• International Journal of Aeronautical and Space Sciences
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• 제11권4호
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• pp.345-350
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• 2010

The repetitive vibrating action of an aerodynamic load causes an external fuel tank's horizontal fin to experience a shorter life cycle than its originally predicted one. Store separation analysis is needed to redesign the fin of an external fuel tank. In this research, free-drop tests were conducted using 15% scaled models in a subsonic wind tunnel in order to analyze the store separation characteristics of an external fuel tank. The store separation trajectory based on grid tests was also obtained to verify the results of the free-drop tests. The results acquired from the free-drop tests correlated well with the grid tests in regards to the trajectories and behavior of the stores separated from the aircraft. This agreement was especially noted in the early stages of the store separation.

• 상하수도학회지
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• 제18권2호
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• pp.222-227
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• 2004

Flotation processes involve the use of very small bubbles (micro-bubbles) to separate particles from water. The process has become a good alternative to sedimentation, especially where the particles are small or of low density. Although the flotation process commences with a collision between particles and bubbles, most research has been focused only on the characteristics of the particles. In this paper, recent theoretical and experimental research on the characteristics of bubbles is summarized. The effect on the collision efficiency of the size and charge of bubbles is calculated through trajectory analysis. The size and charge of bubbles are measured under different conditions and the ramifications of the results are discussed. The results may lead to a better understanding and optimization of the existing process. In particular, we discuss an idea that a new advanced flotation process might be possible by the modification of the characteristics of the bubble alone or of both bubble and particle.

• 대한전자공학회논문지
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• 제26권3호
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• pp.70-78
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• 1989

가변구조 제어방법을 이용하여 로보트 시스템을 제어하는데 있어서 현재까지는 가변구조 제어 파라메타에 대한 정확한 분석없이 슬라이딩 모드 존재조건 만을 고려하여 임의의 파라메타를 선정 사용하고 있기 때문에 가변구조 제어 방법의 장점을 최대로 활용하지 못하고 있다. 본 논문에서는 로보트 시스템 제어에 적용하여 조인트 각과 손의 궤적에 미치는 양향을 분석하였다. 본 논문에서 분석된 결과는 가변구조 제어 방법을 이용하여 경로 궤적계획을 하는데 효과적으로 활용될 수 있다.

• 한국소음진동공학회논문집
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• 제12권11호
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• pp.904-913
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• 2002

In this study, a dynamic analysis of the reciprocating compression mechanism considering viscous friction force of a piston used in small refrigeration compressors is performed. The length of cylinder in this class of compressors is shortening to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder liner is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the compression mechanism dynamics, the change in bearing length of the piston and all corresponding viscous forces and moments are considered in order to determine the trajectories of piston and crankshaft. The piston orbits for viscous friction model and Coulomb friction model were used to compare the effect of the friction forces of piston on the dynamic trajectories of piston. To investigate the effect of friction force acting on the piston for the dynamic characteristics of crankshaft, comparison of the crankshaft loci is given in both viscous model and Coulomb model. Results show that the viscous friction force of piston must be considered in calculating for the accurate dynamic characteristics of the reciprocating compression mechanism.

• Journal of Astronomy and Space Sciences
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• 제38권2호
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• pp.145-155
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• 2021

In this work, preliminary launch opportunities from NARO Space Center to the Sun-Earth Lagrange point are analyzed. Among five different Sun-Earth Lagrange points, L1 and L2 points are selected as suitable candidates for, respectively, solar and astrophysics missions. With high fidelity dynamics models, the L1 and L2 point targeting problem is formulated regarding the location of NARO Space Center and relevant Target Interface Point (TIP) for each different launch date is derived including launch injection energy per unit mass (C3), Right ascension of the injection orbit Apoapsis Vector (RAV) and Declination of the injection orbit Apoapsis Vector (DAV). Potential launch periods to achieve L1 and L2 transfer trajectory are also investigated regarding coasting characteristics from NARO Space Center. The magnitude of the Lagrange Orbit Insertion (LOI) burn, as well as the Orbit Maintenance (OM) maneuver to maintain more than one year of mission orbit around the Lagrange points, is also derived as an example. Even the current work has been made under many assumptions as there are no specific mission goals currently defined yet, so results from the current work could be a good starting point to extend diversities of future Korean deep-space missions.

• 한국도로학회논문집
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• 제18권5호
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• pp.117-125
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• 2016

PURPOSES : The density in uninterrupted traffic flow facilities plays an important role in representing the current status of traffic flow. For example, the density is used for the primary measures of effectiveness in the capacity analysis for freeway facilities. Therefore, the estimation of density has been a long and tough task for traffic engineers for a long time. This study was initiated to evaluate the performance of density values that were estimated using VDS data and two traditional methods, including a method using traffic flow theory and another method using occupancy by comparing the density values estimated using vehicular trajectory data generated from a radar detector. METHODS : In this study, a radar detector which can generate very accurate vehicular trajectory within the range of 250 m on the Joongbu expressway near to Dongseoul tollgate, where two VDS were already installed. The first task was to estimate densities using different data and methods. Thus, the density values were estimated using two traditional methods and the VDS data on the Joongbu expressway. The density values were compared with those estimated using the vehicular trajectory data in order to evaluate the quality of density estimation. Then, the relationship between the space mean speed and density were drawn using two sets of densities and speeds based on the VDS data and one set of those using the radar detector data. CONCLUSIONS : As a result, the three sets of density showed minor differences when the density values were under 20 vehicles per km per lane. However, as the density values become greater than 20 vehicles per km per lane, the three methods showed a significant difference among on another. The density using the vehicular trajectory data showed the lowest values in general. Based on the in-depth study, it was found out that the space mean speed plays a critical role in the calculation of density. The speed estimated from the VDS data was higher than that from the radar detector. In order to validate the difference in the speed data, the traffic flow models using the relationships between the space mean speed and the density were carefully examined in this study. Conclusively, the traffic flow models generated using the radar data seems to be more realistic.

• 한국시뮬레이션학회논문지
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• 제27권2호
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• pp.35-48
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• 2018

북한의 전술탄도미사일(TBM, tactical ballistic missile)에 대한 방공 분야 연구는 빠른 속도로 변화하는 전장 환경을 고려해야 한다. 아군 유도탄의 표적 재지정 연구는 동적인 전장에 대한 대응뿐만 아니라 아군 방어 자산의 효과적인 운용을 가능하게 한다. 현재까지 진행된 연구는 의사 결정 과정에서 중요한 역할을 하는 TBM의 명중 확률이 고정된 값이기 때문에 실시간 전장 상황을 대변하지 못한다. 따라서 본 연구는 실시간 전장 환경을 고려한 명중 확률을 기반으로 의사 결정을 내리는 표적 재지정 알고리즘을 제안한다. 제안 방법론은 랜덤 포레스트와 무빙윈도우(moving window) 기법을 사용하여 현재 TBM의 위치 및 속도 정보로 TBM의 예상 궤적을 예측하는 궤적 예측 모형을 포함한다. 예상 명중 확률은 궤적 예측 모형과 유도탄의 시뮬레이터를 통해서 계산할 수 있으며, 계산된 명중 확률은 유도탄에 대한 표적 재지정 알고리즘의 의사결정 기준이 된다. 실험에서는 TBM 궤적 예측 모형에 사용한 방법론의 타당성이 검증되었으며, 표적 재지정 의사 결정 과정에서 제안된 모델을 통해 명중 확률을 사용하는 것의 우수성이 확인되었다.

• 한국과학교육학회지
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• 제39권6호
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• pp.799-807
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• 2019

이 연구는 과학중점학교의 1학년 프로그램이 학생들의 과학과 핵심역량과 과학학습동기를 향상시키는지 확인하기 위하여 진행되었다. 과학중점학교 1학년 프로그램은 과학탐구 기초교육, 조사 발표, 심화실험, 소논문 기초교육 등으로 구성된다. 프로그램 참여자는 총 262명이며, 설문 검사를 모두 수행한 학생은 169명이다. 집단중심 추세모형 분석을 통해 유사한 점수 변화 보이는 집단으로 구분하였다. 연구 결과 과학중점학교의 1학년 프로그램은 학생들의 과학과 핵심역량과 과학학습동기를 유의미하게 향상시켰다. 집단중심 추세모형분석 결과 약 40~60%의 학생들이 프로그램의 효과를 보았다. 인문계열을 선택한 학생들 중에서도 효과가 나타나는 학생들이 있었으며, 과학중점 계열을 선택한 학생 중에서도 교육적 효과가 나타나지 않는 학생들도 일부 있었다. 집단중심 추세모형 분석을 통해 개별 학생들의 변화 과정을 확인할 수 있는 방법론적 효과를 확인하였다. 이 연구는 과학중점학교 정책의 긍정적 효과를 통계적으로 확인하였으며, 과학중점학교 프로그램의 효과 분석을 위한 사례로서 의미가 있다.

• 사회복지연구
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• 제49권3호
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• pp.209-245
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• 2018

본 연구는 인증 사회적기업의 경제적 사회적 성과지표를 활용하여 유형화를 시도하고, 통계적 적합도 지수를 통해 성과별 유의한 잠재유형을 탐색하는 것이 목적이며, 성과 유형간 조합을 분석하였다. 연구대상은 조상미 외(2011) 연구에 참여한 사회적기업 중 현재까지 운영되고 있는 기업이며 2011년 이후 6년간의 성과를 조사하여 분석하였다. 사회적기업의 경제적 성과인 매출액의 변화유형을 탐색한 결과 잠재유형이 세 개인 최적 모형을 도출하였으며 '매출성숙형', '매출증가형', '매출평균형'으로 명명하였다. 이때 매출평균형이 가장 많은 분포를 보이며, 운영기간이 타유형에 비해 짧은 것으로 나타났다. 사회적 성과인 취약계층고용율의 경우 세계의 최적모형이 탐색되었다, '고용평균형', '고용감소형', '고용증가형'으로 분류되었다. 사회적 성과는 고용평균형이 가장 많이 나타났으며, 다른 유형에 비해 매출액이 높은 것이 특징이다. 또한 사회적기업 경제적 성과의 변화유형에 따른 사회적 성과 변화유형의 분포인 $3{\times}3$의 교차유형을 살펴보았다. 교차유형에서는 '매출평균형 고용평균형', '매출평균 고용감소형'이 주를 이룬다. 이를 통해 사회적기업의 유형의 특징을 알아보고 지원 제도의 현실성 제고를 위한 정책 제안과 실행에 있어 필요한 시사점을 제시하였다.

• Journal of Korean Neurosurgical Society
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• 제62권4호
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• pp.376-381
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• 2019

Objective : To define optimal method that calculate the safe direction of cervical pedicle screw placement using computed tomography (CT) image based three dimensional (3D) cortical shell model of human cervical spine. Methods : Cortical shell model of cervical spine from C3 to C6 was made after segmentation of in vivo CT image data of 44 volunteers. Three dimensional Cartesian coordinate of all points constituting surface of whole vertebra, bilateral pedicle and posterior wall were acquired. The ideal trajectory of pedicle screw insertion was defined as viewing direction at which the inner area of pedicle become largest when we see through the biconcave tubular pedicle. The ideal trajectory of 352 pedicles (eight pedicles for each of 44 subjects) were calculated using custom made program and were changed from global coordinate to local coordinate according to the three dimensional position of posterior wall of each vertebral body. The transverse and sagittal angle of trajectory were defined as the angle between ideal trajectory line and perpendicular line of posterior wall in the horizontal and sagittal plane. The averages and standard deviations of all measurements were calculated. Results : The average transverse angles were $50.60^{\circ}{\pm}6.22^{\circ}$ at C3, $51.42^{\circ}{\pm}7.44^{\circ}$ at C4, $47.79^{\circ}{\pm}7.61^{\circ}$ at C5, and $41.24^{\circ}{\pm}7.76^{\circ}$ at C6. The transverse angle becomes more steep from C3 to C6. The mean sagittal angles were $9.72^{\circ}{\pm}6.73^{\circ}$ downward at C3, $5.09^{\circ}{\pm}6.39^{\circ}$ downward at C4, $0.08^{\circ}{\pm}6.06^{\circ}$ downward at C5, and $1.67^{\circ}{\pm}6.06^{\circ}$ upward at C6. The sagittal angle changes from caudad to cephalad from C3 to C6. Conclusion : The absolute values of transverse and sagittal angle in our study were not same but the trend of changes were similar to previous studies. Because we know 3D address of all points constituting cortical shell of cervical vertebrae. we can easily reconstruct 3D model and manage it freely using computer program. More creative measurement of morphological characteristics could be carried out than direct inspection of raw bone. Furthermore this concept of measurement could be used for the computing program of automated robotic screw insertion.