• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.8
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• pp.662-669
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• 2012

The effect of aspect ratio (AR) on the aerodynamic characteristics of a flapping wing was examined to analyze the design parameters of an insect-based MAV. The experimental model constructed with 4-bar linkages was operated in a water tank with the condition of a low Reynolds number. A water-proof micro-force load cell was fabricated and installed at the root of the wing which is made of a plexiglas. The wing shapes were based on the planform of a fruit fly wing. The ARs selected were 1.87, 3.74 and 7.48 and the Reynolds number was fixed at $10^4$. For AR=1.87 and 3.74, distinct lift peaks which indicate unsteady effects such as 'wake-capture' were observed at the moment of the start of the wing-stroke. However, for AR=7.48, no unsteady effects were observed. These phenomena were also observed in the delayed rotation case. The results indicate that a larger AR provides better aerodynamic performance for the insect-based flapping wing which can be applied in MAV designs.

• Journal of the Korea Society for Simulation
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• v.27 no.4
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• pp.19-26
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• 2018

The aerial launching UAV(Unmanned Aerial Vehicle) mainly uses a set of folding tandem wings to maximize flight performance and minimize the space required for mounting in a mothership. This folding tandem wing has a unique aerodynamic problem that is different from the general type of fixed wing aircraft, such as the rear wing interference problem caused by the wing of the front wing wake and vortex, and the imbalance of the pivot moment applied to the front and rear wings when the wing is deployed. In this paper, we have modeled and simulated various cases through computational fluid dynamics based on the finite volume method and analyzed various aerodynamic phenomena of the tandem wing type aircraft. We find that the front wing shall be installed higher than the rear for minimizing the wake influence and the rear wing can be deployed faster than the front because of the pivot moment due to aerodynamic forces. Also, considering the pivot moment due to aerodynamic force, the rear wing can be deployed much faster than the front wing. Therefore, it is necessary to consider it when developing the wing deploy mechanism.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.29-40
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• 1999

A numerical method in frequency domain for the analysis of the acoustic wave equation governing the sound field generated by a non-cavitating propeller under a steady of unsteady loading condition is developed. Theory shows that only multiples of the blade passage frequency exist and that the wave number consists of the frequency component due to the nonuniformity of the wake and the Doppler effect originated from the rotation of the blades. Correlation with experiments for a two bladed propeller, designed to be load-free at a particular advance speed, indicate that the thickness effect can be significant in steady case, but can be negligible compared to the unsteady loading effect.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.94-101
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• 2016

In this paper, aerodynamic effects on the flow field under the wing with varying aspect ratio were investigated by measuring pressures on the lower surface of wing and analysing velocity components using Particle Image Velocimetry at Reynolds numbers of $1.384{\times}10^5$ and $2.306{\times}10^5$. In case of aspect ratio 4.8 which keeps the wing tip at a distance of 80% chord length from the pylon, the vortex from the wing tip influenced the flow field under the wing by reducing static pressures on the lower surface and increasing the velocity in proximity of the wing tip. Throughout the results, it is observed that aerodynamic effects of wing tip on the flow field around pylon under wing become insignificant as the aspect ratio increases.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.109-117
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• 2002

An off-surface flow visualization experiments have been performed to investigate the flow field over a delta wing with the leading edge extension(LEX). The model is a flat wing with $65^{\circ}$ sweepback angle. The free stream velocity is 6.2 m/s, which corresponds to Reynolds number of $4.4\times10^5$ based on the wing root chord. The angle of attack and sideslip angle range from $16^{\circ}\sim28^{\circ}$ and $0^{\circ}\sim-15^{\circ}$, respectively. The visualization technique of using the micro water-droplet and the laser beam sheet enabled to observe the vortical flow structures, which can not be obtained by 5-hole probe measurements. With sideslip angle, the interaction and breakdown of the LEX and wing vortices was promoted in the windward side, whereas, it was suppressed in the leeward side.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.203-210
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• 2014

In this study, the hydrodynamic characteristics of Weis-Fogh type water turbine were calculated by the advanced vortex method. The wing (NACA0010 airfoil) and both channel walls were approximated by source and vortex panels, and free vortices are introduced away from the body surfaces. The distance from the trailing edge of the wing to the wing axis, the width of the water channel and the maximum opening angle were selected as the calculation parameters, the important design factors. The maximum efficiency and the power coefficient for one wing of this water turbine were 26% and 0.4 at velocity ratio U/V=2.0 respectively. The flow field of this water turbine is very complex because the wing moves unsteadily in the channel. However, using the advanced vortex method, it could be calculated accurately.

• Aerospace Engineering and Technology
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• v.8 no.2
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• pp.149-159
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• 2009

This paper deals with an analytical study on the aileron reversal characteristics of anisotropic composite aircraft wings modelled as thin-walled beam and having extension-twist structural couplings caused by Circumferentially Uniform Stiffness (CUS) layup scheme. For a study on the aileron reversal of CUS composite wings, it is essential to consider the following effects such as extension-twist structural coupling, wing aspect ratio, and ratio of span-wise and chord-wise length of aileron to wing, initial angle of attack, and sweep angle, etc. The results on the aileron reversal could have a significant role in more efficient designs of thin-walled composite wing aircraft for which this aeroelastic instability is one of the most critical ones.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1148_1149
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• 2009

반사형 전동 블라인드는 BEMS(Building Energy Management System)에 이용되는 조명 에너지 절감 장치로서, 블라인드 날개를 반사형 재질로 제작하여, 외부 채광이 블라인드 날개에 반사되어 천장에 반사되고 반사된 빛은 천장에서 확산되어 실내 깊숙이 부드럽고 균일한 조도를 공급해 준다. 이를 이용하면, 실내 거주자의 불편함 없이 실내 인공조명 사용량을 줄일 수 있다. 이를 구현하기 위해서는 태양광선의 고도의 변화에 따라 블라인드의 제어 각도를 계산하여 블라인드 제어 전동 모터를 구동해야 한다. 따라서 본 논문에서는 외부 채광을 실내 천장 면에 균일하게 반사할 수 있는 블라인드 날개의 제어 각도의 최적 조건을 제시하고, 컴퓨터 시뮬레이션을 통해 제시한 블라인드 날개 각도의 최적성을 검증하였다.

• Journal of the Korea Computer Graphics Society
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• v.9 no.2
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• pp.19-26
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• 2003

본 논문은 두개의 날개를 가진 다양한 생명체들의 형상과 움직임을 복잡한 공기역학 없이 body-brain 공진화를 사용하여 생성하는 시스템을 기술한다. 인공생명 기술이 다양한 가상생명체들을 생성하는데 이용되었지만 제한된 기하학적 요소들을 사용한 날개 생성의 어려움과 매우 복잡한 공기역학으로 인하여 하늘의 생명체들을 탐색한 연구들은 매우 드물다. 본 논문의 진화된 생명체들은 시스템의 단순함에도 불구하고 심미적인 모습과 유기적인 날개침 동작을 보여준다. 진화 알고리즘을 위한 유전형 인코딩에 쓰인 자료구조는 제한된 리스트 구조로서 이는 방향그래프와 유사하나 더욱 쉽게 다루어질 수 있다. 본 시스템으로 진화된 생명체는 연속적인 삼각형 패치로 이루어진 두개의 대칭형 날개를 가지며, 새, 나비, 박쥐 혹은 상상적인 용이나 익룡 등을 연상시키는 다양한 모습과 기동을 보여준다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.28-28
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• 1999

본 연구는 이전 연구에서 500KW급 중형 수평축 발전기를 설계하였던 경험을 토대로 750KW급 대형 수평축 풍력발전용 복합재 회전날개를 개발하기 위해 수행되었다. 회전날개의 대형화에 따른 구조강도 확보 및 경량화 문제를 해결하기 위해 날개의 단면구조를 변경하였고, 주 하중을 받는 스파부분을 보강하였으며, 취급이 어렵고 가격이 비싼 노맥스 허니컴 대신에 폼을 사용한 샌드위치 구조를 적용하였다. 또한 경량화를 위해 금속재 플렌지형 허브부분 접합방식을 삽입볼트 접합방식으로 구조 설계를 변경하였다. 이러한 복합재 회전날개의 구조적 안정성을 확인하기 위해 상용 유한요소 해석 코드인 NISA II를 사용하였으며, 선형정적해석, 고유진동수해석, 국부 좌굴해석 등을 수행하여, 무게의 증가는 최대한 억제하면서 대형화에 따른 구조강도의 확보가 이루어졌음을 확인하였고, 피로수명해석을 통하여 20년 이상의 요구 수명을 만족함을 확인하였다.