• Journal of the Korean GEO-environmental Society
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• v.11 no.6
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• pp.5-20
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• 2010

One-dimensional equivalent linear site response analysis is widely used in practice due to its simplicity, requiring only few input parameters, and low computational cost. The main limitation of the procedure is that it is essentially a linear method, in which the time dependent change in the soil properties cannot be modeled and constant values of shear modulus and damping is used throughout the duration of the analysis. Various forms of modified equivalent linear analyses have been developed to enhance the accuracy of the equivalent linear method by incorporating the dependence of the shear strain with the loading frequency. The methods are identical in that it uses the shear strain Fourier spectrum as the backbone of the analysis, but differ in the method in which the strain Fourier spectrum is smoothed. This study used two domestically measured soil profiles to perform a series of nonlinear, equivalent linear, and modified equivalent linear site response analyses to verify the accuracy of two modified procedures. The results of the analyses indicate that the modified equivalent linear analysis can highly overestimate the amplification of the high frequency components of the ground motion. The degree of overestimation is dependent on the characteristics of the input ground motion. Use of a motion rich in high frequency contents can result in unrealistic response.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.573-577
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• 2009

When ultrasound propagates to a crack, transmitted and reflected waves are generated. These waves have useful information for the detection of the crack lying in a structure. In this paper, using finite element analysis, displacements round a inclined crack were obtained for 4 different inclination angles. Fourier transformation is applied to the results to research the frequency characteristics depending on the various locations around the crack. 2-dimensional plane stress model is considered, and finite element software ABAQUS/Explicit is used.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.3
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• pp.385-396
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• 1993

In this paper, a improved method of digital image analysis required in basic medical science for diagnosis of cells was proposed. The object image was the thyroid gland cell image, and the purpose was automatic discrimination of three classes cells(normal cell, follicular neoplastic cells, and papillary neoplastic cells) by difference of chromatin patterns. To segment the cell nucleus from background, the region segmentation algorithm by edge tracing was proposed. And feature parameter was obtained from discrete Fourier transformation of image. After construct a feature sample group of each cells, experiment of discrimination was executed with any verification cells. As a consequency of using features proposed in this paper, get a better recognition rate(70-90%) than previously reported papers, and this method give shape to get objectivity and fixed quantity in diagnosis of cells, The methods described in this paper be used immediately for discrimination of neoplastic cells.

• Journal of Korean Society of Transportation
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• v.33 no.4
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• pp.405-416
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• 2015

This paper developed a method analyze drivers' response characteristics using spectral analysis with car following data. Cross-correlation function and cross spectrum are produced by Fourier transform from speed fluctuations of leading vehicle and following vehicle during the designated time ${\tau}$. Based on the analysis data, a process to calculate the reaction time and stimulus-adaption index of following vehicle was developed and 170 cases of field data was applied. It was reported average of 0.654 and 2.091 seconds of stimulus-adaption index and reaction time respectively. In conclusion, the developed indexes might contribute to enhance vehicle control of autonomous vehicle more efficient and safer.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.4
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• pp.200-206
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• 2013

Fourier analysis and a wavelet method were carried out to elucidate the characteristics of tidal residual components in coastal waters. The result of Fourier analysis shows tide-induced and monsoon-induced residuals are conspicuous at the short period and mid period, respectively. The tidal residuals were decomposed by period from 3 hours to 8 months and the characteristics of their components were shown by reconstituting them with short periods less than 24 hours, mid-periods between 1 day and 16 days and long periods longer than 1 month. The tidal residuals in the short period, i.e., tide-induced components, being based on the tidal elevation prediction errors, appear in the West Sea with high tidal ranges and do not have much seasonal fluctuation. Additionally, the period of typhoon induced surge ranges more or less than 12 hours. The mid-period components were clearly generated mainly in the West Sea during the winter and largely affected by monsoon. Accordingly, the pure surge height components were concentrated on the mid-period and had clear features for each coastal waters. The long period components show similar characteristics at all stations and are considered to stem from variations of mean sea levels.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.1
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• pp.1-11
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• 2020

Behaviors of wake vortices generated by an aircraft affect the performance and flight stability of flying aircraft in formation flight. In the present study, the trajectories of the wake vortices behind airplanes in close formation flight were computed using a Fourier spectral method. The behavior of wake vortices showed complex patterns depending on the initial circulation and the relative positions between the vortices. In the initial stage, the wake vortex movement was affected by the nascent vortex. When the vortex becomes closer to the other vortex, then a new trajectory is formed. When the viscous effect becomes dominant, the core radius increases. Thus, a new vortex moving near the existing vortex can have strong interaction with each other, resulting in the complicated behavior of wake vortices. In the future, the ground effect on the behavior of the wake vortices during take-off and landing will be studied.

• Tribology and Lubricants
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• v.17 no.5
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• pp.373-379
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• 2001

The problem of interest is formulating elastic contact problem of a layered semi-infinite solid in terms of Fourier integral. The plane strain problem is considered for a solid composed of homogeneous isotropic two layers with different mechanical properties. General solutions for the subsurface stress and deformation field of frictionless elastic bodies under normal loading using of Fourier transformation technique are obtained. The numerical results for the stress distribution of coated solid for some particular cases are given.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.5
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• pp.20-24
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• 1999

Grinding System is very difficult to examine closely wear phenomenon or dynamic characterastic because it is very complex and different from a general cutting system, Considering automatization and precision it is very important to examine closely grinding system. In this study grinding wheel surface is acquired by using computer vision system in order to explain wear and loading phenomenon. We investigate the relationship between wear and Fourier spectrum of acquired image and observe the entropy variation in the process of manufacturing.

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.398-400
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• 1987

Using the transmission line model, we have developed a formalism which is fairly accurate and convenient for analyzing the dispersion characteristics of rectangular dielectric waveguides for integrated optics. The fields in open half space regions are expressed as a Fourier integral form. Including all the TE and TM polarized discrete modes in slab waveguide region, our calculation shows that the discrepancies between the previous vectorial wave analysis using one discrete mode and the brute-force numerical analysis for the rectangular dielectric waveguides can be fully reduced with this method.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.2192-2194
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• 2000

광섬유에서 전송되는 신호를 예측하기 위하여 일반화된 단계분할 유한요소법 (split-step finite element method, 55-FEM)을 이용한 비선헝 슈뢰딩거 방정식의 해석 방법을 구현하였다. 사용된 방정식은 분산 및 감쇄, 그리고 비선형 효과를 모두 고려하도록 하였다. SS-FEM으로 계산된 수치 결과는 엄밀해와 잘 일치하였음을 확인하였으며, 계산 시간을 푸리에법과도 비교하였다.