• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.2 no.2
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• pp.31-40
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• 1998

Spectral analysis by energy method is given for a fully discrete methods for hyperbolic integro-differential equations with a weakly singular kernel. Stability and error estimates in $H^1$-norm are derived.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.12 s.243
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• pp.1574-1585
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• 2005

In this paper, a spectral element model is developed for the uniform straight pipelines conveying internal unsteady fluid. Four coupled pipe-dynamics equations are derived first by using the Hamilton's principle and the principles of fluid mechanics. The transverse displacement, the axial displacement, the fluid pressure and the fluid velocity are all considered as the dependent variables. The coupled pipe-dynamics equations are then linearized about the steady state values of the fluid pressure and velocity. As the final step, the spectral element model represented by the exact dynamic stiffness matrix, which is often called spectral element matrix, is formulated by using the frequency-domain solutions of the linearized pipe-dynamics equations. The FFT-based spectral dynamic analyses are conducted to evaluate the accuracy of the present spectral element model and also to investigate the structural dynamic characteristics and the internal fluid transients of an example pipeline system.

• Earthquakes and Structures
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• v.15 no.6
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• pp.629-637
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• 2018

In recent years, selection of strong ground motion records by means of intensity measures representing the spectral shape of the earthquake excitation has been studied by many researchers. These studies indicate the adequacy of this record selection approach in reduction of the scattering of seismic responses. In present study, this method has been studied more in depth to reveal the sufficiency of the spectral shape in predicting structural seismic responses such as the plastic deformation and the dissipated hysteresis energy which are associated with cumulative properties of the selected records. For this purpose, after selecting the records based on the spectral shape, the correlation of some seismic responses and strong ground motion duration of earthquake records are explored. Findings indicate strong correlation of some structural responses with the significant duration of the records. This fact implies that the spectral shape could not reflect all characteristics of the strong ground motion and emphasizes the importance of additional criteria along with the spectral shape in the record selection.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.2
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• pp.601-617
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• 2014

In digital radio broadcasting systems, long delays are incurred in service start time when tuning to a particular frequency because several synchronization steps, such as symbol timing synchronization, frame synchronization, and carrier frequency offset and sampling frequency offset compensation are necessary. Therefore, the operation of the synchronization blocks causes delays ranging from several hundred milliseconds to a few seconds until the start of the radio service after frequency tuning. Furthermore, if spectrum inversed signals are transmitted in digital radio broadcasting systems, the receivers are unable to decode them, even though most receivers can demodulate the spectral inversed signals in analog radio broadcasting systems. Accordingly, fast synchronization techniques and a method for spectral inversion detection are required in digital radio broadcasting systems that are to replace the analog radio systems. This paper presents a joint detection method of frame, integer carrier frequency offset, and spectrum inversion for DRM Plus digital broadcasting systems. The proposed scheme can detect the frame and determine whether the signal is normal or spectral inversed without any carrier frequency offset and sampling frequency offset compensation, enabling fast frame synchronization. The proposed method shows outstanding performance in environments where symbol timing offsets and sampling frequency offsets exist.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.437-447
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• 2003

We propose the methods to design the finite impulse response (FIR) and the infinite impulse response (IIR) lattice filters using Schur algorithm through the spectral factorization of the covariance matrix by circulant matrix factorization (CMF). Circulant matrix factorization is also very powerful tool used fur spectral factorization of the covariance polynomial in matrix domain to obtain the minimum phase polynomial without the polynomial root finding problem. Schur algorithm is the method for a fast Cholesky factorization of Toeplitz matrix, which easily determines the lattice filter parameters. Examples for the case of the FIR Inter and for the case of the IIR filter are included, and performance of our method check by comparing of our method and another methods (polynomial root finding and cepstral deconvolution).

• Journal of KSNVE
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• v.6 no.5
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• pp.617-624
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• 1996

Finite Element Method(FEM) is one of the most popularly used method in analyzing the dynamic behaviors of structures. But unless the number of finite elements is large enough, the results from FEM are somewhat different form exact analytical solutions, especially at high frequency range. On the other hand, as the Spectral Element Method(SEM) deals directly with the governing equations of structures, the results from this method cannot but be exact regardless of any frequency range. However, despite two dimensional structures are more general, the SEM has been applied only to the analysis of one dimensional structures so far. In this paper, therefore, new methodologies are introduced to analyze the two dimensional plate structure using SEM. The results from this new method are compared with the exact analytical solutions by letting the two dimensional plate structure be one dimensional and showed the dynamic responses of two dimensional plate by including various waves propagated into x-direction.

• Structural Engineering and Mechanics
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• v.17 no.3_4
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• pp.445-466
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• 2004

In this paper, several modal identification techniques for output-only structural systems are extensively investigated. The methods considered are the power spectral method, the frequency domain decomposition method, the Ibrahim time domain method, the eigensystem realization algorithm, and the stochastic subspace identification method. Generally, the power spectral method is most widely used in practical area, however, the other methods may give better estimates particularly for the cases with closed modes and/or with large measurement noise. Example analyses were carried out on typical structural systems under three different loading cases, and the identification performances were examined throught the comparisons between the estimates by various methods.

• The Journal of the Acoustical Society of Korea
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• v.18 no.1
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• pp.38-44
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• 1999

In this paper, a new spectral subtraction technique with two microphone inputs is proposed. In conventional spectral subtraction using a single microphone, the averaged noise spectrum is subtracted from the observed short-time input spectrum. This results in reduction of mean value of noise spectrum only, the component varying around the mean value remaining intact. In the method proposed in this paper, the short-time noise spectrum excluding the speech component is estimated by introducing the blocking matrix used in Griffiths-Jim-type adaptive beamformer with two microphone inputs, combined with the spectral compensation technique. A simulation was conducted to verify the effectiveness of the method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.691-698
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• 1985

This paper presents a method for the identification of vibration sources in a multiple input system where the input source may be coherent with each other. Using multi-dimensional spectral analysis, it is found that one of the most significant vibration sources of a gasoline engine is the pressure variation within the cylinder. In this analysis the concepts of residual spectral analysis and the partial coherence function are applied. Finally, the overall levels of the acceleration on the cylinder block obtained by multi-dimensional spectral analysis are compared with those by the frequency response function approach. The experimental results have shown a good agreement with the results calculated by this method the input sources are coherent strongly each other.

• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.3
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• pp.37-43
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• 2009

The objective of this study was to investigate the basic relationships between spectral reflectance and varying concentrations of sediment in surface waters. An experimental method for determining suspended sediment concentration (SSC) in the water by use of a spectroradiometer above the water surface, in visible and near-infrared (NIR) wavelengths, is applied. The main advantage of the method is the direct comparison of spectral reflectance and the SSC, but it requires an accurate knowledge of the water body and sediment. Therefore numerous spectroradiometric measurements are carried out in situ measurements, for SSC, ranging from zero to 100 percentage and two types of sediment applied in the water tank. The results indicate that the suspended sediment causes increasing spectral reflectance response in waters. We observed that spectral reflectance increases with SSC, first at the lower wavelengths (430-480 nm), then in the middle wavelengths (570-700 nm), and finally, in the NIR domain (800-820 nm); a characteristic maximum reflectance appears at 400-670 nm. Relationships between the wavelength, integral value, and the SSC were evaluated on the basis of the regression analysis. The regression curve for the relation between the wavelength, integral value, and the SSC were determined ($R^2$>0.98). Finally, the specular wavelength can be estimated to recognize the sediment and to improve SC estimation accuracy in the water.