• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.595-602
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• 2004

In this study, the roughness of fracture surfaces in cementitious material has been characterized by roughness number (RN). A systematic experimental investigation was carried out to examine the dependency of fracture parameters on the aggregate sizes as well as the loading rates. Three aggregate sizes (0.1875 in, 0.5 in, and 0.75 in) and two loading rates (slow and fast loading rate) were used. A total of 52 compression tests and 53 tension tests were performed. All fracture parameters exhibited an increase, to varying degrees, when aggregates were added to the mortar matrix. The fracture surfaces of the specimens were digitized and analyzed. Fracture roughness was monotonically increased as maximum aggregate sizes increase.

• Journal of the Korean Society of Safety
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• v.18 no.3
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• pp.22-28
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• 2003

This study proposes the construction of chaos simulator for cutting characteristics evaluation of non-ferrous metals. Also this paper aims to find the optimal cutting conditions of diamond turning machine by measuring surface form and roughness to perform the cutting experiment of non-ferrous metals, which are aluminum, with diamond tool. As well, according to change cutting conditions such as fled rate, using diamond turning machine to perform cutting processing, by measuring cutting force and surface roughness and according to cutting conditions the aluminum about cutting properties. Trajectory changes in the attractor indicated a substantial difference in fractal characteristics. Constructed chaos simulator in this study can be used for cutting characteristics evaluation of non-ferrous metals.

• Korean Journal of Materials Research
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• v.7 no.3
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• pp.188-195
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• 1997

Copper ions were adsorbed on amorphous Si films by spincoating of Cu solutions and were employed as surface nucleation sites for low-temperature crystallization. The crystallization temperature can bc lo~vered down to $500^{\circ}C$ and rhe crystallization time can be shortened by Cu adsorption. The Cu-adsorbed amorphous films were crystallized by fractal growth with the shape of tree branches. The fractal size ranged from $30 to 300{\mu}m$, depending on the Cu solution concentration. The fractals consisted of f e a t h e r like elliptical grains with the size of $0.3~0.4{\mu}m$. which was comparable to that of the intrinsic films crystallized at $600^{\circ}C$. Both the nucleation activation energy and grotvth activation energy decreased as the Cu concentration in the solution increased. The results suggest thcit the adsorbed Cu increases preferred nucleation sites at the surface and enhmces crystallization by reducing thc activation energies of nucleation and growth.

• 한국전기화학회:학술대회논문집
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• 2004.04a
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• pp.55-55
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• 2004

• 한국전기화학회:학술대회논문집
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• 2003.04a
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• pp.60-60
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• 2003

• Journal of Korea Water Resources Association
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• v.45 no.9
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• pp.943-957
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• 2012

In this study, a technique based on Fractal Theory with Erosion Model was developed to interpolate the river morphology data at the border area between river bed and river side where both surface and under water surveyings can not be committed easily. Three dimensional river morphology data along the Ara River was generated by the developed technique. The Ara River is an artificially constructed waterway for vessels between the Han River and West Sea of Korea. The result was compared with the survey data by RMSE of 0.384, while the IDW interpolation result has RMSE of 0.802. Consequently, the developed river morphology data interpolation technique using Erosion Model based Fractal Theory is conceived to be superior to the IDW which has been generally used in generating the river morphology data.

• Korean Journal of Agricultural Science
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• v.41 no.4
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• pp.379-384
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• 2014

In general, fractal analysis which is based on self-similarity as a basic theory has been mainly used to define the characteristics of complex mathematical figures, however, considering its basic theory, it can be also used to analyze the surface ununiformity of unknown materials. In this study, the soil samples were collected from the reclaimed (remodelled) agricultural fields which mean that the external soil is artificially piled up (mainly up to 1m) on the lands, Naju, Jellanam-do and Gumi, Gyeongsangbuk-do, and the conventional agricultural fields, Anseong, Gyeonggi-do and Hwasoon, Jellanam-do, and compared using fractal dimension analysis on the basis of the results of chemical properties. The score of fractal dimension ($D_0$) for organic matter was lower in Hwasoon (1.46) and Naju (1.58) than Anseong (1.86) and Gumi (1.96), and this trend showed similarly in soil pH. On the basis of the results of chemical properties, fine textured-soils (Hwasoon and Naju) and conventional agricultural fields were chemically uniform compared to coarse textured-soils (Anseong and Gumi) and the reclaimed. Therefore, it is required to develop technical methods for integrated soil management to the reclaimed lands.

• The Journal of Engineering Geology
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• v.15 no.3
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• pp.269-280
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• 2005

We assigned points on surface of standard roughness profile by 0.1mm along the length and measured coordinates of points. Then, the lengths of profile were measured with different scales using modified divider method. The fractal dimensions and intercepts of slopes were determined by plotting the length vs scale in log-log scale. The fractal dimensions as well as intercepts of slopes show well correlation with joint roughness coefficients(JRC). However, multiplication of the kactal dimension by intercept show better correlation with IRC and we derived a new equation to estimate JRC from fractal dimension and intercept. The crossover length in which we can determine the correct fractal dimension was between 0.3-3.2mm. We measured joint roughness of 26 natural joints and calculated JRC using the equation suggested by Tse and Cruden(1979) and new equation derived by us. IRC values calculated by both equations are almost the same, indicating new equation is effective in measuring IRC.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.997-1009
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• 1999

Silica particle formation and growth process including chemical reaction, coagulation and sintering was studied in a counterflow diffusion flame burner. The counterflow geometry provides a one dimensional flow field, along the stagnation point streamline, which greatly simplifies interpretation of the particle growth characteristics. $SiCl_4$ has been used as the source of silicon in hydrogen/oxygen/argon flames. The temperature profiles obtained by calculation showed a good agreement with experiment data. Using one and two dimensional sectional method, aerosol dynamics equation in a flame was solved, and these two results were compared. The two dimensional section method can consider sintering effect and growth of primary particle during synthesis, thus it showed evolution of morphology of non-spherical particles (aggregates) using surface fractal dimension. The effects of flame temperature and chemical loading on particle dynamics were studied. Geometric mean diameter based on surface area and total number concentration followed the trend of experiment results, especially, the change of diameters showed the sintering effect in high temperature environment.

• Structural Engineering and Mechanics
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• v.72 no.5
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• pp.557-568
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• 2019

Accurate modeling of contact interface in bolted joints is crucial in predicting the dynamic behavior for bolted assemblies under external load. This paper presents a contact pressure distribution based non-uniform virtual material method to describe the joint interface of assembly structure, which is connected by sparsely distributed multi-bolts. Firstly, the contact pressure distribution of bolted joints is obtained by the nonlinear static analysis in the finite element software ANSYS. The contact surface around bolt hole is divided into several sub-layers, and contact pressure in each sub-layer is thought to be evenly. Then, considering multi-asperity contact at the micro perspective, the relationship between contact pressure and interfacial virtual material parameters for each sub-layer is established by using the fractal contact theory. Finally, an experimental platform for the dynamic characteristics testing of a beam lap structure with double-bolted joint is constructed to validate the efficiency of proposed method. It is found that the theoretical results are in good agreement with experimental results by impact response in both time- and frequency-domain, and the relative errors of the first four natural frequencies are less than 1%. Furthermore, the presented model is used to examine the effect of rough contact surface on dynamic characteristics of bolted joint.