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Abstract The influence of the particle size on the vertical plate penetration into dense cohesionless granular materials was numerically investigated. Simulations were performed in quasi-two-dimensional conditions by changing the mean particle diameters d50 but maintaining the plate thickness B from B/d50 = 63–2.6. The initial bulk packing fraction was kept high, irrespective of the particle size. In the smallest particle size case (B/d50 = 63), the size ratio reached almost the same level as that in the laboratory experiments using natural sand particles. The results demonstrated that the mean penetration resistance force acting on the plate tip surface increases with a decrease of B/d50, while the tangential force acting on the side surfaces does not change with B/d50. Tip resistances increase linearly with the penetration depth, while the tangential resistances increase with the square of the depth regardless of B/d50. The behavior of the resistance fluctuations changes qualitatively between B/d50 = 31 and 21. For all cases, we confirmed the formation of a wedge-shaped flow with a high forward velocity in front of the plate tip. The wedge flow width was larger than the plate thickness by almost a mean particle diameter, and was responsible for the increase in the mean resistance depending on the particle size. For the large B/d50 cases only, the resistance exhibited quasi-periodic fluctuations, which was attributable to the intermittent nucleation and disappearance of the shear bands. Moreover, we investigated the dependence of B/d50 on the band evolutions by analyzing the band thickness. Graphic abstract The influence of the particle size on the vertical plate penetration into dense cohesionless granular materials was numerically investigated using DEM. Simulations were performed in quasi-two-dimensional conditions by changing the median particle diameters d50 but maintaining the plate thickness B. The initial bulk packing fraction was kept high, irrespective of the particle size. Upper and lower figures show the result of small (B/d50 = 63) and large particle size case (B/d50 = 21), respectively. In the small particle size case (B/d50 = 63), the size ratio reached almost the same level as that in the laboratory and the dynamics of 35.5 million particles was considered. Right and left figures illustrate instantaneous shear strain rate and local packing fraction distributions, respectively. Large qualitative change in the granular behaviors as well as penetration resistance was observed between B/d50 = 31 and 21. The intermittent nucleation and disappearance of the shear bands were clearly observed only for large B/d50 cases.

The response of granular materials to plate drag is numerically studied using a large-scale discrete element method (DEM) simulation. The effect of the initial volume fraction of the materials on the drag force acting on the plate is examined. The results show that a volume-fraction-dependent bifurcation occurs in the force; in an initially loose granular bed, the force reaches an approximately constant value as the plate advances, while in an initially dense bed, the force oscillates with a large amplitude. The force oscillation is attributed to the periodic evolution of a shear band formed only in the dense bed. The behaviors of the drag force and shear band, which depend on the initial volume fraction in the DEM simulation, are in close agreement with those obtained experimentally in previous studies [N. Gravish et al., Phys. Rev. Lett. 105, 128301 (2010); Phys. Rev. E 89, 042202 (2014)]. Further analysis using the DEM simulation shows that the formation of the shear band is explained by the local dilation and compaction of the granular materials induced by the plate drag. Independent of the volume fraction, materials dilate in a wedge-shaped flow region that formed in front of the plate. In the loose bed, a compacted front builds up ahead of the flow region. Because the compacted front advances into a weaker undisturbed region, the flow region behind the front can constantly advance. On the other hand, in the dense bed, the materials largely dilate in a disturbed flow region formed in front of the plate. Because a denser undisturbed region is more stable compared to the flow region, the flow region is strongly confined. As a result, the shear strain is localized along a flow boundary between these regions, and the shear band develops.

Particle detachment from an obliquely oscillating plate was studied experimentally and theoretically. The plate was placed in a horizontal position, and vibrations were applied in the horizontal and vertical directions by piezoelectric vibrators. The frequency of vibration was constant at 280 Hz. The amplitude of vibration increased with time and approached a constant value in each experiment. The movement of micrometer-sized spherical particles was analyzed using images captured by a high-speed microscope camera, which showed that the particles rolled on the plate before detaching from the surface, and that the rolling significantly reduced the adhesive force between the particles and surface. Furthermore, the removal efficiency, defined by the number ratio of detached particles to total particles, was analyzed as a function of the horizontal and vertical vibration accelerations. It was found that the removal efficiency was significantly affected by the horizontal vibration acceleration. These experimental results can be explained by the force and moment balance model.

The saltation of fine particles on an obliquely oscillating plate was simulated using a mass-point model that considered the gravity, fluid resistance, restitution, and friction. To examine the effects of the restitution and fluid resistance on the horizontal transport velocity, the two-dimensional movements of three particles with different coefficients of restitution and diameters were calculated. The results showed that a particle with a higher restitution and smaller diameter had a smaller transport velocity. This can be explained as follows. A particle with a higher restitution bounces forward and backward repeatedly, whereas a particle with a lower restitution only bounces forward, because the higher bounce height increases the impulse exerted on the particle during a collision, which induces a drastic change in the horizontal velocity from the collision. The horizontal velocity of a smaller particle is decreased by the drag force during its flight between successive collisions., New Paradigm of Particle Science and Technology Proceedings of The 7th World Congress on Particle Technology

Particle saltation on an obliquely oscillating plate is simulated using a mass-point model that considers gravity, fluid resistance, restitution, and friction. The calculated results are in good agreement with results obtained experimentally for particles with different diameters and restitutions. A large particle with high restitution bounces forward and backward repeatedly, whereas a particle with low restitution only bounces forward and consequently has a high transport velocity. The mechanism for the difference in the motion of the particles can be explained by taking into account the phase angle of the oscillating plate and the impulse during particle collision.

This paper presents a microscopic analysis of the saltation of particles on an obliquely oscillating plate driven by sine waves with an amplitude on the order of tens of micrometers and a frequency on the order of hundreds of hertz. To examine the effect of the diameter of a particle on its motion, the trajectories and velocities of different-sized particles, from 0.5 to 500 μm in mass median diameter, are analyzed using images captured by a high-speed microscope camera. The results show that larger particles bounce higher, whereas smaller particles easily agglomerate and bounce only slightly, owing to the low restitution caused by their loosely packed structure. In addition, larger particles bounce forward and backward repeatedly, while the agglomerated particles always bounce forward, and consequently have the highest transport velocity among these particles. The particle motion and the transport velocity can be explained by a theoretical probability model.

The movement of particles in the range from 0.5 to 500 μm in mass median diameter on a two-dimensional vibrating plate is observed through a high-speed digital camera with a zoom lens. The results show that larger particles saltate higher, while smaller particles easily agglomerate and slightly saltate because of the low restitution of their loosely packed structure. The salation heights are in good agreement with the results calculated by a model based on gravity, adhesion, drag force, and restitution., "Powders and Grains 2013"; Conference date: 8–12 July 2013; Location: Sydney, Australia

We demonstrate that a vibration-induced air inflow can cause vigorous bubbling in a bed of fine particles and report the mechanism by which this phenomenon occurs. When convective flow occurs in a powder bed as a result of vibrations, the upper powder layer with a high void ratio moves downward and is compressed. This process forces the air in the powder layer out, which leads to the formation of bubbles that rise and eventually burst at the top surface of the powder bed. A negative pressure is created below the rising bubbles. A narrow opening at the bottom allows the outside air to flow into the powder bed, which produces a vigorously bubbling fluidized bed that does not require the use of an external air supply system.

An anionic surfactant comprising a hydrophilic poly(ethylene glycol) (PEG) chain, hydrophobic alkyl chain, and polymerizable vinyl group was synthesized as a capping agent of nanoparticles. TiO(2) nanoparticles modified by this surfactant were completely dispersible in various organic solvents with a wide range of polarities, such as nitriles, alcohols, ketones, and acetates. Furthermore, these particles were found to be dispersible in various polymers with different properties, such as thermosetting epoxy resins and radical polymerized poly(methylmethacrylate) (PMMA). A polymer composite of surface-modified TiO(2) nanoparticles in epoxy resins prepared by using the developed surfactant also possessed temperature-induced shape memory properties.

The surface of TiO(2) nanoparticles which were well dispersed into acidic aqueous solution was successfully modified by silane alkoxides without strong aggregate formations. By adding decyltrimethoxysilane (DTMS) as silane alkoxides into the TiO(2) aqueous solution which were carefully diluted with methanol, DTMS slowly attached onto the TiO(2) surface without rapid hydrolysis and condensation reaction among DTMS. Because of the hydrophobicity of DTMS, the dispersed TiO(2) nanoparticles slowly formed flocks as DTMS reacted on TiO(2). These flocks were able to be completely redispersed into nonpolar solvents even after they were collected by centrifugation and drying under vacuum as dry powder. Furthermore the surface of TiO(2) nanoparticles have been successfully tuned by combining silane alkoxides which contains hydrophobic and hydrophilic groups such as DTMS and 3-aminopropyltrimethoxysilane (APTMS), respectively, toward their complete redispersion into various solvents. While TiO(2) nanoparticles modified by DTMS were redispersible into toluene, those modified by mixed alkoxides of 50 mol % DTMS and 50 mol % APTMS were redispersible into a mixed solution of toluene and methanol. Further when they were modified by mixed alkoxides of 25 mol % DTMS and 75 mol % APTMS, they were redispersible into polar solvents such as methanol with a little addition of acids.