• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.683-686
• /
• 2002

The hydrodynamic instability of the three-dimensional boundary-layer over a rotating disk has been numerically investigated for three cases flows using linear stability theory (i.e. Rossby number, Ro = -1, 0, and 1). Detailed numerical values of the disturbance wave number, wave frequency, azimuth angle, radius (Reynolds number, Re) and other characteristics have been calculated for $K{\acute{a}}rm{\acute{a}}n$, Ekman and $B{\"{o}}ewadt$ boundary-layer flows. Neutral curves for these flows are presented. Presented are the neutral stability results concerning the two instability modes (Type I and Type II) by using a two-point boundary value problem code COLUEW that was based upon the adaptive orthogonal collocation method using B-spline. The prediction from the present results on both instability modes among the three cases agrees with the previously known numerical and experimental data well.

• Proceedings of the IEEK Conference
• /
• 1999.11a
• /
• pp.27-30
• /
• 1999

A spatio-temporal vector channel model is introduced for the position location (PL) estimation problem for CDMA cellular system environment. Two common ways for the PL make use of the AOA (Angle Of Arrival) and TDOA (Time Difference Of Arrival) from a subscriber to the multiple sensors (base stations). In this paper, we applied the derived vector channel to simulate the multipath channel for the angle of the signal arrival in CDMA systems. Cross-correlation method is a good candidate among other direction finding algorithms available in literature, especially in wideband modulation as in the CDMA system. The PL estimation errors are evaluated for different channels, which are obtained as a parameter of scattering radius of the suggested model. We noted that the number of sensors (base-stations) are related to the PL errors in favor of the available data.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.17 no.2
• /
• pp.140-149
• /
• 1988

The problem of heat and mass transfer accompanying the absorption of water vapor into LiBr-$H_2O$ liquid solution flowing over the outside of the horizontal cylinder was theoretically studied to understand the absorption process occuring in the absorber of the absorption heat pump. Numerical results are presented for various quantities of interest relating to temperature, concentration, heat flux and mass flux. Also, the effects of mass flowrate, initial average velocity, and the radius of the cylinder were investigated.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1998.10a
• /
• pp.212-218
• /
• 1998

This paper presents a study of the elastohydrodynamic lubrication of elliptical contacts where lubricant entrainment coincides with the major axis of the Hertzian contact ellipse. A finite difference method and the Newton-Raphson method are applied to analyze the problem. Film contours and pressure distributions are compared with the results for lubricant entrainment coincides with the minor axis. Variations of the minimum and central film thicknesses with the radius ratio are also examined. Therefore, the present numerical scheme can be used generally in the analysis of the EHL of elliptical contacts where the lubricant entraining vector did not coincide with either of the principal axis of the conjunction.

• Journal of The Korean Astronomical Society
• /
• v.40 no.4
• /
• pp.91-97
• /
• 2007

The Fokker-Planck (FP) model is one of the commonly used methods for studies of the dynamical evolution of dense spherical stellar systems such as globular clusters and galactic nuclei. The FP model is numerically stable in most cases, but we find that it encounters numerical difficulties rather often when the effects of tidal shocks are included in two-dimensional (energy and angular momentum space) version of the FP model or when the initial condition is extreme (e.g., a very large cluster mass and a small cluster radius). To avoid such a problem, we have developed a new integration scheme for a two-dimensional FP equation by adopting an Alternating Direction Implicit (ADI) method given in the Douglas-Rachford split form. We find that our ADI method reduces the computing time by a factor of ${\sim}2$ compared to the fully implicit method, and resolves problems of numerical instability.

• Structural Engineering and Mechanics
• /
• v.51 no.3
• /
• pp.361-375
• /
• 2014

The main aim of this paper is to investigate the relationship between thickness and height of the axially symmetric cylindrical reinforced concrete (RC) walls by the help of a meta-heuristic optimization procedure. The material cost of the wall which includes concrete, reinforcement and formwork, was chosen as objective function of the optimization problem. The wall thickness, compressive strength of concrete and diameter of reinforcement bars were defined as design variables and tank volume, radius and height of the wall, loading condition and unit cost of material were defined as design constants. Numerical analyses of the wall were conducted by using superposition method (SPM) considering ACI 318-Building code requirements for structural concrete. The optimum wall thickness-height relationship was investigated under three main cases related with compressive strength of concrete and density of the stored liquid. According to the results, the proposed method is effective on finding the optimum design with minimum cost.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.24 no.1
• /
• pp.98-102
• /
• 2015

This paper proposes an autonomous navigation method for a nonholonomic mobile robot, based on the generalized Voronoi diagram (GVD). We define the look-ahead point for a given motion constraint to determine the direction of motion, which solves the problem of a minimum turning radius for the real nonholonomic mobile robot. This method can be used to direct the robot to explore an unknown environment and construct smooth feedback curves for the nonholonomic robot. As the trajectories can be smoothed, the position of the robot can be stabilized in the plane. The simulation results are presented to verify the performance of the proposed methods for the nonholonomic mobile robot. Furthermore, this approach is worth drawing on the experience of any other mobile robots.

• Proceedings of the KSME Conference
• /
• 2001.06a
• /
• pp.837-841
• /
• 2001

The column-type sensing element in building and mechanical construction parts was designed as three forces and three moments sensor by attaching strain gages approximately. Compared to conventional multi-component sensor, the designed sensor can solve the problem about low stiffness and high cost. The radius of the column was designed analytically and compared with finite element analysis. The coupling errors between components were minimized by using addition and subtraction procedure of signals. The fabricated sensor was tested by using a deadweight force standard machine and a six-component force calibration machine in Korea Research Institute of Standards and Science(KRISS). The calibration showed that the multi-component force/moment sensor had coupling error less than 19.8 % between $F_x$ and $M_y$ components, and 9.0 % in case of other components.

• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.339-344
• /
• 2000

In this study, the fracture phenomena of optical disks are discussed and then some recommendations are presented to prevent the fracture. The fracture occurs when disks have crack on the inner radius of the disks. Since the crack growth and the fracture result from the stress concentration on the tip of the crack, a measure should be taken to overcome the stress concentration. This problem can be resolved by the structural modification of a disk. This study proposes 3 types of improved optical disks, which are robust to the disk fracture due to the high spinning speed of a disk. The first type is a disk reinforced by wire rings, the second type is a disk added by texture fibers, and the third type is a rubber-coated disk.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1068-1073
• /
• 2003

Method for contact failure mitigation is studied in this paper. The focus is laid on the contact shape that eventually influences the internal stresses. Contact mechanics is consulted within the frame of plane problem. Hertzian contact, rounded punch and uniform traction profiles are considered. Frictional as well as frictionless contact is also considered. As results, the higher traction profile induced by the rounded punch reveals the greatest among the considered shapes. Therefore, it is suggested to increase the edge radius as large as possible if a contact body of punch shape needs to be designed. It is also found that uniform traction cannot always provide the solution of contact failure mitigation.