• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.84-88
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• 2008

The UAV propulsion system that will be operated for long time at more than 40,000ft altitude should have not only fuel flow minimization but also high reliability and durability. If this UAV propulsion system may have faults, it is not easy to recover the system from the abnormal, and hence an accurate diagnostic technology must be needed to keep the operational reliability. For this purpose, the development of the health monitoring system which can monitor remotely the engine condition should be required. In this study, a fuzzy trend monitoring method for detecting the engine faults including mechanical faults was proposed through analyzing performance trends of measurement data. The trend monitoring is an engine conditioning method which can find engine faults by monitoring important measuring parameters such as fuel flow, exhaust gas temperatures, rotational speeds, vibration and etc. Using engine condition database as an input to be generated by linear regression analysis of real engine instrument data, an application of the fuzzy logic in diagnostics estimated the cause of fault in each component. According to study results, it was confirmed that the proposed trend monitoring method can improve reliability and durability of the propulsion system for a long endurance UAV to be operated at medium altitude.

• International Journal of Industrial Entomology and Biomaterials
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• 제48권1호
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• pp.48-58
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• 2024

Reports of a global decline in pollinator populations, especially mason bees, have raised concerns regarding the maintenance of pollination interactions. Although addressing local factors causing bee decline is a potential mitigation strategy at the landscape scale, regional rates and high-latitude threats to bee diversity are unclear. We investigated the distribution of mason bees (Osmia. spp. (O. pedicornis, O. corniforns, O. taurus, and O. satoi) and measured species richness and species ratios at regional, latitudinal, and altitudinal scales. We examined the association between bee species richness and three putative environmental conditions: high-low, altitude-dependent, and latitude-dependent. The species richness of the O. pedicornis bee was the highest and it was found between latitudes 35° and 37°, and at 500-600 m in both the northern and southern hemispheres, showing an inverse latitudinal gradient of bee species richness in South Korea. Mason bee species richness and global climate are important predictors of flowering plant diversity. Climate change threatens bee and vascular plant diversity; however, the overlap between bee abundance and plant diversity can be improved by employing suitable conservation strategies.

• 항공우주
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• 제31권
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• pp.30-33
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• 1995

• E2M - 전기 전자와 첨단 소재
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• 제25권3호
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• pp.3-10
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• 2012

• 한국수소및신에너지학회논문집
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• 제28권2호
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• pp.150-155
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• 2017

Proper cooling of PEM fuel cell stack is essential for the high-performance operation of fuel cell system. Insufficient cooling of the stack can cause significant damage to components due to overheating and also can decrease cell performance by dehydration of the polymer electrolyte. In the present study, we performed a computational analysis to assess the condition of the cooling system to secure the proper temperature in fuel cell stack system for high altitude long endurance (HALE) unmanned aerial vehicle (UAV).

• International Journal of Aeronautical and Space Sciences
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• 제12권4호
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• pp.354-359
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• 2011

This study proposes a design for an airborne wind turbine generator. The proposed system comprises a cycloidal wind turbine adopting a cycloidal rotor blade system that is used at a high altitude. The turbine is mounted on a tethered balloon. The proposed system is relatively easier to be realized and stable. Moreover, the rotor efficiency is high, which can be adjusted using the blade pitch angle variation. In addition, the rotor is well adapted to the wind-flow direction change. This article proves the feasibility of the proposed system through a sample design for a wind turbine that produces a power of 30 kW. The generated wind power at 500 m height is nearly 3 times of that on the ground.

• 한국전자파학회논문지
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• 제29권6호
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• pp.415-423
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• 2018

본 논문에서는 HEMP(High-altitude Electromagnetic Pulse)와 같은 외부전자파 환경에 노출된 EMP 방호시설에 연결된 전송선로에 유기된 HEMP 위협에 대한 전도성 방호 성능 평가를 위한 E1 펄스에 대해 연구한다. 기존 E1 펄스 발생장치는 Marx Generator 고전압 승압 방식을 사용하지만, 본 연구에서는 광대역 출력전압(30~350 kV) 가변이 용이한 Tesla Transformer 방식을 사용한다. E1 펄스 발생장치의 구성 요소인 제어기, 전원장치, 고전압 승압장치, 펄스성형장치도 각각 분석한다. Tesla Transformer를 이용한 E1 펄스는 시뮬레이션을 통해 성능을 예측하고, 실제 개발된 장비를 이용하여 결과를 검증한다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.197-202
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• 2006

The low-altitude earth observation satellite is generally equipped with high performance camera as a main payload which is vulnerable to vibration environment. During the launch process of a satellite, the combustion and jet noise of launch vehicle produce severe acoustic environment and the acoustic loads induced may damage the critical equipments of the satellite including the camera. Therefore to predict and simulate the effect of the acoustic environment which the satellite has to sustain at the lift-off event is very important process to support the load-resistive design and test-qualification of components. Statistical Energy Analysis(SEA) has been widely used to estimate the vibro-acoustic responses of the structures and gives statistical but reliable results in the higher frequency region with less modeling efforts and calculation time than the standard FEA. In this study, SEA technique has been applied to a 3-Dimensional model of a low-altitude earth observation satellite to predict the acceleration responses on the structural components induced by the high level acoustic field in the launch vehicle fairing. In addition, the expected response on each critical component panel was calculated by the classical method in consideration of the mass loading and imposed sound pressure level, and then compared with SEA results.

• 한국태양에너지학회 논문집
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• 제32권4호
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• pp.71-81
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• 2012

This study for the understanding of the radiation environment according to the altitude in urban area in the summer observes the long and short wave radiation environment at the 4 urban areas with different height and the 1 suburban area. The results of this study are as follows. (1) When the altitude was high, the more short wave radiation was observed. (2) As the altitude was high, the temperature of atmosphere got lower. And because of that the downward long wave radiation was also lower. This general trend was confirmed through the study. (3) Through the observation of long wave radiation, the upper atmosphere of suburban area had the atmosphere characteristic which the temperature was rising and decreasing faster. Therefore, the difference radiation characteristics between the urban and suburban area were confirmed. (4) The result of the ratio of short wave radiation to long wave radiation(short wave radiation/long wave radiation) according to the altitude and location, the value was increased when the distance was far from the artificiality structure or a heat source, and the urban effect became smaller. Thus, it is expected that the ratio will be an evaluation index for evaluating urbanization effect.

• 한국환경복원기술학회지
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• 제7권2호
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• pp.52-61
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• 2004

This study has been carried out to classify forest vegetation in south and north slopes of Donghaksa valley for supplying basic data for conservation and restoration of the valley. With the phytosociological method, the forest of the south and north slopes of Donghaksa valley was classified as four groups; Quercus variabilis community, Quercus mongolica community, Pinus densiflora community and Carpinus laxiflora community. The dominant species were found in the order of Pinus densiflora, Quercus variabilis, Carpinus laxiflora, and Quercus mongolica. Comparing the north and south slopes, Quercus variabilis were the highest dominant species in the south and Carpinus laxiflora in the north. Pinus densiflora were the next dominant species in both south and north slopes. According to the DBH analysis result, Pinus densiflora and Quercus variabilis had density of normal distribution style among the entire community. Therefore, their dominance are expected to continue for now. But, Quercus mongolica and Carpinus laxiflora are expected to extend their influence in the future in terms of competition with Pinus densiflora. The correlation between each community and the environment according to DCCA ordination was examined in this study. The result told us that Quercus variabilis is distributed mainly on the south slope in a mid-steep and mid-altitude area. Quercus mongolica community appeared on the north slope in the steep high-altitude area that has high percentage in total nitrogen and CEC. Pinus densiflora community is distributed on both south and north slopes in a gentle slope and low-altitude area. Carpinus laxiflora is distributed on the north slope in a mid-steep and mid-altitude area.