• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.6
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• pp.429-439
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• 2013

The purpose of current study is to develop the rotor analysis solver and perform a rotor aerodynamic analysis in the wind fence. To this end, the rotor analysis solver based on actuator disk model was employed. To consider the asymmetric effect of the rotor in the wind fence, the flapping motion analysis was conducted with blade element theory for the effective angle of attack calculation. The validation cases which are the rotor with wall and ground were accomplished by developed solver. The decrease of rotor performance by wind fence was confirmed. The wind fence configuration was suggested which guarantees more than 95% rotor performance compared with the no fence case.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.10
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• pp.833-844
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• 2018

This paper aims to predict the aerodynamic characteristics of individual rotor for the gust and flight conditions. Transformation procedure into the wind frame is conducted to analyze the gust. Hover, forward, and climb flight conditions of an individual rotor are analyzed using the blade element momentum theory (BEMT) considering the rigid blade flapping motion. XFOIL is used to derive aerodynamic results. Validation for hover, forward flight, and climb conditions are conducted using the present BEMT. In addition, a static experimental environment is constructed. The experimental results and the present BEMT are compared and verified.

• Journal of Mechanical Science and Technology
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• v.16 no.10
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• pp.1303-1313
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• 2002

Effects of the reduced frequency of upstream wake on downstream unsteady boundary layer flow were simulated by using a Wavier-Stokes code. The Wavier-Stokes code is based on an unstructured finite volume method and uses a low Reynolds number turbulence model to close the momentum equations. The geometry used in this paper is the MIT flapping foil experimental set-up and the reduced frequency of the upstream wake is varied in the range of 0.91 to 10.86 to study its effect on the unsteady boundary layer flow. Numerical solutions show that they can be divided into two categories. One is so called the low frequency solution, and behaves quite similar to a Stokes layer. Its characteristics is found to be quite similar to those due to either a temporal or spatial wave. The low frequency solutions are observed clearly when the reduced frequency is smaller than 3.26. The other one is the high frequency solution. It is observed for the reduced frequency larger than 7.24. It shows a sudden shift of the phase angle of the unsteady velocity around the edge of the boundary layer. The shift of phase angle is about 180 degree, and leads to separation of the boundary layer flow from corresponding outer flow. The high frequency solution shows the characteristics of a temporal wave whose wave length is half of the upstream frequency. This characteristics of the high frequency solution is found to be caused by the strong interaction between unsteady vortices. This strong interaction also leads to destroy of the upstream wake strips inside the viscous sublayer as well as the buffer layer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.5
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• pp.397-403
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• 2007

Insect and birds in nature flap their wings to generate fluid dynamic forces that are required for locomotion. To develop a feasible flapping MAV, it is of crucially important to study the fundamental relations between flapping motion and thrust generation. In this paper, the onset conditions of the thrust generation of a heaving flat plate is investigated using a Lattice-Boltzmann method. For a fixed heaving amplitude of h/C=0.5, the effect of reduced frequency on the thrust generation is investigated. For several values of heaving amplitude(h/C=0.25, 0.325, 0.50), the effect of reduced frequency on the thrust generation is also investigated. It can be said that Strouhal number is more important rather than reduced frequency in case of thrust generation. It is found that the critical Strouhal number over which the flat plate starts to produce thrust is around 0.1. Thrust is an exponential function of the Strouhal number.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.173-179
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• 2017

This paper analyzes actuator characteristics for main wing and tail surfaces of an ornithopter by using a motion capture test. Experiments with the ornithopter are conducted indoor, and its fuselage is held on a jig to reduce interaction with vibration generated by flapping motion. The motion capture system detects the movement of markers attached on the main wing and tail wing tip. Experimental results show that the main wings tend to change its amplitude according to the flapping frequency, and the lift and thrust generation simulation is implemented by applying the experimental results and the ornithopter specification to Modified Strip Theory. Step input excitation is applied for experimental analysis of the tail wing in horizontal and vertical directions. As a result, horizontal and vertical tail wings have different characteristics in terms of overshoot, final value, damping ratio and natural frequency because they have different wing structures and linkages.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.3 s.108
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• pp.291-297
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• 2006

The BVI(blade vortex interaction) noise Prediction has been one of the most challenging acoustic analyses in helicopter aeromechanical Phenomenon. It is well known high resolution airloads data with accurate tip vortex positions are necessary for the accurate prediction of this phenomenon. The truly unsteady time-marching free-wake method, which is able to capture the tip vortices instability in hover and axial flights, is expanded with the rotor flapping motion and trim routine to predict unsteady airloads in forward and descent flights. And Farassat formulation 1-A based on the FW-H equation is applied for the noise prediction considering the blade flapping motion. Main objective of this study is to validate the newly developed prediction code. To achieve the objective, the descent flight condition of AH-1 OLS(operational loads survey) configuration is analyzed using present code. The predicted sectional thrust distribution and sectional airloads time histories show the present scheme is able to capture well the unsteady airloads caused by a parallel BVI. Finally, the predicted noise data, observed in two different positions where are 3.44 times of rotor radius far from the hub center, are quite reasonable agreements with the experimental data compared to the other analysis results.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.43-54
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• 2004

A visualization study was carried out to investigate the effects of phase difference qualitatively by examining wake pattern on the phase difference of a dragonfly type wing model. The model was built with scaled-up, flapping wings composed of a paired wing with fore- and hind-wings in tandem that mimick the wing form of a dragonfly. The present study was conducted by using the smoke-wire technique and an electronic device below the tandem wings was mounted to find the exact wing position angles. Uncertainties in wing position angle are about $\pm$$1.0^{\cire}$ and instantaneous wing positional angle varies from $-16.5^{\cire}$ to $+22.8^{\cire}$. The tests were made at phase differences between the fore-wing and hind-wing at $0^{\cire}$, $90^{\cire}$, $180^{\cire}$ and $270^{\cire}$. The results show that Karman vortex structures were produced at phase differences of $90^{\cire}$, $180^{\cire}$ and $270^{\cire}$, but Karman vortex structures were not observed at the phase difference of $0^{\cire}$.

• International Journal of Industrial Entomology and Biomaterials
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• v.1 no.2
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• pp.91-93
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• 2000

Insects have many excellent features and functions in their small bodies, such as hexapod walking, flapping flight, vision systems, sensory hairs, etc, and those characteristics can be thought as good models for many types of robots. Insects also will be good models far micro-machines because of its size. Insect behavior consists of simple reflex acts and programmed behavior, Some robots were made in order to clarify the emergent mechanism of insect behavior, Through some experiments it would be found that even if insect behavior consists of some simple action patterns, it looks intelligent through interactions its sensors and actuators with its complex environment. In the near futures small robots inspired by insects will be used in many fields of our life. I hope that insect-model based robots will play an active part in many fields and that they will make us happy.

• MALSORI
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• no.37
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• pp.1-12
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• 1999

In this paper, we examine the allophones of an underlying segment /l/ in Korean dialects. In particular, we examine how an underlying /l/ sound surfaces in the Korean dialect spoken at Yonbyon, China. To do so, we employ the following processes: First, we perform the phonetic studies on the allophones of an underlying /l/ in the Yonbyon dialect. Secondly, we compare the phonological environments of the allophones of an underlying /l/ in the Yonbyon dialect with the South Korean dialect. Finally, we discuss the phonological implications of the allophones of the underlying /l/ in terms of Feature Geometry and Syllable Contact Law. Based on the phonetic study, we will argue that the distinctive feature [sonorant] should be placed outside the root node and that the flap, an allophone of an underlying /l/, should be understood as an obstruent, not a sonorant.

• Journal of the Korean Solar Energy Society
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• v.32 no.spc3
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• pp.269-274
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• 2012

The research of the biological mimics robot which utilizes the operation of the organism is progressed on the ground, aerial, and underwater robot sector. In the field of flying robot, the research for implementing the wing movement structure of the bird and insect is progressed. The joint structure for the wing movement of the bird is implemented. The operation of the wing is simulated. For this purpose, by using the Matlab/Simulink, the joint structure of the wing is modelled. The joint movement of the wing is tested through the simulation.