• Proceedings of the KWS Conference
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• 2010.05a
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• pp.47-47
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• 2010

지구온난화의 심화로 사회적으로 환경의 중요성에 대한 인식이 확산되면서 $CO_2$ 배기가스 및 연비와 직결되어 있는 자동차 중량 절감의 중요성이 강조됨에 따라 차체 경량화 기술은 환경 친화적인 자동차 개발의 핵심기술로 연구되고 있다. 그러나 충돌보호 장치 및 편의장치의 증가로 차체 중량은 지속적으로 증가하고 있어 차체 중량을 혁신적으로 절감할 수 있는 초경량 차체기술이 요구된다. 차체 경량화 방법으로 기존 강재를 알루미늄재로 대체하는 방안이 연구되고 있으며, 일부 해외 고급 차종에서 알루미늄재를 이용한 스페이스 프레임 및 부품 개발을 검토 적용 중이다. 그러나 알루미늄 단일재 사용은 안전성등에서 요구 성능을 만족시키기 어렵기 때문에 강재와 알루미늄재의 적절한 사용이 필요하다. 이를 위하여 강재와 알루미늄간 이종접합부가 발생하며 이를 위한 적정 공정 개발이 필요하다. 전자기 펄스 용접(MPW)은 고상접합의 한 종류로서 고전류를 순간적으로 방전하여 발생된 고에너지를 통하여 접합이 이루어진다. 이러한 고에너지는 외부재의 전 자기적 성질에 의하여 에너지량이 결정되므로 외부재의 전도도(conductivity)는 매우 중요하며 이러한 이유로 Aluminum 1xxx계 중심의 전자기 펄스 용접 공정이 연구되었다. 그러나 자동차 스페이스 프레임 및 드라이브 샤프트등과 같은 부품에 알루미늄재를 적용하기 위해서는 일정 강도를 확보할 수 있는 6xxx계의 관련 연구가 필요하다. 따라서 본 연구에서는 고품질의 접합부 확보를 위한 1xxx계와 6xxx의 최적의 공정변수(충전전압, 외부재와 내부재 사이의 간격, 외부재 두께)를 도출하였다. 이를 위하여 전자기 펄스 용접 장치는 한국생산기술연구원과 웰메이트(주)에서 공동으로 개발한 $120{\mu}F$의 캐패시터 6개로 구성된 'W-MPW36'을 사용하였으며 접합 후 누수시험을 통하여 접합부의 품질을 검토하였다.

• Journal of Korean Society of Steel Construction
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• v.23 no.5
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• pp.581-593
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• 2011

The underlying advantages of using thin-walled corrugatedwebs instead of plate girders with stiffeners are the elimination of instability problems associated with buckling of the thin-walled flat plate, and elimination of the need for transverse stiffeners, which alsoresults in economic advantages. This paper focuses on two aspects related to the structural design technique forsinusoidal corrugated web steel beams, and the optimum design of the beams using real-value genetic algorithms. The structural design process and design variables used in this optimization werecomposed with EN 1993-1-5, DASt-R015 standard and Pasternak et al. (2004), and the valid design capacity of shear buckling of the standards were compared. For the optimum structural design, the objective function, presented as the fullweight of the sinusoidal corrugated web beams, and the slenderness, member forces, and maximum deflection of the beam, were considered constraints. Finally, the simple beam under the uniform load was adopted as a numerical example, and the effective probability parameters of the genetic operators were considered to find the global minimum point.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.2
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• pp.113-120
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• 2013

A steam reformer is a chemical reactor to produce high purity hydrogen from fossil fuel. In the steam reformer, since endothermic steam reforming is heated by exothermic combustion of fossil fuel, the heat transfer between two reaction zones dominates conversion of fossil fuel to hydrogen. Steam Reforming is complex chemical reaction, mass and heat transfer due to the exothermic methane/air combustion reaction and the endothermic steam reforming reaction. Typically, a steam reformer employs burner to supply appropriate heat for endothermic steam reforming reaction which reduces system efficiency. In this study, the heat of steam reforming reaction is provided by anode-off gas combustion of stationary fuel cell. This paper presents a optimization of heat transfer effect and average temperature of cross-section using two-dimensional models of a coaxial cylindrical reactor, and analysis three-dimensional models of a coaxial cylindrical steam reformer with chemical reaction. Numerical analysis needs to dominant chemical reaction that are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming(DSR) reaction. The major parameters of analysis are temperature, fuel conversion and heat flux in the coaxial reactor.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1230-1231
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• 2008

The effect of content of $Al_2O_3+Y_2O_3$ sintering additives on the densification behavior, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at 1,700[$^{\circ}C$] temperatures with an addition of $Al_2O_3+Y_2O_3$(6:4 mixture of $Al_2O_3$ and $Y_2O_3$) as a sintering aid in the range of 8${\sim}$20[wt%]. Phase analysis of $SiC-ZrB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $ZrB_2$ and In Situ YAG($Al_5Y_3O_{12}$). The relative density, flexural strength, Young's modulus and vicker's hardness showed the highest value of 89.01[%], 81.58[Mpa], 31.437[GPa] and 1.34[GPa] for $SiC-ZrB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature respectively. Abnormal grain growth takes place during phase transformation from ${\beta}$-SiC into ${\alpha}$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites. In this paper, it is convinced that ${\beta}$-SiC based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.

• Journal of Radiation Protection and Research
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• v.20 no.4
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• pp.227-236
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• 1995

Using beam data and accurate 3D dose model, a study of the spatial dose distribution for various arcs was carried out. The dose dirstibution generated by the accurate dose model could be represented by a simple approximate analytic form which is convenient and very efficient for calculating dose distribution iteratively in the optimization procedure. We developed an empirical cylindrical dose model to compute dose for one full rotational arc or partial rotational arc. After a tedious search for fits to a collection of 200 points of accurate dose data, we found simple formular with 7 parameters search. As a consequence, the programs required approximately less than 1 second to compute dose for one single arc on a 20 by 20 matrix (400 points) using fast approximate dose model. In conclusion the fast approximate dose model give dose distributions similar to the accurate dose model, which makes this fast dose model an attractive alternative to the accurate 3D dose model.

• Preventive Nutrition and Food Science
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• v.22 no.2
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• pp.131-137
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• 2017

Maximum production of isoquercetin and quercetin simultaneously from rutin by subcritical water hydrolysis (SWH) was optimized using the response surface methodology. Hydrolysis parameters such as temperature, time, and $CO_2$ pressure were selected as independent variables, and isoquercetin and quercetin yields were selected as dependent variables. The regression models of the yield of isoquercetin and quercetin were valid due to the high F-value and low P-value. Furthermore, the high regression coefficient indicated that the polynomial model equation provides a good approximation of experimental results. In maximum production of isoquercetin from rutin, the hydrolysis temperature was the major factor, and the temperature or time can be lower if the $CO_2$ pressure was increased high enough, thereby preventing the degradation of isoquercetin into quercetin. The yield of quercetin was considerably influenced by temperature instead of time and $CO_2$ pressure. The optimal condition for maximum production of isoquercetin and quercetin simultaneously was temperature of $171.4^{\circ}C$, time of 10.0 min, and $CO_2$ pressure of 11.0 MPa, where the predicted maximum yields of isoquercetin and quercetin were 13.7% and 53.3%, respectively. Hydrolysis temperature, time, and $CO_2$ pressure for maximum production of isoquercetin were lower than those of quercetin. Thermal degradation products such as protocatechuic acid and 2,5-dihydroxyacetophenone were observed due to pyrolysis at high temperature. It was concluded that rutin can be easily converted into isoquercetin and quercetin by SWH under $CO_2$ pressure, and this result can be applied for SWH of rutin-rich foodstuffs.

• Advances in environmental research
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• v.2 no.1
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• pp.19-33
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• 2013

Microalgae are receiving an increasing attention because of their potential use as $CO_2$ capture method and/or as feedstock for biofuels production. On the other hand the current microalgae-based technology is still not widespread since it is characterized by technical and economic constraints that hinder its full scale-up. In such contest the growth kinetics of Nannochloris eucaryotum (a relatively unknown marine strain) in batch and semi-batch photobioreactors is quantitatively investigated with the aim of obtaining the corresponding kinetic parameters suitable for process engineering and its optimization. In particular the maximum growth rate was evaluated to be 1.99 $10^{-3}\;h^{-1}$. Half saturation concentrations for nitrates ($K_N$) and phosphates uptake ($K_P$) were evaluated as 5.4 $10^{-4}\;g_N\;L^{-1}$ and 2.5 $10^{-5}\;g_P\;L^{-1}$, respectively. Yield factors for nitrogen ($Y_N$) and phosphorus ($Y_P$) resulted to be 5.9 $10^{-2}\;g_N\;g^{-1}$ biomass and 6.0 $10^{-3}\;g_P\;g^{-1}{_{biomass}}$, respectively. The possibility of using 100% (v/v) $CO_2$ gas as carbon source is also evaluated for the first time in the literature as far as N. eucaryotum is concerned. The strain showed a good adaptability to high concentrations of dissolved $CO_2$ as well as to low pH. The lipid content under 100% $CO_2$ is about 16.16 %wt $wt^{-1}$ and the fatty acid methyl esters composition of the extracted oil is in compliance with the European regulation for quality biodiesel.

• Structural Engineering and Mechanics
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• v.64 no.2
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• pp.243-257
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• 2017

Investigating the properties and durability of high-strength concrete exposed to sulfuric acid attack for the purpose of its application in structures exposed to this acid is of outmost importance. In this research, the resistance and durability of high-strength concrete containing macro-polymeric or steel fibers together with the pozzolans of silica fume or nano-silica against sulfuric acid attack are explored. To accomplish this goal, in total, 108 high-strength concrete specimens were made with 9 different mix designs containing macro-polymeric and steel fibers at the volume fractions of 0.5, 0.75, and 1.0%, as well as the pozzolans of silica fume and nano-silica with the replacement levels of 10 and 2%, respectively. After placing the specimens inside a 5% sulfuric acid solution in the periods of 7, 21, and 63 days of immersion, the effect of adding the fibers and pozzolans on the compressive properties, ultrasonic pulse velocity (UPV), and weight loss of high-strength concrete was investigated and the respective results were compared with those of the reference specimens. The obtained results suggest the dependency of the resistance and durability loss of high-strength concrete against sulfuric acid attack to the properties of fibers as well as their fraction in concrete volume. Moreover, compared with using nano-silica, using silica fume in the fibrous concrete mix leads to more durable specimens against sulfuric acid attack. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized was found using response surface method (RSM).

• Earthquakes and Structures
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• v.11 no.6
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• pp.943-966
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• 2016

Recently, magnetorheological elastomer (MRE) material and its devices have been developed and attracted a good deal of attention for their potentials in vibration control. Among them, a highly adaptive base isolator based on MRE was designed, fabricated and tested for real-time adaptive control of base isolated structures against a suite of earthquakes. To perfectly take advantage of this new device, an accurate and robust model should be built to characterize its nonlinearity and hysteresis for its application in structural control. This paper first proposes a novel hysteresis model, in which a nonlinear hyperbolic sine function spring is used to portray the strain stiffening phenomenon and a Voigt component is incorporated in parallel to describe the solid-material behaviours. Then the fruit fly optimization algorithm (FFOA) is employed for model parameter identification using testing data of shear force, displacement and velocity obtained from different loading conditions. The relationships between model parameters and applied current are also explored to obtain a current-dependent generalized model for the control application. Based on the proposed model of MRE base isolator, a second-order sliding mode controller is designed and applied to the device to provide a real-time feedback control of smart structures. The performance of the proposed technique is evaluated in simulation through utilizing a three-storey benchmark building model under four benchmark earthquake excitations. The results verify the effectiveness of the proposed current-dependent model and corresponding controller for semi-active control of MRE base isolator incorporated smart structures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.785-791
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• 2000

GDI (Gasoline Direct Injection) engines are considered as one of the candidates for next generation engines of passenger cars, which reduce exhaust emissions and fuel consumption. In GOI engines, a high-pressure gasoline supply system is required to directly inject the fuel to combustion chambers. Because of low lubricity of gasoline fuel, the clearance between a plunger and a barrel in GDI fuel pumps is too wide to achieve smooth hydrodynamic lubrication. Thus, it is difficult to generate high-pressure condition in GDI fuel pump since large amount of leakage flow occurs between the plunger and the barrel In this study, an optimum plunger design is presented to minimize leakage in the aspect of flow control. This paper analyzes leakage flow characteristics in the clearance to improve pumping performance of GDI fuel pumps. Effects of groove in the plunger are studied according to variations of depth and width. Evaluations of pumping performance are determined by the amount of pressure drop in the leakage path assuming a constant leakage flows. Both of turbulence and incompressible models are introduced in CFD (Computational Fluid Dynamics) analysis. Design parameters have been introduced to minimize leakage in limited space, and a methodological study on geometrical optimization has been conducted. As results of CFD analysis in various geometrical cases, optimum groove depths have been found to generate maximum sealing effects on gasoline fuel between the plunger and the barrel. This procedure offers a methodological way of an enhancement of plunger design for high-pressure GDI fuel pumps.