• 전자공학회논문지 IE
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• v.45 no.3
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• pp.42-49
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• 2008

This paper proposes a new beamforming algorithm to select beamforming gain or/and diversity gain in CDMA2000, W-CDMA, W-LAN channel according to signal environment on the multipath. In this paper, we present the criteria to obtain deversity gain at any point that based on quantized experimental value. Proposed method proposes represents a performance better than conventional algorithm adopting the largest two eigenvector when angle spread is exit. From the results of performance analysis through various simulation, it is confirmed that proposed method is far superior about $3{\sim}4$ times compare to conventional method in signal environment.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.359-366
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• 2000

A numerical study has been performed for the 2-dimensional film cooling employed in the cooling of hot components such as gas turbines. The flow and heat transfer characteristics are numerically simulated using FLUENT software. Blowing ratios vary from 0.25 to 5.0 and coolant injection angles vary from $15^{\circ}\;to\;60^{\circ}\;in\;15^{\circ}$ increment. The result shows that, for all cases, there exists a blowing ratio which maximizes film cooling effect (measured by the distance from the slot exit to the downstream wall location at which temperature increases to 900 K) for a given injection angle. It is also observed that the film cooling effectiveness decreases when downstream wall is sunk or lifted. The simulation has been performed using both constant properties and temperature dependent variable properties. It is found that the cases with constant properties overestimate the film cooling effect considerably.

• International Journal of Aeronautical and Space Sciences
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• v.4 no.1
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• pp.26-33
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• 2003

Recess is a geometrical configuration shape that the exit surface of an inner injector is located at a certain length inward from that of an outer injector. It is known to have the characteristics that it can augment mixing efficiency and flame stabilization through internal mixing of propellant in it. So, various experiments, such as backlit stroboscopic photography, phase Doppler particle analyzer(PDPA) and mechanical patternator, were performed at several recess lengths to grasp its effect on the spray characteristics of spray angle, breakup length, atomization and' mixing. Recess length was normalized to dimensionless recess number and two principal mechanisms of impingement and swirl recovery were introduced to explain its influence on the spray characteristics. The effect of recess on SMD doesn't appear significantly near the recess number where mixing efficiency attains to the maximum, whereas mass distribution and mixing efficiency are changed considerably. Thus, it can be inferred that a certain optimum recess number exists, where mixing efficiency becomes the maximum.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.2
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• pp.142-149
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• 2004

Recently, the government introduced the thermal storage system for reducing the electric power load. Especially, the ice slurry type has gained lots of interest due to its good heat transfer and flowing characteristics. This study was peformed to understand the effects of transporting ice slurry through elbows of various angle. Propylene glycol water solution was used and about 2 mm ice particles were circulated. The experiments were carried out under various conditions, such as concentration and velocity of water solution ranging between 0∼20 wt％, 1.5∼2.5 m/s, respectively. And elbows with 4 different angles of 30$^{\circ}$, 45$^{\circ}$, 90$^{\circ}$, 180$^{\circ}$. The differential pressure and IPF (ice packing factor) between the pipe entry and exit were measured. The tendency of pressure loss and outlet IPF in elbow is that the pressure loss was reduced as concentration and flow velocity of water solution is increased, and low value appeared at 10 wt％ and 2.5 m/s. The variation of outlet IPF was compared with the inlet IPF in the range of $\pm$20％.

• Journal of ILASS-Korea
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• v.9 no.4
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• pp.31-37
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• 2004

This paper presents spray and combustion characteristics of hydrocarbon fuel injected from pressure-swirl nozzles. Three commercial nozzles with orifice diameters of 0.256, 0.308 and 0.333mm and injection pressures ranging from 0.7 to 1.3 MPa were selected f9r the experiments. Spray characteristics such as breakup length. spray angle and drop size (SMD) were analyzed using photo image analyses and Malvern Panicle Size Analyzer. The drop size was measured with and without a blower at the same measuring locations. The flame length and width were measured using photo image analyses. The temperature distribution along the axial distance and the gas emission such as CO, $CO_2\;and\;NO_x$ were studied. The breakup length decreased with an increase in injection pressure for each nozzle but increased with an increase in nozzle orifice diameter. The spray angle increased and SMD decreased with an increase in injection pressure. The flame with an increased linearly with an increase in injection pressure and in nozzle orifice diameter. The flame temperature increased with an increase in injection pressure but decreased along the axial distance. The maximum temperatures occurred closer to the burner exit and flame at axial distance of 242mm from the diffuser tip. The experimental results showed that the level of CO decreased while that of $CO_2\;and\;NO_x$ increased with an increase in injection pressure and nozzle orifice diameter.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.486-491
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• 2008

The spray characteristics and drop size measurements have been experimentally studied in liquid jets injected into subsonic crossflow. With water as fuel injection velocity, injection angle and atomizer internal flows were varied to provide of jet operation conditions. The injector internal flow was classified as three modes such as a non-cavitation flow, cavitation, and hydraulic flip flows. Pulsed Shadowgraph Photography measurement was used to determine the spatial distribution of the spray droplet diameter in a subsonic crossflow of air. And this study also obtains the SMD(Sauter Mean Diameters) distribution by using PLLIF(Planar Liquid Laser Induced Fluorescence) technique. The objectives of this research are getting a droplet distribution and drop size measurement of each condition and compare with the other flows effect. As the result, This research have been showed the droplet size were spatially dependent on air-stream velocity, fuel injection velocity, injection angle effects and normalized distance from the injector exit length.(x/d, y/d)There are also different droplet size characteristics between cavitation, hydraulic flip and the non-cavitation flows.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.6
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• pp.725-732
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• 2014

The silencer for the medium caliber gun was studied to reduce the propagation of gun-generated noise from the firing test range to the community. Three types of silencer were made to compare the reduction of sound pressure level and the effect of chamber volume and the exit angle to the reduction of sound pressure was considered. The structural analysis and measurement of pressure in the silencer showed that the structure is safe in terms of strength. The increase of recoil force to buffer must be considered in the development of silencer. The hypothesis test on the muzzle velocity for the existence of silencer showed that there are no difference at the significance level of 0.05.

• The KSFM Journal of Fluid Machinery
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• v.1 no.1 s.1
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• pp.41-48
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• 1998

This study was carried out to investigate the effect of design parameters on the volume flow-rate and the noise level and to finally find the optimal design variables. Eighteen cross-flow fans were designed by the method of orthogonal array, and the flow-rate and the noise level were measured. These data were analyzed by the neural network system. The effects of eight design variables(scroll exit angle, scroll arc length et al.) on the fan performance and the noise level were valuated and discussed. This experiment shows that the design solutions suggested by neural network system may increase its volume flow-rate and reduce noise simultaneously.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.4
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• pp.410-416
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• 1983

This study presents the combustion characteristics and flame structure of annular swirling flow when there were changes the equivalence ratio and swirl number of swirling jet of fuelair mixture. The conclusions of this study are as follows; During the investigations in which the change of equivalence ratio and swirl number were studied, three basic shapes of flame were observed in this study. Visible flame lengths of swirling jet results in the decrease with increasing of swirl number and air-fuel ratio of mixture. Radial distribution of flame temperature with strong swirl is higher than that of weak swirl at the same equivalence ratio of mixture. The angle of spread of the annular jet increases with the increase of swirl number. When the swirl intensity is increased in a jet, the decay of concentration of carbon dioxide is decreased with the distance from nozzle exit of burner.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.5
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• pp.97-103
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• 1998

The flow structure of particles for two different injectors has been investigated experimentally by means of a Phase Doppler Particle Analyzer(PDPA). Two injectors used in the present study are the pipe and contraction nozzle. Particles of 0.8${\mu}{\textrm}{m}$, 30${\mu}{\textrm}{m}$, 60 ${\mu}{\textrm}{m}$, and 100${\mu}{\textrm}{m}$ diameter were injected with a constant mass loading ratio of 0.01 and a Reynolds number of 13200. The initial mean velocity and turbulent intensity of particle are strongly influenced by the particle size and the injector geometry. The flow angles of particle at nozzle exit are sensitive to the particle size rather than the injector geometry.