Published papers

The properties of ultrasonic propagation velocity in water-based and kerosene-based magnetic fluids and an MR fluid are examined experimentally. The ultrasonic frequency used is 1 MHz and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and is swept at a constant rate dB/dt (sweep rate). The ultrasonic propagation velocity changes with applied magnetic field and hysteresis is observed. The properties of ultrasonic propagation seem to be highly influenced by the formation of chain-like clusters (in the magnetic fluids) and robust clusters (in the MR fluid).

The frequency response of a tuned liquid damper (TLD) which uses the sloshing of a magnetic fluid (a tuned magnetic fluid damper (TMFD)) is investigated. Effective mass, stiffness and damping are estimated from experimental results, using a single-degree-of-freedom tuned mass damper (TMD) analogy. TLD is a passive mechanical damper that uses sloshing liquid to dampen oscillations, but TMFD is semi-active damper because of application of magnetic field. We first compare results obtained by numerical simulation and experiment to show that a TMFD cannot be modeled by a simple analytical model based on analogy with TMD. Then we propose a new analytical model of TMFD and examine the validity of this new model experimentally.

The properties of ultrasonic propagation velocity in water-based and kerosene-based magnetic fluids and an MR fluid are examined experimentally. The ultrasonic frequency used is 1 MHz and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and is swept at a constant rate dB/dt (sweep rate). The ultrasonic propagation velocity changes with applied magnetic field and hysteresis is observed. The properties of ultrasonic propagation seem to be highly influenced by the formation of chain-like clusters (in the magnetic fluids) and robust clusters (in the MR fluid).

Velocity and attenuation of ultrasonic propagation in magnetic fluids subjected to a magnetic field are examined experimentally. Measurements are taken while changing the magnetic field intensity and the angle between the magnetic field direction and the ultrasonic propagation direction. The ultrasonic propagation velocity and attenuation are dependent on the intensity and the elapsed time of the magnetic field. When the magnetic field is applied to magnetic fluid, magnetic particles form clustering structures and they effect on ultrasonic propagation in a magnetic fluid. Based on experimental results, the influence of the inner structure of the magnetic fluids on the properties of ultrasonic propagation is discussed.

Experimental results for the properties of ultrasonic propagation velocity and attenuation in a kerosene-based magnetic fluid (EXP04019) are reported. The ultrasonic frequency used is 2MHz and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0mT to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is adjusted from 0° to 90°. We observed various characteristic properties of ultrasonic propagation. The ultrasonic propagation velocity and attenuation change with the elapsed time of external magnetic field application and with magnetic field intensity. When the magnetic field is applied to magnetic fluid, some of the magnetic particles in the magnetic fluid form clustering structures. These structures cause the properties of ultrasonic propagation. We discussed influence of inner structure in magnetic fluid on ultrasonic propagation.

A TMFD (Tuned Magnetic Fluid Damper) is a Tuned Liquid Damper using a magnetic fluid. Natural frequency of the TMFD can be controlled by a constant nonuniform magnetic field of vertical direction. Analysis of the TMFD is carried out by using a simple analogy model of a TMD (Tuned Mass Damper). We used two different cylindrical TMFDs, whose diameters are different. The experimental frequency responses are compared with approximation curves that are calculated under a condition of constant parameters of the TMD model. The approximation curve corresponds well to the experimental curve in smaller TMFD but does not well in larger TMFD. Frequency responses of some temperature of the magnetic fluid are obtained to know temperature dependency of the TMFD. Frequencies of resonance and a best damping point do not change but amplitudes of them are changed by the fluid temperature.

The ultrasonic technique can be applied to an opaque fluid, such as MR fluid. The ultrasonic propagation velocity can be found by the pulsation methods. Based on these results, the clustering structures of these fluids are analyzed experimentally in term of elapsed time dependence, effect of the external magnetic field, effect of the after remove of the magnetic field, and hysteresis phenomena. It has been shown that MR fluid does not reach a new equilibrium state immediately when the external magnetic field is applied and after removed. Because the sizes of magnetic particle are relatively large in MR fluids, it is importance to consider the influence of sedimentation of the magnetic particles.

We measured ultrasonic propagation velocity in an MR fluid precisely to study the cluster formation. Based on these results, the clustering structures of these fluids are analyzed experimentally in terms of time dependence, time interval, of-removal the magnetic field, and the angle of the magnetic field applied. The ultrasonic propagation velocity in an MR fluid change according to the magnetic field intensity, interval time and angle. The ultrasonic propagation velocity increases when a higher magnetic field is applied. The result also shows that the intensity of the external magnetic field has an influence on the ultrasonic propagation velocity even after the magnetic filed is removed. The ultrasonic velocity propagation also decreases when the interval time between application of the magnetic field and measurements increases.

The frequency response of a simple structure with a TMFD usually has two resonance frequencies and one best damping point. The frequency response is nonlinear because fluid sloshing is used. When a strong magnetic field is applied on a TMFD using one electromagnet, a bulge with many spikes is formed on the surface of the magnetic fluid. This bulge also affects nonlinearity. Frequency responses to magnetic fields with varying excitation amplitudes are obtained experimentally. Hardening or softening characteristics appear in resonant frequencies and the best damping point.

容器内の磁性流体自然対流が印加磁場によって制御できる事を明らかにし、その熱伝達特性を調べた。

A new finite element technique which is based on the multiplier method is presented to analyze incompressible flow problems. We apply this method to the flow analysis in a stenosed tube which is modeled by a cosine curve. Calculations are carried out for the flow whose Reynolds number is less than 1000. These results are compared with those obtained by a finite difference method. Separation and reattachment points agree with experimental results.

The initial stage of flows due to uniformly accelerated flat plate, elliptic and circular cylinders from rest in incompressible viscous fluids are numerically studied by the finite difference method. The time dependence of stream lines and equi-vorticity lines are shown in flow patterns. The Dufort-Frankel technique is used for solving the vorticity transport equation and the finite Fourier tranform for solving the stream function, which is applied to the analysis of a block tridiagonal matrix equation. The main conclusions are as follows; (1) The Fourier series method is more than ten times faster than the SOR method. (2) Numerical experiments here are in very good agreement with real experiments on a flat plate and a circular cylinder. (3) The length of vortex pairs behind a uniformly accelerated elliptic cylinder at the angle of attack 90° is obtained as a resultant of numerical experiments. (4) The growing process of the secondary vortices behind a circular cylinder is revealed at Reynolds number 731.

二重円管内の極性流体の軸方向定常流れを理論解析し，その流動特性を明らかにした。

円管内の極性流体の振動流を壁面でスピンがある場合の境界条件に基づいて理論解析を行い，速度分布と角速度分布を求めた。そして，振動特性に及ぼす諸パラメータの影響を調べた。

円管内の極性流体の振動流を壁面でスピンがない場合の境界条件に基づいて理論解析を行い，速度分布と角速度分布に及ぼす寸法効果パラメータや極性効果パラメータの影響を調べた。

A few fundamental steady flows of polar fluid, i.e., flow in a circular tube, flow between two parallel plates and flow between two coaxial cylinders are analyzed with the help of the theory of Eringen. Couple stress and spin angular momentum are considered in this approach. The exact solutions for velocity, micro-rotation, vorticity and shearing stress are obtained mathematically. These solutions are characterized by two parameters, i.e., the ratio of viscosities ε and the size effect parameter λ which do not appear in a Newtonian fluid. ε is the ratio of vortex visoosity to shear viscosity. λ means the size relation between the corpuscle and the characteristic length. The solutions are compared with those of Newtonian fluid and it is investigated how they vary with ε and λ. Apparent viscosity is determined for each flow. Material constants of polar fluid can be decided from these apparent viscosities.

This study deals with a transient laminar flow, which is started from rest, in the entrance region of a porous pipe. This flow analysis is applied to transpiration cooling systems and research equipment for production of tidal current. In this report, the problem is analyzed by a modified momentum integral method using the integral form of the equations of continuity, momentum and energy. The following conclusions were obtained ; (1) Dynamic distributions of velocity profiles, wall frictions and pressures are obtained numerically. (2) The relation between the flow rate of injection or suction and inlet length of the entrance region is made clear. (3) Each dynamic state in the pipe is found with changeable inlet velocities and with variable sections or injections. (4) It is confirmed that the modified momentum integral method is valid for the slip velocity on the porous wall which makes the inlet length short.

Distorted pressure histories in a linear tapered tube equipped with a tank at the end are experimentally investigated by the step pressure input. And also this problem is theoretically solved by two methods, i.e., eigenfunction expansion and asymptotic expansion. The peak pressure in the tube can be controlled by the capacity of the tank. Large capacity leads to an open end situation. The height of the pressure wave is proportional to the inverse of the tube radius. A one dimensional wave equation including the viscous term in the equation of motion and the effect of the variable cross section is simplified by special transformation, and the simplified equation is solved by the method of the Laplace transform. The resultant analytical solution has a clearer representation than Schuder-Binder's solution.

A new complete set of basic equations for magnetic suspensions is derived on the theory of micropolar fluids developed by Eringen and a solution to these basic equations is obtained analytically for a steady motion of magnetic suspensions in a circular pipe which is placed in a homogeneous magnetic field parallel to the flow direction. A phenomenological treatment is given for the specification of material constants of a micropolar fluid, which are vortex viscosity and spin viscosity. In order to clarify the dynamical flow characteristics in the presence of a magnetic field, six dimensionless parameters to show the magnetic effect, polar effect, wall surface effect and so on are introduced into the solution for the rotational Peclet number. Some discussions are presented on velocity profiles, distribution of microrotations and distribution of vorticities. In particular, the suspension is non-Newtonian even if a magnetic field does not exist.

A phenomenological treatment is given for steady magnetic fluid flows in annular pipes in the presence of uniform external magnetic fields. It is found that the apparent viscosity of a dilute colloidal suspension of ferromagnetic particles is a marked function of both the magnitude and direction of an externally applied magnetic field. The experimental fact shown by McTague(1969) that the additional viscosity is greater by a factor of 2 for the field parallel to the flow than for the field perpendicular to the flow is theoretically explained. Analytical expressions are derived for the distributions of velocities and angular velocities of the magnetic fluid in annular pipes under the influence of the external field. The induced magnetization calculated here to the first order is skewsymmetric with respect to the plane through the center line of the pipe and perpendicular to the applied magnetic field.