• Applied Science and Convergence Technology
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• 제23권6호
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• pp.357-365
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• 2014

A non-invasive method for ion energy distribution measurement at a RF biased surface is proposed for monitoring the property of ion bombardments in capacitively coupled plasma sources. To obtain the ion energy distribution, the measured electrode voltage is analyzed based on the circuit model which is developed with the linearized sheath capacitance on the assumption that the RF driven sheath behaves like a simple diode for a bias power whose frequency is much lower than the ion plasma frequency. The method is verified by comparing the ion energy distribution function obtained from the proposed model with the experimental result taken from the ion energy analyzer in a dual cathode capacitively coupled plasma source driven by a 100 MHz source power and a 400 kHz bias power.

• 한국농공학회논문집
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• 제46권5호
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• pp.27-39
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• 2004

In the first part of this study, five homogeneous regions in view of topographical and geographically homogeneous aspects except Jeju and Ulreung islands in Korea were accomplished by K-means clustering method. A total of 57 rain gauges were used for the regional frequency analysis with minimum rainfall series for the consecutive durations. Generalized Extreme Value distribution was confirmed as an optimal one among applied distributions. Drought rainfalls following the return periods were estimated by at-site and regional frequency analysis using L-moments method. It was confirmed that the design drought rainfalls estimated by the regional frequency analysis were shown to be more appropriate than those by the at-site frequency analysis. In the second part of this study, LH-moment ratio diagram and the Kolmogorov-Smirnov test on the Gumbel (GUM), Generalized Extreme Value (GEV), Generalized Logistic (GLO) and Generalized Pareto (GPA) distributions were accomplished to get optimal probability distribution. Design drought rainfalls were estimated by both at-site and regional frequency analysis using LH-moments and GEV distribution, which was confirmed as an optimal one among applied distributions. Design rainfalls were estimated by at-site and regional frequency analysis using LH-moments, the observed and simulated data resulted from Monte Carlotechniques. Design drought rainfalls derived by regional frequency analysis using L1, L2, L3 and L4-moments (LH-moments) method have shown higher reliability than those of at-site frequency analysis in view of RRMSE (Relative Root-Mean-Square Error), RBIAS (Relative Bias) and RR (Relative Reduction) for the estimated design drought rainfalls. Relative efficiency were calculated for the judgment of relative merits and demerits for the design drought rainfalls derived by regional frequency analysis using L-moments and L1, L2, L3 and L4-moments applied in the first report and second report of this study, respectively. Consequently, design drought rainfalls derived by regional frequency analysis using L-moments were shown as more reliable than those using LH-moments. Finally, design drought rainfalls for the classified five homogeneous regions following the various consecutive durations were derived by regional frequency analysis using L-moments, which was confirmed as a more reliable method through this study. Maps for the design drought rainfalls for the classified five homogeneous regions following the various consecutive durations were accomplished by the method of inverse distance weight and Arc-View, which is one of GIS techniques.

• 한국방재학회 논문집
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• 제9권6호
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• pp.99-109
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• 2009

본 연구에서는 강원도내 정확한 극치강수분포를 파악하여 최근 증가하고 있는 재해를 예방하고자 지역빈도해석 방법을 이용하여 산정한 확률강수량과 공간분석을 통하여 강원도의 강수분포를 분석하였다. 강수자료는 강원도내 기상청 관할의 66개 관측소의 자료를 사용하였다. 지역빈도해석결과 GLO 분포형이 강원도에 가장 적합한 분포형으로 나타났다. 강수분포를 지속기간별로 분석한 결과 지속기간이 증가할수록 설악동, 대관령 및 청일 일원에서 높은 확률강수량을 나타내었으며, 지속기간에 따라서 강수의 공간분포가 확연히 변화됨을 확인하였다. 또한 재현기간별로 분석한 결과 재현기간이 길어질수록 지역별 강수 특성이 강하게 나타났다. 강원도 강수분포를 공간분석한 결과 영동지방에서는 일관적으로 높은 강수량이 발생하였으나 영서지방에서는 지속기간 및 재현기간에 따라 다양한 분포를 나타내었다. 따라서 지역별 강수량의 보다 정확한 예측을 위해서는 지역빈도해석 이외에 다양한 지리 및 기상조건을 고려할 수 있는 모형에 대한 연구가 필요할 것으로 판단된다.

• 대한기계학회논문집
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• 제18권4호
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• pp.1050-1056
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• 1994

When a vibration data for a rotating machine such as a pump or a compressor is concerned, the frequency fluctuation of the energy contents at an instant time may provide useful information on understanding the vibration characteristics of the rotating machinery, rather than the averaged energy distribution along the frequency axis. Especially, when a periodic signal has different spectral contents, the approach to use the averaged frequency distribution, called the normal frequency analysis, may not be appropriate to extract vibration source characteristics of the structure. This paper introduces a way to analyze the signal based on an instant time. In order to evaluate the performance of the various approach, the investigatation compares three different algorithms which are frequently implemented in the instantaneous frequency analysis. Also for the noise effect embodied in the true signal, various cases for different SN ratio have been examined. The result shows that the noise level is crucial to evalute the instantaneous frequency analysis. In order to implement the instantaneous frequency analysis, the extraction of the relevant information from the measured signal should have the high S/N ratio, i, e., 40 dB or above.

• 한국지리정보학회지
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• 제7권2호
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• pp.47-56
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• 2004

본 연구는 강우-유출 침식성 인자의 빈도별에 따른 토양유실량을 평가하고 이롤 바탕으로 유역의 토침칭식 위험지역을 분석하는 것을 목적으로 한다. RUSLE는 토양침식량을 분석하는데 이용하였다. 연구지역은 섬진강 수계의 관촌유역을 선정하였다. 빈도별 강우-유출 침식성인자를 얻기 위하여 39년간의 일일최대 강우량 자료를 이용하였다. 확률강우량은 Normal 분포, Log-Normal 분포, Pearson type III 분포, log-Pearson type III 분포 및 Extreme-I 분포를 이용하였다. 이 중 적합도가 가장 높은 것으로 판단되는 Log-Pearson type III 분포를 채택하였다. Log-Pearson type III 분포는 24시간 확률 강우량을 산정하는데 이용하였고, 빈도별 강우-유출 침식성 인자는 Huff 분포비로 평가하였다. 분석결과 2년빈도에서 200년 빈도까지 토양유실량은 평균 $12.8{\sim}68.0ton/ha{\cdot}yr$로 분석되었다. 유역의 토양유실량 분포를 4개 분류등급으로 구분하여 토양침식 위험지역을 분석하였으며, 침식발생 위험지역으로 판단되는 지역은 분류등급 IV로 하였다. 분류등급 IV의 면적은 $0.01{\sim}5.28km^2$로 전체 농경지 면적의 0.02~9.00%로 나타났다. 특히, 200년빈도의 경우 분류등급 IV에서 밭작물 재배지역이 전체 농경지 면적의 77.1%를 차지하는 것으로 나타났다. 농경지의 경작상태에 따라 토양유실이 큰 영향을 받는 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제49권2호
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• pp.373-379
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• 2017

Seismic probabilistic safety assessments are used to help understand the impact potential seismic events can have on the operation of a nuclear power plant. An important component to seismic probabilistic safety assessment is the seismic hazard curve which shows the frequency of seismic events. However, these hazard curves are estimated assuming a normal distribution of the seismic events. This may not be a strong assumption given the number of recorded events at each source-to-site distance. The use of a normal distribution makes the calculations significantly easier but may underestimate or overestimate the more rare events, which is of concern to nuclear power plants. This paper shows a preliminary exploration into the effect of using a distribution that perhaps more represents the distribution of events, such as the t-distribution to describe data. The integration of a probability distribution with potentially larger tails basically pushes the hazard curves outward, suggesting a different range of frequencies for use in seismic probabilistic safety assessments. Therefore the use of a more realistic distribution results in an increase in the frequency calculations suggesting rare events are less rare than thought in terms of seismic probabilistic safety assessment. However, the opposite was observed with the ground motion prediction equation considered.

• 소음진동
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• 제7권5호
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• pp.747-756
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• 1997

Wigner-Ville distribution which is a time-frequency analysis has a fatal drawback, when the signal has multiple components. This is the cross-talk and often causes a neagative value in the distribution. Wingner-Ville distriution is an expression of power, therefore the cross-talk must be avoided. Smoothing the Wigner-Ville distribution by convoluting it with a window, is most commonly used to reduce the cross-talk. There can be infinite number of distributions depending on the windows. But, the smoothing reduces resolution in time-frequency plane; this motives to design a more effective window in reducing cross-talk while remaining resolution. The domain in which the cross-talk and legitimate components can be easily distinguished, is the ambiguity function. In the ambiguity function domain, the legitimate components appear as linear lines passing through the orgine. But, the cross-talk is widely distributes in the ambiguity function plane. Based on the relative distributions of cross-talk and legitimate components, rotating window can be designed to minimize cross-talk. Applying the rotating window to the ambiguity function corresponds to smoothing the Wigner-Ville distribution. Therefore, the effects of rotating window is estimated in terms of the bias error due to smooting the Wigner-Ville distribution. By applying the rotating window, not only the Wigner-Ville distribution but also its properties are changed. The properties of the new distribution are checked, in order to complete analyzing the rotating window.

• 한국소음진동공학회논문집
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• 제22권3호
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• pp.291-297
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• 2012

Conventional Fourier analysis can give only limited information about the dynamic characteristics of nonstationary signals. Instead, time-frequency analysis is widely used to investigate the nonstationary signal in detail. Several time-frequency analysis methods are compared for a typical acoustic emission burst generated during the impact between a ferrite ceramic and aluminum plate. This AE burst is inherently nonstationary and random containing many frequency contents, which leads to severe interference between cross terms in bilinear convolution type distributions. The smoothing and reassignment processes can improve the readability and resolution of the results. Spectrogram and scalogram of the AE burst are obtained and compared to get the characteristics information. Renyi entropies are computed for various bilinear time-frequency transforms to evaluate the randomness. These bilinear transforms are reassigned by using the improved algorithm in discrete computation.

• 대한기계학회논문집A
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• 제30권7호
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• pp.865-872
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• 2006

High frequency induction welding is widely employed for longitudinal seam welding of small scale tubes and pipes because of its relatively high processing speed and efficiency. This research is aimed at understanding the variables that affect the quality of the high frequency induction welding. The welding variables include the welding frequency, weld speed, V-angle and tube thickness. Temperature distribution of the tube is calculated through three dimensional coupled electromagnetic and thermal FE analysis. The skin and proximity effects are considered in the electromagnetic analysis. The influence of the impeder is also analyzed. The effects of the operating welding variables on the temperature distribution are investigated quantitatively by exhibiting the heat affected zone (HAZ). The results explain the mechanism of significant enhancement of welding efficiency when the impeder is used. The proper welding conditions without the overheated edge are obtained through FE analysis.

• 천문학회보
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• 제43권1호
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• pp.56.3-56.3
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• 2018

The present study formulates the theory of spontaneously emitted electromagnetic fluctuations in magnetized plasmas containing particles with an anisotropic suparthermal (bi-Kappa) velocity distribution function. The formalism is general applying for an arbitrary wave vector orientation and wave polarization, and for any wave-frequency range. As specific applications, the high-frequency electromagnetic fluctuations emitted in the upper-hybrid and multiple harmonic electron cyclotron frequency range are evaluated. The fluctuations for low-frequency are also applied, which include the kinetic $Alfv\acute{e}n$, fast magnetosonic/whistler, kinetic slow mode, ion Bernstein cyclotron modes, and higher-order modes. The model predictions are confirmed by a comparison with particle-in-cell simulations. The study describes how energetic particles described by kappa velocity distribution functions influence the spectrum of high and low frequency fluctuations in magnetized plasmas. The new formalism provides quantitative analysis of naturally occurring electromagnetic fluctuations, and contribute to an understanding of the electromagnetic fluctuations observed in space plasmas, where kappa-distributed particles are ubiquitous.