• 한국항공우주학회지
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• 제36권2호
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• pp.163-170
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• 2008

혼합 보 이론과 적정변형 보 이론에 입각한 공탄성 해석 시스템을 결합하여 유연면을 갖는 복합재료 무힌지 로터에 대한 정지 및 전진 비행시의 공탄성 해석을 수행하였다. 블레이드에 작용하는 공기력은 Leishman-Beddoes의 비정상 공력 모델을 이용하여 구했다. 인장, 회전면 내외의 굽힘, 그리고 비틀림이 상호 연계된 블레이드에 대한 운동방정식은 Hamilton의 원리에 입각하여 유도하였다. 헬리콥터 블레이드의 공탄성 해석에 주요한 요소들인 단면 벽의 두께, 탄성연계, 그리고 구성방정식에 대한 적합한 가정과 같은 주요 구조 모델링 문제들에 대한 효과들을 고찰하였다. 이러한 요소들은 블레이드 단면의 복합재료 적층 구조에 민감하게 반응하며, 블레이드 안정성에도 적지 않은 영향을 나타냄을 보였다.

• 동의생리병리학회지
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• 제22권5호
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• pp.1215-1222
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• 2008

Recent studies indicate that the deposition of ${\beta}$-amyloid ($A{\beta}$) is associated with the pathogenesis of Alzheimer's disease (AD), but the underlying mechanism is not clear yet. To investigate the effects of Jangwonhwangagambang (JWHG) extract on AD pathogenicity, we have generated transgenic Drosophila model in which GMR-APP-GAL4/UAS-GRIM system was designed to overexpress amyloid precursor protein(APP), We examined fly's survival ratio, flight behavior, and morphological patterns of chest and eye. We found that JWHG treatment improved fly's survival ratio by inhibiting apoptosis and flight behavior. APP-GRIM transgenic flies treated with JWHG showed had significantly lower levels of APP deposition in the chest and eye compared to control animals. JWHG treatment further inhibited chest and eye degeneration. These results suggest that JWHG prevents APP-induced neurotoxicity, and thus may be applicable for the development of preventive or therapeutic agents for AD treatment.

• Journal of Biosystems Engineering
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• 제37권6호
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• pp.342-351
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• 2012

Purpose: Aerial spraying with an agricultural unmanned helicopter became a new paradigm in the agricultural practice. Laterally tilting behavior of a conventional agricultural helicopter, resulting in the biased down-wash and uneven spray deposit is a physically intrinsic phenomenon while hovering and cruise flights. Authors studied and developed a roll-balanced agricultural helicopter with a raised pylon tail rotor system. In this study, the attitude of the roll-balanced helicopter was determined using the Kalman filter algorithm, and the quality of roll balancing of a bare-airframe helicopter was evaluated. Methods: Instantaneous attitudes were estimated using the advantage of gyroscope, followed by the long term correction and prediction using accelerometer data for the advantage of convergence. The attitudes of the fuselage were calculated by applying the Kalman filter algorithm. The spraying maneuver of the helicopter was performed at a field of 50 m long, and the attitude data were acquired and evaluated. Results: The determination of attitude using the inertial measurement unit(IMU) and Kalman filter was reliable and practical. The intrinsic attitude of the developed helicopter was stable and roll-balanced. The deviation of roll angle was ${\pm}6.3^{\circ}$ with an average of $0^{\circ}$, referring to roll-balanced. Conclusions: Handling quality of the roll attitude determined to be steadily balanced. The balancing behavior of the developed helicopter would result in an even spray pattern during aerial application.

• Journal of Welding and Joining
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• 제25권4호
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• pp.35-41
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• 2007

In kinetic spraying process, the critical velocity is an important criterion which determines the deposition of a feedstock particle onto the substrate. In other studies, it was experimentally and numerically proven that the critical velocity is determined by the physical and mechanical properties and the state of materials such as initial temperature, size and the extent of oxidation. Compared to un-oxidized feedstock, oxidized feedstock required a greater kinetic energy of in-flight particle to break away oxide film during impact. The oxide film formed on the surface of particle and substrate is of a relatively higher brittleness and hardness than those of general metals. Because of its physical characteristics, the oxide significantly affected the deposition behavior and critical velocity. In this study, in order to investigate the effects of oxidation on the deposition behavior and critical velocity of feedstock, oxygen contents of Al feedstock were artificially controlled, individual particle impact tests were carried out and the velocities of in-flight Al feedstock was measured for a wide range of process gas conditions. As a result, as the oxygen contents of Al feedstock increased, the critical velocity increased.

• Journal of Contemporary Eastern Asia
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• 제23권1호
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• pp.18-34
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• 2024

In what was labeled the "nut rage" incident, the vice president of Korean Air, Hyun-Ah Cho (Heather Cho), demonstrated behavior that exemplifies corporate transgression and deviation from societal moral standards toward a flight attendant aboard a flight. Such behavior instigated the public to express negative sentiment on various social media platforms. This study investigates word-of-mouth network on YouTube in response to the crisis, patterns of co-commenting activities across selected YouTube videos, as well as public responses to the incident by employing social and semantic network analysis. A total of 512 YouTube videos featuring the crisis from December 8, 2014 through November 11, 2018, and 52,772 public comments to the videos were collected. The central videos in the network successfully attracted the public's attention and engagements. The results suggest that the video network was decentralized, with multiple videos acting as hubs in the network. The public commented on various videos instead of focusing on a few. The contents of influential videos uploaded by popular news organizations revealed not only Cho's behaviors related to the nut rage crisis but also unrelated illegal behaviors and the moral violations committed by the family members of Korean Air. The public attached derogatory remarks to Cho and her family, and the comments also addressed ethical concerns, management issues of the company, and boycott intentions. The results imply that adverse public reaction was related to the long-standing problem caused by family ownership and governance in large Korean corporations. This Korean Air scandal illustrates backlash toward a leadership breakdown by the family business conglomerate prevalent in the Korean society. This study provides insights for effective handling of similar crises.

• 한국항공우주학회지
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• 제34권7호
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• pp.105-111
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• 2006

항공기 엔진은 항공기가 각종 기동을 수행하도록 추력을 발생하는 것 외에 기동 수행을 위해 작동되는 조종면에 공급될 유압계통의 동력과 각종 항전장비 작동을 위한 전기계통의 동력을 공급한다. 엔진으로부터 제공되는 동력은 엔진의 고압압축기로부터 추출되기 때문에 축마력(Horsepower Extraction, HPX)이라하며, 추출되어 제공되는 엔진 축마력이 유압계통과 전기계통에서 요구하는 요구 축마력보다 작게 되면 엔진에 과도한 부하가 걸려 엔진회전수 감소(Rollback) 및 심한 경우 실속(stall)등이 발생할 수 있다. T/A-50체계개발 동안 요구 축마력과 엔진의 공급 축마력에 대한 비교 해석을 수행하였고, 해석 결과 엔진 축마력이 요구 축마력보다 작은 것을 확인하였다. 엔진 축마력 증가를 위한 엔진 제어 스케쥴 변경이 수행되었으며, 변경된 제어 스케쥴이 장착된 엔진을 이용하여 T/A-50비행시험을 수행하였다. 비행시험 결과를 통해 해석 결과 및 변경된 제어 스케쥴의 타당성을 검증하였다.

• 한국전산유체공학회지
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• 제20권2호
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• pp.16-22
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• 2015

The pressure is generally lower than that of the freestream at the base of a missile body due to the energy loss by the flow separation around the edge of the base. The base pressure changes in the presence of the thrust jet due to the interaction between the base flow of the missile and the jet flow. In this study, behavior of the missile base pressure by the change of the jet exit pressure and the freestream condition is investigated using the CFD(Computational Fluid Dynamics) method. Effects of the grid type and the freestream condition are tested. The results are compared with the semi-empirical predictions and the flight test data. The CFD results agree well with the flight test data. The semi-empirical predictions overestimate the base pressure when jet thrust is strong for low freestream speed.

• 한국군사과학기술학회지
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• 제12권6호
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• pp.808-814
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• 2009

Numerical flow-filed computations have been conducted around a projectile with a triangular ballute at Mach numbers of 0.3 ~ 0.9 and angles of attack of $0^{\circ}\;{\sim}\;30^{\circ}$. The expansion shape of a triangular ballute has been determined from both the manufacturing dimensions and the wind tunnel test results. It has been assumed that the shape does not alter after the ballute has been expanded completely. The computed results showed a good agreement with the wind tunnel test results. A sensitivity analysis on the aerodynamic coefficients has been performed to evaluate the quantitative effects on the flight performance. Trajectory simulation results were also in good agreement with the flight test results.

• 한국항공운항학회지
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• 제23권1호
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• pp.24-29
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• 2015

In order to increase endurance flight efficiency of long endurance electric powered UAV, main wing of UAV should have high aspect ratio and low structural weight. Since a spar which consists of thin and slender structure for weight reduction can cause catastrophic failure during the flight, it is important to develop verification method of structural integrity of the spar with the light weight design. In this paper, process of structural analysis using non-linear finite element method was introduced for the verification of structural integrity of the spar. The static strength test of the spar was conducted to identify structural characteristic under the static load. Then, the experimental result of the spar was compared to the analytical result from the non-linear finite element analysis. It was found that the developed process of structural analysis could predict well the non-linear structural behavior of the spar under ultimate load.

• 한국위성정보통신학회논문지
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• 제12권1호
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• pp.22-27
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• 2017

최근 드론에 대한 관심이 높아지면서 이를 활용하는 분야도 지속적으로 증가하고 있다. 향후 드론시장은 크게 향상될 것으로 기대되며, 활용 또한 점점 더 높아지게 될 것이다. 하지만 그에 따른 부작용 역시 적지 않다. 드론을 보다 안전하고 보편적으로 이용하기 위해서는 안전과 사생활보호 등 고려해야 할 문제도 많다. 본 연구는 드론비행으로 인한 사생활침해 등 법률위반 관계를 검토하고, 이를 해결하기 위반 방안을 연구하였다. 드론비행으로 인한 인간의 삶과 행동에 평안함과 즐거움을 제공하고 있지만 이로 인한 문제점도 새롭게 발생하고 있다. 때문에 드론비행으로 인한 역기능을 줄이는 대책도 반드시 필요하다.