The authors model the non-conductive ferrofluid combination of ferromagnetic particles and liquid particles as solid-liquid two phase flow to analyze the ferrofluid motion under magnetic field. The ferromagnetic particles are moved by the electromagnetic force, while the liquid particles are moved by the influence of the motion of the ferromagnetic particles. The details of the above will be discussed in the presentation.

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It is believed that when a liquid drop drips on the same liquid bath, a liquid drop immediately coalesces with the same liquid due to surface tension when they touch each other. But they do not sometimes. The drop can float on the liquid bath surface without coalescing. It is a surprising phenomenon considered physically. We suppose that this phenomenon occurs due to local high pressure generated in the thin gas film between the liquid bath and the drop. When they touch each other, the distance may come close to the mean free path of gaseous molecules. Such a gas flow cannot be treated as a continuum. Therefore, in the present study, the gas flow is analyzed by using the molecular gas film lubrication (MGL) equation based on the Boltzmann equation. The objective of this study is to investigate the mechanism of the drop floating phenomenon by performing the numerical simulations of the drop motion and the gas film simultaneously. A study of coalescence of a drop and a surface of the same kind is important in application such as phase separation technology of liquid and stabilization of emulsion.

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Using two different types of ionomers which are comprised of Nafion and hydrocarbon, we constructed systems of the ionomers on Pt catalyst surface, and investigated water content dependence on oxygen permeability in the ionomers using molecular dynamics simulations. We have found that the oxygen permeability of the Nafion-based ionomer is better than that of the hydrocarbon-based ionomer. Furthermore, the number of permeated oxygen molecules decreases with increasing water content on the both ionomers. Moreover, we analyzed density distributions of the ionomer components and solubility distributions of oxygen in the ionomers. As the results, in the ionomer-gas interface and bulk region of the both ionomers, the solvent molecules which increase as water content increases, block the oxygen permeation. In the ionomer-Pt interface of Nafion-based ionomer, the solvent occupies the pathways for oxygen permeation, while in the interface of hydrocarbon-based ionomer, the solvent which are piled up on the surface of high-density polymers, blocks the oxygen permeation.

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We report the channel size dependence of the forces that act on water droplets in a nano-meter order channel. Considering the several different-sized channel models, we evaluate forces between the two hydrophobic walls and water droplets by molecular dynamics simulation and show the channel size dependence in terms of the mechanical coefficients, such as friction coefficient. As a result, we show that the friction coefficient depends on the channel size due to the normal pressure. From these results, we clarify that there is the different channel size dependence of the static and dynamic properties of the water droplet compared with the macroscopic case.

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We are developing a method to analyze gas flows in nanoscale porous materials, based on actual structures of polymer electrolyte fuel cell (PEFC) catalyst layer material obtained by focused ion beam-scanning electron microscope (FIB-SEM). Direct simulation Monte Carlo (DSMC) is employed for the analysis of rarefied gas flows. The previous research pointed out two drawbacks of the flow analysis. One is an unrealistic anisotropy of the structures reconstructed from FIB-SEM images. This is due to the method used to reduce a background structure effect in them. The second one is an underestimation of oxygen diffusion resistances calculated from DSMC result, compared with the experimental values. This is because the DSMC calculation did not take into account the adsorption and diffusion of gas molecules on solid surfaces. To solve those problems, we are improving the method to separate structures and pores on cross-sectional images, and introducing a gas耀urface interaction model which is more appropriate for the nano-scale simulation.

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An elucidation of electrical double layer (EDL) structure including bio-molecules is helpful for controlling bio-interfacial functions for biosensing devices. In this study, the effect of double strand DNA on the EDL structure at the SiO2/NaClaq interface in 1.0 M concentration was investigated by the classical molecular dynamics simulation. In the 1.0 M NaClaq, the negatively charged ds-DNA shielded electrically by cations did not influence the potential profile of EDL structure. This result indicated that the simulated bio-interfacial structure would allow to detect ionic charges adsorbed directly at a substrate in a concentrated solution regardless of shielded bio -molecular charges such as DNA or proteins.

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In the present study, molecular dynamics (MD) simulations on simple liquids like monatomic Lennard-Jones and water bulk liquids in periodic boundary systems were performed to clarify the effect of the system size and shape on self-diffusion coefficient. So far, in the previous publications, the system size effect in cubic computational domains has been reported, and these studies showed that the diffusion coefficient becomes smaller as the system size decreases. Here we examined the system size effect not only in the cubic cell systems, but also in the rectangular cell systems which were created by changing one side length of the cubic cell with the system density kept constant. It is found that the diffusion coefficient in the direction perpendicular to the long side of the rectangular cell significantly increases more or less linearly as the side length increases for both liquids. On the other hand, the diffusion coefficient in the direction along the long side is almost constant. In consequence, anisotropy of the diffusivity appears in the rectangular cell with a periodic boundary condition even though the diffusion property of bulk liquids is examined.

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This paper investigates how the details of molecular structure affect the thermal properties of liquids. We carried out the nonequilibrium molecular dynamics simulations for the liquids of a systematic series of branched-alkanes. In the simulations, the thermal conductivity as well as the corresponding heat flux were calculated. Particularly, the heat transfer by way of side chain was analyzed in detail. It is shown that the heat flux associated with one side chain atom is not significantly different for the different alkane species, and thus the total heat flux of side chain is proportional to the number density of side chain atoms.

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Adaptive mesh refinement (AMR) automatically makes finer computational grids at only the important part of flows and improves accuracy of flow simulations. AMR needs methods which detect the important part such as shock waves. One of the methods is neural network for detection of flow discontinuities. The neural network is based on spatiotemporal visual processing which can detect discontinuities of illumination. So, the neural network detects discontinuities in numerical simulations of a supersonic flow. However, the neural network has not been yet applied to AMR. In this study, we applied neural network for detection of flow discontinuities to adaptive mesh refinement and showed its performance.

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This paper presents numerical results for vibration responses of two side-by-side circular cylinders which are placed in smooth flow. The two cylinders are treated as a system of two degrees of freedom in the in-line and cross-flow directions. Spatial discretization of a computational region is performed by the third-order upwind finite element scheme with ALE approach and the Newmark-β method is applied to compute the vibration equations of two circular cylinders.

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A 3-D unsteady RANS simulation of the flow field of a supersonic impulse turbine stage designed for a rocket engine is presented using a commercial CFD software package. The nozzle employs a partial admission design, with 45% of nozzle flow passage blocked, which creates a complex supersonic flow field in the nozzle-rotor interface. The numerical results revealed a highly 3 dimensional feature in the interface region, exihibiting a large separated flow along the hub surface. The acceleration and deceleration of the circumferential flow as it enters and exits the blocked section of the nozzle also have a significant spanwise variation, which of course was not seen in the earlier 2-D studies.

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[in Japanese]

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A freestream preservation property is focused in the high-order conservative ux-reconstruction scheme on a three-dimensional stationary-curvilinear grid. Although the sufficient condition for the freestream preservation with the nonconservative (cross product form) metric was reported in the previous study to be that the order of solution polynomial has to be greater than or equal to the twice of the order of a shape function, a special case is newly found in the present study: when the Radau polynomial is used for the correction function, the freestream is preserved even if the solution order is lower than the known condition. Using the properties of Legendre polynomials, the mechanism for this special case is analytically explained, considering the cancellation of aliasing errors.

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An aeroheating measurement test campaign on an HTV-R capsule model with turbulent boundary layers was performed in the free-piston shock tunnel HIEST at JAXA Kakuda Space Center. When flow became turbulent flow, heat flux on rear body was 2-3 times larger than one in laminar flow. In order to reproduce the turbulent heat flux by numerical simulation, we constructed high order CFD code towards LES in hypersonic flow. Since robustness near shock and high resolution in boundary layer is needed for LES in hypersonic flow, we employed recently improved WENO method. We calculated the hypersonic flow (M_∞=17) around cylinder and investigated the robustness for strong shock by this method. We could obtain smooth pressure distribution and good agreement with the calculated heat flux by NASA LAURA code. The hypersonic flowfield around HTV-R was also calculated towards predicting turbulent heat flux on after body.

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[in Japanese]

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[in Japanese]

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A simulation of electromagnetic flux compression method has been carried out using 3D thermal-electromagnetic-structural coupling analysis (electromagnetic forming analysis). The analysis result shows an imploded and complex deformation behavior of an inner coil used to generate ultrahigh electromagnetic flux field and also shows detailed information of eddy current distribution on the surface of the inner coil. It is found that the 3D thermal-electromagnetic-structural coupling analysis can be helpful in simulating electromagnetic forming behavior.

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[in Japanese]

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