• Transactions of Materials Processing
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• v.17 no.3
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• pp.161-169
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• 2008

In the present work, the two-back stress model is proposed and continuum damage mechanics (CDM) is incorporated into the plastic constitutive relation in order to describe the plastic deformation localization and the damage evolution in a deforming continuum body. Coupling between damage mechanics and isothermal rate independent plasticity is performed using the kinematic hardening rule, which in turn is formulated by combining the nonlinear Armstrong-Frederick rule and the Phillips rule. The numerical analyses are carried out within h deformation theory. It is noted that the damage evolution within a work piece accelerates the plastic deformation localization such that the material with lower hardening exponent results in a rapid shear band formation. Moreover, the results from the numerical analysis reflected closely with the micro-structures around the fractured regime. The effects of the various hardening parameters on deformation localization are also investigated. As the nonlinear strain rate description in the back stress evolution becomes dominant, the strain localization becomes intensified as well as the damage evolution.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.192-198
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• 1997

In the concurrent engineering, the CAD-based design model is necessary for multidisciplinary analysis and for computer-aided manufacturing (CAM). A shape and configuration design velocity field computation of structure has been developed using a computer-aided design (CAD) tool, Pro/ENGINEER. The design Parameterization with CAD tool is to characterize the change in dimensions and movements of geometric control points that govern the shape/orientation of the structural boundary. The boundary velocity is obtained by using a CAD-based finite difference method and the domain velocity field is obtained from finite element analysis (FEA) using the boundary displacement method. In this paper, the continuum configuration DSA for NVH problem, which requires the shape velocity field and the orientation velocity field at the same time, is developed using linear shape functions. For validation of continuum design sensitivity coefficients, design sensitivity coefficients are compared with the coefficients computed using by the finite difference method.

• Journal of The Korean Astronomical Society
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• v.11 no.1
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• pp.37-46
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• 1978

A hydrostatic model atmosphere of a typical umbral core is constructed on the basis of both Na I $D_2$ line profile and umbral core-to disk continuum intensity ratio. The observations were obtained by Mullan and Wyller with photoelectric means over the range from $4000{\AA}\;and\;6500{\AA}$. The computed line profile of Na I $D_2$ and the emergent continuum intensity distribution are compared with the observations. The temperature of umbral cores is found to be lower by $300^{\circ}K\;to\;500^{\circ}K$ than that of their ambient umbral region. The detailed physical structure of a working model of umbral cores is proposed.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.63.1-63.1
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• 2011

In understanding AGN physics, it is fundamental to determine black hole masses. Based on the gas kinematics of the broad-line region, black hole masses can be derived from the product of the width of the broad emission lines and the continuum/line luminosities. For a sample of 37 intermediate-luminosity AGN at z~0.4, we obtained high quality spectra (S/N~100) using the Low Resolution Imaging Spectrometer(LRIS) at the KECK telescope, in order to calibrate various black hole mass estimators based on the Mg II (2798A), the $H{\beta}$ (4861A), and the $H{\alpha}$ (6563$\bar{A}$) emission lines. Based on our multicomponent fitting analysis, we subtract continuum, FeII emission, and host galaxy starlight, reducing systematic errors in measuring emission line widths. Combining low S/N SDSS spectra with our high S/N keck spectra, we determine a set of ~30 black hole masses of the sample for each emission line. Then by comparing various sets of black hole masses, we internally calibrate each mass estimators and investigate uncertainties and limitations of each mass estimator.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.8
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• pp.397-400
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• 2006

An optimized iron core structure of stimulating coil are presented in order to control the induced electric field distribution using the Continuum Design Sensitivity Analysis (CDSA) combined with a commercially available generalized finite element code (OPERA). The results show that a Figure-Of-Eight (FOE) coil as well as a circular coil with the proposed iron core structure can increase induced electric field intensity by more than two times and make better field localization, compared with those of existing stimulation coil with a air core. After considering manufacturing constraints, a practical iron core structure based on the proposed optimized one is proposed and its performance is analyzed.

• Structural Engineering and Mechanics
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• v.59 no.3
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• pp.475-502
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• 2016

Nanobeams are widely used as a structural element for nanodevices and nanomachines. The development of nano-sized machines depends on proper understanding of mechanical behavior of these nano-sized beam elements. Small length scales such as lattice spacing between atoms, surface properties, grain size etc. are need to be considered when applying any classical continuum model. In this study, Eringen's nonlocal elasticity theory is incorporated into classical beam model considering the effects of axial extension and the shear deformation to capture unique static behavior of the nanobeams under continuum mechanics theory. The governing differential equations are obtained for curved beams and solved exactly by using the initial value method. Circular uniform beam with concentrated loads are considered. The displacements, slopes and the stress resultants are obtained analytically. A detailed parametric study is conducted to examine the effect of the nonlocal parameter, mechanical loadings, opening angle, boundary conditions, and slenderness ratio on the static behavior of the nanobeam.

• Coupled systems mechanics
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• v.4 no.1
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• pp.1-18
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• 2015

The state-based peridynamics is considered a nonlocal method in which the equations of motion utilize integral form as opposed to the partial differential equations in the classical continuum mechanics. As a result, the enforcement of boundary conditions in solid mechanics analyses cannot follow the standard way as in a classical continuum theory. In this paper, a new approach for the boundary condition enforcement in the state-based peridynamic formulation is presented. The new method is first formulated based on a convex kernel approximation to restore the Kronecker-delta property on the boundary in 1-D case. The convex kernel approximation is further localized near the boundary to meet the condition that recovers the correct boundary particle forces. The new formulation is extended to the two-dimensional problem and is shown to reserve the conservation of linear momentum and angular momentum. Three numerical benchmarks are provided to demonstrate the effectiveness and accuracy of the proposed approach.

• Publications of The Korean Astronomical Society
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• v.22 no.4
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• pp.97-101
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• 2007

We are often faced with the task of having to estimate the hydrogen and helium ionizing luminosities of massive stars in the study of H II regions and the warm ionized medium (WIM). Using the results of the most complete compilation of stellar parameters (the effective temperature, stellar radius and surface gravity) and the latest Kurucz stellar atmosphere models, we calculate the ionizing photon luminosities in the $H^0\;and\;He^0$ continua from O3 to B5 stars. We compared the theoretical Lyman-continuum luminosity with the observationally inferred luminosity of the H II region around ${\alpha}$ Vir, and found that the theoretical value is higher than the observed value in contrast to the eariler result.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.71.1-71.1
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• 2016

Photometric reverberation mapping is an effective alternative to time consuming spectroscopy. It usually employs narrow bands to track the luminosity variations of broad emission lines, such as Balmer lines, and broadbands for the continuum variability. Here, we investigate the feasibility of substituting these for medium bands, with 50nm widths, that are currently being used on the SED Camera for QUasars in EArly uNiverse (SQUEAN) installed on the 2.1m Otto Struve Telescope at McDonald Observatory. Three targets with recent variability and/or short expected time lags were selected, and observed for 15 minutes each in the medium band containing $H{\alpha}$, and the two adjacent bands for continuum subtraction afterwards. Analysis shows that for one of the objects, SDSS J0350+0037, the pure $H{\alpha}$ emission line flux has a S/N ~ 12, so that variabilities up to ~ 8% are detectable. Thus, future observations using these medium bands on SQUEAN seem to be practical.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.3-26
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• 2009

Superloading yield surface concept is newly introduced together with subloading yield surface conception in order to describe full gradation continuously of the mechanical behavior of soils from typical sand through intermediate soil to typical clay (All Soils). Finite deformation theory has been applied to the soil skeleton-pore water coupled continuum mechanics, which enables us to discuss things in a perpetual stream from stable state to unstable state like from deformation to failure and vice versa like from liquefaction to post liquefaction consolidation of sand (All States). Incremental form of the equation of motion has been employed in the continuum mechanics in order to incorporate a rate type constitutive equation, which is "All Round" enough to predict ground behavior under both static and dynamic conditions. The present paper is the shortened version of the lecture note delivered in 2008 Theoretical and Applied Mechanics Conference, Science Council Japan, but with newly developed application examples.