• Computers and Concrete
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• v.14 no.5
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• pp.613-633
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• 2014

A double-skinned composite tubular (DSCT) column, which consists of concrete and inner and outer tubes, was finally developed to overcome the weaknesses of concrete filled tube columns by reducing the self-weight of the column and confining the concrete triaxially. Research pertaining to the stiffness and strength of the column and the confining effect in a DSCT column has been carried out. However, detailed studies on the confining stress, especially the internal confining stress in a DSCT column, have not been carried out. Internal and external confining stresses should be evaluated to determine the effective confining stress in a DSCT column. In this paper, the confining stresses of concrete before and after insertion of an inner tube were studied using finite element analysis. The relationship between the internal or external confining stresses and the theoretical confining stress was investigated by parametric studies. New modified formulae for the yield and buckling failure conditions based on the formulae suggested by former researchers were proposed. Through analytical studies, the modified formulae were verified to be effective for economic and reasonable design of the inner tubes in a DSCT column under the same confining stress.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.97-100
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• 2008

A hybrid sounding rocket carrying about 10kg payload reaching up to 15km altitude has been designed. The commercial seamless aluminium tube and liquid ${N_2}O$ without pressurization devices were chosen as rocket motor case and oxidizer supply system respectively. A hybrid rocket engine performing required propulsion impulse is designed with time dependent internal ballistic scheme. Engine performance, aerodynamic characteristics, and trajectory were predicted by a integral technique of internal ballistics and external ballistics. The design results were evaluated by comparison with previous experimental data, technical reports, and literatures.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1243-1249
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• 2004

This study is focused on the comparison between the internal saturation temperature of the working fluid and the surface temperature of adiabatic zone of two-phase closed thermosyphons with various helical grooves. Distilled water, methanol and ethanol have been used as the working fluid. In the present work, a copper tube of the length of 1200mm and 14.28mm of inside diameter is used as the container of the thermosyphon. Each of the evaporator and the condenser section has a length of 550mm, while the remaining part of the thermosyphon tube is adiabatic section. A experimental study was carried out for analyzing the performances of having 50, 60, 70, 80, 90 helical grooves. A plain thermosyphon having the same inner and outer diameter as the grooved thermosyphons is also tested for the comparison. The results show that the numbers of grooves and the type of working fluids are very important factors for the operation of thermosyphons. A good agreement between the internal saturation temperature of working fluid and the surface temperature of adiabatic zone of two-phase closed thermosyphons with various helical grooves is obtained.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.12
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• pp.1297-1303
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• 2015

The internal chromium plating of a long-axis tube is widely used in military and industrial application, with the thick hard plating formed using a mixed solution of Chromium acid and catalytic $H_2SO_4$. A large-caliber gun can endure a high explosive force as a result of the increased stiffness and wear resistance provided by this internal hard chromium surface. The internal chromium layer of a tube is prone to exfoliation caused by the high kinetic energy of the projectile and high pressure of the explosion. Therefore, we reviewed the plating process. Chromium plating comprises many steps, including the removal of Grease, water cleaning, electrolytic abrasion, etching, plating, water cleaning, and hydrogen brittleness removal. The exfoliated chromium plating layer is affected by the adhesion property of the plating. In particular, the Fe concentration of the electrolyte affects the adhesion property. The optimum Fe concentration for effectively suppressing the exfoliation of the plating layer was established by using a scanning electron microscope to determine the surface roughness, and the effectiveness was proved in an adhesion test, etc.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.8
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• pp.94-101
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• 2005

The silent discharge type ozonizer with three electrodes(central electrode, internal electrode, and external electrode) and one discharge gap(discharge gap between internal electrode and external electrode) has been designed and manufactured. It is a silent discharge type ozonizer for which the AC high frequency voltages applied to the central electrode within vacuum discharge tube and the internal electrode for which the external electrode is a ground Ozone is generated by silent discharge in discharge gap. At the moment, discharge characteristics and ozone generation characteristics were investigated in accordance with vacuum of discharge tube, frequency of AC power source, discharge power of ozonizer, and quantity of supplied oxygen gas. In consequence, ozone characteristics proportional to vacuum of discharge tube and frequency of AC power source. The maximum value of ozone can be obtained 7,700[ppm], 460[mg/h] and 70[g/kwh].

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.226-234
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• 2008

Grain design has always been a vital and integral part of Solid Rocket Motor(SRM) design. Basing on the design objectives set by the system designer, the SRM designer has many options available for selecting the Grain configuration. Many of the available configurations may fulfill the required parameters of volumetric loading fraction, web fraction & Length to diameter ratios and produce internal ballistic results that may be in accordance to the design objectives. However, for any given set of design objectives, it is deemed necessary that best possible configuration be selected, designed and optimized. Hence optimal results of all applicable configurations are vital to be attained in order to compare and finalize the design that will produce most efficient performance. Generally the engineers pay attention and have skills on a specific grain configuration. The designing methodologies and computer codes available usually focus on single grain configuration may it be Star, Wagon Wheel or slotted tube. Hardly one can find a software or a design methodology where all such configurations can be worked on jointly and not only adequate designs be found but optimal solutions reached by applying an optimization method to find final design best suited for any design objective. In the present work design requirements have been set, grain configurations have been selected and their designing has been conducted. The internal ballistic parameters have been calculated and after finding the preliminary design solutions, the optimal solutions have been found. In doing so, software has been developed comprising of computer programs for designing the 2D grains including Star, Wagon Wheel and Slotted Tube configurations. The optimization toolbox of Matlab Fmincon has been used for getting optimal solutions. The affects of all the independent geometric design variables on the optimized solutions have been analyzed. Based on results attained from Optimization Method, an in depth comparison of Grain Configurations and analysis of performance prediction outputs have been conducted to come to conclusion as to which grain configuration is ideal for the current design requirement under study.

• Journal of Korean Society of Steel Construction
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• v.21 no.5
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• pp.461-470
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• 2009

A column resisting axial load and seismic load is one of the main members in a structural system. The heated column by event of a fire can lose its strength and it may damage its structural system or cause the collapse of the entire structural system. In this study, the fire resistance capacity of internally confined hollow concrete filled tube (ICH CFT) column was investigated. In an ICH CFT column, the yield strength of the external tube is important as a concrete filled tube (CFT) column because the external tube confines the filled concrete and the strength of the column depends on the confined effect. A study was performed by finite element analyses considering the confined effect and material nonlinearity as the temperature changes by the fire. The hollow ratio, the thickness of the external tube, and the strength of concrete were selected as the parameters for the analyses. The analyses were performed by using a commercial FEA program (ABAQUS) and nonlinear concrete model program. The analysis results showed that the hollow ratio and the strength of concrete mainly affect the fire resisting capacity of an ICH CFT column.

• Korean Journal of Adult Nursing
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• v.21 no.6
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• pp.570-579
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• 2009

Purpose: The aim of this research was to determine knowledge and management of tracheal tube cuffs among nurses of ICU. Methods: This descriptive survey recruited 150 nurses working at 8 different adult ICUs within 2 tertiary hospitals in Seoul. A survey questionnaire was developed to measure cuff management. The internal reliability of the tool was examined by Cronbach's ${\alpha}$. Descriptive statistics and multiple regressions were used to analyze data. Results: Among the 150 nurses, 94.0% replied that they would measure the pressure themselves. With regard to nurses' knowledge about tracheal tube cuffs, only 6% answered that they knew 'the appropriate cuff pressure'. The existence of a measuring device (p < .001), a guideline (p < .001), the level of knowledge on its related complications(p = .003), and clinical experience (p < .001) together accounted for 35.0% of the total variation in cuff management. They pointed out that the lack of time and the lack of education were major barriers to appropriate management; whereas education update was the most imperative factor for good management. Conclusion: ICU nurses have inappropriate knowledge and practice in cuff management. Therefore continuing education is necessary for better practice of tracheal tube cuff management.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.241-250
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• 2000

In this study, condensation heat transfer tests were conducted in flat aluminum multi-channel tubes using R-22. Two internal geometries were tested ; one with smooth inner surface and the other with micro-fins. Data are presented for the followin~ range of variables ; vapor quality($0.1{\sim}0.9$), mass flux($200{\sim}600kg/m^2s$) and heat flux($5{\sim}15kW/m^2$). The micro-fin tube showed higher heat transfer coefficients compared with those of the smooth tube. The difference increased as the vapor quality increased. Surface tension force acting on the micro-fin surface at the high vapor quality is believed to be responsible. Different from the trends of the smooth tube, where the heat transfer coefficient increased as the mass flux increased, the heat transfer coefficient of the micro-fin tube was independent of the mass flux at high vapor quality, which implies that the surface tension effect on the fin overwhelms the vapor shear effect at the high vapor quality. Present data(except those at low mass flux and high quality) were well correlated by equivalent Reynolds number, Existing correlations overpredicted the present data at high mass flux.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.6
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• pp.140-145
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• 2012

Recently, various after-treatment systems, such as LP-EGR(Low Pressure-Exhaust Gas Recirculation), SCR(Selective Catalytic Reduction) and LNT(Lean NOx Trap), were developed to obey the stringent emission regulations of diesel engine. There are many researches on LP-EGR system because it has advantages of NOx reduction and low fuel consumption. But, condensation water is generated in internal of intercooler tube and it contains various types of anion that cause the corrosion of aluminium tube. In this study, it is examined that the condensation water effects on corrosion of aluminium tube. And method for improvement of corrosion characteristics is investigated using the dipping and electrochemical test.