• 한국수산과학회지
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• 제55권2호
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• pp.195-206
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• 2022

The separation of spectrally overlapped broadband echo signals from free-swimming Japanese needlefish Hypohamphus sajori using the fractional Fourier transform (FrFT) was investigated. The broadband echo signals were measured over frequency ranges of 40-80 and 110-220 kHz. The overlapped echo signals were separated after eliminating noise signals in the smoothed pseudo-Wigner-Ville distribution domain. The echo signal from a 40 mm WC sphere suspended just below a chirp transducer was used to calibrate the broadband of the chirp echo sounder and estimate the frequency dependence of target strength for the separated echo signals. The experimental results show that the proposed FrFT method can analyze the time-frequency image of broadband echo signals from free-swimming individual fish effectively and can be used as a quantitative tool for extracting the acoustic features used for fish species identification.

• Structural Engineering and Mechanics
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• 제63권1호
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• pp.89-102
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• 2017

In this work, we present a theoretical framework to study the thermovisco-elastic responses of homogeneous, isotropic and perfectly conducting medium subjected to inclined load. Based on recently developed generalized thermoelasticity theory with fractional order strain, the two-dimensional governing equations are obtained in the context of generalized magnetothermo-viscoelasticity theory without energy dissipation. The Kelvin-Voigt model of linear viscoelasticity is employed to describe the viscoelastic nature of the material. The resulting formulation of the field equations is solved analytically in the Laplace and Fourier transform domain. On the application of inclined load at the surface of half-space, the analytical expressions for the normal displacement, strain, temperature, normal stress and tangential stress are derived in the joint-transformed domain. To restore the fields in physical domain, an appropriate numerical algorithm is used for the inversion of the Laplace and Fourier transforms. Finally, we have demonstrated the effect of magnetic field, viscosity, mechanical relaxation time, fractional order parameter and time on the physical fields in graphical form for copper material. Some special cases have also been deduced from the present investigation.

• Journal of Power Electronics
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• 제16권4호
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• pp.1526-1540
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• 2016

This work mainly discusses an accurate and fast islanding detection based on fractional wavelet packet transform (FRWPT)for multibus microgrid systems. The proposed protection scheme uses combined desirable features retrieved from discrete fractional Fourier transform (FRFT) and wavelet packet transform (WPT) techniques, which provides precise time-frequency information on minute perturbation signals introduced in the system. Moreover, this study focuses on the design of decoupling control with a distributed controller based on state feedback for the efficient operation of microgrid systems that are transitioning from the grid-connected mode to the islanded mode. An IEEE 9-bus test system with inverter based distributed generation (DG) units is considered for islanding assessment and smooth operation. Finally, tracking errors are greatly reduced with stability improvement based on the proposed controller. FRWPT based islanding detection is demonstrated via a time domain simulation of the system. Simulated results show an improvement in system stability with the application of the proposed controller and accurate islanding detection based on the FRWPT technique in comparison with the results obtained by applying the wavelet transform (WT) and WPT.

• 대한수학회지
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• 제32권3호
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• pp.615-623
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• 1995

Consider a function m defined in $R^n$ and the associated convolution operator T given by the Fourier transform $\hat{T} = m\hat{f}$.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권3호
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• pp.256-265
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• 2017

In this paper, an ascheme is proposed for multiuser underwater acoustic communication by using the multi-chirp rate signals. It differs from the well known TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access) or CDMA (Code Division Multiple Access), by assigning each users with different chirp-rate carriers instead of the time, frequency or PN code. Multi-chirp rate signals can be separated from each other by FrFT (Fractional Fourier Transform), which can be regarded as the chirp-based decomposing, and superior to the match filter in the underwater acoustic channel. VTRM (Virtual Time Reverse Mirror) is applied into the system to alleviate the ISI caused by the multipatch and make the equalization more simple. Results of computer simulations and pool experiments prove that the proposed multiuser underwater acoustic communication based on the multi-chirp rate exhibit well performance. Outfield experments carrie out in Xiamen Port show that using about 10 kHz bandwidth, four users could communicate at the same time with 425 bps with low BER and can match the UAC application.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.436-450
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• 2017

Recently, the method based on fractional order partial differential equation has been used in image processing. Usually, the optional order of fractional differentiation is determined by a lot of experiments. In this paper, a denoising model is proposed based on adaptive fractional order anisotropic diffusion. In the proposed model, the complexity of the local image texture is reflected by the local variance, and the order of the fractional differentiation is determined adaptively. In the process of the adaptive fractional order model, the discrete Fourier transform is applied to compute the fractional order difference as well as the dynamic evolution process. Experimental results show that the peak signal-to-noise ratio (PSNR) and structural similarity index measurement (SSIM) of the proposed image denoising algorithm is better than that of other some algorithms. The proposed algorithm not only can keep the detailed image information and edge information, but also obtain a good visual effect.

• Structural Engineering and Mechanics
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• 제68권2호
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• pp.215-226
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• 2018

In this article, the theory of fractional order two temperature generalized thermoelasticity is employed to study the wave propagation in a fiber reinforced anisotropic thermoelastic half space in the presence of moving internal heat source. The whole space is assumed to be under the influence of gravity. The surface of the half-space is subjected to an inclined load. Laplace and Fourier transform techniques are employed to solve the problem. Expressions for different field variables in the physical domain are derived by the application of numerical inversion technique. Physical fields are presented graphically to study the effects of gravity and heat source. Effects of time, reinforcement, fractional parameter and inclination of load have also been reported. Results of some earlier workers have been deduced from the present analysis.

• 지구물리와물리탐사
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• 제26권3호
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• pp.126-137
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• 2023

본 연구에서는 해양 모니터링 중에 기록된 돌고래 클릭 신호를 분류하기 위해 순환 신경망(RNN)을 적용하는 방법을 검토했다. 클릭 신호 분류의 정확도를 높이기 위해 단일 시계열 자료를 분수 푸리에 변환을 사용하여 분수 영역으로 변환하여 특징을 확장했으며, 분류를 위한 최적의 네트워크를 결정하기 위해 세 가지 순환 신경망 모델(LSTM, GRU, BiLSTM)을 비교 분석하였다. 순환 신경망 모델의 입력 자료로써 이용된 분수 영역 자료의 경우, 분수 푸리에 변환 시 회전 각도에 따라 다른 특성을 가지므로, 각 네트워크 모델에 따라 우수한 성능을 가지는 회전 각도 범위를 분석했다. 이때 네트워크 성능 분석을 위해 정확도, 정밀도, 재현율, F1-점수와 같은 성능 평가 지표를 도입했다. 수치실험 결과, 세 가지 네트워크 모두 높은 성능을 보였으며, BiLSTM 네트워크가 LSTM, GRU에 비해 뛰어난 학습 결과를 제공했다. 마지막으로, 현장 자료 적용 가능성 측면에서 BiLSTM 네트워크가 다른 네트워크에 비해 낮은 오탐지 결과를 제공하였다.

• 한국정보통신학회논문지
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• 제22권3호
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• pp.418-424
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• 2018

수중 표적 탐지 및 식별은 군사 및 비군사적으로 중요한 문제이다. 최근 패턴인식 분야에서 딥러닝 기술이 발전되면서 많은 성능개선 결과가 발표되고 있다. 그중 DBN(Deep Belief Network)기법은 DNN(Deep Neural Network)을 사전 훈련하는데 사용되어 좋은 성능을 보여주고 있다. 본 논문에서는 능동 소나를 이용한 수중 표적의 식별 문제에 DBN을 사용하여 실험을 진행하고, 그 결과를 비교하였다. 표적신호는 3차원 하이라이트 모델을 사용하여 합성된 능동 소나 신호를 사용하였고, 특징추출 방법으로는 FrFT(Fractional Fourier Transform) 기반의 특징추출을 사용하였다. 단일 센서, 즉, 단일 방위 데이터 기반의 실험에서 DBN을 이용한 식별 결과는 기존의 BPNN(Back Propagation Neural Network)에 비해 약 3.83 % 향상되었다. 또한, 다중 방위 기반의 식별 실험에서는 관측열의 개수가 3을 초과하면 95% 이상의 성능을 얻을 수 있었다.

• Structural Engineering and Mechanics
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• 제73권6호
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• pp.725-735
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• 2020

The present investigation deals with the thermomechanical interactions in an orthotropic thermoelastic homogeneous body in the context of fractional order theory of thermoelasticity due to time harmonic sources. The application of a time harmonic concentrated and distributed sources has been considered to show the utility of the solution obtained. Assuming the disturbances to be harmonically time dependent, the expressions for displacement components, stress components and temperature change are derived in frequency domain. Numerical inversion technique has been used to determine the results in physical domain. The effect of frequency on various components has been depicted through graphs.