• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.414-421
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• 1996

The study of the vibration characteristics of annular sector plates which are clamped along their inner circumferential edge is important for structural engineers. The present analysis consists of experimental method and numerical method. The experimental method using time-average holographic interferometry is obtained vibration modes and frequencies. The experimental results are verified by a numerical method using F.E.M. The important aspects of the present paper is the dependence of the natural frequencies and the mode shape on the annular area changing sector angle. The radial nodal lines converge to the center of the plate. As increasing sector angle, the radial modes are predominant.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.334-334
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• 2015

The results of flow feature around two circular cylinders in various arrangements are carried out using two-dimensional simulation at Reynolds number of 200. In this work, time-averaged fluid force acting on the upstream and downstream cylinders were calculated for staggered angle ${\alpha}=0{\sim}90^{\circ}$ in the range of L/D = 1.1~5, where ${\alpha}$ is the angle between the free-stream flow and the line connecting the centers of the cylinders, L is centre-to-centre distance and D is cylinder diameter. The dependence of magnitudes and trends of fluid force coefficient on the spacing ratio L/D and ${\alpha}$ are discussed. In all arrangements of two cylinders, tandem arrangement (${\alpha}=0^{\circ}$) is the case produced a minimum drag coefficient for downstream cylinder. Moreover, the locations of separation and stagnation points or pressure coefficient on surface of the cylinder were examined. Acknowledgement: "This research was a part of the project titled 'Development of integrated estuarine management system', funded by the Ministry of Oceans and Fisheries, Korea."

• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.255-261
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• 2008

This paper reports a side-coupled asymmetric $1{\times}2$ plastic optical fiber coupler for an optical sensor system. The dependence of the optical power coupling ratio on the coupling angle and refractive index of the adhesion layer in both the forward and backward directions was examined based on the geometrical optics. It was confirmed experimentally that the coupling ratios can be optimized by controlling the coupling angle and refractive index of the adhesion layer. A maximum forward coupling efficiency > 93% was achieved.

• Geomechanics and Engineering
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• v.17 no.4
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• pp.385-392
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• 2019

The present fractional-order plasticity models for granular soil are mainly established under the triaxial compression condition, due to its difficult in analytically solving the fractional differentiation of the third stress invariant, e.g., Lode's angle. To solve this problem, a three dimensional fractional-order elastoplastic model based on the transformed stress method, which does not rely on the analytical solution of the Lode's angle, is proposed. A nonassociated plastic flow rule is derived by conducting the fractional derivative of the yielding function with respect to the stress tensor in the transformed stress space. All the model parameters can be easily determined by using laboratory test. The performance of this 3D model is then verified by simulating multi series of true triaxial test results of rockfill.

• Current Optics and Photonics
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• v.5 no.1
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• pp.72-76
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• 2021

The polarized micro-photoluminescence spectrum was analyzed to investigate the anisotropic localized states in a single GaAs quantum ring. An energy difference of ~0.1 meV was observed from the perpendicularly polarized spectrum measured by a pair of linear analyzers. Spectral dependence of the polarized emission was also characterized in terms of rotation and ellipticity angles using four Stokes parameters. While the rotation angle indicates the symmetric axis of an anisotropic quantum ring with a small variation (± 2°), the ellipticity angle varies from 7.4° down to -2.5°. We conclude that optical anisotropy and birefringence are induced by the crescent-like lateral shape of localized states.

• Journal of radiological science and technology
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• v.31 no.4
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• pp.379-387
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• 2008

Among methods to eliminate aliasing effects, the method of increasing velocity scale gradually eliminated the phenomenon in which the direction of the blood flow appeared in reverse. It was done by increasing the velocity scale while maintaining other parameters in the same state. The method of setting the Doppler angle to $0^{\circ}$ did not show significant changes in the wave pattern of the spectrum according to the angle. In actual ultrasonography tests, more accurate tests are expected to be carried out by applying variations to the velocity scale under the considerations of speed, accuracy, and convenience of the examination. The results showed that blood flow velocity increases exponentially according to the Doppler Angle. When the angle goes over $70^{\circ}$, the velocity value increases to an unmeasurable state. This indicates that in blood flow velocity measurements, the blood flow velocity is very dependent on the Doppler Angle. It also shows that the error increases when the incidence angle to the direction of blood flow exceeds $60^{\circ}$, and when the angle exceeds $70^{\circ}$, the error becomes even greater. In addition, he experiment results showed that an angle below $60^{\circ}$ is appropriate and for blood flow velocity measurements in extremity vessels, the most appropriate Doppler Angle is from $45^{\circ}$ to $60^{\circ}$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.10
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• pp.35-41
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• 2005

The problem of an orthotropic composite material with a central crack inclined with respect to the principal axes of material symmetry is studied. The material is subjected to uniform biaxial loading along its outer boundaries. The normal stress ratio theory is applied to predict initial crack extension behavior in cracked composite materials. The dependence of the crack extension angle with respect to the biaxial loading and the principal axes of material symmetry is discussed. Our analysis shows significant effects of horizontal loading, crack angle and fiber angle on the crack extension.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.4
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• pp.1-7
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• 2013

Optical characteristics including the view angle and color temperature uniformity of LED packages with an integrated lens fabricated by compression molding method are investigated according to lens shape, lens materials, and phosphor coating methods. Four types of lens shape are designed and their optical output power dependence on the refractive index of silicone encapsulant are evaluated. Also, spatial color temperature uniformities of packages fabricated with different phosphor coating methods-direct coating on a chip vs. uniformly mixed with silicone encapsulant- are compared at various view angles. As the result, it is found that phosphor coating method is more effective on color temperature uniformity than lens shape. The maximum color temperature difference of a package with direct coating of phosphor on a chip is 1,340K according to the view angle at the color temperature of 5,000K, and that of a package with uniformly mixed phosphor is 250K, which indicates 1,090K improvement of color uniformity for the latter case.

• Journal of Korea Foundry Society
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• v.31 no.4
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• pp.191-197
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• 2011

Transparent organic materials have been frequently used as an analog of the solidifying metallic materials, because their transparency permits an in-situ observation of the microstructural development during solidification through optical microscopy. Pivalic acid (PVA)-ethanol system showing an anisotropic property in solid-liquid interfacial energy and interface kinetics was adopted in the present experiment, and the detailed experiments performed are as follows: (1) variation of dendrite tip temperature with growth velocity, (2) correlation between primary dendrite arm spacing (${\lambda}_1$) and the growth orientation away from the heat flow direction (tilt angle: ${\theta}$), (3) variation of dendrite tip radius (R) with growth velocity (V), (4) dendrite tip stability parameter (${\sigma}^*$) and its dependence on the concentration. Concerning the correlation between the dendrite tip temperature and growth velocity the present result is well suited to Hunt-Lu equation. As the tilt angle increases, the average primary dendrite spacing tends to increase.

• Nuclear Engineering and Technology
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• v.52 no.1
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• pp.148-154
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• 2020

The radiation induced segregation of Cr at grain boundaries (GBs) in Ferritic/Martensitic steels was modeled assuming vacancy and interstitialcy diffusion mechanisms. In particular, the dependence of segregation on temperature and grain boundary misorientation angle was analyzed. It is found that Cr enriches at grain boundaries at low temperatures primarily through the interstitialcy mechanism while depletes at high temperatures predominantly through the vacancy mechanism. There is a crossover from Cr enrichment to depletion at an intermediate temperature where the Cr:Fe vacancy and interstitialcy diffusion coefficient ratios intersect. The bell-shape Cr enrichment response is attributed to the decreasing void sinks inside the grains as temperature rises. It is also shown that low angle grain boundaries (LAGBs) and special Σ coincidence-site lattice (CSL) grain boundaries exhibit suppressed radiation induced segregation (RIS) response while high angle grain boundaries (HAGBs) have high RIS segregation. This different behavior is attributed to the variations in dislocation density at different grain boundaries.