• Journal of Welding and Joining
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• v.26 no.6
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• pp.54-58
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• 2008

Laser welding with AZ61 filler wire was carried out to improve formability though reduction of porosity and formation of under fill bead. Optimum welding condition and mechanical properties of butt joint for $400{\times}500{\times}1.3mm$ magnesium sheets were studied. Optimal welding conditions of laser power, welding speed, and defocusing length are 1000W, 3m/min, and 2mm, respectively. Results of tensile test indicated that both tensile strength and elongation of specimens welded with filler wire were improved at room temperature because of reduction of porosity and under-filled bead formation in addition to the precipitation hardening and microstructure refinement by Al-Mn and Mg-Al-Zn precipitates. At elevated temperature of $200{\sim}350^{\circ}C$, fracture location of tensile specimen was shifted from weld metal to base metal, indicating less softening of weld metal than base metal.

• Journal of Ocean Engineering and Technology
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• v.32 no.4
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• pp.228-236
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• 2018

The performance of a porous swash bulkhead for the reduction of the resonant liquid motion in a swaying rectangular tank was investigated based on the assumption of linear potential theory. The Galerkin method (Porter and Evans, 1995) was used to solve the potential flow model by adding a viscous frictional damping term to the free-surface condition. By comparing the experimental results and the analytical solutions, we verified that the frictional damping coefficient was 0.4. Darcy's law was used to consider the energy dissipation at a porous bulkhead. The tool that was developed with a built-in frictional damping coefficient of 0.4 was confirmed by small-scale experiments. Using this tool, the free-surface elevation, hydrodynamic force (added mass, damping coefficient) on a wall, and the horizontal load on a bulkhead were assessed for various combinations of porosity and submergence depth. It was found that the vertical porous bulkhead can suppress sloshing motions significantly when properly designed and by selecting the appropriate porosity(${\approx}0.1$) and submergence depth.

• Journal of Forest and Environmental Science
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• v.32 no.2
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• pp.212-218
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• 2016

The research was conducted windward of an irrigated Acacia amplicips Maslin windbreak established to protect As Salam Cement Plant from winds and moving sands. Two belts with approximate optical porosities of 50% and 20% were studied in River Nile State, Sudan. The research aimed at assessing the efficiency of the two belts in wind speed reduction and sand deposition. Research methods included: (i) estimation of optical porosity, (ii) measurements of windward wind speeds at a control and at distances of 0.5 h (h stands for windbreak height), 1 h and 2 h at two vertical levels of 0.25 h and 0.5 h, (iii) estimation of relative wind speeds at the three positions (distance and height) at windward and (iv) estimation of wind erosive forces and prediction of zones of sand deposition. Results show that while the two belts reduced windward wind speeds at the two levels for the three distances, belt II was more effective. Nearest sand deposition occurred at 2 h and 1h windward of belt II and belt I, respectively, at level 0.25 h. At level 0.5 h, sand was deposited only at 2 h windward of belt II and no sand deposition occurred windward of belt I. The study concludes that less porous windbreaks are more effective in reducing wind speed and in depositing sand in windward direction at a distance of not less than twice the belt height.

• Journal of The Geomorphological Association of Korea
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• v.23 no.1
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• pp.77-85
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• 2016

To understand the difference of runoff discharge processes between Gwangneung deciduous and coniferous forest catchments, we collected hydrological data (e.g., precipitation, soil moisture, runoff discharge) and conducted hydrochemical analyses in the deciduous and coniferous forest catchments in Gwangneung National Arboretum in the northwest part of South Korea. Based on the end-member mixing analysis of the three storm events during the summer monsoon in 2005, the hillslope runoff in the deciduous forest catchment was higher 20% than the coniferousforest catchment during the firststorm event. Howerver, hillslope runoff increased from the second storm event in the coniferous catchment. We conclude that low soil water contents and topographical gradient characteristics highly influence runoff in the coniferous forest catchment during the first storm events. In general, coniferous forests are shown high interception loss and low soil moisture compared to the deciduous forests. It may also be more likely to be a reduction in soil porosity development when artificial coniferous forests reduced soil biodiversity. The forest soil porosity is an important indicator to determine the water recharge of the forest. Therefore, in order to secure the water resources, it should be managed coniferous forests for improving soil biodiversity and porosity.

• Journal of Powder Materials
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• v.30 no.1
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• pp.35-40
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• 2023

In this study, a graphite block is fabricated using artificial graphite processing byproduct and phenolic resin as raw materials. Mechanical and electrical property changes are confirmed due to the preforming method. After fabricating preforms at 50, 100, and 150 MPa, CIP molding at 150 MPa is followed by heat treatment to prepare a graphite block. 150UP-CIP shows a 12.9% reduction in porosity compared with the 150 MPa preform. As the porosity is decreased, the bulk density, flexural strength, and shore hardness are increased by 14.9%, 102.4%, and 13.7%, respectively; and the deviation of density and electrical resistivity are decreased by 51.9% and 34.1%, respectively. Therefore, as the preforming pressure increases, the porosity decreases, and the electrical and mechanical properties improve.

• Steel and Composite Structures
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• v.52 no.3
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• pp.249-271
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• 2024

In this scientific work, an analytical solution for the dynamic analysis of cross-ply and angle-ply laminated composite plates is proposed. Due to technical issues during the manufacturing of composite materials, porosities and micro-voids can be produced within the composite material samples, which can carry on to a reduction in the density and strength of the materials. In this research, the laminated composite plates are assumed to have new distributions of porosities over the plate cross-section. The structure is modeled using a simple integral shear deformation theory in which the transverse shear deformation effect is included. The governing equations of motion are obtained employing the principle of Hamilton's. The solution is determined via Navier's approach. The Maple program is used to obtain the numerical results. In the numerical examples, the effects of geometry, ratio, modulus ratio, fiber orientation angle, number of layers and porosity parameter on the natural frequencies of symmetric and anti-symmetric laminated composite plates is presented and discussed in detail. Also, the impacts of the kinds of porosity distribution models on the natural frequencies of symmetric and anti-symmetric laminated composite plates are investigated.

• Journal of ILASS-Korea
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• v.26 no.4
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• pp.163-170
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• 2021

Emergency generators normally use diesel engines. The generators need to conduct weekly no-load operation inspections to ensure stable performance at emergency situations. In particular, the generators with large diesel engines mainly use rectangle type filter substrates. In order to minimize hazardous emissions generated by generators, optimizing the reduction efficiency through CFD analysis of flow characteristics of PM/NO_X reduction system is important. In this study, we analyzed internal flow by CFD, which is difficult to confirm by experimental method. The main factors in our numerical study are the changes of flow uniformity and back pressure. Therefore, changes in flow characteristics were studied according to urea injector locations, selective catalyst reduction (SCR) diffuser angle, and filter porosity.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.3
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• pp.214-224
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• 2004

A large cage system for the purpose of fishes farming in the open sea was influenced by various forces from the ocean environment. The deformation of the cage by these forces affects the safety of the cage itself, as well as that of the cultivated creatures. In this research, theoretical model was established to analyzing dynamic movement influenced by current for cage. Also, to increase the accuracy of calculations, the reduction ratio of flow speed acquired using the flume tank experiment. Applying the reduction ratio of flow speed to the numerical calculation, the calculation values were compared with the measured values in the flume tank experiment using cage model. The results were as follows ; 1. When the flow speed of the flume tank is fixed, the decrease of the velocity of flow which is passed the upper panel side is proportion to the increase of porosity ratio of netting. 2. When the porosity ratio is fixed, the increase of the velocity of flow which is passed the upper panel side is proportion to the increase of velocity of flow. 3. When the porosity ratio and the flow speed of the flume tank are fixed, the decrease of the velocity of flow which is passed the upper panel side is proportion to the increase of attack angle. 4. As a result of comparison between the underwater shape by simulation which is applying the reduction ratio of flow speed from the experiment using plane netting and that by model experiment, it was found out that the result of the simulation was very close to that of model gear within ${\pm}$ 5 % error range.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.36 no.4 s.107
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• pp.77-82
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• 2004

Expression-deliquoring tests using three types of paper sludges (tissue, newsprint, and paperboard) as deliquoring agent were carried out in order to investigate the effects of sludge dosage and pressure on the expression-deliquoring of slurry. The addition of deli­quoring agent causes expression-deliquoring of slurry to be faster than would be the case without the deliquoring agent. In case of the tissue sludge, the highest compression rate was achieved when $5\%$ of deliquoring agent was added, while in cases of the news­print and the paperboard sludge, $7\%$. Compression rate was increased as pressure increases. Porosity was decreased as pressure increases. The lowest porosity was observed when $5\%$ of tissue sludge was added. When compared the weight of cake where deliquoring agent was not added and the weight of cake that was fastest expression-deliquoring, there was about $17.5\%$ of the weight reduction

• The Korean Journal of Ceramics
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• v.1 no.3
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• pp.147-151
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• 1995

Porous composite of $Al_2O_3$ and AIN based mullite and SiC can be prepared by alumium reaction synthesis and atmosphere controllied sintering in order to improve the durability of a gas filter body. The porous $Al_2O_3$-AIN-mullite, which has a strength of 168 kg/$\textrm{cm}^2$ and porosity of 51.59%, could be obtained by stmospheric firing at $1600^{\circ}C$ and the porous $Al_2O_3$-AIN-SiC with a porosity of 33% and strength of 977 kg/$\textrm{cm}^2$, could also be prepared. The average pore size has been changed from 0.2$\mu\textrm{m}$ in a reduction atmosphere and to 2$\mu\textrm{m}$ in an air atmosphere, respectively.