This paper aims to describe an industrial application of the Discrete Element Method (DEM). The DEM is often employed in granular and solid-fluid mixture systems. The DEM is a Lagrangian approach, where individual particles are simulated based on Newton’s second law of motion. In my group, novel models are developed to apply the DEM in industrial powder systems, i.e., coarse grain model of the DEM for efficient calculation of large-scale powder systems and combination of signed distance functions and immersed boundary method for efficient creation of arbitrary shaped wall boundary. These models are shown to be crucial for a numerical simulation of an industrial powder system.

Nanoparticles have been attracting much attention as a key material for new biomedical and pharmaceutical applications. For success in these applications, the nanoparticles are required to translocate across the cell membrane and to reach to inside of the cell. In this article, our computational studies regarding the permeation of nanoparticles across cell membrane were presented. Firstly, an all-atomistic molecular dynamics simulation study on the interaction of fullerenol C₆₀(OH)_n with the cell membrane was presented. Permeability of various C₆₀(OH)_n with different number of OH groups was investigated by a simple one-dimensional stochastic modeling based on a thermodynamic analysis derived from MD simulation. Secondly, permeation of cationic gold nanoparticle across a cell membrane under an external electric field was simulated by means of a coarse-grained molecular dynamics. We found a unique permeation pathway: when a weak electric field was applied the NP directly permeated across cell membrane without membrane disruption, suggesting that by controlling an external electric field NPs can be directly delivered into the cell with less cellular damage.

A chemical transport model (CTM) is a type of numerical model that represents atmospheric behavior of various trace substances. This article describes a regional CTM and its application to numerical simulations of particulate matter with a diameter of 2.5 μm or less (PM_2.5). A regional CTM is driven by meteorological fields produced by a meteorological model with emission data derived from various emission inventories and boundary concentrations calculated by a global CTM. Two sets of PM_2.5 simulations are presented: one is an application of a regional CTM with a tracer method to an estimate of the contribution of long-range transport (LRT) from the Asian Continent to PM_2.5 concentration in Japan, and the other is an application of an online-type regional CTM with meteorology-chemistry feedbacks to an evaluation of the impacts of the aerosol direct effect on simulated PM_2.5 fields in East Asia.

Dendrite morphology is drastically changed due to the liquid flow, such as forced and natural convections, during the solidification of metallic alloys. We have developed a phase-field lattice Boltzmann method to simulate the dendrite growth during the alloy solidification in the presence of the liquid flow. Here, we have employed the phase-field and lattice Boltzmann methods to express the dendrite growth and liquid flow, respectively. In addition, a parallel computation using multiple graphical processing units in a supercomputer has been enabled to accelerate the phase-field lattice Boltzmann simulation. In this report, the phase-field lattice Boltzmann model is briefly explained, and some dendrite growth simulations using the model are introduced.

The motion of single bubbles rising in a highly viscous hydrophobically modified alkali-soluble emulsion (HASE) polymer solution is experimentally examined. In the experiment, a 1.6 wt% HASE polymer solution, which is adjusted to pH ≈ 7.0 by adding a sodium hydroxide solution, is used. In this study, we focus on the long threadlike shapes formed at the bottom of a bubble. Our observations are recorded using two high-speed video cameras. The morphology of trailing edges with threadlike branches is sensitive to the bubble size. For increasing bubble size, the number of threadlike branches observed also increases; more than 10 threadlike-branches are observed for large sized bubbles. Besides reporting on bubble morphology for single bubbles rising in a highly viscous HASE material, we also report on a discontinuity change in the relation of bubble rise velocity vs bubble volume.