• 한국항공우주학회지
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• 제30권4호
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• pp.44-52
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• 2002

비정상, 비압축성 Navier-Stokes 코드를 이용하여, 저 레이놀즈수 유동에서 flapping 운동을 하는 익형의 공력특성을 수치해석적인 방법으로 연구하였다. 비정상 유동장의 효율적인 계산을 위하여, 개발된 코드는 MPI 프로그래밍 기법을 이용하여 병렬처리 되었으며, 난류 유동장의 계산을 위해 2방정식 난류모델의 하나인 k-$\omega$ SST 모델을 적용하였다. 익형의 3가지 운동모드 즉, pitching, plunging, flapping과 주파수 및 진폭의 변화 그리고 두께와 캠버의 변화에 의한 공력특성을 살펴보았고, 이를 위해 NACA4자 계열의 익형을 이용하였다. 해석 결과는 실험치와 비교하여 보았을 때 잘 일치하였으며, 각 운동모드에서의 공기역학적 특성을 파악할 수 있었다.

• 한국항공우주학회지
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• 제34권3호
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• pp.6-13
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• 2006

본 연구에서는 저 레이놀즈수 유동에서 flapping운동을 하는 익형이 가질 수 있는 2차원 평면상의 운동궤적에 따른 공력특성을 연구하였다. 익형이 유동흐름방향으로 왕복 운동하는 lead-lag운동과 plunging운동의 조합으로 2차원 평면상에 나타날 수 있는 여러 운동궤적을 합성하여 flapping 주파수 변화에 따른 공력계수들의 변화를 살펴보았다. 상하방향의 순수 plunging운동에 lead-lag운동을 추가함으로써, 평균추력계수와 평균양력계수를 증가시킬 수 있는 운동궤적이 존재함을 확인하였다. 아울러 운동주기 동안 나타나는 추력계수와 양력계수의 변화를 비교하여 upstroke와 downstroke시 나타나는 공력특성을 파악하였다.

• 한국항공우주학회지
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• 제39권6호
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• pp.498-504
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• 2011

속도와 샤프트각 그리고 피치 변화에 따른 토크 평형상태의 자동회전에서 플래핑 거동 특성과 전진비의 변화를 조사하였다. 속도 증가에 따른 압축성 효과를 모사하기 위해 압축성 Navier-Stokes 솔버로 해석된 2차원 데이터를 Pitt/Peters 유도흐름 이론과 함께 사용하였고 토크 평형상태에 대한 세 변수의 조합을 찾기 위해 과도모사법(TSM)을 이용하였다. 토크 평형상태에서 최대 플래핑각을 속도, 샤프트각, 피치와의 관계로 나타내고 전진비 변화와 비교함으로써 후진깃의 역풍영역 확대가 로터의 자동회전 특성에 관여하는 현상을 정성적으로 고찰하였다.

• 한국항공운항학회지
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• 제14권2호
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• pp.39-44
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• 2006

The unsteady vortex lattice method is used to model lead-lag in flapping motions of a rectangular flat plate wing. The results for plunging and pitching motions were compared with the limited experimental results available and other numerical methods. They show that the method is capable of simulating many of the features of complex flapping flight. The lift, thrust and propulsive efficiency of a rectangular flat plate wing have been calculated for various lead-lag motion and reduced frequency with an amplitude of flapping angle(20o). To describe a motion profile of wing tip such as elliptic, line and circle, the phase difference of flapping and lead-lag motion was changed. And the effects of the motion profile on the aerodynamic characteristics of the flapping wing are discussed by examination of their trends.

• 한국전산유체공학회지
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• 제8권2호
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• pp.24-32
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• 2003

In this work, we propose a new idea of flapping airfoil design for optimal aerodynamic performance from detailed computational investigations of flow physics. Generally, flapping motion which is combined with pitching and plunging motion of airfoil, leads to complex flow features such as leading edge separation and vortex street. As it is well known, the mechanism of thrust generation of flapping airfoil is based on inverse Karman-vortex street. This vortex street induces jet-like flow field at the rear region of trailing edge and then generates thrust. The leading edge separation vortex can also play an important role with its aerodynamic performances. The flapping airfoil introduces an alternative propulsive way instead of the current inefficient propulsive system such as a propeller in the low Reynolds number flow. Thrust coefficient and propulsive efficiency are the two major parameters in the design of flapping airfoil as propulsive system. Through numerous computations, we found the specific physical flow phenomenon which governed the aerodynamic characteristics in flapping airfoil. Based on this physical insight, we could come up with a new kind of airfoil of tadpole-shaped and more enhanced aerodynamic performance.

• Smart Structures and Systems
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• 제10권1호
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• pp.67-87
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• 2012

A dragonfly inspired flapping wing is investigated in this paper. The flapping wing is actuated from the root by a PZT-5H and PZN-7%PT single crystal unimorph in the piezofan configuration. The non-linear governing equations of motion of the smart flapping wing are obtained using the Hamilton's principle. These equations are then discretized using the Galerkin method and solved using the method of multiple scales. Dynamic characteristics of smart flapping wings having the same size as the actual wings of three different dragonfly species Aeshna Multicolor, Anax Parthenope Julius and Sympetrum Frequens are analyzed using numerical simulations. An unsteady aerodynamic model is used to obtain the aerodynamic forces. Finally, a comparative study of performances of three piezoelectrically actuated flapping wings is performed. The numerical results in this paper show that use of PZN-7%PT single crystal piezoceramic can lead to considerable amount of wing weight reduction and increase of lift and thrust force compared to PZT-5H material. It is also shown that dragonfly inspired smart flapping wings actuated by single crystal piezoceramic are a viable contender for insect scale flapping wing micro air vehicles.

• 소음진동
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• 제5권2호
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• pp.215-224
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• 1995

In this paper, the three-dimensional finite element model is established to investigate the structural dynamic characteristics of rotor blade using a finite element analysis. Six natural frequencies and mode shapes are calculated by computer simulation. The first three flapping modal frequencies, the first two lead-lag modal frequencies, and the first feathering modal frequency are validated through comparison with the modal test results of the fixed rotor blade. The computer simulation results are found in good agreement with experimentally measured natural frequencies. The important results are obtained as follows: (1) Natural frequencies are changed due to the variation of rotational speed and fiber angle of rotor blade, (2) Weak coupling between flapping mode shape and lead-lag mode shape are detected, (3) Centrifugal force has more effect on flapping modal frequency than lead-lag modal frequency.

• Smart Structures and Systems
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• 제6권7호
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• pp.867-887
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• 2010

An energy-based variational approach is used for structural dynamic modeling of the IPMC (Ionic Polymer Metal Composites) flapping wing. Dynamic characteristics of the wing are analyzed using numerical simulations. Starting with the initial design, critical parameters which have influence on the performance of the wing are identified through parametric studies. An optimization study is performed to obtain improved flapping actuation of the IPMC wing. It is shown that the optimization algorithm leads to a flapping wing with dimensions similar to the dragonfly Aeshna Multicolor wing. An unsteady aerodynamic model based on modified strip theory is used to obtain the aerodynamic forces. It is found that the IPMC wing generates sufficient lift to support its own weight and carry a small payload. It is therefore a potential candidate for flapping wing of micro air vehicles.

• 로봇학회논문지
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• 제11권4호
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• pp.256-261
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• 2016

An insect-like flapping-wing flying-robot should be able to produce flight forces and control moments at the same time only by flapping wings, because there is no control surface at tail just like an insect. In this paper, design principles for the flapping mechanism and control moment generator are briefly explained, characteristics measured force and moment generations of the robot are presented, and finally controlled flight of the flying robot is demonstrated. The present insect-like robot comprises a lightweight flapping mechanism that can produce a flapping angle larger than $180^{\circ}$ and a control moment generator that produces pitch, roll, and yaw moments by adjusting location of the trailing edges at the wing roots. The measured force and moment data show that the control input angles less than $9^{\circ}$ would not significantly reduce the vertical force generation. It is also observed that the pitch, roll, and yaw control moments are produced only by the corresponding control input. The simple PID control theory is used for the controlled flight of the flying robot, controlling pitch, roll, and yaw motions. The flying robot successfully demonstrated controlled flight for about 40 seconds.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.1999-2010
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• 2023

Undesirable flapping motion of discs can cause the failure of swing check valves in nuclear passive safety systems. Time-resolved particle image velocimetry (PIV) was employed to investigate the flow characteristics around a free-to-rotate plate and the motion response, with the Reynolds numbers, based on the hydraulic diameter of the channel, from 1.32 × 10⁴ to 3.95 × 10⁴. Appreciable flapping motion (±3.52°) appeared at the Reynolds number of 2.6 × 10⁴ with the frequency of 5.08 Hz. In the low-Reynolds-number case, the plate showed negligible flapping. In the high-Reynolds-number case, the deflection angle increased with reduced flapping amplitude. The torque from the fluid determined the flapping amplitude. In the low-Reynolds-number case, Karman vortices were absent. With increasing Reynolds numbers, Karman vortices developed behind the plate with larger deflection angles. Strong interaction between the wake flow from the leading and trailing edge of the plate was observed. Based on power spectrum density (PSD) analysis, the vortex shedding frequency coincided with the flapping frequency, and the amplitude was positively correlated to the strength of the vortices. Proper orthogonal decomposition (POD) modes evince that, in the case of appreciable motion, coherent structures exhibited a larger spatial scale, enhancing the magnitude of the external torque on the plate.