• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.1507-1508
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• 2011

• Structural Engineering and Mechanics
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• v.28 no.1
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• pp.53-67
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• 2008

Anisotropic materials are increasingly required in modern technological applications. Certainly, civil, mechanical and naval engineers frequently deal with the situation of analyzing the dynamical behaviour of structural elements being composed of such materials. For example, panels of anisotropic materials must sometimes support electromechanical engines, and besides, holes are performed in them for operational reasons e.g., conduits, ducts or electrical connections. This study is concerned with the natural frequencies and normal modes of vibration of rectangular anisotropic plates supported by different combinations of the classical boundary conditions: clamped, simply - supported and free, and with additional complexities such holes of free boundaries and attached concentrated masses. A variational approach (the well known Ritz method) is used, where the displacement amplitude is approximated by a set of beam functions in each coordinate direction corresponding to the sides of the rectangular plate. Consequently each coordinate function satisfies the essential boundary conditions at the outer edge of the plate. The influence of the position and magnitude of both hole and mass, on the natural frequencies and modal shapes of vibration are studied for a generic anisotropic material. The classical Ritz method with beam functions as spatial approximation proved to be a suitable procedure to solve a problem of such analytical complexity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.2
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• pp.202-208
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• 2003

In this paper, we proposed a microstrip patch array antenna for DBS reception which had high gain and high tilted angle through mutual coupling driver patch to parasitic patch in H-plane edge and broadside direction in different layers. It was designed and fabricated in 16$\times$8 array by using low cost polyester based copper-clad laminate and foam instead of high cost dielectric substrate. It had gain of 22.9 dBi, beamwidth of 4.6$^{\circ}$, and tilted angle from broadside direction of 43.9$^{\circ}$.

• Journal of the Optical Society of Korea
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• v.19 no.1
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• pp.7-12
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• 2015

Up to ${\sim}520{\mu}J$ broadband mid-infrared (IR) supercontinuum (SC) generation in telecommunication multimode fiber (MMF) directly pumped by a $2.054{\mu}m$ nanosecond Q-switched Tm, $Ho:YVO_4$ laser is demonstrated. An average output power of 3.64 W is obtained in the band of ~1900 to ~2600 nm, and the corresponding optic-to-optic conversion efficiency is 67% by considering the coupling efficiency. The spectrum has extremely high flatness with negligible intensity variation (<2%) in the wavelength interval of ~2070 to ~2475 nm. The SC long-wavelength edge is limited by the silicon glass material loss, and by optimizing the MMF length, the SC spectrum could extend out to ${\sim}2.6{\mu}m$. The output SC pulse shapes are measured at different output powers, and no splits are found. The SC laser beam is nearly diffraction limited with an $M^2=1.15$ in $2.1{\mu}m$ measured by the traveling knife-edge method, and the laser beam spot is monitored by an infrared vidicon camera.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.7
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• pp.542-550
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• 2018

This paper presents design of a bearingless main rotor of SNUF (Seoul National University Flap) blade equipped with active trailing-edge flap to reduce the hub vibratory loads during helicopter forward flight. For that purpose, sectional design of the flexbeam is carried out using the thin-walled composite material rotating beam vibration analysis program (CORBA77_MEMB) in EDISON. Using the multi-body dynamics analysis program, DYMORE, blade dynamic characteristics and those of the loads control are examined using the active trailing-edge flap in terms of the flexbeam sectional design.

• Structural Engineering and Mechanics
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• v.68 no.4
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• pp.497-505
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• 2018

Three points bending flexural test was modeled numerically to study the crack propagation in the pre-cracked beams. The pre-existing edge cracks in the beam models were considered to investigate the crack propagation and coalescence paths within the modeled samples. The effects of particle size on the single edge-notched round bar in bending test were considered too. The results show that Failure pattern is constant by increasing the ball diameter. Tensile cracks are dominant mode of failure. These crack initiates from notch tip, propagate parallel to loading axis and coalescence with upper model boundary. Number of cracks increase by decreasing the ball diameter. Also, tensile fracture toughness was decreased with increasing the particle size. In the present study, the influences of particles sizes on the cracks propagations and coalescences in the brittle materials such as rocks and concretes are numerically analyzed by using a three dimensional particle flow code (PFC3D). These analyses improve the understanding of the stability of rocks and concretes structures such as rock slopes, tunnel constructions and underground openings.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.388-393
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• 2001

An experimental study is conducted to investigate the interaction of vortices over a delta wing with leading edge extension(LEX) through the off-surface flow visualization and the 5-hole probe measurements of the wing wake region. Especially, the application of a new visualization technique is employed by ultrasonic humidifier water droplet and laser beam sheet. The results, both the off-surface visualization and the 5-hole probe, show that LEX tends to stabilize the vortices of the delta wing up to the high angle of attack even though the model is yawed. With increasing yaw, the windward leading edge vortex moves inward, and closer to the wing surface, while the leeward vortex moves outwards and away from the wing surface. The vortex interaction is promoted in the windward side, and is delayed in the leeward side.

• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.258-262
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• 2004

The uncertainty of the detector-based candela scale is limited by the area measurement uncertainty of radiometric apertures. The apertures were fabricated with a diamond-turning machine which trimmed the edge of the apertures as sharply as a knife edge. The positions of the apertures were controlled by a digital feedback algorithm to scan the laser spot with the beam waist less than 5 ${\mu}{\textrm}{m}$. The knife edge scan yielded a set of coordinates on the edges of the aperture. The areas of the apertures were obtained by fitting the coordinates to the ellipses. The relative standard uncertainty of the measurement was estimated to be 8${\times}$10$^{-5}$.

• Transactions of the Society of Information Storage Systems
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• v.2 no.3
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• pp.178-183
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• 2006

A Blu-ray disc, which has a more than 25GB optical capacity, has been known as a promising next-generation optical disc format. It commonly has a 1.1 mm thick substrate and a 0.1 mm thick cover layer for beam transmitting and the protection of the reflecting surface. The cover layer is generally formed by the spin coating process. However, in conventional spin coating, small bumps are formed along the rim of the disc, which results in the fatal reading error. Numerical simulation of the thin film flow behaviors during spin coating with the commercial solver and optimal spinning conditions was obtained. Thickness distribution of the cover layer according to the variation of substrate's edge shape could be calculated as well. By modifying the shape of the substrate edge shape, the bumps along the disc rim could be minimized, and it was proved that the chamfered edge, around $5{\sim}10$ degree, is the simplest and most effective way to minimize the bumps.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.1
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• pp.106-115
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• 2007

In this study, first, child headform model was built up, satisfying requirement in the headform validation test. Also, for decreasing both acceleration peak and deformation, a new hood with dome shaped forming in inner panel was investigated. Next, headform impact, complying with draft of EEVC W/G 17, on the central portion of the newly proposed hood were simulated for a steel hood and three aluminum hoods with different thickness for examining the material and thickness effect on HIC value and inner panel deformation. The analysis results explained that aluminum hoods with dome shaped forming in inner panel were highly promising not only for meeting headform safety regulations but also for leading to weight savings. Finally, hood edge design technology in order to reduce pedestrian injury due to the high stiffness of beam type edge and the rigid support, was discussed. Various types of the foam filled edge were designed and their headform safety performance were evaluated. The edge structure with foam filled in upper one third of section exhibited excellent results.