• Advances in aircraft and spacecraft science
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• 제10권2호
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• pp.141-158
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• 2023

In current research work, the aerodynamics performance of a newly designed large flying V aircraft is numerically investigated. Three Flying V configurations, with V-angles of 50°, 70° and 90° that represent the minimum, moderate, and maximum configurations respectively, were designed and modeled to assess their aerodynamic performance at cruise flight conditions. The unstructured mesh was developed using ICEM CFD and Ansys-Fluent was used as an aerodynamic solver. The developed models were numerically simulated at cruise flight conditions with a Mach number equal to 0.15. K-ω SST turbulence model was chosen to account for flow turbulence.The authors performed steady flow simulations.The results obtained from the experimentation reveal that the maximum main angle configuration of 90° had the highest C_Lmax value of 0.46 compared to other configurations. While the drag coefficient remained the same for all three configurations, the 50° V-angle configuration achieved the maximum stall angle of 35°. With limited stall delay benefits, the flying V possesses no sufficient stability, due to the flow separation detected at whole elevon and winglet suction side areas at AoA equal and higher than 30°.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.275-276
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• 2002

Active-head sliders with a unimorph piezoelectric actuator for flying height control were experimentally evaluated. It was found that the normalized stroke of the actuator is 5.2 to 6 nm/V/mm without flying over the disk. However, the normalized adjustment range of flying height is about 1.6 nm/V/mm when the active-head slider is flying over the disk. This value is smaller than the measured value when the slider is not flying, because of the air pressure generated at the active pad when the pad approaches the disk surface.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.189-191
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• 2019

본 논문에서는 작은 필터인덕턴스를 갖는 새로운 소프트스위칭 3레벨 Flying Capacitor 컨버터를 제안한다. 제안한 컨버터는 보조 인덕터 La와 보조 커패시터 Ca로 인해 모든 스위치의 ZVS 턴 온을 성취하여 높은 효율을 달성할 수 있고, Flying capacitor로 인해 필터 인덕터에 걸리는 전압이 감소하며 스위치간의 위상차로 인해 동작주파수가 2배가 되어 필터 인덕턴스를 줄일 수 있다. 또한 3레벨 구조로써 800V~1000V의 고전압 응용에서 600V의 Si-MOSFET을 사용할 수 있어 도통손실을 줄일 수 있다. 제안하는 컨버터의 동작원리, 비교분석, 인터리빙 효과를 제시하고 시작품을 통해 본 논문의 타당성 및 성능을 검증하였다.

• 전기전자학회논문지
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• 제22권4호
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• pp.1006-1011
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• 2018

본 논문은 멀티비트 플라잉 커패시터의 전압제어를 이용한 3-레벨 벅 변환기를 제안한다. 기존의 3-레벨 벅 변환기는 플라잉 커패시터 전압을 제어하지 못하여 동작이 불안정하거나 플라잉 커패시터 전압을 제어하는 회로가 PWM방식에 적용되지 못하는 문제가 있었다. 또한 부하전류에 증가할 때 인덕터 전압에 오차가 발생하였다. 본 논문에서 제안하는 구조는 입력이 4개인 차동증폭기와 공통모드 피드백 회로를 이용하여 PWM모드에서 플라잉 커패시터 전압을 제어할 수 있다. 또한 3비트 플라잉 커패시터 전압 제어회로를 제안하여 부하전류에 따른 3-레벨 벅 변환기의 동작을 최적화할 수 있으며 슈미트 트리거 회로를 이용한 삼각파 생성 회로를 제안하였다. 제안하는 3-레벨 벅 변환기는 $0.18{\mu}m$ CMOS 공정으로 설계되었으며 2.7~3.6V의 공급 전압 범위와 0.7V~2.4V의 출력 전압 범위를 갖는다. 동작 주파수는 2MHz, 부하전류 범위는 30mA~500mA이며 출력 전압 리플은 최대 32.5mV로 측정되었다. 측정 결과 130mA의 부하전류에서 약 85%의 최대 전력변환 효율을 보인다.

• 전기학회논문지
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• 제61권2호
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• pp.194-198
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• 2012

This paper describes flying inspection apparatus for 22.9kV distribution line. This apparatus is composed of multi-copter(more than 4 propellers), camcorder and remote controller. The existing inspections, such as hot-line inspection job and optical inspection method and distribution Line Checking Robot, have many restrictions. A electric working vehicle and hot-line job license are essential in hot-line inspection job. Besides its high cost, it can't be applied to the electric pole over 18m and road-blocked area. Optical method can't inspect upper side of electric facilities mounted on the electric pole. Robot method can't be applied to the corroded overhead earth wire and nothing of overhead earth wire. To solve the problems, in Korea Electric Power Co., we have applied flying inspection apparatus to the 22.9kV distribution line. The results of trial application show that this paper is practical and effective for the inspection technical method in 22.9kV distribution line

• Animal Systematics, Evolution and Diversity
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• 제24권2호
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• pp.169-172
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• 2008

Sequences of mitochondrial DNA (mtDNA) cytochrome b gene (1,140 bp) and control region (803 bp) of Siberian flying squirrels from Korea (Pteromys volans aluco) and Mt. Changbai of northeast China (P. v. arsenjevi) were obtained to reexamine the taxonomic status of the Korean subspecies. In the cytochrome b gene, six haplotypes of P. v. aluco formed a clade with six haplotypes of P. v. arsenjevi, and in control region, seven haplotypes of P. v. aluco formed a clade with six haplotypes of P. v. arsenjevi. Furthermore, six haplotypes of cytochrome b gene of P. v. aluco from this study formed a clade with four haplotypes of P. v. arsenjevi in far-east Russia obtained from GenBank. We also investigated the research papers previously published that reported the length of tail vertebrae of P. volans, and found that the length was not sufficiently large as to be a key character of P. v. aluco. This result is not consistent with morphological description for its haplotype. Therefore, we conclude that P. v. aluco from Korea might possibly be a synonym of P. v. arsenjevi from northeast China and nearby Russia.

• 한국항공우주학회지
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• 제40권3호
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• pp.193-200
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• 2012

스키점프 공력 특성에 관한 자료 획득을 목적으로 전산 수치 해석을 수행하였다. 한국인의 체형을 고려한 인체 모델링 기법을 적용하였으며 해석 결과의 검증을 위해 기존 풍동실험 연구 결과를 비교 분석하였다. 다양한 비행 조건에서 공력 계수를 분석하여 최대 양항비를 나타내는 비행 자세를 발견하였다. 본 연구가 대한민국 스키점프 선수들의 비행 자세 교정과 국내 스포츠 과학 발전에 기여할 수 있을 것으로 기대한다.

• Journal of Biosystems Engineering
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• 제32권4호
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• pp.230-236
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• 2007

In this study, a tail rotor system for an agricultural RF controlled helicopter was developed and tested. This study concluded the mechanical development of the 'Agro-heli' by completing the tail rotor system and its radio console. The RF control system was closely related with the tail system for the control of flying attitude. The thrust of the tail system balance off the reaction torque, created by the main rotor. Lifting tests with and without the tail system were compared for estimating the consumption of power. The tail system would use $4{\sim}5%$ of the total power which was in an acceptable range. Flying performance and attitude was visually inspected. It showed reliable and safe control during the distance flying trials and could be adapted for utilization in aerial applications. Aerial application using an RF controlled agricultural helicopter may make precise and timely spraying possible.

• 한국환경복원기술학회지
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• 제20권2호
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• pp.1-12
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• 2017

This study aims to provide the basic habitat data for the alternative breeding sites of Family Ardeidae including Ardea cinerea, Egretta alba modesta, Egretta intermedia, Egretta garzetta, Bubulcus ibis and Nycticorax nyciticorax. Species numbers, flight directions for detecting foraging grounds and current vegetation structure were investigated nesting at Gunsan urban forest area. Data were collected over a period of 10 weeks, from 15 June - 31 August 2014. The total nest and population of Family Ardeida were 684 and 1,712 respectively. Percentage of birds observed flying in 8 major compass directions were as follows. 57.27% of all birds were observed flying northwest, 22.09% were observed flying south and 13.40% were flying north. For possible foraging areas, to the northwest, there are Geumgang river tidal flats, and to the south, paddy fields and streams within 2km. Flying directions by species (${\chi}^2=287.18$, P<.001, Cramer's V=0.12) and by seasons(${\chi}^2=839.94$, P<.001, Cramer's V=0.19) showed significant difference statistically. In relation between species and directions, 60.31% and 24.05% of Bubulcus ibis and 59.40% and 23.00% of Ardea cinerea were observed flying northwest and south respectively. Vegetation in the sites consist of an overstory of 3 to 7 species. At site 1, Pinus thunbergii was the dominant species and site 2, Chamaecyparis obtusa. Understory vegetation is composed of shrubs, saplings and small trees of Chamaecyparis obtusa, Quercus acutissima, Smilax china and Platycarya strobilacea. Egrets and herons usually nested at the dense population and canopy overlayed forest, and especially branches and leaves of smallwood with less than 10cm of breast height diameter were relatively severely damaged due to the nesting and excreta.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.143-148
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• 2004

The numerical analysis of the hard disk drive slider is presented. The pressure distribution was calculated using the finite element method. The generalized Reynolds equation was applied in order to include the gas rarefaction effect. The balance of the air bearing force and preload force was considered. The characteristics of the small vibrations near the equilibrium were studied using the perturbation method. Triangular mesh with variable element size was employed to model the two-rail slider. The flying height, pitching angle, rolling angle, stiffness and damping of the two-rail slider were calculated for radial position changing from the inner radius to the outer radius and for a wide range of the slider crown values. It was found that the flying height, pitching angle and rolling angle were increased with radial position while the stiffness and damping coefficients were decreased. The higher values of crown resulted in increased flying height, pitching angle and damping and decreased stiffness.