In this study, we have performed 3D DEM simulations about granular packings with slow tilt motion. It would be expected to obtain more detailed destabilization processes of tilting granular layers using numerical simulations than using experimental methods. Our simulation results agreed well with some experimental results about rearrangements of the particles at the surface layer. Most of the previous studies relate stability of the packings with mobilization of friction forces between the particles. However our simulation results show that the mobilization of friction forces does not change when the tilt angle increases up to 10° and further, the correlation between the mobilization of friction forces and global stability is insignificant. However, the direction of contacts and distribution of contact forces changed during our simulation time. Our simulation results indicate that we can estimate stability of the packings through contact forces and their directions rather than the mobilization of friction forces.

The development and fundamental study of an electrostatic field strength sensor (novel sensor) with an air motor is investigated on a laboratory scale in this paper. This novel sensor was developed in order to measure the electrostatic field of charged dust clouds formed during the processing of large amounts of powder. The novel sensor consists mainly of the rotating sector, the sensing electrode, the air motor, the hall element, a signal cable, an enclosure and the air supply line. As for the results, the reliability of the detected signal obtained by the novel sensor with the air motor was confirmed. In other words, the electrostatic field of the simulated charge material and detected signal were clearly in direct correlation. The detected signals were mainly unaffected by air pressure. In addition, it was found that the polarity of a charged material can be discriminated through the detected signals of the novel sensor and the hall element.

Plate drag in granular materials is a simple but important because it provides an understanding of how tools interact with soil in soil cutting and tillage. We numerically study the response of dry granular materials to plate drag as a function of initial volume fraction of the materials using a large-scale discrete element method (DEM) simulation. In the simulation, a flat plate is translated horizontally through initially homogeneous materials with different volume fraction and 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 are in close agreement with those obtained experimentally in previous studies. Further analysis 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. In addition, the relationship between the evolution of the shear band and the drag force can be explained quantitatively by using a three-dimensional wedge model considering the variation of the local volume fraction inside the shear band.

Discrete Element Method (DEM) is widely used to simulate particulate systems to obtain particle-level information which could be difficult to achieve experimentally or in continuum approaches. One of the existing challenges in DEM is the high computational cost to perform industrial scale simulations since an enormous number of particles need to be tracked. Hence, the scale-up particle model, which is also known as the coarse grain, similarity and discrete parcel models, is often employed to reduce computational cost. In this review, the author’s recent development of the scale-up particle model is presented. The model is derived from the continuum assumption of particles and different scaling laws are applied to inter-particle and body forces. The scaling laws are written in a generic form and applicable to any force acting on particles as long as the continuum assumption is valid. Several test simulations are presented to prove that the scale-up particles proposed can effectively mimic the movement of the original particles.