• International Journal of Aeronautical and Space Sciences
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• v.17 no.4
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• pp.631-640
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• 2016

A dual-mode power management for a hybrid-electric UAV with a cruise power of 200W is proposed and empirically verified. The subject vehicle is a low-speed long-endurance UAV powered by a solar cell, a fuel cell, and a battery pack, which operate in the same voltage bounds. These power sources of different operational characteristics can be managed in two different methods: passive management and active management. This study proposes a new power management system named PMS2, which employs a bypass circuit to control the individual power sources. The PMS2 normally operates in active mode, and the bypass circuit converts the system into passive mode when necessary. The output characteristics of the hybrid system with the PMS2 are investigated under simulated failures in the power sources and the conversion of the power management methods. The investigation also provides quantitative comparisons of efficiencies of the system under the two distinct power management modes. In the case of the solar cell, the efficiency difference between the active and the passive management is shown to be 0.34% when the SOC of the battery is between 25-65%. However, if the SOC is out of this given range, i.e. when the SOC is at 90%, using active management displays an improved efficiency of 6.9%. In the case of the fuel cell, the efficiency of 55% is shown for both active and passive managements, indicating negligible differences.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.7
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• pp.581-593
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• 2017

In order to develop high efficiency propeller for multicopter type UAV, we designed, analyzed and tested aerodynamic and structural dynamics. For the design of the high efficiency propeller, the optimum design method was applied for the determination of the airfoil and the three-dimensional planform is designed to reduce induced power of the propeller. The flight suitability of the derived shape was determined through structural design and analysis. The rotation test was performed to confirm the performance of the analytically designed shape. In this paper, we propose a procedural propeller design methodology using these design analysis test methods.

• Journal of the Korean housing association
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• v.20 no.4
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• pp.19-29
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• 2009

The purpose of this study is to evaluate the air diffusion performance of a range of indoor units for room airconditioners; the wall-mounted type, floor-standing type, and ceiling-mounted type. These types of units, which have been widely used in housing spaces, will be studied with respect to thermal comfort and the energy performance using CFD analysis. In this study, current air conditioning status and related problems in housing spaces are examined, and a CFD analysis is performed in order to compare and analyze the thermal comfort and energy efficiency across each type of indoor-unit using the PMV, ADPI, EUC and FCEI indexes. The analysis results collectively considering thermal comfort and energy performance indicated that the ceiling-mounted type 4-way indoor unit showed the best diffusion performance in terms of thermal comfort, and had the second best diffusion performance in terms of energy performance after the wall-mounted type under certain conditions.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.11
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• pp.83-89
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• 2008

The Effect of Space Velocity(SV) on NOx conversion rate was performed to develop NOx reduction after-treatment system. SV is calculated from engine exhaust gas volume and SCR catalyst volume. Found the Urea injection duty of maximum efficiency for NOx conversion if increase SV, NOx Conversion rate is down. Especially, when SV is more than $110,000h^{-1}$, NOx conversion rate decrease suddenly. Same case, if SV is lower than $40,000h^{-1}$, NOx conversion rate is down. Also, the characterization of Urea-SCR system was performed. Three candidate injectors for injecting Urea were tested in terms of 속 injection rate and NOx reduction rate. The performances of SCR catalytic converter on temperature were investigated. The performance of Urea-SCR system was estimated in the NEDC test cycle with and without EGR. It was found that nozzle type injector had high NOx conversion rate. SCR catalytic converter had the highest efficiency at the temperature of $350^{\circ}C$. EGR+Urea-SCR system achieved NOx reduction efficiency of 73% through the NEDC test cycle.

• Journal of the Optical Society of Korea
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• v.19 no.3
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• pp.272-276
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• 2015

The PbS quantum dot is an emerging photovoltaic material, which may provide high efficiency breakthroughs. The most crucial element for the high efficiency solar cells's development is to understand charge transport characteristics of PbS quantum dot solids, which are also important in planning strategic research. We have investigated charge transport characteristics of PbS quantum dot solids thin films using space charge limited conduction analysis and assessed thickness dependent photovoltaic performances. The extracted carrier drift mobility was $low-10^{-2}cm^2/Vs$ with the estimated diffusion length about 50 nm. These and recently reported values were compared with those from a commercial photovoltaic material, and we present an essential element in further development of PbS quantum dot solids materials.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.12
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• pp.73-82
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• 2018

The objective of this study was to evaluate particle collection performance of electrostatic precipitator (ESP) integrated with double skin façade in naturally ventilated residential buildings using numerical method. To evaluate the efficiency, computational fluid dynamics (CFD) simulation based on electric potential and Lagrangian method was applied. The CFD model was validated by comparing the simulated results with the experimental data including thermal characteristic of double skin façade (DSF) and particle removal characteristic of electrostatic precipitator. The validation results showed that the root mean square error (RMSE) between predicted values and measured values of velocity and temperature in intermediate space of DSF was 1.2%. The adequacy of ion space charge density and turbulent model were determined. The RMSE between predicted values and measured values of collection efficiency of ESP was 9.2%. In addition, the case study was performed to present the application of the numerical method based on validation results of ESP integrated with façade.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.5
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• pp.533-551
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• 2015

The rock fracturing during waterjet cutting is very complicated because rock is inhomogeneous and anisotropic, compared with artificial materials (e.g., metal or glass). Thus, it is very important to verify the effects of rock properties on waterjet rock cutting performance. Properties affecting the rock cutting efficiency have been variously described in the literature, depending on the experimental conditions (e.g., water pressure, abrasive feed rate, or standoff distance) and rock-types studied. In this study, a rock-property-related literature review was performed to determine the key properties important for waterjet rock cutting. Porosity, uniaxial compressive strength, and hardness of the rock were determined to be the key properties affecting waterjet rock cutting. The results of this analysis can provide the basic knowledge to determine the cutting efficiency of waterjet rock cutting technology for rock excavation-related construction.

• Fashion & Textile Research Journal
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• v.13 no.6
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• pp.966-971
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• 2011

This study is designed to develop programs that analyze the distance of clothes from human skin and cross-sectional body figures based on 3D human body scan data, and to verify accuracy and efficiency of the program so that it can be used for clothing fit evaluation and 3D human body research. The auto cross-sectional imaging program was developed by using Visual C++ and OpenGL, and the 3D human body scan data were adopted to measure the space between skin and clothing. The space measurements were obtained by two widely used programs, RapidForm and AutoCAD, and a program devised by the researchers of this study. Measuring time and space measurements from different programs were compared in order to verify accuracy and efficiency of the newly-devised program. As a result, no significant difference was found in the measurements. However, the required time to measure one cross section was different within the significance level of 0.05, and the differences become more remarkable as the number of measuring and the angle of space between skin and clothing increase. Therefore, the program developed by this study is expected to be useful for research on body shapes and fit evaluation based on 3D human body scan data in the fashion field.

• Publications of The Korean Astronomical Society
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• v.29 no.3
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• pp.53-58
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• 2014

We improved the antenna efficiency of the Taeduk Radio Astronomy Observatory (TRAO) 13.7-m radio telescope by adjusting the antenna panels based on digital photogrammetric measurements. First of all, we measured the surface accuracy of the main reflector of this antenna at three elevation angles of $35^{\circ}$, $45^{\circ}$, and $60^{\circ}$. We performed a total of four sets of the photogrammetric measurements and panel adjustments. When adjusting the panels, we positioned the antenna to the zenith and applied the measured data sets at the elevation of $45^{\circ}$. We found that the antenna surface accuracy has been improved by a factor of ~ 3 times after the final adjustment in comparison with the value before the adjustments. And we also found that the antenna surface accuracy tended to be slightly better at the elevation angles of $35^{\circ}$ and $60^{\circ}$ than that at the elevation angle of $45^{\circ}$. After the final panel adjustment, the aperture and beam efficiencies of the telescope have has been improved from 35% to 44%, and from 41% to 51%, respectively.

• Journal of Dental Anesthesia and Pain Medicine
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• v.21 no.1
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• pp.29-39
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• 2021

Background: Impacted mandibular third molar removal is one of the most commonly performed oral surgical procedures. This procedure can lead to several postoperative complications, such as trismus, facial swelling, and pain, which occur as a result of the inflammatory responses to surgery. This study compared the efficiency of preoperative injections of 4 mg versus 8 mg dexamethasone into the pterygomandibular space to reduce postoperative sequelae. Methods: This was a randomized, prospective, split-mouth, controlled study, including 52 mandibular third molar surgeries in 26 patients. Each patient was randomized to either the 4 mg or 8 mg dexamethasone injection group. Dexamethasone was injected into the pterygomandibular space after numbness from local anesthesia. Data were collected for trismus, facial swelling, visual analog scale (VAS) pain score, and the number of analgesics taken during the evaluation period. The level of significance was set at P < 0.05. Results: Statistically significant differences in postoperative facial swelling (P = 0.031, diff = 1.4 mm) and pain (P = 0.012, diff = 0.020) were found between the 8 mg and 4 mg dexamethasone groups. However, there were no significant differences between the groups for trismus and the total number of analgesics consumed (P > 0.05). Conclusion: Compared to the 4 mg preoperative dexamethasone injection, the 8 mg preoperative dexamethasone injection into the pterygomandibular space was more effective in reducing postoperative swelling and pain following the surgical removal of the impacted mandibular third molar. However, the difference in trismus could not be evaluated clinically. Therefore, the recommendation of administering the 4 mg dexamethasone preoperative injection is optimal in the third molar surgical procedure.