• International Journal of Aeronautical and Space Sciences
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• 제9권2호
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• pp.48-57
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• 2008

The noise is one of the serious problems concerning helicopters operations. The issue of helicopter external noise generated mainly from a helicopter rotor has always affected the use of rotorcrafts, especially in the urban environment. The noise sources depend on the flight configurations. In particular, a noise generated by the interaction between blades and tip vortices mainly occurs during descent flight. This noise is called blade-vortex interaction (BVI) noise, and this BVI noise is particularly penalizing for helicopters. In this paper, a numerical study to capture the BVI noise is carried out. The numerical study is performed in two phases. In the first phase, a 2D simulation based on parallel BYI event of Kitapliglu et al experiment is performed. In the second phase, 3D simulation based on HART Ⅱ experiment is performed. Several experimental data such as thrust, torque, blade sectional load, its derivative and vortex location are compared with calculation results and the comparison showed reasonably good agreement.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.300-305
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• 2004

A preliminary study on. field emitter array cathodes was conducted aiming at applying for electrodymanic tether (EDT) propulsion systems. The EDT propulsion systems are assumed to use for active removal systems of post-mission spacecraft, which would otherwise become space debris. A survey on field emit-ter array cathode technology was conducted, and it showed that carbon nanotube (CNT) emitters are suit-able to EDT application. Trial fabrications and evaluation tests of CNT emitters were conducted, which demonstrated a target emission current density of 10 ㎃/$\textrm{cm}^2$. It was found out that the most important technical issue for developing CNT emitters is to improve the performance against voltage breakdown between the emitter and the opposite electrode.

• Nuclear Engineering and Technology
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• 제47권6호
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• pp.678-699
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• 2015

Although the harsh space environment imposes many severe challenges to space pioneers, space exploration is a realistic and profitable goal for long-term humanity survival. One of the viable and promising options to overcome the harsh environment of space is nuclear propulsion. Particularly, the Nuclear Thermal Rocket (NTR) is a leading candidate for nearterm human missions to Mars and beyond due to its relatively high thrust and efficiency. Traditional NTR designs use typically high power reactors with fast or epithermal neutron spectrums to simplify core design and to maximize thrust. In parallel there are a series of new NTR designs with lower thrust and higher efficiency, designed to enhance mission versatility and safety through the use of redundant engines (when used in a clustered engine arrangement) for future commercialization. This paper proposes a new NTR design of the second design philosophy, Korea Advanced NUclear Thermal Engine Rocket (KANUTER), for future space applications. The KANUTER consists of an Extremely High Temperature Gas cooled Reactor (EHTGR) utilizing hydrogen propellant, a propulsion system, and an optional electricity generation system to provide propulsion as well as electricity generation. The innovatively small engine has the characteristics of high efficiency, being compact and lightweight, and bimodal capability. The notable characteristics result from the moderated EHTGR design, uniquely utilizing the integrated fuel element with an ultra heat-resistant carbide fuel, an efficient metal hydride moderator, protectively cooling channels and an individual pressure tube in an all-in-one package. The EHTGR can be bimodally operated in a propulsion mode of $100MW_{th}$ and an electricity generation mode of $100MW_{th}$, equipped with a dynamic energy conversion system. To investigate the design features of the new reactor and to estimate referential engine performance, a preliminary design study in terms of neutronics and thermohydraulics was carried out. The result indicates that the innovative design has great potential for high propellant efficiency and thrust-to-weight of engine ratio, compared with the existing NTR designs. However, the build-up of fission products in fuel has a significant impact on the bimodal operation of the moderated reactor such as xenon-induced dead time. This issue can be overcome by building in excess reactivity and control margin for the reactor design.

• Journal of Astronomy and Space Sciences
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• 제34권1호
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• pp.7-17
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• 2017

In South Korea, there are about 80 Global Positioning System (GPS) monitoring stations providing total electron content (TEC) every 10 min, which can be accessed through Korea Astronomy and Space Science Institute (KASI) for scientific use. We applied the computerized ionospheric tomography (CIT) algorithm to the TEC dataset from this GPS network for monitoring the regional ionosphere over South Korea. The algorithm utilizes multiplicative algebraic reconstruction technique (MART) with an initial condition of the latest International Reference Ionosphere-2016 model (IRI-2016). In order to reduce the number of unknown variables, the vertical profiles of electron density are expressed with a linear combination of empirical orthonormal functions (EOFs) that were derived from the IRI empirical profiles. Although the number of receiver sites is much smaller than that of Japan, the CIT algorithm yielded reasonable structure of the ionosphere over South Korea. We verified the CIT results with NmF2 from ionosondes in Icheon and Jeju and also with GPS TEC at the center of South Korea. In addition, the total time required for CIT calculation was only about 5 min, enabling the exploration of the vertical ionospheric structure in near real time.

• 항공우주정책ㆍ법학회지
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• 제32권2호
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• pp.247-276
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• 2017

2000년대에 들어서면서 우주자산의 보호가 우주공간의 군사적 이용의 정당성 논거로서 등장하기 시작했다. 특히 미국의 경우, 우주자산의 보호를 위해서는 적대적 세력의 공격에 대한 방어만이 아니라 대응하고 차단해야한다는 정책이 공식화되었다. 이에 우주의 군사적 이용이 평화적 목적을 위한 정찰이나 통신만이 아니라 적대적 세력의 우주자산의 파괴 등의 공격적 목적을 위한 이용으로 바뀌고 있다. 우주공간에서의 공격을 상정하는 무기배치와 사용은 일방에 의한 공격만이 아니라 상대방 교전 당사자의 대응을 전제로 한다. 중국과 러시아는 UN 등에서의 국제적 논의를 통해서 우주공간에 무기의 배치를 통제하려는 노력으로 대응하고 있다. UN헌장에 따른 무력사용의 금지의 측면에서 살펴 볼 때에, 우주공간에 무기의 배치는 무기의 사용 이전에 무력사용을 억제할 수 있다는 점에서, 부당한 무력의 위협이 아닐 수 있다. 우주공간에서의 전투는 공역에서의 전투의 단순한 연장이 아니라는 점에서 전쟁법 규범의 시각에서 공역에서의 전투와 다르다. 지상에서의 전투에 사용되는 하나의 공간으로서의 공역이 이해되고 공역에서의 전투에 대한 규율 논리가 인정되어 왔다면, 우주공간은 그렇지 않다. 또한 우주공간에서의 전투는 전투원이 현장에 없을 뿐만 아니라 실제 전장에서 상당히 멀리 위치한다는 점에서 다르다. 그래서 기존의 전쟁법 규범의 패러다임만으로는 규율하기에 부족하다. 우주공간에서의 전투는 상대방이 위치한 공간만을 황폐화시킬 수 있다는 특징을 갖고 있다. 우주 폐기물 문제가 그것이다. 제한전쟁론의 측면에서 볼 때에, 우주공간에서의 전투를 과거 중세유럽에서의 single war와 같이 부수적 피해가 크지 않으므로, 그런 의미에서의 제한전쟁으로 수행하는 경우이다. 이는 우주공간에서의 전쟁의 결과에 교전국이 지상전을 수행하지 않고서도 승복하는 경우이다. 이 경우가 "허용되는 중간상태"에 가장 가까운 형태라고 판단된다. 이 경우에도 비례의 원칙 및 무차별금지원칙을 위반한다면, 위법한 전쟁이라고 보아야 할 것이다. 우주공간에서의 무기 배치와 사용의 법적 지위는 국가들의 정책 변화와 무기체계의 발전에 따라서 국가들이 어떻게 제한할 것인가에 관한 합의에 따라 결정된다고 판단된다.

• 한국항공우주학회지
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• 제37권8호
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• pp.819-827
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• 2009

본 논문에서는 한국우주인이 국제우주정거장에서 수행한 한국우주식품 10품목에 관한 관능평가결과를 분석하였다. 개인의 기호도 차이 때문에 관능평가 점수가 낮은 품목도 있었지만 대부분 높은 점수를 받았다. 해외우주인도 한국우주식품에 관하여 높은 평가를 하고 있어 향후 한국우주식품의 국제화 가능성도 확인할 수 있었다. 향후 유인우주탐사를 대비하여 한국우주식품의 품목 다양화와 우주에서 편리하게 사용할 수 있는 기능성을 갖춘 한국우주식품용 포장지 개발이 필요하다.

• International Journal of Fluid Machinery and Systems
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• 제10권3호
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• pp.240-253
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• 2017

Latin hypercube sampling is widely used design-of-experiment technique to select design points for simulation which are then used to construct a surrogate model. The exploration/exploitation properties of surrogate models depend on the size and distribution of design points in the chosen design space. The present study aimed at evaluating the performance characteristics of various surrogate models depending on the Latin hypercube sampling (LHS) procedure (sample size and spatial distribution) for a diverse set of optimization problems. The analysis was carried out for two types of problems: (1) thermal-fluid design problems (optimizations of convergent-divergent micromixer coupled with pulsatile flow and boot-shaped ribs), and (2) analytical test functions (six-hump camel back, Branin-Hoo, Hartman 3, and Hartman 6 functions). The three surrogate models, namely, response surface approximation, Kriging, and radial basis neural networks were tested. The important findings are illustrated using Box-plots. The surrogate models were analyzed in terms of global exploration (accuracy over the domain space) and local exploitation (ease of finding the global optimum point). Radial basis neural networks showed the best overall performance in global exploration characteristics as well as tendency to find the approximate optimal solution for the majority of tested problems. To build a surrogate model, it is recommended to use an initial sample size equal to 15 times the number of design variables. The study will provide useful guidelines on the effect of initial sample size and distribution on surrogate construction and subsequent optimization using LHS sampling plan.

• 한국지능정보시스템학회:학술대회논문집
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• 한국지능정보시스템학회 2001년도 The Pacific Aisan Confrence On Intelligent Systems 2001
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• pp.37-44
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• 2001

This paper describes the modeling of work environment for the extraction of abstract operation rules for cooperative work with multiple agent. We propose the modeling method using a potential field. In the method, it is applied to a box pushing problem, which is to move a box from a start to a goal b multiple agent. The agents follow the potential value when they move and work in the work environment. The work environment is represented as the grid space. The potential field is generated by Genetic Algorithm(GA) for each agent. GA explores the positions of a potential peak value in the grid space, and then the potential value stretching in the grid space is spread by a potential diffusion function in each grid. However it is difficult to explore suitable setting using hand coding of the position of peak potential value. Thus, we use an evlolutionary computation way because it is possible to explore the large search space. So we make experiments the environment modeling using the proposed method and verify the performance of the exploration by GA. And we classify some types from acquired the environment model and extract the abstract operation rule, As results, we find out some types of the environment models and operation rules by the observation, and the performance of GA exploration is almost same as the hand coding set because these are nearly same performance on the evaluation of the consumption of agent's energy and the work step from point to the goal point.

• 한국멀티미디어학회논문지
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• 제19권10호
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• pp.1782-1791
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• 2016

Various color spaces such as RGB, HSV, log-chromaticity have been used in the field of person re-identification. However, not enough studies have been done to find suitable color space for the re-identification. This paper reviews color invariance of color spaces by diagonal model and explores the suitability of each color space in the application of person re-identification. It also proposes a method for person re-identification based on a histogram refinement technique and some fusion strategies of color spaces. Two public datasets (ALOI and ImageLab) were used for the suitability test on color space and the ImageLab dataset was used for evaluating the feasibility of the proposed method for person re-identification. Experimental results show that RGB and HSV are more suitable for the re-identification problem than other color spaces such as normalized RGB and log-chromaticity. The cumulative recognition rates up to the third rank under RGB and HSV were 79.3% and 83.6% respectively. Furthermore, the fusion strategy using max score showed performance improvement of 16% or more. These results show that the proposed method is more effective than some other methods that use single color space in person re-identification.

• 우주기술과 응용
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• 제4권2호
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• pp.87-104
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• 2024

큐브위성은 저비용, 짧은 개발 기간, 임무 지향적 성능 고도화, 군집 및 편대 비행을 통한 다양한 임무 수행이 가능하여 지구관측, 우주탐사, 우주 과학기술 검증 등 다양한 분야에서 활용성이 높다. 최근 큐브위성의 활용성이 높아지고 응용 분야가 확대됨에 따라 대용량 데이터의 고속 전송에 대한 요구가 전례 없이 증가하고 있는 추세이다. 레이저 기반 자유공간 광통신 기술은 기존 전파통신 방식 대비 고속으로 대용량 데이터 전송이 가능하고, 비면허대역 스펙트럼 사용, 저비용, 저전력, 높은 보안 특성 및 소형 통신 플랫폼의 활용 가능성 등 다양한 장점이 있어 큐브위성 임무 지원을 위한 고성능 통신 수단으로 적합하다. 본 논문에서는 큐브위성 기반 우주 레이저 통신 핵심 구성요소 및 특징을 살펴보고, 최근 연구동향, 대표 기술개발 사례 그리고 실증 결과와 함께 향후 개발 계획 등에 대해 살펴보고자 한다.