• Title/Summary/Keyword: Time-Frequency Analysis Method

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Adaptive Short-time Fourier Transform for Guided-wave Analysis (유도 초음파 신호 분석을 위한 적응 단시간 푸리에 변환)

  • Hong, Jin-Chul;Sun, Kyung-Ho;Kim, Yoon-Young
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.3 s.96
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    • pp.266-271
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    • 2005
  • Although time-frequency analysis is useful for dispersive wave analysis, conventional methods such as the short-time Fourier transform do not take the dispersion phenomenon into consideration in the tiling of the time-frequency domain. The objective of this paper is to develop an adaptive time-frequency analysis method whose time-frequency tiling is determined with the consideration of signal dispersion characteristics. To achieve the adaptive time-frequency tiling, each of time-frequency atoms is rotated in the time-frequency plane depending on the local wave dispersion. To carry out this adaptive time-frequency transform, dispersion characteristics hidden in a signal are first estimated by an iterative scheme. To examine the effectiveness of the present method, the flexural wave signals measured in a plate were analyzed.

Adaptive Short-time Fourier Transform for Guided-wave Analysis (유도 초음파 신호 분석을 위한 적응 단시간 푸리에 변환)

  • Sun, Kyung-Ho;Hong, Jin-Chul;Kim, Yoon-Young
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2004.11a
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    • pp.606-610
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    • 2004
  • Although time-frequency analysis is useful for dispersive wave analysis, conventional methods such as the short-time Fourier transform do not take the dispersion phenomenon into consideration in the tiling of the time-frequency domain. The objective of this paper is to develop an adaptive time-frequency analysis method whose time-frequency tiling is determined with the consideration of signal dispersion characteristics. To achieve the adaptive time-frequency tiling, each of time-frequency atoms is rotated in the time-frequency plane depending on the local wave dispersion. To carry out this adaptive time-frequency transform, dispersion characteristics hidden in a signal are first estimated by an iterative scheme. To examine the effectiveness of the proposed method, the flexural wave signals measured in a plate were analyzed.

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Blind modal identification of output-only non-proportionally-damped structures by time-frequency complex independent component analysis

  • Nagarajaiah, Satish;Yang, Yongchao
    • Smart Structures and Systems
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    • v.15 no.1
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    • pp.81-97
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    • 2015
  • Recently, a new output-only modal identification method based on time-frequency independent component analysis (ICA) has been developed by the authors and shown to be useful for even highly-damped structures. In many cases, it is of interest to identify the complex modes of structures with non-proportional damping. This study extends the time-frequency ICA based method to a complex ICA formulation for output-only modal identification of non-proportionally-damped structures. The connection is established between complex ICA model and the complex-valued modal expansion with sparse time-frequency representation, thereby blindly separating the measured structural responses into the complex mode matrix and complex-valued modal responses. Numerical simulation on a non-proportionally-damped system, laboratory experiment on a highly-damped three-story frame, and a real-world highly-damped base-isolated structure identification example demonstrate the capability of the time-frequency complex ICA method for identification of structures with complex modes in a straightforward and efficient manner.

Damage evaluation of seismic response of structure through time-frequency analysis technique

  • Chen, Wen-Hui;Hseuh, Wen;Loh, Kenneth J.;Loh, Chin-Hsiung
    • Structural Monitoring and Maintenance
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    • v.9 no.2
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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.

Evaluation of the Corroded Pipe by Time-Frequency Analysis (시간-주파수 해석에 의한 부식된 배관의 평가)

  • Ahn, S.H.;Kim, J.W.;Do, J.Y.;Nam, K.W.
    • Journal of Power System Engineering
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    • v.10 no.2
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    • pp.89-92
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    • 2006
  • In this study, the pressure vessel piping with corrosion used during long term were investigated from the time-frequency analysis method. The damage of piping could be evaluated the attenuation factor by ultrasonic parameters such as center frequency and echo waveform. Based on NDE analysis by time-frequency analysis method, it should also be possible to evaluate from various damages and defects in piping members.

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Nondestructive Characterization Evaluation by Time-Frequency Analysis on Pressure Vessel Piping with Corrosion (압력용기용 부식 배관의 시간-주파수 해석에 의한 비파괴적 특성 평가)

  • Nam, K.W.;Kim, J.W.;Ahn, S.H.;Park, I.D.;Lee, S.S.;Park, S.S.
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.290-295
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    • 2004
  • In this study, the pressure vessel piping with corrosion used during long term were investigated from the time-frequency analysis method. The damage of piping could be evaluated the attenuation factor by ultrasonic parameters such as center frequency and echo waveform. Based on NDE analysis by time-frequency analysis method, it should also be possible to evaluate from various damages and defects in piping members.

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Time-Frequency Analysis of the Doppler Signals by Moving Targets (이동 표적에 의한 도플러 신호의 시간-주파수 분석)

  • Son, Joong-Tak;Lee, Seung-Houn;Park, Kil-Houm
    • Journal of the Korea Institute of Military Science and Technology
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    • v.8 no.2 s.21
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    • pp.38-48
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    • 2005
  • Instantaneous frequency of doppler signals is used to get the information of the relative velocity and the miss distance between a missile and a corresponding target. In this paper, we have performed time-frequency analysis and instantaneous frequency estimation with Short Time Fourier Transform(STFT), Wigner Ville Distribution(WVD) and Continuous Wavelet Transform(CWT) about the doppler signals generated by moving targets. Performance evaluation was performed using simulated doppler signals generated by a single moving target and two moving targets. From the results of the time-frequency analysis, we found that WVD method was the most efficient instantaneous frequency estimator among the three methods. But in case of two moving targets, WVD method got cross talks and CWT method got oscillation when two doppler frequencies were close to each other.

Dispersion-Based Continuous Wavelet Transform for the Analysis of Elastic Waves

  • Sun, Kyung-Ho;Hong, Jin-Chul;Kim, Yoon-Young
    • Journal of Mechanical Science and Technology
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    • v.20 no.12
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    • pp.2147-2158
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    • 2006
  • The continuous wavelet transform (CWT) has a frequency-adaptive time-frequency tiling property, which makes it popular for the analysis of dispersive elastic wave signals. However, because the time-frequency tiling of CWT is not signal-dependent, it still has some limitations in the analysis of elastic waves with spectral components that are dispersed rapidly in time. The objective of this paper is to introduce an advanced time-frequency analysis method, called the dispersion-based continuous wavelet transform (D-CWT) whose time-frequency tiling is adaptively varied according to the dispersion relation of the waves to be analyzed. In the D-CWT method, time-frequency tiling can have frequency-adaptive characteristics like CWT and adaptively rotate in the time-frequency plane depending on the local wave dispersion. Therefore, D-CWT provides higher time-frequency localization than the conventional CWT. In this work, D-CWT method is applied to the analysis of dispersive elastic waves measured in waveguide experiments and an efficient procedure to extract information on the dispersion relation hidden in a wave signal is presented. In addition, the ridge property of the present transform is investigated theoretically to show its effectiveness in analyzing highly time-varying signals. Numerical simulations and experimental results are presented to show the effectiveness of the present method.

Source Identification of Non-Stationary Sound.Vibration Signals Using Multi-Dimensional Spectral Analysis Method (다차원 스펙트럼 해석법을 이용한 비정상 소음.진동 신호의 소음원 규명)

  • Sim, Hyoun-Jin;Lee, Hae-Jin;Lee, You-Yub;Lee, Jung-Youn;Oh, Jae-Eung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.9 s.252
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    • pp.1154-1159
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    • 2006
  • In this paper, time-frequency analysis and multi-dimensional spectral analysis methods are applied to source identification and diagnostic of non-stationary sound vibration signals. By checking the coherences for concerned time, this simulation is very well coincident to expected results. The proposed method analyzes the signal instantaneously in both time and frequency domains. The MDSA (Multiple Dimensional Spectral Analysis) analyzes the signal in the plane of instantaneous time and instantaneous frequency at the same time. And it was verified by using the 1500cc passenger car which is accelerated from 70Hz to 95Hz in 4 seconds, the proposed method is effective in determining the vehicle diagnostic problems.

Time Domain Analysis of a Tension Leg Platform in Multi-Directional Irregular Waves (다방향 불규칙파중의 인장계류식 해양구조물의 시간영역 해석)

  • Lee, Chang-Ho;Kim, Chuel-Hyun
    • Journal of Ocean Engineering and Technology
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    • v.20 no.5 s.72
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    • pp.36-41
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    • 2006
  • The main object of this study is to develop an accurate and convenient method for the response analysis of offshore structures in real sea states. A numerical procedure is described for predicting the motion responses and tension variations of the ISSC TLP in multi-directional irregular waves. The developed numerical approach in the frequency domain is based on acombination of the three dimensional source distribution method, the dynamic response analysis method, and the spectral analysis method. Frequency domain analysis in the multi-directional irregular waves is expanded to a time domain analysis by using a convolution integral after obtaining the impulse response by Fourier transformation. The results of the comparison between responses in the frequency and time domain confirmed the validity of the proposed approach.