• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.906-910
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• 2003

This paper numerically analyzes the dynamic characteristics of a spindle system supported by two identical journal bearings considering bearing span that has dynamic load due to its mass unbalance. The Reynolds equation is transformed to solve a herringbone grooved journal bearing. The Reynolds equations are solved using FEM in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or angular displacement of a rotor, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This research shows that the same bearing spans of upper and lower journal bearings produce the minimum runout and friction torque of a spindle system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.3
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• pp.301-312
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• 2009

This paper presents a theoretical approach to calculate the resonant frequency of a thickness vibration mode in the radial direction for a 1-3 piezoelectric composite transducer of circular arch shape. For the composite transducer composed of a piezoelectric ceramic and a polymer, vibration parameters were derived according to the volume ratio of a ceramic, and a vibration characteristic equation was derived from the piezoelectric governing equations with adequate boundary conditions. The fundamental resonant frequencies were calculated numerically and verified by comparing them with those obtained from the finite element analysis and the experiment. The volume ratio and the thickness are more substantial than the curvature radius to determine the fundamental resonant characteristics, and the fundamental resonant frequency becomes higher for the larger volume ratio of the piezoelectric ceramic and for the smaller thickness.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.242-248
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• 2000

This paper has focused on the optimization of the cutting parameters for turning operation based on the Taguchi method. Four cutting parameters, namely, cutting speed, feed, depth of cut and nose radius are optimized with consideration of the surface roughness. The design and analysis of experiments are conducted to study the performance characteristic. The effects of these parameters on the surface roughness have been investigated using the signal-to-noise (S/N) ratio, analysis of variance (ANOVA). The experiments have been peformed using coated tungsten carbide inserts without any cutting fluid. Experimental results illustrate the effectiveness of this approach.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.11
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• pp.930-936
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• 2008

This paper studies the effect of pad at initial stage and wear during braking on the dynamic contact pressure distribution. Wear is influenced by variable factor (contact pressure, sliding speed, radius, temperature) during dynamic braking and variation in contact pressure distribution. Many researchers have conducted complex eigenvalue analysis considering wear characteristic with Lim and Ashby wear map. The conventional analysis method is assumed the pad has smooth and flat surfaces. The purpose of this paper is to validate that wear rate induced by braking is considered for the precise squeal prediction. After obtaining pad wear from experiment, it is incorporated with FE model of brake system. Finally, the comparisons in fugitive nature of squeal will be carried out between the complex eigenvalue analysis and noise dynamometer experiment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1202-1209
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• 2002

This paper presents the characteristics of the radial vibration of cylindrical piezoelectric transducers. The differential equations of piezoelectric radial motion have been derived in terms of the radial displacement and electric potential, which are functions of the radial and axial coordinates. Applying mechanical and electrical boundary conditions has yielded the characteristic equation of radial vibration. Numerical results of the natural frequencies have been compared with the experimental observations reported earlier for the transducers of several sizes, and have shown a good agreement for the fundamental mode. The paper discusses the dependence of the natural frequencies on the radius and thickness of the piezoelectric cylinders and the difference between Piezoelectric and elastic resonances

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.4
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• pp.373-380
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• 2010

An interest is increased of environment and energy so, importance on railroad high energy efficiency is magnified. And after Gyeong-bu High speed rail is completed, share rate freight transportation of railroad is expected to be gradually increased due to expand investment for railroad and operate mainly freight transportation on convention line. Therefore a research on DMT freight cars is necessary under like this situation. In paper, we developed analysis model for DMT freight car and DMT freight was analyzed numerically using VI-Rail in each condition of railway having different curve and carried out vibration analysis on curving using developed analysis model. And we carried out test on driving stability follow changing curve radius then measure against UIC code 518.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.9 s.90
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• pp.779-784
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• 2004

This paper numerically analyzes the dynamic characteristics of a spindle system supported by two identical journal bearingsconsidering bearing span that has dynamic load due to its mass unbalance. The Reynolds equation is transformed to solve a herringbone grooved journal bearing. The Reynolds equations are solved using FEM in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or angular displacement of a rotor, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This research shows that the same bearing spans of upper and lower journal bearings produce the minimum runout and friction torque of a spindle system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1152-1156
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• 2003

Hard disk drives (HDD) in computer are used extensively as data storage capacity. The trend in the computer industry to produce smaller disk drives rotating at higher speeds requires an improved understanding of fluid motion in the space between disks. PIV measurement was used fer the unsteady flow between the center pair of four disks of four times larger than common radius of HDD disk at several rpm in a fixed cylindrical enclosure. The boundary between inner region and outer region is detected using PIV measurement and the number of dominant vortices s determined clearly. Tip vortices generated by an obstruction with actual-like configuration can be found at inner region. Oscillating flow from the obstruction appears at outer region with complex flow pattern.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.945-956
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• 2000

The axisymmetric bodies considered in this study have hemispherical and ellipsoidal noses. The near-field pressure fluctuations over each nose model at $Re_D=2.43{\times}10^5$ were investigated in the laminar separation region and developing turbulent boundary layers using a 1/8' pin-holed microphone sensor. The wall pressure fluctuations were also measured in an axisymmetric boundary layer on a cylinder parallel to mean flow at a momentum thickness Reynolds number of 850 and a boundary layer thickness to cylinder radius ratio of 1.88.

• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.2
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• pp.80-87
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• 2011

Low temperature hole transport characteristics of gate-all-around p-channel metal oxide semiconductor (PMOS) type silicon nanowire field-effect-transistors with the radius of 5 nm and lengths of 44-46 nm are presented. They show coexisting two single hole states randomly switching between each other. Analysis of Coulomb diamonds of these two switching states reveals a variety of electrostatic effects which is originated by the potential of a single hole captured in the trap near the nanowire.