• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1989년도 제10회 학술강연회초록집
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• pp.94-99
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• 1989

This paper analyzes file stiffness, damping coefficient, friction force and flow coefficient of externally pressurized oil journal beating, including the effect of journal rotation according to the Sommerfeld number. This paper assumed that the oil in the whole pocket has constant pressure, and that the oil in the whole bearing region has constant viscosity, temperature and density. Reynolds equation is derived from Nuvier - Stokes equation and continuity equation. And solved bearing pressure by ADI method for whole bearing region and fitted with out flow rate of pocket region. The model for numerical simulation is hydro - static oil journal bearing for high-speed, high-accuracy lathe spindle.

• 한국재료학회지
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• 제23권7호
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• pp.373-378
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• 2013

In order to clarify the effect of C/Ti atom ratios(${\chi}$) on the deformation behavior of $TiC_{\chi}$ at high temperature, single crystals having a wide range of ${\chi}$, from 0.56 to 0.96, were deformed by compression test in a temperature range of 1183~2273 K and in a strain rate range of $1.9{\times}10^{-4}{\sim}5.9{\times}10^{-3}s^{-1}$. Before testing, $TiC_{\chi}$ single crystals were grown by the FZ method in a He atmosphere of 0.3MPa. The concentrations of combined carbon were determined by chemical analysis and the lattice parameters by the X-ray powder diffraction technique. It was found that the high temperature deformation behavior observed is the ${\chi}$-less dependent type, including the work softening phenomenon, the critical resolved shear stress, the transition temperature where the deformation mechanism changes, the stress exponent of strain rate and activation energy for deformation. The shape of stress-strain curves of $TiC_{0.96}$, $TiC_{0.85}$ and $TiC_{0.56}$ is seen to be less dependent on ${\chi}$, the work hardening rate after the softening is slightly higher in $TiC_{0.96}$ than in $TiC_{0.85}$ and $TiC_{0.56}$. As ${\chi}$ decreases the work softening becomes less evident and the transition temperature where the work softening disappears, shifts to a lower temperature. The ${\tau}_c$ decreases monotonously with decreasing ${\chi}$ in a range of ${\chi}$ from 0.86 to 0.96. The transition temperature where the deformation mechanism changes shifts to a lower temperature as ${\chi}$ decreases. The activation energy for deformation in the low temperature region also decreased monotonously as ${\chi}$ decreased. The deformation in this temperature region is thought to be governed by the Peierls mechanism.

• 천문학회지
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• 제29권2호
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• pp.207-215
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• 1996

To derive coronal temperature, electron density and nonthermal velocity, we have analyzed high resolution spectra (e.g., Fe XII 338.3, Fe XII 352.1, Fe XIV 334.2, Fe XIV 353.8, Fe XV 284.2, Fe XV 321.8, Fe XV 327.0, Fe XVI 335.4, and Fe XVI 360.8) taken from AR 6615 by SERTS (Solar Extreme Ultraviolet Rocket Telescope and Spectrograph). Important findings emerging from the present study are as follows: (1) Temperature estimated from Fe XVI 335.4 and Fe XIV, 334.2 is $\~2.4\times10^6 K$ and no systematic difference in temperature is found between the active region and its adjacent quiet region; (2) Mean electron density estimated from Fe XV is $\~3\times10^9 cm^{-3}\;and\;\~10^{10} cm^{-3}$ from Fe XII and Fe XIV; (3) Mean density of the active region is found to be higher than that of the quiet region by a factor of 2; (4) Nonthermal velocity estimated from Fe XV and Fe XVI is $20\times25 km\;s^{-l}$ which decreases with increasing ionization temperatures. This supports the notion that the nonthermal velocity declines outwards above the transition region.

• 한국기계가공학회지
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• 제2권1호
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• pp.22-31
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• 2003

The compressive residual stress, which is induced by shot peening process, seems to be an Important factor in increasing the fatigue strength. And then it was showed that residual stress was disappearenced at the high temperature. The fatigue charateristic investigation of a SUP9 spring steel processed shot peening is performed by considering the high temperature service conditions in the range of room temperature through $180^{\circ}C$ in the range of stress ratio of 0.3 by means of opening mode displacement. The fatigue resistance characteristics and fracture strength at high temperature is considerable lower than that of room temperature in the early stage and stable of fatigue crack growth region.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.347-353
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• 2002

The compressive residual stress, which is induced by shot peening process, seems to be an important factor of increasing the fatigue strength. And then it was showed that residual stress was disappearenced at the high temperature. The fatigue characteristic study of a SUP9 spring steel processed shot peening is performed by considering the high temperature service conditions in the range of room temperature through $180^{\circ}C$ in the range of stress ratio of 0.3 by means of opening mode displacement. The fatigue resistance characteristics and fracture strength at high temperature is considerable lower than that of room temperature in the early stage and stable of fatigue crack growth region.

• 한국분무공학회지
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• 제3권3호
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• pp.1-13
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• 1998

In this study, an experimental study was performed to investigate the breakup mechanism of vaporizing droplet. A well-controlled experimental apparatus was used to study breakup mechanisms of a monodisperse stream of drops injected into a transverse high temperature and velocity air stream. The experiments gave information$ about the microscopic structure of the liquid drop breakup process, drop breakup regimes, and drop trajectories in high temperature flow region. The breakup time, drop acceleration and wavelength of surface instability wave were measured from a high-magnification and double spark photography. The two instability theories, i.e., Kelvin-Helmholtz instability and Rayleigh-Taylor instability, were estimated by comparing the calculated data with the measurements. The results showed that the breakup time in high temperature flow condition is shortened because the surface tension is decreased by the increase of gas temperature.

• 한국대기환경학회지
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• 제24권5호
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• pp.523-537
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• 2008

In Korea, the global warming leads to more frequent high temperature region. increasing the need for research into physical damage caused by high temperature. We therefore analyzed the differences of mortality, caused by extreme heat, among gender and age. We also examined the trend of mortality from high temperature-sensitive diseases. Women are more affected by exposure to high temperature than are men; People over 65 years old have higher mortality rate (1.5 times) than under 65. As for high temperature-related diseases, cerebrovascular disease was the number one cause of death, and chronic lower respiratory disease and cardiovascular disease followed.

• 설비공학논문집
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• 제15권12호
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• pp.1078-1087
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• 2003

Kimchi refrigerator is a household electric appliance developed with the wholly domestic technology for maturing and keeping kimchi. However, the principle of keeping is not yet revealed obviously. This numerical study has been conducted to investigate the flow and heat transfer characteristics in a kimchi refrigerator. The effects of arrangement variation of a evaporation tube are examined. Also, the heat transfer characteristics through the insulation material are discussed in detail. The flow and temperature field was simulated using the commercial code of CFX-5.3. A natural convection flow is formed through about 5/6 region from the bottom within the keeping space and accordingly, the 90% region of kimchi containers satisfies the temperature requirement with 0$\pm$0.5$^{\circ}C$. The stagnant flow exists in the upper 1/6 region of the keeping space and accordingly, the stratified high temperature distributions appear in the upper region of kimchi containers. The upward shift of the start location of a evaporation tube improves the temperature concentration toward $0^{\circ}C$ but the pitch variation is of no effect. The heat fluxes on the insulation surfaces show two-dimensional distributions with being higher toward the center. Through the variation of insulation thickness, 3.5% saving of insulation material is obtained under the same heat transfer rate.

• 한국주조공학회지
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• 제42권6호
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• pp.392-397
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• 2022

In order to compliant the stringent exhaust emission regulations, higher fuel efficiency and cleaner exhaust gas in combustion engines have been required. To improve combustion efficiency, an exhaust gas temperature is increasing, therefore higher temperature resistance is required for components in exhaust system, especially turbine wheel in turbocharger. IN100 looks quite attractive candidate as it has high temperature properties with low density, however it has low castability due to poor ductility at high temperature. In this study, the balance of Al and Ti composition was optimized from the base alloy IN100 to improve the high temperature ductility by expanding the γ single phase region below the solidification temperature, while obtaining the high temperature strength by maintaining the volume fraction of γ' phase equivalent to IN100 around 1000℃. Furthermore, the high temperature creep rupture life increased by adding a small amount of Ta. The alloy developed in this study has high castability, low density and high specific strength at high temperature.

• 열처리공학회지
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• 제4권4호
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• pp.44-52
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• 1991

The effect of deformation temperature and manganes contents on the tensile properties of duplex stainless steels with the structure of both ferrite and austenite were investigate. For this investigation, Fe-19% Cr-5% Ni-4~8% Mn alloys were prepared. The result obtained from this experiment are summerized as follows. With decreasing deformation temperature, tensile strengths of duplex stainless steel increased. Elongation showd to be increased and then decreased after representing the highest value at specific temperature. Tensile properties of duplex stainless steel were controlled by TRIP behavior in this experimental range of austenite contents. Tensile strengths decreased with increasing Mn contents. With increasing Mn contents, elongation decreased in the high temperature region, but increased in the low temperature region. The peak temperature representing the maximum elongation were changed to low temperature and the width of peak appeared to be broaden with increasing Mn contents.