• Journal of Korea Foundry Society
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• v.18 no.5
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• pp.431-438
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• 1998

Microstructure of A356 aluminum alloys cast in the permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as ${\beta}-phase$ ($Al_5FeSi$). Morphologies of the ${\beta}-phase$ was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, ${\beta}-phase$ with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the ${\beta}-phase$ with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these ${\beta}-phases$ were considerably decreased with the increased Be:Fe ratio. Beryllium addition improved tensile properties and impact toughness of the A356 aluminium alloy, due to the formation of a script phase or a Be-rich phase instead of a needlelike ${\beta}-phase$. The DSC tests indicated that the presence of Be could increase the amount of Mg which is available for $Mg_2Si$ precipitate hardening, and enhance the precipitation kinetics by lowering the ternary eutectic temperature.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.11a
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• pp.211-218
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• 2004

The WAM wave model has been widely used for wave hindcasting in the ocean by many domestic and foreign researchers due to its relative simplicity and high accuracy. As this model was originally developed for the condition cf deepwater and comparatively coarse grid size covering wide area, it might produce in a fault result mused by the improper distribution of directional spreading. We extensively investigated involved problems based on WAM Cycle 4 model and suggested the improved WAM model so that it is applicable to both shallow water sea and fine mesh wave simulation. The modified WAM model is verified here by comparing the computed result with and the observed data at Ieodo Ocean Research Station for September of 2003.

• Journal of the Korean Geosynthetics Society
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• v.8 no.3
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• pp.25-34
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• 2009

Determination of design parameters of composite ground including colluvial soil layer is far difficult because the maximum particle size of such a soil is remarkably large and particle distribution may vary from area to area. The stress-strain behavior of colluvial soils is in fact dependent upon the engineering characteristics at the boundary between coarse and fine materials. However, strength parameters are in general determined based on the characteristics of fine material, which causes an underestimation of such parameters. In this study, strength parameters of colluvial soil are evaluated by means of BIMROCK model curve. In addition, limit equilibrium analysis is carried out to verify the rational shear strength evaluation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.2
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• pp.459-470
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• 2014

During ship design, welding-induced distortions are roughly estimated as a function of the size of the component as well as the welding process and residual stresses are assumed to be locally in the range of the yield stress. Existing welding simulation methods are very complex and time-consuming and therefore not applicable to large structures like ships. Simplified methods for the estimation of welding effects were and still are subject of several research projects, but mostly concerning smaller structures. The main goal of this paper is the application of a multi-layer welding simulation to the block joint of a ship structure. When welding block joints, high constraints occur due to the ship structure which are assumed to result in accordingly high residual stresses. Constraints measured during construction were realized in a test plant for small-scale welding specimens in order to investigate their and other effects on the residual stresses. Associated welding simulations were successfully performed with fine-mesh finite element models. Further analyses showed that a courser mesh was also able to reproduce the welding-induced reaction forces and hence the residual stresses after some calibration. Based on the coarse modeling it was possible to perform the welding simulation at a block joint in order to investigate the influence of the resulting residual stresses on the behavior of the real structure, showing quite interesting stress distributions. Finally it is discussed whether smaller and idealized models of definite areas of the block joint can be used to achieve the same results offering possibilities to consider residual stresses in the design process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.10
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• pp.4832-4836
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• 2012

In general, there are needed lots of time and experiments for determination of optimum asphalt content and mix design. The experimental results are highly depended on the skill of testers. Bailey suggested the proper aggregate gradation of hot mix asphalt are a function of special size and passing percent of the specified aggregate to reduce the test errors. In this paper, the asphalt mix designs of 19mm dense graded mix and PA-20mm for FHWA were carried out, using Bailey's method. The use of Bailey method can cut down the testing times to get the proper aggregate gradation for asphalt mix design. In case of 19mm dense graded asphalt mixture, the measured values of CA, $FA_c$, $FA_f$ are 0.724, 0.440, and 0.455, which are within the suggested values by Bailey. Also, in case of PA-20 graded asphalt mixture, the measured values of CA, $FA_c$, $FA_f$ are 0.646, 0.476, and 0.450, respectively.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.39 no.4
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• pp.81-89
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• 2016

Distributed genetic algorithm (DGA), also known as island model or coarse-grained model, is a kind of parallel genetic algorithm, in which a population is partitioned into several sub-populations and each of them evolves with its own genetic operators to maintain diversity of individuals. It is known that DGA is superior to conventional genetic algorithm with a single population in terms of solution quality and computation time. Several researches have been conducted to evaluate effects of parameters on GAs, but there is no research work yet that deals with structure of DGA. In this study, we tried to evaluate performance of various genetic algorithms (GAs) for the famous symmetric traveling salesman problems. The considered GAs include a conventional serial GA (SGA) with IGX (Improved Greedy Crossover) and several DGAs with various combinations of crossover operators such as OX (Order Crossover), DPX (Distance Preserving Crossover), GX (Greedy Crossover), and IGX. Two distinct immigration policies, conventional noncompetitive policy and newly proposed competitive policy are also considered. To compare performance of GAs clearly, a series of analysis of variance (ANOVA) is conducted for several scenarios. The experimental results and ANOVAs show that DGAs outperform SGA in terms of computation time, while the solution quality is statistically the same. The most effective crossover operators are revealed as IGX and DPX, especially IGX is outstanding to improve solution quality regardless of type of GAs. In the perspective of immigration policy, the proposed competitive policy is slightly superior to the conventional policy when the problem size is large.

• Resources Recycling
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• v.10 no.3
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• pp.14-22
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• 2001

For the recycle of coal fly ash generated from power stations, we developed an electrocyclone system which can separate unburned carbon form coal fly ash, based on the fact that coarse fly ash particles contain higher amount of unburned carbon and unburned carbon particles are charged positively, and pure ash particles are charged negatively on contacting each other. Additionally, guide vanes were installed in the cyclone to control the cut size. Two types of electrode, stick and grid type, were designed to investigate the effect of electrode type. Results show that by introducing an electric field inside the cyclone, the yield increases by 5 to 15e1o. But the content of unburned carbon in the clean ash does not change significantly.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.3
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• pp.353-360
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• 2006

This study identified a particle size distribution (PSD) of fine particulate matter and emission characteristics of V and Ni by the comparison between anthropogenic sources of oil combustion (industrial boiler, oil power plant, etc.) and lab-scale combustion using a drop-tube furnace. In oil combustion source, the mass fraction of fine particles (less than 2.5 micrometers in diameter) was higher than that of coarse particles (larger than 2.5 micrometers in diameter) in $PM_{10}$ (less than 10 micrometers in diameter) as like in lab-scale oil combustion. In addition to this, it was identified that ultra-fine particles (less than 0.1 micrometers in diameter) had a large distribution in fine particles. Toxic metals like V and Ni had large mass fractions in fine particles, and most of all was distributed in ultra-fine particles. Most of ultra-fine particles containing toxic metals have been emitted into ambient by combustion source because it is hard to control by the existing air pollution control device. Hence, we must be careful on these pollutants because it is obvious that these are associated with adverse health and environmental effect.

• Korean Journal of Soil Science and Fertilizer
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• v.32 no.3
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• pp.211-214
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• 1999

To acknowledge the differences in soil physical properties of cultivated land derived from major parent rocks in Yeong-nam areas, we investigated Riley's projection sphericity(one of the morphological properties) of sand and made up Soil Moisture Characteristics Curve(SMCC). The averages in Riley s projection sphericity range from 0.63 to 0.67 in soils derived from Sedimentary rocks than 0.56 to 0.61 in soils derived from igneous rocks. In case of soils derived from igneous rocks, the Riley's projection sphericity is lower as the particle size get to be smaller. The differences of SMCC were larger in the fine loamy soils than in coarse loamy soils. The moisture retention was higher in the soils derived from Sedimentary rocks than in the soils derived from Igneous rocks. After we transformed the water retention into dimensionless scale value by available water ratio, the SMCC was nearly unchangeable in the tested soils except for fine loamy soils derived from Sedimentary rock, but was not correlated with soil texture or parent rocks.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.821-828
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• 2005

To investigate the role of RH and temperature on the transport of chloride in the concrete, two groups of specimens were configured. For both groups, mix design was based on w/c=0.45, $400kg/m^3$ cement, $794kg/m^3$ fine aggregate and $858kg/m^3$ coarse aggregate. After specimen fabrication these were exposed to four different RH (35, 55, 75 and $95\%$ RH) and temperature (0, 20, 30 and $40^{\circ}C$) conditions. After 3 and 6 months $15\%$ NaCl exposure 5mm cores were taken. These cores were sliced and individual cores were ground to powder. In addition, to evaluate the effect of temperature on the chloride binding some powder samples were leached in the each of four temperature chambers. Chloride titration fur these was performed using FDOT acid titration method. Based upon the resultant data conclusions were reached regarding that 1) effective diffusion coefficient, $D_e$, increased with increasing exposure RH, suggesting that the size and number of water paths increased with elevated moisture content in the specimens, 2) $D_e$ increased with increasing temperature in the range of 0 to $40^{\circ}C$ possibly by elevated thermal activation of chloride ions and reduced chloride binding at higher temperature, 3) water soluble chloride concentration, $[Cl^-]_s$, increased with increasing temperature, and 4) chloride concentration profile for initially dry concrete specimens was higher than for the initially wet ones indicating pronounced capillary suction (sorption) occurred for the dry concrete specimens.