• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.2
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• pp.152-162
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• 2001

Laser-generated ultrasonic technique which is one of the reliable nondestructive evaluation techniques has been applied to evaluate the integrity of structures by analyzing the characteristics of signal obtained from surface crack. Therefore, the signal analysis of the laser-generated ultrasonics is absolutely necessary for the accurate and quantitative estimation of the surface defects. In this study, one-sided measurement by laser-generated ultrasonic has been applied to evaluate the depth of the surface-breaking crack in the materials. However, since the ultrasonic waveform excited by pulse laser is very difficult to distinguish the defect signals, it is necessary to consider the signal analyses of the transient waveform. Wavelet Transform(WT) is a powerful tool for processing transient signals with temporally varying spectra that helps to resolve high and low frequency transient components effectively. In this paper, the analyses of the surface-breaking crack of the ultrasonic signal excited by pulse laser are presented by employing the WT analyses.

• Proceedings of the IEEK Conference
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• 2003.07d
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• pp.1427-1430
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• 2003

본 논문에서는 저작권 보호를 위하여 임계값을 이용한 워터마킹 기법을 제안한다 저작권을 보호하기 위하여 원 영상을 웨이블릿 변환하여 얻어진 웨이블렛 계수의 LSB(least significant bit)와 워터마크 영상을 동적 임계값을 적용하여 생성한 4장의 이진영상을 각 주파수 영역 HL1, LH1, HL2, LH2에서 XOR연산을 하여 워터마크를 삽입한다. 화질 열화가 많은 저주파 영역과 손실압축에 약한 고주파 영역을 제외한 영역에 워터마크를 삽입하였다. 실험결과로써, 화질의 열화가 적은 워터마크 삽입영상을 얻을 수 있었으며, 강인하게 워터마크가 추출이 되었다.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2003.06a
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• pp.130-133
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• 2003

본 논문에서는 웨이블렛 압축 기반인 SPIHT 알고리즘의 압축효율을 개선시킬 수 있는 방법을 제안한다. 특히 초기치에서 발생될 수 있는 비트소비를 줄임으로써, 낮은 비트율에서 더욱 빠른 점진적인 전송을 구현하였다. 트리구조에 따르는 최적화 된 임계값 설정과 웨이블렛 변환된 계수들의 계수값을 통해 비트율 향상을 얻을 수 있었다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.11a
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• pp.295-298
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• 2009

웨이블렛 변환(Wavelet Transform)은 영상압축에 효율적인 방법으로 알려져 있으며 lifting scheme을 이용해서 쉽게 구현이 가능하다. 가장 널리 쓰이는 방법으로는 Daubechies 5/3 필터가 있고, 이를 바탕으로 하여 영상의 기하학적인 특성을 이용한 적응적 예측 방법이 많이 소개되었다. 본 논문에서는 적응적 예측을 위해 템플릿 매칭을 적용한 새로운 알고리즘을 제안하였다.

• Journal of Ocean Engineering and Technology
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• v.16 no.5
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• pp.61-65
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• 2002

The fault detection and diagnosis of rotating machinery widely used in plants including the ship are important for maintaining the performance of Plants. Recently, the wavelet transform has been recognized an efficient method to detect a little variation of physical quantities by the synchronous localization of time and frequency domains using the translation and dilation of signals. In this Paper, In order to develop efficient and reliable fault detection and diagnosis system rotating machines, the performance of wavelet transformation to detect a little variation of machine status and neural network to diagnose the cause of machine faults are investigated and experimented.

• Proceedings of the KIEE Conference
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• 2009.04a
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• pp.318-321
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• 2009

누전차단기 설치 상태에서도 전기화재가 지속적으로 발생함에 따라 전기화재의 원인이 되는 전기 아크에 대한 관심이 증가하고 있는 실정으로 본 논문에서는 UL1699의 아크 저해시험(inhibition tests)에서 제시하고 있는 직렬 아크코장시험(Arc generator test)을 실시하고, 아크고장전류 분석방법으로 최근에 많이 사용되고 있는 이산 웨이블렛 변환을 이용한 3가지 분석방법에 대하여 아크고장전류 검출 확률을 분석하였다. 분석결과, (1) 근사계수 분석에 의한 최대치 변화율 실효치 변화율 분석방법은 46%의 검출 확률을 얻을 수 있었고, (2) 상세계수 분석에 의한 최대치 변화율 실효치 변화율 분석방법은 62%, (3) 근사계수 분석에 의한 잡음량 변화율 shoulder 변화율 분석방법은 100% 검출 확률을 얻을 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1759-1766
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• 2001

Vibration transient generated by developing localized fault in gear can be used as indicators in gear fault detection. In this paper, we propose the zoomed phase map for a fault signal using continuous wavelet transfers to detect this vibration transient. Local fault induces the abrupt fluctuation of load exciting tooth and phase lag in the vibration signal measured on the gearbox. The relatively large fault like "tip breakage" easily can be detected by the clear fluctuation of exciting load. However, minor fault like "initial pitting"cannot be detected using the load fluctuation. To defect this kind of minor fault, the phase map for a fault signal is taken into account. The phase lag by minor fault is observed well in the zoomed phase map.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.943-947
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• 2008

Dynamic response characteristics of a beam undergoing impulsive force are investigated using the wavelet transform method in this study. When an impulse is applied to an arbitrary position of a beam, it will generate a structural deformation wave. The characteristics of the wave are changing in the domain of time and space. The maximum amplitude of each natural frequency mode and the time to reach the maximum amplitude are obtained in this study. The effects of the location of impulse on the variations of the dynamic characteristics is also investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.115-120
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• 2002

The rigid body properties of a structure may be estimated easily if the mass-line of the structure could be taken exactly. However, the exact mass-line may be hard to be obtained exactly in experiments. The mass line value can be read from the mass line in frequency response function. However, the mass lines in the frequency response function sometimes show the fluctuation with frequency, and it cannot be read correctly. In this paper, the wavelet transform is applied to obtain the good mass line value. The mass line calculated by using wavelet transform has unique value and showed in the range of fluctuated values of frequency response function. The rigid body properties obtained by wavelet transform also showed better results than those by fourier transform.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.9
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• pp.725-730
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• 2002

The rigid body properties of a structure may be estimated easily if the mass-line of the structure could be taken exactly. However, the exact mass-line nay be hard to be obtained exactly in experiments. The mass line value can be read from the mass line in frequency response function. However, the mass lines in the frequency response function sometimes show the fluctuation with frequency, and it cannot be read correctly. In this paper, the wavelet transform is applied to obtain the good mass line value. The mass line calculated by using wavelet transform has unique value and showed in the range of fluctuated values of frequency response function. The rigid body properties obtained by wavelet transform also showed better results than those by fourier transform.