• 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.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권1호
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• pp.86-94
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• 2011

This paper compares frequency domain and time domain predictions from the ShipMo3D ship motion library with observed motions from model tests and sea trials. ShipMo3D evaluates hull radiation and diffraction forces using the frequency domain Green function for zero forward speed, which is a suitable approach for ships travelling at moderate speed (e.g., Froude numbers up to 0.4). Numerical predictions give generally good agreement with experiments. Frequency domain and linear time domain predictions are almost identical. Evaluation of nonlinear buoyancy and incident wave forces using the instantaneous wetted hull surface gives no improvement in numerical predictions. Consistent prediction of roll motions remains a challenge for seakeeping codes due to the associated viscous effects.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.73-78
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• 2000

On this study, the fatigue crack propagation of super duplex stainless steel is investigated in conditions of various volume fraction of austenite phase by changing heat treatment temperature. And we analysed acoustic emission signals during the fatigue test by time-frequency analysis methods. As the temperature of heat treatment increased, volume fraction of austenite decreased and coarse grain was obtained. The specimen heat treated at $1200^{\circ}C$ had longer fatigue life and slower rate of crack growth. As a result of time-frequency analyze of acoustic emission signals during fatigue test, main frequency was $200{\sim}300kHz$ having no correlation with heat treatment and crack length, and 500kHz was obtained by dimple and separate of inclusion

• 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.

• Structural Monitoring and Maintenance
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• 제9권2호
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• pp.107-127
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• 2022

Structural health monitoring (SHM) has been related to damage identification with either operational loads or other environmental loading playing a significant complimentary role in terms of structural safety. In this study, a non-parametric method of time frequency analysis on the measurement is used to address the time-frequency representation for modal parameter estimation and system damage identification of structure. The method employs the wavelet decomposition of dynamic data by using the modified complex Morlet wavelet with variable central frequency (MCMW+VCF). Through detail discussion on the selection of model parameter in wavelet analysis, the method is applied to study the dynamic response of both steel structure and reinforced concrete frame under white noise excitation as well as earthquake excitation from shaking table test. Application of the method to building earthquake response measurement is also examined. It is shown that by using the spectrogram generated from MCMW+VCF method, with suitable selected model parameter, one can clearly identify the time-varying modal frequency of the reinforced concrete structure under earthquake excitation. Discussions on the advantages and disadvantages of the method through field experiments are also presented.

• 한국정보시스템학회지:정보시스템연구
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• 제27권3호
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• pp.123-140
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• 2018

Purpose The purpose of this study is to explore the optimal trading frequency which is useful for stock price prediction by using deep learning for charting image data. We also want to identify the appropriate time for accurate forecasting of stock price when performing pattern analysis. Design/methodology/approach In order to find the optimal trading frequency patterns and forecast timings, this study is performed as follows. First, stock price data is collected using OpenAPI provided by Daishin Securities, and candle chart images are created by data frequency and forecasting time. Second, the patterns are generated by the charting images and the learning is performed using the CNN. Finally, we find the optimal trading frequency patterns and forecasting timings. Findings According to the experiment results, this study confirmed that when the 10 minute frequency data is judged to be a decline pattern at previous 1 tick, the accuracy of predicting the market frequency pattern at which the market decreasing is 76%, which is determined by the optimal frequency pattern. In addition, we confirmed that forecasting of the sales frequency pattern at previous 1 tick shows higher accuracy than previous 2 tick and 3 tick.

• 한국전자파학회논문지
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• 제19권9호
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• pp.1000-1009
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• 2008

본 논문의 목적은 $3.1{\sim}4.8$ GHz 대역에서 UWB를 허용하기 위해 국내에서 제시한 DAA 기술 기준을 적용하여 MB-OFDM UWB(Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wide Band) 시스템과 피 간섭신호간의 성능을 평가하는 것이다. DAA 기술 기준에서 정한 피 간섭 신호로는 유럽에서 DAA 적용 시스템으로 검토하고 있는 WiMAX나 국내에 도입될 것으로 예상되는 4G 시스템 등이 있다. MB-OFDM UWB 시스템은 TFC(Time Frequency Code)에 따라 심볼마다 3개 주파수 대역을 호핑하는 TFI(Time frequency Interleaving) 모드와 하나의 주파수 대역을 선택하여 신호를 전송하는 FFI(Fixed Frequency Interleaving) 모드를 지원한다. 본 논문에서는 호핑 모드에 따른 간섭 영향을 정확하게 분석하기 위해 TFC에 따른 평균 송신 출력 및 동기 구조를 반영하여 시뮬레이션을 수행하였다. 분석 결과, 국내 DAA 기술 기준을 적용할 경우, UWB 간섭 신호로부터 Wi-MAX 통신 시스템은 철저히 보호되는 반면, MB-OFDM UWB 시스템은 DAA 검출 레벨의 간섭 신호에 의해 주파수 다양성 효과를 얻을 수 있는 주파수 호핑 모드에서 조차 심각한 성능 저하가 발생하였다.

• 한국실내디자인학회논문집
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• 제22권5호
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• pp.152-161
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• 2013

This study is about the visual appreciation by sex with the analysis of time range of observing data which was got through observation experiment with the space of lobby in hospitals. The observation data of the subjects who observed the space include the frequency and time, through which the process of visual appreciation could be evaluated with the definition of the frequency and the time of observation. First, the fact that men had higher frequency of observation than women means the former had more movement than the latter, and another fact of their fewer times can be understood as the time of their staying was shorter. That is, even though the men had more movements of sight, they showed the feature of staying shorter. Second, the rate high and low of observation frequency and times made it possible for observation characteristics to be defined as 'intensive search' 'active search' 'fixed concentration' and 'search wandering.' The definition of understanding this process of visual appreciation can be available for a frame of effective analysis of observation characteristics according to the passage of time. Third, the intense search is the case of 'high frequency' having the feature of high visual appreciation owing to the active visual actions for acquiring information. Men were found to have more intense search which decreased gradually as time passed, while women showed the feature of many times of intense search. Fourth, it was found that with many observation data in a certain range of time the subjects had fixed concentration, where women were found to have repetitive fixed concentration along with the change of observation time while men were seen to have more observation tendency for fixed concentration. Fifth, at the cross tabulation of frequency and times, men had the feature of dispersed visual appreciation while women had more distinction between fixation and movement, which revealed that there is surely the difference between men and women in the process of visual appreciation.

• 한국철도학회논문집
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• 제9권2호
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• pp.187-192
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• 2006

The regularity of railway track alignment is a crucial component fur maintaining travel safety and the smoothness of passenger ride. The conventional spectral analysis has been considered to estimate the severity of the track irregularity from measured data. The time domain data used to be changed into the frequency domain by Fourier transform. Because the measuring points can be regarded as the time points, the spatial-frequency can be introduced instead of the time-frequency. Although FFT(Fast Fourier Transform) and/or PSD(Power Spectral Density) function could provide fairly localized information within frequency domain, but chronical configurations of data could be missed. In this study, we attempt to apply the Morlet wavelet transform for the purpose of a frequency-time-domain analysis rather than a frequency-domain analysis. The applicability of wavelet transform is examined for the estimation of the track irregularity with real measured track data on the section of Kyoung-bu line by EM-120 measuring vehicle. It is shown that the wavelet transform can be an effective tool to manage the track irregularity.

• 대한전자공학회논문지SP
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• 제47권5호
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• pp.100-108
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• 2010

본 논문은 피치를 추출하는 방법으로 자기상관을 이용하였다. 시간과 주파수 영역의 자기상관은 서로 다른 특성을 가지고 있으며, 각각 피치주기와 기본주파수에 대응된다. 본 논문에서는 시간과 주파수 영역에서의 자기상관을 결합하는 방법을 이용하였다. 이 방법은 자기상관에서 발생하는 피치 doubling과 having 에러를 크게 개선시킬 수 있었다. 하지만, 시간과 주파수 영역에서 유성음의 주기적 특성인 피치주기와 기본주파수는 서로 역수 관계이며, 특히 기본주파수의 에러는 FFT의 분해능에 의하여 발생된다. 이러한 영향을 줄이기 위하여 시간 영역과 주파수 영역에서의 자기상관 결합에 보간법을 적용함으로써 피치 검출율을 향상 시킬 수 있었다. 자기상관을 결합할 때 시간영역에서 찾은 피치후보들에 대해서만 주파수영역의 자기상관을 구함으로써 계산량은 감축될 수 있었다. 또한, 선형보간을 이용하여 기존방법 보다 FFT 계수를 8배 줄일 수 있었다. 그 결과, FFT 연산량과 주파수영역의 자기상관 계산량을 크게 감축하여 기존 방법 대비 알고리즘 처리시간을 약 9.5배 줄일 수 있었다.