• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.54-64
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• 1996

It seems that blowing air bubble out of the bulb surface of a ship of flat bottom will reduce the frictional resistance, since wetted area of the hull surface is reduced owing to air bubble staying close to the surface. To as certain this concept, at first, the limiting streamlines around the bow was observed, and local distribution of pressure and shear stress, due to the change of air-blowing position, air supply pressure, and the model speed, was investigated. It was found that the local friction was reduced near the bulb and air-bubble formations also play an important role as a drag component. This paper can be considered as a preliminary study on the drag reduction of conventional ships by the micro-bubble injection.

• 한국전산유체공학회:학술대회논문집
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• 2000.10a
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• pp.32-38
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• 2000

Wing flap deflection angles of a supersonic transport are optimized to improve transonic cruise performance. For this end, a numerical optimization method is adopted using a three-dimensional unstructured Euler code and a discrete adjoint code. Deflection angles of ten flaps; five for leading edge and five fur railing edge, are employed as design variables. The elliptic equation method is adopted for the interior grid modification during the design process. Interior grid sensitivities are neglected for efficiency. Also tested is the validity of the approximate gradient evaluation method for the present design problem and found that it is applicable for loading edge flap design in cases of no shock waves on the wing surface. The BFGS method is used to minimize the drag with constraints on the lift and upper surface Mach numbers. Two design examples are conducted; one is leading edge flap design, and the other is simultaneous design of leading edge and trailing edge flaps. The latter gave a smaller drag than the former by about two counts.

• Ocean Systems Engineering
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• v.3 no.4
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• pp.309-325
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• 2013

Ocean Thermal Energy Conversion (OTEC) systems utilize the temperature difference between the surface water and deep ocean water to generate electrical energy. In addition to ocean surface waves, wind and current, in certain locations like the Andaman Sea, Sulu Sea and the South China Sea the presence of strong internal waves may become a concern in floating OTEC system design. The current paper focuses on studying the dependence of the CWP hydrodynamic drag on relative velocity of the flow around the pipe, the effect of drag amplification due to vortex induced vibrations and the influence of internal waves on the floating semi and the cold water pipe integrated OTEC system. Two CWP sizes are modeled; the 4m diameter pipe represents a small scale prototype and the 10m diameter pipe represents a full commercial size CWP. are considered in the study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.6 s.237
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• pp.755-762
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• 2005

To evaluate the aerodynamic efficiency of TR-S2 configuration designed by SUDC, wind tunnel tests of $40\%$ scaled model were done in KARI LSWT. The aerodynamic characteristics of plain and Semi-Slotted Flaperon were compared, and vortex generators were installed to improve flow pattern along the wing surface. Effects of the control surface such as elevator, rudder, aileron, and incidence angle of horizontal tail are measured for various testing conditions. Test results showed that Semi-Slotted Flaperon produced more favorable lift, lift/drag, and stall margins and application of vortex generator would be best choice to enhance wing performance. Longitudinal, lateral and directional characteristics of TR-S2 were found to be stable for the pitch and yaw motions.

• Journal of Mechanical Science and Technology
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• v.20 no.7
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• pp.1051-1058
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• 2006

The steady aerodynamic characteristics of a wing flying over a channel are investigated using a boundary-element method. The present method is validated by comparing the computed results with the measured data. Compared with a flat ground surface, the channel fence augmented the lift increase and induced drag reduction. When the fence is lower than the wing height, the gap between the wingtip and the fence does not affect the aerodynamic characteristics of the wing much. When the fence is higher than the wing height, the close gap increased the lift. The induced drag is reduced when the wing is placed near the ground or at the same height as the fence. It is believed that present results can be used in the conceptual design of the high-speed ground transporters flying over the channel.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.464-467
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• 2008

An ejector is designed for the purpose of engine bay cooling. The primary flow of the ejector is the exhaust gas of the PW206C turboshaft engine. The mass flow of secondary flow is calculated by using the approximate analytic equation. And the effect of exhaust gas flow on the fuselage surface is investigated by using the Fluent Code. Three types of exhaust duct shape were compared in the viewpoint of surface temperature and aerodynamic drag. As a result, exhaust duct shape P3 shows minimum interference of exhaust gas and fuselage and minimum increment of drag among the three candidate shapes.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.7
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• pp.149-156
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• 1999

In this study, aerodynmaic characteristics of the notch-back and fast-backpassenger vehicle models(1/10~1/12 acale) attached with winglets were experimentally investigated in a low speed wind tunnel. For various positions(X/L). tilted angles($\beta$) of a winglet, the aerodynamic forces on the vehicle model and rear-surface pressures were measured at various flow speeds. Also a flow of model surface was visualized by tuft method. The experimental results showed that winglets effect aerodynamic characteristics of vehicle models. A maximum of 3% reduction in lift coefficient was achieved with winglets at $\alpha$=-30$^{\circ}$. A maximum of 10% reduction in drag coefficient was achieved for a model with winglets and a rear-spoiler.

• 한국전산유체공학회:학술대회논문집
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• 2008.08a
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• pp.50.3-50.3
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• 2008

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.34 no.4
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• pp.433-441
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• 1998

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.357-361
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• 1997

In this work surface damage of head and disk of head disk drive was analysed using an Atomic Force Microscpoe. The initial damage of the disk occurred by generation of extermely small wear particles. Also it was show that wear particles tend to pile up near the front side of the slider. The surface damage mechanism of drag test and contact-start-stop test was found to be quite similar.