• 한국군사과학기술학회지
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• 제3권1호
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• pp.106-115
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• 2000

This paper presents the measuring technique of time and velocity when rocket motor is burnt out for 2.751" rocket. This technique use doppler effect, frequency spectrum analysis and curve fitting. In this study, we use muzzle velocity radar for doppler signal acquisition, short-time fourier transform for spectrum analysis and curve fitting for smoothing.

• Journal of Welding and Joining
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• 제21권6호
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• pp.33-39
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• 2003

Wavelet transform analysis results show a spectrum energy distribution of CWT along scale factors distinguish the partial, full and over penetration in a electron beam welding by analyzing the curve of spectrum energy at small scale, middle and large scale range, respectively. Two types of signals collected by Ion collector and x-ray sensors and analyzed. The acquired signals from sensors are very complicated since these signals are very closely related the dynamics of keyhole which interact the very high density energy with materials during welding. The results show the wavelet transform is more effective to diagnosis than Fourier Transform, further for the general welding defects which are not a periodic based, but a transient, non-stationary and time-varying phenomena.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1189-1194
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• 2002

Acoustic intensity is usually estimated by the cross-spectrum of acoustic pressure at two adjacent micrphones. The cross-spectrum calculated by digital Fourier transform technique will unavoidally have leakage error since the period of signal will not be usually coincident with record length. Therefore, the acoustic intensity estimated by the conventional r]n analyzer will show distorted value. In this paper the expression of the Fourier transformed data of a harmonic signal is formulated when there is leakage error. The method to elimate the effect of leakage error from the contaminated data is also proposed. Some numerical examples show the validation of the proposed method.

• 한국해안해양공학회지
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• 제19권4호
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• pp.355-360
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• 2007

본 논문에서는 수심이 일정한 수조에서의 비선형 천해파의 변형 과정에 대한 연구를 수행하였다. 파랑의 최초 쇄파에 대한 특성을 자세히 분석하고, 비선형파의 경사 및 퓨리에 스펙트럼을 산정하였다. 분석결과 스펙트럼의 진폭은 실용적으로 추산이 가능한 파랑 경사를 이용하여 표현할 수 있다.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2010년도 제42차 하계학술발표논문집 18권2호
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• pp.35-38
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• 2010

본 논문에서는 일상생활 속에서 무자각적으로 생체신호를 측정하고 분석하여 감성을 평가할 수 있는 임베디드 시스템에 관하여 연구하였다. 지속적으로 변화하는 감성을 일관적이며 신뢰성이 높은 생리적인 방법으로 평가하기 위해 심전도(ECG:Electrocardiogram), 맥파(PPG:Photoplethysmogram)의 두 가지 생체신호를 측정하고, 무선전송(Bluetooth) 장치를 이용하여 측정한 생체신호를 실시간으로 노트북PC로 전송하여 분석하였다. 생체신호의 분석방법은 FFT(Fast Fourier Transform)과 전력스펙트럼밀도(Power Spectrum Density)를 이용한 주파수 분석방법으로 두 생체신호의 특정 주파수 대역이 가지는 자율신경계의 활성도의 비율을 분석하여 비교 연구하였다. 또한 보다 빠르고 정확한 감성을 평가하기 위하여 분석알고리즘의 연산을 최소화 하였으며 그래프를 이용한 분석결과의 시각화를 하였다. 본 논문에서는 무자각적인 생체신호 측정 시스템을 이용하여 다양한 상황에서 생체신호를 측정하고, 개발한 분석 알고리즘으로 분석한 결과의 차이를 연구하여 정확도 및 신뢰도를 기준으로 감성을 평가하기 위한 분석 시스템을 평가하였다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1995년도 춘계학술대회
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• pp.37-41
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• 1995

In this paper, we proposed the 2-stage ultrasound liver image classifier which uses the fractal dimensions obtained from the original image and its 1/2 subsampled image, and the Normalized Fourier Power Spectrum. The fractal dimension based on Fractional Brownian Motion (FBM) is calculated from the variance of the same scale pixels instead of the mean of them. Since the actual ultrasound. liver images does not fully match the FBM, to get the fractal dimension, we use the scale vectors which satisfy the FBM model. In 2-stage classifier, we first classified normal and diffuse liver and then classified the fat liver and cirrhosis from the diffuse liver. For the test liver images. 70% of normal liver and 80% of fat liver and 90% of cirrhosis is classified classified with our 2-stage classifier.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1156-1161
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• 2001

Acoustic intensity is usually estimated by the cross-spectrum of acoustic pressure at two adjacent microphones. The cross-spectrum calculated by digital Fourier transform technique will unavoidally have leakage error since the period of signal will not be usually coincident with record length. Therefore, the acoustic intensity estimated by the conventional FFT analyzer will show distorted value. In this paper, the expression of the Fourier transformed date of a harmonic signal with a single frequency is formated when there is leakage error. The method to elimate the effect of leakage error from the contaminated data is also proposed. Some numerical examples show the validation of the proposed method.

• 한국음향학회지
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• 제9권3호
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• pp.56-61
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• 1990

수중폭발음의 Energy spectrum 분석에 보다 정밀한 이론적 뒷받침을 하기 위하여 폭발음의 파형에 Gaussian formula를 도입하였으며 이 파형에 따른 Energy spectrum 모델을 새로이 유도하였다. Impulse formula를 이용한 Weston 모델이 낮은 폭발 에너지나 음원의 작동수심이 깊을 경우 이론적 모델로서 한계성을 갖는데 비해 이 모델은 이러한 조건에서도 실험결과와 잘 일치되고 있음을 확인할 수 있었다.

• 대한전기학회논문지:전력기술부문A
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• 제49권2호
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• pp.50-55
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• 2000

This paper presents the feature extraction of fault currents related to the multi-shot reclosing scheme in the power distribution system. In order to get the fault current waveform, we have measured the fault currents by the fault recorders which have been installed at the secondary side of 154/22.9[kV] substation transformer. These waveforms are classified into temporary and permanent fault. For the classified waveforms, Fourier transform is used to extract the feature of the fault current waveforms. After the waveforms are analyzed by using Fourier transform, the magnitude spectrum and the relative variation of THD (Total Harmonic Distortion) are calculated. And then the relative variation of THD is great in the temporary faults, and is small in the permanent faults.

• 한국생산제조학회지
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• 제19권3호
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• pp.407-413
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• 2010

This paper reports on the research which analyzes acoustic signals acquired in progressive compressing, hole blanking, and burr compacting process. An acoustic sensor was set on the bed of hydraulic press. Acoustic signal is generated from progressive stamping process. First the signal acquired from the unit process; compressing, blanking or compacting, is studied by Fourier Transform and Short Time Fourier Transform. The blanking process emitted ultrasonic signal with more than 20kHz, but the compressing and compacting processes emitted acoustic signals with lower than 10kHz. The combined signals periodically acquired right after the tool grinding were then analyzed. 70-80kHz signals appeared in time-frequency domain, but not in the frequency domain, the magnitude of which was related to the tool wear. Short Time Fourier Transform made up for the Fourier Transform in analyzing the emitted signal for stamping process in the ultrasonic domain.