• Journal of Magnetics
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• v.16 no.1
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• pp.64-70
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• 2011

Surface-mounted permanent magnet (PM) machines were examined experimentally and theoretically, through power loss measurements and calculations. Windage, friction and copper losses were calculated using simple analytical equations and finite element (FE) analyses. Stator core losses were calculated by determining core loss coefficients through curve-fitting and magnetic behavior analysis through non-linear FE calculations. Rotor eddy current losses were calculated using FE analyses that considered the time harmonics of phase current according to load. Core, windage and friction open-circuit losses and copper loss were determined experimentally to test the validity of the analyses.

• Journal of Welding and Joining
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• v.34 no.2
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• pp.11-15
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• 2016

FE analyses for weldment of ship structure are required for various reasons such as stress concentration for bead tow, residual stress and distortion after welding, and hydrogen diffusion for prediction of low temperature crack. These analyses should be done by solid element modeling, but most of ship structures are modeled by shell element. If we are able to make solid element in the shell element FE modeling it is easily to solve the requirement for solid elements in weld analysis of large ship structures. As the nodes of solid element cannot take moments from nodes of shell element, these two kinds of element cannot be used in one model by conventional modeling. The PSCM (Perpendicular shell coupling method) can connect shell to solid. This method uses dummy perpendicular shell element for transferring moment from shell to solid. The target of this study is to develop a FE pre-processing system applicable at welding at ship structure by using PSCM. We also suggested glue-contact technique for controlling element numbers and element qualities and applied it between PSCM and solid element in automatic pre-processing system. The FE weldment modeling through developed pre-processing system will have rational stiffness of adjacent regions. Then FE results can be more reliable when turn-over of ship-block with semi-welded state or ECA (Engineering critical assessment) of weldment in a ship-block are analyzed.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.2
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• pp.124-131
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• 2007

Methane is partially oxidized to produce the syngas by the lattice oxygen of metal oxides in the absence of gaseous oxygen. The present work deals with ferrite including copper component, which does not chemisorb methane, to investigate the suppression of the carbon deposition during the reduction of metal oxides by methane. Iron-based oxides of $Cu_xFe_{3-x}O_4$(X=0.25, 0.5, 1.0) was synthesized by the co-precipitation method. Thermogravimetric Analysis(TGA) was used to observe the isothermal reduction behavior of $Cu_xFe_{3-x}O_4$ and $Fe_3O_4$ at $600-900^{\circ}C$ under methane atmosphere. The crystal structures of reduced specimens were characterized by X-rays powder diffraction(XRD) technique. From the analyses of TGA, it is concluded that the reduction kinetics of $CuFe_2O_4$ was the fastest among $Fe_3O_4$ and $Cu_xFe_{3-x}O_4$(X=0.25, 0.5, 1.0). The X-ray diffraction analyses indicated that $Cu_xFe_{3-x}O_4$ was decomposed to Cu and $Fe_3O_4$ phase at $600^{\circ}C$ and was reduced to Cu and Fe phase at $800^{\circ}C$. $Fe_3O_4$, which was reduced at $900^{\circ}C$, showed Fe, graphite and $Fe_3C$ phases. On the contrary, $Cu_xFe_{3-x}O_4$ does not show the graphite or $Fe_3C$ phases. This results infer that Cu component suppress the carbon deposition on Cu-ferrite.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.5
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• pp.535-540
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• 2015

We propose an enhanced Green's function approach to predict thermal stresses by considering temperature-dependent material properties. We introduce three correction factors for the maximum stress, the time taken to reach maximum stress, and the time required to attain steady state based on the Green's function results for each temperature. The proposed approach considers temperature-dependent material properties using correction factors, which are defined as polynomial expressions with respect to temperatures based on Green's functions, that we obtain from finite-element (FE) analyses at each temperature. We verify the proposed approach by performing detailed FE analyses on thermal transients. The Green's functions predicted by the proposed approach are in good agreement with those obtained from FE analyses for all temperatures. Moreover, the thermal stresses predicted using the proposed approach are also in good agreement with the FE results, and the proposed approach provides better predictions than the conventional Green's function approach using constant, time-independent material properties.

• Structural Engineering and Mechanics
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• v.64 no.5
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• pp.653-660
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• 2017

The aim of this study is to accurately estimate seismic damage and the collapse mechanism of the historical stone masonry minaret "Hafsa Sultan", which was built in 1522. Surveying measurements and material tests were conducted to obtain a 3D solid model and the mechanical properties of the components of the minaret. The initial Finite Element (FE) model is analyzed and numerical dynamic characteristics of the minaret are obtained. The Operational Modal Analysis (OMA) method is conducted to obtain the experimental dynamic characteristics of the minaret and the initial FE model is calibrated by using the experimental results. Then, linear time history (LTH) and nonlinear time history (NLTH) analyses are carried out on the calibrated FE model by using two different ground motions. Iron clamps which used as connection element between the stones of the minaret considerably increase the tensile strength of the masonry system. The Concrete Damage Plasticity (CDP) model is selected in the nonlinear analyses in ABAQUS. The analyses conducted indicate that the results of the linear analyses are not as realistic as the nonlinear analysis results when compared with existing damage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.709-715
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• 2010

The coupled model with hydrogen transport and elasto-plasticity behavior was introduced. In this paper, the effective factor of the hydrogen diffusion equation has been described. To assess the effective factor, finite element (FE) analyses including hydrogen transport and mechanical loading for boundary layer specimens with low-strength steel properties are carried out. The results of the FE analyses are compared with those from previous studies conducted by Taha and Sofronis (2001).

• Journal of the Korean Society for Precision Engineering
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• v.25 no.8
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• pp.80-87
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• 2008

This paper investigated into the impact characteristics of the stainless sheet with thickness of 0.7 mm on the stretching boundary condition through three-dimensional finite element analysis. High speed tensile tests were carried out to obtain strain-stress relationships with the effects of the strain rate. The FE analysis was performed by the ABAQUS explicit code. In order to improve an accuracy of the FE analysis, the hyper-elastic model and the damping factor were introduced. Through the comparison of the results of the FE analyses and those of the impact tests, a proper FE model was obtained. The results of the FE analyses showed that the absorption rate of energy maintains almost 82.5-83.5% irrespective of the impact energy level and the diameter of the impact head. From the results of FE analyses, variations of stress, strain, dissipation energy, strain energy density, and local deformation characteristics in the stainless sheet during the collision and the rebound of the impact head were quantitatively examined. In addition, it was shown that the fracture of the specimen occurs when the plastic strain is 0.42 and the maximum value of the plastic dissipation energy of the specimen is nearly 1.83 J.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.18-22
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• 2006

Effects of V substitution of Fe on the magnetic properties of $Fe_3O_4$ have been investigated by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), conversion electron Mossbauer spectroscopy (CEMS), and vibrating sample magnetometry (VSM) measurements on sol-gel-grown films. XRD data indicates that the $V_xFe_{3-x}O_4$ films maintain cubic structure up to x=1.0 with little change of the lattice constant. Analyses on V 2p and Fe 2p levels of the XPS data indicate that V exist as $V^{3+}$ mostly in the $V_xFe_{3-x}O_4$ films with the density of $V^{2+}$ ions increasing with increasing V content. Analyses on the CEMS data indicate that $V^{3+}$ ions substitute tetrahedral $Fe^{3+}$ sites mostly, while $V^{2+}$ ions octahedral $Fe^{2+}$ sites. Results of room-temperature VSM measurements on the films reveal that the saturation magnetization for the x=0.14 sample is larger than that of $Fe_3O_4$, while it becomes smaller than that of $Fe_3O_4$ for $x{\geq}0.5$. The coercivity of the $V_xFe_{3-x}O_4$ films is found to increase with x, attributed to the increase of anisotropy by the substitution of $V^{2+}(d^3)$ ions into the octahedral sites.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.48-53
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• 2007

The objective of this paper is to investigate the influence of impact conditions on the impact characteristics of the stainless sheet for the case of the fixed boundary conditions. In order to examine impact characteristics of the sheet, three-dimensional finite element analyses and impact tests have been performed. High speed tensile tests have been carried out to obtain strain-stress relationships including the effects of the strain rate. In order to improve an accuracy of the FE analysis, the hyper-elastic model and the damping factor have been introduced. The results of the FE analyses and the impact tests have been shown that the diameter of the impact head does not affect the absorption energy of the stainless sheet. In addition, it has been shown that the absorption rate of energy maintains almost $82.5\;\sim\;83.5\;%$ irrespective of the impact energy level and the diameter of the impact head. From the results of FE analyses, the variation of stress and strain energy in the stainless sheet has been quantitatively examined.

• Aerospace Engineering and Technology
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• v.11 no.1
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• pp.91-97
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• 2012

The structural analyses and experimental results for the bellows of a gas-generator liquid oxygen shut-off valve were presented. The bellows experiences axial compression and external high pressure loadings at cryogenic temperatures. The analyses were performed using EJMA (Expansion Joint Manufacturing Association) standard and the commercial FE (finite element) analysis program, Abaqus v6.9, at room and cryogenic temperatures. The spring modulus, the induced stress and the expected fatigue life of the bellows were compared respectively. The effects by the contact and the material plasticity on the FE analysis results were also analyzed. Also, FE analyses related to a burst test were presented.