• Journal of Astronomy and Space Sciences
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• v.32 no.3
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• pp.257-268
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• 2015

Characteristics of delta-V requirements for deploying an impactor from a mother-ship at different orbital altitudes are analyzed in order to prepare for a future lunar CubeSat impactor mission. A mother-ship is assumed to be orbiting the moon with a circular orbit at a 90 deg inclination and having 50, 100, 150, 200 km altitudes. Critical design parameters that are directly related to the success of the impactor mission are also analyzed including deploy directions, CubeSat flight time, impact velocity, and associated impact angles. Based on derived delta-V requirements, required thruster burn time and fuel mass are analyzed by adapting four different miniaturized commercial onboard thrusters currently developed for CubeSat applications. As a result, CubeSat impact trajectories as well as thruster burn characteristics deployed at different orbital altitudes are found to satisfy the mission objectives. It is concluded that thrust burn time should considered as the more critical design parameter than the required fuel mass when deducing the onboard propulsion system requirements. Results provided through this work will be helpful in further detailed system definition and design activities for future lunar missions with a CubeSat-based payload.

• Journal of Preventive Medicine and Public Health
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• v.6 no.1
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• pp.65-70
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• 1973

The study in the fild of medical instrument has been out of the interest by any of the life scientist in Korea. Especially, the recent developments in the medical electromics are remarkable one. Authors planned this study to ascertain the possibility of setting up the thermister thermometer with available accessories of demestic prouducts including some specific foreign assembly parts. By proper use of the thermister as one of the wheatstone bridge, we could detect tile resistance variations due to the environmental temperature variace. The intensive care for the bridge circuit and compensation scheme was required. The calibration procedure adopted here makes it possible to read the current as the temperature. The temperature range was determined by the examination and construction of the graph of the resistance-temperature variation. The determination of electric current, available ambient-temperature, the reduction of excessive current and self-heating of the thermister were made. Renovation in response-velocity was under taken too. This electronic thermometer was designed and assembled by the circuitry developed in accordance with the maximum availability of domestic products with some foreign-made parts. The result of our experiment showed very stable function and proved to be the most promissing item in the actual application as long as the thermistor thermister is concerned.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.9
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• pp.816-822
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• 2011

In this study, a program has been coded to evaluate propeller thrust rapidly following the effects of propeller shapes and the environmental facts. At this time, Semi-infinite Helical Vortices model is used to predict the induction factor which is introduced by Kawada. This program is based on Wrench's Propeller lifting line theory, and it can predict aerodynamic coefficients such as thrust, power, and efficiency. First of all, this program is compared with test results of NACA reports to verify of the reliability. Secondly, subsonic wind tunnel test has been performed following variations of propeller's rpm and inflow velocities.

• Journal of the korean Society of Automotive Engineers
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• v.2 no.1
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• pp.39-50
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• 1980

This paper presents the variations obtained in heat flow rate and engine performance of a four-stroke cycle Diesel engine when there were changes in the temperature of cooling water, compression ratio, injection timing of fuel, and other factors. Heat dissipation of engine cylinder was calculated by the heat transfer coefficient of Nusselt's empirical equation and the analysis of distribution of temperature in cylinder barrel was obtained by the finite element method of two-dimensional steady state heat conduction. In this experiment, the out side temperature of cylinder liner was measured by the data logger, and the temperature distribution of liner was computed by the analysis of triangular finite element model under the assumption due to surface heat flux of cylinder inner surface. The results obtained by this study are as follows. Under the given operating condition, the temperature distribution of cylinder liner by using finite element method shows that the mean temperature of barrel is in accordance with the experimental results of Eichelberg and temperature difference is lower than 4.23.deg. C. The heat dissipation of engine decrease in accordance with the decrease of piston mean velocity, compression ratio, and the increase of coolant temperature. Influence on the delay of injection timing of fuel brings about the decrease of heat rejection over the cylinder at constant test conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.17-26
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• 2005

Numerical investigation has been made on the aerodynamic characteristics of supersonic air-launching rocket, as a new concept launching mechanism. Parametric study on the variations of launching velocity, incident angle and mounting location of the rocket has been performed using three dimensional Euler equations. Influential factors at separating stage of the rocket were extracted through comprehensive analyses, and, the response surface models were constructed for those factors. From the study, the aerodynamic behavior of the air-launching rocket at supersonic speed and useful guidelines for the optimal mounting location of the rocket have been obtained.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.591-596
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• 2005

The objectives in the present study are to investigate that the enhancement heat transfer was experimentally measured and was compared with the acoustic pressure obtained by numerical analysis. From the results of the present study, a strong Fluid motion initiated by ultrasonic vibrations can affect heat and mass transfer. This phenomenon. called acoustic streaming, clearly observed by PIV measurement leads to increase in velocity of a Fluid which is a crucial physical concept to explain the enhancement heat transfer. The heat transfer coefficient is increased with increase in the ultrasonic intensities. The largest enhancement heat transfer (about 26%) is measured at the ultrasonic intensity of 300W. Acoustic streaming results from sudden acoustic pressure variations in the liquid. The results of numerical analysis reveal that acoustic pressure is increased by 59.5% at the ultrasonic intensity of 300W. The higher acoustic pressure near four ultrasonic transducers develops more intensive flow destroying the flow instability. Also, the profiles of acoustic pressure variation are consistent with those of enhancement heat transfer.

• Journal of Drive and Control
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• v.15 no.3
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• pp.8-13
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• 2018

This paper presents a phase portrait analysis-based safety control algorithm for excavators, using adaptive sliding mode control. Since working postures and material types cause the excavator's rotational inertia to vary, the rotational inertia was estimated, and this estimation was used to design an adaptive sliding mode controller for collision avoidance of the excavator. In order to estimate the rotational inertia, the recursive least-squares estimation with multiple forgetting was applied with the information of the swing velocity of the excavator. For realistic evaluation, an actual working scenario-based performance evaluation was conducted. Based on the estimated rotational inertia and an analysis of estimation errors, sliding mode control inputs were computed. The actual working scenario-based performance evaluation of the designed safety algorithm was conducted, and the results showed that the developed safety control algorithm can efficiently avoid a collision with an object in consideration of rotational inertia variations.

• The Journal of Korea Robotics Society
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• v.9 no.1
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• pp.67-77
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• 2014

An electric motor is the one of the most important parts in robot systems, which mainly drives the wheel of mobile robots or the joint of manipulators. According to the requirement of motor performance, the controller type and parameters vary. For the wheel driving motors, a speed tracking controller is used, while a position tracking controller is required for the joint driving motors. Moreover, if the mechanical parameters are changed or a different motor is used, we might have to tune again the controller parameters. However, for the beginners who are not familiar about the controller design, it is hard to design pertinently. In this paper, we develop a nominal robust controller model for the velocity tracking of wheel driving motors and the position tracking of joint driving motors based on the disturbance observer (DOB) which can reject disturbances, modeling errors, and dynamic parameter variations, and propose the methodology for the determining the least control parameters. The proposed control system enables the beginners to easily construct a controller for the newly designed robot system. The purpose of this paper is not to develop a new controller theory, but to increase the user-friendliness. Finally, simulation and experimental verification have performed through the actual wheel and joint driving motors.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.2
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• pp.77-89
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• 1991

Based on Boussinesq equation, the parabolic approximation equation is used to analyse the propagation of shallow water waves with currents over slowly varying depth. Rip currents (jet-like) occur mainly in shallow waters where the Ursell parameter significatly exceeds the range of application of Stokes wave theory. We employ the nonlinear parabolic approximation equation which is valid for waves of large Ursell parameters and small scale currents. Two types of currents are considered; relatively strong and relatively weak currents. The wave propagating over rip currents on a sloping bottom experiences a shoaling due to the variations of depth and current velocity as well as refraction and diffraction due to the vorticity of currents. Numerical analyses for a nonlinear theory are valid before the breaking point.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.285-295
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• 2001

The transport phenomena in a wedge-shaped pool of twin-roll continuous caster are affected by the various operating parameters such as the melt-feed pattern, roll-gap thickness, melt-superheat, and casting speed. A computer program has been developed for analyzing the two-dimensional, steady conservation equations for transport phenomena during twin-roll continuous casting process in order to estimate the turbulent melt-flow, temperature fields, and solidification in the wedge-shaped pool. The turbulent characteristics of the melt-flow were considered using a low-Reynolds-number K-$\xi$ turbulence model. Based on the computer program, the effects of the different melt-feed patterns, roll-gap thicknesses, and superheats of melt on the variations of the velocity and temperature distributions, and the mushy solidification were examined. The results show that the liquidus line is located considerably at the upstream region, and in the lower region appear the well-mixed melt-flow and most widely developed mushy zone. Besides, the variation of melt-flow due to varying melt-feed patterns, affects mainly the liquidus line, and scarcely has effects on the solidus line in the outlet region.