Presentations

Magnetic fluid flow in a square duct under magnetic fields has been studied by an experimentally. We measured pressure drop with applying DC, AC and DC+AC magnetic fields. Flow resistance increased under magnetic fields so that pressure drop and friction factor increased. From FFT analysis of the pressure drop, we obtained different power spectrum for AC and DC+AC.

MR流体に異なる周波数の交流磁場を印加した時に形成されるクラスタの変化を超音波伝播速度を用いて評価した。結果として、交流磁場周波数の2倍の周波数でクラスタの形成崩壊が繰り返されることが確認された。

Magnetic fluid flow in a square duct under fields was investigated experimentally. We used DC, AC and DC+AC magnetic fields. Pressure drop in a test section was measured and influence of magnetic fields on flow resistance was discussed. Periodic pressure drop was investigated by FFT analysis. Different power spectra for AC and DC + AC were obtained.

This study reports the theoretical damping force of a magnetorheological (MR) shock absorber depending on a magnetic field. We used Bingham plastic model to represent the dynamic behavior of MR fluid flow in a circular pipe with tapered metering pins under a magnetic field theoretically. Since MR fluid has yield stresses, the flow is divided into two regions; shear and plug flows. We revealed the relationship between the damping force of MR shock absorber and an applied magnetic field. Analytical results indicated that the radius of a pipe and the velocity of the piston effect on the damping force. We conducted drop impact tests and compared experimental results with analytical results. The comparison results indicated that the effect of magnetic field on the damping force depends on the development of the flow, and that the effect increases in a developing flow.

This paper reports experimental analysis of magnetorheological fluid (MR fluid) under oscillating magnetic fields. The experiments were carried out under oscillating magnetic fields. As a result, clusters in MR fluids have dependence of intensity and frequency of oscillating magnetic fields. The frequency of ultrasonic propagation velocity change is twice the frequency of oscillating magnetic fields.

乱流領域における磁場影響下での磁性流体強制対流熱伝達について実験的に研究を行った。磁場強度とRe数を用いた無次元数Mhを提案し，伝熱の抑制やその回復距離をMh数によって整理した。

MR流体に交流磁場を印加し，超音波伝播速度を測定することで，クラスタ形成を評価した。10 mT，30 mT，50 mTの交流磁場を1，2，3 Hzの周波数でそれぞれ印加し，計測を行った。結果として，クラスタ形成には時間依存性，磁場強度依存性，周波数依存性があることが確認できた。

This study reports the theoretical damping force of a magnetorheological (MR) shock absorber changed by a magnetic field. We used Bingham plastic model to represent the dynamic behavior of MR fluid flow in a circular pipe under a magnetic field theoretically. Since MR fluid has yield stresses, the flow is divided into two regions; shear and plug flows. We revealed the relationship between the damping force of MR shock absorber and an applied magnetic field. Analytical results indicated that the radius of a pipe and the velocity of the piston affect on the damping force.

同調磁性流体ダンパー（TMFD）とは磁場により特性変化をもたらす制振装置であり，制振効果のある振動数を変化させることができる。TMFDでは制振質量として磁性流体を用いており，流体の容器には任意形状のものが使用できる。流体容器として二重円筒容器を用いた場合に，二重円筒容器中央の空洞部に鉄心を挿入すると制振効果のある振動数の変化量が増大する。この変化量の増大効果を半径比の異なる二重円筒容器について調べた。

スロッシング固有振動数を変化させることが可能である。磁性流体の容器として同軸二重円筒容器を用いた場合，TMFDにおける鉄心による制御領域改善効果を周波数応答測定により実験的に求めた。

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.

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.

内部微粒子の濃度変化がMR流体内の超音波伝播特性におよぼす影響を，実験的に調べた。

The rheological response of magnetorheological fluid (MRF) results from the polarization induced in the suspended particles by application of an external magnetic field. Characteristics of an MRF depend on the volume faction, that is the percentage of magnetic particles in the carrier liquid. We propose a qualitative investigation of these volume fraction effects by measuring properties of ultrasonic wave propagation velocity in MRFs having various volume fractions. The ultrasonic wave propagation velocity changes under the effect of an external magnetic field as a result of arrangement of clusters along the direction of the field in the MRF.

A tuned magnetic fluid damper (TMFD) is a semi-active dynamic absorber using a magnetic fluid as a damping mass. A characteristic of the TMFD is to change a natural frequency of a sloshing. When a magnetic field is applied to a container filled with a magnetic fluid from below, the natural sloshing frequency increases and a range of a damping frequency is spread. In this paper, pressure measurements were used to control the appropriate magnetic field.

Applying magnetic field changes properties of a magnetorheological (MR) fluid. A fascinating occurrence so called hysteresis in the MR fluid appears when the magnetic field is increased to and decreased from a certain value. This occurrence appears to be influenced by the formation of clusters in proportion to the magnetic field intensity and its direction. Results show that the hysteresis in MR fluid is changes when the direction of ultrasonic measurement also changes. The change of hysteresis curve is related to the cluster formation.

A natural frequency of a tuned magnetic fluid damper (TMFD) changes in a mganetic field. Change of the natural frequency of the TMFD with a coaxial cylindrical container is smaller than that with a cylindrical container. The natural frequency of the TMFDs varies according to a theory of the cylindrical container qualitatively. When a maximum supplied current to an electromagnet is constant, a variation area of the natural frequency does not change linearly with a radius-ratio of a inner and a outer cylinders. There is an optimum radius-ratio in the TMFD with the coaxial cylindrical container.

MR流体に磁場を印加した時に内部に生じるクラスター成長を超音波の伝播速度変化を用いて実験的に調べた。ある一定の磁場強度に達するまでの時間を変化させ，超音波伝播速度がどのように変化するかを調べた。また，同じ時間を費やして磁場を減少させ，ヒステリシスに関する検討を行った。

波力発電用の往復流型タービン翼にNACA0020を用いたウェールズタービンの諸性能を，数値計算によって調べた。計算には，FLUENTを使用した。チップ間隔を変化させ，タービン性能がどのように変化するかについて検討を行った。

磁場印加によるMR流体中を伝播する超音波特性変化を実験的に調べた。