• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.4
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• pp.65-65
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• 1999

Heat transfer performance is studied for boiling and condensation of R-11 on integral-fin tubes. Nine tubes with trapezoidal integral-fins having fin densities from 748 to 1654fpm and 10,30 grooves and finned tubes with caves of 0.55 and 0.64 mm height respectively are tested. in case of condensation CFC-11 condensates at saturation stat of 32℃ on the outside surface cooled by inside cooling water flows. And in case of boiling the refrigerant evaporates at a saturation state of 1 bar on the outside tube surface and heat is supplied by hot water which circulates inside of the tube,. The tube having fin transfer coefficient concerns fin tubes with caves show higher valve than low fin tube having find density of 1299fpm and 30grooves. The overall heat transfer coefficient of fin tube with caves is about 5155 W/mK at 2.8m/s of water velocity, The value is abuot 2.7 times higher than plain tube and 1.3 times higher than low fin tube having fin density of 1299fpm and 30 grooves.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.5
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• pp.551-556
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• 2014

This paper proposes a balancing control and driving control of a bicycle robot based on dynamic modeling of the bicycle robot, which has been derived using the Lagrange equations. For the balancing control of the bicycle robot, a reaction wheel pendulum method has been adopted in this research. By using the dynamics equations of the bicycle robot, an LQR controller has been designed for a balancing and driving control of a bicycle robot. The performance of the balance control is verified experimentally before the driving control, which shows a stable posture within one degree vibrations. To show the dynamic characteristics of the bicycle robot during driving, a trapezoidal velocity trajectory is selected as the references. Through simulations and real experiments, the effectiveness of the proposed algorithm has been demonstrated.

• The Journal of Korea Robotics Society
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• v.12 no.3
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• pp.279-286
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• 2017

In this paper, we proposed a method to determine the acceleration/deceleration time of the motion for reducing the residual vibration caused by the resonance of the robot in the high-speed motion. The relationship between the acceleration/deceleration time and the residual vibration was discussed for the trapezoidal velocity profile by analyzing the time when the jerk happens. The natural frequency of the robot can be estimated in advance through the dynamics simulation. The simulation and experiment for both cases where the moving distance of the robot is long enough and the distance is short, are implemented in the 1-DOF linear robot. Simulation and experimental results show that when the acceleration/deceleration time is a multiple of the vibration period, the settling time and the amplitude of the residual vibration become less than when the time is not a multiple.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.3 s.180
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• pp.110-117
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• 2006

This paper presents the acceleration optimization of a high-speed LCD (Liquid Crystal Display) transfer system for the minimization of vibration. To reduce vibration is one of key requirements for the dynamic control of a high-speed LCD transfer system. In this paper, the concept of finite jerk (the first derivative of acceleration) has been introduced for realizing input acceleration. The profile of finite jerk has been optimized using a genetic algorithm so that vibration effect can be minimized. In order to incorporate a genetic algorithm, the dynamic model of a LCD transfer system which is realized by using the ADAMS software has been linked to the simulation system constructed by the MATLAB. The simulation results illustrated that the duration of finite jerk can be optimized so as to minimize the magnitude of vibration. It has been also shown that the acceleration optimization with finite jerk can make the high-speed motion of a LCD transfer system result in low vibration, compared with the conventional motion control with trapezoidal velocity profile.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.12
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• pp.50-56
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• 2007

Femtosecond laser ablation of the Invar alloy and hole drilling for a shadow mask are studied. We used a regenerative amplified Ti-sapphire laser with a 1kHz repetition rate, 184fs pulse duration and 785nm wavelength. Femtosecond laser pulse was irradiated on the Invar alloy with air blowing at the condition of various laser peak power. An ablation characteristic of the Invar alloy was appeared non-linear at $125J/cm^2$ of energy fluence. For the application to a shadow mask, the hole drilling of the Invar alloy with the cross section of a trapezoidal shape was investigated. The ablated micro-holes were characterized using an atomic force microscopy(AFM). The optimal condition of hole pattern f3r a shadow mask was $4\;{\mu}m$ z-axis feed rate, 0.2mm/s circular velocity, $26.4{\mu}J$ laser peak power. With the optimal processing condition, the fine circular hole shape without burr and thermal damage was achieved. Using the femtoseocond laser system, it demonstrates excellent tool for the Invar alloy micro-hole drilling without heat effects and poor edge.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1264-1274
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• 1994

Heat transfer performance of integral-fin tube which is used in recipro turbo refrigerator or high compact heat exchangers is studied. Eight tubes with trapezoidal shaped integral-fins having fin densities from 748 to 1654 fpm and 10, 30 internal grooves are tested. A plain tube having the same(inner and outer) diameter as the fin tubes is also tested for comparison. Pool boiling heat transfer of R-11 is investigated experimentally and theoretically on single tube arrangement. The refrigerant evaporates at saturation state of 1 bar on the outside tube surface and heat is supplied by not water which circulates inside of the tube. From the result of eight fin tubes and one plain tube tested, a tube having 1299 fpm-30 grooves shows the best performance. A maximum overall heat transfer coefficient of this tube is about 4000 $W/m^{2}K$ at 2.8m/s of water velocity. The maximum heat transfer enhancement (i.e., the ratio of overall heat transfer coefficients of finned to plain tubes)is about 2.1.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.624-628
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• 2008

Two-dimensional flow analysis is a way to provide good estimates for complex flow features in flow around islands and obstructions, flow at confluence and flow in braided channel. One of difficult problems to develop a two-dimensional hydraulic model is to analyze dry and wet area in river channel. Dry/wet problem can be encountered in river and coastal engineering problems, such as flood propagation, dam break analysis, tidal processes and so on. The objective of this study is to develop an accurate and robust two-dimensional finite element method with dry/wet technique in complex natural rivers. The dry/wet technique with Deforming Grid Method was developed in this study. The Deforming Grid Method was used to construct new mesh by eliminating of dry nodes and elements. The eliminated nodes and elements were decided by considering of the rising/descending velocity of water surface elevation. Several numerical simulations were carried out to examine the performance of the Deforming Grid Method for the purpose of validation and verification of the model in rectangular and trapezoidal channel with partly dry side. The application results of the model were displayed reasonable flow distribution.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1275-1287
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• 1994

Heat transfer performance improvement by fin and grooves is studied for condensation of R-11 on integral-fin tubes. Eight tubes with trapezoidal shaped integral-fins having fin densities from 748 to 1654 fpm and 10, 30 grooves are tested. A plain tube having the same diameter as the finned tubes is also tested for comparison. R-11 condenses at saturation state of $32^{\circ}C$ on the outside tube surface cooled by inside water flow. All of test data ate taken at steady state. Beatty and Katz's, Rudy's and Webb's theoretical models are used to predict the R-11 condensation coefficient of tubes having 748, 1024 and 1299 fpm. The predicted value by Betty and Katz's model is within 10% of experimental values in this study at fpm<1024 and Rudy's model predicted the experimental data at fpm>1024 within 15%. The tube having fin density of 1299 fpm and 30 grooves has the best overall heat transfer performance. This tube shows the overall heat transfer coefficient of 11500 $W/m^{2}K$,/TEX> at coolant velocity of 3.0m/s.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.6
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• pp.445-452
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• 2016

This paper discusses the dynamics and control problem of an overhead shuttle system (OSS), which is a critical part of the automated container terminal at a port. The main purpose of the OSS is efficient automated transport function of containers, which also requires high precision and safety. A major difference between the OSS and the conventional container crane is the configuration of the cables for hoisting the spreader. A mathematical model of the OSS is developed here for the first time, which results in an eight-pole system. Also, open loop control methods (trapezoidal and notch-type velocity profiles) are investigated so that the command input to the overhead shuttle produces the minimum possible sway of the payload. Simulation results show that the vibration suppression capability of the OSS is superior to the conventional overhead container crane, which is partially due to the cable configuration.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.6
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• pp.998-1005
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• 2010

Rifling force has a torsion impulse effect on the gun tube and thus generates undesirable vibration of the gun tube about its bore axis, putting additional stress on the projectile. High rifling force at the muzzle of the gun tube may adversely influence the trajectory of the projectile. And, the service life of rifled gun barrels is known to depend on the rifling force. Rifling force along the path of the projectile in the longitudinal direction of the gun tube can be described with projectile mass, projectile velocity, gas pressure curve and rifling angle. Under the same conditions, the character of the rifling of the gun barrel decisively influences the rifling force curve. To reduce the above mentioned harmful effect, locally distinct maximum of rifling force has to be avoided and maximum rifling force needs to be minimized. The best way to minimize the maximum rifling force is to design a rifling angle function so that the rifling force curve has a near trapezoidal shape. In this paper a new approach to make the optimal rifling force curve is described. The rifling angle determining the rifling force is developed by combined Fourier series and polynomial function to satisfy both the convergence and boundary condition matching problems.