• Wind and Structures
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• 제12권4호
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• pp.383-400
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• 2009

Low rise building roofs can be subjected to large fluctuating pressures during a tropical cyclone resulting in fatigue failure of cladding. Following the damage to housing in Tropical Cyclone Tracy in Darwin, Australia, the Darwin Area Building Manual (DABM) cyclic loading test criteria, that loaded the cladding for 10000 cycles oscillating from zero to a permissible stress design pressure, and the Experimental Building Station TR440 test of 10200 load cycles which increased in steps to the permissible stress design pressure, were developed for assessing building elements susceptible to low cycle fatigue failure. Recently the 'Low-High-Low' (L-H-L) cyclic test for metal roofing was introduced into the Building Code of Australia (2007). Following advances in wind tunnel data acquisition and full-scale wind loading simulators, this paper presents a comparison of wind-induced cladding damage, from a "design" cyclone proposed by Jancauskas, et al. (1994), with current test criteria developed by Mahendran (1995). Wind tunnel data were used to generate the external and net pressure time histories on the roof of a low-rise building during the passage of the "design" cyclone. The peak pressures generated at the windward roof corner for a tributary area representative of a cladding fastener are underestimated by the Australian/New Zealand Wind Actions Standard. The "design" cyclone, with increasing and decreasing wind speeds combined with changes in wind direction, generated increasing then decreasing pressures in a manner similar to that specified in the L-H-L test. However, the L-H-L test underestimated the magnitude and number of large load cycles, but overestimated the number of cycles in the mid ranges. Cladding elements subjected to the L-H-L test showed greater fatigue damage than when experiencing a five hour "design" cyclone containing higher peak pressures. It is evident that the increased fatigue damage was due to the L-H-L test having a large number of load cycles cycling from zero load (R=0) in contrast to that produced during the cyclone.

• 한국환경복원기술학회지
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• 제22권6호
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• pp.1-14
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• 2019

Carbon storage is one of the regulating ecosystem services provided by urban street trees. It is important that evaluating the economic value of ecosystem services accurately. The carbon storage of street trees was calculated by measuring the morphological parameter on the field. As the method is labor-intensive and time-consuming for the macro-scale research, remote sensing has been more widely used. The airborne Light Detection And Ranging (LiDAR) is used in obtaining the point clouds data of a densely planted area and extracting individual trees for the carbon storage estimation. However, the LiDAR has limitations such as high cost and complicated operations. In addition, trees change over time they need to be frequently. Therefore, Structure from Motion (SfM) photogrammetry with unmanned Aerial Vehicle (UAV) is a more suitable method for obtaining point clouds data. In this paper, a UAV loaded with a digital camera was employed to take oblique aerial images for generating point cloud of street trees. We extracted the diameter of breast height (DBH) from generated point cloud data to calculate the carbon storage. We compared DBH calculated from UAV data and measured data from the field in the selected area. The calculated DBH was used to estimate the carbon storage of street trees in the study area using a regression model. The results demonstrate the feasibility and effectiveness of applying UAV imagery and SfM technique to the carbon storage estimation of street trees. The technique can contribute to efficiently building inventories of the carbon storage of street trees in urban areas.

• 항공우주기술
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• 제9권2호
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• pp.161-167
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• 2010

지구관측을 위한 광학위성에 탑재되는 고해상도 영상 획득을 목적으로 하는 위성카메라의 카메라전자부(CEU : Camera Electronic Unit)는 CC(Camera Controller)와 FPA(Focal Plane Assembly), CEUP(CEU Power supply)로 구성된다. 본 논문은 광학위성 탑재체(CEU)의 전자파시험결과와 이를 토대로 한 시스템 양립성 검토결과를 설명하였다. CEU의 1차 전자파시험은 전도성 방출시험, 전도성 감응시험, 복사성 방출시험 및 복사성 감응시험을 수행하였고 2차 시험에서는 1차 시험에서 규격을 만족하지 못함으로서 시스템 성능에 중요한 영향을 미칠 수 있는 복사성 방출시험과 복사성 감응시험을 차폐제를 이용하여 기구적인 차폐를 보강 후 수행하였다. 2차 시험결과에 대한 시스템 양립성은 탑재체(CEU)에서 방출하는 노이즈의 주파수성분이 위성의 GPS/S-Band 수신 성능에 미치는 영향성을 분석하였다. 기구적인 차폐보강이 전제되었을 때, 두 수신대역 내에서 발생하고 있는 노이즈 주파수성분에 대하여 6dB 이상의 마진을 갖는 것으로 나타났다.

• 한국항공우주학회지
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• 제41권7호
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• pp.588-595
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• 2013

항공탑재 SAR 시스템은 유/무인 항공기에 탑재되어 고해상 영상정보 수집과 지상 이동 표적 탐지의 임무를 담당하는 영상 레이더 시스템으로, 선진국을 중심으로 운용되고 있으며 국내에서도 현재 개발이 진행 중에 있다. 본 논문에서는 항공탑재 SAR 시스템 운용을 위한 운용요구조건 및 운용 요구조건을 만족하기 위한 다중모드 및 실시간 SAR 시스템 운용개념에 대하여 기술한다. 항공 시스템과의 연동개념, 시스템 상태정의 및 천이개념, 임무정의파일 기반 임무수행 개념, 고장진단 및 관리개념, 촬영자료 저장 및 전송 개념에 대해 설명하고, 지상검증시험을 통한 SAR 시스템 운용개념 검증 결과에 대해 기술한다.

• 한국산학기술학회논문지
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• 제9권1호
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• pp.114-121
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• 2008

비디오 데이터를 효율적으로 처리하기 위해서는 비디오 데이터가 가지고 있는 내용에 대한 정보를 데이터베이스에 저장하고 사용자들의 다양한 질의를 처리할 수 있는 의미기반 검색 기법이 요구된다. 본 논문에서는 주석기반 검색과 특징기반 검색을 이용하여 대용량의 비디오 데이터에 대한 사용자의 다양한 의미검색을 지원하는 에이전트 기반에서의 자동화되고 통합된 환경 교육 컨텐츠 검색을 위한 비디오 의미기반 검색 시스템을 제안한다. 사용자의 기본적인 질의와 질의에 의해 추출된 키 프레임의 이미지를 선택함으로써 에이전트는 추출된 키 프레임의 주석에 대한 의미를 더욱 구체화시킨다. 또한, 사용자에 의해 선택된 키 프레임은 질의 이미지가 되어 제안하는 특징기반 검색기법을 통해 가장 유사한 키 프레임을 검색한다. 설계하고 구현한 시스템은 실험을 통한 성능평가에서 90% 이상의 높은 정확도를 보였다.

• 한국강구조학회 논문집
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• 제22권6호
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• pp.523-532
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• 2010

콘크리트가 충전된 각형강관기둥(이하, 각형 CFT기둥)은 높은 내화성능과 하중저항능력을 보유하고 있지만, CFT기둥의 외부에 내화피복을 함으로써 기둥의 내화성능을 향상시킬 필요가 있다. 본 연구는 내화 피복된 각형 CFT기둥의 온도분포에 대한 실험결과이다. 실험을 위하여 특수 제작된 전기로를 이용하여 축소모형 시험체의 재하가열실험을 수행하였다. 축하중을 받는 내화 피복된 각형 CFT기둥의 온도 분포 특성을 파악하기 위하여 내화피복의 종류와 두께, 강관의 두께 및 가열시간 등을 변수로 설정하였다. 실험결과 전기로의 온도에 따른 시험체별 온도분포와 콘크리트와 강재의 온도분포 특성을 파악하였다. 또한 시험체의 온도변화에 따른 축변위와 국부좌굴 등의 거동을 파악하였다.

• Advances in aircraft and spacecraft science
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• 제4권5호
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• pp.503-514
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• 2017

The attitude control of an aircraft is usually fulfilled by means of thrusters at high altitudes. Therefore, the possibility of using also aerodynamic surfaces would produce the advantage of reducing the amount of fuel for the thrusters to be loaded on board. For this purpose, Zuppardi already considered some aerodynamic problems linked to the use of a wing flap in a previous paper. A NACA 0010 airfoil with a trailing edge flap of 35% of the chord, in the range of angle of attack 0-40 deg and flap deflections up to 30 deg was investigated. Computer tests were carried out in hypersonic, rarefied flow by a direct simulation Monte Carlo code at the altitudes of 65 and 85 km of Earth Atmosphere. The present work continues this subject, considering the same airfoil and free stream conditions but two flap extensions of 45% and 25% of the chord and two flap deflections of 15 and 30 deg. The main purpose is to compare the influence of the flap dimension with that of the flap deflection. The present analysis is carried out in terms of: 1) percentage variation of the global aerodynamic coefficients with respect to the no-flap configuration, 2) increment of pressure and heat flux on the airfoil lower surface due to the Shock Wave-Shock Wave Interaction (SWSWI) with respect to the same quantities with no SWSWI or in no-flap configuration, 3) flap hinge moment. Issues 2) and 3) are important for the design of the mechanical and thermal protection system and of the flap actuator, respectively. Under the above mentioned test and geometrical conditions, the flap deflection is aerodynamically more effective than the flap extension, because it involves higher variation of the aerodynamic coefficients. However, tests verify that a smaller deflection angle involves the advantage of a smaller increment of pressure and heat flux on the airfoil lower surface, due to SWSWI, as well as a smaller hinge moment.

• Journal of Astronomy and Space Sciences
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• 제28권1호
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• pp.55-62
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• 2011

The precise orbit determination (POD) of low earth orbiter (LEO) has complied with its required positioning accuracy by the double-differencing of observations between International GNSS Service (IGS) and LEO to eliminate the common clock error of the global positioning system (GPS) satellites and receiver. Using this method, we also have achieved the 1 m positioning accuracy of Korea Multi-Purpose Satellite (KOMPSAT)-2. However double-differencing POD has huge load of processing the global network of lots of ground stations because LEO turns around the Earth with rapid velocity. And both the centimeter accuracy and the near real time (NRT) processing have been needed in the LEO POD applications--atmospheric sounding or urgent image processing--as well as the surveying. An alternative to differential GPS for high accuracy NRT POD is precise point positioning (PPP) to use measurements from one satellite receiver only, to replace the broadcast navigation message with precise post processed values from IGS, and to have phase measurements of dual frequency GPS receiver. PPP can obtain positioning accuracy comparable to that of differential positioning. KOMPSAT-5 has a precise dual frequency GPS flight receiver (integrated GPS and occultation receiver, IGOR) to satisfy the accuracy requirements of 20 cm positioning accuracy for highly precise synthetic aperture radar image processing and to collect GPS radio occultation measurements for atmospheric sounding. In this paper we obtained about 3-5 cm positioning accuracies using the real GPS data of the Gravity Recover and Climate Experiment (GRACE) satellites loaded the Blackjack receiver, a predecessor of IGOR. And it is important to reduce the latency of orbit determination processing in the NRT POD. This latency is determined as the volume of GPS measurements. Thus changing the sampling intervals, we show their latency to able to reduce without the precision degradation as the assessment of their precision.

• 조명전기설비학회논문지
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• 제21권7호
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• pp.103-108
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• 2007

신경회로망은 많은 제어 시스템 분야에서 이용되고 있으나, 단일 궤환 신경회로망 제어기로 사용할 경우 입출력 패턴을 구하기 쉽지 않고, 부하급변 및 외란이 인가되는 경우에는 만족할만한 성능을 얻을 수 없었다. 이러한 문제를 해결하기 위해 본 논문에서는 신경회로망 출력노드의 활성화 함수 대신에 제어 대상체를 사용하는 새로운 알고리즘을 제안하였다. 결과적으로 제안된 신경회로망 자율 적응 제어 시스템은 구조가 간략화 되었으며 입출력 패턴의 문제가 해결되었고 일반적인 역전파 알고리즘을 이용하여 실시간으로 학습이 가능하게 되었다. 제안된 신경망 자율 적응 제어의 알고리즘 효과는 고속연산을 실행하는 DSP(TMS320C32)에 알고리즘을 탑재하여 A.C. 서보 모터의 속도제어에 의해서 확인하였다.

• 한국통신학회논문지
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• 제21권12호
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• pp.3205-3214
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• 1996

In this paper, the microstrip phased array antennas with coupling-slots for the base station of mobile communication is proposed and anlyzed with accurate analysis method which is based on both reciprocity principle and full-wave analysis. The basis functions used for the numerical analysis are determined depending upon the accuracy, convergence properties of the solution, and the computation time. The patch uses 3 EB mode and the slot uses IPWS mode. The designed phased array antenna has 8 slot-coupled microstrip patch array elements and the beam scanning capability is obtained by using the 4-bit PIN-diode phase shifters as switching devices which are consisted of the loaded line phase shifters for 30.deg. and 60.deg. and the reflection type phase shifters for 90.deg. and 180.deg. repectively. The 4-bits phase shifters which aremade by connecting each phase shifter have about 2.deg.-3.deg. phase errors and their insertion loss are about 3dB for each phase state. The fabricated 8-element phased array antenna with 4-bits phase shifters provides 12.deg.-14.deg. beamwidths depending on the scanning angle and is capable of scanning its beam to .+-.45.deg. with 9.deg. intervals, and the gain 12dBi. The overall results show that the slot-coupled phased array antenna has great advantages of wideband, high gain and reduced spurious radiation. Also, the antenna can be made small and thin. Furthermore, the scanning property of this antenna allows for its application in several areas, such as mobile communication system and PCS.