• Journal of applied mathematics & informatics
• /
• v.25 no.1_2
• /
• pp.51-66
• /
• 2007

A layer of compressible, rotating, elastica-viscous fluid heated & soluted from below is considered in the presence of vertical magnetic field to include the effect of Hall currents. Dispersion relation governing the effect of viscoelasticity, salinity gradient, rotation, magnetic field and Hall currents is derived. For the case of stationary convection, the Rivlin-Erickson fluid behaves like an ordinary Newtonian fluid. The compressibility, stable solute gradient, rotation and magnetic field postpone the onset of thermosolutal instability whereas Hall currents are found to hasten the onset of thermosolutal instability in the absence of rotation. In the presence of rotation, Hall currents postpone/hasten the onset of instability depending upon the value of wavenumbers. Again, the dispersion relation is analyzed numerically & the results depicted graphically. The stable solute gradient and magnetic field (and corresponding Hall currents) introduce oscillatory modes in the system which were non-existent in their absence. The case of overstability is discussed & sufficient conditions for non-existence of overstability are derived.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.7 no.9
• /
• pp.131-137
• /
• 1999

Under magnetism , as the magneticfluid is being itself magnetized, increase the apparent viscosity because of its body force and has the magnetic characteristics in response ot magnetism, the magnetic fluid is getting attention in various field. The magnetic fluid has the fluidity, which is a special characteristics of fluid and the magneticism , which is a special one of solid. Using this characteristics, this study has been proceeded to show the basic data for developing of a viscous damper with magnetism fluid as hydraulic fluid. Experimental study shows that the application of magnetic field is effective reducing the resonance characteristics of the spring-mass system.

• The KSFM Journal of Fluid Machinery
• /
• v.16 no.3
• /
• pp.32-38
• /
• 2013

This paper deals with the study on the rotordynamic and experimental analysis of turbine-generator system connected with a magnetic coupling. Although magnetic coupling has been used to torque transmission of chemical processing pump rotating at under 3,600rpm, magnetic coupling in this study is applied to high-speed turbine-generator system using a working fluid that is refrigerant such as ammonia or R-124a. Results of rotordynamic design analysis are as follows. The first, shaft diameter nearest to outer hub of magnetic coupling has a big effect on the $1^{st}$ critical speed of generator rotor. The second, if the $1^{st}$ critical speeds of turbine rotor and generator rotor have enough to separation margin in comparison to rated speed, the $1^{st}$ critical speed of turbine-magnetic coupling-generator rotor train has enough to separation margin regardless of connection stiffness of magnetic coupling. The analytical FE model is guaranteed by impact test on the prototype and condition monitoring such as measurements of vibration and bearing temperature is also performed.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.3
• /
• pp.240-249
• /
• 2008

This paper presents an electromagnetic design method for magneto-rheological (MR) valves. Since the apparent viscosity of MR fluids is adjusted by applying magnetic fields, the MR valves can control high-level fluid power without any mechanical moving parts. In order to improve the performances of the MR valve, it is important that the magnetic field is effectively supplied to the MR fluid. For the purpose, the magnetic circuit composed with the yoke for forming magnetic flux path, the electromagnetic coil and the MR fluid should be well designed. In order to improve the static characteristic of the MR valve, the length of the magnetic flux path is decreased by removing the unnecessary bulk of the yoke. Also, in order to improve its dynamic and hysteretic characteristics, the magnetic reluctance of the magnetic circuit should be increased by minimizing the cross-sectional area of the yoke through which the magnetic flux passes. After two MR valves, one is a conventional type valve and the other is the proposed one, are designed and fabricated, their performances are evaluated experimentally.

• Journal of the Korean Ceramic Society
• /
• v.31 no.7
• /
• pp.723-730
• /
• 1994

Stable aqueous dispersion of magnetite colloid was obtained by allowing a fatty acid, such as nonanoic acid, decanoic acid and undecanoic acid, dissociated with NH4OH solution to adsorb on the monomolecular adsorption of oleate. To obtain a stable dispersion, added amounts of sodium oleate and nonanoic acid for magnetite 20g were more than 2.63$\times$10-2 mol and 0.04 mol respectively. In this colloid, good dispersions of magnetite which is sterically stabilized in aqueous system were achieved about pH 7.7. Water-based magnetic fluids using in this study were able to redisperse to water-based magnetic fluids by adding NH4OH solution to dried water-based magnetic fluid powders. Changing a magnetic fluid carrier such as kerosene was also attemped by adding kerosene to dried water-based magnetic fluid powders. In this study, we can obtain a kerosene-based magnetic fluids using drying process.

• Journal of the Korean Magnetics Society
• /
• v.23 no.1
• /
• pp.26-30
• /
• 2013

This article is experimentally to investigate thermal-flow characteristics of the magnetic fluid for concentric annuli under externally fixed magnetic fields using visualization technique. Temperatures of the inner tube and outer tube in the tested concentric annuli were constantly maintained at both $30^{\circ}C$ and $25^{\circ}C$ and the middle tube was filled with the magnetic fluid. Magnetic field was uniformly applied using 4 permanent magnets at 4 directions of the concentric annuli. As a result, the thermal-flow characteristics of the magnetic fluid for concentric annuli could be controlled by directions of the external magnetic fields.

• Tribology and Lubricants
• /
• v.14 no.3
• /
• pp.32-38
• /
• 1998

This paper presents the magnetic flux distributions of a ferrofluid seal at the sealing gap between the pole pieces and the rotating shaft. The optimized shape of pole pieces has been determined by using the computer simulations. The computed results indicate that the sloped pole piece of 27$^{\circ}$ shows good flux distributions compared with that of the conventional flat pole pieces and may reduce frictional heats due to a reduced surface contact areas of magnetic fluids.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.05a
• /
• pp.227-230
• /
• 2005

The paper presents the identification of dynamic property of a rotor system with a squeeze film damper (SFD) using magnetic fluid. An electromagnet is installed in the inner damper of the SFD. The magnetic fluid is well known as a functional fluid. Its rheological property can be changed by controlling the applied current to the fluid and the fluid can be used as lubricant. Basically, the proposed SFD has the characteristics of a conventional SFD without an applied current, while the damping and stiffness properties change according to the variation of the applied electric current. Therefore, when the applied current is changed, the whirling vibration of the rotor system can be effectively reduced. The clustering-based hybrid evolutionary algorithm (CHEA) is used to identify linear stiffness and damping coefficients of the SFD based on measured unbalance responses.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.11 s.104
• /
• pp.1262-1267
• /
• 2005

The paper presents the identification of dynamic property of a rotor system with a squeeze film damper (SFD) using magnetic fluid. An electromagnet Is installed in the inner damper of the SFD. The magnetic fluid is well known as a functional fluid. Its rheological property can be changed by controlling the applied current to the fluid and the fluid can be used as lubricant. Basically, the proposed SFD has the characteristics of a conventional SFD without an applied current, while the damping and stiffness Properties change according to the variation of the applied electric current. Therefore, when the applied current is changed, the whirling vibration of the rotor system can be effectively reduced. The clustering-based hybrid evolutionary algorithm (CHEA) is used to identify linear stiffness and damping coefficients of the SFD based on measured unbalance responses.

• Journal of the Korean Ceramic Society
• /
• v.31 no.3
• /
• pp.298-304
• /
• 1994

Water-based magnetic fluids were made of the synthesized ultrafine magnetite with surfactants such as sodium oleate and loeic acid. The water-based magnetic fluid was prepared under the condition that added amounts of sodium oleate and oleic acid dissolved with NH4OH were 2.64$\times$10-2 mol, 1.5~2.0$\times$10-2 mol respectively. The water-based magnetic fluid was stable and should be dispersed well dispersion in the range of pH 9.0 to pH 11.0. As the solid content increased from 0.05 g/cc to 0.4 g/cc, the viscosity of water-based magnetic fluids increased from 2.5 cP to 152 cP and their magnetization at 5 KOe linearly increased from 3.1 emu/g to 26 emu/g. The aggregated powder after drying the water-based magnetic fluid was also successfully re-dispersed in dilute NH4OH solution and in kerosene.