Magnetorheological Fluids (MRF) whose apparent viscosity is controllable by applying magnetic fields are known as a kind of functional fluids. It is generally considered that such viscosity changes are caused by the formation of chain-like clusters of magnetic particles dispersed in the fluid. Many researches have been conducted to understand the mechanism of the viscosity change of MRF but there are few report which directly indicate the relation between the cluster formation and the viscosity change because of the difficulty of the observation such phenomena simultaneously. In this study, the relation between particle clustering and viscosity change has been investigated using DEM-DNS simulation. The simulations are conducted just a few chain-like clusters of magnetic particles in simple shear flow and the simulation results indicate that the apparent viscosity corresponds to both of the chain length and the angle between magnetic field direction and chain axis which depend on the Mason number.

The history force on a particle depends on background flow and needs to be studied to understand dilute particle-laden turbulence. In this study, we numerically investigate the history force on the translating sphere in some non-uniform flows in which the undisturbed streamlines are curved, over a range of the particle Reynolds number being 5 ≤ Re_p ≤ 40. For the axisymmetric straining flow, the applicability of the history force model which is based on the result of the uniform flow is highly influenced by the direction of the straining. For the non-axisymmetric shear flows, the history force perpendicular to the particle translating velocity agrees with the model for 5 ≤ Re_p ≤ 10. In conclusion, the limited applicability of the history force model is clarified for some non-uniform flows.

Segregation becomes one of the big problems in industrial powder processes. This paper describes the influence of hopper shape on segregation. Change of the volume rate was evaluated when two size of particles (2 mm, 6 mm) were discharged from the hopper. In this study, effects of hopper diameter and slope angle on the segregation was investigated numerically. First, the influence of hopper inlet diameter was studied. As it decreased, segregation in last 10% flow became less prominent. Next, the influence of hopper slope was studied. As its slope was smaller, segregation was easy to occur. From observation of powder flow, funnel flow was occurred, and then large-sized particles moved to central area on the surface of powder bed by the rolling segregation. It was suggested that the difference of the vertical velocity between particles near the wall and that of center caused the rolling segregation.

Mechanical analysis of basic powder phenomena, development of new powder operation and design of materials related to powders using powder simulation are described. The behavior of slow flow of powders is very different from that of fluid. The mechanism of the slow flow was elucidated using DEM simulation. A method for preparing a functional coating film by electrostatic powder coating is introduced as an example of development of new powder operation. The design of piezoelectric ceramics was performed using an estimation model for electromechanical properties as electromechanical coupling coefficient, dielectric and piezoelectric constants.

Nowadays, Discrete Element Method (DEM) is widely used to study the phenomena concerning granular materials or powders or to develop granular facilities and processes. When DEM is used, the spring constant in the contact force model of DEM is often reduced to reduce the calculation time or calculation cost. However, it has been pointed out that the reduction in the spring constant largely changes the agglomeration behavior of cohesive particles. When one uses the technique of reducing spring constant, it is required to understand the physics of particle-particle interaction. In this article, the way of thinking to use the technique of reducing spring constant is presented based on the authors’ previous studies.