Park M.-J.,KAIST |
Jang J.-S.,ADD |
ARF 2015 - 4th Asian-Australian Rotorcraft Forum | Year: 2015
In recent years, UAV has been developed and researched for a wide variety of applications such as drone deliveries, broadcasting, scouting, crop dusting, firefighting, etc. In order to use UAV's widely, the investigation of aeroacoustic characteristics exactly should be conducted. The noise prediction method of the ducted fan UAV with complicated geometry was performed. Generally, in order to increase the calculation efficiency, ducted fan UAV without struts which have the function to fix a fuselage to a duct is simulated. However, the numerical prediction of noise and aerodynamics were different according to the strut existence and nonexistence. In case of aerodynamic analysis, total thrust is similar with and without struts due to increase in the thrust of blade as much as the drag of struts in strut model. In case of noise analysis, without the struts, tonal noise has occurred at different frequency when compared with that of experimental values. However, with the struts, the dominant tonal noises were in good agreement with the BPF(Blade Passage Frequency) of the experimental results. In the ducted fan UAV system, the noise sources were found using suggested noise contribution contour in this paper. Thus, the way of noise reduction can be suggested using numerical results compared with the measured noises. © 2015 by the Asian-Australian Rotorcraft Forum. All rights reserved. All rights reserved.
Yang E.,ADD |
2011 3rd International Asia-Pacific Conference on Synthetic Aperture Radar, APSAR 2011 | Year: 2011
ΣΔ STAP which uses sum and difference beams of an antenna has significant practical advantages in clutter suppression. On the other hand, when we use ΣΔ STAP for target detection, we use mono-pulse strategy to estimate off-axis target angle. However, signals used for target estimation are contaminated by clutter and induce erroneous result. The conventional ΣΔ STAP is modified to estimate target angle accurately and to improve target detectability, simultaneously. © 2011 KIEES.
Lee M.-S.,ADD |
Lee C.-H.,Chungnam National University
IEICE Transactions on Information and Systems | Year: 2014
For battery based real-time embedded systems, high performance to meet their real-time constraints and energy efficiency to extend battery life are both essential. Real-Time Dynamic Voltage Scaling (RT-DVS) has been a key technique to satisfy both requirements. This paper presents EccEDF (Enhanced ccEDF), an efficient algorithm based on ccEDF. ccEDF is one of the most simple but efficient RT-DVS algorithms. Its simple structure enables it to be easily and intuitively coupled with a real-time operating system without incurring any significant cost. ccEDF, however, overlooks an important factor in calculating the available slacks for reducing the operating frequency. It calculates the saved utilization simply by dividing the slack by the period without considering the time needed to run the task. If the elapsed time is considered, the maximum utilization saved by the slack on completion of the task can be found. The proposed EccEDF can precisely calculate the maximum unused utilization with consideration of the elapsed time while keeping the structural simplicity of ccEDF. Further, we analytically establish the feasibility of EccEDF using the fluid scheduling model. Our simulation results show that the proposed algorithm outperforms ccEDF in all simulations. A simulation shows that EccEDF consumes 27% less energy than ccEDF. Copyright © 2014 The Institute of Electronics, Information and Communication Engineers.
Jeong S.,Agency for Defense Development |
26th Electric Vehicle Symposium 2012 | Year: 2012
This paper describes development process of a driving cycle for a hybrid electric tactical wheeled vehicle. The process is composed of documentation of a mission profile, acquisition of driving simulation data and generation of driving cycle by data processing. The document of a mission profile describes a military operation including vehicle maneuver and operation of mission equipment. A virtual driving simulation environment was built and used to acquire driving simulation data. Driving simulation was carried out 5 to 10 times in order to increase the reliability of data. The most suitable data was selected and the final driving cycle was generated after data processing. The driving cycle developed in this research is used to improve the fuel economy of a hybrid electric tactical wheeled vehicle.
Oh H.-U.,Chosun University |
Lee K.-J.,ADD |
Aerospace Science and Technology | Year: 2013
To enhance the pointing performance by isolating disturbances induced by a spaceborne payload mounted cryogenic cooler during the on-orbit operation, a passive launch and on-orbit vibration isolation system has been proposed and investigated. The isolation system is also effective for reducing the transmitted launch loads to the cooler. In order to demonstrate the effectiveness of the isolation system, launch environment tests such as sine, random and shock tests and a micro-vibration measurement test of the cooler combined with the isolator have been performed. The test results indicate that the isolation system guarantees both the structural safety of the cooler under the launch environment and the micro-vibration isolation of the cooler under the on-orbit condition. © 2012 Elsevier Masson SAS. All rights reserved.
Bang K.-H.,Korea University |
Chung G.-Y.,Korea University |
Korean Journal of Chemical Engineering | Year: 2011
The preparation of C/C composites by the chemical vapor infiltration (CVI) of the pyrolysis carbon from propane was studied. Pyrolysis carbon was deposited at 30 torr and at temperatures between 1,173 and 1,233 K. The rate of carbon deposition increased slightly with time. The main gas products in the exit gas were methane, ethylene, and acetylene. The fraction of ethylene decreased and that of acetylene increased with the reaction temperature and the propane concentration. The produced propyl radicals reacted further at a high temperature and at a high propane concentration. These trends were similar to those of the reported data. Changes of the shapes of deposited carbon in the pores of preform were confirmed with SEM photos. The mathematical modeling of the system with the deposition rate constant from the reference estimated experimental data well. © 2010 Korean Institute of Chemical Engineers, Seoul, Korea.
Bang B.H.,Korea University |
Yoon S.S.,Korea University |
Kim H.Y.,Korea University |
Heister S.D.,Purdue University |
And 2 more authors.
International Journal of Multiphase Flow | Year: 2011
A two-phase flow model using the boundary element method was applied to investigate the physics of a liquid drop impacting onto a solid, dry plate. Xu et al. showed that air pressure plays an important role in splashing: as air pressure was reduced, splashing of an ethanol drop with a Weber number of 838 was suppressed. This remarkable observation provided the motivation for the current modeling effort. We numerically investigate how air pressure affects the behavior of an impacting drop. Surveying both inside and outside the impacting drop, velocities of both the liquid and gas are computed. Simulations show that gas speed, as it is displaced by the falling drop, is more than three times higher than the incoming drop speed. Air entrainment induced by the displaced gas seems to be an important contributor to corona formation, which always precedes any instability, fingering, or splashing of the liquid. To describe drop-impact phenomena, the maximum spreading diameter of the drop and the topology of the impacting fluid are reported as functions of Weber number and gas density. © 2010 Elsevier Ltd.
PubMed | ADD, Korea Electronics Technology Institute and Seoul National University of Science and Technology
Type: Journal Article | Journal: Microscopy (Oxford, England) | Year: 2015
The scanning electron microscope is used in various fields to go beyond diffraction limits of the optical microscope. However, the electron pathway should be conducted in a vacuum so as not to scatter electrons. The pretreatment of the sample is needed for use in the vacuum. To directly observe large and fully hydrophilic samples without pretreatment, the atmospheric scanning electron microscope (ASEM) is needed. We developed an electron filter unit and an electron detector unit for implementation of the ASEM. The key of the electron filter unit is that electrons are transmitted while air molecules remain untransmitted through the unit. The electron detector unit collected the backscattered electrons. We conducted experiments using the selected materials with Havar foil, carbon film and SiN film.
Oh H.-U.,Chosun University |
Lee K.-J.,ADD |
Transactions of the Japan Society for Aeronautical and Space Sciences | Year: 2013
This study demonstrates the isolation performance of a non-linear passive isolator to enhance the pointing performance through isolating disturbances induced by a spaceborne cryogenic cooler. In this paper, a non-linear passive isolation system with varying stiffness under launching and under on-orbit conditions to attenuate the micro-vibration of the cooler is proposed. The isolation system provides low stiffness for small excitation of the cooler during on-orbit operation and high stiffness when the excitation range is relatively larger under the launch environment. The performance of the passive isolation system is investigated through both a launch environment test and a micro-vibration measurement test of the cooler combined with non-linear passive isolators. © 2013 The Japan Society for Aeronautical and Space Sciences.
Add | Date: 2010-10-20
The invention relates to an electronic monitoring system enabling real fuel consumption and CO_(2 )emissions to be calculated for a machine in motion, stopped, or working, with optional exclusion of thefts of fuel, the system comprising both a sentinel onboard a machine that itself comprises at least an engine, a tank, an electrical power supply circuit, and also a non-mobile surveillance tool to which the onboard sentinel is suitable for being connected by wire or wireless means.