• 대한수학회논문집
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• 제37권2호
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• pp.521-535
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• 2022

In this paper, we introduce the k-Hankel-Wigner transform on R in some problems of time-frequency analysis. As a first point, we present some harmonic analysis results such as Plancherel's, Parseval's and an inversion formulas for this transform. Next, we prove a Heisenberg's uncertainty principle and a Calderón's reproducing formula for this transform. We conclude this paper by studying an extremal function for this transform.

• 수산해양기술연구
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• 제37권4호
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• pp.313-320
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• 2001

In the presence of incident waves with different frequencies, there are second order sum and difference frequency wane exciting forces due to the nonlinearty of the incident waves. Although the magnitudes of these nonlinear forces are small, they act at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency wane loads occurring close to the natural frequencies of TLPs often give greater contributions to high and low frequency resonant responses. The components of the second order forces which depend on first order quantities have been evaluated using the three dimensional source distribution method. The numerical results of time domain motion analysis for the nonlinear wave exciting forces in regular waves are compared with the numerical ones of frequency domain analysis. The results of comparison confirmed the validity of the proposed approach.

• 한국터널지하공간학회 논문집
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• 제11권1호
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• pp.71-83
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• 2009

숏크리트는 터널에서 적용되는 요요한 주지보재이다. 숏크리트의 품질평가는 터널의 안전한 시공과 효과적인 운영을 위한 핵심 요소이다. 숏크리트가 암반에 적절히 타설되었다 하더라도, 막장 및 벤치부에서의 발파, 수축, 지반의 변형 등으로 인해 숏크리트 균열발생 및 배면공동 등의 문제를 야기한다. 본 논문에서는 비파괴 시험인 충격 반항 기법(Impact-Echo) 및 지하레이다 탐사(GPR)를 이용하여 경임에 타설된 숏크리트 배면의 접착상태를 평가하고자 하였다. 기존의 수치해석 연구에 대한 검증과 더불어 현장 적용성에 대한 검토를 위해 실험적 연구를 수행하였다. 숏크리트의 접착상태는 완전 접착, 접착력 상실 및 공동 조건으로 구분할 수 있다. 실내 실대형 시험체에 이 세 가지 숏크리트 접착상태를 조사하였다. 충격반향시험으로부터 획득된 신호는 시간영역, 주파수 영역, 및 시간-주파수 영역에서 각각 분석되었다. 능동적 신호 처리 기법인 Short-Time Fourier Transform(STFT)을 이용하여 숏크리트 배면의 접착상태를 효과적으로 예측할 수 있었으며, 그 결과는 기존의 수치해석 연구로부터 획득한 신호특성과 잘 부합하였다. 숏크리트 배면의 접착상태가 불량할수록 다음과 같은 특징들을 나타낸다. 즉, 주파수 영역에서 자기스펙트럼밀도가 커지며, 기하학적 감쇠비는 감소하고, 시간-주파수 영역에서 윤곽선은 시간축에 평행한 형상을 나타내며, 숏크리트 두께가 얇을수록 그 공진시간이 길어진다. 또한 본 연구에서 제시한 상관계수를 이용하여 숏크리트의 접착상태를 정량적으로 평가할 수 있다. 본 연구 결과를 바탕으로 숏크리트의 접착상태를 평가할 수 있는 평가 기법 및 평가 기준을 제안하였다.

• Journal of Positioning, Navigation, and Timing
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• 제9권2호
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• pp.89-98
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• 2020

Prediction of clock behaviors is necessary to generate very high stable system time which is essential for a satellite navigation system. For the purpose, we applied the Auto-Regressive Integrated Moving Average (ARIMA) model to the prediction of two hydrogen masers' behaviors with respect to the rapid Coordinated Universal Time (UTCr). Using the packaged programming language R, we made an analysis and prediction of time series data of [UTCr - clocks]. The maximum variation width of the residuals which were obtained by the difference between the predicted and measured values, was 6.2 ns for 106 days. This variation width was just one-sixth of [UTCr-UTC (KRIS)] published by the BIPM for the same period. Since the two hydrogen masers were found to be strongly correlated, we applied the Vector Auto-Regressive Moving Average (VARMA) model for more accurate prediction. The result showed that the prediction accuarcy was improved by two times for one hydrogen maser.

• 응용통계연구
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• 제33권6호
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• pp.805-812
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• 2020

본 논문은 최근 금융시계열 분야에서 자주 등장하는 고빈도 시계열 변동성 분석을 다루고 있다. 고빈도 시계열 변동성 분석을 위해 차원 축소를 목적으로 하는 함수형 주성분분석을 적용하였으며 이를 수행하는 R의 두 함수를 비교하고 있다. 응용으로서, KOSPI 고빈도 자료에 적용해 보았다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2010년도 학술발표회
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• pp.581-585
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• 2010

This study introduced a Bayesian based frequency analysis in which the statistical trend seasonal analysis for hydrologic extreme series is incorporated. The proposed model employed Gumbel and GEV extreme distribution to characterize extreme events and a fully coupled bayesian frequency model was finally utilized to estimate design rainfalls in Seoul. Posterior distributions of the model parameters in both trend and seasonal analysis were updated through Markov Chain Monte Carlo Simulation mainly utilizing Gibbs sampler. This study proposed a way to make use of nonstationary frequency model for dynamic risk analysis, and showed an increase of hydrologic risk with time varying probability density functions. In addition, full annual cycle of the design rainfall through seasonal model could be applied to annual control such as dam operation, flood control, irrigation water management, and so on. The proposed study showed advantage in assessing statistical significance of parameters associated with trend analysis through statistical inference utilizing derived posterior distributions.

• 대한전기학회논문지:시스템및제어부문D
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• 제55권7호
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• pp.344-351
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• 2006

The fatigue of back muscle in the repetitive lifting motion was studied using multiple parameters(FFT_MDF, RMS, 2C, NT) in this study. Recent developments in the time-frequency analysis procedures to compute the IMDF(instantaneous median frequency) were utilized to overcome the nonstationarity of EMG signal using Cohen-Posch distribution. But the above method has a lot of computation time because of its complexity. So, in this study, FFT_MDF(median frequency estimation based on FFT) algorithm was used for median frequency estimation of back muscle EMG signal during muscle work in uniform velocity portion of lumbar movement. The analysis period of EMG signal was determined by using the run test and lumbar movement angle in dynamic task, such as lifting. Results showed that FFT_MDF algorithm is well suited for the estimation of back muscle fatigue from the view point of computation time. The negative slope of a regression line fitted to the median frequency values of back muscle EMG signal was taken as an indication of muscle fatigue. The slope of muscle fatigueness with FFT_MDF method shows the similarity of 77.8% comparing with CP_MDF(median frequency estimation based on Cohen Posch distribution) method.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2001
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• pp.36-43
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• 2001

In Korea, we are absolutely short of earthquake data in good quality from moderate and large earthquakes, which are needed fur the study of strong ground motion characteristics. This means that the best use of the available data is needed far the time being. In this respect, several methods are suggested in this paper, which can be applied in the process of data selection and analysis. First, it is shown that the calibration status of seismic stations can be easily checked by comparing the spectra from accelerometer and velocity sensor both of which are located at the same location. Secondly, it is recommended that S/N ratio in the frequency domain should be checked before discarding the data by only look of the data in time domain. Thirdly, the saturated earthquake data caused by ground motion level exceeding the detection limit of a seismograph are considered to see if such data can be used for spectrum analysis by performing numerical simulation. The result reveals that the saturated data can still be used within the dominant frequency range according to the levels of saturation. Finally, a technique to minimize the window effect that distorts the low frequency spectrum is suggested. This technique involves detrending in displacement domain once the displacement data are obtained by integration of low frequency components of the original data in time domain. Especially, the low frequency component can be separated by using discrete wavelet transform among many alternatives. All of these methods mentioned above may increase the available earthquake data and frequency range.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.249-256
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• 2003

To investigate the safety and stability of the concrete lining, numerous studies have been conducted over the years and several methods have been developed. Most signal processing method of NDT techniques has based on the Fourier analysis. However, the application of Fourier analysis to analyze recorded signal shows results only in frequency domain, it is not enough to analyze transient waves precisely. In this study, a new NDT technique .using the wavelet theory was employed for the analysis of non-stationary wave propagation induced by mechanical impact in the concrete lining. The wavelet transform of transient signals provides a method for mapping the frequency spectrum as a function of time. To verify the availability of wavelet transform as a time- frequency analysis tool, model experiments have been conducted on the concrete lining model. From this study, it was found that the contour map by Wavelet transform provides more distinct results than the power spectrum by Fourier transform and it was concluded that Wavelet transform was an effective tool for the experimental analysis of dispersive waves in concrete structures.

• 한국군사과학기술학회지
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• 제10권3호
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• pp.148-153
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• 2007

In this paper, the evolutionary adaptive wavelet transform(EAWT) is applied to the scattering analysis of radar target. EAWT algorithm uses evolutionary programming for the time-frequency parameter extraction instead of FFT and the bisection search method used in the conventional adaptive wavelet transform(AWT). Therefore, the EAWT has a better performance than the conventional AWT. In the simulation using wire target(Airbus-like), the comparisons with the conventional AWT are presented to show the superiority of the EAWT algorithm in the analysis of scattering phenomenology. The EAWT can be effectively applied to the radar target recognition.