• Tribology and Lubricants
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• v.38 no.5
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• pp.205-212
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• 2022

This paper presents experimental measurements of the structural characteristics of a two-pad beam-type gas foil journal bearing and its rotordynamic performance for a high-speed motor-driven turbocompressor. The test bearing had two top foils and two beam foils, each with an arc length of ~180°. Each beam foil was etched to obtain 40 beams with six geometries of different lengths and widths. The insertion of beam foils into the bearing housing produces equivalent beam heights. The structural tests of the bearing with a non-rotating journal revealed a smaller bearing clearance and larger structural stiffness for the load-on-pad configuration than for the load-between-pads configuration. Rotordynamic performance measurements during driving tests up to 100 krpm demonstrated synchronous vibrations and subsynchronous vibrations with large amplitudes. The test was repeated after inserting the shim between the top foil and beam foil to reduce the bearing radial clearance. The reduced bearing clearance resulted in a reduction in the peak amplitude of the synchronous vibrations and an increase in the speed at which the peak amplitude occurred. In addition, the onset speed and amplitude of the subsynchronous vibrations were dramatically increased and diminished, respectively. The rotor coast-down tests at 100 krpm show that the reduction in the bearing clearance extends the time to rotor stop, thus implying an improvement in hydrodynamic pressure generation and a reduction in bearing frictional torque.

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.195-197
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• 2006

The present study examined the characteristics of high speed welding thin metal sheet using single mode fiber laser of averaged maximum output power 300 W. Due to the fiber laser that has a good quality of beam can make a very small focusing beam size, thin metal sheet welding and high speed key hole welding can be peformed by high power density.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.415-418
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• 1999

This paper presents a study in the ductility of reinforced concrete beam-column-slab joints Three assemblies were designed 2/3 scale (f'c=240kg/$\textrm{cm}^2$, f'c=700kg/$\textrm{cm}^2$) and tested to investigate seismic behavior. From the test results, 1) flexural cracks emerge to inside of beam deeply for high strength concrete member, 2) the high-strength specimens degraded in stiffness and strength, and unstable hysteretic behaviors were observed, owing to the brittleness of high-strength concrete beyond its range. 3) The confinement provided by the additional hoops to the column bar is probably the main reason for this improvement in behavior.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.323-326
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• 2005

Although many structures. with high strength concrete have been recently constructed, the flexural behavior of reinforced and prestressed concrete beams with high strength concrete is not exactly defined. This paper presents an experimental study on the flexural strength of the high strength concrete beams. Five large scale beams simply supported were tested and measured. Each beam was loaded by two symmetrical concentrated loads applied at 1.25m from the center of span. The concrete strength, the prestressed force and longitudinal tensile reinforcement ratio vary from beam to beam. From the experimental tests, the flexural strength from tests is larger than the nominal flexural strength of codes. Moreover, the initial crack-load is affected by the prestressed force and the crack width and spacing are controlled by the longitudinal tensile reinforcement ratio.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.2
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• pp.245-250
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• 2011

A high-resolution shadow mask, a nanostencil, is widely used for high resolution lithography. This high-resolution shadowmask is often fabricated by a combination of MEMS processes and focused ion beam (FIB) milling. In this study, FIB milling on 500-nm-thin SiN membrane was tested and characterized. 500 nm thick and $2{\times}2$ mm large membranes were made on a silicon wafer by micro-fabrication processes of LPCVD, photolithography, ICP etching and bulk silicon etching. A subsequent FIB milling enabled local membrane thinning and aperture making into the thinned silicon nitride membrane. Due to the high resolution of the FIB milling process, nanoscale apertures down to 60 nm could be made into the membrane. The nanostencil could be used for nanoscale patterning by local deposition through the apertures.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.501-501
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• 2012

A 2.45 GHz electron cyclotron resonance (ECR) plasma source with a belt magnet assembly configuration (BMC) was developed for hyperthermal neutral beam (HNB) generation. A plasma source for high flux HNB generation should be satisfied with the requirements: low pressure operation, high density, and thin plasma. The ECR plasma source with BMC achieved high density at low operation pressure due to electron confinement enhancement caused by high mirror ratio and drifts in toroidal direction. The 2.45 GHz microwave launcher had a circularly bended WR340 waveguide with slits. The microwave E-field profile induced by the microwave launcher was studied in this paper. The E-field profile was a cups field perpendicular to B-filed at ECR zone. The optimized E-field profile and B-field were found for effective ECR heating.

• Proceedings of the Korea Concrete Institute Conference
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• 1990.10a
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• pp.63-67
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• 1990

The purpose of this study was to investigate the effects of flexural strength ratio(Mr=$\Sigma$Mc/$\Sigma$Mb) with High-Strength Concrete up to 800Kg/$\textrm{cm}^2$. Five specimens were tested under reversed cyclic loadings. The primary variables were flexural strength ratio of the beam-column, compressive strength of concrete and loading patterns. The results showed that the failure at the beam-column joint in case of high strength concrete was severe more than in case of normal strength concrete when flexural strength ratio 1.4. Thus the part for low limit of flexural strength ratio(Mr=1.4) should be revised for high strengthconcrete.

• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.49-54
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• 1989

Thin solid film systems polarizing beam splitter and disk amplifier used in the high power laser system ({{{{ lambda }}0=1060nm) are designed by computer aided optimization technique. Extinction ratio of designed polarizing beam splitter for incidence angle 30$^{\circ}$, 45$^{\circ}$, 55.60$^{\circ}$ are 1:93, 1:895, 1:1991. respectively. Maximum reflectance of designed thin film system of disk amplifier is less than 3% for pumping band (500-900nm) and 0.15% for laser beam. Further, SiO film chosen as one of the suitable thin films in the high power laser system is prepared by the sol=-gel process which gives high damage threshold. When the withdrawal speed is 6.15cm/min -16.62 cm/min and the mixing ratio is in the range of 1 mol (ethylsilicate): 4-8mol(ethylalcohol) : 2mol(water), the thickness of deposited film is in the range of 500{{{{ ANGSTROM }}-1500{{{{ ANGSTROM }}.

• Current Optics and Photonics
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• v.2 no.5
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• pp.431-435
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• 2018

A modified setup of a CMD technique for high power coherent beam combining was presented to address an issue of low damage threshold of electro-optic modulators. The feasibility of the modified setup was demonstrated by combining eight fiber beams, and it was successfully performed with ${\lambda}/44$ of residual phase error and 100 Hz of control bandwidth. It is expected that the modified CMD setup facilitates ultra-high power coherent beam combination without a limitation caused by the low damage threshold of electro-optic modulators.

• Journal of Welding and Joining
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• v.21 no.5
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• pp.568-574
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• 2003

In the welding for the steel structure of H-beam with mild steel and 490N/$\textrm{mm}^2$ high tensile steel, we applied the fillet weld mostly and 6-8mm weld length(AISC-spec.). And a new developed metal-cored-wire is used in automatic welding as well as semi-automatic welding. In this study we have attempted to raise the welding productivity and to stabilize the quality on horizontal positions of fillet welding with the following items: - We improved the weld productivity using metal based cored wire with a high deposition rate in the steel structure of H-beam. - We tested the weldability and evaluated the quality of the weldmetal by horizontal fillet $CO_2$ welding. The process is carried out in combination with a special purpose metal-based FCW with excellent resistance to porosity and high welding speed. - We studied the micro structure of the weldmetal by the various welding conditions. - We studied the effect of welding residual stress by the welding conditions in T-joint. Therefore, it can be assured that more productive and superior quality of the weldmetal can be taken from this study results.