• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.383-390
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• 2019

A helideck is one of the essential structures in offshore platforms for the transportation of goods and operating personnel between land and offshore sites. As such, it should be carefully designed and installed for the safety of the offshore platform. In this study, a structural design optimization method for a lightweight offshore helideck is developed based on a genetic algorithm and an attainable design set concept. A helideck consists of several types of structural members such as plates, girders, stiffeners, trusses, and support elements, and the dimensions of these members are typically pre-defined by manufacturers. Therefore, design sets are defined by collecting the standard section data for these members from the American Institute of Steel Construction (AISC), and integer section labels are assigned as design variables in the genetic algorithm. The objective is to minimize the total weight of the offshore helideck while satisfying the maximum allowable stress criterion under various loading conditions including self-weight, wind direction, landing position, and landing condition. In addition, the unity check process is also utilized for additional verification of structural safety against buckling failure of the helideck.

• Journal of the Korean Magnetics Society
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• v.22 no.2
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• pp.49-57
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• 2012

From among the NDT (Non-Destructive Testing) methods, the MFL (Magnetic Flux Leakage) PIG (Pipeline Inspection Gauge) is especially suitable for testing pipelines because the pipeline has high magnetic permeability. MFL PIG showed high performance in detecting the metal loss and corrosions. However, MFL PIG is difficult to detect the crack which occured by exterior-interior pressure difference in pipelines and the shape of crack is very long and narrow. Therefore, the new PIG is needed to be researched and developed for detecting the cracks. The CMFL (Circumferential MF) PIG performs magnetic fields circumferentially and can maximize the magnetic flux leakage at the cracks. In this paper, CMFL PIG is designed and the distribution of the magnetic fields is analyzed by using 3 dimensional nonlinear finite element method (FEM). By Simulating and Measuring the magnetic leakage field, it is possible to detect of axial cracks in the pipeline.

• Composites Research
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• v.30 no.2
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• pp.102-107
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• 2017

The preceramic polymer can realize a variety of complex ceramic structures that can not be obtained by conventional ceramic processes. Polycarbosilane, which is a typical preceramic polymer, can control the molecular structure, molecular weight and molecular weight distribution for preparing complex morphology and microstructure of SiC ceramics, including SiC fiber. In this paper, synthesis and molecular structure control technique of polycarbosilane is explained. The silicon carbide fiber prepared by melt spinning, stabilization and heat treatment, and ceramic fiber composites technology made by PIP process are also discussed. In addition, we introduce an example of the development of a complex silicon carbide material such as a silicon carbide hollow fiber having a nanoporous structure.

• Geotechnical Engineering
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• v.14 no.5
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• pp.39-52
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• 1998

The pupose of the present paper is to estimate the effects of constraint condition of pile head, ground condition(dry unit weight. $\gamma_4$) and embedded pile lengths on the behavior of single pile which is embedded in normally consolidated clay. BBperiment functions can be quantified to these effects obtained from the results of model teats. The ground of model tests is normally consolidated( NC ) clay under three kinds of effective vertical stress. The results of the model tests using the steel pile of two different embedded pile length and of free-head and fired-head show that the lateral load-deflection relationship is to be elasto plastic behavior below $\gamma_d/\gamma_{dmax}$: 0.84 and that the reduction of lateral load of beyond maximum lateral load($Q_{max}$) at each model test is significantly time-dependent. In this study, it is shown that the displacement relationship can be fitted to exponential function of time by model best results. The effect of ground conditions on the ultimate and yield lateral load is fitted to exponential function including the ratio of dry unit weight to maximum dry unit weight. When tests by results are compared with those from Broms and Budhu et at., the predicted results are over-estimated about 27-87 ayo. In effectivity of constraint condition of pile head on the lateral load-deflection response, the $Q_{fixed}/Q_{gree}-y/D$ relationship is highly non-linear and fitted to parabolic function.

• Journal of Korea Water Resources Association
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• v.39 no.10 s.171
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• pp.891-904
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• 2006

The estimation of the probability precipitation is essential for the design of hydrologic projects. The techniques to calculate the probability precipitation can be determined by the point frequency analysis and the regional frequency analysis. The regional frequency analysis includes index-flood technique and L-moment technique. In the regional frequency analysis, even if the rainfall data passed homogeneity, suitable distributions can be different at each point. However, the regional frequency analysis can supplement the lacking precipitation data. Therefore, the regional frequency analysis has weaknesses compared to parametric point frequency analysis because of suppositions about probability distributions. Therefore, this paper applies kernel density function to precipitation data so that homogeneity is defined. In this paper, The data from 16 rainfall observatories were collected and managed by the Korea Meteorological Administration to achieve the point frequency analysis and the regional frequency analysis. The point frequency analysis applies parametric technique and nonparametric technique, and the regional frequency analysis applies index-flood techniques and L-moment techniques. Also, the probability precipitation was calculated by the regional frequency analysis using variable kernel density function.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.389-398
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• 2006

Structural optimization design has been developed with finite element analysis using effective and fast computational technology. Especially topology optimization design has been recently often used since it yields an optimal topology as well as an optimal shape under satisfied constraints. In general in finite element analysis, it is assumed that the structural material properties such as Young's modulus and Poisson's ratio and the variable of applied loading are fixed with obvious values in structure. However practically these values may take uncertainties because of environmental effect or manufactural error of structures. Therefore static or dynamic analysis of the structures may make an error, then finally it may have an influence on qualify of optimal design. In this study, the topology optimization design of structure is carried out using so called the interval finite element method, and the analysis method Is proposed. The results are also validated by comparing with conventional topology optimization results of density distribution method and finite element analysis results. The present method can be used to predict the optimal topology of linear elastostatic structures with respect to structural uncertainty of behavior.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11A
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• pp.1908-1924
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• 2001

Interoperability and inter-working in the various network and media environment with different technology background is very important to enlarge the opportunity of service access and to increase the competitive power of service. The ITU-T and advanced counties are planning ahead for provision of GII enabling user to access advanced global communication services supporting multimedia communication applications, embracing all modes of information. In this paper, we especially forced the heterogeneity of end user applications for multimedia networking. The heterogeneity has several technical aspects, like different medium access methods, heterogeneous coding algorithms for audio-visual data and so on. Among these elements, we have been itemized bit rate shaping algorithm on the compressed moving video. Previous manipulations of video has been done on the uncompressed signal domain. That is, compressed video should be converted to linear PCM signal. To do such a procedures, we should decode, manipulate and then encode the video to compressed signal once again. The traditional approach for processing the video signa1 has several critical weak points, requiring complexity to implement, degradation of image quality and large processing delay. The bit rate shaping algorithm proposed in this paper process the manipulation of moving video on the completely compressed domain to cope with above deficit. With this algorithms. we could realized efficient video bit rate shaping and the result of software simulation shows that this method has significant advantage than that of pixel oriented algorithms.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.47-61
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• 1998

The behavior of horizontally curved I-girder bridges is complex because the flexural and torsional behavior of curved girders are coupled due to their initial curvature. Also, the behavior is affected by cross beams. To investigate the behavior of horizontally curved I-girder bridges, it is necessary to consider curved girders with cross beams. In order to perform free vibration analyses of horizontally curved I-girder bridges, a finite element formulation is presented here and a finite element analysis program is developed. The formulation that is presented here consists of curved and straight beam elements, including the warping degree of freedom. Based on the theory of thin-walled curved beams, the shape functions of the curved beam elements are derived from homogeneous solutions of the static equilibrium equations. Third-order hermits polynomials are used to form the shape functions of the straight beam elements. In the finite element analysis program, global stiffness and mass matrix are composed, based on the Cartesian coordinate system. The Gupta method is used to efficiently solve the eigenvalue problem. Comparing the results of several examples here with those of previous studies, the formulation presented is verified. The validity of the program developed is shown by comparing results with those analyzed by the shell element.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.468-477
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• 2019

The numerical model of Boussinesq approximation, which is mainly used for evaluating the port calmness due to the irregular waves, has a limit of applicability of lattice size in ports such as marinas with narrow port openings of around 30m. The SWASH model controls the partial reflection according to the depth, porosity coefficient and structure size when applying the reflected wave incident on the structure and terrain. In this study, the partial reflection evaluation at the front of the structure according to the bottom shape and the shape of the structure are examined. In order to evaluate the reproducibility of the model due to the diffraction waves entering the term, the area of incidence at right angles and inclination of the structure is constructed and compared with the diffraction theory suggested by Goda et al. (1978). The experimental results of the sectional structure reflectances calculated as the depth mean show reflectances similar to the approximate values of the reflectances presented by Stelling and Ahrens (1981). It is considered that the reflected wave is well reproduced according to the control of the reflected wave at the boundary and the shape and topography of the structure. Compared with previous studies to examine the diffraction of the wave incident from the breakwater opening, the wave incidence angle and the shape of the diffraction wave are very similar to the theoretical values, but both oblique and rectangular incidence In the case where the direction concentration is small, the diffraction degree is underestimated in some sections with the crest ratio of 0.5 to 0.6.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.2
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• pp.165-174
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• 2010

The numerical modeling of a coal gasification reaction occurring in an entrained flow coal gasifier is presented in this study. The purposes of this study are to develop a reliable evaluation method of coal gasifier not only for the basic design but also further system operation optimization using a CFD(Computational Fluid Dynamics) method. The coal gasification reaction consists of a series of reaction processes such as water evaporation, coal devolatilization, heterogeneous char reactions, and coal-off gaseous reaction in two-phase, turbulent and radiation participating media. Both numerical and experimental studies are made for the 1.0 ton/day entrained flow coal gasifier installed in the Korea Institute of Energy Research (KIER). The comprehensive computer program in this study is made basically using commercial CFD program by implementing several subroutines necessary for gasification process, which include Eddy-Breakup model together with the harmonic mean approach for turbulent reaction. Further Lagrangian approach in particle trajectory is adopted with the consideration of turbulent effect caused by the non-linearity of drag force, etc. The program developed is successfully evaluated against experimental data such as profiles of temperature and gaseous species concentration together with the cold gas efficiency. Further intensive investigation has been made in terms of the size distribution of pulverized coal particle, the slurry concentration, and the design parameters of gasifier. These parameters considered in this study are compared and evaluated each other through the calculated syngas production rate and cold gas efficiency, appearing to directly affect gasification performance. Considering the complexity of entrained coal gasification, even if the results of this study looks physically reasonable and consistent in parametric study, more efforts of elaborating modeling together with the systematic evaluation against experimental data are necessary for the development of an reliable design tool using CFD method.