• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.910-913
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• 2001

Rapid Prototyping(RP) techniques have unique characteristics according to their working principle: the stair-stepped surface of a part due to layer-by-layer stacking, low building speed, and additional post-processing to improve surface roughness. A new RP process, Variable Lamination Manufacturing by using expandable polystyrene foam(VLM-S), has been developed to overcome the unfavorable characteristics. The objective of this study is to investigate the thermal characteristics and skeleton size effects as the hotwire cuts EPS foam sheet in order to improve dimensional accuracy of the parts, which is produced by VLM-S. Empirical and analytical approaches are performed to find the relationship between cutting speed and heat input, and the relationship between maximum available cutting speed and heat input. In addition, empirical approaches are carried out to find the relationship between cutting error and skeleton size, and cutting deviation and skeleton size. Based on these results, the optimal hotwire cutting condition and available minimum skeleton size are derived. The outcomes of this study are reflecting in the enhancement of VLM-S input data generation S/W.

• Journal of Korea Foundry Society
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• v.30 no.6
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• pp.217-223
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• 2010

Foamed metal has become an attractive material, which has unique physical, thermal, acoustic, damping and mechanical properties, because large amount of pores are distributed in the metal matrix. Therefore, metal foam can be used for the light weight application in automotive, locomotive, aerospace fields. Aluminum foams have been developed successfully and will be employed in the next generation of energy absorption boxes. Magnesium alloys are most eligible candidate to substitute aluminum alloy, especially for lower density and higher damping properties in wide industrial fields. Magnesium alloy foams are expected to be particularly advantageous due to two thirds the density of aluminum. However, foaming magnesium have been weakness of high activity, difficult processing and very dangerous. In order to upgrade this problem, AM50 magnesium alloy which has better characteristic is safe to use through foaming time and alloying element in this study.

• Journal of computational fluids engineering
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• v.20 no.2
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• pp.23-36
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• 2015

The $2^{nd}$ generation ice accretion analysis program has been developed and validated for various icing conditions. The essential feature of the $2^{nd}$ generation code lies in its capability of handling general 3-D geometry and improved accuracy. The entire velocity fields are obtained based on Navier-Stokes equations in order to take the massively separated flow field into account. Unlike $1^{st}$ generation code, the droplet trajectories are calculated using Eulerian approach, which is adopted to yield appropriate collection efficiency even in the shadow region. For improved thermodynamic analysis on the surfaces, water film model and modified Messinger model are newly included in the present analysis. The ice shape for a given time step is obtained by considering the exact amount of ice accreted on the surface. Each module of the icing analysis code has been seamlessly integrated on the OpenFOAM platform. The developed code was validated against available experimental data for 2D airfoils and 3D DLR-F4. Due to the lack of experimental data, the computed results of DLR-F4 were compared with those obtained from FENSAP-ICE, which is state-of-the-art 3D icing analysis code. It was clearly shown that the present code produces comparable results to those of FENSAP-ICE, in terms of prediction accuracy and the capability of handling general 3-D geometries.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.1
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• pp.1-11
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• 2013

Additives such as glycerol, methanol, acetone, and ethanol were used to prevent $NaBO_2$ from precipitation, and their effects on hydrogen generation properties of $NaBH_4$ hydrolysis were investigated. When the concentration of additives was 5 wt%, the additives such as methanol, acetone, and ethanol could not prevent $NaBO_2$ precipitation. Although glycerol prevented $NaBO_2$ precipitation, conversion efficiency decreased to 78.0% due to its viscosity. Based on test results, hydrogen generation tests were also performed at various concentration of glycerol and methanol to investigate the concentration effects on hydrogen generation properties. As the concentration of glycerol increased from 1 wt% to 3 wt%, conversion efficiency increased owing to additive effect. When its concentration increased to 5 wt%, conversion efficiency decreased due to its viscosity. As the concentration of methanol increased from 5 wt% to 10 wt%, conversion efficiency increased owing to additive effect. When its concentration increased to 15 wt%, conversion efficiency decreased due to $NaB(OCH_3)_4$ precipitate. Although conversion efficiency decreased about 1% when 3 wt% glycerol was added, $NaBO_2$ precipitation was prevented. Consequently, addition of 3 wt% glycerol to $NaBH_4$ solution improves stability of hydrogen generation system.

• Transactions of the Korean hydrogen and new energy society
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• v.35 no.2
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• pp.152-161
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• 2024

In this study, a fuel cell system for future defense unmanned vehicles was designed and validated. A Co/Al₂O₃-Ni foam catalyst for NaBH₄ hydrolysis was characterized using several analytical methods. A NaBH₄ hydrogen generation system with the Co/Al₂O₃-Ni foam catalyst continuously generated hydrogen at elevated reaction temperatures. The fuel cell system with the NaBH₄ hydrogen generation system was designed and tested. The performance of the fuel cell system was comparable to that of the fuel cell system using pure hydrogen. Therefore, the fuel cell system with the NaBH₄ hydrogen generation system is a suitable power source for future defense unmanned vehicles owing to its easy refueling and simple system.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.124.1-124.1
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• 2005

• Journal of the Korean Society for Precision Engineering
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• v.18 no.8
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• pp.64-70
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• 2001

In all the Rapid Prototyping (RP) techniques, the computer-aided design (CAD) model of a three-dimensional part is sliced into horizontal layers of uniform, but not necessarily constant, thickness in the building direction. Each cross- sectional layer is successively deposited and, at the same time, bonded onto the previous layer. The stacked layers form a physical part of the model. The objective of this study is to develop a software for automatic generation of unit shape part(USP) for a new RP process, Variable Lamination Manufacturing using the linear hotwire cutting technique and expandable polystyrene foam sheet as part material(VLM-S). In order to examine the applicability of the developed software to VLM-S, USPs of general three-dimensional shapes, such as an auto-shift lever knob and a pyramid shape were generated.

• Journal of the Korean Applied Science and Technology
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• v.34 no.4
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• pp.1058-1065
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• 2017

Amino acid based surfactants as protein-surfactants is eco-friendly compound. So, amino acid based surfactants is expected as next generation surfactants. Amino acid based surfactants has high biodegradability, low toxicity and surface active properties. In this experiment, amino acid based surfactants, cocoyl glycine, was synthesized by glycine and triglyceride such as coconut oil and palm oil. And it was tested the surface tension, emulsifying properties, foam stability and HLB value. The synthesized surfactants was confirmed by FT-IR. Surface tension of surfactants synthesized by coconut oil on diluted aqueous solutions of surfactants was 31.2 dyne/cm at $1.0{\times}10^{-4}mol/L$. Surface tension of surfactants synthesized by palm oil on the diluted aqueous solutions of surfactants was 42.1 dyne/cm at $3.2{\times}10^{-5}mol/L$. Foam stability measured the foam height as time passed. Initial foam height of surfactants synthesized by coconut oil is 14.5 cm, and 10.7 cm after five minutes. Initial foam height of surfactants synthesized by palm oil is 3.0 cm, and 2.8 cm after five minutes. Foam height of surfactants synthesized by coconut oil was higher than surfactants synthesized by palm oil. But foam stability of surfactants synthesized by palm oil was better than surfactants synthesized by coconut oil. The emulsifying properties of synthesized surfactants are observed in benzene and soybean oil and emulsifying properties in organic solvent is better than in soybean oil.

• Computers and Concrete
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• v.33 no.4
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• pp.471-479
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• 2024

In urban areas, appropriate backfilling design is necessary to prevent surface subsidence and subsurface cavities after excavation. Expandable foam grout (EFG), a mixture of cement, water, and an admixture, can be used for cavity filling because of its high flowability and volume expansion. EFG volume expansion induces a porous structure that can be quantified by the entrapped air content. This study observed the unit weight variations in the EFG before and after expansion depending on the various admixture-cement and water-cement ratios. Subsequently, the air content before and after expansion and the gravimetric expansion ratios were estimated from the measured unit weights. The air content before expansion linearly increased with an increase in the admixture-cement ratio, resulting in a decrease in the unit weight. The air content after the expansion and the expansion ratio increased nonlinearly, and the curves stabilized at a relatively high admixture-cement ratio. In particular, a reduced water-cement ratio limits the air content generation and expansion ratio, primarily because of the short setting time, even at a high admixture-cement ratio. Based on the results, the relationship between the maximum expansion ratio of EFG and the mixture ingredients (water-cement and admixture-cement ratios) was introduced.

• Transactions of Materials Processing
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• v.10 no.7
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• pp.558-564
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• 2001

An experimental modeling is applied to investigate the formation of forms in molten aluminum By using a specially designed equipment, the effect of process variables, such as the shape of stirrer, stirring velocity and fluid viscosity, on the formation of foams were studied in the glycerine added water. Bubbles formed in water had various diameter from 1 to 10 mm and the number of bubbles was 0 to 20/$cm^2$. It turned out that among various variables the stirring velocity and fluid viscosity played important roles on the formation of bubbles. The results obtained from the model experiment were preyed to be convincible also in the real aluminum foam.