Yasushi Ido

Numerical simulation of microstructure formation of suspended particles in magnetorheological fluids

Microstructure formation of magnetic particles and nonmagnetic particles in magnetorheological (MR) fluids is investigated using the particle method simulation based on simplified Stokesian dynamics. Spherical nonmagnetic particles are rearranged in the field direction due to the formation of magnetic particles in chain-like clusters. Cluster formation of spherocylindrical magnetic particles forces spherical nonmagnetic particles to arrange in the direction of the field. In contrast, the spherocylindrical nonmagnetic particles, with an aspect ratio of two or three, are not sufficiently rearranged in the field direction by cluster formation of spherical magnetic particles. Even after cluster formation in the presence of a magnetic field, the uniformity of distribution of particles on the plane perpendicular to the field direction shows very little change. However, the deviation of uniformity in particle distribution is reduced when the volume fraction of magnetic particles is the same as that of nonmagnetic particles.

Nonequilibrium Theory of Viscoelastic Magnetic Fluids

A new complete set of equations for magnetic fluids is derived using the thermodynamical method and micropolar theory. The present constitutive equations, which take consideration of both viscoelasticity and internal freedom, satisfy the principle of material frame indifference. It is shown that the constitutive equations of magnetization is related to the magnetic field, its change in time and angular velocity of suspended particles. Furthermore, it is made clear that the electromagnetic pressure is independent of the dissipative parts of the magnetization and the electric polarization.

Flip-Flopping Flow Around Two Bluff Bodies in Tandem Arrangement

At sufficiently high Reynolds numbers flow around two tandem circular cylinders of the same diameter has two patterns which switch randomly in time if the distance between their centres is in an appropriate range. For the distance at which the two patterns occurred at the same probability, the interval of time during which each pattern prevailed was a random variable whose probability density distribution was approximately the Gamma distribution. The average time interval for two patterns was much larger than both the vortex-shedding period and the time scale of the free-stream turbulence, being strongly dependent on the turbulence intensity.

A comparison of field-dependent rheological properties between spherical and plate-like carbonyl iron particles-based magneto-rheological fluids

This work proposes different sizes of the plate-like particles from conventional spherical carbonyl iron (CI) particles by adjusting milling time in the ball mill process. The ball mill process to make the plate-like particles is called a solid-state powder processing technique which involves repeated welding, fracturing and re-welding of powder particles in a high-energy ball mill. The effect of ball milling process on the magnetic behavior of CI particles is firstly investigated by vibrating sample magnetometer. It is found form this investigation that the plate-like particles have higher saturation magnetization (about 8%) than that of the spherical particles. Subsequently, for the investigation on the sedimentation behavior the cylindrical measurement technique is used. It is observed from this measurement that the plate-like particles show slower sedimentation rate compared to the spherical particles indicating higher stability of the MR fluid. The field-dependent rheological properties of MR fluids based on the plate-like particles are then investigated with respect to the milling time which is directly connected to the size of the plate-like particles. In addition, the field-dependent rheological properties such as the yield stress are evaluated and compared between the plate-like particles based MR fluids and the spherical particles based MR fluid. It is found that the yield shear stress of the plate-like particles based MR fluid is increased up to 270% compared to the spherical particles based MR fluid.

Damping force of a semiactive damper utilizing magnetic particles under applied magnetic field

Damping properties of a damper utilizing magnetic particles are investigated experimentally. A group of magnetic particles is treated as the working fluid in a damper instead of oil. In the presence of magnetic field, the damping force of the particles damper drastically increases. The maximum damping force appears near the dead center of vibration and higher frequency produces stronger maximum damping force, when the vibration frequency is in the range of low frequency below 5 Hz.

Fluid transportation mechanisms by a coupled system of elastic membranes and magnetic fluids

The basic properties of the fluid transportation mechanism that is produced by the coupled waves propagating along a thin elastic membrane covering a magnetic fluid layer in a shallow and long rectangular vessel are investigated. It is shown that the progressive magnetic field induced by the rectangular pulses generates sinusoidal vibration of the displacement of elastic membrane and makes the system work more efficiently than the magnetic field induced by the pulse-width-modulation method.

Numerical Analysis of the Polishing Process of Inner Tube Wall Using Micron-Size Particles in Magnetic Fluids

Distribution and behaviour of micron-size magnetic particles and nonmagnetic particles in magnetic fluids in the polishing process of inner wall of small tube is investigated numerically by using the particle method based on the simplified Stokes dynamics. In this study, it is shown that chain-like clusters of both magnetic particles and those of nonmagnetic abrasive particles are formed between the two magnetic poles. The clusters are strongly held during the polishing process. The clusters of the nonmagnetic abrasive particles are surrounding the clusters of magnetic particles and they are combined with each other.

Magnetic microchains and microswimmers in an oscillating magnetic field

Superparamagnetic micro-bead chains and microswimmers under the influence of an oscillating magnetic field are studied experimentally and numerically. The numerical scheme composed of the lattice Boltzmann method, immersed boundary method, and discrete particle method based on the simplified Stokesian dynamics is applied to thoroughly understand the interaction between the micro-bead chain (or swimmer), the oscillating magnetic field, and the hydrodynamics drag. The systematic experiments and simulations demonstrated the behaviors of the microchains and microswimmers as well as the propulsive efficiencies of the swimmers. The effects of key parameters, such as field strengths, frequency, and the lengths of swimmer, are thoroughly analyzed. The numerical results are compared with the experiments and show good qualitative agreements. Our results proposed an efficient method to predict the motions of the reversible magnetic microdevices which may have extremely valuable applications in biotechnology.

Effectiveness of using a magnetic compound fluid with a pulsed magnetic field for flat surface polishing

The effects of the frequency of a pulsed magnetic field on flat polishing were investigated to obtain basic data for increasing the performance and precision of polishing using MCFs. We clarified that the profile curves after polishing differ for a direct-current magnetic field and for a pulsed magnetic field and flattening occurred over a wide range when the frequency of a pulsed magnetic field is 0.1 Hz.

Microprocessing characteristics of inner surface of tube using magnetic functional fluid

We proposed a microprocessing method using a magnetic compound fluid for the inner surface of a tube made of a material that is difficult to cut, and clarified the processing characteristics and magnetic field distribution of the tool. The tool inserted into the tube comprises a stack of ring-shaped permanent magnets with spacers between them. There is an almost proportional relationship between the amount of material removed and the processing time, and the processed surface acquires a mirror finish. Moreover, for tools with shorter permanent magnets, the circularity is improved by processing.