• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.10
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• pp.797-805
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• 2014

The purpose of this study was to investigate the drag and lift characteristics of the cavitator of a supercavitating underwater vehicle and the pressure loss due to water intake. These investigations were performed by changing the diameter, velocity, radius of curvature of the intake, and angle of attack of the cavitator. With increasing ratio of the intake diameter to the cavitator diameter ratio($d/D_1$), the drag coefficient and the pressure loss coefficient of the water intake decreased. The greater the increase in the ratio of the intake velocity-to-free stream velocity ratio(S), the smaller was the decrease in the drag coefficient and the lift coefficient. When the intake had a radius of curvature(c), the pressure loss coefficient decreased. On the contrary, the effect of the radius of curvature on the drag coefficient was imperceptible. For angles of attack (${\alpha}$) of the caviatator in the range of $0^{\circ}$ to $10^{\circ}$, the drag coefficient and the pressure loss coefficient changed slightly, whereas the lift coefficient increased linearly with increasing angle of attack.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.205-212
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• 2006

Atmospheric drag is the most significant factor effecting the low Earth satellites under the altitude of 800 km Although the atmospheric density of the low Earth orbit is very low compared to that of the sea level, the accumulated effect of the atmospheric drag slowly lowers the satellite velocity at the perigee. Decrease in velocity at perigee directly causes decrease in altitude at apogee which changes the eccentricity of the orbit. The orbit finally reaches a circular orbit before reentering the Earth. This paper states the methods of calculating the atmospheric drag and the lifetime of the satellite. The lifetime of the kick motor and the satellites which will be used on KSLV-L are calculated by Satellite Tool Kit.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.359-362
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• 2010

BBU for 155mm projectile has been verified its stable performance and quality reliability through the production for several years. We have researched substitution test for flight test of BBU. Through this research, we expect the verification of quality stability and other collateral effect like the cost reduction and delivery on time.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2868-2872
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• 2007

In this study, a passive control using a boat-tail device is conducted for a three-dimensional car model in ground proximity. We consider various boat-tails and investigate the mechanism of drag reduction by them. By varying the length and slant angle of boat-tail, we obtain drag reductions up to 40%. From the oil-surface flow visualization and hot-wire measurement, the drag reduction by the boat-tail is characterized by the shear-layer instability and reattachment on the boat-tail, forming a small separation bubble at the upstream part of boat-tail surface, resulting in the delay of main separation and drag reduction. At high slant angles, the flow fully separates and drag is nearly same as that of no control.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.527-528
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• 2012

DBD (Dielectric Barrier Discharge) plasma actuator was designed for aerodynamic drag reduction using plasma flow control, and the drag reduction was measured by wind-tunnel tests using 2D test model. At the zero wind velocity, the plasma flow control had no effect on the drag reduction because the flow separation and surface friction drag were not occurred. At the wind velocity of 2m/s, 9.7% of drag was reduced by the flow separation control. The drag reduction decreased as the wind velocity increased.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.2
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• pp.156-162
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• 2013

The characteristics of the unsteady flowfield of a square prism having a detached splitter plate at the wake side were investigated by advanced vortex method. The instantaneous and average velocity field and pressure field around a square prism without and having splitter plate were calculated by forcing the gap ratio having the maximum drag reduction rate, at Reynolds number $Re=1.0{\times}10^4$ and the width ratio H/B=1.0 of splitter to the prism width. The drag and lift coefficients on the square prism were also obtained. The calculated results agree with the measured drag coefficients and pressure distributions on the square prism. The vortices of the opposite direction at upside and down side of the splitter plate were generated by installing of the plate. And the drag on the square prism was decreased by increasing of the pressure of back face of the prism with the vortices.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.10
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• pp.20-27
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• 2004

In this study, CFD analysis for 2D ellipse and 3D CRW UAV are performed. Furthermore, flow analysis around a hub connecting body and rotor is analyzed and a strategy to reduce the drag caused by the hub is sought. Also, the idea of fairing installation is confirmed by a wind tunnel test.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.4
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• pp.24-32
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• 2008

We made a new propellant formulation to improve the productivity of Base Bleed Unit(aka BBU) by reducing of the curing time. We made an experiment with new propellant formulation such as binder characteristics and manufacturing process. In addition, we already tested several basic characteristics and the final performance of the new propellant. According to the test report, it was not only satisfied with all requirements in the specification, but it also contributed to improve productivity and reduced 53% of the curing time.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.479-483
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• 2005

BBU is the weapon system for the extension of range through the reduction of base drag in 155mm. It has been mass-produced since 2000. The purpose of this research is productivity increase through the reduction of process lead time. Development process is as follows. First, formulation tests about propellent and liner, Second, spin test and final firing test about end products.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.2
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• pp.71-76
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• 2018

Recently, various technologies have been developed for road facilities to reduce the load, some of which use technologies employing perforated plates for wind load reduction. Currently, there are no regulations concerning the drag coefficient of perforated plates for domestic road facilities. In the United States, the regulations regarding the drag coefficient of perforated plates in the 'Minimum design loads for buildings and other structures' were revised based on the studies of Letchford (2001) and Giannoulis (2012). In this study, a wind tunnel test was carried out to analyze the feasibility of applying regulations involving the perforated plates' drag coefficient. The results of the wind tunnel test and the drag coefficient used in the regulation were compared and analyzed. In addition, the reduction effect of the cross area of road signs calculated by applying the drag coefficient was analyzed. The results of the wind tunnel test and the value of the drag coefficient used in the regulation in the US were found to be very similar. Therefore, it was found that it is possible to apply the formula involving the drag coefficient of the perforated plate to the regulation and that the cross area of the perforated plate used for the post of the road sign is reduced by about 9.45% and that of the horizontal post by about 6.45%.