• 정보학연구
• /
• 제7권2호
• /
• pp.69-76
• /
• 2004

본 논문은 여러 가지 환경조건하(염무, 안개, 비)에서 오손된 실키콘애자의 누설전류파형과 파형의 스펙트럼 분석 결과를 나타내었다. 200ms동안 누설전류의 크기가 더욱 커지면 커질수록, 60Hz에서의 스펙트럼의 크기도 커짐을 알 수 있었다. 만일 오손된 애자들이 고밀도의 염무에 접촉되면 낮은 스펙트럼을 갖은 누설전류파형이 계측되었고, 간헐적으로 높은 파형이 계측되었다. 누설전류자료 분석의 경우, 전기적인 활동은 염무 측정시 애자표면에 누적된 오손물질로 인한 일시적인 아크거동으로 특성지어진다. 이것은 애자표면을 따라 흐르는 누설전류에 대한 경로를 제공하게 된 것이다. 그것은 특별한 애자의 퍼포먼스 측정을 평가하기위하여 오손누적의 지표를 갖은 것으로서 중요한 것이다. 만일 표면 저항의 떨어짐이 크게 되면, 그때의 누설전류는 전력품질이 저하시킨 섬락을 중단시키는 공급된 전류이 점차로 증가되어진다.

• 한국해양공학회지
• /
• 제37권1호
• /
• pp.20-30
• /
• 2023

Modeling a nonlinear ocean wave is one of the primary concerns in ocean engineering and naval architecture to perform an accurate numerical study of wave-structure interactions. The high-order spectral (HOS) method, which can simulate nonlinear waves accurately and efficiently, was investigated to see its capability for nonlinear wave generation. An open-source (distributed under the terms of GPLv3) project named "HOS-ocean" was used in the present study. A parametric study on the "HOS-ocean" was performed with three-hour simulations of long-crested ocean waves. The considered sea conditions ranged from sea state 3 to sea state 7. One hundred simulations with fixed computational parameters but different random seeds were conducted to obtain representative results. The influences of HOS computational parameters were investigated using spectral analysis and the distribution of wave crests. The probability distributions of the wave crest were compared with the Rayleigh (first-order), Forristall (second-order), and Huang (empirical formula) distributions. The results verified that the HOS method could simulate the nonlinearity of ocean waves. A set of HOS computational parameters was suggested for the long-crested irregular wave simulation in sea states 3 to 7.

• 교육시설 논문지
• /
• 제19권4호
• /
• pp.29-38
• /
• 2012

Recently large scale earthquake s are occurred around the world following the damage of buildings. So the interest of preparing for earthquake seismic design and seismic performance has becoming high. School buildings are though used for educational purpose; they are also used as emergency shelter for local residents during earthquake disaster. However, the current seismic design ratio of our country (Korea) is 3.7% and if massive earthquake is occurred it follows a serious damage. In order to overcome this situation, seismic performance evaluation is carried out for existing school building and an accurate and appropriate seismic retrofit is required based on performance evaluation to upgrade the existing school buildings. In this paper, nonlinear static analysis on existing school buildings for ATC-40 and FEMA-356 are carried out using the capacity spectrum method to evaluate seismic performance and to determine the need for retrofitting. In addition, after reinforcement to verify the effect of retrofit enhance the seismic performance is applied the seismic performance evaluation is carried out to verify the effect of seismic retrofit time history analysis using nonlinear dynamic analysis is also performed and nonlinear behavior of earthquake load of seismic retrofit of structures was also investigated.

• 한국광학회:학술대회논문집
• /
• 한국광학회 2009년도 창립 20주년기념 특별학술발표회
• /
• pp.233-234
• /
• 2009

In this paper, we report the characteristics of the continuous wave laser output of the $lima{\varsigma}on$-shaped InGaAsP microcavity laser pumped by current injection. In order to find the directions of emission far-field patterns are measureed by rotating an optical fiber around the microcavity. We observe high directionality of the $lima{\varsigma}on$-shaped microcavity laser. For the analysis of lasing properties we also investigate its polarization and spectrum using the Glan-Thompson polarizer and spectrum analyzer.

• 한국정보통신학회논문지
• /
• 제4권2호
• /
• pp.379-388
• /
• 2000

Previous studies on high impedance faults assumed that the erratic behavior of fault current would be random. 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 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. In addition, qualitative analysis such as phase planes, Poincare maps obtained from fault currents indicate that the irregular behavior is described by strange attractor.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2006년도 학술대회 논문집 전문대학교육위원
• /
• pp.154-158
• /
• 2006

The switching-mode power converter has been widely used because of its features of high efficiency and small weight and size. These features are brought by the ON-OFF operation of semiconductor switching devices. However, this switching operation causes the surge and EMI(Electromagnetic Interference) which deteriorate the reliability of the converter themselves and entire electronic systems. This problem on the surge and noise is one of the most serious difficulties in AC-to-DC converter. Random Pulse Width Modulation (RPWM) is peformed by adding a random perturbation to switching instant while output-voltage regulation of converter is performed. RPWM method for reducing conducted EMI in single switch three phase discontinuous conduction mode boost converter is presented. The more white noise is injected, the more conducted EMI is reduced. But output-voltage is not sufficiently regulated. This is the reason why carrier frequency selection topology is proposed. In the case of carrier frequency selection, output-voltage of steady state and transient state is fully regulated. A RPWM control method was proposed in order to smooth the switching noise spectrum and reduce it's level. Experimental results are verified by converter operating at 300v/1kW with $5%{\sim}30%$ white noise input. Spectrum analysis is performed on the Phase current and the CM noise voltage. The former is measured with Current Probe and the latter is achieved with LISN, which are connected to the spectrum analyzer respectively.

• 한국통신학회논문지
• /
• 제19권6호
• /
• pp.994-1003
• /
• 1994

본 논문에서는 차량 잡음 환경하에서 하나의 마이크로폰 구조를 사용하여 스펙트럼 차감법을 이용한 잡음 제거 방법을 제안하였다. 변화하는 잡음에 의하여 손상된 음성신호에서 잡음의 성분을 제거하기 위하여 여러 상황에서의 차량 잡음을 분석하고 특성을 알아보았다. 음성/비음성의 분류와 잡음의 스펙트럼을 추정하기 위하여 잡음 분석을 바탕으로 음성/비음성 분류함수를 제안하였다. 이 분류함수에 의하여 적은 계산량으로 간단하게 정확한 음성/비음성의 분류가 가능하다. 또한 정확한 잡음의 스펙트럼 추정이 가능하다. 제안된 음성/비음성 분류함수에 의한 잡음의 스펙트럼 추정으로 인하여 왜곡이 거의 없는 깨끗한 음성신호를 추출할 수 있었다.

• Smart Structures and Systems
• /
• 제10권4_5호
• /
• pp.331-351
• /
• 2012

In this study an output-only system identification technique for civil structures under ambient vibrations is carried out, mainly focused on using the Stochastic Subspace Identification (SSI) based algorithms. A newly developed signal processing technique, called Singular Spectrum Analysis (SSA), capable to smooth a noisy signal, is adopted for preprocessing the measurement data. An SSA-based SSI algorithm with the aim of finding accurate and true modal parameters is developed through stabilization diagram which is constructed by plotting the identified system poles with increasing the size of data matrix. First, comparative study between different approaches, with and without using SSA to pre-process the data, on determining the model order and selecting the true system poles is examined in this study through numerical simulation. Finally, application of the proposed system identification task to the real large scale structure: Canton Tower, a benchmark problem for structural health monitoring of high-rise slender structures, using SSA-based SSI algorithm is carried out to extract the dynamic characteristics of the tower from output-only measurements.

• Wind and Structures
• /
• 제10권1호
• /
• pp.45-60
• /
• 2007

Transmission tower is a vital component in electrical system. In order to accurately compute the dynamic response and reliability of transmission tower under the excitation of wind loading, a new method termed as probability density evolution method (PDEM) is introduced in the paper. The PDEM had been proved to be of high accuracy and efficiency in most kinds of stochastic structural analysis. Consequently, it is very hopeful for the above needs to apply the PDEM in dynamic response of wind-excited transmission towers. Meanwhile, this paper explores the wind stochastic field from stochastic Fourier spectrum. Based on this new viewpoint, the basic random parameters of the wind stochastic field, the roughness length $z_0$ and the mean wind velocity at 10 m heigh $U_{10}$, as well as their probability density functions, are investigated. A latticed steel transmission tower subject to wind loading is studied in detail. It is shown that not only the statistic quantities of the dynamic response, but also the instantaneous PDF of the response and the time varying reliability can be worked out by the proposed method. The results demonstrate that the PDEM is feasible and efficient in the dynamic response and reliability analysis of wind-excited transmission towers.

• Journal of Radiation Protection and Research
• /
• 제43권4호
• /
• pp.137-142
• /
• 2018

Background: Gamma-ray detectors having a thin window of a material with low atomic number can increase the true coincidence summing effects for radionuclides emitting X-rays or gamma-rays. This effect can make efficiency calibration or spectrum analysis more complicated. In this study, a Cu shield was tested as an X-ray filter to neglect the true coincidence summing effect by X-rays and gamma-rays in gamma-ray spectrometry, in order to simplify gamma-ray energy spectrum analysis. Materials and Methods: A Cu shield was designed and applied to an n-type high-purity germanium detector having an $X-{\gamma}$ summing effect during efficiency calibration. This was tested using a commercial, certified mixed gamma-ray source. The feasibility of a Cu shield was evaluated by comparing efficiency calibration results with and without the shield. Results and Discussion: In this study, the thickness of a Cu shield needed to avoid true coincidence summing effects due to $X-{\gamma}$ was tested and determined to be 1 mm, considering the detection efficiency desired for higher energy. As a result, the accuracy of the detection efficiency calibration was improved by more than 13% by reducing $X-{\gamma}$ summing. Conclusion: The $X-{\gamma}$ summing effect should be considered, along with ${\gamma}-{\gamma}$ summing, when a detection efficiency calibration is implemented and appropriate shielding material can be useful for simplifying analysis of the gamma-ray energy spectra.