• Proceedings of the KSME Conference
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• 2001.11b
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• pp.622-627
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• 2001

Microjet flows are often encountered in many industrial applications of micro-electro-mechanical systems as well as in medical engineering fields such as a transdermal drug delivery system for needle-free injection of drugs into the skin. The Reynolds numbers of such microjets are usually several orders of magnitude below those of larger-scale jets. The supersonic microjet physics with these low Reynolds numbers are not yet understood to date. Computational modeling and simulation can provide an effective predictive capability for the major features of the supersonic microjets. In the present study, computations using the axisymmetic, compressible, Navier-Stokes equations are applied to understand the supersonic microjet flow physics. The pressure ratio of the microjets is changed to obtain both the under- and over-expanded flows at the exit of the micronozzle. Sonic and supersonic microjets are simulated and compared with some experimental results available. Based on computational results, two microjets are discussed in terms of total pressure, jet decay and supersonic core length.

• Interaction and multiscale mechanics
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• v.2 no.1
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• pp.1-14
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• 2009

This paper proposes an interaction field concept based on the field theory of plasticity. Relative deformation between two arbitrary scales, e.g., macro and micro fields, is defined which can be implemented in the crystal plasticity-based constitutive framework. Differential geometrical quantities responsible for describing dislocations and defects in the interaction field are obtained, based on which dislocation density and incompatibility tensors are further derived. It is shown that the explicit interaction exists in the curvature or incompatibility tensor field, whereas no interaction in the torsion or dislocation density tensor field. General expressions of the interaction fields over multiple scales with more than three scale levels are derived and implemented into the present constitutive equation.

• Current Optics and Photonics
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• v.3 no.6
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• pp.522-530
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• 2019

We present simulation methods to accurately determine the transmission efficiency and far-field patterns (FFPs) of a shallow-etched waveguide grating antenna (WGA) formed on a silicon-on-insulator wafer based on the finite-difference time-domain (FDTD) approach. The directionality and the FFP of a WGA with >1-mm in length can be obtained reliably by simulating a truncated WGA structure using a three-dimensional FDTD method and a full-scale WGA using a two-dimensional FDTD with the effective index method. The developed FDTD methods are applied to the simulation of an optical phased array (OPA) composed of a uniformly spaced WGA array, and the steering-angle dependent transmission efficiency and FFPs are obtained in OPA structures having up to 128-channel WGAs.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.513-518
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• 1997

In this study, nine reinforced concrete infilled frames involved bare frames were tested during vertical and cyclic loads simultaneously. This test programs were carried to investigate the horizontal strength and the crack propagation in variance with hoop reinforcement ratio. All specimens were modeling in one-third scale size. In this experimental program structural performance of reinforced concrete shear wall were focus at connection types. Based on the test results, the following conclusions are made. In the boundary column member of reinforced concrete shear wall, increasing the ratio of hoop bar in two or three times, in the fully babel type, the shear and horizontal strength of specimens were increased 1.1-1.2 times than that of fully rigid frame. And infilled shear wall specimen were increased 1.17-1.27 times than that. Fully rigid babel type shear wall specimens were increased 5.7~8.0 times, and infilled shear wall specimens were increased about 4.0~5.6 times than that of infilled shear wall specimens.

• Ocean and Polar Research
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• v.23 no.2
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• pp.161-172
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• 2001

A model-to-model comparison is attempted between Princeton Ocean Model (POM) and Miami Isopycnic Coordinate Ocean Model (MICOM) as a first step to extend our knowledge of models' performances in studying the East Sea circulation. The two models have fundamentally different numerical schemes and boundary conditions imposed on these models are not exactly the same each other. This study indicates that MICOM has a critical weak point in that it does not reproduce the shallow surface currents properly while it handles the thermohaline processes and associated movements of intermediate and deep waters efficiently. It is suggested that the mixed layer scheme needs to be modified so that it can match with inflow boundary conditions in order to reproduce the surface currents properly in MICOM. POM reproduces the surface current pattern better than MICOM, although the surface currents in POM appear to undergo the unrealistic seasonal variation and have exaggeratedly large vertical scale. These defects seem to arise during the process of adapting POM to the East Sea, and removing these defects is left as a future task.

• Food Science and Biotechnology
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• v.18 no.5
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• pp.1293-1297
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• 2009

In this study, drying kinetics of onion slices was examined in a laboratory scale vacuum dryer at an air temperature in a range of $50-70^{\circ}C$. Moisture transfer from onion slices was described by applying the Fick's diffusion model, and the effective diffusivity was calculated. Temperature dependency of the effective diffusivity during drying process obeyed the Arrhenius relationship. Effective diffusivity increased with increasing temperature and the activation energy for the onion slices was estimated to be 16.92 kJ/mol. The experimental drying data were used to fit 9 drying models, and drying rate constants and coefficients of models tested were determined by non-linear regression analysis. Estimations by the page and Two-term exponential models were in good agreement with the experimental data obtained.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.1
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• pp.1-8
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• 2016

Permanent deformation plays a key role in performance based earthquake resistant design. In order to estimate permanent deformation after earthquake, it is essential to secure reliable response history analysis(RHA) as well as earthquake scenario. This study focuses on permanent deformation of an inverted T-type wall under earthquake. The study is composed of two separate parts. The first one is on the verification of RHA and the second one is on an effect of input earthquake motion. The former is discussed in this paper and the latter in the companion paper. The verification is conducted via geotechnical dynamic centrifuge test in prototype scale. Response of wall stem, ground motions behind the wall obtained from RHA matched pretty well with physical test performed under centrifugal acceleration of 50g. The rigorously verified RHA is used for parametric study to investigate an effect of input earthquake motion selection in the companion paper.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.71.2-71.2
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• 2016

Merging galaxy clusters, such as PLCKG287.0+32.9, provide a window into the formation process of the large scale structure of the universe. PLCKG287.0+32.9 is an enormous merging galaxy cluster with mass estimated to be ~10^15 Msun. It hosts a pair of mega-parsec sized radio relics with projected offsets from the X-ray center of approximately 350kpc and 2.7Mpc, suggesting a NW-SE merging scenario with relics originating from two separate passes (Bonafede et al. 2014). A detected radio halo coincides with the center of x-ray emission. We present the motivation for our weak lensing study of the merging galaxy cluster PLCKG287.0+32.9 using recent Subaru optical imaging. We discuss the basics of weak-lensing and the criteria for source selection. In addition, we describe our method of PSF modeling and mass reconstruction.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.659-674
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• 2020

The present paper employs nonlocal strain gradient theory (NSGT) to study buckling behavior of functionally graded magneto-electro-thermo-elastic (FG-METE) nanoshells under various physical fields. NSGT modeling of the nanoshell contains two size parameters, one related to nonlocal stress field and another related to strain gradients. It is considered that mechanical, thermal, electrical and magnetic loads are exerted to the nanoshell. Temperature field has uniform and linear variation in nanoshell thickness. According to a power-law function, piezo-magnetic, thermal and mechanical properties of the nanoshell are considered to be graded in thickness direction. Five coupled governing equations have been obtained by using Hamilton's principle and then solved implementing Galerkin's method. Influences of temperature field, electric voltage, magnetic potential, nonlocality, strain gradient parameter and FG material exponent on buckling loads of the FG-METE nanoshell have been studied in detail.

• Journal of Korea Multimedia Society
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• v.14 no.5
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• pp.642-649
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• 2011

Among the various aspects of offline handwritten character patterns, it is the great variety of writing styles and variations that renders the task of computer recognition very hard. The immense variety of character shape has been recognized but rarely studied during the past decades of numerous research efforts. This paper tries to address the problem of measuring image distortions and handwritten character patterns with respect to reference patterns. This work is based on mass-spring mesh model with the introduction of simulated electric charge as a source of the external force that can aid decoding the shape distortion. Given an input image and a reference image, the charge is defined, and then the relaxation procedure goes to find the optimum configuration of shape or patterns of least potential. The relaxation process is based on the fourth order Runge-Kutta algorithm, well-known for numerical integration. The proposed method of modeling is rigorous mathematically and leads to interesting results. Additional feature of the method is the global affine transformation that helps analyzing distortion and finding a good match by removing a large scale linear disparity between two images.