• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.348-357
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• 2008

The classification of the effect of ionospheric disturbances on the radio occultation signal amplitude has been introduced based on an analysis of more than 2000 seances of radio occultation measurements per formed with the help of the CHAMP German satellite. The dependence of the histograms of variations in the radio occultation signal amplitude on the IMF variation index has been revealed. It has been indicated that it is possible to introduce the radio occultation index characterizing the relation between ionospheric disturbances and solar activity. An amplitude radio occultation (RO) method is proposed to study connection between the ionospheric and solar activity on a global scale. Sporadic amplitude scintillation observed in RO experiments contain important information concerning the seasonal, geographical, and temporal distributions of the ionospheric disturbances and depend on solar activity. The probability of strong RO amplitude variations (RO $S_4$ index greater than 0.2) in the CHAMP RO signals diminishes sharply with the weakening of solar activity from 2001 to 2008. The general number of RO events with strong amplitude variations can be used as an indicator of the ionospheric activity. We found that during 2001-2008 the daily globally averaged RO $S_{4a}$ index depends essentially on solar activity. The maximum occurred in January 2002, minimum has been observed in summer 2008. Different temporal behavoir of $S_{4a}$ index has been detected for polar (with latitude greater than $60^{\circ}$) and low latitude (moderate and equatorial) regions. For polar regions $S_{4a}$ index is slowly decreasing with solar activity. In the low latitude areas $S_{4a}$ index is sharply oscillating, depending on the solar ultraviolet emission variations. The different geographical behavoir of $S_{4a}$ index indicates different origin of ionospheric plasma disturbances in polar and low latitude areas. Origin of the plasma disturbances in the polar areas may be connected with influence of solar wind, the ultraviolet emission of the Sun may be the main cause of the ionospheric irregularities in the low latitude zone. Therefore, the $S_{4a}$ index of RO signal is important radio physical indicator of solar activity.

• Wind and Structures
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• 제5권2_3_4호
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• pp.291-300
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• 2002

An efficient large eddy simulation algorithm is used to compute surface pressure distributions on an eleven story (target) building on the NIST campus. Local meteorology, neighboring buildings, topography and large vegetation (trees) all play an important part in determining the flows and therefore the pressures experienced by the target. The wind profile imposed at the upstream surface of the computational domain follows a power law with an exponent representing a suburban terrain. This profile accounts for the flow retardation due to friction from the surface of the earth, but does not include fluctuations that would naturally occur in this flow. The effect of neighboring buildings on the time dependent surface pressures experienced by the target is examined. Comparison of the pressure fluctuations on the single target building alone with those on the target building in situ show that, owing to vortices shed by the upstream buildings, fluctuations are larger when such buildings are present. Even when buildings are lateral to or behind the target, the pressure disturbances generate significantly different flows around this building. A simple grid-free mathematical model of a tree is presented in which the trunk and the branches are each represented by a collection of spherical particles strung together like beads on a string. The drag from the tree, determined as the sum of the drags of the component particles, produces an oscillatory, spreading wake of slower fluid, suggesting that the behavior of trees as wind breakers can be modeled usefully.

• 전기학회논문지
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• 제65권1호
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• pp.23-30
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• 2016

Wake effects cause wind turbine generators (WTGs) within a wind power plant (WPP) to produce different levels of active power and subsequent reactive power capabilities. Further, the impedance between a WTG and the point of interconnection (POI)-which depends on the distance between them-impacts the WPP's reactive power injection capability at the POI. This paper proposes a voltage control scheme for a WPP based on the available reactive current of the doubly-fed induction generators (DFIGs) and its impacts on the POI to improve the reactive power injection capability of the WPP. In this paper, a design strategy for modifying the gain of DFIG controller is suggested and the comprehensive properties of these control gains are investigated. In the proposed scheme, the WPP controller, which operates in a voltage control mode, sends the command signal to the DFIGs based on the voltage difference at the POI. The DFIG controllers, which operate in a voltage control mode, employ a proportional controller with a limiter. The gain of the proportional controller is adjusted depending on the available reactive current of the DFIG and the series impedance between the DFIG and the POI. The performance of the proposed scheme is validated for various disturbances such as a reactive load connection and grid fault using an EMTP-RV simulator. Simulation results demonstrate that the proposed scheme promptly recovers the POI voltage by injecting more reactive power after a disturbance than the conventional scheme.

• 대한기계학회논문집A
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• 제38권1호
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• pp.1-9
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• 2014

로터에 작용하는 불균형한 반복 하중은 풍력발전기에 구조적 하중을 발생시키고 이러한 하중이 구조물에 지속적으로 누적되면 피로 파괴와 수명 단축을 발생시킨다. Individual pitch control(IPC)는 이러한 구조적 하중을 저감시키고 풍력발전기의 작동 수명 연장에 효과가 있는 제어 방법이다. 본 연구에서는 Decentralized LQR(DLQR)과 Disturbance accommodating control(DAC)를 이용한 IPC 설계를 제시한다. DLQR은 로터 회전속도 제어를 위해 사용하였고 DAC는 블레이드에 외란으로 작용하는 바람(난류) 효과를 상쇄하도록 구성하였다. 제시된 IPC제어기의 구조적 하중 저감 효과는 Gain-scheduled PI로 설계된 Collective pitch control(CPC)과 비교하여 확인하였다. 또한, IPC의 구조물 하중 저감 효과를 확인하기 위해 피로 누적에 의한 손상정도를 나타내는 피로등가하중(DEL)을 이용하였다.

• 정보와 통신
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• 제15권9호
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• pp.97-106
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• 1998

태양면의 교란으로 야기되는 지구근방 우주환경의 변화는 인류에게 막대한 사회경제적인 손실을 유발하므로 이를 예측하는 것은 매우 중요한 일이다. 본 연구에서 도입한 자기폭풍 예보코드는 이러한 변화양상을 지자기활동지수인 AE 및 Dst, 극관횡단전위차, 극지방전리층에서 소모되는 에너지 그리고 여기에 수반되는 열권의 온도상승 등의 형태로 예보하도록 고안되었다. 본 예보코드는 플레어 관측으로부터 태양풍 그리고 행성간자기장을 예측하는 부분과 추정된 태양풍파라미터로 표현되는 태양풍-자기권상호작용함수인 $\varepsilon$으로부터 상기 물리량들은 추정하는 부분으로 나누어져 있다. 1993년 11월 초에 발생한 자기폭풍에 이 예보코드를 적용하여 그 결과를 일본인공위성인 Geotail에 의한 태양풍관측결과와 지자기관측소에서 얻은 지자기 활동지수들과 비교하였다. 비록 많은 부분에서 아직 개선되어야할 여지가 발견되었지만 태양 플레어로 야기되는 지구근방 우주환경에 교란상태를 예측하는데 근사적이지만 본 예보모델이 사용될 수 있음을 확인하였다.

• 한국항해항만학회지
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• 제34권10호
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• pp.735-740
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• 2010

이 연구는 천수역에서 강한 바람과 조류하에 근접 항행중인 두 선박간의 상호유체력이 선박조종운동에 미치는 영향에 대해서 다룬다. 천수역에서 추월 및 피추월관계에 있는 대형선박의 조종운동은 바람, 조류 및 두 선박간의 상호유체력으로 인하여 상당히 복잡해진다. 이 연구의 목적은 안전항행을 위하여 천수역에서 강한 바람 및 조류하에 근접 항행중인 두 대형선박에게 요구되어지는 두 선박간의 속도에 따른 안전항과거리에 대해서 검토, 고찰하고자 한다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.1166-1171
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• 2008

Through Korean high speed train development project "G7 Leading Technology Development Project" from 1996 to 2002, HSR-350X has been developed. It can run the maximum operating speed of 350 km/h. Based on this technology, KTX-2 which will be served commercially has been developed till 2007. This paper introduces the aerodynamic analysis of the High-Speed EMU and shows the results of optimized aerodynamic nose shape design techniques and clean pantograph panhead original techniques study. These are the important parts of developments for high speed train which maximum speed is 400 km/h. Especially for decrease of tunnel micro pressure waves, the optimized nose area distributions were derived and the characteristics of micro pressure wave were analyzed. The robust optimized pantograph panhead shapes investigated to improve the performance and decrease the vortex flow which is thought to be its noise source. These shapes are clean and robust to external disturbances like unsteady accelerated flow or side wind was derived. Finally aerodynamic performances was verified with PIV and smog visualization by wind tunnel test.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 1999년도 추계학술대회논문집
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• pp.333-344
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• 1999

Currently many studies on the unmanned gantry crane for the automated container terminal are accomplished. This is needed for the development of large scale, automation, high speed, unmanned system and information system in port facility. In order to do efficient container handling job in port yard, the automated handling system is well adapted to the job environments and all-season weather, In order to realize the automatic and unmanned system for container handling job, the required functions and main structure system are studied. The major problems of operation of the conventional gantry crane are that the vibration of gantry structure body is occurred by operation and that high-speed and precision position-velocity control and the capability to dope to the external disturbances caused by the wind, rain, fog and job environments. In this paper, the fundamental study for establishment of the concept and the dynamic modelling of the major sub system of the unmanned gantry crane is presented. These studies are useful for design and manufacturing of the new concept model of the unmanned gantry crane for efficient operation of the automated container terminal.

• 해양환경안전학회지
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• 제24권7호
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• pp.953-959
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• 2018

본 논문에서는 바람, 파도, 조류 등의 큰 외란조건에서 선박계류시스템의 계류안정성 확보를 위한 동적제어기 설계를 연구하였다. 선박계류시스템의 비선형 동요를 억제하기 위해 슈퍼트위스팅 알고리즘(STA)을 포함한 슬라이딩 모드 제어(SMC) 기법이 적용되었다. 외란이나 파라미터의 불확실성에 대한 강인성의 장점에도 불구하고, 채터링은 슬라이딩 모드 제어기를 적용하는데 주요 단점이 되고 있다. 1차계 SMC는 정확히 제어 목표치에 수렴 하도록 정밀한 제어는 가능하나, 채터링과 같은 파괴적인 현상과 연계되어 적용에 주요한 장애가 된다. 대신에, STA는 큰 외란에도 불구하고 비교적 높은 정확도를 보이며 채터링 현상을 완전히 제거한다. 1차계 슬라이딩 모드 제어기의 채터링 문제를 피할 수 있는 STA기반의 SMC는 비선형 계류시스템의 동적제어를 위한 아주 효과적인 수단으로 판단된다. 아울러, STA로 제어된 선박계류시스템의 위치오차 궤적은 경계 구역 내에서 형성된다. 끝으로, 슬라이딩 표면과 위치궤적의 오차결과를 통해 STA의 이득제어 효과도 관측할 수 있다.

• 천문학회보
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• 제38권2호
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• pp.93.1-93.1
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• 2013

The Earth's radiation belts consist of an inner belt and an outer belt, being separated by the slot region. It is well known that the variations of the inner edge of the outer belt and the location of the plasmapause (Lpp) are closely related to each other. Different waves exist inside and outside the plasmasphere, playing different roles in the particle dynamics. The plasmapause is well known to be influenced by solar wind conditions and geomagnetic disturbances. Therefore, it is important to precisely determine the location of the plasmapause and develop a prediction scheme. In this study, we identified the location of the plasmapause using the plasma density data from the Time History of Events and Macroscale Interactions During Substorms (THEMIS). The plasmapause is determined by requiring density gradient of a factor of 15 within L-change = 0.5. We statistically determined Lpp as a function of preceding geomagnetic indices. Also, we determined the relations between Lpp and preceding solar wind conditions by estimating correlation coefficients. These relations give us predicting models of Lpp as a function of preceding solar wind parameters and geomagnetic indices. As our database covers a period over the ascending phase from near-sunspot minimum, our statistical results differ somewhat from previous works that cover near-sunspot maximum. Finally, we give some comparative examples obtained from the Van Allen Probes data.