. A pilot scale thin cell vibratory separator has been developed to investigate the potential for WEEE recycling applications. Shredded copper and polypropylene particles have been chosen to mimic metallic and non-metallic fractions in WEEE. Vibratory separation experiment with controlled environment and addition of solid lubricant are presented in this paper. The result demonstrates the effect of relative humidity and solid lubricant on improving flowability of granular system hence successful vibratory separation. The proposed mechanisms for the presence of moisture and solid lubricant are lubricant effect and elimination of static electricity.

Influence of Contactopy on Two-Dimensional Brazil-Nut Effect

Using hard sphere collision scheme and molecular dynamics method simulation, two-dimension Brazil-Nut Effect (BNE) is conducted. BNE inital configurations are artificially created to obtain number of contacts between the grains, called as contactopy. It is observed that from initial condition until the end of BNE observation, center-of-mass in vertical direction tends to decrease, while contactopy tends to increase, which are similar to the reported results in a Gedankenexperiment (Viridi et al., 2014). Initial configurations which are also dependent on contactopy influence the rise time since it can override influence of density ratio that should affect rise time (Möbius et al., 2001). We investigate on how the intruder rise time influenced by contactopy, as well as density.

3-Dimensional Motion of an Intruder in Brazil Nut Effect

The purposes of this article were to experimental setup for finding the position of an intruder inside a vibrating granular bed which is the important information for one to understand the mechanism of the Brazil nut effect. However the intruder is difficult to be observed without using some sophisticated methods. And then shown is a simple method to reconstruct the 3-dimensional motion of an intruder inside a vibrating granular bed in annular container case

Transport Properties and Segregation Phenomena in Vibrating Granular Beds

Granular materials are common in daily life and in many industrial processes. Both fundamental research and industrial application studies are crucial for understanding the transport properties and segregation mechanisms of vibrating granular beds. One major related research topic is granular materials subjected to external vibration; such granular materials exhibit complex movement and Brazil nut segregation. Understanding the transport properties and the rising of an intruder immersed in granular materials is a challenge in granular flow research. This paper presents a review of transport properties and segregation phenomena in a vibrating granular bed, and discusses the relationship between transport properties and granular segregation. Furthermore, how the vibration conditions, liquid bridge force, bed height, surface roughness of granular materials, and a bumpy base of granular beds affect the transport properties, convection, and granular segregation are reported. The results indicate that the transport properties and segregation behavior are significantly influenced by the addition of small amounts of liquids and by the surface roughness and a bumpy base. Diffusive and convective motions are weakened as the base roughness increases, leading to a weaker Brazil nut effect.

Multisized immersed granular materials and bumpy base on the Brazil nut effect in a three-dimensional vertically vibrating granular bed

In this study, the Brazil nut segregation problem was experimentally investigated in a 3D vertically vibrating granular bed. A high-speed camera was used to record the rise time of larger particles (i.e., intruders). The results showed that the rise time decreased with an increase in the size ratio of monosized immersed granular materials. The percolation effect is the dominant mechanism that influences the Brazil nut segregation behavior of monosized immersed granular materials. The percolation effect is stronger when the size ratio is higher, leading to a stronger Brazil nut effect. In addition, the results indicated that the rise times of the intruder are shorter with multisized immersed granular materials than those with monosized immersed granular materials. The rise velocity does not increase monotonically with an increase in the filling bed height. In addition, the base roughness significantly influences granular segregation. The Brazil nut effect is mitigated, resulting in longer rise times with the bumpy base.

Fluctuation Theorem Application on 2-D Granular Materials Configurations

Probability occurrence between two successive 2-d granular materials configuration, which are related to their entropy, can be used to check history line of the materials configurations. As an example, a well-known Brazil-nut effect will be presented. In small region it seems that this effect violates principle of minimum energy but not as the whole system, where the energy does decrease. In this work effect of temperature is considered constant since the configurations are observed in frozen states instead of dynamic or fluidized states.

Energy dissipation and periodic segregation of vibrated binary granular mixtures

For a vertically vibrating column filled with binary mixtures consisting of big copper beads and small glass beads, the phenomenon of periodic segregation (PS) is observed experimentally, in which distinct segregation patterns of Brazil nut effect (BNE), reversed Brazil nut (RBN) and sandwich (SW) are emerged successively under a certain vibration condition. The periodic time increases with increasing vibration frequency or decreasing acceleration, and the SW pattern holds 90% duration of a cycle. Since the three segregation patterns emerging sequentially in a cycle are all well defined, the energy dissipation power for each segregation pattern is measured under the same vibration condition. It is found that the dissipation power is the largest in RBN pattern and the smallest in BNE pattern during a cycle. Moreover, in the periodic segregation region the same patterns (BNE, RBN or SW) emerging at different vibration accelerations have almost the same dissipation power within the experimental error. Based on the viewpoint of competition between condensation and percolation from Hong, the periodic segregation phenomenon can be explained qualitatively by combining with our measurements of energy dissipation power.

Distribution of boulders and the gravity potential on asteroid Itokawa

The small asteroid Itokawa was visited in 2005 by the Japanese spacecraft Hayabusa. The images of the surface showed a scenario different to previously visited asteroids. Itokawa has a small number of large craters and many large boulders randomly distributed on most of the surface.We analyse images taken at different surface resolution and configurations corresponding to several regions on the asteroid’s surface. By overlapping visual images and maps of the total potential and surface gravity, we observe a correlation between the distribution of boulders and these parameters. The boulders on the surface were identified by visual inspection of several images. After fitting ellipses to every boulder, we computed their size and the size distribution from decimeters to several meters at different locations in the surface. We found that the size distribution is correlated with the total potential and the surface gravity. A steeper size distribution shifted towards the small objects is observed in the low negative total potential (high surface gravity), which corresponds to the Muses-C region. Meanwhile, in the “head” and “bottom” regions of high potential (low surface gravity), we obtain a shallower size distribution, shifted towards the large boulders.We confirm there is a size segregation that is correlated with the gravity field which can be explained under the action of the Brazil nut effect. There is a global relocation of boulders, with large ones going into the high potential regions and small ones into the low potential ones. A shape segregation is also observed on the location of the boulders: more rounded ones are found in the regions of high potential, while more elongated ones are frequent in regions of low potential.

The Brazil nut effect and its application to asteroids

Out of the handful of asteroids that have been imaged, some have distributions of blocks that are not easily explained. In this paper, we investigate the possibility that seismic shaking leads to the size sorting of particles in asteroids. In particular, we focus on the so-called Brazil Nut Effect (BNE) that separates large particles from small ones under vibrations. We study the BNE over a wide range of parameters by using the N-body code PKDGRAV, and find that the effect is largely insensitive to the coefficients of restitution, but sensitive to friction constants and oscillation speeds. Agreeing with the previous results, we find that convection drives the BNE, where the intruder rises to the top of the particle bed. For the wide-cylinder case, we also observe a "whale" effect, where the intruder follows the convective current and does not stay at the surface. We show that the non-dimensional critical conditions for the BNE agree well with previous studies. We also show that the BNE is scalable for low-gravity environments and that the rise speed of an intruder is proportional to the square root of the gravitational acceleration. Finally, we apply the critical conditions to observed asteroids, and find that the critical oscillation speeds are comparable to the seismic oscillation speeds that are expected from non-destructive impacts.

Investigation of the effect of a bumpy base on granular segregation and transport properties under vertical vibration

This study experimentally investigates the effect of a bumpy base on the Brazil-nut phenomenon in a vertically vibrated granular bed. The rise dynamics of an intruder is determined by the particle tracking method. The results indicate that the rise time increases with an increase in the base roughness, and the variation of the rise time with different base factors is more pronounced with smaller vibration acceleration and higher vibration frequency. A theoretical model is employed to measure the penetration length of the intruder and the drag force between the intruder and the immersed beads. The penetration length is reduced and the drag force is enhanced with surface roughness of the base. Additionally, the transport properties of the vibrated glass beads are also measured and discussed. With greater base roughness, the strength of the diffusive and convective motion is reduced leading to a weaker Brazil-nut effect.

CYCLIC SEGREGATION STATE IN VERTICALLY VIBRATED BINARY GRANULAR MIXTURES

In this paper, the vertically vibrated binary granular mixtures at atmospheric pressure are studied experimentally. We find a nonstationary segregation state, of which the structure changes with time cyclically. The period of the cyclic segregation is measured and its variation with the vibration conditions is shown. The transition between the segregation states is also discussed, and a phase diagram on the plot of frequency against acceleration amplitude is given. In order to observe the effect of air flow in the segregation process, an alternative container with ventilated bottom is designed. Our experiments show that both regions of the Brazil nut segregation state and the cyclic segregation state shrink obviously by use of the latter container and disappear completely if the whole system is placed in vacuum. These results testify that the air pressure plays a positive role in both the Brazil nut effect and cyclic segregation.

Convecting particle diffusion in a binary particle system under vertical vibration

We studied the separation behaviour of binary granular particles in a vertically vibrated container. The final separation of the binary particle system exhibited the Brazil-Nut (BN) effect, though it was not complete. Particle convection occurred, and four different typical convection modes were observed when the frequency f changed from 20 Hz to 80 Hz at constant dimensionless acceleration Γ = 4πAf(2)/g. However, when Γ changed from 2 to 4 at constant f, the system's convection mode stayed almost the same. In our experiments, one type of particle generally moved much faster than the other, so the former was termed the 'convecting' particle, and the latter was termed the 'non-convecting' particle. To study the separation results qualitatively, we divided the system into vertical layers and calculated the mass distribution of the binary particles along the z axis. The results showed that when f increased at constant Γ or Γ decreased at constant f, the convecting particles, usually the smaller and lighter ones, distributed less to the top side and more to the bottom side of the container. Finally, to explain the experimental results, we derived a mass conservation equation for the convecting particles considering simultaneous convection and diffusion. The equation described the experimental results well. We also analysed the effects of f, Γ, diameter ratio, density ratio, etc., on the final separation results.