• Title/Summary/Keyword: Wavelet transform

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A New NDT Technique on Tunnel Concrete Lining (터널 콘크리트 라이닝의 새로운 비파괴 검사기법)

  • 이인모;전일수;조계춘;이주공
    • Proceedings of the Korean Geotechical Society Conference
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    • 2003.03a
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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.

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An Effective Image Restoration Using Genetic Algorithm in Wavelet Transform Region (웨이브릿 변환 영역에서 유전자 알고리즘을 적용한 효율적인 영상복원)

  • 김은영;안주원;정희태;문영득
    • Proceedings of the IEEK Conference
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    • 2000.11d
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    • pp.89-92
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    • 2000
  • In this paper, an effective image restoration using Genetic Algorithm(GA) in wavelet transform region is proposed. First, a wavelet transform is used for decomposition of a blurred image with white Gaussian noise as a preprocessing of the proposed method. The wavelet transform decomposes a degraded image into a wavelet subband coefficient planes. In this wavelet transformed subband coefficient planes, three highest subbands is composed entirely of noise elements on a degraded image. So, these subbands are removed. And remained subbands except for the lowest subband are individually applied to GA. For the performance evaluation, the proposed method is compared with a conventional single GA algorithm and a conventional hybrid method of wavelet transform and GA for a Lenna image and a boat image. As an experimental result, the proposed algorithm is prior to a conventional methods as each PSNR 3.4dB, 1.3dB.

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Time Delay Estimation using Wavelet Transform (웨이블릿 변환을 이용한 시간 지연 추정법)

  • Kim Doh-Hyoung;Park Youngjin
    • Proceedings of the Acoustical Society of Korea Conference
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    • spring
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    • pp.165-168
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    • 2000
  • A fast estimation method using wavelet transform for a time delay system is proposed. Main point of this method is to get the wavelet transform of the correlation between the input signal and delayed signal using transformed signals. But wavelet transform using Haar wavelet functions has basis with different phases and can offers a bisection method to estimate a time delay of a signal. Selective computation of the transform of correlation is performed and the computational complexity is reduced. Computational order of this method is O(N log N) and it is much love. than a simple correlation esimation when the length of signal is long.

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Noise Attenuation of Marine Seismic Data with a 2-D Wavelet Transform (2-D 웨이브릿 변환을 이용한 해양 탄성파탐사 자료의 잡음 감쇠)

  • Kim, Jin-Hoo;Kim, Sung-Bo;Kim, Hyun-Do;Kim, Chan-Soo
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.8
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    • pp.1309-1314
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    • 2008
  • Seismic data is often contaminated with high-energy, spatially aliased noise, which has proven impractical to attenuate using Fourier techniques. Wavelet filtering, however, has proven capable of attacking several types of localized noise simultaneously regardless of their frequencies. In this study a 2-D stationary wavelet transform is used to decompose seismic data into its wavelet components. A threshold is applied to these coefficients to attenuate high amplitude noise, followed by an inverse transform to reconstruct the seismic trace. The stationary wavelet transform minimizes the phase-shift errors induced by thresholding that occur when the conventional discrete wavelet transform is used.

Decoupling of Free Decay Roll Data by Discrete Wavelet Transform (이산 웨이블렛 변환을 이용한 자유감쇠 횡요 데이타의 분리)

  • Kwon, Sun-Hong;Lee, Hee-Sung;Lee, Hyoung-Suk;Ha, Mun-Keun
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2001.10a
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    • pp.169-173
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    • 2001
  • This study presents the results of decoupling of free decay roll test data by discrete wavelet transform. Free roll decay test was performed to decide the coefficients of damping terms in equation of motion. During the experiment, a slight yaw motion was found while the model was in the free roll decay motion. Discrete wavelet transform was applied to the signal to extract the pure roll motion. The results were compared to those of the Fourier transform. DWT was able to decouple the two signals efficiently while the Fourier transform was not.

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Wheel Loading Diagnosis and De-noising by Wavelet Transform (Wavelet 변환에 의한 숫돌로딩 진단과 노이즈 제거)

  • Yang, J.Y.;Ha, M.K.;Kwak, J.S.;Park, H.M.;Lee, S.J.
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.1 no.1
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    • pp.29-37
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    • 2002
  • The wavelet transform is a popular tool for studying intermittent and localized phenomena in signals. In this study the wavelet transform of cutting force signals was conducted for the diagnosis of grinding conditions in grinding process. We used the Daubechies wavelet analyzing function to detect a sudden change in cutting signal level. STD11 workpiece was 85 times of machined pieces cut by the WA wheel and a tool dynamometer obtained cutting force signals. From the results of the wavelet transform, the obtained signals were divided into approximation terms and detailed terms. At dressing time, the approximation signals were slowly increased and 45 machined times noticed dressing time.

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Detection of Tool Failure by Wavelet Transform (Wavelet 변환을 이용한 공구파손 검출)

  • Yang, J.Y.;Ha, M.K.;Koo, Y.;Yoon, M.C.;Kwak, J.S.;Jung, J.S.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2002.05a
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    • pp.1063-1066
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    • 2002
  • The wavelet transform is a popular tool for studying intermittent and localized phenomena in signals. In this study the wavelet transform of cutting force signals was conducted for the detection of a tool failure in turning process. We used the Daubechies wavelet analyzing function to detect a sudden change in cutting signal level. A preliminary stepped workpiece which had intentionally a hard condition was cut by the inserted cermet tool and a tool dynamometer obtained cutting force signals. From the results of the wavelet transform, the obtained signals were divided into approximation terms and detailed terms. At tool failure, the approximation signals were suddenly increased and the detailed signals were extremely oscillated just before tool failure.

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A Study on the Wear Detection of a Milling Using the Wavelet Transform (웨이브렛 변환을 이용한 밀링 공구의 마모 감지 연구)

  • Jeon, Do-Young;Lee, Gun;Kim, Kyoung-Ho
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2002.05a
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    • pp.211-214
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    • 2002
  • The detection of tool wear is very important in an automated manufacturing system. This paper presents a tool condition monitoring system based on the wavelet transform analysis of the AC servo motor current in a milling process. The current measurement is relatively simple and does not affect machining operations. The discrete wavelet transform was used to decompose the current of a spindle AC servo motor in the time and frequency domain. The feature vectors were extracted from the decomposed signals and compared to clarity normal and wear conditions. The results show the feasibility of the wavelet transform analysis for the tool condition monitoring.

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Application of Wavelet Transform for Correlation Analysis between Water Quality and Rainfall Data (수질 및 강우자료의 상관분석을 위한 웨이블렛 변환의 적용)

  • Jin, Young Hoon;Oh, Chang Ryol;Park, Sung Chun
    • Journal of Korean Society on Water Environment
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    • v.22 no.5
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    • pp.831-837
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    • 2006
  • The present study applies wavelet transform for the extraction of various periodicities which are included in TOC and pH time series of water quality and rainfall data. The primary objective of the present study is to detect the relationships between the respective data through the correlation analysis using the approximation components which are decomposed by wavelet transform. The results reveal the approximation components of TOC and pH in the 5th level of wavelet transform can explain more than 99% of the whole energy for the raw data respectively and there are considerably high correlation between the approximation components of the respective data used for the study even through no significant correlation between the raw data has been detected.

Identification of Mass-lines and Rigid Body Properties Using Wavelet Transform (웨이블렛 변환을 이용한 질량선 및 강체특성의 규명)

  • 안세진;정의봉;황대선
    • 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.