• International Journal of Aeronautical and Space Sciences
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• v.8 no.2
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• pp.44-53
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• 2007

A three-dimensional viscous flow solver has been developed for the prediction of the aerodynamic performance of hovering helicopter rotor blades using unstructured hybrid meshes. The flow solver utilized a vertex-centered finite-volume scheme that is based on the Roe's flux-difference splitting with an implicit Jacobi/Gauss-Seidel time integration. The eddy viscosity are estimated by the Spalart- Allmaras one-equation turbulence model. Calculations were performed at three operating conditions with varying tip Mach number and collective pitch setting for the Caradonna-Tung rotor in hover. Additional computations are made for the UH-60A rotor in hover. Reasonable agreements were obtained between the present results and the experiment in both blade loading and overall rotor performance. It was demonstrated that the present vertex-centered flow solver is an efficient and accurate tool for the assessment of rotor performance in hover.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.4
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• pp.60-68
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• 2002

Experiments have been conducted to investigate the effects of emulsified fuels on the spray characteristics and exhaust emissions in a diesel engine. Four different fuels were examined : diesel, emulsified fuels with water contents which were varied with 13, 15, and l7wt%. Characteristics of fuel spray were measured by an optical method, PLLIF(planar liquid laser induced fluorescence). Compared to diesel fuel, emulsified fuels which had relatively high kinematic viscosity showed smaller spray angle and longer spray tip penetration. The qualitative droplet distributions of emulsified fuels showed worse atomization process than that of diesel fuel. As the water contents were increased, PM and NOx could be reduced simultaneously. It was specially noted that the emulsified fuel with l7wt% water content was found to be the best in reducing rates, NOx 30% and PM 40%.

• Journal of Ocean Engineering and Technology
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• v.12 no.3 s.29
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• pp.60-67
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• 1998

In this study, the J-Resistance Curve and material tearing modulus of SA508-C3 steel, which is one of the used nuclear pressure vessel steel, are measured ar room temperature, $200^{circ}C$ and $300^{circ}C$ according to load ratio analysis and ASTM E813, ASTM E1152, respectively. It is observed that J-R curve and Tmat value decrease as the temperature level increase. Applicability of $T_j$ proposed by Paris et al as instability parameter for ductile material is investigated. It is concluded that results are the $T_j$ parameter may be used as a crack instability parameter.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.60-66
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• 2010

Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.3
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• pp.134-140
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• 2008

Micro electrochemical machining (ECM) is conducted on stainless steel 304 using non-toxic electrolyte of citric acid. Electrochemical dissolution region is minimized by applying a few hundred second duration pulses between the tungsten SPM tip and the work material. ECM characteristics according to citric acid concentration, feeding velocity and electric conditions such as pulse amplitude, pulse frequency, and offset voltage are investigated through a series of experiments. Micro holes of $60{\mu}m$ in diameter with the depth of $50{\mu}m$ and $90{\mu}m$ in diameter with the depth of $100{\mu}m$ are perforated. Square and circular micro cavities are also manufactured by electrochemical milling. This research can contribute to the development of safe and environmentally friendly micro ECM process.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2136-2138
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• 1999

In this study, we describe the change of electrical properties of XLPE with electrical-tree degradation. XLPE insulation was used as specimen which was cut off from 22.9kV XLPE insulated cable and made in a type of block. The applying voltages are 8kV, 10kV, 12kV and frequency is 60Hz Ogra needles having tip radius of 10$\mu\textrm{m}$ were inserted in blocks. PD quantity and $tan{\delta}$ and DC current were measured from inception of tree to breakdown and their characteristics were analyzed.

• Ocean and Polar Research
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• v.40 no.1
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• pp.23-35
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• 2018

A small cyclopoid copepod M. subtilis (Giesbrecht, 1893 ["1892"]) belonging to the genus Monothula $B{\ddot{o}}ttger-Schnack$ and Huys, 2001 was collected by using $60{\mu}m$ mesh net and firstly recorded in the epipelagic layer of the equatorial Pacific Ocean. We redescribed its morphological characteristics for both female and male, comparing with those of previous studies. Specimens of M. subtilis from the equatorial Pacific Ocean differ from those previously reported by others in terms of the length of the seta G on antenna, being much shorter than setae E and F; in the distal spine on the swimming leg 4, being longer than the length of the third segment on P4. The outer spine of the P3 enp-3 in male is slightly over the tip of conical process. The spine lengths of the distal endopods of P2-P4 for both sexes showed variations among individuals, and the proportions of spine lengths in female are higher than those in male.

• Journal of the Speleological Society of Korea
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• v.20 no.21
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• pp.34-43
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• 1989

Cheju island is situated at about 60km south of southern most tip of the Korean peninsula. Its shape is an ellips with size of 80*40$\textrm{km}^2$, and it is characterized by a symmetrical form whose peak is Mt. Halla(1950m). Major chemical composition of the rock samples from Manjang gul cave is determined by XRF using the fundamental parameter method consisting of fully auto quantitative analysis, semi quantitative analysis (order estimation) and group quantitative analysis. Judging from chemical composition (SiO$_2$ = 53.07Wt％, Fe$_2$O$_3$ = 11.34Wt％, MgO=6.48Wt％, Na$_2$O=3.07Wt％, $K_2$O=1.05Wt％), this rocks from the Manjang gul cave are also determined. The discrepancy of K-Ar ages is found. They are 0.03 Ma and 0.42Ma, respectively. This paper describes some problems experienced in dating young volcanic rocks and then discusses chemical composition, X-ray fluorescence analysis and the age of the formation of a lava tunnel such as Manjang gul cave in cheju Island.

• Journal of Environmental Science International
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• v.7 no.2
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• pp.157-164
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• 1998

preliminary study on the chemical compositions of forty seven precipitations from March 1994 to May 1995 In Yeoncheon-gun, which Is adjacent to the southern boundary of demilitarized zone (DMZ) in the northernmost tip of Kyunggi Province has been Performed. The metal cation and anion concentrations were measured by atomic absorption spectrometer and ion chromatography, respectively. pH/lon meter and direct nesslerization method were used for the concentration measurements of $H^+$ ion and $NH_46+$ ions, respectively Based on the data, the quantitative orders of the cation and anion average concentrations were $Ca^{2+}>NH_4^+>Na^+>K^+>Mg^{2+}>H^+ and SO_4^{2+}>Cl^-> NO_3^-$, respectively..The ratio of average total anion concentration to average total cation concentration was 0.97. The average pH value of the precipitations was 5.60. These results, correlation coefficients between the ion concentrations, and monthly variations of pH value and precipitation amount are used for chemical analysis on the environmental Pollution and Pollutant sources In Yeoncheon-gun of Kyunggi province near DMZ.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.824-829
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• 1994

High-frequency and complex vibration ultrasonic wire bonding systems are propsed and their welding characteristic are studied. Ultrasonic wire bonding is used widely for joining thin connecting wire of various electronic devices including IC or LSI. Conventional bonding systems use vibration frequency of 40 or 60 kHz and linear vibration welding tips. Complex vibration welding tip which vibrates in elliptical to circular or rectangular to square in the same or different frequency is effective to join welding specimens in shorter welding time and under smaller vibration amplitude, and furthermore high-frequency systems such as 90, 120, 190 kHz are also significantly effective. High-frequency and complex vibration welding system of 90, 120 and 190 kHz are designed. Welding characteristics of these systems are found very superior than a conventional system. Welding specimens of aluminum wire of 0.1mm diameter are successfully.