• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.295-295
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• 2018

본 연구는 보 상류 하상경사 변화에 따른 보 하류부의 세굴 문제점 개선을 위해 하상경사에 대한 세굴영향을 분석하기 위한 실험연구이다. 세굴실험은 상류 하상경사 변화에 대해 보 하류부의 세굴변화를 중심으로 세굴영향을 검토하였다. 본 실험은 상류 하상경사 변화에 대한 세굴영향을 분석하기 위한 것으로 총 6개 하상경사에 대해 국부세굴 및 퇴적경향을 비교분석하였다. 보의 높이 및 물받이 길이는 0.3 m로 설치하였고, 실험 단위폭당 유량은 $0.117m^3/s/m$로 모든 케이스에 동일하게 적용하여 수행하였다. 보를 통과하는 고속사류로 인한 국부세굴의 영향분석을 위해 광대역 레이저 스캐너(RIEGL LMS-Z390)를 이용하여 세 퇴적량을 측정 및 분석하였다. 연구결과, 상류 하상경사 변화에 따른 보 하류부 세굴 특성 분석 결과 상류부의 하상경사가 급해질수록 세굴길이 및 세굴심도의 값은 크게 변화하는 것을 확인하였다. 이는 하상경사 변화에 따라 수류의 총에너지 경사가 급하게 변화하게 되고 따라서 보 하류부의 소류력 증가에 기인한 것으로 판단된다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.762-768
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• 2015

This study examined the integration value of a low level pilotis space, a component that has been often selected as an essential planning element of the recent high-rise apartment complex, and compared the main outdoor unit spaces with that of an average integration value of the individual complexes. Furthermore, this study provided the preliminary data for the next level of research, which is the observation of the pilotis space usage behaviors and the frequency of utilization. The results of this present research are as follows. First, from the main outdoor unit spaces of the high-rise apartment complexes including the pilotis space, a 'complex entrance' or a 'plaza' space showed the highest integration value. Second, the spatial integration value of a pilotis space in a high-rise apartment complex was generally lower that of the integration value of other main outdoor units. Third, from the pilotis spaces of the high-rise apartment complex, those with a 'projecting entry access + pilotis addition type' that did not provide an access to the individual units, had the lowest space utilization rate by the inhabitants; thus, had a high likelihood of the spaces becoming used for illegitimate activities or becoming vacant.

• Journal of the Korean Association of Geographic Information Studies
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• v.17 no.4
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• pp.112-128
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• 2014

This study aims to analyse the variation of spatial accessibility pattern based on 2SFCA(2 Step Floating Catchment Area) by changing its parameter values. The general pattern of the result of 2SFCA analysis shows that the spatial accessibility value is decreased by growing base population, while the spatial accessibility value is increased by growing PPR(Provider to Population Ratio). The three characteristics of local pattern in the Gumi City are founded by cluster analysis on the sensitive analysis procedure. Firstly, the variation of the accessibility values is insignificant in the fringe area of the Gumi City. Secondly, the variation of the accessibility values is diverse in the surrounding area of the welfare facilities. Especially, Dong areas are more sensitive to PPR variation, while others are more sensitive to base population variation. Thirdly, the larger parameter values, the more the spatial accessibility of the central areas, where elder people can access welfare facilities more easily, is improved. It needs to choose parameter values with caution to analyse spatial accessibility based on 2SFCA.

• Journal of the Korean earth science society
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• v.22 no.4
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• pp.327-338
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• 2001

In this study, the short-term variability of methane concentrations were investigated over 24-hr scale. The data obtained form the Moo-Ahn (MAN) station located in the western coastal area of Korea were analyzed from various respects to describe its distribution characteristics over short term scale. The MAN data were compared with those obtained from the two major background observatory sites: Point Barrow (Alaska) and Mauna Loa (Hawaii). The mean concentration of methane for the whole study period, when computed using the daily mean values, was found to be 1898${\pm}$85.3ppb (N=812). The mean values for the two comparable sites were observed to be 1832${\pm}$29.6ppb (N=823) for Point Barrow and 1745${\pm}$14.8ppb (N=818) for Mauna Loa. According to the analysis of frequency distribution. the mode value for the MAN area is found to be 1900ppb, but the mean concentration for Point Barrow and Mauna Loa are shown to have relatively low values of 1850 and 1750ppb, respectively. When examined over diurnal scale, the CH$_4$data for the MAN area exhibit a rather consistent trend; CH$_4$level is low during the daytime (after 6:00 A.M) and rises during the nighttime. The findings of the generally enhanced methane concentration in the MAN station may be explained form various respects. One of the most important reasons is that the MAN area is under the influence of various source processes relative to all the other stations under consideration. The short-term distribution patterns for the MAN station are hence characterized not only by the high methane concentration but also by the high oscillation in its CH$_4$concentration level.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.1
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• pp.1-12
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• 2022

Wind tunnel test for a small scale electric ducted fan with a 104mm diameter was conducted to analyze the aerodynamic characteristics when it was used as a propulsion system of tilt-propeller UAV. Experimental conditions were derived from flight conditions of a sub-scaled OPPAV. Forces and moments of the ducted fan model were measured by a 6-axis balance and 3-dimensional wake vectors which could induce an aerodynamic influence in the vehicle were measured by 5-hole probes. Thrust and torque on hover and cruise conditions were measured and analyzed to drive out the operating conditions when it was applied in the sub-scaled OPPAV. On transition conditions, thrust keep its value with tilt angle variation below 40° and increase after that. But, sideforce increase constantly until 75°. The maximum axial velocity in the wake on hover and cruise conditions was around 60m/s and tangential velocity was around 12m/s. The position of the maximum axial velocity and vortex center move off the fan rotation center line as the tilt angle increases.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.104-110
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• 1997

To predict the effect of ring expansion and ring compression on residual stress relief of Al 7175 ring rot]s, 2-D axisymmetric thermal analysis and elastoplastic analysis were performed. The residual stress distributions along the thickness of T73, T7351 and T7352 treated rings were measured using three step sectioning method. The measured results were compared to numerical ones for quenched and stress relieved rings. After quenching, calculated hoop and axial residual stresses were similar to measured ones for T73 treated rings. The residual stresses of T7351 and T7352 treated rings were decreased remarkably compared to T73 treated rings. The effect of axial residual stress relief was superior to that of hoop one, and also ring compression to ring expansion. It was concluded that ring compression is advantageous over ring expansion in view of stress relief effect and practicality, and vice versa in view of dimensional control and press power.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.37-46
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• 2013

The gas jet from a coaxial porous injector for two-phase flows is discharged radially from the porous surface, which encloses the center liquid jet. Several hot-firing test using ethanol/nitrous oxide propellants was conducted to analyze the effect of oxidizer/fuel ratio on the combustion performance, and the uncertainty analysis was performed for the results. The characteristic velocity was affected by oxidizer/fuel ratio similarly with the results of CEA calculation except that the maximum characteristic velocity was appeared in the stoichiometric ratio. The characteristic velocity efficiency was increased as the oxidizer/fuel ratio increases.

• Aerospace Engineering and Technology
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• v.12 no.1
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• pp.32-39
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• 2013

All spacecraft components shall be checked for compatibility with vacuum using CVCM and TML in advance. CVCM and TML of the PZT-5 piezoelectric vibrator has to be less than 0.1% and 1.0% respectively. Also, it has less than $500ng/cm^2/hr$ of TQCM for vacuum bake-out test using high temperature and high vacuum. Thus, the piezoelectric vibrator may be employed in the vacuum environments. Finally, it can be confirmed that the characteristics change of the piezoelectric vibrator is less than 1% under vacuum environments. Also, the temperature dependency of the characteristics in the PZT-5 piezoelectric vibrator with the lateral mode was investigated in the range of $-100^{\circ}C$ to $90^{\circ}C$ using the thermal vacuum chamber to utilize the vibrator to the aerospace industries. As the results, at room temperature, the resonant and anti-resonant frequencies had the minimum value, whereas, the dielectric constant increased linearly from about 2500 to 7500 in the given temperature range. The mechanical loss decreased linearly from 0.08 to 0.03.

• Journal of the Korean Data Analysis Society
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• v.20 no.6
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• pp.3227-3238
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• 2018

This study attempts to investigate the trajectories of socio-economic deprivation on the depression trajectories among middle-aged individuals using a latent growth model over the last five years. Using the Korea welfare panel study data ranged from the year 2013 (8th wave) to the year 2017 (12th wave), a sample of 7,437 aged over 40 was selected. Three hypothesis was proposed as follows. Is the trajectory of depression changing over the years? Are the initial values of socio-economic deprivation causally related to the initial values of depression? Are the rates of change in socio-economic deprivation causally related to the rates of change in depression? Results showed that the growth curve of depression tended to decline negatively over the five-year period. As the intial values of socio-economic deprivation increased, so did the initial values of depression move upwards. Finally, as the changes of socio-economic deprivation tended to get larger, those changes of depression also accordingly increased as well. The public policy implications based on the current study were discussed to pay more attention to those middle-aged individuals suffering from socio-economic deprivations.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.49-49
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• 2020

하천 보 상류영역에서 발생하는 박리 흐름을 분석하기 위해 실험수로에 하천보 모형을 설치하고, 보 주변에서 발생하는 흐름 구조를 입자 영상 유속계(PIV)로 이용하여 정밀하게 측정하였다. 본 연구에 사용된 보는 하천 설계기준을 따른, 전방 수직벽과 하류 경사램프가 있는 유한한 마루 길이 보이다. 실험 조건은 보 상·하류부 수심으로 인한 4가지 흐름(Hydraulic jump, Plunging jet, Surface wave, Surface jet)을 기반으로 설정하여 수리조건에 따른 유속 특성을 규명하였다. 실험에서 측정한 수직-수평방향 평균 유속·유선도를 분석한 결과, 보 전방의 하부에서 재순환 흐름이 관측되었고, 역방향 흐름도 이 지역에서 발견되었다. 유속 편차의 제곱 평균(Root Mean Square) 흐름장에서 보 전방과 재순환 흐름 영역에 불안전한 흐름이 강하게 발견되었다. 역방향 흐름은 박리 흐름에서 발견되는 주요 특성으로, 역방향 흐름의 전체 면적을 매 관측마다 측정하여 이를 분석한 결과, 재순환 흐름의 면적은 오른쪽으로 기울어진 분포를 가지고, 항상 0보다 큰 값을 가지는 것으로 나타났다. 재순환 면적에 따른 흐름 특성은 역방향 흐름 면적에 대한 조건부 평균을 이용하여 파악했는데, 조건부 평균의 구간은 재순환 흐름의 중심에서 지배적인 주기값을 이용했다. 역방향 흐름이 작은 영역에선, 보 상류의 흐름이 재순환 흐름으로 말려들어가는 열린 박리흐름이 나타나며, 역방향 흐름이 큰 경우에는 재순환 영역의 흐름은 보 상류의 흐름과 분리되는 닫힌 박리흐름이 발생하였다. 역방향 흐름이 가장 큰 경우, 보 전방의 박리흐름은 보의 상단을 넘는 것으로 관찰되었다. 이러한 결과를 통해 보 마루에서 발생하는 박리흐름이 보 전방에 박리흐름에 영향을 미치는 것으로 파악되었다. 조건부 평균된 역방향 흐름의 면적과 박리 지점(separation point)의 관계를 분석한 결과, 역방향 흐름의 오른쪽으로 기울어진 분포와 대규모 흐름 방출 현상이 관측되었다. 박리 지점의 위치와 수리 매개변수의 관계를 분석한 결과, 상류의 수심 증가에 따라 증가하는 경향이 나타났다.