• Journal of the Korean Society for Railway
• /
• v.17 no.1
• /
• pp.14-18
• /
• 2014

Wheel/rail contact is a significant problem in railway dynamics. In this paper, the wheel/rail contact is examined analytically and numerically as a contact problem between two cylinders where torque and friction have effect. Furthermore, the contact of a real wheel and rail is investigated numerically where the normal and shear force act. This study demonstrates that the wheel/rail contact is a process that generates traction force through creep where rolling and sliding occurs simultaneously depending on the shape of the wheel and rail, and the friction coefficient between them.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.17 no.1
• /
• pp.8-15
• /
• 2005

This study concerns the characteristics of helical flow in a concentric and eccentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and $0.2\%$ aqueous of sodium carboxymethyl cellulose(CMC), respectively, when the inner cylinder rotates at the speed of $0\~500$ rpm. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. This study shows the change of skin friction coefficient and wall shear stress corresponding to the variation of rotating speed of the inner cylinder, radius ratio, eccentricity, and working fluids.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.17 no.6
• /
• pp.708-716
• /
• 1988

Local heat transfer coefficients were measured on semi-cylinders on which a circular water jet impinged in crossflow. The ratio of the semi-cylinder's diameter and the nozzle outlet diameter were varied parametrically, as were the Reynolds number and the supplementary water heights. The measurements showed that the circumferential distribution of the heat transfer coefficient peaked at the stagnation point. For a fixed supplementary water height, the peak heat transfer coefficient was not depend on the curvature of test specimen(d/D). Optimum height of supplementary water which brought about the augmentation of heat transfer at the stagnation point was S/D=1. The Nusselt number decreased as the circumferential distance or angle increased. The circumferential distribution of dimensionless heat transfer (Nu/Nus) was independent of d/D ($d/D{\geq}8.33$), but for the d/D<8.33, it was depended on d/D. At a fixed angle of specimen, dimensionless heat transfer (Nu/Nus) decreased as the ratio d/D increased. The extent of the decrease between d/D=6.67 and 8.33 was markedly greater than that between d/D=8.33 and 10, or d/D=10 and 11.67.

• Conservation Science in Museum
• /
• v.2
• /
• pp.9-17
• /
• 2000

This is a case study of conservation treatment of the textiles and costumes excavated from Soonchun Park's tomb in Eumsung, North Chungcheong province. When excavated, the objects were found fairly wet and badly smelled since they decayed in wooden coffin. They were wet-treated with deionized water to remove dirt and dried at room temperature, during which the objects were blocked and flattened to keep them in shape. Silk crepeline was under-layed and stitched to the damaged areas with silk-hair threads. Each costume was individually stored in a tray made of paulownia wood and flat textiles were rolled up in paper cylinders with 6 and 10 cm in diameter. Thymol was used to prevent microorganisms.

• Journal of Institute of Control, Robotics and Systems
• /
• v.13 no.5
• /
• pp.434-443
• /
• 2007

Presently, the exploration of an unknown environment is an important task for thee new generation of mobile service robots and mobile robots are navigated by means of a number of methods, using navigating systems such as the sonar-sensing system or the visual-sensing system. To fully utilize the strengths of both the sonar and visual sensing systems. This paper presents a technique for localization of a mobile robot using fusion data of multi-ultrasonic sensors and vision system. The mobile robot is designed for operating in a well-structured environment that can be represented by planes, edges, comers and cylinders in the view of structural features. In the case of ultrasonic sensors, these features have the range information in the form of the arc of a circle that is generally named as RCD(Region of Constant Depth). Localization is the continual provision of a knowledge of position which is deduced from it's a priori position estimation. The environment of a robot is modeled into a two dimensional grid map. we defines a vision-based environment recognition, phisically-based sonar sensor model and employs an extended Kalman filter to estimate position of the robot. The performance and simplicity of the approach is demonstrated with the results produced by sets of experiments using a mobile robot.

• Journal of the Korean Magnetics Society
• /
• v.21 no.3
• /
• pp.99-103
• /
• 2011

In this study, we have performed systematical FEM analysis for design of open-ended 3-layer magnetic shield. For the simulation to calculated shielding factors, the relative permeability was varied in the range of $2{\times}10^3\sim1{\times}10^5$, and the length of the magnetic cylinders and length difference between layers were changed. We found that the shielding factor of -60 dB were obtained with the relative permeability of over 20000 and the lengths of magnetic layers of 40 cm, 45 cm and 50 cm, and the uniform magnetic field could be obtained in the range of $10cm{\times}10cm-\phi$.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.9 no.1
• /
• pp.56-63
• /
• 1985

Methods for evaluating the added masses of square and hexagonal structures with fluid gap are presented. For a sufficiently small fluid gap, an analytical expression for the added mass is found using the method of matched asymptotic expansion. Experimental data and numerical results using finite element method are also obtained for various sizes of fluid gap. It is shown that added masses increase in inverse proportion to the fluid gap as it becomes smaller. Experimental data, theoretical and numerical results are in good agreement.

• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.2
• /
• pp.61.2-61.2
• /
• 2016

Nuclear rings at centers of barred galaxies exhibit strong star formation activities. They are thought to undergo gravitational instability when sufficiently massive. We approximate them as rigidly-rotating isothermal objects and investigate their gravitational instability. Using a self-consistent eld method, we first construct their equilibrium sequences specified by two parameters: ${\alpha}$ corresponding to the thermal energy relative to gravitational potential energy, and $R_B$ measuring the ellipticity or ring thickness. The density distributions in the meridional plane are steeper for smaller ${\alpha}$, and well approximated by those of infinite cylinders for slender rings. We also calculate the dispersion relations of nonaxisymmetric modes in rigidly-rotating slender rings with angular frequency ${\Omega}$ and central density ${\rho}_c$. Rings with smaller are found more unstable with a larger unstable range of the azimuthal mode number. The instability is completely suppressed by rotation when ${\Omega}$ exceeds the critical value. The critical angular frequency is found to be almost constant at $0.7(G{\rho}_c)^{1/2}$ for ${\alpha}$ > 0.01 and increases rapidly for smaller ${\alpha}$. We apply our results to a sample of observed star-forming rings and confirm that rings without a noticeable azimuthal age gradient of young star clusters are indeed gravitationally unstable.

• Fibers and Polymers
• /
• v.4 no.1
• /
• pp.15-19
• /
• 2003

The self-assembly of asymmetric ABC triblock copolymers in the ordered structure is investigated using an isothermal-isobaric molecular dynamics simulation. Unlike symmetric A BC triblock copolymers, more fascinating mophologies are observed in asymmetric ones because of a larger difference of incompatibility between the components. Various modes of self-assembly in assymmetric ABC triblock copolymers are also observed depending on the block composition. When the composition of block A Is changed from 0.125: to 0.25 at the same $f_B$ : 0.25, the morphological transition from the “cylinder in cylinder” to “cylinders at cylinder” structure is observed in the simulation. In the case of ABC triblocks with $f_B$=0.5, a lamellar-type structure is changed to a cylinder-type structure with increasing the length of block A. When the midblock length increases further to $f_B$=0.625, the “spheres on cylinder” structure is observed in both the $A_{10}$$B_{50}$$C_{20}$ and $A_{20}$$B_{50}$$C_{10}$ triblocks. From these results, the phase diagram of ABC triblock copolymers can be constructed.

• 연구논문집
• /
• s.29
• /
• pp.57-67
• /
• 1999

This paper presents the status quo of the development of a piecewise bendable switch system for the urban transit MagLev. MagLev system as well as railroad requires switch systems to reach its destination. Requirements of the switch system for commercial lines are high speed operation satisfying about 2-3 minute headway and system reliability, etc. Parallel moving type switch system was installed on the test track of urban transit MagLev in KIMM. In this system, switch operation from one position to another can be done in about 90 seconds. Therefore, we concluded that this system can not satisfy the headway for the commercial lines. We decided to develop a high speed piecewise bendable switch system in which switching can be done in 20 seconds. Designed switch system is very complicated in view of operating mechanism. It consists of 11 segmented girder beams driven by hydraulic cylinders. To gain the idea of a piecewise bendable switch system, we manufactured and tested a 1/5 scale switch model. We are going to construct a full scale piecewise bendable switch system next year.