• Journal of the Korean Society of Environmental Restoration Technology
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• v.20 no.6
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• pp.35-50
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• 2017

This study is to see the recovery effect of the Deltacon method by investigating the amount of sand deposition, the topographical cross section and the vegetation structure; and to derive the effective recovery method of coastal erosion area. The target areas of this study include Jinri coastal dune, Bajireum coastal dune and Seopori coastal dune in Deokjeok-do Island, Ongjin-gun, Incheon. In order to assess the current status of the coastal erosion area recovery, the soil profile structure map was prepared on the site and then the amount of sand deposition within 1m was calculated indoors. The vegetation recovery status of the costal erosion area was assessed via the analyses of the topographical profile structure and the plant community structure, and we aim to derive the effective recovery plan of the Deltacon method with the results. With the Deltacon method, structures with ductile material, special non-woven fabric bags filled with soil and vegetation can be performed therefore the structuralstability and prevention of sand erosion can be achieved. The amounts of sand deposition of Bajireum coastal dune, Seopori costal dune and Jinri costal dune were calculated $0.98{\sim}2.54m^3$, $1.02{\sim}2.96m^3$, and $0.27{\sim}0.75m^3$, respectively, and it is considered that the costal erosion recovery is actively performed for Bajireum costal dune and Seopori costal dune. The analysis results of vegetation structures by topography show that the installation of the send collecting net in steep areas has been highly effective and the Deltacon-constructed target areas have been restored to vegetation and the costal dune, which is similar to the natural dune. The investigation of the plant community structure in Deokjeok-do Island costal dune, Incheon displayed similar research results of the existing costal dune flora and confirmed the emergence of Lathyrus japonicus, Carex kobomugi, Elymus mollis, Vitex rotundifolia, and Calystegia soldanella and others. In order to carry out further effective recovery with the Deltacon method, improvements to rootage of herbaceous vegetation are needed in areas without foredune herbaceous vegetation, and continuos maintenance & management monitoring of connected windbreak forest to costal dunes are also necessary.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.3
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• pp.233-240
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• 2018

Radar cross section (RCS) analysis of chaff clouds is essential for the accurate detection and tracking of missile targets using radar. For this purpose, we compare the performance of two existing methods of predicting RCS of chaff clouds. One method involves summing up the RCS values of individual chaffs in a cloud, while the other method predicts the RCS values using aerodynamic models based on the probability density function. In order to compare and analyze the two techniques more precisely, the RCS of a single chaff computer-aided design model consisting of a half wavelength dipole was calculated using the commercial electromagnetic numerical analysis software, FEKO 7.0, to estimate the RCS values of chaff clouds via simulation. Thus, we verified that our method using the probability density distribution model is capable of analyzing the RCS of chaff clouds more efficiently.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.1
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• pp.29-35
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• 2015

The concept design of a riser for Ocean Thermal Energy Conversion in 10 MW is proposed and its dynamic behaviour characteristics is analyzed with numerical method. A riser pipe with a hollow along its thickness in the cross-section to increase the effective modulus of its cross-section is designed considering the manufacture. The riser pipe without hollows along its thickness needs a lumped weight at the bottom end of a riser in order to keep its vertical hanging configuration from large buoyancy and the strong current. The riser is designed to control its density by inserting materials in high or low density into a hollow. The dynamic behaviour characteristics of the two designed risers is evaluated with the developed numerical analysis tool. The combined stress of the riser with a lumped weight is showed to be dominated by weight of a lumped mass. The riser with no hollow shows large combined stress near sea surface by strong current. Local structural analysis for the cross-section of a hollow riser is needed in detail.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.193-198
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• 2002

In 1his paper, applicability of laser welding to joining process of single crystal nickel base superalloy turbine blades was investigated. Because heat input of laser welding is more precisely controlled 1han TIG welding, it is possible to optimize solidification microstructure of the welds. Since in single crystal nickel base superalloy the crystal orientation have a significant effect on the strength, it is important to control the solidification microstructure in the fusion zone. A single crystal nickel base supera1loy, CMSX-4, plates were bead-on welded and butt welded using a $CO_2$ laser. The effects of microstructure and crystal orientation on properties of the weld joints were investigated. In bead-on weldling, welding directions were deviated from the base metal [100] direction by 0, 5, 15 and 30 degrees. The welds with deviation angles of 15 and 30 degrees showed fusion zone transverse cracks. As the deviation angles became larger, the fusion zone had more cracking. In the cross section microstructure, the fusion zone grains in 0 and 5 degrees welds grew epitaxially from the base metal spins except for the bead neck regions. The grains in the bead neck regions contained stray crystals. As deviation angles increased, number of the stray crystals increased. In butt welding, the declinations of the crystal orientation of the two base metals varied 0, 5 and 10 degrees. All beads had no cracks. In the 5 degrees bead, the cross section and surface microstructures showed that the fusion zone grains grew epitaxially from the base metal grains. However, the 10 degrees bead, the bead cross section and surface contained the stray crystals in the center of the welds. Orientations of the stray crystals accorded with the heat flow directions in the weld pool. When the welding direction was deviated from the base metal [100] direction, cracks appeared in the area including the stray crystals. The cracks developed along the grain boundaries of the stray crystals with high angles in the final solidification regions at the center of the welds. The fracture surfaces were covered with liquid film. The cracks, therefore, found to be solidification cracks due to the presence of low melting eutectic. As the results, in both bead-on welding and butt welding the deviation angles should be control within 5 degrees for preventing the fusion zone cracks. To investigate the mechanical properties of the weld joints, high temperature tensile tests for bead-on welds with deviation angles of 0 and 5 degrees and the butt welds with dec1ination angles of 0, 5 and 10 degrees were conducted at 1123K. The the tensile strength of all weld joints were more 1han 800MPa that is almost 80% of the tensile strength of the base metal. The strength of the laser weld joints were more than twice that of tue TIG weld joints with a filler metal of Inconel 625. The results reveals 1hat laser welding is more effective joining process for single crystal nickelbase superalloy turbine blades 1han TIG welding.

• Journal of Korean Society of Steel Construction
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• v.26 no.3
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• pp.219-229
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• 2014

The experiment and FE analysis of ultimate behavior of GFRP cylindrical shell structure stiffened by steel pipe ring instead of rectangular cross-section ring was presented. Four kinds of test models were designed and flexural failure experiment was performed to investigate ultimate behavior characteristic according to the size of cross section of steel pipe ring and diameter of GFRP shell. Material properties of specimens were experimented by bending, tensile and compressive test. Displacements and strains were measured to evaluate failure behavior of steel pipe ring and GFRP shell structure. The experimental results were compared with the FEA results by commercial program ABAQUS. It is observed that GFRP shell structure stiffened by steel ring have enough ductility to bending failure, and an increase of bending rigidity of steel ring is very effective to increase of failure strength of GFRP shell structure.

• Journal of the Korean Wood Science and Technology
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• v.19 no.3
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• pp.62-71
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• 1991

An evaluation of bending test of composite I and Box beams for determining the ultimate strength limit design criteria was presented. Maxium loads of composite I beams were found in beams composed of thicker upper flanges and/or vertical LVL flanges. These loads of plywood web beams were greater than those of PB web beams. Maximum loads of unsymmetrical box beams were less than those of symmetrical box beams. Thus, it took on different phase in box type beams. Ultimate loads of composite beams were greater than those of solid. The failure of composite beams were abrupt and failure mode was classified into following categories; Edgewise shear failure in web, delamination in flange-web joint, tension failure and tearing in LVL flanges, and web delamination. These failures of composite beams were appeared at the mixed mode. The influence factor affecting the performance of tested composite beams was shear strength of PB-web composite beams and compressive strength in plywood-web composite beams. It was also assumed that the influence factors on structural performance on composite beams were flange quality, web material and geometry of cross section. As one of the design methods resisting to compressive stress that was required in the case of small span to depth ratio and deep beams. composite I-beams composed of thicker upper flanges comparing to lower flanges were very effective in structural performance.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1297-1303
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• 2020

In this study, nuclear radiation shielding and rigidity parameters of Y (0.1-x)B0.6Bi1.8O3La2x glassy system were investigated in order to determine it's suitability for use as nuclear radiation shielding materials. Therefore, a group of bismuth borate glass samples with La₂O₃ additive were synthesized using the technique of melt quenching. According to the results, the increase of the La₂O₃ additive increases the density of the glass samples and the mass attenuation coefficient (μ_m) values, whereas the half-value layer (HVL) and mean free path (MFP) values decrease. The effective atomic number (Z_eff) is also enhanced with an increment of both mass removal cross section for neutron (Σ_R) and absorption neutron scattering cross section (σ_abs). In addition to the other parameters, rigidity parameter values were theoretically examined. The increase of La₂O₃ causes some other important magnitudes to increase. These are the average crosslink density, the number of bonds per unit volume, as well as the stretching force constant values of these glass samples. These results are in concordance with the increase of elastic moduli in terms of the Makishima-Mackenzie model. This model showed an increase in the rigidity of the glass samples as a function of La₂O₃.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.1-6
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• 2018

Hydro-forming technology has spread dramatically throughout automotive industry over the last 20 years. This technology has many advantages for automotive applications in terms of better structural integrity of the parts, lower cost from fewer parts, material savings, weight reduction, lower springback, improved strength, durability, and design flexibility. In this study, various simulation technologies were developed to investigate the formability of hydro-forming components. Through this technology, to establish the effective forming process for appropriate components design, the bending process, pre-forming process, die closing process, etc. were considered for good forming. This paper proposes the forming amount, section length (corresponding to the hydro-forming press capacity), and minimum curvature (curvature effect evaluation according to the hydro-forming pressure) among the considerations in the design of the hydro-forming part. In addition, a design method is proposed for hydro-forming molding by carrying out cross section analysis of a real sub-frame part for automobiles. The effects of pre-bending, axial feed, hydraulic pressure, press load, and friction among the hydro-forming process parameters were analyzed. Therefore, whether these processes are necessary factors for hydro-forming were examined.

• Journal of the Korean Association of Geographic Information Studies
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• v.10 no.4
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• pp.142-152
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• 2007

Geotechnical information database, foundation of underground geographic information system in 2nd NGIS plan, had been developing by Ministry of Construction and Transportation since 2000. This database contains not only soil condition, such as depth, type and color of layer, and ground water level, but also engineering properties used for foundation design and construction, for instance, standard penetration test, compression test. But, it is difficult to apply this database for analyzing and designing geotechnical works, because report document is only offered. In this paper, we have developed web-based geospatial information system for the effective uses. First, underground cross-section model is generated by location, layer, and engineering properties of geotechnical information database at the realtime process. Second, earth volume, bearing capacity, and settlement is calculated and potentials of soft ground, liquefaction are evaluated through pre-defined empirical formula. This process is operated by web-based client. We wish to strengthen the application capacity through this system in construction planning and design works.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.88-97
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• 2012

The objective of this research is to investigate the seismic performance and flexure-shear behavior of square reinforced concrete bridge piers with solid and hollow cross section. Test specimens were nonseismically designed with the aspect ratio 4.5 Two reinforced concrete columns were tested under constant axial load while subjected to lateral load reversals with increasing drift levels. Longitudinal steel ratio was 2.217 percent. The transverse reinforcement ratio As/($s{\cdot}h$), corresponding to 58 percent of the minimum lateral reinforcement required by Korean Bridge Design Specifications for seismic detailing, which represent existing columns not designed by the current seismic design specifications or designed by limited ductility concept. This study are to provide quantitative reference data for the limited ductility design concept and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, collapse, etc. Failure behavior, ultimate displacement/drift ratio, displacement ductility, response modification factor, equivalent viscous damping ratio, residual deformation, effective stiffness, plastic hinge length, strain of reinforcements and nonlinear analysis are investigated and discussed in this paper.