• Journal of Advanced Navigation Technology
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• v.25 no.3
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• pp.211-216
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• 2021

Multiple UAV System has been used for various purposes such as reconnaissance, networking and aerial photography. In such systems, it is essential to form and maintain the formation of multiple UAVs. This paper proposes the algorithm that produces an autonomous distributed control for each vehicle for a flexible formation. This command is a repulsive force in the form of the second-order system by the nearest UAV or mission area. The algorithm uses the relative position/speed through sensing and communication for calculating the command without external intervention. The command allows each UAV to follow the reference distance and fill the mission area as densely as possible without overlapping. We determine the reference distance via optimization technique solving the packing problem. The mission area comprises the desired formation outline and can be set flexibly depending on the mission. Numerical simulation is carried out to verify the performance of the proposed algorithm under a complex and flexible environment. The formation is formed in 26.94 seconds and has a packing density of 71.91%.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.691-697
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• 2022

In this work, a straightforward component design of a direct current (DC) relay equipped in electric vehicles is discussed. The work aims to provide and evaluate effective measures for reducing high-frequency sound from the DC relay carrying electric power. From the operation experiments for the relay, it is observed that noise is caused by the resonance from the forced vibration by the electromagnetic repulsive force originating at the area of electric contacts with a resonance frequency of around 710 Hz ~ 730 Hz. A finite element model for the relay was established to conduct vibration mode analysis, consisting of stationary and movable contacts and a contact spring. Vibration mode analysis indicates that in the resonance frequency, the movable contact with two-point contacts experiences rotational vibration mode. For the proposed relay with a three-point contact, vibration mode analyses give reasonable results of reducing noise at that frequency. Furthermore, for the fabricated relays with the three-point contact, similar results have been obtained. In conclusion, one can see that the proposed measures provide one of the feasible solutions to the reduction of relay noise.

• Journal of the Korean Vacuum Society
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• v.21 no.6
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• pp.312-321
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• 2012

The electric potential of plasma column is measured with the high voltage probe in a pair of atmospheric plasma jets operated by AC-voltage. According to the polarity of voltage applied to the electrodes, the polarity of plasma column potential has the same polarity of applied voltage. The high potential of plasma column at the side of high voltage electrode is decreased linearly along the plasma column to the ground side. Therefore, the plasma column seams to be a kind of resistor whose resistivity is a few 10s $M{\Omega}/m$. In the experiment of double-jets system, the polarity of plasma potential is verified to be the same polarity to the applied voltage. When the different voltage polarities are applied to the electrodes of double plasma jets, the attractive force is acted between two plumes at the merged plasma and the plasma potential is measured to be low as a few 10s V. When the same polarity of voltage is applied to the electrode, the repulsive force is acted and the plasma potential is measured to be high as a several 100s V at the merged plumes. In the exposure of plasma plume on the bio-substrate with the double plasma jets, the electric shock and thermal damage might be proportional to the plasma power which is the multiplication of the plasma potential and the plasma current.

• Journal of Korean Society of Transportation
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• v.34 no.5
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• pp.409-420
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• 2016

Korea is expected to enter 'Super Aged Society' in 2026. However, as walking is the very basic human right of mobility, securing safe and convenient moving of elderly people comprising the majority of transportation vulnerable is thought to be the most basic welfare, which can be easily neglected. From this perspectives, this study provides the walking characteristics of elderly people to be used in design of pedestrian facilities. The analysis of the measurements using Motion Analysis Systems shows that all walking factors of elderly people is 75% level of the younger group. Elderly group shows slower movement, reduced shoulder movement and increased ankle movement compared to the others. Also, foots are risen less and ground repulsive force is increased. Cluster analysis shows that the group of the elderly shows high variability inside the group, and 2 or 3 clusters can be formed with factors of Walking, Balance and Muscles. These walking characteristics can be used in designing pedestrian road, slope and step height of roadway facilities.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.26 no.2
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• pp.77-83
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• 2020

A series of foamed plastic sheets containing biomass (as HMR container) were developed via different foaming process temperatures, and their density, porosity, WVTR, and pore morphology were evaluated. Thermal stability of samples during re-heating the food in oven, change in morphology, density, porosity, and WVTR were investigated using a simulated thermal shock process according to MIL-STD-883E assay. As such, the pore size of samples was generally increased with increasing temperature of the foaming process. It can be explained that as foaming temperature increased, the viscosity of molten resins and the repulsive force against pore expansion decreased. In addition, an increase in the thermal shock cycle reduced the pore size and WVTR, while density increased because high temperature treatment that softened the sheet matrix was followed by a low temperature incubation, which contracted the matrix, thereby changing the physical and morphological properties of samples. However, an insignificant change in density was observed and WVTR tended to be decreased, indicating that as-prepared foamed plastic sheets could be used as a high thermal stable container for HMR application. Therefore, it found that the properties of newly developed HMR containers containing biomass were dependent on the foaming process temperature. Moreover, to better understanding of these newly developed containers, further investigations dealing with foaming process temperature based on various food items and cooking conditions are needed.