• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.199-203
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• 1997

Fine displacement of spherical suface was detected and analyzed by Twyman-Green interferometer and the interferogram analysis using Fourier transform method. The surface profile was obtained from single interferogram by introducing the carrier freguency to the interferogram. The interferogram was processed in the spatial frequency domain by fast Fourier transform, and the phase distribution was obtained by inverse Fourier transform. The 3-dimensional distribution for the surface displacement was obtained. It was compared with the calculated surface displacement and the error was less than λ/10.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.298-306
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• 2018

This paper presents a harmonic analysis of the modular multilevel converter (MMC) using a double Fourier series (DFS) algorithm. First, the application of DFS for harmonic calculation in the MMC is made by considering the effect of arm inductor. The analytical results are then confirmed by comparing with the simulation results of using the fast Fourier transform (FFT) algorithm. Finally, distribution of harmonics and total harmonic distortion (THD) in the MMC will be analyzed in three cases: harmonics versus number of levels of MMC, harmonics versus total switching frequency and harmonics versus modulation index. The simulation results are performed in the PSCAD/EMTDC simulation program in order to verify the analytical results obtained by Matlab programming.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2005.11a
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• pp.302-305
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• 2005

Recently, many methods to analyze signal have been proposed and representative methods are the Fourier transform and wavelet transform. In these methods, the Fourier transform represents signal with combination cosine and sine at all locations in the frequency domain. However, it doesn't provide time information that particular frequency occurs in signal and denpends on only the global feature of the signal. So, to improve these points the wavelet transform which is capable of multiresolution analysis has been applied to many fields such as speech processing, image processing and computer vision. And the wavelet transform, which uses changing window according to scale parameter, presents time-frequency localization. In this paper, we proposed a new approach using a wavelet of cosine and sine type and analyzed features of signal in a limited point of frequency-time plane.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.2
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• pp.495-513
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• 2020

The correlation identification of the subsurface is a novel electrical prospecting method which could suppress stochastic noise. This method is increasingly being utilized by geophysicists. It achieves the frequency response of the underground media through division of the cross spectrum of the input & output signal and the auto spectrum of the input signal. This is subject to the spectral leakage when the cross spectrum and the auto spectrum are computed from cross correlation and autocorrelation function by Discrete Fourier Transformation (DFT, "To obtain an accurate frequency response of the earth system, we propose an improved correlation identification method which uses all phase Fast Fourier Transform (APFFT) to acquire the cross spectrum and the auto spectrum. Simulation and engineering application results show that compared to existing correlation identification algorithm the new approach demonstrates more precise frequency response, especially the phase response of the system under identification.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.1 s.94
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• pp.246-252
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• 1999

In this paper, the frequency response characteristics of the velocity controlled EHS system obtained by linear simulation method, nonlinear simulation method, and experimentation are compared one another, in order to verify propriety of the linearization method in case of analysis of hydraulic systems. The Bode diagrams are obtained by transforming time domain data of experimental results and nonlinear simulated ones with Fourier transform. The results of nonlinear simulation are more similar to the frequency response of the real systems than those of linear simulation. It is found that nonlinearity of hydraulic systems is mainly occurred from servo valve, and nonlinearity is increased as displacement of servo valve spool increases.

• Geomechanics and Engineering
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• v.19 no.5
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• pp.369-381
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• 2019

The objective of this paper is to study the two dimensional deformation in transversely isotropic thermoelastic medium without energy dissipation due to time harmonic sources using new modified couple stress theory, a continuum theory capable to predict the size effects at micro/nano scale. The couple stress constitutive relationships have been introduced for transversely isotropic thermoelastic medium, in which the curvature tensor is asymmetric and the couple stress moment tensor is symmetric. Fourier transform technique is applied to obtain the solutions of the governing equations. Assuming the deformation to be harmonically time-dependent, the transformed solution is obtained in the frequency domain. The application of a time harmonic concentrated and distributed sources have been considered to show the utility of the solution obtained. The displacement components, stress components, temperature change and couple stress are obtained in the transformed domain. A numerical inversion technique has been used to obtain the solutions in the physical domain. The effects of angular frequency are depicted graphically on the resulted quantities.

• Journal of KSNVE
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• v.10 no.5
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• pp.800-805
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• 2000

To determine the modal matrix and modal frequency of engine mount system, we most solve so-called eigen-value problem. However eigen-value problem of engine mount system with hydraulic mount can not be solved by general eigne-analysis algorithm because the properties of hydraulic mount vary with frequency. so in this paper the method for modal analysis of rigid body motions of an engine supported by hydraulic mount is proposed. Natural frequencies and mode shapes of this nonlinear system are obtained by using complex exponential method and Laplace transformation method. In time domain, impulse response functions are calculated by (two-sided) discrete inverse Fourier Transformation of forced frequency response functions achieved by Laplace transformation of the differential equation of motion. Considering the fact that frequency response functions synthesized by modal parameters form proposed method are in good agreement with original FRFs, it is proved that the proposed method is very efficient and useful for the analysis of eigne-value problem of hydraulic engine mount system.

• Structural Engineering and Mechanics
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• v.77 no.3
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• pp.315-327
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• 2021

Here, in this research we have studied a two dimensional problem in a homogeneous orthotropic magneto-thermoelastic medium with higher order dual-phase-lag heat transfer with combined effects of rotation and hall current in generalized thermoelasticity due to time harmonic sources. As an application the bounding surface is subjected to uniformly distributed and concentrated loads (mechanical and thermal source). Fourier transform technique is used to solve the problem. The expressions for displacement components, stress components and temperature change are derived in frequency domain. Numerical inversion technique has been used to obtain the results in physical domain. The effect of frequency has been depicted with the help of graphs.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.55 no.2
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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.

• Coupled systems mechanics
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• v.11 no.4
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• pp.297-313
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• 2022

The objective of this paper is to study the effect of frequency in a two-dimensional orthotropic thermoelastic rotating solid with fractional order heat transfer in generalized thermoelasticity with two-temperature due to inclined load. As an application the bounding surface is subjected to uniformly and linearly distributed loads (mechanical and thermal source). The problem is solved with the help of Fourier transform. Assuming the disturbances to be harmonically time dependent, the expressions for displacement components, stress components, conductive temperature and temperature change are derived in frequency domain. Numerical inversion technique has been used to determine the results in physical domain. The results are depicted graphically to show the effect of frequency on various components. Some particular cases are also discussed in the present research.