Published papers

Nonlinear axisymmetric shape oscillations have been revealed through experiments conducted with large-amplitude forced vertical vibrations of a magnetic fluid column supported by a magnetic field in the presence of gravity. Those nonlinear shape oscillations are characterized by the jumping phenomena, mode transition, and subharmonic motions.

Experimental results for anisotropy and hysteresis of the ultrasonic propagation velocity(1 MHz) in a magnetic fluid subject to a magnetic field are reported. Measurements were made by the pulse method while the magnetic field intensity was varied from 0 mT to 570 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation was varied between 0 deg and 180 deg. Some interesting results that seem to be caused by cluster formation in the magnetic fluid were obtained.

We performed measurements of ultrasonic propagation velocity and attenuation in various magnetic fluids. These measurements were taken under changing external magnetic field intensity, direction of magnetic field, and time of applying magnetic field. Based on these results, influence of the chain-like cluster formation on ultrasonic propagation was discussed.

The magnetorheological response of magnetorheological fluids (MRF) results from the polarization induced in the suspended particles by application of an external magnetic field. We proposed a qualitative analysis of these effects by measuring properties of ultrasonic propagation. Hysteresis was appeared when magnetic field increased to and decreased from the certain value, 290 mT in our experiment. The change rate of the ultrasonic wave propagation velocity increased during the increasing process of the external magnetic field. However, it was kept almost the same value during the decreasing process.

A magnetic fluid damper (TMFD) uses hydrodynamic force of sloshing of a magnetic fluid to dampen oscillation. Hydrodynamic force and displacement of surface of the fluid in the TMFD change according to the forced amplitude. Hydrodynamic force changes linearly with surface displacement. The changing rate between hydrodynamic force and surface amplitude varies around a characteristic forced frequency.

This paper would be elaborate experiment result of inner structure of MR fluid by means of visualization using optical microscope and CCD camera. The results show the rate of cluster formation is increase when the strength of magnetic field is increase, means that cluster formations are more robust and larger size for high magnetic field. The investigation of inner structure of MR fluids using image processing was successful. The growth of cluster formation is clearly seen in our image analysis. The cluster develops more robust when the magnetic field intensity is increase.

A magnetic fluid is a functional fluid under a magnetic field. A theoretical analysis of a sloshing of the magnetic fluid in a cylindrical container is carried out. Vertical and horizontal components of the magnetic field are considered in the sloshing analysis. The magnetic field is assumed nonuniform and axsymmetric. A natural sloshing frequency of the magnetic fluid in the cylindrical container is obtained. It is found from the analysis that the natural sloshing frequency is affected by field gradients of both vertical and horizontal components of the magnetic field. An experiment using a tuned magnetic fluid damper is also carried out to measure a change of the natural sloshing frequency by the magnetic field. The analysis of present paper is confirmed by using the experimental results.

磁性流体同調液柱管ダンパーはU字管内の磁性流体液柱を付加振動系とする制振装置で、磁場印加によって液柱固有振動数の制御が可能である。本研究では異なる三つの形状のU字管容器で加振実験を行い、それぞれの比較検討を行った。2014年12月の磁性流体連合講演会で発表された論文が，査読されて本論文集に掲載された。

We investigate the stability and strength of a reinforced, rectangular-hull knockdown pontoon to determine the feasibility of the usage of knockdown pontoons for emergency procedures in case of Mt. Fuji volcanic hazards. The stability of the self-propelled ship is evaluated by the metacentric height of the ship. However, a pontoon with a rectangular hull exhibits a large metacentric height that could cause the loss of ship stability. We propose a new technique to avoid an overly optimistic evaluation of a pontoon’s stability. The hull strength evaluation method that is used in case of the reinforced knockdown pontoon differentiates between two types of load distributions, divided load and concentrated load. By comparing the evaluations that were obtained using these two types of load distribution, we clarified the differences between these approaches.

ナビエ・ストークス方程式を解くための新しい有限要素法を提案し，その有効性について報告した。

空気菅路内に圧力波が入射された場合の圧力波動のステップ応答について実験と理論解析を実施し，その特性を詳細に調べた。

二次元流路内の圧力伝播の様子を特性曲線法を用いて数値解析を行い，速度分布，圧力分布の様子を明らかにした。

A new FEM scheme using simultaneous relaxation of velocity and Bernoulli function is presented for unsteady incompressible viscous flow. This is an improved version of the GSMAC(Generalized Simplified Marker and Cell) FEM. To verify the scheme, transient 2-D Poiseuille flow and 3-D flow in a lid-driven cubic cavity are numerically calculated.

The magnetic fluid motion in a rotating magnetic field was examined at first. Influences of the magnetic field intensity, its frequency and the radius ratio of the concentric cylinders on flow patterns were investigated experimentally. According to these results, a new transport system of a magnetic fluid was presented. It consisted of the spiral tube wound around a circular cylinder. When the rotating magnetic field was applied, the height difference of fluid columns was observed, which corresponded to the pressure head between the entrance and exit of the tube. The pressure head was influenced by the magnetic field intensity, its frequency and diameter of the spiral tube. Effects of these parameters were discussed.

Magnetic fluids have been studied in the various fields for over two decades. In the present paper, following three different experimental studies were carried out in order to present interesting characteristics of a magnetic fluid: lateral fluid--sloshing in a container, natural convection of a magnetic fluid between two coaxial annuli and rotational flow driven by a rotating magnetic field.

The surface flow patterns of a magnetic fluid in a cylinder and annular cylinders under the rotating magnetic field were precisely examined. On the basis of these experimental results, a new transport system of a magnetic fluid using rotating magnetic field was proposed. When the rotating magnetic field was applied, the height difference of fluid columns was observed. The pressure head was influenced by the magnetic field intensity, its frequency, diameters of the spiral tube and core cylinder. Effects of these parameters were examined.

This paper presents experimental results on natural convection of magnetic fluids in a cubic enclosure with isothermal hot and cold walls under magnetic fields. The vertical magnetic fields were applied uniformly and nonuniformly using a permanent magnet and a electromagnet, respectively. Temperature distributions on a front wall were visualized by a thermosensitive liquid crystal. The horizontal temperature distributions on the central cross-section and Nusselt numbers were measured. The effects of uniform and non-uniform magnetic fields on the heat transfer and natural convection flow were discussed in detail.

Magnetic fluid is a stable suspension of solid magnetic particles and is an opaque fluid. This paper presents an application of the Ultrasound Velocity Profile monitor in measuring flow of a magnetic fluid in a cylindrical container. Velocity profiles of rotating flow of a magnetic fluid caused by an applied magnetic field were measured by UVP method and the 3-D flow structure was clarified.

Axisymmetric mode oscillations of a magnetic fluid column supported by a magnetic field are examined experimentally in the presence of gravity. A magnetic fluid column, height 9.78 mm, is formed vertically in a magnetic field generated by Helmholtz like coils fastened on an electrodynamic exciter, and vibrated vertically to produce axisymmetric oscillations. Nonlinear jumping phenomena, transition from the (0, 1) mode standing wave to the progressive wave and mode coupling are observed at larger amplitude oscillations. One-half subharmonic oscillations such as the (3, 1), (4, 1) and (5, 1) modes arise beyond some threshold values of the excitation amplitude. These new phenomena are useful to discuss the liquid column oscillations in a microgravity environment in the Floating Zone Technique.

Experiments were performed to measure how the ultrasonic propagation attenuation in an MR fluid under an external magnetic field was affected by temperature, elapsed time, magnetic field intensity, magnetic field angle, removal of the magnetic field, and hysteresis. The influence of the clustering structures on change of ultrasonic propagation attenuation in MR fluids is discussed.