• 전력전자학회논문지
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• 제24권1호
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• pp.1-8
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• 2019

In this study, a maximum power point tracking (MPPT) algorithm based on the perturb and observe (P&O) method with variable step size is proposed to improve the dynamic response characteristic of MPPT, using the existing P&O method. The proposed algorithm, which we verified by simulation and experiment, can track the maximum power point (MPP) through duty control and consisted of three operation modes, namely, constant voltage mode, fast mode, and variable step mode. When the insolation is constant, the voltage variation of the operating point at the MPP is reduced through the step size reduction of the duty in the variable step mode. Consequently, the vibration of the operating point is reduced, and the power generation efficiency is increased. When the insolation changes, the duty and the photovoltaic (PV) voltage are kept constant through the constant voltage mode. The operating point then rapidly tracks the new MPP through the fast-mode operation at the end of the insolation change. When the MPP is reached, the operation is changed to the variable step mode to reduce the duty step size and track the MPP. The validity of the proposed algorithm is verified by simulation and experiment of a PV system composed of a PV panel and a boost converter.

• Wind and Structures
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• 제30권5호
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• pp.533-546
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• 2020

Large Eddy Simulation (LES) is used to study the effects of steady slot suction on the aerodynamic forces of and flow around a wall-mounted finite-length square cylinder. The aspect ratio H/d of the tested cylinder is 5, where H and d are the cylinder height and width, respectively. The Reynolds number based on free-stream oncoming flow velocity U_∞ and d is 2.78×10⁴. The suction slot locates near the leading edge of the free end, with a width of 0.025d and a length of 0.9d. The suction coefficient Q (= U_s/U_∞) is varied as Q = 0, 1 and 3, where U_s is the velocity at the entrance of the suction slot. It is found that the free-end steady slot suction can effectively suppress the aerodynamic forces of the model. The maximum reduction of aerodynamic forces occurs at Q = 1, with the time-mean drag, fluctuating drag, and fluctuating lift reduced by 3.75%, 19.08%, 40.91%, respectively. For Q = 3, all aerodynamic forces are still smaller than those for Q = 0 (uncontrolled case), but obviously higher than those for Q = 1. The involved control mechanism is successfully revealed, based on the comparison of the flow around cylinder free end and the near wake for the three tested Q values.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.7-12
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• 2007

액체로켓엔진에서 고주파 연소불안정을 제어하기 위하여 다단 접선 유입구를 갖는 스월 인젝터를 분석하였다. 음향흡수자로서 인젝터의 효과를 분석하기 위하여 인젝터는 1/4 파장 공명기로 해석하였고, 상온에서 감쇠 효과의 적합성을 검증하였다. 이러한 인젝터는 모델 챔버의 고유주파수에 동조 시킬 수 있는 고유주파수를 갖게 된다. 각각의 모드에 동조된 인젝터를 배(anti-node point)에 장착하여야만, 타겟모드의 진폭을 감소시킬 수 있었고, 큰 지름의 인젝터를 사용하였을 때 보다 큰 진폭의 감쇠를 동반하면서 모드 분리 현상이 나타났다. 이러한 실험 결과로부터 타겟모드에 동조된 인젝터를 적당한 볼륨으로 배(anti-node point)에 장착한다면, 모드 진폭이 감쇠하게 되고, 완전한 배(anti-node point)에서는 모드분리현상이 발생됨을 확인하였다.

• Smart Structures and Systems
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• 제6권9호
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• pp.1057-1077
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• 2010

An early detection of structural damages is critical for the decision making of repair and replacement maintenance in order to guarantee a specified structural reliability. Consequently, the structural damage detection, based on vibration data measured from the structural health monitoring (SHM) system, has received considerable attention recently. The traditional time-domain analysis techniques, such as the least square estimation (LSE) method and the extended Kalman filter (EKF) approach, require that all the external excitations (inputs) be available, which may not be the case for some SHM systems. Recently, these two approaches have been extended to cover the general case where some of the external excitations (inputs) are not measured, referred to as the adaptive LSE with unknown inputs (ALSE-UI) and the adaptive EKF with unknown inputs (AEKF-UI). Also, new analysis methods, referred to as the adaptive sequential non-linear least-square estimation with unknown inputs and unknown outputs (ASNLSE-UI-UO) and the adaptive quadratic sum-squares error with unknown inputs (AQSSE-UI), have been proposed for the damage tracking of structures when some of the acceleration responses are not measured and the external excitations are not available. In this paper, these newly proposed analysis methods will be compared in terms of accuracy, convergence and efficiency, for damage identification of structures based on experimental data obtained through a series of laboratory tests using a scaled 3-story building model with white noise excitations. The capability of the ALSE-UI, AEKF-UI, ASNLSE-UI-UO and AQSSE-UI approaches in tracking the structural damages will be demonstrated and compared.

• 한국지능시스템학회논문지
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• 제24권1호
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• pp.96-101
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• 2014

풍력은 전 세계적으로 가장 각광을 받고 있는 신재생 에너지이며 당분간 이러한 추세는 계속될 것으로 기대되고 있다. 최근 풍력발전시스템의 O&M(Operation & Maintenance) 비용의 절감에 대한 필요성이 꾸준히 대두되고 있는 실정이다. O&M 비용의 절감을 위한 가장 효율적인 방법은 CMS(Condition Monitoring System)의 도입이며 이는 풍력발전기 부품들의 악화, 적절한 선제적 유지보수, 발전중지시간의 단축 및 궁극적으로 풍력발전기의 운전 효율을 증대시키는 것을 가능케 한다. 풍력발전기의 터빈 로터와 관련하여 질량 불평형 및 공력비대칭과 같은 고장이 발생될 수 있다. 일반적으로 이러한 고장은 다양한 형태의 진동을 야기 시킨다. 이에 본 연구에서는 진동신호에 대한 스펙트럼과 간단한 max-min 진단 로직으로 구성된 고장검출 알고리즘을 제안한다. 또한 제안된 진단기법의 유용성의 확인을 위해 GH-Bladed 프로그램을 이용한 다양한 시뮬레이션 고찰을 수행한다.

• Structural Engineering and Mechanics
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• 제52권3호
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• pp.485-505
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• 2014

This study aimed to develop an approach to accurately predict the wind models and wind effects of large wind turbines. The wind-induced vibration characteristics of a 5 MW tower-blade coupled wind turbine system have been investigated in this paper. First, the blade-tower integration model was established, which included blades, nacelle, tower and the base of the wind turbine system. The harmonic superposition method and modified blade element momentum theory were then applied to simulate the fluctuating wind field for the rotor blades and tower. Finally, wind-induced responses and equivalent static wind loads (ESWL) of the system were studied based on the modified consistent coupling method, which took into account coupling effects of resonant modes, cross terms of resonant and background responses. Furthermore, useful suggestions were proposed to instruct the wind resistance design of large wind turbines. Based on obtained results, it is shown from the obtained results that wind-induced responses and ESWL were characterized with complicated modal responses, multi-mode coupling effects, and multiple equivalent objectives. Compared with the background component, the resonant component made more contribution to wind-induced responses and equivalent static wind loads at the middle-upper part of the tower and blades, and cross terms between background and resonant components affected the total fluctuation responses, while the background responses were similar with the resonant responses at the bottom of tower.

• 문화기술의 융합
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• 제6권1호
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• pp.477-483
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• 2020

콘크리트 박스 구조물이 열화되어 보수보강이 필요할 경우 스프레이 장비로 구조물 단면에 보수재를 분사하여 부착시키는 방법에 의존하고 있는데 천장 또는 벽체부위의 경우 시공 후 보수재 자중 또는 중력에 의해 부착력이 저하될 수 있으며 지하철 구조물의 경우 진동 등에 의해 초기 부착력이 떨어지는 문제점이 발생한다. 또한 작업자의 숙련도와 시공환경에 따라 보수품질이 변동되기에 이에 대한 보완책이 필요한 실정이다. 본 연구에서는 중력에 의한 보수재의 부착력 저하 및 인력시공에 의한 보수품질의 변동과 같은 문제점을 해결하고자 보수재 시공 후 소정의 압력을 가할 수 있는 기계식 가압장비를 개발하였다. 그리고 가압장비의 성능을 알아보고자 현장조건을 모사할 수 있는 챔버를 제작하여 가압 유무, 단면부위 및 환경조건을 달리한 부착강도를 측정한 결과 가압할 경우 그렇지 않은 경우보다 부위별로 차이가 있었으나 최대 70% 부착강도가 증가하는 효과를 얻을 수 있었다.

• 한국정밀공학회지
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• 제28권12호
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• pp.1434-1440
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• 2011

In this paper, we assessed muscular activities of lower limbs and foot pressure for car and bus drivers according to operating three electronic pedals that we developed. To analyze drivers' physical exhaustion, muscular fatigue of lower limbs was evaluated. Eleven car drivers and six urban bus drivers were participated in this experiment. The virtual driving system was used for the real driving environment. The virtual driving system was comprised of a spring seat, a steering wheel, pedals (clutch, excel and brake pedals), a manual transmission and a virtual driving simulation. For the real vibration like situation on the road, six degree of freedom motion base system was used. Measured muscles were rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius (Gn) muscles. For the quantitative muscular activities, integrated electromyography (IEMG) was analyzed. Muscular fatigues also were analyzed through the analysis of the median frequency. In addition, foot pressures were analyzed and compared through the peak and averaged pressure during the operating three developed electronic pedals. The experiments are conducted with total 17 drivers, 11 general public and 6 drivers. As a result of the analysis, electromyogram and fatigue analysis through intermediate frequency reduction for pedal-1 more efficient than other pedals. And foot pressure also was decreased. Consequently, we suggested the most efficient pedal and method to minimize the amount of cumulative fatigue.

• 공업화학
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• 제17권2호
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• pp.138-143
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• 2006

Ethosome은 에탄올에 용해된 레시틴을 친수성 용액으로 수화시켜 만들어지는 액정형 베시클이다. Ethosome을 약물전달체로 개발하기 위해서는 베시클의 높은 포집효율과 작은 입자크기가 필수적이기 때문에 ethosome의 포집효율과 입자크기에 영향을 주는 인자들에 대한 연구를 시도하였다. Calcein을 친수성 지표물질로 사용하여 ethosome을 만들고, 구성 성분비와 제조조건에 따른 ethosome의 특성의 변화를 관찰하였다. 에탄올과 calcein 용액의 첨가량 레시틴 중 포스파티딜콜린의 함량, 제조온도, 교반속도 및 PBS 첨가방법 등이 ethosome의 특성에 상당히 큰 영향을 미치는 것을 확인하였다. 초음파 처리를 한 경우에는 ethosome의 포집효율이 감소하는 결과가 나타났는데 이러한 결과는 강한 초음파 진동에 의해 베시클에 포집되었던 성분이 방출되었기 때문이다.

• Earthquakes and Structures
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• 제10권2호
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• pp.329-350
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• 2016

A parametric study was conducted to investigate the seismic deformation demands in terms of drift ratio, plastic base rotation and compression strain on rectangular wall members in frame-wall systems. The wall index defined as ratio of total wall area to the floor plan area was kept as variable in frame-wall models and its relation with the seismic demand at the base of the wall was investigated. The wall indexes of analyzed models are in the range of 0.2-2%. 4, 8 and 12-story frame-wall models were created. The seismic behavior of frame-wall models were calculated using nonlinear time-history analysis and design spectrum matched ground motion set. Analyses results revealed that the increased wall index led to significant reduction in the top and inter-story displacement demands especially for 4-story models. The calculated average inter-story drift decreased from 1.5% to 0.5% for 4-story models. The average drift ratio in 8- and 12-story models has changed from approximately 1.5% to 0.75%. As the wall index increases, the dispersion in the calculated drifts due to ground motion variability decreased considerably. This is mainly due to increase in the lateral stiffness of models that leads their fundamental period of vibration to fall into zone of the response spectra that has smaller dispersion for scaled ground motion data set. When walls were assessed according to plastic rotation limits defined in ASCE/SEI 41, it was seen that the walls in frame-wall systems with low wall index in the range of 0.2-0.6% could seldom survive the design earthquake without major damage. Concrete compressive strains calculated in all frame-wall structures were much higher than the limit allowed for design, ${\varepsilon}_c$=0.0035, so confinement is required at the boundaries. For rectangular walls above the wall index value of 1.0% nearly all walls assure at least life safety (LS) performance criteria. It is proposed that in the design of dual systems where frames and walls are connected by link and transverse beams, the minimum value of wall index should be greater than 0.6%, in order to prevent excessive damage to wall members.