• Proceedings of the Korean Society of Computer Information Conference
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• 2018.01a
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• pp.219-222
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• 2018

최근 SNS의 부정적 활용에 관한 사례들이 증가하면서, 청소년들의 모방 가능성에 대한 우려도 함께 커졌다. 본 논문에서는 청소년들의 긍정적 SNS 활용 경험 제고를 위한 방안으로 SNS 활용 교육에 Dragonfly Effect 모델의 적용을 제안하였다. Dragonfly Effect 모델은 작은 생각을 SNS를 통해 큰 변화로 바꾸는 방법에 관한 모델이며, 본 논문에서는 이를 교육에 적용하기 위한 방안으로 요소 분리형 교육 프로그램과 요소 통합형 교육 프로그램 구성을 예시 프로그램과 함께 제안하였다. Dragonfly Effect 모델을 적용한 수업은 청소년들이 SNS를 통한 선한 사례의 주인공이 되도록 할 것이며, 또한 이것은 SNS 상에 선순환 구조가 만들어지는 작은 단초가 될 것이다.

• Journal of the Korea Institute of Military Science and Technology
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• v.9 no.4
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• pp.120-127
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• 2006

An experimental study was carried out in order to investigate the effects on the fore- and hind-wings of a dragonfly-type model. A model with two pairs of wing was developed to measure the lift and thrust of a dragonfly-type model. The fore-wing and hind-wing had incidences angle of $0^{\circ}\;and\;10^{\circ}$. The freestream velocity is 1.6m/sec and the corresponding chord Reynolds number was $Re=2.88{\times}10^3$. Also, these experiments were carried out with a phase difference of $90^{\circ}$ between the fore- and hind-wing, aerodynamic forces caused by fore-wing only and two pairs of wings were investigated according to the reduced frequency. The results show that the model with fore-wings only generates a thrust component; however, the dragonfly-type model with hind-wings with an incidence angle of $10^{\circ}$ generates a drag component. The total drag is also increased with reduced frequency due to the increased lift of hind-wings.

• Smart Structures and Systems
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• v.10 no.1
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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.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.14 no.2
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• pp.1-8
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• 2006

Unsteady lift measurements were carried out in order to investigate the effects of phase difference and reduced frequency of a dragonfly-type model with two pairs of wing. A load-cell was employed to measure the lift generated by a plunging motion of the dragonfly-type model with the incidence angles of 0$^{circ}$. Experimental conditions are as follows: phase differences between fore- and hind-wings are 0$^{circ}$, 90$^{circ}$, 180$^{circ}$, and 270$^{circ}$, and reduced frequencies are 0.075, 0.15 and 0.225, respectively. The freestream velocity was 143 m/sec and corresponding chord Reynolds number was $3.4{\times}10^3$. The variation of phase-averaged lift coefficients during one cycle of the wing motion is presented. Results show that the total value of the positive lift coefficient during one cycle of the wing motion is the largest at the phase difference of 90$^{circ}$, and that the maximum lift coefficient and lift coefficient per unit of time increases with reduced frequency.

• Journal of Species Research
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• v.9 no.1
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• pp.1-10
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• 2020

A new dragonfly species, Nannophya koreana sp. nov., is described from Korea on the basis of morphology and mitochondrial cytochrome oxidase c subunit I (COI) gene sequences. Nannophya materials from Korea and other areas in Southeast Asia were compared. The new species was previously recognized in Korea as the endangered pygmy dragonfly Nannophya pygmaea Rambur, 1842, which is widely distributed in insular and peninsular Southeast Asia. However, male adults of the Nannophya population in Korea could be distinguished from other N. pygmaea populations by the presence of a thick, incomplete black stripe on the lateral synthorax that terminated at half-length (vs. continuous to wing base), light orange (vs. red) anal appendages, and 4-5 (vs. 2-3) black teeth on the ventral superior appendages. In addition, the body length of N. koreana was generally larger (1.2-1.4 times) than that of N. pygmaea, regardless of life stage. COI gene sequences from the two groups exhibited substantial genetic differences (>12%), thereby sufficiently substantiating their differentiation. The taxonomic status, distribution, and habitat of the new species are discussed.

• Journal of the Korean Institute of Landscape Architecture
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• v.25 no.1
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• pp.100-111
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• 1997

Owing to the urbanization, the industrialization and joining to WTo, there are lots of fallow and abandoned farmlands in Korea. Those results have occurred inefficient land use and destruction of agricultural ecosystem with the secondary succession and invasion of alien weeds. Using these fallow and abandoned farmlands, Korean government tries to create the ecological parks for the nature conservation, amenity, education and research, etc. For these purposes, materials on the ecological park construction were gathered from abroad such as England, Germany, Switzerland and Japan and also field trips to those countries were executed in April,1996. Accordingly, the goal for the ecological parks could be set suitably to Korean situation as of Japanese styles which are characterized by man-made biotopes. For a case study, dragonfly was selected as an indicator of the rehabilitation of water-side ecosystem, arid a site was selected for the dragonfly biotope under the criteria of selection to the Experimental Farm of Korea University including near abandoned farmlands (Dogok-ri, Wabu-eup, Namyangju city Kyunggi-do). Natural and cultural factors of this site were inventoried and analyzed, and then with the results dragonfly biotope was planned to the site with the detailed ecotechnology.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.18-25
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• 2006

Unsteady aerodynamic force measurements were carried out in order to investigate the effects of phase difference of a dragonfly-type model with two pairs of wing. A load-cell was employed to measure the aerodynamic force generated by a plunging motion of the dragonfly-type model. The dragonfly-type model has a dynamic similarity with real one, and incidence angles of fore- and hind-wing are 0° and 10°, respectively. Other experimental conditions are as follows: The freestream velocity was 1.6 m/sec and corresponding chord Reynolds number was 2.88×103, and phase differences of fore- and hind-wing were 0°, 90°, 180° and 270°. The variation of aerodynamic coefficients during one cycle of the wing motion is presented. Results show that the lift is generated during the downstroke motion and the drag generated during the hind-wing‘s downstroke motion with the lift generation.

• Journal of the Korean Society of Visualization
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• v.8 no.2
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• pp.16-22
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• 2010

A flow visualization has been conducted to investigate unsteady flight characteristics of a model of dragonfly. The mechanism of lift generation by flapping wings is analyzed using smoke-wire and high speed camera. The experimental results of flow visualization show a discernible sequential dynamics that three mechanisms and high incidence angle of the wings are responsible for the lift generation. The leading edge vortex by the rapid acceleration of leading edge of the wing during initial stage of stroke causes a strong lift enhancement. Delayed stall during the stroke, fast supination and pronation of the wing near the end of each stroke are also responsible for the lift generation.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1566-1569
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• 2008

The flow visualization is conducted in order to investigate an unsteady flight characteristic of a model dragonfly. The flapping wings are analyzed using smoke-wire and high speed camera. The results of this experiment show that three mechanisms and high incidence angle of the wings are responsible for the lift. The leading edge vortex, which is induced by the rapid acceleration of the wing at the beginning of a stroke, causes the lift enhancement. The delayed stall during the stroke and the fast supination and pronation of the wing near the end of each stroke are also responsible for the lift generation.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1586-1591
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• 2004

Flow visualization experiments have been performed to investigate the effects of phase lag, reduced frequency qualitatively by examining wake pattern on a dragonfly type wing. The model was built with a scaled-up, flapping wings, composed of paired wings with fore- and hindwing in tandem, that mimicked the wing form of a dragonfly. The present study was conducted by using the smoke-wire technique, and an electronic device was mounted to find the exact positional angle of wing below the tandem wings, which amplitude is ranged from $-16.5^{\circ}$ to $+22.8^{\circ}$. Phase lag applied on the wings is $0^{\circ}$, $90^{\circ}$, $180^{\circ}$ and $270^{\circ}$. The reduced frequency is 0.15, 0.3 and 0.45 to investigate the effect of reduced frequency. It is inferred through observed wake pattern that the phase lag clearly plays an important role in the wake structures and in the flight efficiency as changing the interaction of wings. The reduced frequency also is closely related to wake pattern and determines flight efficiency.