• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.11
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• pp.891-899
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• 2013

This paper suggests a test and evaluation procedure of conformal load-bearing antenna structure(CLAS) for high speed military jet application. A log periodic patch type antenna was designed for multi-band communication and navigation antenna. Carbon/Glass fiber reinforced polymer was used as a structure supporting aerodynamic loads and honeycomb layer was used to improve antenna performance. Multi-layers were stacked and cured in a hot temperature oven. Gain, VSWR and polarization pattern of CLAS were measured using anechoic chamber within 0.15~2.0 GHz frequency range. Tension, shear, fatigue and impact load test were performed to evaluate structural strength of CLAS. Antenna performance test after every structural strength test was conducted to check the effect of structural test to antenna performance. After the application of new test and evaluation procedure to validate a new CLAS, a design improvement was found.

• Journal of Environmental Science International
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• v.25 no.8
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• pp.1065-1076
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• 2016

This study analyzes the $PM_{10}$ characteristics (particulate matter with aerodynamic diameter less than $10{\mu}m$), concentration, and emissions in eight large South Korean cities (Seoul, Incheon, Daejeon, Daegu, Gwangju, Ulsan, Busan, Jeju). The annual median of $PM_{10}$ concentration showed a decline of $0.02{\sim}1.97{\mu}g/m^3$ in the regions, except for Incheon, which recorded an annual $0.02{\mu}g/m^3$ increase. The monthly distribution levels were high in spring, winter, fall, and the summer, but were lower in summer for all regions except for Ulsan. These differences are thought to be due to the dust in spring and the cleaning effect of precipitation in summer. The variation in concentrations during the day (diurnal variation) showed that $PM_{10}$ levels were very high during the rush hour and that this was most extreme in the cities (10.00 and 18.00-21.00). The total annual $PM_{10}$ emissions analysis suggested that there had been a general decrease, except for Jeju. On-road mobile (OM) sources, which contributed a large proportion of the particulates in most regions, decreased, but fugitive dust (FD) sources increased in the remaining regions, except for Daegu. The correlation analysis between $PM_{10}$ concentrations and emissions showed that FD could be used as a valid, positive predictor of $PM_{10}$ emissions in Seoul (74.5% (p<0.05)), Dajeon (47.2% (p<0.05)), and Busan (59.1% (p<0.01)). Furthermore, industrial combustion (IC) was also a significant predictor in Incheon (61.7% (p<0.01)), and on-road mobile (OC) sources were a valid predictor in Daegu (24.8% (p<0.05)).

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.378-383
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• 2013

A butterfly throttle valve has been used to control the brake power of an SI engine by controlling the mass flow-rate of intake air in the induction system. However, the valve has a serious effect on the volumetric efficiency of the engine due to the pressure resistance in the induction system. In this study, a new intake air controlling valve named "Variable Geometry Throttle Valve(VGTV)" is proposed to minimize the pressure resistance in the intake system of an SI engine. The design concept of VGTV is on the application of a venturi nozzle in the air flow path. Instead of change of the butterfly valve angle in the airflow field, the throat width of the VGTV valve is varied with the operating condition of an SI engine. In this numerical study, CFD(computational fluid dynamics) simulation technique was incorporated to have an aerodynamics performance analysis of the two air flow controlling systems; butterfly valve and VGTV and compared the results to know which system has lower pressure resistance in the air intake system. From the result, it was found that VGTV has lower pressure resistance than the butterfly valve. Especially VGTV is effective on the low and medium load operating condition of an SI engine. The averaged pressure resistance of VGTV is about 49.0% lower than the value of the conventional butterfly throttle valve.

• Korean Journal of Agricultural and Forest Meteorology
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• v.13 no.2
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• pp.56-68
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• 2011

Wet canopy evaporation ($E_{WC}$) has been recognized as a significant component of total evapotranspiration, especially in forests and therefore it is critical to accurately assess $E_{WC}$ to understand forest hydrological cycle. In this review, I focused on the measurement methods and evaluating the magnitudes of $E_{WC}$ at diverse forest types (e.g., deciduous, coniferous, mixed, and rain forests). I also present the general issues to be considered for $E_{WC}$ measurements. The commonly used measurement methods for $E_{WC}$ include the water balance, energy balance, and the Penman-Monteith (PM) methods. The magnitudes of $E_{WC}$ ranged from 5 to 54% of precipitation based on the literature review, showing a large variation even for a similar forest type possibly related to canopy structure, rainfall intensity, and other meteorological conditions. Therefore, it is difficult to draw a general conclusion on the contribution of $E_{WC}$ to evapotranspiration from a particular forest type. Errors can arise from the measurements of precipitation (due to varying wind effect) and throughfall (due to spatial variability caused by canopy structure) for water balance method, the measurements of sensible heat flux and heat storage for energy balance method, and the estimation of aerodynamic conductance and unaccounted sensible heat advection for the PM method. For a reliable estimation of $E_{WC}$, the combination of ecohydrological and micrometeorological methods is recommended.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.7
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• pp.677-687
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• 2017

Aircraft can often be exposed to a variety of environments and vibrations such as engine, hydraulic pump, aerodynamic force. These may cause cracking and destruction of the mechanical structure and sub-components by high-cycle fatigue. The axial piston type pump which is usually applied to the aircraft hydraulic pump can be necessarily accompanied by the fluid pulsation by continuous rotation of the axial piston. The fatigue crack was identified at the dampener fitting welding zone to prevent vibration damping during the running of aircraft equipped with this type of pulsation hydraulic pump. In order to understand the root cause of this matter, fracture and component analyses were carried out and also integral type dampener fitting was applied to prevent recurrence of the crack as a subject of design improvements. Structural integrity stress analysis, fatigue analysis, qualification test and aircraft system equipped test was conducted to verify the design validity in application to integral type dampener fitting. The test results were sufficiently satisfactory with the demand lifetime of the material from the various types of test as conducted and the subject of design improvement in this study could be objectively evaluated that shall be applied to the operational aircraft.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.373-381
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• 2017

Kyeonggi Provincial Government is considering double decker bus service to solve the problem of heavy rush hour traffic. However, the height-to-width ratio is more than 1.16 times larger than that of a general high-speed single decker bus, and the center of gravity is higher. This could cause driving stability problems, such as turnover and breakaway from the lane, especially under strong side-wind conditions at high speed. In this numerical study, the driving characteristics of a model double decker bus were reviewed under side-wind and superelevation conditions at high driving speed. The rolling, pitching, and yawing moment of the model bus were calculated with CFD numerical simulation, and the results were compared to the recovery angular moments of the model bus to evaluate the dynamic stability under given driving conditions. As the model vehicle moves on a straight level road, it is stable under any side-wind conditions. However, on a curved road under side-wind conditions, it could reach unstable conditions dynamically. There is a chance that the bus will turn over when it moves on a curved road with a radius of gyration less than 100 m under side-wind (15 m/s). However, there is a very small chance of breakaway from the lane under any driving conditions.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.29 no.1
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• pp.30-36
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• 2018

Background and Objectives : The effect of palliative injection laryngoplasty in cancer-related unilateral vocal cord paralysis patients on voice and swallowing function is uncertain and there are few previous studies of its suitability, benefits as a palliative treatment option. The purpose of this study is to confirm the objective results of voice and swallowing function after palliative office-based hyaluronic acid injection laryngoplasty in cancer-related unilateral vocal cord paralysis patients. Materials and Method : 36 patients who had unilateral vocal cord paralysis from non-thyroidal, extralaryngeal neoplasms were included in this study. To evaluate the clinical outcome, we analyzed perceptual GRBAS grading, acoustic analysis, aerodynamic study, Electroglottography (EGG), Voice Handicap Index (VHI-30) about voice function and disability rating scale (DRS), gastric tube dependency, aspiration pneumonia about swallowing function and 36-Item Short Form Survey version 2 (SF-36v2) about quality of life. Results : In GRBAS scale, G (p<0.001), R (p=0.004), B (p=0.001), A (p=0.011), and S (p=0.007) showed significant improvement. Jitter, shimmer, speaking fundamental frequency, maximal phonation time, VHI-30, DRS score, gastric tube dependency, aspiration pneumonia, and SF-36v2 were significantly improved after injection (p=0.016, p=0.011, p=0.045, p=0.005, p<0.001, p<0.001 p=0.003, p<0.001, and p<0.001 respectively). Conclusion : From this study we concluded office-based hyaluronic acid injection can be used as a useful palliative treatment option in cancer-related ill patients with unilateral vocal cord paralysis. Palliative hyaluronic acid injection laryngoplasty avoids the need for tube feeding, thus reducing the risk of aspiration pneumonia. These outcomes are accompanied by significant improvement in voice quality.

• Journal of Korea Water Resources Association
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• v.40 no.7
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• pp.571-583
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• 2007

The effects of climatic changes owing to urbanization, geographical and topographical conditions on Penman-Monteith reference evapotranspiration, and energy and aerodynamic terms of Penman-Monteith reference evapotranspiration have been studied. In this study, 56 climatological stations including the Seoul metropolis in South Korea have been selected, and the area of study site was set at $314\;km^2$. The climatological station is centrally located In the study area with a 10 km radius. The geographical and topographical characteristics of these sites were examined using GIS analysis. Land use status of the study area was also examined to estimate the extent of urbanization. The study results indicated that the variation of reference evapotranspiration rate is closely related to urbanization in most climatological stations. The level of change in reference evapotranspiration was higher in areas with higher urbanization rates. The change in reference evapotranspiration appears to be caused by temperature rises following heat island phenomena due to urbanization, and by the decrease in humidity, wind speed and sunshine duration due to the Increase in residential areas in urban districts. Especially, the humidity decrease causes a significant decrease in evapotranspiration rate. The study results showed that climatic change due to urbanization and proximity to the coast had the greatest effect on reference evapotranspiration.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.1
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• pp.32-41
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• 2006

In this study, the thrust generation by simultaneous flapping airfoils in tandem configuration is parametrically studied with respect to flapping frequency, amplitude and relative location. Navier-Stokes solver with overset grid topology is employed to calculate the unsteady flowfields. The computation results indicate that when the two airfoils stroke in-phase - flapping phase lag is zero - the maximum propulsive efficiency and thrust can be obtained for most frequency and amplitude range. At a flapping amplitude of 0.2 chord and a reduced frequency of 0.75, the propulsive efficiency of aft airfoil is enhanced by about 37 % compared with that of forward airfoil. However, if flapping frequency exceeds some critical value, the strength of the leading edge vortex of aft airfoil is fortified by the trailing edge vortex of the forward airfoil, resulting in poor propulsive efficiency. It is also found that out-of-phase flapping has relatively low propulsive efficiency and thrust since vortical wake of the forward airfoil interacts with the leading edge vortex of aft airfoil in the unfavorable fashion. The total thrust and propulsive efficiency are shown to decrease with the horizontal miss distance of the aft airfoil. On the contrary, the vertical miss distance has little effect on the overall aerodynamic performance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.9
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• pp.712-722
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• 2018

This paper conducts parametric studies on flapping wing design, one of the most important design parameters of insect-mimicking aerial vehicles. Experimental study on wing shape was done through comparison and analysis of thrust, pitching moment, power consumption, and thrust-to-power ratio. A two-axis balance and hall sensor measure force and moment, and flapping frequency, respectively. Wing configuration is biplane configuration which can develop clap and fling effect. A reference wing shape is a simplified dragonfly's wing and studies on aspect ratio and wing area were implemented. As a result, thrust, pitching moment, and power consumption tend to increase as aspect ratio and area increase. Also, it is found that the flapping mechanism was not normally operated when the main wing has an aspect ratio or area more than each certain value. Finally, the wing shape is determined by comparing thrust-to-power ratio of all wings satisfying the required minimum thrust. However, the stability is not secured due to moment generated by disaccord between thrust line and center of gravity. To cope with this, aerodynamic dampers are used at the top and bottom of the fuselage; then, indoor flight test was attempted for indirect performance verification of the parametric study of the main wing.