• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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• pp.397-399
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• 2012

Dye-sensitized solar cells (DSSCs) have received considerable attention as the most promising candidates for renewable energy systems in recent years. Among these, organic dyes which have many advantages such as large absorption coefficients, customized molecular design for desired photophysical and photochemical properties, inexpensiveness and environment-friendliness, are suitable as photosensitizers for DSSCs. We have studied on the design and synthesis of two organic dyes (BECZ 1 and BECZ 2) with a 9-ethyl-9H-carbazole core for dye-sensitized solar cells (DSSCs). Two organic dyes comprised of two 9-ethyl-9H-carbazole moiety as electron-donor, two types of cyanoacrylic acid moiety acting as acceptor. In addition, n-ethyl unit introduced for increasing the solubility and the donating power. The obtained organic dyes were comprehensively characterized by NMR, GC-MS, FAB-MS and UV/Vis spectroscopies. DSSCs sensitized by the dyes BECZ1 and BECZ2 produced ${\eta}$ value 3.31% and a ${\eta}$ value 3.21%.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.49-53
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• 2004

LabVIEW is mostly preferred to use in experiment, measurement and control as one of the useful thing in America and Europe. So, We tried performance experiment of a single-stage closed-type centrifugal pump by using the LabVIEW. The pump rpm and the shaft torque are measured by rpm sensor and torque sensor The test pump's maximum rpm, head, kW are 1,750, 13m, and 1.5kW, respectively The casing is made up with transparency acrylic for confirmation the flow patterns. We installed experimental equipment for air water two phase flow. This paper tries to analyze the single-phase flow characteristics through this air water two phase flow experimental apparatus. The performance results of a single-stage closed-type centrifugal pump satisfied reappearance and coincide well with head and coefficients according to the change of rpm.

• Journal of Power Electronics
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• 제15권4호
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• pp.1047-1053
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• 2015

A time-domain simulation tool to predict the dynamic power output of wind turbines in an offshore wind farm was developed in this study. A wind turbine model consisting of first or second order transfer functions of various wind turbine elements was combined with the Ainslie's eddy viscosity wake model to construct the simulation tool. The wind turbine model also includes an aerodynamic model that is a look up table of power and thrust coefficients with respect to the tip speed ratio and pitch angle of the wind turbine obtained by a commercial multi-body dynamics simulation tool. The wake model includes algorithms of superposition of multiple wakes and propagation based on Taylor's frozen turbulence assumption. Torque and pitch control algorithms were implemented in the simulation tool to perform max-Cp and power regulation control of the wind turbines. The simulation tool calculates wind speeds in the two-dimensional domain of the wind farm at the hub height of the wind turbines and yields power outputs from individual wind turbines. The NREL 5MW reference wind turbine was targeted as a wind turbine to obtain parameters for the simulation. To validate the simulation tool, a Danish offshore wind farm with 80 wind turbines was modelled and used to predict the power from the wind farm. A comparison of the prediction with the measured values available in literature showed that the results from the simulation program were fairly close to the measured results in literature except when the wind turbines are congruent with the wind direction.

• 대한전자공학회논문지SP
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• 제37권4호
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• pp.65-71
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• 2000

본 논문에서는 SDFT(sliding discrete-Fourier transform)을 순환식(recursive)으로 구현할 때 유한 비트 고정소수점 계산하여 발생하는 오차의 영향을 해석적으로 구하는 방법을 제시하고 이의 유도 과정을 기술하였다. 유한 비트 오차는 계수의 양자화 때문에 발생하는 계수오차와, 곱셈연산 후 반올림되는 유효자리 때문에 발생하는 반올림오차로 구성된다. 각각의 오차는 주파수 스펙트럼 추정오차를 야기 시키며, 이 스펙트럼 오차의 전력과 실제 스펙트럼의 전력 비(noise-to-signal power ratio NSR)를 진동계수를 표현하는 비트 수, DFT 값을 표현하는 비트 수, 그리고 DFT 구간길이에 대한 식으로 유도하였다. 유도과정은 SDFT 순환식(recursive equation)을 통해 유도한 오차방정식(error-dynamic equation)과 계수오차 및 반올림오차의 확률분포특성에 근거하였다. 해석적으로 유도한 NSR 결과를 시뮬레이션 실험을 통해 얻은 결과와 비교하여 타당성을 확인하였다.

• 한국정보통신학회논문지
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• 제10권7호
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• pp.1188-1195
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• 2006

본 논문은 개량된 분기한정법(branch-and bound method)을 이용하여 고속연산이 가능한 2차원 상태공간 디지털 필터의 설계방법을 제안하였다. 설계된 디지털 필터가 갖는 계수행렬의 모든 요소 값들은 오직 2개의 2의 멱수 (powers-of-two) 의 합으로만 표현되어진다. 따라서 제안된 방법으로 설계한 2 차원 상태공간 디지털필터는 간단한 가산연산만으로 수행이 이루어지므로 고속연산이 가능하고, 또한 구조가 간단하며 저가격으로 실현이 가능하다는 장점을 가진다 . 본 논문에서 제안된 방법의 타당성을 설계예시를 통해 고찰한 결과, 설계된 디지털 필터의 근사오차와 군지연특성이 동일한 설계사양으로 연속계수공간에서 설계되어진 디지털필터와 비교하여 유사한 결과를 얻을 수 있었다.

• Current Photovoltaic Research
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• 제2권3호
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• pp.135-139
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• 2014

Different power output of solar cells can be observed at high-temperature regions such as desert areas. In this study, performance dependence on operating temperature of crystalline silicon solar cells with different emitter types was analyzed. Based on the light current-voltage (LIV) measurement, temperature coefficients of short-circuit current density ($J_{SC}$), open-circuit voltage ($V_{OC}$), fill factor (FF) and power conversion efficiency were measured and compared for two groups of crystalline silicon solar cells with different emitter types. One group had homogeneously doped (conventional) emitter and another selectively doped (selective) emitter. Varying the operating temperature from 25 to 40, 60, and $80^{\circ}C$, LIV characteristics of the cells were measured and the properties of saturation current densities ($J_0$) were extracted from dark current-voltage (DIV) curve. From the DIV data, effect of temperature on the performance of the solar cells with different electrical structures for the emitter was analyzed. Increasing the temperature, both emitter structures showed a slight increase in $J_{SC}$ and a rapid degradation of $V_{OC}$. FF and power conversion efficiency also decreased with the increasing temperature. The degrees of $J_{SC}$ increase and $V_{OC}$ degradation for two groups were compared and explained. Also, FF change was explained by series and shunt resistances from the LIV data. It was concluded that the degradation of solar cells shows different values at different temperatures depending on the emitter type of solar cells.

• 한국멀티미디어학회논문지
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• 제7권11호
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• pp.1505-1514
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• 2004

시퀀스 매칭은 시계열 데이터베이스로부터 질의 시퀀스와 변화의 추세가 유사한 데이터 시퀀스들을 검색하는 연산이다. 기존의 대부분의 연구에서는 효과적인 시퀀스 매칭을 위하여 다차원 인덱스를 사용하며, 데이터 시퀀스를 이산 푸리에 변환(Discrete Fourier Transform: DFT)한 후, 단순히 앞의 두 개 내지 세 개의 DFT 계수만을 구성 속성 (organizing attributes)으로 사용함으로써 고차원의 경우 발생하는 차원 저주(dimensionality curse) 문제를 해결한다. 본 논문에서는 기존의 단순한 기법이 가지는 성능 상의 문제점들을 지적하고, 이러한 문제점들을 해결하는 최적의 다차원 인덱스 구성 기법을 제안한다. 제안된 기법은 대상이 되는 시계열 데이터베이스의 특성을 사전에 분석함으로써 변별력이 뛰어난 요소들을 다차원 인덱스의 구성 속성으로 선정하며, 비용 모델(cost model)을 기반으로 한 시퀀스 매칭 비용의 추정을 통하여 다차원 인덱스에 참여하는 최적의 구성 속성의 수를 결정한다. 제안된 기법의 우수성을 규명하기 위하여 실험을 통한기존 기법과의 성능 비교를 수행하였다 실험 결과에 의하면, 제안된 기법은 기존의 기법에 비교하여 매우 큰 성능 개선 효과를 가지는 것으로 나타났다.

• Ocean Systems Engineering
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• 제3권4호
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• pp.275-294
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• 2013

Side-by-side offloading operations are widely utilized in engineering practice. The hydrodynamic interactions between two vessels play a crucial role in safe operation. This study focuses on the coupled effects between two floating bodies positioned side-by-side as a shuttle tanker-FPSO (floating production, storage and offloading) system. Several wave directions with different side-by-side distances are studied in order to obtain the variation tendency of the horizontal hydrodynamic coefficients, motion responses and mean drift forces. It is obtained that the coupled hydrodynamics between two vessels is evidently distinguished from the single body case with shielding and exaggerating effects, especially for sway and yaw directions. The resonance frequency and the peak amplitude are closely related with side-by-side separation distance. In addition, the horizontal hydrodynamics of the shuttle tanker is more susceptible to coupled effects in beam waves. It is suggested to expand the gap distance reasonably in order to reduce the coupled drift forces effectively. Attention should also be paid to the second peaks caused by hydrodynamic coupling. Since the horizontal mean drift forces are the most mainly concerned forces to be counteracted in dynamic positioning (DP) system and mooring system, prudent prediction is beneficial in saving consumed power of DP system and reducing tension of mooring lines.

• 한국해양공학회지
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• 제27권3호
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• pp.73-78
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• 2013

CFD (computational fluid dynamics) analyses that considered the dynamic interaction effects between the flow and a turbine were performed to evaluate the power output characteristics of two representative vertical-axis tidal-current turbines: an H-type Darrieus turbine and Gorlov helical turbine (GHT). For this purpose, a commercial CFD code, Star-CCM+, was utilized, and the power output characteristic were investigated in relation to the scale ratio using the relation between the Reynolds number and the lift-to-drag ratio. It was found that the power coefficients were significantly reduced when the scaled model turbine was used, especially when the Reynolds number was lower than $10^5$. The power output characteristics of GHT in relation to the twisting angle were also investigated using a three-dimensional CFD analysis, and it was found that the power coefficient was maximized for the case of a Darrieus turbine, i.e., a twisting angle of $0^{\circ}$, and the torque pulsation ratio was minimized when the blade covered $360^{\circ}$ for the case of a turbine with a twisting angle of $120^{\circ}$.

• 대한전자공학회논문지SP
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• 제44권1호
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• pp.76-84
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• 2007

본 논문에서는 워터마크 예측과 LDPC 코드를 이용하여 워터마크의 성능을 향상시키는 알고리듬을 제안한다. 워터마크 추출의 경우 삽입된 워터마크의 파워(power)가 원본 영상의 파워에 비해 아주 작기 때문에 워터마크의 추출 성능을 높이기 위해서는 워터마크의 예측이 필수적이다. 본 논문에서는 웨이블릿 영역에서 잡음 제거 필터를 사용하여 워터마크의 예측을 수행하였다. 이렇게 예측된 워터마크에 에러가 발생할 경우 LDPC 코드를 사용하여 수정하였다. 에러 수정 시 삽입된 워터마크의 통계적인 특성을 사용하여 기존의 LDPC 코드의 성능보다 우수한 실험 결과를 도출하였다.