• Bulletin of the Korean Mathematical Society
• /
• v.47 no.2
• /
• pp.433-442
• /
• 2010

$\tilde{G}(P,\;Q)$, a new generalization of the set of gap numbers of a pair of points, was described in [1]. Here we study gap numbers of local subring $R\;=\;\cal{K}\;+\;C$ of algebraic function field over a finite field and we give a formula for the number of elements of $\tilde{G}(P,\;Q)$ depending on pure gaps and R.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.9 no.3
• /
• pp.312-322
• /
• 1997

The natural convective flow in a two-dimensional square enclosure with horizontal partitions is investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and two identical partitions were positioned perpendicularly at the mid-height of the right and left walls, respectively. The governing equations are solved by using the finite element method with Galerkin method. Calculations are made for different partition lengths, partition conductivites, and Rayleigh numbers based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). An oscillatory motion of the natural convective flow is affected significantly by the variation of the gap width and Rayleigh number. When the gap width is comparatively short, the heat transfer rate is raised with the increase of the thermal conductivity of partitions. However, for sufficiently large gap widths at higher Rayleigh numbers, the average Nusselt numbers of the conductive partitions are smaller than those of the adiabatic partitions.

• Proceedings of the KIEE Conference
• /
• 1998.07a
• /
• pp.116-118
• /
• 1998

This paper describes a basic structure, analysis of characteristics and test method for high speed axial-gap BLDC motor. The newly designed axial-gap BLDC motor has 2-stator disks with 3-rotor disks and is easy to increase power capacity by increasing the numbers of stator/rotor disks. For high speed operating, the rotor is composed of light and strong strength material and has several separated magnets to reduce stress concentraction by centrifugal force.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.35 no.10
• /
• pp.1075-1081
• /
• 2011

A leak-detection method has been developed by measuring the pressure variation between the inner and outer heattransfer tubes of a double-wall tube steam generator. An experiment was carried out to measure the leak rate in the gap between two surfaces pressed with a hydraulic press in order to simulate the phenomena, and a correlation was determined for the leak rate in a micro gap. However, in the correlation, the gap width and friction coefficient were coupled with the surface roughness, which affects the two parameters. The two parameters were separated using a surface-contact model to develop a correlation for the friction coefficient. The correlation was compared with the existing correlations used for crack analysis. Although the applied ranges of Reynolds numbers were different, the developed correlation for Reynolds numbers of 0.1.0.35 showed similar tendencies to existing correlations used for higher Reynolds numbers.

• 전기의세계
• /
• v.21 no.4
• /
• pp.22-26
• /
• 1972

The vibration of power lines in rainy environments was researched using the concentric cylindrical gap to which D.C. voltage was applied. Consequently, it has been solidly conformed that the vibration of power lines begins at threshold voltage of corona, and that the amplitude of the vibration increases as the numbers of falling water drop per unit time increase. The vibration phenomen take place in straight line, elliptic or circular motion as voltage is applied the numbers of vibration nearay accord with the elastic vibrarion theory.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.6
• /
• pp.2046-2056
• /
• 1996

The constrained melting inside an isothermally heated horizontal cylinder has been repeatedly investigated in many studies only for the moderate Rayleigh numbers. This study extends the range of Rayleigh numbers to systematically investigate the transition during melting processes, especially focusing on the complex multi-cellular flow pattern and thermal instability. The enthalpy-porosity formulation, with appropriate source terms to account for the phase change, is employed. For low Rayleigh numbers, initially developed single-cell base flow keeps the flow stable. For moderate Rayleigh numbers, even small disturbances in balance between thermal buoyance force and viscous force result in branched flow structure. For high Rayleight numbers, Benard type convection is found to develop within a narrow gap between thee wall and the unmelted solid. The marginal Rayleigh number and the corresponding wave number are in excellent agreement with those from linear stability theory.

• ETRI Journal
• /
• v.39 no.4
• /
• pp.546-557
• /
• 2017

In a long term evolution-advanced (LTE-A) system, the traffic overload of machine type communication devices is a challenge because too many devices attempt to access a base station (BS) simultaneously in a short period of time. We discuss the challenge of the gap between the theoretical maximum throughput and the actual throughput. A gap occurs when the BS cannot change the number of preambles for a random access channel (RACH) until multiple numbers of RACHs are completed. In addition, a preamble partition approach is proposed in this paper that uses two groups of preambles to reduce this gap. A performance evaluation shows that the proposed approach increases the average throughput. For 100,000 devices in a cell, the throughput is increased by 29.7% to 114.4% and 23.0% to 91.3% with uniform and Beta-distributed arrivals of devices, respectively.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.1
• /
• pp.62-70
• /
• 2009

In this paper, the fluid flow behavior past a pair of rectangular cylinders placed in a two dimensional horizontal channel has been investigated using Lattice-Boltzmann Method(LBM). The LBM has built up on the D2Q9 model and the single relaxation time method called the Lattice-BGK(Bhatnagar-Gross-Krook)model. Streamlines, velocity, vorticity and pressure contours are provided to analyze the important characteristics of the flow field for a wide range of non dimensional parameters that present in our simulation. Special attention is paid to the effect of spacing(d) between two cylinders and the blockage ratio A(=h/H), where H is the channel height and h is the rectangular cylinder height. for different Reynolds numbers. The first cylinder is called upstream cylinder and the second one as downstream cylinder. The downstream fluid flow fields have been more influenced by its blockage ratios(A) and Reynolds numbers(Re) whereas the upstream flow patterns(in front of downstream cylinder) by the gap length(d) between two cylinders. Moreover, it is observed that after a certain gap, both upstream and downstream flow patterns are almost similar size and shape. The simulation result has been compared with analytical solution and it is found to be in excellent agreement.

• The Korean Journal of Ecology
• /
• v.23 no.1
• /
• pp.1-8
• /
• 2000

The pattern of gap regeneration and vegetational changes were carried out in gaps with different ages and in an intact forest in a Quercus mongolica (mongolian oak) stand located at Munsubong of Mt. Worak. In the early stage of gap formation, Lespedeza maximowiczii, Fraxinus rhynchophylla, Tripterygium regelii, Quercus mongolica, and Stephanadra incisa were dominants in shrub layers. The numbers of shrubs with smaller diameters at ground surface were abundant in the early stage of gap formation. On the other hand, as gap age increased, the number of individuals of Quercus mongolica and Fraxinus rhynchophylla forming tall tree layer decreased. However the diameter at ground surface of Quercus mongolica and Fraxinus rhynchophylla increased. There were few young Quercus mongolica, but those over 130 years old appeared in mature Quercus mongolica stands. The last regeneration episode ended about 130 years ago and the new one started 40 years ago in this study site. Considering the presence of Quercus mongolica below 40 years old in gap and the absence of Quercus mongolica from 40 to 130 years old in closed stand, it is concluded that Quercus mongilica forest is maintained by discontinued regeneration.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.5
• /
• pp.1262-1275
• /
• 1993

The drag reduction effect of a freely-rotatable splitter plate was experimentally investigated in the 2-D wake behind a circular cylinder. By arranging the splitter plate to be aparted with a certain gap from the cylinder, the splitter plate was able to be aligned itself automatically to the flow direction in the tested range of 6.2$\times$$10^3$$\times$$10^4$. As a result, it was proven that the self-adjustable splitter plate always reduced effectively the drag imposed on the body against any arbitrary flow directions. In a specific range of Reynolds numbers, the drag reduction effect was dependent not only on the length of the splitter plate but also on the gap distance between the plate and the trailing edge of the body. For a splitter plate with a specific length, there existed a unique optimum range of gap distance to obtain successfully the drag reduction effect, however, the optimum range of gap distance was dependent on Reynolds number.