• Structural Engineering and Mechanics
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• v.63 no.6
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• pp.751-760
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• 2017

In recent years, multifractal-based analysis methods have been widely applied in engineering. Among these methods, multifractal detrended cross-correlation analysis (MFDXA), a branch of fractal analysis, has been successfully applied in the fields of finance and biomedicine. For its great potential in reflecting the subtle characteristic among signals, a structural health monitoring (SHM) system based on MFDXA is proposed. In this system, damage assessment is conducted by exploiting the concept of multifractal theory to quantify the complexity of the vibration signal measured from a structure. According to the proposed algorithm, the damage condition is first distinguished by multifractal detrended fluctuation analysis. Subsequently, the relationship between the q-order, q-order detrended covariance, and length of segment is further explored. The dissimilarity between damaged and undamaged cases is visualized on contour diagrams, and the damage location can thus be detected using signals measured from different floors. Moreover, a damage index is proposed to efficiently enhance the SHM process. A seven-story benchmark structure, located at the National Center for Research on Earthquake Engineering (NCREE), was employed for an experimental verification to demonstrate the performance of the proposed SHM algorithm. According to the results, the damage condition and orientation could be correctly identified using the MFDXA algorithm and the proposed damage index. Since only the ambient vibration signal is required along with a set of initial reference measurements, the proposed SHM system can provide a lower cost, efficient, and reliable monitoring process.

• Journal of the Korean GEO-environmental Society
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• v.17 no.3
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• pp.21-26
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• 2016

Soil particle shape analysis was conducted with sands from Jumujun, Korea and Ras Al Khair, Saudi Arabia. Two hundred times enlarged digital images of the particles of those two sands were obtained with an optical microscope. The resolution of the digital images was $640{\times}320$. By conducting digital image processing, the coordinates of the soil particle boundary were extracted. After mapping those coordinates to the complex space, Fourier transformation was performed and the coefficients of each trigonometry term were computed. The coefficients reflect the shape characteristics of the sand grains and are invariant to translation. To evaluate the shape itself excluding the size of the soil particle, the coefficient was normalized by the equivalent radius of soil particle; this is called Fourier descriptor. After analyzing the Fourier descriptors, it was found that the major characteristics of Jumunjin and Ras Al Khair sands were elongation and asymmetry. Furthermore, it was found that the particle shapes reflect the self-similar, fractal nature of the textural features. The effects of resolution on soil particle shape analysis was also studied. Regarding this, it was found that the significant Fourier descriptors were not significantly affected by the image resolution investigated in this study, but the descriptors associated with textural features were affected.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.4
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• pp.341-353
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• 2022

Pipelines are buried in urban area, and the position (depth and orientation) of buried pipeline should be clearly identified before ground excavation. Although various geophysical methods can be used to detect the buried pipeline, it is not easy to identify the exact information of pipeline due to heterogeneous ground condition. Among various non-destructive geo-exploration methods, ground penetration radar (GPR) can explore the ground subsurface rapidly with relatively low cost compared to other exploration methods. However, the exploration data obtained from GPR requires considerable experiences because interpretation is not intuitive. Recently, researches on automated detection technology for GPR data using deep learning have been conducted. However, the lack of GPR data which is essential for training makes it difficult to build up the reliable detection model. To overcome this problem, we conducted a preliminary study to improve the performance of the detection model using finite difference time domain (FDTD)-based numerical analysis. Firstly, numerical analysis was performed with homogeneous soil media having single permittivity. In case of heterogeneous ground, numerical analysis was performed considering the ground heterogeneity using fractal technique. Secondly, deep learning was carried out using convolutional neural network. Detection Model-A is trained with data set obtained from homogeneous ground. And, detection Model-B is trained with data set obtained from homogeneous ground and heterogeneous ground. As a result, it is found that the detection Model-B which is trained including heterogeneous ground shows better performance than detection Model-A. It indicates the ground heterogeneity should be considered to increase the performance of automated detection model for GPR exploration.

• Journal of the Korean Geotechnical Society
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• v.17 no.1
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• pp.85-97
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• 2001

Tse와 Cruden(1979)에 의해 암석 절리면 거칠기 정량화에 대한 연구가 시작된 이후 통계적인 정량화방법, 프랙탈 차원을 이용하는 방법 그리고 스펙트럼 분석을 이용하는 방법이 제안되었다. 이러한 통계적 정량화방법은 치수의존적이라는 단점이 있으며, 프랙탈 차원을 이용하는 방법은 크로스오버 차원이라는 문제점이 있는 것으로 평가되고 있다. 이 문제점들을 보완하는 방법으로 스펙트럼 분석법이 제시되어 많은 연구가 이루어졌다. 본 연구에서는 Barton과 Choubey(1977)가 제안한 10개의 절리면 프로파일을 수치화하고 통계적 분석, 프랙탈 차원 분석 그리고 스펙트럼 분석을 실시하여 이들 문제점을 살펴보고 스펙트럼 분석법이 위상이 변조된 프로파일에 대하여 문제가 있음을 확인하였다. 이들 문제점을 해결하기 위하여 측정간격과 프로파일의 기울기를 의미하는 통계적 파라미터의 관계를 선형으로 회귀분석하였다. 이렇게 구한 10개의 1차식의 기울기와 절편은 JRC와 매우 상관성이 높게 나타났다. 이 기울기와 절편을 거칠기 정량화의 변수로 사용함으로서 통계적 분석법에서의 치수의존적인 문제와 스펙트럼 분석에서의 위상변조의 문제를 해결하였다.

• Journal of Fashion Business
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• v.18 no.1
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• pp.164-181
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• 2014

As the boundary between fashion and architecture is getting blurred, the interactions of the two fields are turning out abundant as well as essential. This study investigates the tectonic strategies in architectural fashion design as a novel aesthetic in the 21st century by combining literary survey and case analysis on architecture and contemporary fashion. The tectonic strategies in the works of architectural fashion designers were categorized as follows: organic geometry, technological garment construction, and independent space. Organic geometry transforms basic geometric shapes into subtle organic forms after being thrown on the body. Technological garment construction explores the garment structure and volume by applying the structural principle of suspension and fractal geometry. Independent space refers to maintaining the firm three-dimensionality of garment structure which keeps the distance from the body, assuming the similarity to architecture.

• Structural Engineering and Mechanics
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• v.32 no.4
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• pp.489-500
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• 2009

The aim of this paper is to compare wavelet, kurtosis and pseudofractal based techniques for structural health monitoring in the presence of measurement noise. A detailed comparison and assessment of these techniques have been carried out in this paper through numerical experiments for the calibration of damage extent of a simply supported beam with an open crack serving as an illustrative example. The numerical experiments are deemed critical due to limited amount of experimental data available in the field of singularity based detection of damage. A continuous detectibility map has been proposed for comparing various techniques qualitatively. Efficiency surfaces have been constructed for wavelet, kurtosis and pseudofractal based calibration of damage extent as a function of damage location and measurement noise level. Levels of noise have been identified for each technique where a sudden drop of calibration efficiency is observed marking the onset of damage masking regime by measurement noise.

• Tribology and Lubricants
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• v.23 no.1
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• pp.29-36
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• 2007

It necessarily follows that wear particles are generated through a friction and wear in a mechanical moving system. The wear particles are relative to the failure and the life of machine elements directly. To analyze the wear particle, its shape characteristics were calculated quantitative values such as diameter, roundness and fractal parameters by digital image processing. In this study, the histograms of shape parameters of wear particles were used for the purpose of analyzing the distribution of wear particles in various conditions. We consider that the histogram of shape parameter can be effectively represented to study a wear mechanism.

• Steel and Composite Structures
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• v.6 no.2
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• pp.87-101
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• 2006

The deformation and dynamic behavior mechanism of submerged shell-like lattice structures with membranes are in principle of a non-conservative nature as circulatory system under hydrostatic pressure and disturbance forces of various types, existing in a marine environment. This paper deals with a characteristic analysis on quasi-periodic and chaotic behavior of a circular arch under follower forces with small disturbances. The stability region chart of the disturbed equilibrium in an excitation field was calculated numerically. Then, the periodic and chaotic behaviors of a circular arch were investigated by executing the time histories of motion, power spectrum, phase plane portraits and the Poincare section. According to the results of these studies, the state of a dynamic aspect scenario of a circular arch could be shifted from one of quasi-oscillatory motion to one of chaotic motion. Moreover, the correlation dimension of fractal dynamics was calculated corresponding to stochastic behaviors of a circular arch. This research indicates the possibility of making use of the correlation dimension as a stability index.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.450-452
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• 1995

The Tree observation technique is being highlighted as a research area for deterioration of insulation because of high-voltage power system. For the measurement of tree, image processing is actively studied as a experimental technique of electrical tree, because the conventional directed visual method is impossible to analyze on tree degradation area and tree pattern. In this paper, we have developed the tree measuring system using image processing. By using an image processing technique, the treeing can be easily measured and effectively observed.

• Journal of the Korean Institute of Intelligent Systems
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• v.9 no.5
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• pp.545-549
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• 1999

Previous studies on high impedance faults assumed that the erratic behavior of fault current would be random. In this paper we prove that the nature of the high impedance faults is indeed a deterministic chaos not a random motion. Algorithms for estimating Lyapunov spectrum and the largest Lyapunov exponent are applied to various fault currents in order to evaluate the orbital instability peculiar to deterministic chaos dynamically and fractal dimensions of fault currents which represent geometrical self-similarity are calculated. In addition qualitative analysis such a s phase planes Poincare maps obtained from fault currents indicate that the irregular behavior is described by strange attractor.