• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2000년도 하계학술대회 논문집 D
• /
• pp.2525-2527
• /
• 2000

The analysis of distribution line faults is essential to the proper protection of power system. A high impedance fault(HIF) dose not make enough current to cause conventional protective device operating, so it is well known that undesirable operating conditions and certain types of faults on electric distribution feeders cannot be detected by using conventional protection system. In this paper, we prove that the nature of the high impedance faults is indeed a deterministic chaos, not a random motion. Algorithms for estimating Lyapunov spectrum and the largest Lyapunov exponent are applied to various fault currents detections in order to evaluate the orbital instability peculiar to deterministic chaos dynamically, and fractal dimensions of fault currents which represent geometrical self-similarity are calculated. Wavelet transform analysis is applied the time-scale information to fault signal. Time-scale representation of high impedance faults can detect easily and localize correctly the fault waveform.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1789-1794
• /
• 2004

The present study investigates flow characteristics in an optical disc drive. Detailed knowledge of the flow characteristics is essential to analyze flow-induced noise and vibration, forced convection and flow friction loss. The ODD used in the personal computer is used for the experiment and rotating velocity of disc is under the 4500 rpm. Time-resolved velocity components and velocity spectrum are obtained using the laser Doppler anemometry (LDA). The results show that the front holes reduce now-induced noise and the position of pickup body affects flow near the window. In addition, il is possible for cooling of heat sources in an optical disc drive through measuring the flow fields under the tray.

• Bulletin of the Korean Chemical Society
• /
• 제30권1호
• /
• pp.145-148
• /
• 2009

Nucleotides are the building blocks of nucleic acids and essential for many cellular functions. In this study, ultrasonic absorption spectra of $\beta$-cyclodextrin ($\beta$-CD) and adenosine 5'-monophosphate (AMP) in aqueous solution were measured over the broad frequency range 0.1-40 MHz with emphasis on the low-frequency range below 1 MHz. Here we show that the interaction of $\beta$-CD and AMP complies with a typical spectrum of a single relaxation process. We determined reliable rate (kb) and equilibrium (K) constants and a standard volume change ($\Delta$V) of the reaction. They are $k_b=2.3{\times}{{10^{-6}}_s}^{-1},\;K=89M^{-1},\;and\;{\Delta}V=13.8(10^{-6}m^3mol^{-1})$, respectively.

• Steel and Composite Structures
• /
• 제20권2호
• /
• pp.337-355
• /
• 2016

Steel coupling beam in reinforced concrete (RC) coupled shear wall system is a proper substitute for deep concrete coupling beam. Previous studies have shown that RC coupled walls with steel or concrete coupling beam designed with strength-based design approach, may not guarantee a ductile behavior of a coupled shear wall system. Therefore, seismic performance evaluation of RC coupled shear wall with steel or concrete coupling beam designed based on a strength-based design approach is essential. In this paper first, buildings with 7, 14 and 21 stories containing RC coupled shear wall system with concrete and steel coupling beams were designed with strength-based design approach, then performance level of these buildings were evaluated under two spectrum; Design Basis Earthquake (DBE) and Maximum Considered Earthquake (MCE). The performance level of LS and CP of all buildings were satisfied under DBE and MCE respectively. In spite of the steel coupling beam, concrete coupling beam in RC coupled shear wall acts like a fuse under strong ground motion.

• 한국광학회지
• /
• 제11권1호
• /
• pp.43-46
• /
• 2000

Kerr 렌즈 모드록킹된 티타늄 사파이어 레이저에서 상용화된 광학부품만을 이용하여 9 fs의 펄스를 생성하였다. 공진기 내부와 출령경을 지나면서 발생하는 군속도 분산을 각각 용융 프리즘 쌍을 이용하여 보상하였고, 넓은 스펙트럼을 얻기 위하여 광대역 거울을 사용하였다. 이전에 사용했던 광대역 거울과 반사율을 비교해 봄으로서 10fs 미만의 극초단 펄스를 생성하기 위해서는 180nm 이상의 넓은 반사대역을 갖는 거울을 선택하는 것이 필수적임을 확인하였다.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2008년도 지능정보 및 응용 학술대회
• /
• pp.149-150
• /
• 2008

일반적으로, 소나 표적의 식별을 위한 PSR(Propeller Shaft Rate) 추정 알고리즘은 다음의 문제점들을 가지고 있다. 즉, 주파수 스펙트럼으로부터 하모닉군을 구별하는 것은 필수적이면서도 어렵기 때문에 정확하고 효율적인 구별법을 요구한다. 나아가, 구조와 파라메터에 있어서 용이한 설계 절차를 요구한다. 이 문제들을 해결하기 위해서 전문가 지식 및 진화 전략(ES : Evolution Strategy)을 이용하는 진화적인 PSR 추정기가 제안되었다. 시뮬레이션 결과는 제안된 알고리즘이 그 문제점들을 효과적으로 해결할 수 있음을 보여준다.

• 대한전기학회논문지:전력기술부문A
• /
• 제48권1호
• /
• pp.16-21
• /
• 1999

The analysis of distribution line faults is essential to the proper protections of the power system. A high impedance fault test, which was carried in Korean electric power systems, it was found that a arcing phenomenon occurred during the high level portion of conductor voltage in each cycle. In this paper, we propose a new method for detection of high impedance faults, which uses the arcing fault current difference during high voltage and low voltage portion of conductor voltage waveform. To extract this difference, we diveded one cycle fault current into equal spanned four data windows according to the magnitude of voltage waveform and applied fast fourier transform(FFT) to each data window. The frequency spectrum of current wavefrom in each portion are used as the inputs of neural network and is trained to detect high impedance faults. The proposed method shows improved accuracy when applied to staged fault data and fault-like load.

• Journal of Power Electronics
• /
• 제12권5호
• /
• pp.739-747
• /
• 2012

This paper applies carrier phase shifted pulse-width modulation (CPS-PWM) to transformerless modular multilevel converters (MMC) to improve the output spectrum. Because the MMC topology is characterized by the double-star connection of six legs consisting of cascaded modular chopper cells with floating capacitors, the balance control of the DC-link capacitor voltage is essential for safe operation. This paper presents a leg-balancing control strategy to achieve DC-link voltage balance under all operating conditions. This strategy based on circulating current decoupling control focused on DC-link balancing between the upper and lower legs in each phase pair by considering the six legs as three independent phase-pairs. Experiments are implemented on a 100-V 3-kVA downscaled prototype. The experimental results show that the proposed leg-balancing control is both effective and practical.

• 한국자기공명학회논문지
• /
• 제16권2호
• /
• pp.103-110
• /
• 2012

Membrane proteins play a essential role in the biological systems and it is not easy to handle a membrane protein for its structural study. Solid-state NMR (ssNMR) can be a good tool to investigate the structures and dynamics of membrane proteins. In ssNMR, Magic Angle Spinning (MAS) and Cross Polarization (CP) can be utilized to reduce the line-broadening, leading to high resolution and sensitivity in the spectrum. ssNMR, if combined with other spectroscopic methods, can provide us a enough knowledge on structures and dynamics of membrane proteins in biological condition.

• Structural Engineering and Mechanics
• /
• 제35권4호
• /
• pp.479-491
• /
• 2010

Advances in geological studies, have identified increased seismic activity in the world's ocean once believed to be far from seismic hazards. The increase in demand of oil and other hydrocarbons leaves no option but to install a suitable offshore platform on these seismically sensitive offshore basins. Therefore, earthquake based design criteria for offshore structures are essential. The focus of the present review is on various computational techniques involved for seismic response study. The structural and load modeling approaches, the disturbed fluid-structure and soil-structure interaction as well as hydrodynamic damping due to earthquake excitation are also discussed. A brief description on the reliability-based seismic design approach is also presented.