• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.625-633
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• 2015

The effect of altitude on thermal conduction, surface temperature, and thermal radiation of partial arc was investigated on the basis of molecular gas dynamics to facilitate a deep understanding of the pollution surface discharge mechanism. The DC flashover model was consequently modified at high altitude. The validity of the modified DC flashover model proposed in this paper was proven through a comparison with the results of high-altitude simulation experiments and earlier models. Moreover, the modified model was found to be better than the earlier modified models in terms of forecasting the flashover voltage. Findings indicated that both the thermal conduction coefficient and the surface thermodynamics temperature of partial arc had a linear decrease tendency with the altitude increasing from 0 m to 3000 m, both of which dropped by approximately 30% and 3.6%, respectively. Meanwhile, the heat conduction and the heat radiation of partial arc both had a similar linear decrease of approximately 15%. The maximum error of DC pollution flashover voltage between the calculation value according to the modified model and the experimental value was within 6.6%, and the pollution flashover voltage exhibited a parabola downtrend with increasing of pollution.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.216-221
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• 2002

A spherical Earth surface is used fur realistic analysis of the geometrical performance characteristics about the variation of satellite altitude and 2-dimensional line-of-sight(LOS) tilt angle in a satellite imager using Time Delay and Integration(TDI) technique with fixed integration time. In the spherical Earth surface model TDI synchronization using LOS tilt is investigated as a solution to compensate geometric performance degradation due to altitude decrease. This result can be used fur a TDI CCD imager with variable integration time in a certain as well.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.5
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• pp.683-688
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• 2009

A research was conducted about the Reynolds number effect on the projectile with an altitude change. The atmosphere conditions change in accordance with an altitude change. It effects the Reynolds number. To confirm how the phenomena affect the trajectory of the projectile, a computer program is designed with an altitude and a range considered. The MISSILE DATCOM which is based on the semi-empirical method was utilized to get aerodynamic coefficients. The result shows that the Reynolds number considerably changes as the altitude change. It causes to change the drag coefficient of the projectile. As the Reynolds number decreases, the skin friction drag increases significantly. It causes to decrease the maximum altitude and the range.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.5
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• pp.383-388
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• 2021

Air-breathing engines used in aircraft have a performance limit as the altitude increases, and this determines the service and absolute ceiling altitude. The method of maintaining altitude and speed in a fixed-wing aircraft in level flight using classical control method is generally using thrust for speed increase/deceleration and pitch attitude for altitude increase/decrease. If this method is used near the service ceiling altitude, increasing the pitch to reduce the altitude error results in a speed reduction. Therefore, it is necessary to use a control method that maintains the speed first using the pitch attitude. Especially in the case of unmanned aerial vehicles, these two methods should be automatically available at the right time. In this paper, we propose a method of switching the speed and altitude maintenance algorithm near service ceiling altitude.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.3
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• pp.228-233
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• 2014

Reduction of the atmospheric pressure in high altitude affects brake booster system which was operated by the difference between the intake pressure and the atmospheric pressure. So, braking system can not stably perform due to decrease of brake boost pressure. In this study, effects of altitude change on engine intake pressure was analyzed by prediction model of engine intake pressure which was studied previously. And engine intake pressure was simulated by simulation model in various driving conditions and environmental conditions.

• Journal of The Geomorphological Association of Korea
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• v.19 no.2
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• pp.99-111
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• 2012

The purpose of this study is to identify the change of geographical (or geomorphological) location environment of the dwelling site and its cause in Daejon Basin during transition from the Bronze Age to the Proto Three Kingdoms Period. In order to achieve this goal, it was divided into (1) 'comparison of the total number of dwelling sites of a group of remains (or high-density dwelling remains)' and (2) 'comparison of the total number of dwelling sites in certain remains including locations of dwelling of two periods' and location environment was compared to each other in aspects of altitude, gradient, 'distance from the river of water available for use' and 'the difference between the highest altitude and lowest altitude of river bed of water available for use' based on change of period. The results were as follows: 1. looking at a change of individual factors, the altitude was elevated and the gradient was increased. The distance from the river of water available for use was decreased or increased in case of 'small scale river' and it was very little difference or increased in case of 'medium scale river'. The difference between the highest altitude and lowest altitude of river bed of water available for use was increased in case of 'small scale river' and it was increased or decreased in case of 'medium scale river'. If comparing the individual factors to each other, the increase and decrease of altitude, gradient and the difference between the highest altitude and lowest altitude of river bed of water available for use have the similar pattern. Especially, it was shown that the increase of gradient affected the increase of altitude and the difference between the highest altitude and lowest altitude of river bed of water available for use. In addition, it was shown that the increase and decrease of distance from the river of water available for use had the different pattern from those of altitude, gradient and 'the difference between the highest altitude and lowest altitude of river bed of water available for use'. 3. With above results, it was thought that combination of micro landform characteristics (eg. Characteristics of gradient) of low hills distributed within Daejeon Basin and rich aquatic environment surrounding the low hills affected the selection of location of dwelling sites at the time. Especially, it was shown that 'gradient and distance from the river of water available for use' were relatively more important factors for the inhabitants at the time to select the location of dwelling sites compared to 'altitude and difference between the highest altitude and lowest altitude of river bed of water available for use' upon selecting the location of dwelling.

• Korean Journal of Remote Sensing
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• v.18 no.2
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• pp.91-96
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• 2002

The performance characteristics of a satellite imager using a Time Delay and Integration(TDI) Charge Coupled Device (CCD) with fixed integration time is investigated for the variation of satellite altitude and tilt angle. In consequence of the investigation TDI synchronization using tilt imaging is proposed as a solution to compensate geometric performance degradation due to altitude decrease. The tilt angle optimized for the TDI synchronization at decreased altitude is presented. This result can be used for a TDI CCD imager with variable integration time in a certain range as well.

• Journal of Astronomy and Space Sciences
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• v.40 no.1
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• pp.35-44
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• 2023

Surveillance and reconnaissance intelligence in the space domain will become increasingly important in future battlefield environments. Moreover, to assimilate the military provocations and trends of hostile countries, imagery intelligence of the highest possible resolution is required. There are many methods for improving the resolution of optical satellites when observing the ground, such as designing satellite optical systems with a larger diameter and lowering the operating altitude. In this paper, we propose a method for improving ground observation resolution by using an optical system for a previously designed low orbit satellite and lowering the operating altitude of the satellite. When the altitude of a satellite is reduced in a circular orbit, a large amount of thrust fuel is required to maintain altitude because the satellite's altitude can decrease rapidly due to atmospheric drag. However, by using the critical inclination, which can fix the position of the perigee in an elliptical orbit to the observation area, the operating altitude of the satellite can be reduced using less fuel compared to a circular orbit. This method makes it possible to obtain a similar observational resolution of a medium-sized satellite with the same weight and volume as a small satellite. In addition, this method has the advantage of reducing development and launch costs to that of a small-sized satellite. As a result, we designed an elliptical orbit. The perigee of the orbit is 300 km, the apogee is 8,366.52 km, and the critical inclination is 116.56°. This orbit remains at its lowest altitude to the Korean peninsula constantly with much less orbit maintenance fuel compared to the 300 km circular orbit.

• Journal of The Korean Society of Grassland and Forage Science
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• v.20 no.3
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• pp.155-160
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• 2000

This syudy was conducted to increase the utility of forage rye which are suitable to be cultivated at high altitude Taekwllyong area. For that purpose two cultivars of rye (winter-more, kool-glazer) were cultivated for 3years using a randomized block design with 3 replications. The dry matter digestibility (DMD) was evaluated with the pelleted rye hay produced by adding sodium hydroxide and then the TDN value was calculated by the DMD. By adding NaOH, DMD and TDN value of rye pellets (Y=46.92+ 1.8X, ~ 0 . 9 7 )w ere increased significantly (p<0.05) and NDF (neutral detergent fiber) decrease significantly. However, ADF (acid detergent fiber) and lignin did not significantly decrease (p<0.05). Rye could be cultivated as a second crop after com at high altitude area in the same year and pelleted with NaOH in order to increase the nutritive values (p< 0.05). (Key words : Dry matter digestibility (DMD), Forage rye, NDF, ADF, Sodium hydroxide)

• Korean Journal of Remote Sensing
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• v.20 no.2
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• pp.117-124
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• 2004

A spherical earth surface is used for realistic analysis of the geometrical performance characteristics generated by 2-dimensional line-of-sight (LOS) tilt of the satellite imager using the Time Delay and Integration(TDI) technique. A 2-dimensional LOS tilt ever the spherical Earth surface is proposed to compensate geometric performance degradation caused by the satellite altitude decrease below the normal operation altitude. The compensation can be achieved by TDI re-match without degradation of modulation transfer function and with ground sample distance slightly increased. Effective methods of LOS tilt for the compensation are investigated. This study can be useful for mission assurance and flexibility in imager operation.