• Journal of the Korean Society for Precision Engineering
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• v.14 no.11
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• pp.69-76
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• 1997

The rotating bending fatigue tests were performed using the specimens taken from Cr-Mo-V steel, widely sued in thermal power plant turbines, at various temperatures such as room temperature, 300 .deg. C, 425 .deg. C and 550 .deg. C. The characteristics of fatigue crack propagation were examined and analyzed by using fracture mechanics parameter. The plastic replica method was also applied in order to measure the crack length on the basis of serial observation of fatigue crack propagation behavior on the defected specimen surface. The fatigue crack propagation behavior of Cr-Mo-V steel was investigated within the frame work of elastic-plastic fracture mechanics. The propagation law of fatigue crack is obtained uniquely by using the term .sigma. $^{n}$ sub a/where .sigma. $_{a}$ is the service stress, a is the crack length and n is a constant. The values of constant n are nearly equal to 2.48, 2.60 and 8.61 at room temperature, 300 .deg. C and 425 .deg. C.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.449-458
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• 2016

The temperature data were measured for two years in a bridge specimen and the bridge in service nearby in order to calculate the effective temperature for thermal loads in steel box girder bridge. The maximum and minimum effective temperatures were calculated in the bridge specimen and the bridge according to air temperature in 2014, 2015 and 2years. The effective temperatures calculated in this study were compared the Euro code and the Highway Bridge Design Criteria. The coefficients of determination in the maximum effective temperature and the Euro code for 2 year were calculated from R = 0.927, R = 0.894 in a bridge specimen and the bridge respectively. Those of minimum temperature and the Euro code were analyzed from R = 0.992, R = 0.813 in two bridge respectively. Also, the results were evaluated as being very similar, or slightly increased as compared with the maximum temperature of the Korean Highway Bridge Design Code(Limit State Design).

• Journal of the Korean Society of Safety
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• v.38 no.1
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• pp.25-33
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• 2023

In this study, we determined the failure rate and fire status of electric motors widely used in domestic and industrial devices and analyzed the associated fire risks by identifying the electrical and temperature characteristics of electric motors under the normal and restrained operation modes in industrial sites and laboratories. A 2.2kW motor used for driving a conveyor during the vulcanization process in a rubber product manufacturing plant was employed as the study object and was exposed to a high- temperature environment as this motor is widely used in industrial sites. The current amplitude was 4.45-4.50 A during normal operation and 38.2-41.5 A during restrained operation due to the pinching of products and semi-finished products (i.e., 8.5 times higher than that during normal operation). The leakage current amplitude was 0.33 mA during both operation modes. The temperature of the workplace in summer was 42.38℃, indicating a poor environment for the installed motor. In the laboratory, the current and temperature of the coil inside a 3.7kW motor were measured under the restrained operation mode as performing measurements of the coil inside the motor in industrial sites is challenging. The current amplitude during normal operation was 3.5 A, whereas that during restrained operation for 30 s was 51.7-58.6 A, which is 14.8-16.7 times higher than that of normal operation. Moreover, the temperature of the motor coil increased from 22.9℃ to 101℃. Based on the experimental data, we derived the temperature increase formula according to the restrained operation time by performing a regression analysis and verified the time at which the temperature exceeded the stipulated limit for the insulation grade. The findings presented in this paper can be utilized to establish fire-prevention measures and perform safety management of motors of the same type or with a similar capacity.

• Journal of environmental and Sanitary engineering
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• v.23 no.2
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• pp.35-45
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• 2008

In order to recommend criteria for the administration law on indoor air quality, this study was conducted to examine the distribution and the concentration of indoor air pollutants ($PM_{10},\;CO_2$, CO, HCHO, TBC, $NO_2$, Rn, VOCs, asbestos, $O_3$) in public facilities in the Chung-Nam area. The concentrations of indoor air pollutants were obtained from sixty seven public facilities such as a cinema, an office, a restaurant, a theater and an academy. This study was performed from August to December, 2005. The results of this study showed that the concentrations of indoor air pollutants such as $PM_{10},\;CO_2$, CO, HCHO, TBC, Rn and $O_3$ were less than the recommended limits. However, the average concentration of VOCs was $521.73{\mu}g/m^3$ (GM : $221.69{\mu}g/m^3$), which was higher than the recommended limit of $400{\mu}g/m^3$. Moreover, the average concentration of $NO_2$ was 345.66ppb (GM : 69.95ppb), which was higher than the recommended limit of 50 ppb. The correlation between the concentrations of indoor air pollutants and the type of facilities with respect to $CO_2$, TBC and Rn was statistically low (p<0.05). However, the correlation was high in terms of the CO and $O_3$ concentrations (p<0.01). No relationship between the indoor air pollutants and the type of facilities was observed for $PM_{10}$, VOCs and $NO_2$. The year of construction was compared to the concentrations of indoor air pollutants. Specifically, when the construction date was less than 3 years, the HCHO, VOCs and TBC concentrations were $44.75{\mu}g/m^3,\;555.07{\mu}g/m^3$ and $337.79CFU/m^3$, respectively. These concentrations were $120{\mu}g/m^3$ and $211.84CFU/m^3$ higher for VOCs and TBC than the concentrations obtained from the facilities more than 3 years. However, the concentration of HCHO was similar between the facilities older and younger than 3 years of age. Year, temperature, humidity and indoor air pollutant correlation analyses showed that temperature and humidity, temperature and TBC, temperature and $O_3,\;PM_{10}$ and $NO_2$, HCHO and VOCs, $CO_2$ and Rn had positive relationships. However temperature and Rn, humidity and $CO_2,\;CO_2$ and $O_3,\;O_3$ and Rn had negative relationships. Accordingly, it will be necessary to manage the factors affecting indoor air quality so that the residents can have a more comfortable and healthier living environment. Ultimately, the results of this study are expected to be utilized as baseline data.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.291-299
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• 2003

The effect of temperature and soil confining stress on geosyntheic creep behaviour was studied by performing the temperature dependent confined creep tests for HDPE geogrid and geomembrane specimen. The visco-elastic creep coefficients of the geosynthetics were evaluated by the test results and it was proposed that the simple expressions for the instantaneous and limit creep strain of geosynthetics was considered as a function of temperature and confining stress on geosynthetics. Based on the time-temperature superposition principle, a master curve has been drawn for extrapolating tensile creep strains to longer time intervals(1$\times$10 $^7$min.∼1$\times$10$^{10}$min.). By using this master curves, the shift factors which can be used in establishing master curve considering confining stress on geosynthetics were carried out. Each tests was performed during 8,000∼12,000 min., with temperature ranging between 5$^{\circ}C$ and 4$0^{\circ}C$ and with confining stress ranging between 0 t/$m^2$ and 9 t/$m^2$.

• Tribology and Lubricants
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• v.33 no.6
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• pp.288-295
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• 2017

In order to improve the efficiency and reliability of the machine, the friction should be minimized. The most widely used method to minimize friction is to maintain the fluid lubrication state. However, we can reduce friction only up to a certain limit because of viscosity. As a result of several recent studies, surface texturing has significantly reduced the friction in highly sliding machine elements, such as mechanical seals and thrust bearings. Thus far, theoretical studies have mainly focused on isothermal/iso-viscous conditions and have not taken into account the heat generation, caused by high viscous shear, and the temperature conditions on the bearing surface. In this study, we investigate the effect of dimple depth and film-temperature boundary conditions on the thermohydrodynamic (THD) lubrication of textured parallel slider bearings. We analyzed the continuity equation, the Navier-Stokes equation, the energy equation, and the temperature-viscosity and temperature-density relations using a computational fluid dynamics (CFD) code, FLUENT. We compare the temperature and pressure distributions at various dimple depths. The increase in oil temperature caused by viscous shear was higher in the dimple than in the bearing outlet because of the action of the strong vortex generated in the dimple. The lubrication characteristics significantly change with variations in the dimple depths and film-temperature boundary conditions. We can use the current results as basic data for optimum surface texturing; however, further studies are required for various temperature boundary conditions.

• Journal of The Korean Society of Integrative Medicine
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• v.7 no.2
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• pp.49-57
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• 2019

Purpose: This study aimed to investigate the application of temperature to balance the training by observing the effect of sensory changes in the foot sole area on dynamic equilibrium ability through change in the sole temperature. Methods: Participants (n=49), who were selected as a certain standard, applied cold and hot packs for ten minutes at two-week intervals, and the laboratory's internal temperature was maintained at $25^{\circ}C$. The subjects were measured before and after the cold and hot applications in the stable condition with bare feet. Before each experiment applied the cold and hot packs, the balance ability of the ordinary temperature was measured once by conducting a limit of stability test using Biorescue, and the changes in balance ability were observed by measuring once after applying the temperature to the foot sole by means of the ice pack and the hot pack. Results: The results of the dynamic balance test, both before and after the temperature application, were compared, and it was confirmed that the moving area before and after cold application decreased significantly, and the moving area before and after application was not significantly different. The mean of pre-post area differences was found to have decreased at a statistically significant rate in the forward, backward, rightward, leftward, and total areas for the group that received the cold application compared to the group that received the hot application. Conclusion: These findings showed that cold application to the foot sole decreased dynamic balance. There was no significant difference in the dynamic balance ability both before and after the hot application to the foot sole, so it is difficult to conclude that the hot application affected dynamic balance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.62-65
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• 2008

Extrusion characteristics of Mg alloys were studied experimentally. The Al-Zn-Mg alloys, AZ31, AZ6l, AZ80, and AZ91 were extruded with hot hydrostatic extrusion process. The hydrostatic process was efficient to reduce surface friction and extend steady state region in extrusion which made it more convenient to examine deformation behavior of the alloys avoiding the disturbance caused by temporary contact state between billet and die, and billet and container. High pressure was cooperative to expand forming limit of the alloys which were applied on the billet during the extrusion process. Extrusion limits were traced in temperature and extrusion speed domain with changing composition of the alloying elements. Effects of process parameters on extrusion load and microstructure evolution were investigated also.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.146-151
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• 2001

Several design parameters for a 100 kW molten carbonate fuel cell stack was described. Approximately 170 cells are required to generate 100 kW at a current density of $125\;mA/cm^{2}$ with $6000\;cm^{2}$ cells. An overall heat balance was calculated to predict exit temperature. In order to limit the stack temperature in the range of $600-700^{\circ}C$, current load cannot exceed $75\;mA/cm^{2}$ at atmospheric operation. The 100 kW power is expected only under pressurization. Recycle of cathode gas by more than 50% is recommended to run the stack at $125\;mA/cm^{2}$ and 3 atm. Manifolds should be designed based on gas flow rates for the suggested operating condition.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.198-202
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• 2005

Gas generator is the equipment to produce high enthalpy gas used to generate sufficient power to operate turbine and pump system for propellant feeding in liquid rocket engine. Since the limit in operating temperature is imposed due to turbine blade, the gas generator has to be operated at the temperature far below stoichiometric maintaining fuel rich combustion. In this research, fundamental study was performed to understand the non-equilibrium combustion process with in-house code and CFD-ACE as well.