• Korean Journal of Computational Design and Engineering
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• v.22 no.2
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• pp.190-201
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• 2017

This paper proposes how to solve a problem of FDM 3D printer's irregular output when changing volume of extrusion, adjusting movement speed of the printer's head and a way to fill new inner part. Existing slicers adjust directly to change the rotation speed of the stepper. In this method, the change of the extrusion area is delayed due to the gap between the stepper and the nozzle, so that precise control is difficult. We control the extrusion area adjusting the moving speed of the print head and making constantly the rotation speed of the stepper. Thus, the output time can be shortened by generating an efficient path having a short travel distance. For evaluation, we applied our method to lithophanes with detailed variation. Comparing existing methods, our method reduced output time at least 30%.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.66-71
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• 2008

Two cases with circumferential grooves were designed for a transonic compressor, and 3-D numerical simulations were conducted for stall mechanism at three representative speeds. A conclusion can be drawn from the comparison between compressors with or without casing treatment that: with the rising of rotation speed, stall margin increases dramatically under the help of casing treatments, and the case with middle grooves has reasonable compromise between stall margin increment and efficiency cutting. At lower speed, the increment reduces, and grooves at the back of blade tip have more influence on stall margin. Further investigation shows there is a transition in mechanism of compressor stall with the decline of rotational speed: at high rotation speed, the expansion of stall margin mainly results from the suppression of tip leakage vortex by casing treatments, yet it benefits more from the depression of boundary layer separation from suction surface of blade tip.

• Korean Journal of Materials Research
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• v.34 no.1
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• pp.55-62
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• 2024

Fluorine-doped tin oxide (FTO) has been used as a representative transparent conductive oxide (TCO) in various optoelectronic applications, including light emitting diodes, solar cells, photo-detectors, and electrochromic devices. The FTO plays an important role in providing electron transfer between active layers and external circuits while maintaining high transmittance in the devices. Herein, we report the effects of substrate rotation speed on the electrical and optical properties of FTO films during ultrasonic spray pyrolysis deposition (USPD). The substrate rotation speeds were adjusted to 2, 6, 10, and 14 rpm. As the substrate rotation speed increased from 2 to 14 rpm, the FTO films exhibited different film morphologies, including crystallite size, surface roughness, crystal texture, and film thickness. This FTO film engineering can be attributed to the variable nucleation and growth behaviors of FTO crystallites according to substrate rotation speeds during USPD. Among the FTO films with different substrate rotation speeds, the FTO film fabricated at 6 rpm showed the best optimized TCO characteristics when considering both electrical (sheet resistance of 13.73 Ω/□) and optical (average transmittance of 86.76 % at 400~700 nm) properties with a figure of merit (0.018 Ω^-1).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.7-13
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• 2017

A comfortable indoor environment is important considering that many hours are spent in residential or office space. A humidifier is used to control the indoor humidity. In particular, an element type humidifier has the advantage of a simple structure and low energy consumption. Two types of humidifiers - stationary or rotor - are commonly used for residential purposes. In this study, performance optimization was conducted for a rotor-type humidifying element used in a residential humidifier. The optimization included the rotation speed, water submersion depth, etc. The test range consisted of an open area to the air from 57 to 90%, rotation speed from 0.2 to 2.0 rpm, frontal air velocity from 0.5 to 2.5 m/s. The results showed that the optimal open area to air was 70%. On the other hand, the effects of the rotation speed on the moisture transfer rate was negligible. On the other hand, the pressure drop increased with increasing rotation speed. As the frontal air velocity increased, both the moisture transfer rate and pressure drop increased. The humidification capacity of the present element was 0.08 ~ 0.31 kg/hr. A comparison of the data with the theoretical results was made.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.7
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• pp.113-120
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• 2021

An experimental device was designed to control the opening of a damper via operating the folding blade drive of the device and to control the amount of air flowing through the damper. In addition, an inverter was installed in the blower to control its fan rotation speed and hence the amount of air flowing through the damper. An experimental study was conducted on the opening of the folding blade damper and changes in the rotational speed of the blower. From the results, the theoretical air volume of the folding blade damper and experimental air volume were observed to be in good agreement within an error range of ±3%. As the mass flow rate of the air passing through the folding blade damper increases proportionally with the changes in damper opening and fan rotation speed, the performance of the damper can be controlled proportionally. The mass flow rate was also observed to increase linearly; therefore, the mass flow rate of the air passing through the folding blade damper increases proportionally with changes in the rotation speed of the blower, such that the performance of the damper is proportional to a constant air volume even with varying rotation speeds of the blower.

• Korean Journal of Child Studies
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• v.20 no.3
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• pp.293-306
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• 1999

This study investigated children's spatial skills and short term memory ability based on their practice with computer games. The 40 four-year-old and 40 six-year-old subjects were divided by experimental and control groups. Spatial skills of children were assessed by visual speed, mental rotation, and spatial visualization tasks. Short term memory was measured with a digit span task. Results showed that computer game practice enhanced children's memory ability and spatial skills. Even 4-year-olds performed better on mental rotation and spatial visualization tasks after practice. The treatment effect was significant for visual speed of 6-year-olds, short term memory ability and mental rotation of 4-year-olds, and spatial visualization of both 4- and 6-year-olds.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.6
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• pp.15-20
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• 2007

Recently the machine industry is rapidly advanced for improving productivity. Especially an effort decreased error factors of machine tool continuously is being studied. In this paper, we propose a method that decreased vibration in the high speed spindle. By appling 6-sigma technique(DMADOV), we can grasp the influence between the housing design and a rotation accuracy. For a correct conclusion, we measure an actual spindle and analysis by $ARMD^{(R)}$(rotation analysis program). inally we find out influenceable design factors and the improvement condition about 20.7%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.279-282
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• 2004

In this paper, A new type of piezoelectric step motor using piezoelectric torsional actuator and a pair of one-way clutch bearing is designed, manufactured and tested. The torsional actuator consists of 16-polygonal tube that can produce angular displacement using shear mode of piezoceramic. One-way clutch bearing convert oscillation of torsional actuator into continuous rotation. After performance testing of torsional actuator, the optimum condition for driving motor is investigated in terms of wave shape, excitation frequency and electrical field. The performance of the motor is experimentally evaluated. As a result, square wave has larger rotation speed than sin wave, and the maximum rotation speed of 57 rpm is measured at 3850 Hz and 100V/mm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.614-618
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• 2018

The changes in the mechanical properties according to the width of the tool shoulder, rotation speed and moving speed in friction stir welding (FSW) are evaluated using Al 6061-T6. The results indicated that the tensile strength value increases with increasing rotation speed. The higher the moving speed of the tool shoulder, the lower the tensile strength, regardless of the tool type. A higher tensile strength value was generally obtained with a tool shoulder diameter of 12mm (TSD12) than with 8mm. When the moving and rotation speeds exceed a limiting value, a stabilization stage is reached, in which (the tool shoulder diameter?) no longer affects the material properties. At a tool shoulder diameter of 8mm (TSD8), the material properties are decreased and the mixture of material in the welding area is incomplete in comparison with the tool type of TSD12. The tensile strength value is decreased at a rotation speed of 1500 rpm. As a result, a rotation speed higher than the threshold value is needed in order for and the transition temperature to be reached, which allows the complete mixing of the material in the welding area.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.184-193
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• 2006

Rotation of intake and exhaust valves are very closely related to the long term durability of automotive engines. If the valves do not rotate even at a rated engine speed, it causes the uneven wear of the valve seat and valve head contact area, which eventually shortens the engine life. A principle of valve rotation mechanism was presumed based on some findings from experiments, and computer programs were developed to simulate the valve rotation phenomena. In this study we investigated the valve rotation mechanism by using the computer simulation models.