• Transactions of Materials Processing
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• v.3 no.3
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• pp.271-281
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• 1994

Titanium-6242 $({\alpha}+{\beta})$ alloy has been used for aircraft engine components such as disks and blades, because it has an excellent strength/weight ratio at high temperatures. When this material is forged to manufacture disks, process parameters should be carefully designed to control strain and temperature distributions within the process windows by which desirable mechanical properties can be produced. In the present investigation, it was intended to design the process parameters for a conventional hot forging of this material by using a rigid-thermoviscoplastic finite element analysis technique. It was assumed that the process was performed by a screw press which is capable of maintaining a constant ram speed during loading. From the analysis results, it was found out that the initial temperature of the workpiece and the die shape were important parameters to control the forging process. In result, these parameters were properly designed for hot forging of a disk with specific dimensions.

• Structural Engineering and Mechanics
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• v.67 no.2
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• pp.143-153
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• 2018

Thermal buckling of nonlocal flexoelectric nanoplates incorporating surface effects is analyzed for the first time. Coupling of strain gradients and electrical polarizations is introduced by flexoelectricity. It is assumed that flexoelectric nanoplate is subjected to uniform and linear temperature distributions. Long range interaction between atoms of nanoplate is modeled via nonlocal elasticity theory. The residual surface stresses which are usually neglected in modeling of flexoelectric nanoplates are incorporated into nonlocal elasticity to provide better understanding of the physic of problem. A Galerkin-based approach is implemented to solve the governing equations derived from Hamilton's principle are solved. The verification of obtained results is performed by comparing buckling loads of flexoelectric nanoplate with previous data. It is shown that buckling loads of flexoelectric nanoplate are significantly affected by thermal loading type, temperature change, nonlocal parameter, surface effect, plate thickness and boundary conditions.

• Bulletin of the Korean Chemical Society
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• v.14 no.6
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• pp.700-704
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• 1993

The photocatalytic alanine and hydrogen production reaction were studied by using CdS as a semiconductor photocatalysts. The rate of alanine and hydrogen production depends strongly on the temperature in heat treatment of CdS powder. In particular, the rate of alanine production, which was observed using Pt/CdS(A)-(CdS from Mitsuwa), was increased about six times than that of using Pt/CdS(B)-(CdS from Furruchi) under the same heat treatment condition at 500$^{\circ}$C. And the photocatalytic activity for alanine production using bare CdS(A) or Pt/CdS(A) was almost same with increasing temperature in heat treatment in the range of 100-600$^{\circ}$C. From X-ray diffraction data and photoluminescence spectrum, we conclude that the crystal structure changes of CdS(A) or strong interaction at interface of Pt and CdS contribute to increasing the rate of alanine and hydrogen production reaction.

• Journal of Aerospace System Engineering
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• v.15 no.6
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• pp.1-9
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• 2021

In this study, a new design of an extension-type actuator (ExACT) is proposed based on a chevron structure with displacement amplification mechanisms by local heating. ExACT comprises diamond-shaped displacement amplification structures (DASs) containing axially oriented V-shaped chevron beams, a support bar that restricts lateral heat deformation, and a loading slot for thin-film heaters. On heating the thin film heater, the diamond-shaped DASs undergo thermal expansion. However, lateral expansion is restricted by the support bar, leading to displacement amplification in the axial direction. The performance parameters of ExACT such as temperature distribution and extended displacement is calculated using thermo-mechanical analysis methods with the finite element method (FEM) tool. Subsequently, the ExACTs are fabricated using a polymer-based 3D printer capable of reproducing complex structures, and the performance of ExACTs is evaluated under various temperature conditions. Finally, the performance evaluation results were compared with those of the FEM analysis.

• Advances in nano research
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• v.7 no.3
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• pp.181-190
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• 2019

The thermal buckling temperature values of the graded carbon nanotube reinforced composite shell structure is explored using higher-order mid-plane kinematics and multiscale constituent modeling under two different thermal fields. The critical values of buckling temperature including the effect of in-plane thermal loading are computed numerically by minimizing the final energy expression through a linear isoparametric finite element technique. The governing equation of the multiscale nanocomposite is derived via the variational principle including the geometrical distortion through Green-Lagrange strain. Additionally, the model includes different grading patterns of nanotube through the panel thickness to improve the structural strength. The reliability and accuracy of the developed finite element model are varified by comparison and convergence studies. Finally, the applicability of present developed model was highlight by enlighten several numerical examples for various type shell geometries and design parameters.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2069-2087
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• 2023

In nuclear power plant (NPP) accidents, the containment is subject to high temperatures and high internal pressures, which may further trigger serious chain accidents such as core meltdown and hydrogen explosion, resulting in a significantly higher accident level. Therefore, studying the mechanical performance of a containment under high temperature and high internal pressure is relevant to the safety of NPPs. Based on similarity principles, the 1:3.2 scale model of a prestressed concrete containment vessel (PCCV) of a NPP was designed. The loading method, which considers the thermal-pressure coupling conditions, was used. The mechanical response of the PCCV was investigated with a simultaneous increase in internal pressure and temperature, and the failure mechanism of the PCCV under thermal-pressure coupling conditions was revealed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.129-139
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• 2015

Concrete-Face Rock-Fill Dams (CFRDs) are rock-fill dams with watertight-concrete slabs on its upstream slope instead of its central earth cores. The design for CFRDs are still largely empirical and typically based on past experiences. This paper presents a description of the concrete face slabs and leakage behaviors of two post-constructed CFRDs based on the data gathered through instrumentation during the initial impoundment. The results show that the strain on the concrete face slab and the horizontal displacements of the vertical slab joints are slightly affected by both the seasonal temperature change and water loading during the initial impoundment. The deformation of perimetric joints are less affected by the temperature change, however it is significantly affected by the water loading during the initial impoundment. The leakage rate is significantly affected by the hydrostatic load and the deformation of the perimetric joints.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.3
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• pp.277-285
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• 2007

Porous cordierite beads, of which the average pore size was $130{\mu}m$ and porosity was about 80%, were prepared by the foaming method and then their application as support of the $Pt/{\gamma}-alumina$ catalyst for $NO_x$, reduction with propene was investigated. The pressure drop of a 2 mm porous beads filter was less than that of a 1 mm porous beads filter and the difference in pressure drop between these two increased as the flow rate increased. The catalytic activity of $Pt/{\gamma}-alumina$ washcoated on the porous bead was tested with varying Pt loading $(0.005{\sim}0.1g/cm^3),\;C_3H_6/NO$ mole ratio $(0.5{\sim}8)$, space velocity $(20,000{\sim}30,000h^{-1})$ and oxygen contents (1 and 8). Pt loading of $0.04g/cm^3$ showed the highest activity for $NO_x$ conversion. The $De-NO_x$, test was operated in the temperature range of $200{\sim}400^{\circ}C$ and the best operation temperature of the catalytic filter is about $250^{\circ}C$. As the C/N ratio increased, increase of the $NO_x$, conversion might result from the increase in exhaustion of the amount of oxygen by the reduction of hydrocarbon. $NO_x$ conversion at $20,000h^{-1}$ of space velocity shows a maximum 34% higher conversion than that at $30,000h^{-1}$. On condition that $O_2$ was 5%, space velocity was $20,000h^{-1}$ and the C/N ratio was 8, the $NO_x$ conversion exhibited a maximum of 40% at $250^{\circ}C$.

• Journal of Korean Society for Atmospheric Environment
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• v.13 no.6
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• pp.487-495
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• 1997

The most desirable diesel oxidation catalyst (DOC) should have the properties of oxidizing CO, HC and SOF effectively at low exhaust gas temperature while minimizing the formation of sulfate at high exhaust gas temperature. Precious metals such as platinum and palladium have been known to be sufficiently active for oxidizing SOF and also to have high activity for the oxidation of sulfur dioxide $(SO_2)$ to sulfur trioxide $(SO_3)$. There is a need to develop a highly selective catalyst which can promote the oxidation SOF efficiently, on the other hand, suppress the oxidation of $SO_2$. In this study, a Pt-V catalyst was prepared by impregnating platinum and vanadium onto a Ti-Si wash coated ceramic monolith substrate. A prepared Pt-V catalytic converter was installed on a heavy duty diesel engine and the effect of fuel sulfur on particulate matter (PM) of heavy duty diesel engine was measured. The effect of fuel sulfur on PM of Pt-V was also compared with that of a commercialized Pt catalyst currently being used in some of the heavy duty diesel engines in advanced countries. Only 1 $\sim$ 3% of sulfur in the diesel fuel was converted to sulfate in PM for the engine without catalyst, but almost 100% of sulfur conversion was achieved for the engine with Pt catalyst at maximum loading condition. In the case of Pt-V catalyst, there was no big difference in conversion with the base engine even at maximum loading condition. The reason of SOF increase according to the increase of suflate emission was identified as the washing off effect of bound water in sulfate.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.210-213
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• 2008

The purpose of this study is to investigate the performances of organic removal and methane recovery in the full scale two-phase anaerobic system. The full scale two-phase anaerobic system was consists of an acidogenic ABR (Anaerobic Baffled Reactor) and a methanognic UASB (Upflow Anaerobic Sludge Blanket) reactor. The volume of acidogenic and methanogenic reactors is designed to 28.3 $m^3$ and 75.3 $m^3$. The two-phase anaerobic system represented 60-82% of COD removal efficiency when the influent COD concentration was in the range of 7,150 to 16,270 mg/L after screening (average concentration is 10,280 mg/L). After steady-state, the effluent COD concentration in the methanogenic reactor showed 2,740 $\pm$ 330 mg/L by representing average COD removal efficiency was 71.4 $\pm$ 8.1% when the operating temperature was in the range of 19-32$^{\circ}C$. The effluent SCOD concentration was in the range of 2,000-3,000 mg/L at the steady state while the volatile fatty concentration was not detected in the effluent. Meanwhile, the COD removal efficiency in the acidogenic reactor showed less than 5%. The acidogenic reactor played key roles to reduce a shock-loading when periodic shock loading was applied and to acidify influent organics. Due to the high concentration of alkalinity and high pH in the effluent of the methanogenic reactor, over 80% of methane in the biogas was produced consistently. More than 70 % of methane was recovered from theoretical methane production of TCOD removed in this research. The produced gas can be directly used as a heat source to increase the reactor temperature.