Published papers

A new numerical method for obtaining the forces on a body immersed in viscous fluids is derived for a uniformly accelerated elliptic cylinder from rest. In an analytical study, Fourier series expansion and boundary layer variable expansion are used because of good convergence and accuracy at high Reynolds numbers. An application of discrete Fourier transform to a block tridiagonal matrix leads to a high speed calculation over ten times as fast as the SOR method. From this analysis, the coefficients of drag, lift and moment exerted on a unit spanlength are obtained, and they consist of two components due to pressure and viscous force. Distribution of vorticities on the surface, which is important for the characteristics of heat conduction, is reveal ed in detail. Furthermore, the authors confirm that the separation time shown by Blasius at the trailing edge has a larger error when the eccentricity of the elliptic cylinder goes to unity.

This paper describes one such development. A new method of solving a one-dimensional wave equation in linear tapered compound pipes with arbitrary cross-sections has been devised. Results obtained by this theory are compared with experiments in pipes with square cross-sections. And we obtained the following conclusions: (1) Damping coefficients in an arbitrary cross-section are defined and are expressed analytically for some representative cross-sections. (2) The viscous solution of a wave equation obtained by Laplace transform explains well distorted pressure histories in a linear tapered pipe with an arbitrary cross-section. (3) Pressure waves in a square cross-section include higher modes of frequency and damp more rapidly than those in a circular cross-section. but fundamental characteristics as waves are independent of the cross-section of the pipe except for the small aspect ratio.

This paper considered a flow normal to an infinite thin elliptic cylinder which is uniformly accelerated from rest in a direction perpendicular to its generating lines in a viscous fluid. The Dufort-Frankel method for vorticity transport equation is used for the numerical simulation of viscous incompressible flows, and a new finite Fourier transform method is introduced in order to handle the stream function equation for accurate and efficient calculation. A major part of the present paper is devoted to physical properties of the flow during the early stages of wake developement behind an obstacle, for a Reynolds number of 98.11. A computer-aided flow visualization technique is used to demonstrate the main features of the hydrodynamic field for the flow. The rest of this paper demonstrates the important unsteady forces such as time-dependent drag, lift and moment acting on a body immersed in a viscous fluid, and presents specific numerical results for various transitions.

The rotational form of the Navier-Stokes equations in which velocity and the Bernoulli function are variables is used in the GSMAC method. Velocity components and Bernoulli function are interpolated as a linear function and a constant function, respectively. This interpolation is simple and convenient for creating the mesh system. However, the approximation which is mentioned above makes it difficult to analyze inlet-outlet flows including the Neumann boundary conditions. The present paper shows a new modified GSMAC method which is applicable to high Reynolds flows with Neumann boundary condition (especially the pressure boundary). The modified scheme consists of an algorithm which satisfies the continuity equation much better than the previous GSMAC method.

We experimentally studied shear flow of a water-based magnetic fluid between concentric annuli. The experiment was carried out by changing the angular velocity of the outer cylinder, and the moment acting on the inner cylinder was measured. Experimental results were discussed in the following three ways. At first the magnetic fluid was treated as a Newtonian fluid, and a small difference in the flow curves was found. Next the power-law fluid theory was applied in order to explain these differences. Finally we examined this flow problem using the micropolar theory, which gives the theoretical relation between the moment acting on the inner cylinder and the angular velocity of the outer one. We measured the coefficient which denoted the micropolar effect, and showed the influence of the substructure on the fluid.

This paper presents the stability and dynamic characteristics of an axisymmetrically oscillating magnetic liquid column subjected to a uniform magnetic field in the presence of gravity. Initially, the axisymmetric mode response of a magnetic liquid column is analyzed using potential theory based on a magnetic field perturbation method. Then, an experiment is described in which a liquid column is formed between Helmholtz coils and vibrated vertically to produce axisymmetric oscillations by an electodynamic exciter. The surface frequency response of the column is measured optically using a high-speed video camera, a strobovision-snalyzer and a stroboscope. The results show that the magnetic field exerts a stabilizing effect on the column and the resonance frequency increases for increased liquid column aspect ratio(diameter / height). Both the experimental interfacial response and resonance frequency show good agreement with the theoretical prediction.

Experimental results for the properties of ultrasonic propagation velocity in kerosene-based and water-based magnetic fluids are reported. The ultrasonic propagation velocity in magnetic fluids is dependent on temperature, elapsed time of applying the magnetic field, and magnetic field intensity. Hysteresis and anisotropy of ultrasonic propagation velocity are observed. These interesting results seem to be related to chain-like cluster formation in the magnetic fluids and the characteristic period of Brownian motion of the magnetic particles.

矩形，円筒，球形容器に内に満たされた磁性流体のスロッシング現象に及ぼす磁場の影響を調べた。その結果，印加磁場の増加に伴って共振振動数が高周波数側に移行し，液面動揺も抑えられる事が明らかとなった。また，実験結果は理論解析結果ともよく一致し，理論解析の妥当性が確認できた。

Since free surface flows are seen in nature phenomena and artificial systems, the analysis for these flows has been more important in mechanical engineering. However, theoretical analyses are almost impossible because the boundary conditions are nonlinear equations in analyzing the free surface flows. Thus, numerical analyses are needed. Finite element method (FEM) which can be used for unstructured grid can easily treat boundary conditions. Thus, FEM is used in many technological fields. In this thesis, free surface flow problems were analyzed using the finite element method. In solving these problems, an arbitrary Lagrangian-Eulerian (ALE) kinematical description of the fluid domain was adopted, in which the nodal point can be displaced independently of the fluid motion. The ALE method was introduced into the Generalized Simplified Marker and Cell (GSMAC) method. Damping out the alternating errors was examined in this scheme.

The dynamic behavior of a magnetic fluid in a laterally oscillated rectangular container was studied experimentally. Frequency responses of magnetic fluid-container system were measured under vertical non-uniform magnetic fields. Relations between the resonant frequency and the applied magnetic field were discussed, and experimental results were characterized by Froude number with consideration of the magnetic effect. Since the apparent viscosity of the magnetic fluid increases with magnetic field, its effect on sloshing phenomenon was examined in detail. Internal pressure on the wall and displacement of surface waves were simultaneously displacement.

This paper presents velocity profile measurements of an oscillatory pipe flow of magnetic fluid by Ultrasonic Velocity Profile (UVP) method. Experiments are performed at Reynols number Rc=367, defined by mean velocity amplitude and a pipe diameter, and non dimensional angular frequency W=4.76. It is shown that velocity amplitude increases in the center of a pipe and decreases in the near wall region under non-uniform magnetic field. The comparison of measured data under non magnetic field with those obtained from the theory of Newtonian-fluid reveals that noticeable discrepancies exist between them.

The authors experimentally studied a shear flow of a water-based magnetic fluid between concentric annuli. The experiment was carried out by changing the roll accerelation of the outer cylinder, and the moment acting on the inner cylinder was measured. Experimental results were discussed in the following three ways. At first the magnetic fluid was treated as a Newtonian fluid, and a small difference in the flow curves was found. Next the power law theory was applied in order to explain these differences. Finally the authors examined this flow problem using the micropolar theory, which gives the theoretical relation between the moment acting on the inner cylinder and the roll accerelation of the outer one. In this relation, a coefficient denotes the micropolar effect. The authors measured this value and showed the effect of the substructure on the fluid.

Oscillating pipe flow of a magnetic fluid was investigated experimentally by using the Ultrasonic Velocity Profiler (UVP) method. The test liquids are two kinds of water-based magnetic fluid W-40 and MSG11. UVP method is a useful technique for measuring the velocity components of a magnetic fluid. When this method is applied to magnetic fluid flow, it is necessary for the ultrasonic propagation velocity to be accurate. However, when an external magnetic field is applied to a magnetic fluid, some of the inner particles coagulate and form clustering structures. These clustering structures affect the ultrasonic propagation. Therefore, the properties of ultrasonic propagation in test magnetic fluids were also analyzed exactly before the measurement by UVP. Based on this analysis, UVP method is applied to magnetic fluid. In the result of velocity profile measurement, unique phenomena of oscillating pipe flow of the magnetic fluids subject to magnetic field were observed. It seems that the change of clustering structures under magnetic field cause these unique phenomena.

We investigated the forced convective heat transfer of magnetic fluid by applying magnetic field in a vertical, a parallel and an axial direction against heat transfer direction by using a rectangular duct. In the case of laminar flow, heat transfer was enhanced in the vertical direction and slightly enhanced in the axial direction, but hardly changed in the parallel direction. In contrast, in the case of turbulent flow, heat transfer was suppressed in all directions. The suppression level in vertical and parallel direction is similar, but the suppression in axial direction is much weaker than those in other directions.

We present the equation of motion of a MF-TLCD (Tuned Liquid Column Damper with a Magnetic Fluid), and solved it numerically using a 4th-order Runge-Kutta method. Using the numerical results, we demonstrate the frequency responses of a MF-TLCD and the effect of the magnetic field on the natural frequency of a MF-TLCD. We also compare numerical results with experimental results, and show that they are coincident qualitatively.

Magnetic fluid tuned liquid column damper (MF-TLCD) is a kind of semi-active damper that uses magnetic fluid as its working fluid. An MF-TLCD alters the natural frequency of the magnetic fluid column that forms the resident liquid inside the MF-TLCD by applying a magnetic field. We quantitatively investigated the damping coefficient generated by the flow of magnetic fluid, which is strongly related to the damping performance. Three kind of U-pipes that have each different shape were prepared and single-degree-of-freedom oscillation was performed with each those pipes. Finally, we discussed the effect to the damping performance of MF-TLCD induced by various damping coefficient subjected to magnetic field and configurations of those U-pipes.

Dynamic pressure change of a magnetic fluid in a lateral oscillating container was investigated. An experimental approach based on the measurement of pressure at several points by small disc-type pressure transducers was used. Several frequency response spectra are received. These results indicated that the free surface disturbance caused by the sloshing was suppressed by the applied magnetic field.

This paper reports experimental studies about anisotropy and attenuation as characteristics of ultrasonic propagation in a magnetorheological fluid (MRF) under AC magnetic fields. Parameters of this studies are magnitude of AC magnetic fields, frequencies of AC magnetic fields and angles between directions of ultrasonic propagation and magnetic field. As results of change rate of sound velocity, MRF has characteristics of time dependence, frequencies dependence and anisotropy under AC magnetic fields. Also, length of clusters in MRF became short with increase of frequencies of AC magnetic fields. Attenuation decreased with increase of the angles between directions of ultrasonic propagation and magnetic field. But, attenuation did not change with increase of frequencies of AC magnetic fields.

The characteristics of the inner structure of a magnetic fluid (MF) under high pressure were investigated experimentally. The ultrasonic propagation velocity was changed with the application of magnetic fields and pressure. The change was related to cluster formation in the MF fluid. Based on the experimental results, the effect of pressure on the inner structure in MF was analyzed.

The ultrasonic propagation velocity of MR fluid under various magnetic field sweep rates was measured. A magnetic flux density was applied from 0 to 400 mT over different lengths of time. On the basis of the experimental results, the effect of the magnetic field sweep rates on the cluster formation of MR fluid was analyzed.