• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.512-519
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• 2009

Flow pulsation in the gap connecting with two parallel channels is investigated by RANS and URANS approaches. The two parallel channels are connected by a small channel called for a gap. The parallel channels are designed to have different cross section area with its ratio of 0.5. Computations are conducted using a CFX 11.0 code. The bulk Reynolds number is 60,000. Predicted results are compared with the previous experimental data. Mean velocity profile at the center of gap region are compared with experiments for its validation. Spectral analysis on the lateral velocity in the center of the gap was performed. Auto correlation for the axial-flow velocity pattern was presented. The unsteady structure of the flow pulsation was visualized in the region of the gap in the parallel channel.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2810-2815
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• 2008

Flow pulsation in the gap connecting with two parallel channels is investigated by RANS and URANS approaches. The two parallel channels are connected by a small channel called for a gap. The parallel channels are designed to have different cross section area with its ratio of 0.5. Computations are conducted using a CFX 11.0 code. The bulk Reynolds number is 60,000. Predicted results are compared with the previous experimental result. Mean velocity profile at the center of gap region are compared with experiments for its validation. Spectral analysis on the lateral velocity in the center of the gap is presented. Auto and cross correlation for the axial-flow velocity pattern are presented. The unsteady structure of the flow pulsation was visualized in the region of the gap in the parallel channel.

• Wind and Structures
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• v.10 no.5
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• pp.463-479
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• 2007

A series of wind tunnel sectional model dynamic tests of a twin-deck bridge were conducted at the CLP Power Wind/Wave Tunnel Facility (WWTF) of The Hong Kong University of Science and Technology (HKUST) to investigate the effects of gap-width on the self-excited vibrations and the dynamic and aerodynamic characteristics of the bridge. Five 2.9 m long models with different gap-widths were fabricated and suspended in the wind tunnel to simulate a two-degrees-of-freedom (2DOF) bridge dynamic system, free to vibrate in both vertical and torsional directions. The mass, vertical frequency, and the torsional-to-vertical frequency ratio of the 2DOF systems were fixed to emphasize the effects of gap-width. A free-vibration test methodology was employed and the Eigensystem Realization Algorithm (ERA) was utilized to extract the eight flutter derivatives and the modal parameters from the coupled free-decay responses. The results of the zero gap-width configuration were in reasonable agreement with the theoretical values for an ideal thin flat plate in smooth flow and the published results of models with similar cross-sections, thus validating the experimental and analytical techniques utilized in this study. The methodology was further verified by the comparison between the measured and predicted free-decay responses. A comparison of results for different gap-widths revealed that variations of the gap-width mainly affect the torsional damping property, and that the configurations with greater gap-widths show a higher torsional damping ratio and hence stronger aerodynamic stability of the bridge.

• Journal of the Korean institute of surface engineering
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• v.53 no.3
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• pp.124-129
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• 2020

This study is for the development of high temperature ALD SiO₂ film process, optimized for gap-fill process in manufacturing memory products, using a space-divided PE-ALD system equipped with an independent control dual plasma system and orbital moving unit. Space divided PE-ALD System has high productivity, and various applications can be applied according to Top Lid Design. But space divided ALD system has a limitation to realize concentric deposition map due to process influence due to disk rotation. In order to solve this problem, we developed an orbit rotation moving unit in which disk and wafer. Also we used Independent dual plasma system to enhance thin film properties. Improve productivity and film density for gap-fill process by having deposition and surface treatment in one cycle. Optimize deposition process for gap-fill patterns with different depths by utilizing our independently controlled dual plasma system to insert N₂and/or He plasma during surface treatment, Provide void-free gap-fill process for high aspect ratio gap-fill patterns (up to 50:1) with convex curvature by adjusting deposition and surface treatment recipe in a cycle.

• Journal of Labour Economics
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• v.42 no.1
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• pp.43-72
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• 2019

As a result of decomposing the wage gap between large enterprises and SMEs using Oaxaca's wage gap decomposition method, the total wage gap of supply side factors was 44.2%, and the service years and educational background were the biggest influences. and As a result of decomposing the wage gap by firm size based on demand side factors such as business performance, total wage gap was 44.9%, and the influence on wage gap was in the order of labor productivity, union and outsourcing ratio. The results of this analysis suggest that it is necessary to consider the demand side factors such as business performance and capital structure of supply side companies such as differences in human capital in order to solve wage gap by firm size.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.7
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• pp.643-655
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• 1991

The analysis method on air gap permeance distribution, air gap MMF distribution, air gap flux density distribution, cogging torque and BEMF about the skewed stator slots or the skewed rotor magnet segments for BLDCM, respectively, is studied as a function of the skew ratio. The proposed method describes the differences between the skewed stator slots and teh skewed rotor magnet segments for the air gap permeance distribution, air gap MMF distribution and air gap flux density distribution. The reliability of the method is also confirmed by the waveform of the cogging torque and BEMF through experiments. And the result shows that the effects on the cogging torque and BEMF due to the skewed stator slots or the skewed rotor magnet segments are the same. In case of the skewed stator slots, the effects of the variations of the winding resistance and inductance are also studied.

• Journal of Korea Foundry Society
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• v.29 no.6
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• pp.270-276
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• 2009

After casting button-type small ingots of ternary Fe-Mn-S alloys which had three different Mn/S ratios (1, 5 and 70) in a vacuum arc furnace, the effect of the ratio on the sulfide formation was investigated. In case of the Mn/S ratio of 1, if alloy composition was located in an iron-rich corner on a Fe-Mn-S ternary phase diagram, only duplex MnS-FeS sulfide films were observed in the grain boundary. If the alloy composition was located in the miscibility gap area of the phase diagram, primary globular dendritic sulfides and dendritic sulfide slags were generated within the grain and tubular monotectic sulfides were also detected in the grain boundary. When the Mn/S ratio was 5, if the alloy composition was in the iron-rich corner, only bead-like sulfides were generated. On the other hand, if the composition was in the miscibility gap area, globular dendritic sulfides and dendritic sulfide slags were generated in the form of primary sulfide inclusions and rod-like eutectic sulfides were observed in the grain boundary. Especially, if the contents of Mn and S increased more in the miscibility gap area of the phase diagram, primary globular sulfides containing iron intrusions were observed. In case of Mn/S ratio of 70, if the contents of Mn and S was decreased in the Fe corner of the phase diagram, only bead-like sulfides were observed in the grain boundary. Despite the composition was outside the miscibility gap area of the phase diagram, if the contents of Mn and S increased, clusters of fine sulfide particles as well as fine spherical primary monophase sulfides were observed in the grain boundary.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.387-392
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• 2003

This study is put a focus on the identification of sound characteristics according to the interior configuration of sound absorption material and air gap. Noise barrier is general consists of front perforated panel, air layer, sound absorption material, air gap and back plate. Noise barrier is required to the NRC value of 0.7. The absorbing performance of the noise barrier relies on the opening ratio of the perforated panel and the efficiency of the absorbing material. This study has observed the effect of opening ratio and hole size, the increase of sound absorbing performance by the configurations of sound absorption material and air gap. New designed noise barrier is achieved the acoustical performance of 0.87 the measurement in a reveration room.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.199-208
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• 2021

The extrudability of 3D printed concrete and its member strength can be highly influenced by water cement ratio (W/C) and printing time gap (PTG). In this study, mold cast specimens and 3D printed specimens were fabricated with variables of W/C ratio and PTG, and their shear bond strength and interlayer surface moisture content were measured and analyzed. The test results showed that the shear bond strength is greatly influenced by the amount of interlayer surface moisture. It is thus recommended that proper amount of interlayer surface moisture with respect to PTG needs to be maintained to have a required interlayer shear bond strength. In addition, further research is required to estimate the effect of many environmental factors that can influence the interlayer surface moisture content.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.171-173
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• 1995

Slot field harmonics exist in air gap due to inevitable slot constructure of induction motors. They give rise to noise by the electromagnetic vibration and mechanical pulsation. We calculate the slot field harmonics for varying the ratio of slot width vs teeth pitch using the carter's coefficent. We computate the flux density in air gap by FEM(Finite Element Method) and analyze it in frequency domain using DFT(Discrete Fourier Transform). We develop the new algorithm mixing FEM with DFT.