Hitoshi Nishida

DIFFERENCES IN STEADY CHARACTERISTICS AND RESPONSE TIME OF ERF ON ROTATIONAL FLOW BETWEEN ROTATING DISK AND CONCENTRIC CYLINDER

We made an experimental investigation of the steady characteristics of torque, current density, and response time of ERF on rotational flow of the disk and the concentric cylinder. We used smectite particles suspension ERF and D.C. electric field. We compared the steady shearstress, current density, and the rise and settling time of the concentric cylinder and with those of the rotating disk. Then we clarified the differences. At a larger electric field strength, the shear stress, yield stress, and apparent viscosity to a constant shear rate in the case of the rotating disk are larger than they are in the case of the rotating concentric cylinder. However, at a larger electric field strength, the current density to a constant shear rate in the case of the rotating disk is smaller than it is in the case of the rotating concentric cylinder. Rise time of torque in the case of the rotating disk is faster than it is in the case of the rotating concentric cylinder. However, rise time of current density in the case of the rotating disk is slower than it is in the case of the rotating concentric cylinder at a small electric field strength. On the other hand, the difference of settling time of torque and current density between the rotating disk and the rotating concentric cylinder is changed by the electric field strength and shear rate. The settling time of torque in the case of the rotating disk is faster than it is in the case of the rotating concentric cylinder at a large electric field strength and large shear rate. The settling time of current density in the case of the rotating disk is slower than it is in the case of rotating concentric cylinder at a small electric field strength. Based on these results, the rotating disk has an efficiency of obtained torque to given electric power greater than that of the rotating concentric cylinder.

Electrorheological Rotating Disk Clutch Mechanism Under AC Electric Field: Part I - Torque and Current Density:

Torque and current density on a rotating disk immersed in suspension-type electrorheological fluid (ERF) under AC electric field were measured. They have steady and varying amplitude components which depend on the angular velocity of the disk, and the frequency and intensity of the electric field. The results were demonstrated by means of a particle aggregation model. The constant torque and current density under DC electric field were compared to those under AC field. The magnitudes of the differences strongly depend on the angular velocity of the disk and the frequency of the electric field. When an AC electric field is used, a smaller frequency should be applied for the sake of greater efficiency.

Numerical Analysis of the Polishing Process of Inner Tube Wall Using Micron-Size Particles in Magnetic Fluids

Distribution and behaviour of micron-size magnetic particles and nonmagnetic particles in magnetic fluids in the polishing process of inner wall of small tube is investigated numerically by using the particle method based on the simplified Stokes dynamics. In this study, it is shown that chain-like clusters of both magnetic particles and those of nonmagnetic abrasive particles are formed between the two magnetic poles. The clusters are strongly held during the polishing process. The clusters of the nonmagnetic abrasive particles are surrounding the clusters of magnetic particles and they are combined with each other.

Effectiveness of using a magnetic compound fluid with a pulsed magnetic field for flat surface polishing

The effects of the frequency of a pulsed magnetic field on flat polishing were investigated to obtain basic data for increasing the performance and precision of polishing using MCFs. We clarified that the profile curves after polishing differ for a direct-current magnetic field and for a pulsed magnetic field and flattening occurred over a wide range when the frequency of a pulsed magnetic field is 0.1 Hz.

Microprocessing characteristics of inner surface of tube using magnetic functional fluid

We proposed a microprocessing method using a magnetic compound fluid for the inner surface of a tube made of a material that is difficult to cut, and clarified the processing characteristics and magnetic field distribution of the tool. The tool inserted into the tube comprises a stack of ring-shaped permanent magnets with spacers between them. There is an almost proportional relationship between the amount of material removed and the processing time, and the processed surface acquires a mirror finish. Moreover, for tools with shorter permanent magnets, the circularity is improved by processing.

Characteristics of braking devices using ERF

We clarified the characteristics of rotating-disk and rotating-concentric-cylinder braking device types using ERF (electro-rheological fluid) with smectite particles. Concerning the steady characteristics of the both braking devices, the current density of the rotating-disk type is smaller than that of the concentric cylinder type. In addition, the input electric power per increment of torque has the same ratio as the enhancement of the shear rate. In contrast, regarding the transition characteristics, the rise time of the torque for the rotating-disk type is shorter than that for the concentric-cylinder type, though the current’s rise time is almost the same in both braking devices. It can be considered that the current density of the rotating-disk type is small and the rise time of the torque of the one type is small due to the influence of the secondary flow. The microscopic tendency of the electric charge can be guessed from the transition characteristic of the electric current.

Electrorheological Rotating Disk Clutch Mechanism Under AC Electric Field: Part II - Efficiency Metrics

Electric power and efficiency on a rotating disk under AC electric field with suspension-type electrorheological fluid (ERF) were investigated. This report also dealt with the time lags of torque and current density from the applied eloctric field. Especially, the time lag of the current density was arranged by the power factor. The time lag of the torque is changed larger than the one of the current density. On the other hand, the data of the torque and the current density have steady and varying characteristics as amplitude components. Therefore, we need to investigate four electric powers: apparent power, effective power, steady power from the steady component of the current density and total power. From the three electric powers, we can deal with three efficiency of the electric power to the torque. They depend on the angular velocity of the disk, frequency and intensity of the electric field. The results were explained with the particles aggregation model.

RHEOLOGY OF ERF ON VARIOUS FLOW FIELDS

This paper is concerned with the experimental investigation of electrorheological effect (ER effect) on apparent viscosity and yield stress obtained from hydrodynamic characteristics of electrorheological fluid (ERF) in various flow fields. Our conducting flow fields are made by using rectangular duct, concentric cylindrical pipe, rotating disk and rotating concentric cylinder. The measured parameters of the former two cases are pressure difference at a given volumetric flow rate, and the latters are torque at a given angular velocity. Our using ERF is suspension type. We arrange these data to obtain increment of apparent viscosity and yield stress with and without a supplying D.C. electric field by using integral method of rheology. It is clarified that qualitative values of increment of apparent viscosity and yield stress are different at each flow field. In addition, the quantitative ER effects of shear rate and electric field strength on the increment of apparent viscosity and yield stress are clarified.

Changes in the Resistance Force of a Magneto-Rheological Shock Absorber Induced by a Magnetic Field

In this study, we report the theoretical resistance force of a magneto-rheological (MR) shock absorber. We use the Bingham plastic model to theoretically represent the dynamic behavior of MR fluid flow in a circular pipe under the effect of a magnetic field. Because an MR fluid has yield stresses, the flow is divided into two regions: shear flow and plug flow. We reveal the relation between the resistance force of the MR shock absorber and the applied magnetic field. We conduct experiments and compare the experimental and analytical results to verify the theoretical approach.

Behavior of both Nonmagnetic Particles and Magnetic Particles in Magnetic Compound Fluids in a Micro-Tube with Axial Flow under Rotating Magnetic Field

Behaviors of both micrometer-size nonmagnetic abrasive particles and micrometer-size magnetic particles in a magnetic fluid are investigated by using the discrete particle method which is based on the simplified Stokes dynamics. Sheet-like clusters of nonmagnetic particles and sheet-like clusters of magnetic particles alternately appear one after another in the axis direction when the flow velocity is small.