Published papers

We designed a novel semi-active TLCD (Tuned Liquid Column Damper) that uses a magnetic fluid (MF) as a working fluid. Two electromagnets were used and a magnetic field was applied symmetrically to both sides of the magnetic fluid column. The frequency response of the MF-TLCD apparatus was measured, and the influence of magnetic fields on the natural frequency of the magnetic fluid column was investigated.

The time-dependent flow structure inside a slender starting vortex, which was bounded in the axial direction either by two solid walls or by a wall and a free surface, has been investigated experimentally in water. Particle traces and the dye-injection method were used for velocity measurements and flow visualizations. Numerical simulations were also carried out in order to identify several mechanisms responsible for the observed phenomena.

Circular flow of a magnetic fluid between coaxial cylinders under a rotating magnetic field was studied experimentally. The moment acting on an inner cylinder was measured when an outer cylinder rotated. Experimental results were arranged for several parameters: directions of the rotation of magnetic field and the outer cylinder, the magnetic field intensity, radial gap between the cylinders.

The surface behaviors of the two-layers liquid in a laterally oscillating rectangular container were studied. A water-based magnetic fluid and a silicone oil were used in the experiments. A vertical non-uniform magnetic field was applied to the container. The resonant frequency of the fluids-container system moved toward the high frequency region with the magnetic field intensity in the same way of a single magnetic fluid.

The magnetic field effects on both the static stability limit and the resonance frequency of a magnetic liquid column are examined theoretically and experimentally. We first derived the theoretical resonance frequency of a column using linear potential theory. Then, in the experiment, a vertical cylindrical magnetic liquid column was formed between two electromagnets. As the magnetic field intensity was decreased, the column's diameter exhibited hysteresis, such that its stability limit extended to a smaller diameter range due to the coaxial magnetic field. The column was also subjected to lateral excitation and the surface frequency response of the non-axisymmetric first two modes were observed. It was found that the resonance frequency of the column increases with increasing magnetic field intensity and decreases with an increase in the aspect ratio of the column (mean diameter / height). The resonance frequency of the first mode was in qualitative agreement with the theory.

磁性流体液柱を用いた微小重力場での液柱振動現象の模擬実験を行った。そして，その模擬実験の有効性を明らかにした。

The dynamic behavior of a magnetic fluid in a laterally vibrated rectangular container subject to a non-uniform vertical magnetic field has been investigated. Flow behavior was observed using the ultrasound velocity profile measuring technique. The effect of the magnetic field on the resonant frequency of the fluid-container system is discussed. Experimental results are compared with the results obtained from nonlinear theory using the perturbation method.

In the present study, successful applications of the ultrasound velocity profile measuring technique to velocity fields of a magnetic fluid are presented. After a brief introduction of its principle, various examples applied for the magnetic fluid flow are demonstrated.

Shape oscillations of magnetic liquid columns subject to vertical vibration in a uniform magnetic field are examined in the presence of gravity. A magnetic liquid column is formed vertically against gravity in an axial magnetic field produced by Helmholtz coils and then vibrated to produce axisymmetric oscillations. A high-speed video camera is used to observe the column's dynamic shape and two high-resolution laser displacement detectors measure the amplitudes of both the exciter table and the column interface. The experimental interfacial amplitude shows good agreement with our theoretical predictions. Two new wave motions are observed: a progressive wave near the resonance range of the fundamental mode (0,1), and a mode (4,1) azimuthal one-half subharmonic oscillation beyond the mode (0,1) frequency. These are the first observations of such wave motions in a terrestrial experiment and may suggest similar liquid column oscillations in a microgravity environment.

Micro-cluster formation of the non-magnetic and ferromagnetic particles in a magnetic fluid was investigated. Using an optical microscope system with cardioid condenser lens, real-time visualization of the Brownian motions of both particles were carried out. The chain-like cluster formation of both particles were observed simultaneously under the magnetic field. Two types of magnetic fluid of a water-based and kerosene-based magnetic fluids were used as test liquids.

The frequency response of a tuned liquid damper (TLD) which uses a magnetic fluid (called a "tuned magnetic fluid damper" (TMFD)) is investigated. A single-degree-of-freedom tuned mass damper (TMD) analogy is used to define the effective mass, stiffness and damping and these parameters are then estimated from experimental results. A numerical simulation is used to examine the TMFD and appropriate magnetic field conditions for effective damping are predicted. In particular, the performance of the TMFD was improved by switching the applied magnetic field at a point near the resonant frequency of the undamped structure.

Since UVP is the method to take the velocity information by using ultrasound, this method is very suitable for measuring the velocity profile of opaque fluid. Oscillating pipe flow of a magnetic fluid was investigated experimentally to examine the applicability of this method to magnetic fluid flow. We used a diluted water-base magnetic fluid and the magnetic field was applied by two permanent magnets. Influence of an applied magnetic field on flow behaviors were discussed. The amplitude and phase of the oscillating velocity varied with intensity of the magnetic field, which yielded increase of the apparent viscosity.

When an external magnetic field is applied to a magnetic fluid, some of the colloidal particles coagulate and form chain-like clusters. Properties of ultrasonic propagation wave are changed by these chain-like clusters. We carried out measurement of the ultrasonic propagation velocity in a magnetic fluid. Measurement were made by changing the magnetic field intensity from 0 mT to 570 mT, and the angle between the magnetic field direction and direction of the ultrasound propagation from 0° to 180°. The ultrasound frequencies were 1 MHz, 2 MHz and 4 MHz. Some of experimental results for the characteristics of ultrasound propagation in a magnetic fluid under a uniform magnetic field were reported.

Oscillating pipe flow of a magnetic fluid subject to a magnetic field was investigated experimentally. Time-dependent velocity profiles are obtained by UVP method. When the magnetic field is applied for some period before measurement, peculiar velocity profiles are obtained because of the growth of chain-like clusters in the magnetic fluid. The influence of the amount of time of pre-applying magnetic field and magnetic field intensity on flow behaviors are examined. The apparent flow rate is introduced to evaluate the correlation between the velocity profile and the growth of chain-like clusters. It is found that the rate of change of the apparent flow rate increases with both magnetic field intensity and the pre-application time of magnetic field.

Experimental results for ultrasonic propagation velocity properties in water-based magnetic fluids are reported. Water-based magnetic fluid samples having 10 wt%, 30 wt% and 40 wt% concentration of magnetic particles were examined. The ultrasonic propagation velocity generally decreases with higher concentrations of magnetic particles, generally increases with increasing external magnetic field intensity and exhibits anisotropy.

A new analytical model of a tuned liquid damper (TLD) using a magnetic fluid (tuned magnetic fluid damper (TMFD)) is proposed in order to better explain the unique damping characteristics of a TMFD. This model is then clarified experimentally using vertical magnetic fields and we investigate an effective method of applying a magnetic field on a tuned magnetic fluid damper (TMFD).

When the magnetic field is applied to magnetic or MR fluids, some of inner particles form clustering structure. These clustering structures influence on the ultrasonic propagation velocity in these fluids. We measured precisely the properties of ultrasonic propagation velocity in these fluids subjected to the magnetic field. The measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is varied from 0° to 90°. Some interesting properties of ultrasonic propagation such as hysteresis and anisotropy are observed. Based on the experimental results, the inner structures of the magnetic or the MR fluids are analyzed experimentally and the application of non-contact inspection in these fluids by ultrasonic techniques is discussed.

Damping parameters of a tuned magnetic fluid damper [TMFD] using a tuned mass damper [TMD] analogy model are obtained from approximation to frequency responses of experiments used some sort of magnetic fluids in a cylindrical container. An effective mass is changed by a magnetic field from downside, however a significant change of surface shape of magnetic fluids causes strange changing tendency. It was found that other parameters are changed according to the surface shape.

Experimental results from studies on the properties of ultrasonic propagation velocity and attenuation in hydrocarbon-based magnetic fluid are reported. The ultrasonic frequency used is 2 MHz and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is adjusted from 0 to 90°. The ultrasonic propagation velocity and attenuation changes are dependent upon the intensity of the magnetic field and the elapsed time of application. Characteristic properties of ultrasonic propagation in magnetic fluid are observed. These particular results seem to be caused by clustering structures in the magnetic fluid. Based on these results, the inner structure of the magnetic fluid is analyzed experimentally and the application of non-contact inspection in opaque fluids by ultrasonic techniques is discussed.

The dynamic behavior of a two-layered fluid in a laterally oscillated rectangular container under a vertical nonuniform magnetic field was studied experimentally. The two-layered fluid was formed of water based magnetic fluid and silicone oil. The dynamic behavior was studied by measuring the velocity profile of the two-layered fluid using an ultrasound velocity profile measuring technique while varying the vertical magnetic field. The displacement of the free surface was measured using a laser sensor. The effect of the magnetic field on the sloshing of the two-layered fluid was considered.