• 제목/요약/키워드: Time-frequency Transform

검색결과 908건 처리시간 0.028초

첩릿변환을 이용한 비틀림 유도파 모드분리 (Mode Separation in Torsional Guided Waves Using Chirplet Transform)

  • 김영완;박경조
    • 한국소음진동공학회논문집
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    • 제24권4호
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    • pp.324-331
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    • 2014
  • The sensor configuration of the magnetostrictive guided wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work we develop the mode decomposition technique employing chirplet transform based on the maximum likelihood estimation, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor, and estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. Simulation results on a carbon steel pipe are presented, which show the accurate mode separation and more discernible time-frequency representation could become enabled using the proposed technique.

Applications of the wavelet transform in the generation and analysis of spectrum-compatible records

  • Suarez, Luis E.;Montejo, Luis A.
    • Structural Engineering and Mechanics
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    • 제27권2호
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    • pp.173-197
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    • 2007
  • A wavelet-based procedure to generate artificial accelerograms compatible with a prescribed seismic design spectrum is described. A procedure to perform a baseline correction of the compatible accelerograms is also described. To examine how the frequency content of the modified records evolves with time, they are analyzed in the time and frequency using the wavelet transform. The changes in the strong motion duration and input energy spectrum are also investigated. An alternative way to match the design spectrum, termed the "two-band matching procedure", is proposed with the objective of preserving the non-stationary characteristics of the original record in the modified accelerogram.

Wavelet Transform을 이용한 Heart Sound Analysis (Analysis of Heart Sound Using the Wavelet Transform)

  • 위지영;김중규
    • 대한전자공학회:학술대회논문집
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    • 대한전자공학회 2000년도 제13회 신호처리 합동 학술대회 논문집
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    • pp.959-962
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    • 2000
  • A heart sound algorithm, which separates the heart sound signal into four parts; the first heart sound, the systolic period, the second heart sound, and the diastolic period has been developed. The algorithm uses discrete intensity envelopes of approximations of the wavelet transform analysis method to the phonocard-iogram(PCG)signal. Heart sound a highly nonstation-ary signal, so in the analysis of heart sound, it is important to study the frequency and time information. Further more, Wavelet Transform provides more features and characteristics of the PCG signal that will help physician to obtain qualitative and quantitative measurements of the heart sound.

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SHIFTING AND MODULATION FOR FOURIER-FEYNMAN TRANSFORM OF FUNCTIONALS IN A GENERALIZED FRESNEL CLASS

  • Kim, Byoung Soo
    • Korean Journal of Mathematics
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    • 제25권3호
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    • pp.335-347
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    • 2017
  • Time shifting and frequency shifting proprerties for the Fourier-Feynman transform of functionals in a generalized Fresnel class ${\mathcal{F}}_{A_1,A_2}$ are given. We discuss scaling and modulation proprerties for the Fourier-Feynman transform. These properties help us to obtain Fourier-Feynman transforms of new functionals from the Fourier-Feynman transforms of old functionals which we know their Fourier-Feynman transforms.

초음파 에코파형의 웨이브렛 변환과 비파괴평가에의 응용 (Wavelet Analysis of Ultrasonic Echo Waveform and Application to Nondestructive Evaluation)

  • 박익근;박은수;안형근;권숙인;변재원
    • 비파괴검사학회지
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    • 제20권6호
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    • pp.501-510
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    • 2000
  • 초음파 에코파형의 시간-주파수해석법으로 Wigner 분포와 웨이브렛 변환 등과 같은 새로운 신호처리 기법이 비파괴평가 분야에 널리 응용되고 있다. 본 연구에서는 웨이브렛 변환(wavelet transform)에 의한 음속과 감쇠계수의 주파수의존성과 초음파 결함신호의 잡음제거의 유용성 유무를 실험적으로 검증하였다. Gabor 함수를 웨이브렛의 기본함수로 사용하였다. 초음파의 에코파형에 포함된 각 주파수성분의 속도와 감쇠계수의 주파수의존성을 추정할 수 있었으며, 초음파탐상에서 결함의 검출능 향상과 결함크기 산정의 정량화에 접근하기 위해 웨이브렛 변환에 의한 S/N비 신호처리 시뮬레이션 결과를 오스테나이트강 스테인레스 용접부에 가공한 EDM 노치의 초음파 결함신호에 적용한 결과 임상에코를 저감하고 S/N비를 개선하는 것이 가능하였다.

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Spanwise coherent structure of wind turbulence and induced pressure on rectangular cylinders

  • Le, Thai-Hoa;Matsumoto, Masaru;Shirato, Hiromichi
    • Wind and Structures
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    • 제12권5호
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    • pp.441-455
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    • 2009
  • Studying the spatial distribution in coherent fields such as turbulence and turbulence-induced force is important to model and evaluate turbulence-induced forces and response of structures in the turbulent flows. Turbulence field-based coherence function is commonly used for the spatial distribution characteristic of the turbulence-induced forces in the frequency domain so far. This paper will focus to study spectral coherent structure of the turbulence and induced forces in not only the frequency domain using conventional Fourier transform-based coherence, but also temporo-spectral coherence one in the time-frequency plane thanks to wavelet transform-based coherence for better understanding of the turbulence and force coherences and their spatial distributions. Effects of spanwise separations, bluff body flow, flow conditions and Karman vortex on coherent structures of the turbulence and induced pressure, comparison between turbulence and pressure coherences as well as intermittency of the coherent structure in the time-frequency plane will be investigated here. Some new findings are that not only the force coherence is higher than the turbulence coherence, the coherences of turbulence and forces depend on the spanwise separation as previous studies, but also the coherent structures of turbulence and forces relate to the ongoing turbulence flow and bluff body flow, moreover, intermittency in the time domain and low spectral band is considered as the nature of the coherent structure. Simultaneous measurements of the surface pressure and turbulence have been carried out on some typical rectangular cylinders with slenderness ratios B/D=1 (without and with splitter plate) and B/D=5 under the artificial turbulent flows in the wind tunnel.

웨이블릿 변환의 저주파수 부대역을 이용한 왜곡 영상 데이터베이스 검색 (Distorted Image Database Retrieval Using Low Frequency Sub-band of Wavelet Transform)

  • 박하중;김경진;정호열
    • 대한임베디드공학회논문지
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    • 제3권1호
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    • pp.8-18
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    • 2008
  • In this paper, we propose an efficient algorithm using wavelet transform for still image database retrieval. Especially, it uses only the lowest frequency sub-band in multi-level wavelet transform so that a retrieval system uses a smaller quantity of memory and takes a faster processing time. We extract different textured features, statistical information such as mean, variance and histogram, from low frequency sub-band. Then we measure the distances between the query image and the images in a database in terms of these features. To obtain good retrieval performance, we use the first feature (mean and variance of wavelet coefficients) to filter out most of the unlikely images. The rest of the images are considered to be candidate images. Then we apply the second feature (histogram of wavelet coefficient) to rank all the candidate images. To evaluate the algorithm, we create various distorted image databases using MIT VisTex texture images and PICS natural images. Through simulations, we demonstrate that our method can achieve performance satisfactorily in terms of the retrieval accuracy as well as the both memory requirement and computational complexity. Therefore it is expected to provide good retrieval solution for JPEG-2000 using wavelet transform.

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Low Complexity Discrete Hartley Transform Precoded OFDM System over Frequency-Selective Fading Channel

  • Ouyang, Xing;Jin, Jiyu;Jin, Guiyue;Li, Peng
    • ETRI Journal
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    • 제37권1호
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    • pp.32-42
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    • 2015
  • Orthogonal frequency-division multiplexing (OFDM) suffers from spectral nulls of frequency-selective fading channels. Linear precoded (LP-) OFDM is an effective method that guarantees symbol detectability by spreading the frequency-domain symbols over the whole spectrum. This paper proposes a computationally efficient and low-cost implementation for discrete Hartley transform (DHT) precoded OFDM systems. Compared to conventional DHT-OFDM systems, at the transmitter, both the DHT and the inverse discrete Fourier transform are replaced by a one-level butterfly structure that involves only one addition per symbol to generate the time-domain DHT-OFDM signal. At the receiver, only the DHT is required to recover the distorted signal with a single-tap equalizer in contrast to both the DHT and the DFT in the conventional DHT-OFDM. Theoretical analysis of DHT-OFDM with linear equalizers is presented and confirmed by numerical simulation. It is shown that the proposed DHT-OFDM system achieves similar performance when compared to other LP-OFDMs but exhibits a lower implementation complexity and peak-to-average power ratio.

태양광 직렬 아크 검출기의 검출 성능 및 DWT 알고리즘 연산 속도 개선 (Arc Detection Performance and Processing Speed Improvement of Discrete Wavelet Transform Algorithm for Photovoltaic Series Arc Fault Detector)

  • 조찬기;안재범;이진한;이기덕;이진;류홍제
    • 전력전자학회논문지
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    • 제26권1호
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    • pp.32-37
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    • 2021
  • This study proposes a DC series arc fault detector using a frequency analysis method called the discrete wavelet transform (DWT), in which the processing speed of the DWT algorithm is improved effectively. The processing time can be shortened because of the time characteristic of the DWT result. The performance of the developed DC series arc fault detector for a large photovoltaic system is verified with various DC series arc generation conditions. Successful DC series arc detection and improved calculation time were both demonstrated through the measured actual arc experimental result.

Effect of time harmonic sources on transversely isotropic thermoelastic thin circular plate

  • Lata, Parveen;Kaur, Iqbal
    • Geomechanics and Engineering
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    • 제19권1호
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    • pp.29-36
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    • 2019
  • The present research deals with the deformation in transversely isotropic thin circular thermoelastic rotating plate due to time-harmonic sources. Frequency effect in the presence of rotation and two temperature is studied under thermally insulated as well as isothermal boundaries. The Hankel transform technique is used to find a solution to the problem. The displacement components, stress components, and conductive temperature distribution with the radial distance are computed in the transformed domain and further calculated in the physical domain using numerical inversion techniques. Some specific cases are also figured out from the current research.