• Proceedings of the KIPE Conference
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• 2003.11a
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• pp.90-94
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• 2003

Recently, many nations have released standard such as IEC 1000-3-2 and IEEE 519 which impose a limit on the harmonic current drawn by equipment connected to AC line in order to prevent the distortion of an AC line. Among the wide variety of active methods for improving power factor and harmonic distortion, the boost converter is very effective because it has a continuous line current , small choke filter and high power factor. In high power application, however, the bridge diode loss in the boost converter has made the efficiency lower and the temperature of the board higher. A new approach without bridge diode to make the same characteristics of the conventional boost converter has also been developed. This paper present the comparisons between the continuous current mode(CCM) operated conventional boost converter and the boundary current mode(BCM) operated the bridgeless boost converter for high efficiency and high power factor.

• Journal of ILASS-Korea
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• v.20 no.1
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• pp.1-6
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• 2015

Visualization of the mixing pattern in a non-element mixer was carried out using laser induced fluorescence(LIF) to evaluate characteristics of mixer consisting of the main flow pipe and branch flow pipes. The branch flows were injected periodically with the period $T_{in}$ normal to the main flow, and rhodamine B was mixed into the most upstream branch flow to visualize mixing pattern in the main flow pipe by LIF. The length of boundary line L of the LIF image was measured. In this study, a numerical analysis was performed to identify the mixing process of the non-element mixer, and the results were compared with experimental results. Each result was almost the same. When the number of branch flows is increased, the mixing pattern became complicated and was supposed to become chaotic. The length of boundary line L increased exponentially with an increase in the number of branch flows.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.472-475
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• 2003

In this paper, insulating varnish has been used for field magnet and armature impregnated insulating material of electric locomotive and traction motor. When it was duplicated coating, it could be accuse internal void, and which could change electrical characteristics. We used to boundary elemental method of simulation tool, and improved optimal insulating design of insulating varnish according to measuring electric distribution in void of specimen.

• Transactions of the Society of Information Storage Systems
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• v.8 no.1
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• pp.27-32
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• 2012

Fluid dynamic bearings have several advantages that low noise, high rotational stability and low friction. So, early 2000s, the HDD spindle motors have been replaced ball bearings to fluid dynamic bearing. Most of studies apply inner boundary condition that is inside of bearing pressure larger than atmosphere pressure. Therefore, they used Half-Sommerfeld or Reynolds Boundary condition. This paper investigates the dynamic coefficients of the plain journal considered vapor pressure. As a result, it shows that the vapor pressure effect cannot ignore.

• Tribology and Lubricants
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• v.17 no.6
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• pp.467-475
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• 2001

Feasibility study of gas-lubricated bearing in micro gas turbine was performed. Based on Reynolds equation, finite difference method with coupled boundary was developed to analyze bearing characteristics, such as load capacity, mass flow rates and stiffness. By the bearing force and mass flow rates analysis with the variation of supply pressure, bearing clearance and capillary radius, acceptable range of design parameters were suggested in terms of load capacity and stiffness of bearings. Additionally, coupled boundary effect on pressure distribution was investigated and it is stated that coupling could reduce an excitation force due to narrow pressure distribution.

• Tribology and Lubricants
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• v.18 no.1
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• pp.9-15
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• 2002

The nonlinear vibration characteristics of hydrodynamic journal bearings with a circumferential groove we analyzed numerically when the external sinusoidal disturbances are given to the rotor-bearing system continuously. Furthermore, a cavitation algorithm, implementing the Jakobsson-Floberg-Olsson boundary condition, is adopted to predict cavitation regions in a fluid film more accurately than the conventional analysis. which uses the Reynolds boundary condition. It is found that the difference between linear and nonlinear analysis is much more remarkable as the amplitude of external disturbance increases, and it depends upon the excitation frequency of the external disturbance. It is also shown that the cavity region in the fluid film increases as the amplitude or excitation frequency of the external disturbance increases. The whirling center of the steady state orbit moves closer to the bearing center as the amplitude or excitation frequency of the external disturbance increases.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1995.03a
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• pp.9-16
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• 1995

The thermal deformation of machine tool spindle influences the performance of the manufacturing systems for precision products. In this research thermal analysis of a high speed machine tool spindle with the rolling bearing and the built-in motor is carried out using Finite Difference Method. The thermal boundary conditions describing the hear generation in the bearing and built-in motor are considered in the simulation. And various convective boundary conditions are assumed with the empirical formula in the references. From the simulation results the characteristics of each element affecting the dynamic thermal behaviour of the machine tool spindle systems have been clarified. This model can be well applied to the future development of the high speed spindle systems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.10
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• pp.836-843
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• 2008

An efficient domain/boundary decomposition method is applied for heat transfer problems with non-linear thermal radiation boundaries. The whole domain of solids or structures is considered as set of subdomains, an interface, and radiation interfaces. In a variational formulation, simple penalty functions are introduced to connect an interface or radiation interfaces with neighboring subdomains that satisfy continuity conditions. As a result, non-linear finite element computations due to the thermal radiation boundaries can be localized within a few subdomains or radiation interfaces. Therefore, by setting up suitable solution algorithms for the governing finite element equations, the computational efficiency can be improved considerably. Through a set of numerical examples, these distinguishing characteristics of the present method are investigated in detail.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.802-807
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• 2003

The purpose of this paper is to investigate the free vibration characteristics of tapered beams with translational and rotational springs and tip masses at the ends. The beam model is based on the classical Bernoulli-Euler beam theory. The governing differential equation for the free vibrations of linearly tapered beams is solved numerically using the corresponding boundary conditions. Numerical results are compared with existing solutions by other methods for cases in which they are available. The lowest three natural frequencies are calculated over a wide range of non-dimensional system parameters: the translational spring parameter, the rotational spring parameter, the mass ratio and the dimensionless mass moment of inertia.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.273-281
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• 2001

Feasibility study of gas-lubricated bearing in micro gas turbine was performed. Based on Reynolds equation, finite difference method with coupled boundary was developed to analyze bearing characteristics, such as load-carrying capacity, mass flow rates and stiffness. By the bearing force and mass flow rates analysis with the variation of supply pressure, bearing clearance and capillary radius, acceptable range of design parameters were suggested in terms of load capacity and stiffness of bearings. Additionally, coupled boundary effect on pressure distribution was investigated and it is stated that coupling could reduce all excitation force due to narrow pressure distribution.