• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.1
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• pp.33-43
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• 2007

Using the more common conventional chordwise aerodynamic approach, flapping a flat plate wing with zero degree chordwise pitch angle of attack and no relative wind should not produce lift. However, in hover, with no forward relative velocity and zero degree chordwise pitch angle of attack, flapping flat plate wings does in fact produce lift. In the experiments peformed for this paper, the flapping motion is considered pure(downstroke and upstroke) with no flapping stroke plane inclination angle. No changes in chordwise pitch angle are made. The total force is measured using a force transducer and the net aerodynamic force is determined from this measured total force by subtracting the experimentally determined inertial contribution. These experiments were repeated at various flapping frequencies and for various wing planform sizes for flat plate wings. The trends in the aerodynamic lift variation found using a force transducer have nearly identical shape for various flapping frequencies and wing planform sizes.

• Journal of Power System Engineering
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• v.12 no.4
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• pp.18-25
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• 2008

This paper investigated the new calibration algorithm of a straight-type five-hole pressure probe necessary for calculating three-dimensional flow velocity components. The new data reduction method Includes a look-up, a geometry transformation such as the translation and reflection of nodes, and a binary search algorithm. This new calibration map was applied up to the application angle, ${\pm}55^{\circ}$ of a probe. As a result, this data reduction method showed a perfect performance without any kind of interpolation errors In calculating yaw and pitch angle from the calibration map.

• Journal of Astronomy and Space Sciences
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• v.17 no.2
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• pp.309-316
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• 2000

KOMPSAT-2 will carry MSC(Multi-Spectral Camera) which provides 1m resolution panchromatic and 4m resolution multi-spectral images at the altitude of 685km sun-synchronous mission orbit. The mission operation of KOMSPAT-2 is to provide the earth observation using MSC with nadir pointing. KOMPSAT-2 will also have the capability of roll/pitch tilt maneuver using reaction wheel of satellite as required. In order to protect MSC from thermal distortion as well as direct sunlight, MSC shall be operated within the constraint of sun incidence angle. It is expected that the sunlight will not violate the constraint of sun incidence angle for normal mission operations without roll/pitch maneuver. However, during roll/pitch tilt operations, optical module of MSC may be damaged by the sunlight. This study analyzed sun incidence angle of payload using KOMPSAT-2 AOCS (Attitude and Orbit Control Subsystem) Design and Performance Analysis Soft ware for KOMPSAT-2 normal mission operations.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.411-413
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• 2005

This paper proposes a modeling of wind turbine simulator which includes the dynamic characteristics such as pitch angle control, torsional vibration, and tower effect. Simulation results using PSCAD are provided to show the wind turbine simulator performance.

• Tribology and Lubricants
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• v.39 no.2
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• pp.56-60
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• 2023

In this study, we evaluate the anisotropic flow of droplets according to the directionality of asperities. We manufacture a mold with an inclined hole by adjusting the jig angle using a high-power diode laser. Using the manufactured mold, we prepare specimens for wettability studies by the micro molding technique. We fabricate twelve kinds of surfaces with micro-asperities inclined at 0°, 15°, 30°, and 45° for asperity pitches of 100 ㎛, 200 ㎛, and 300 ㎛. We evaluate the static and dynamic behaviors of the droplets as a function of the asperities pitch and inclination angles. The anisotropic effect increases as the pitch increases between asperities, and the anisotropic flow characteristics increase as the inclination angle of the asperities increases. On the surface with hole pitches of 100 ㎛ and 200 ㎛, the contact angle of the droplet shows high hydrophobicity at approximately 160°, but on the surface with the 300-㎛ hole pitch, the contact angle is approximately 110°, indicating that the hydrophobic effect rapidly reduces. Additionally, when the inclination angle of the asperities is approximately 30°, the left and right contact angle deviations of the droplet are the lowest, showing that the roll-off angle is relatively low.

• Journal of Biosystems Engineering
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• v.25 no.3
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• pp.233-240
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• 2000

A commercially available Doppler radar was modified and evaluated for on-board monitoring of ground speed. The radar output was corrected for pitch angle of aircraft based on the output of an electrolytic tilt sensor. The effects of aircraft speed, height and mounting angle on error in the ground speed were evaluated. The speed error decreased with an increase of the mounting angle since the radar contact angle with respect to the ground approached to the mounting angle. The error increased with an increase of the nominal aircraft speed. The altitude insignificantly affected the speed error. The Doppler radar provided acceptable percent errors within 5% in most measurements. The error can be reduced within ${\pm}$1.5% by increasing the mounting angle ($43^{\circ}$). The error of -3.8% at the mounting angle of $29^{\circ}$could be reduced by adjusting the mounting angle with respect to the radar contact angle.

• The KSFM Journal of Fluid Machinery
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• v.19 no.1
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• pp.11-17
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• 2016

In this paper, a numerical analysis was performed to investigate the effect of the pitch angle of a helical nozzle on the performance characteristics of a vortex tube. Three-dimensional numerical simulation has been performed with standard $k-{\varepsilon}$ turbulence model by using FLUENT 13.0. The effect of the pitch angle of helical nozzle was described in term of ${\beta}$. A CFD analysis was performed on ${\beta}=0^{\circ}$, $5^{\circ}$, $10^{\circ}$, $15^{\circ}$. In order to realize the influence of ${\beta}$ on performances of the vortex tube. Computation results were expressed by the ${\beta}-{\Delta}T_{h,c}$ graph and radial profiles of axial velocity and swirl velocity. The results showed that ${\beta}$ which improves energy separation capacity of vortex tube was $5^{\circ}$ at ${\alpha}=0.33$, 0.5 and $10^{\circ}$ at ${\alpha}=0.33$. Besides, It was confirmed that the results were closely related to axial velocity and swirl velocity.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.317-322
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• 2012

The low speed aerodynamic characteristics for a modified sonic arc airfoil which is designed by using the nose shape function of sonic arc, the shape function of NACA four-digit wing sections, and Maple are experimentally investigated. The small rotor blades of a modified sonic arc and NACA0012 airfoil are precisely fabricated with a commercially available light aluminum(Al 6061-T6) and are spin tested over a low speed range (3000rpm-5000rpm). In a consuming power comparison, the consuming powers of NACA0012 are higher than that of modified sonic arcs at each pitch angle. The measured rotor thrust for each pitch angle is used to estimate the rotor thrust coefficient according to momentum theory in the hover state. The value of thrust coefficients for both two airfoils at each pitch angle show almost constant values over the low Mach number range. However, the rotor thrust coefficient of NACA0012 is higher than that of the modified sonic arc at each pitch angle. In conclusion, the aerodynamic performance of NACA0012 is better than that of modified sonic arcs in the low speed regime. This test model will provide a convenient platform for improving the aerodynamic performance of small scale airfoils and for performing design optimization studies.

• Transactions of the Korean hydrogen and new energy society
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• v.15 no.3
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• pp.194-200
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• 2004

Thermal energy performance of a brazed plate heat exchanger has been evaluated experimentally. The effects of plate pitch as well as chevron angle of a plate heat exchanger on the heat transfer rate and pressure drop have been investigated in the wide range as mass flow rates in detail. This problem is of particular interest in the design of a plate heat exchanger. The results obtained indicate that both heat transfer rate and pressure drop are increased as mass flow rate is increased, as expected. It is also found that the heat transfer rate is increased with a decrease in the plate pitch while the heat transfer is decreased with a decrease in the chevron angle. Friction factor correlations are suggested based on the measured pressure drop and effectiveness of plate heat exchangers are also compared.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.6
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• pp.487-497
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• 2011

Numerical analysis has been performed to investigate the rotor speed and pitch range variations when the airspeed is increased in autorotation. Transient Simulation Method(TSM) was used to obtain the steady states of autorotation. The rotor blade was analyzed by the two-dimensional compressible Navier-Stokes solver in order to adapt to the airspeed increase and the results were used in the transient simulation method. Meanwhile, the Pitt/Peters inflow theory was used to supply the induced velocity fields. For the prescribed torque equilibrium state, the combinations of velocity, shaft angle, and pitch angle were produced to investigate the rotor speeds and variable ranges. The rotor tip Mach number and rotor speed were correlated and the trim range of pitch angle was observed with respect to the shaft angle decrease.