• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.7
• /
• pp.85-93
• /
• 2003

Droplet vaporization at various ambient pressures is studied numerically by formulating one dimensional evaporation model in the mixture of hydrocarbon fuel and air. The ambient pressure ranged from atmospheric conditions to the supercritical conditions. The modified Soave-Redlich-Kwong state equation is used to account for the real gas effects in the high pressure condition. Non-ideal thermodynamic and transport properties at near critical and supercritical conditions are considered. Some computational results are compared with Sato's experimental data for the validation of calculations. The comparison between predictions and experiments showed quite a good agreement. The droplet lifetime increases with increasing pressure at temperature lower than the critical temperature, however, it decreases with increasing pressure at temperature higher than the critical temperature. The solubility of nitrogen can not be neglected in the high pressure and it becomes higher as the temperature and the pressure go up.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.49 no.7
• /
• pp.539-547
• /
• 2021

Helicopter rotor blade is required to be designed by considering the interacting effects among aerodynamics, flexibility, and controllability. The reverse design allows the structural components to have common characteristics by using the configuration numerics and experimental results. This paper aims to design the composite rotor blade which will feature common characteristics with that of BO-105. The present engineering design procedure is done by dividing the rotor blade into a few sections and composite laminates across the cross section. For each section, variational asymptotic beam sectional analysis (VABS) program is used to evaluate its flapwise, lagwise, and torsion stiffnesses to have discrepancy smaller than certain tolerance. Finally, CAMRAD II is used to predict the stress acting on the rotor blade during the specific flight condition and to check whether the present deign is structurally valid.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.5
• /
• pp.545-552
• /
• 2009

An experimental study was performed on the yLRC composite column. Its external surface was manufactured with y-shape steel sheets and L-shape steel angles, and concrete was poured inside in the field. This composite column has improved the section capacity due to the composite action of steel and concrete, and provides good efficiency in reducing the terms of construction works because of its abridged formworks. The stub column specimens (three small and three large specimens) were tested through concentrical axial loading, and the effect of the width-to-thickness ratio of the steel angle on the column axial strength was examined. The axial strength and behavior of the composite columns were analyzed, and a formula for predicting the axial load capacity was proposed.

• Korean Chemical Engineering Research
• /
• v.50 no.6
• /
• pp.1076-1081
• /
• 2012

For the purpose of development of the latex suitable for latex modified concrete, experimental researches on the preparation of carboxylated styrene butadiene latex by the method of the two-step emulsion polymerization and application to concrete were performed. Sodium dodecylbenzene sulfonate and sodium salt of lauryl sulfonate were selected as anionic emulsifiers, and nonylphenoxy poly(ethyleneoxy) ethanols (n=10, 20, 40) as latex stabilizer. Potassium persulfate and sodium bisulfite were used as redox initiator, besides $Na_2HPO_4$ and $K_2CO_3$ as electrolytes. Polymerization recipe of latex suitable for latex modified concrete were suggested from the experimental researches on the effects of anionic emulsifiers and their concentration on the polymerization stability, and the effect of electrolytes concentration on the particle size of latex. Physical properties, such as slump, air contents, compressive and flexural strength, of latex prepared by suggested polymerization recipe were examined. The experimental results showed that latex modified concrete satisfied the quality standards in slump and air contents. Furthermore, it was turned out that the compressive and the flexural strength of latex modified concrete with 28 days curing time showed appreciably improvements.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.36 no.2
• /
• pp.93-103
• /
• 2023

Warships widely spread numerous chaffs using a blast, which form chaff clouds that create false radar cross-sections to deceive enemy radars. In this study, we established a numerical framework based on a one-way coupling of computational fluid dynamics and discrete element method to simulate the spatiotemporal distribution of chaff clouds for warships in the air. Using the framework, we investigated the effects of wind, initial chaff cartridge angle, and blast pressure on the distribution of chaff clouds. We observed three phases for the chaff cloud diffusion: radial diffusion by the explosion, omnidirectional diffusion by turbulence and collision, and gravity-induced diffusion by the difference in the fall speed. The wind moved the average position of the chaff clouds, and the diffusion due to drag force did not occur. The direction of radial diffusion by the explosion depended on the initial angle of the cartridge, and a more vertical angle led to a wider distribution of the chaffs. As the blast pressure increased, the chaff clouds spread out more widely, but the distribution difference in the direction of gravity was not significant.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.47 no.7
• /
• pp.469-478
• /
• 2019

Multirotor configurations such as VTOL and urban air mobility have been focused on today due to the high maneuverability. Aerodynamic and aeroacoustic characteristics of multirotor have much difference to those of a single rotor. In this study, a numerical analysis based on the free wake vortex lattice method is used for identifying the wake interaction effect. In order to compare the various configurations and operating conditions, the effects of the spacing between the rotors in hovering flight and the effects of the advancing ratio and the formation in forward flight are discussed. In the hovering flight, the unsteady loading of multirotor changes periodically and loading fluctuation increases as decreasing the spacing. It causes the variation in unsteady loading noise and the noise directivity pattern. In the forward flight, the difference in loading fluctuation and noise characteristics are observed according to the diamond and square formation of rotors. By comparing with results of single rotor analysis, multirotor configurations have different directivity pattern and amplitude of loading noise according to the location of each rotor. As a result, wake interaction effect becomes a highly important factor for aerodynamic and aeroacoustic analysis according to multirotor configurations and operating conditions.

• Journal of the Korean Vacuum Society
• /
• v.16 no.2
• /
• pp.145-152
• /
• 2007

The evolution dynamics of nanoscale Ge islands on both Si (001) and (113) surfaces is explored using ultraviolet photoelectron emission microscopy (UV-PEEM). Real-time monitoring of the in-situ growth of the Ge island structures can allow us to study the variation of the size, the shape and the density of the nanostructures. For Ge depositions greater than ${\sim}4$ monolayer (ML) with a growth rate of ${\sim}0.4\;ML/min$ at temperatures of $450-550^{\circ}C$, we observed island nucleation on both surfaces indicating the transition from strained layer to island structure. During continuous deposition the circular islands grew larger via ripening processes. AFM measurements showed that the islands grown on Si (001) were dome-shaped while the islands on Si (113) were multiple-side faceted with flat tops of (113)-orientation. In contrast, for Ge deposition with a lower growth rate of ${\sim}0.15\;ML/min$ on Si(113), we observed the shape transition from circular into elongated island structures. The elongated islands grew longer along the [$33\bar{2}$] during continuous Ge deposition. The shape evolution of the islands is discussed in terms of strain relaxation and kinetic effects.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.13 no.2
• /
• pp.42-53
• /
• 2009

Gas turbine engine simulation program has been developed. In compressor and turbine, 2-D NS implicit code is used with k-$\omega$ SST turbulent model. In combustor, 0-D lumped method chemical equilibrium code is adopted under the limitations, the products are only 10 species of molecular and air-fuel is perfectly mixed state with 100% combustion efficiency at constant pressure. Fluid properties are shared on interfaces between engine components. The outlet conditions of compressor have been used as the inlet condition of combustor. The inlet condition of turbine comes from the compressor The back pressure in compressor outlet is transferred by the inlet pressure of turbine. Unsteady phenomena at rotor-stator in compressor and turbine is covered by mixing-plane method. The state of engine can be determined only by given inlet condition of compressor, outlet condition of turbine, equivalence ratio and rotating speed.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.1A
• /
• pp.205-211
• /
• 2006

The purpose of this study was to evaluate the effects of fly-ash on strength development and durability of latex-modified concrete (LMC) and ordinary portland cement concrete (OPC). Main experimental variables were latex contents (0%, 10%, 15%) and fly-ash content (0, 10%, 20%, 30%). Air content and slump tests were performed to check the basic properties of fresh concretes, and compressive strength, flexural strength, rapid chloride ion permeability and chemical resistance were measured to analyze the basic properties of hardened concretes. The test results showed that air contents of LMC with fly ash decreased as fly-ash contents increased from 0% to 30%. Compressive and flexural strength developments of LMC with fly ash were quite similar to those of LMC without fly ash. However, the long-term flexural strength development of LMC with fly ash after 90 days were bigger than that of LMC without fly ash. Chloride ion permeability and chemical resistance decreased rapidly as the content of fly ash increased. Thus, fly ash could be used at LMC in order to reduce water permeability.

• Journal of the Korean Geotechnical Society
• /
• v.22 no.11
• /
• pp.89-99
• /
• 2006

The PCRW (Precast Concrete Retaining Wall) has many advantages compared with cast in place concrete retaining wall : shorter construction period, excellency of quality and minimum interference with the adjacent structure and traffics. However, shallow foundation type of PCRW, which has comparatively better ground condition, has some disadvantages such as difficulty in transportation and higher cost due to the size of PCRW being expanded by resisting only with self-weight if there is no other supplementary reinforcement. The presented study, in order to complement such disadvantages of PCRW, have applied the micropile method. The micropile method has advantages like low-cost and high-efficiency and does not require huge space, because it can be executed with small size equipment. However, the mechanical behavior characteristics of the PCRW reinforced by micropile, which is installed to improve the reinforcement effect, is not yet clearly identified and there is no suggested standard as to the length, diameter, install angle and install position of micropiles. Hence, this method is yet being designed depend on engineer's experience. In this study, various laboratory model tests as to sliding and overturning were performed in order to identify and present the optimum type of reinforcement and reinforcement effect of the PCRW reinforced by micropiles. In addition, it also executed numerical analysis for the purpose of verifying the optimum type of reinforcement for micropiles based on the results of laboratory model tests. The optimum reinforcement type of micropiles was estimated by model test and numerical analysis. The length of micropiles is 0.4 times wall height and the diameter is 0.04 times wall length.