• 한국추진공학회지
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• 제22권5호
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• pp.141-151
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• 2018

발사체 경량화에 따른 한국형발사체 투입성능 예측을 위해 궤적계산 프로그램을 작성하였다. 이 프로그램을 이용하여 단 별 구조비 감소 및 엔진 성능 개선에 따른 지구 저궤도 및 태양동기궤도 투입성능을 추정하였으며, 목표궤도에 투입 가능한 페이로드 중량을 성능 판단지표로 두었다. 한국형발사체의 구조비를 기존 대비 60% 수준까지 경량화 할 경우, 지구 저궤도 및 태양동기궤도에 최대 4.5톤, 3톤의 우주화물을 수송할 수 있을 것으로 보인다. 구조 경량화와 함께 90톤급, 10톤급의 개선 엔진을 탑재할 경우 태양동기궤도에 최대 3.65톤의 페이로드를 투입할 수 있다.

• Wind and Structures
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• 제38권5호
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• pp.381-398
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• 2024

This study presents a mode analysis of 3D turbulent velocity data around a square-section building model to identify the dynamic system for Kármán-type vortex shedding. Proper orthogonal decomposition (POD) was first performed to extract the significant 3D modes. Magnitude-squared coherence was then applied to detect the phase consistency between the modes, which were roughly divided into three groups. Group 1 (modes 1-4) depicted the main vortex shedding on the wake of the building, with mode 2 being controlled by the inflow fluctuation. Group 2 exhibited complex wake vortexes and single-sided vortex phenomena, while Group 3 exhibited more complicated phenomena, including flow separation. Subsequently, a third-order polynomial regression model was used to fit the dynamics system of modes 1, 3, and 4, which revealed average trend of the state trajectory. The two limit cycles of the regression model depicted the two rotation directions of Kármán-type vortex. Furthermore, two characteristic periods were identified from the trajectory generated by the regression model, which indicates fast and slow motions of the wake vortex. This study provides valuable insights into 3D mode morphology and dynamics of Kármán-type vortex shedding that helps to improve design and efficiency of structures in turbulent flow.

• 한국수자원학회논문집
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• 제50권6호
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• pp.429-440
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• 2017

대한민국 서해안의 4개 갯벌에 대한 변화 탐지를 위해 다중분광 고해상도 다목적 위성인 KOMPSAT 시리즈 영상 자료를 분석하였다. 무감독 분류법을 이용하여 고해상도 위성 이미지에서 생성된 토지이용 및 토피피복 지도의 활용성과 연안 습지 변화의 경향을 결정할 때 시간 궤적 분석과 통합된 변화 탐지 방법론을 평가했다. 자연 현상과 인위적 활동에 대한 토지이용 및 토지피복 변화 분석을 통해 갯벌면적을 추출하고, 양질의 주제지도를 제공하기 위한 고해상도 KOMPSAT 데이터의 실질적인 적용 가능성을 확인하였다. 경기도와 전라북도의 갯벌 지역은 조석 차에 영향으로 면적 변화가 나타난 것으로 추정되었으며, 새만금 지역의 갯벌지역은 대규모 매립 및 도시화로 인한 인위적 활동에 따른 것으로 나타났다. 또한 전라남도 증도 갯벌지역의 경우 연안습지보호지역으로 지정되어 연안 갯벌 보전에 대한 사회적, 환경적 정책의 효과를 확인하였다. 따라서 고해상도 KOMPSAT를 이용한 습지변화 모니터링은 연안환경 관리 및 정책결정을 위해서 유용할 것으로 기대된다.

• 사회복지연구
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• 제45권2호
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• pp.5-30
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• 2014

본 연구의 목적은 아동기와 청소년기에 걸쳐 또래괴롭힘 피해경험 정도의 변화에 따라 구분되는 잠재계층의 수와 그 모양을 파악하고, 각 발달유형별 내면화 및 외현화 문제 수준을 비교하는 데 있다. 이를 위하여 서울아동패널(Seoul Panel Study of Children)의 자료(초등학교 5학년~고등학교 2학년)를 잠재계층성장모형과 공변량분석을 사용하여 분석하였다. 분석 결과 또래괴롭힘 피해경험의 변화 형태에 따라 지속적으로 피해 경험이 낮은 '안정적 저수준 계층'(81.2%), 초기 높은 피해경험 후 피해경험이 점진적으로 줄어드는 '초기 피해후 감소 계층'(15.6%), 높은 수준의 피해경험이 발달기간 동안 지속되는 '지속적 피해계층'(3.5%)으로 세 개 유형의 잠재계층이 도출되었다. 또래괴롭힘 피해의 발달유형에 따라 내면화와 외현화 문제의 수준에 유의미한 차이가 나타났는데, 지속적 피해계층과 초기 피해 후 감소 계층 모두 안정적 저수준 계층에 비하여 3개 내면화 문제(위축성향, 우울 및 불안성향, 자살생각)의 평균추정치가 높은 것으로 나타났다. 외현화 문제의 경우 내면화 문제에 비해 상대적으로 발달유형에 따른 차이가 덜 명확하였으나, 피해지속 계층에 속한 청소년들은 나머지 두 가지 계층에 비하여 공격성과 지위비행에서 유의미하게 높은 평균점수를 보였다. 결론 및 제언에서는 또래괴롭힘 예방 프로그램 개발 및 운영을 위한 실천적 정책적 함의를 제시하였다.

• 한국추진공학회지
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• 제19권6호
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• pp.10-18
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• 2015

로켓 기반 공기흡입추진(RBCC : Rocket Based Combined Cycle) 엔진이 적용된 재사용 발사체의 요구 중량 및 성능을 분석하고 예측하였다. RBCC 엔진을 위해 개발한 엔진 모델과 비행체 궤적 모델을 통합하여 RBCC 기반 재사용 발사체의 궤적 및 성능계산 모델을 개발하였으며, 기존 논문의 결과와 비교함으로써 검증하였다. 개발된 모델과 기존 논문을 바탕으로 총 이륙중량 15톤의 재사용 발사체에 대한 무게분석과 엔진의 요구 조건을 도출하였으며, 엔진의 모드 전환 마하수 변화 등에 따른 비행체의 추진제 요구량 변화를 분석하였다.

• 한국정밀공학회지
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• 제28권1호
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• pp.48-55
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• 2011

Hydraulic excavator is one of the most widely used heavy machines in construction sites including dismantling. In the dismantling sites, the excavators equipped with crusher or breaker carry out dangerous operations, so drivers are always exposed to unexpected danger. For safety operation, remote control of the hydraulic excavator has been studied using proportional control valve, which requires an appropriate motion control of its bucket tip. In this case, kinematics and dynamics analysis have to be preceded through modeling of excavator. However, it is difficult to acquire reasonable results from the analysis due to insufficient information of physical parameters such as mass of each links and locations of mass centers, etc. This study deals with the trajectory control of bucket tip, which is based on experimental estimation of cylinder output force. The estimated forces are fed into the control of each cylinder in order to compensate gravitational and frictional effects in the cylinders. The control was applied to horizontal trajectories that are for flattening work.

• 한국운동역학회지
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• 제22권2호
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• pp.159-171
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• 2012

The purpose of this study was to provide information about kinematic variables of the gliding and delivery motion of Hyung-Keun Lee, a high school shot putter who was ranked 1st at the 2011 National Sports Festivals. Three-Dimensional motion analysis using a system of 4 video cameras at a sampling frequency of 60 Hz was conducted during shot-putting events at the 2011 National Sports Festivals. During the gliding and delivery phase of the player the results showed following characteristics; 1) The gliding technique types of the player appeared to be the short-long technique as the gliding and stance length ratio were $42.3{\pm}3.87$ % and $57.7{\pm}3.87$ %, respectively. In addition, the trajectory of shots during the gliding and delivery phase showed different trajectory patterns with "S-shaped" type of elite players due to the deviation from a central axis of the APSS (athletic-plus shot system). 2) The horizontal velocity of COG made from gliding should maintain the velocity during transition and release phase, but the player showed a small momentum for a gradual decrease of velocity. 3) Therefore, the player requires to adjust an appropriate ratio between gliding and stance length with a strong muscle power at the trunk, throwing arm, and the lower extremity during gliding and delivery phase.

• 한국운동역학회지
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• 제22권3호
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• pp.269-276
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• 2012

The purpose of This study's aim is to examine the difference in the changes of body segment movement, variables for ball quality, and carry at golf driver swing according to the ball quality using comparative analysis. Regarding the impact variables according to the ball quality using the track man and carry, club speed was the fastest at draw shot, ball speed was the fastest at straight shot, and smash factor was the lowest at draw shot. About the vertical launch angle, the fade shot showed the highest launch angle while the max height of the ground and ball was the highest at fade shot. And carry was the longest at draw shot. For the flight time, it was the longest at draw shot. The landing angle was the largest at fade shot. About the club head position change and trajectory, at the overall event point, the fade shot drew a more outer trajectory at the point of the follow through(E6) than the straight or draw shot. Regarding the angular speed of shoulder rotation, at the overall event point, the fade shot showed the greatest angular speed change in the follow through(E6). Also, about the angular speed of pelvic rotation, at the overall event point, the draw shot showed the greatest angular speed change at the point of down swing(E4). Concerning the stance angle change, both straight and fade shots were open as the concept of open stance whereas the draw shot was close as that of close stance. Regarding the previous study, the most important factor of deciding Ball Quality is the club face angle's open and close state at Impact. In short, the Ball Quality and carry were decided by this factor.

• 대기
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• 제17권4호
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• pp.407-420
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• 2007

Optical characteristics of aerosols in Seoul are investigated from the measurements of sky radiance by Skyradiometer at Yonsei University from December 2005 to November 2006. Aerosol optical depth (AOD) shows a maximum in June due to weak ventilation and particle growth by aging process and hygroscopic effect. Single scattering albedo (SSA) and Angstrom Exponent (AE) show the lowest value in spring due to the Asian dust. It is clear that coarse mode is dominant in spring and fine mode is dominant in summer from the volume size distribution measured in this study. The explanations on the changes of aerosol loadings are provided through the correlation between AOD and AE, while the pattern of wavelength dependency related to particle size is shown through the correlation between SSA and AE. Backward trajectory analysis by HYSPLIT provides information about origin of aerosol, which allows us to classify the case according to the source region and the path distance. Although the direction of backward trajectory traces back mostly to west, coarse mode particle is dominant in the case of long pathway and fine mode particle is dominant in the case of short pathway. This discrepancy is caused by the regional difference of emitted particles.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권10호
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• pp.2529-2547
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• 2012

In this paper, we use a quadrotor-based mobile sink to gather sensor data from the terrestrial deployed wireless sensor network. By analyzing the flight features of the mobile sink node, we theoretically study the flight constraints of height, velocity, and trajectory of the mobile sink node so as to communicate with the terrestrial wireless sensor network. Moreover, we analyze the data amount which the mobile sink can send when it satisfies these flight constraints. Based on these analysis results, we propose a data acquisition approach for the mobile sink node, which is discussed detailed in terms of network performance such as the transmission delay, packet loss rate, sojourning time and mobile trajectory when given the flying speed and height of the mobile sink node. Extensive simulation results validate the efficiency of the proposed scheme.