• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.2
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• pp.116-126
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• 2002

A three dimensional numerical analysis of the corrugated louver fin for a vehicle heat exchanger was performed. The heat transfer rate and the air pressure drop of the corrugated louver fins for a slim heater were compared with experimental results at the same operating conditions. As for the slim heater fin, we found an optimum fin pitch at certain operating conditions. As the fin pitch increased, the air pressure drop decreased. The vertical or flat top fin was superior to the common declined fin in the aspect of heat transfer performance. As the louver length increased, both the heat transfer rate and the air pressure drop increased.

• Journal of Aerospace System Engineering
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• v.3 no.3
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• pp.17-23
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• 2009

KARI SUAV (Smart Unmanned Aerial Vehicle) program is currently on the phase of ground and flight test. SUAV is a tilt rotor aircraft having the capability of vertical take-off/landing and high speed forward flight. The SUAV rotor system is 3-bladed, gimbaled hub type, which is not common for conventional helicopter configuration. In this paper, detailed procedure and method of rotor pitch rigging, tracking and balancing were described based on the experience of SUAV ground test.

• Korean Journal of Optics and Photonics
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• v.12 no.5
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• pp.414-417
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• 2001

Experimentally, the aligned direction of AFLCs in electro-optic cells having both the substrates rubbed along the same direction is skewed by a few degrees from the rebbing direction. To explain why, we proposed "Torsional Rigid Body Model" and interpreted their skewing angle as the action of short pitch with the large shear stress. That is, the azimuthal an anchoring strength (about 35 dyn/cm) in the cell is much larger than the maximum shear stress (about 10$^{-6}$ dyn/cm) for the original pitch and so forbids the optic axis to skew. On the side hand, the strength is smaller than the maximum shear stress (about 42 dyn/cm) for short pitch and then allows the optic axis to skew.

• Journal of Korean Foot and Ankle Society
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• v.12 no.2
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• pp.117-121
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• 2008

Purpose: To determine the clinical and radiographic results of arthroereisis using the $Kalix^{(R)}$ implant (Newdeal, Lyon, France) for the treatment of flexible flatfoot deformity. Materials and Methods: From February 2005 to February 2007, we performed the subtalar arthroereisis on 8 patients (9 feet) of symptomatic flexible flat feet after more than 6 months of conservative treatment. Average age was 14.5 years ($11{\sim}29$ years) old. We checked the functional status with AOFAS functional score pre-operatively and at final follow-up. Radiologically, we took weight bearing anterior to posterior and lateral view of the feet, and measured the talo-first metatarsal angle, calcaneal pitch angle in pre-operatively and at final follow-up. Results: Mean follow up period was 34.4 months. Average AOFAS score improved from preoperatively 65.6 to postoperatively 94.8. Average lateral talo-first metatarsal angle reduced from $12.8^{\circ}$ preoperatively to $1.6^{\circ}$ at final follow-up. Average anterior to posterior talo-first metatarsal angle was reduced from $15.1^{\circ}$ preoperatively to $8.3^{\circ}$ at final follow-up. Average calcaneal pitch angle was increased from $9.5^{\circ}$ preoperatively to $12.0^{\circ}$ at final follow-up. Conclusions: Subtalar arthroereisis with Kalix$K^{(R)}$ implant can be considered to be one of treatment options symptomatic flatfoot deformity patients.

• Journal of Korean Foot and Ankle Society
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• v.10 no.2
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• pp.218-222
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• 2006

Purpose: We evaluate the results of subtalar arthroereisis with $Kalix^{(R)}$ implant (Newdeal, Lyon, France) that were performed in painful flatfoot deformity. Materials and Methods: We performed the subtalar arthroereisis on 16 feet of children symptomatic flexible flat feet after more than 6 months of conservative treatment. Average age was 11 years (8-14 years) old. We checked the functional status with AOFAS functional score in pre-operatively and at final follow-up. Radiologically, we took weight bearing anterior to posterior and lateral view of the feet, and measured the talo-$1^{st}$ metatarsal angle, calcaneal pitch angle, cuboid-surface height. Finally, we asked to patient's parents for satisfaction of the surgery. Results: Mean follow up period was 34.1 months. Average AOFAS score improved from preoperatively 71.9 to postoperatively 91.3. Only one patient has subtalar pain. Average lateral $1^{st}$ metatarsal angle reduced from $-18.2^{\circ}$ preoperatively to $-4.6^{\circ}$ at final follow-up. Average anterior to posterior $1^{st}$ metatarsal angle was reduced from $18.9^{\circ}$ preoperatively to $6.5^{\circ}$ at final follow-up. Average calcaneal pitch angle was increased from $8.6^{\circ}$ preoperatively to $12.6^{\circ}$ at final follow-up. Average cuoboid-surface height was improved from 12.1 mm preoperatively to 16.0 mm at final follow-up. All patients had excellent or good satisfaction. Conclusions: Subtalar arthroereisis with $Kalix^{(R)}$ implant is a viable surgical alternative for painful flatfoot deformity of children.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.1059-1065
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• 2014

Wind turbine system can obtain the maximum wind energy using torque control under the rated wind speed, and wind turbine power is controlled as the rated power using pitch control over the rated wind speed. In this paper, we present a method for wind turbine pitch controller using neural networks. The purpose of the pitch control is to control generator speed and power in the above rated wind speed. To improve the neural network pitch controller, the difference between a rated and current speed of generator has been used for another input of neural networks as well as wind speed. Error back-propagation algorithm is used for training the neural network pitch controller and simulation and Matlab/Simulink is used for verifying that this system is controlled well.

• Tribology and Lubricants
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• v.37 no.2
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• pp.48-53
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• 2021

Wind energy is considered as the most competitive energy source in terms of power generation cost and efficiency. The power train of the pitch drive for a wind turbine uses a 3-stage complex planetary gear system in being developed locally. A gear train of the pitch drive consists of an electric or hydraulic motor and a planetary decelerator, which optimizes the pitch angle of the blade for wind generators in response to the change in wind speed. However, it is prone to many problems, such as excessive repair costs in case of failure. Complex planetary gears are very important parts of a pitch drive system because of strength problem. When gears are designed for the power train of a pitch drive, it is necessary to analyze the fatigue strength of gears. While calculating the specifications of the complex planetary gears along with the bending and compressive stresses of the gears, it is necessary to analyze the fatigue strength of gears to obtain an optimal design of the complex planetary gears in terms of cost and reliability. In this study, the specifications of planetary gears are calculated using a self-developed gear design program. The actual gear bending and compressive stresses of the planetary gear system were analyzed using the Lewes and Hertz equation. Additionally, the calculated specifications of the complex planetary gears were verified by evaluating the results from the Stress - No. of cycles curves of gears.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.159-164
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• 1992

In this paper, the complex nonlinear dynamics of a satellite is obtained. And it is shown that several limitations exist when the magnetorquer is used as an active actuator to attitude control. Such limitations cause a delayed convergence of pitch and roll angle. The simulation results insure that the roll angle bias is dependent on the z axis spin rate. And a heuristic algorithm is applied to control the attitude libration through the computer simulations.

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.283-284
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• 2008

In this paper, we report a broadband circular polarization reflectors and color separators realized as cascades of helical films with different pitch thickness. These helical films were prepared by glancing angle deposition technique.

• Journal of Industrial Technology
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• v.14
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• pp.39-48
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• 1994

Up to the present the study on the performance prediction of HAWT was perfomed mainly by assuming the axial flow. So in this paper we aimed at the fully non-axial flow of HAWT. For this purpose, we defined the wind turbine pitch angle in addition to the yaw angle to specify the arbitrary wind direction. And we adopted the Glauert method as the basic analysis method then modified this method suitably for our goal. By comparing the computational results obtained by this modified new Glaurert method with the experimental results, it was proved that our method was a very efficient method.