• 해양환경안전학회지
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• 제17권1호
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• pp.29-37
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• 2011

유속의 변화에 따른 오일펜스 만곡부 후면의 속도장과 압력장, 와도 및 난류 강도를 계측한 PIV 실험의 결과 유속이 증가함에 따라 유동 경계역의 후면부에서의 흐름 방향이 전면부의 흐름 방향에 가까워지는 현상이 나타났고, 압력 분포의 양상이 달라졌으며 난류도 더욱 불규칙적인 형태로 나타났다. PIV 실험과 동일 조건으로 수행한 CFD 해석 결과, 후류의 유동 패턴이 0.3m/s이하의 저속인 경우는 PIV 실험 결과와 유사하게 나타났으나, 유속이 0.4m/s일 때는 오일펜스 자체의 유연성으로 인해 다소 차이가 나타났고, 오일펜스 하단의 압력차로 인한 불규칙한 난류가 수면까지 영향을 주었다.

• 대한조선학회논문집
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• 제43권4호
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• pp.422-430
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• 2006

The horn and movable parts around the gap of the conventional semi-spade rudder are visualized by high speed CCD camera with the frame rate of 4000 fps (frame per second) to study the unsteady cavity pattern on the rudder surface and gap. In addition, the pressure measurements are conducted on the rudder surface and inside the gap to find out the characteristics of the flow behavior. The rudder without propeller wake is tested at the range of $1.0{\leq}{\sigma}_v\;1.6$ and at the rudder deflection angle of $-8{\leq}{\theta}{\leq}10^{\circ}$. The time resolved cavity images are captured and show strong cavitation around the rudder gap in all deflection angles. As the deflection angle gets larger, the flow separated from the horn surface increases the strength of cavitation. The accelerated flow along the horn decreases its pressure and the separated flow from the horn increases the pressure abruptly. The pressure distribution inside the gap reveals the flow moving from the pressure to suction side. In the negative deflection angle, the turning area on the movable part initiates the flow separation and cavitation on it.

• 대한조선학회논문집
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• 제51권4호
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• pp.311-320
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• 2014

Test uncertainty of a towed underwater Stereoscopic Particle Image Velocimetry (SPIV) system was assessed in a towing tank. To estimate the systematic error and random error of mean velocity and turbulence properties measurement, velocity field of uniform flow was measured. Total uncertainty of the axial component of mean velocity was 1.45% of the uniform flow speed and total uncertainty of turbulence properties was 3.03%. Besides, variation of particle displacement was applied to identify the change of error distribution. In results for variation of particle displacement, the error rapidly increases with particle movement under one pixel. In addition, a nominal wake of a model ship was measured and compared with existing experimental data by five-hole Pitot tubes, Pitot-static tube, and hot wire anemometer. For mean velocity, small local vortex was identified with high spatial resolution of SPIV, but has serious disagreement in local maxima of turbulence properties due to limited sampling rate.

• 대한기계학회논문집B
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• 제29권8호
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• pp.948-955
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• 2005

A three-dimensional computation was conducted to understand effects of the inlet boundary layer thickness on the internal flow in a low-speed axial compressor operating at the design condition($\phi=85\%$) and near stall condition($\phi=65\%$). At the design condition, the flows in the axial compressor show, independent of the inlet boundary layer thickness, similar characteristics such as the pressure distribution, size of the hub comer-stall, tip leakage flow trajectory, limiting streamlines on the blade suction surface, etc. However, as the load is increased, the hub corner-stall grows to make a large separation region at the junction of the hub and suction surface for the inlet condition with thick boundary layers at the hub and casing. Moreover, the tip leakage flow is more vortical than that observed in case of the thin inlet boundary layer and has the critical point where the trajectory of the tip leakage flow is abruptly turned into the downstream. For the inlet condition with thin boundary layers, the hub corner-stall is diminished so it is indistinguishable from the wake. The tip leakage flow leans to the leading edge more than at the design condition but has no critical point. In addition to these, the severe reverse flow, induced by both boundary layer on the blade surface and the tip leakage flow, can be found to act as the blockage of flows near the casing, resulting in heavy loss.

• 천문학회보
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• 제43권1호
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• pp.52.2-53
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• 2018

A stationary Type IV (IVs) radio burst was observed on September 24, 2011. Observations from the Nançay RadioHeliograph (NRH) show that the brightness temperature (TB ) of this burst is extremely high, over 10^11K at 150 MHz and over 10^8K in general. The degree of circular polarization (q ) is between -60%~-100%, which means that it is highly left-handed circularly polarized. The flux-frequency spectrum follows a power-law distribution, and the spectral index is considered to be roughly -3~-4 throughout the IVs. Radio sources of this event are located in the wake of the coronal mass ejection and are spatially dispersed. They line up to present a formation in which lower-frequency sources are higher. Based on these observations, it is suggested that the IVs was generated through electron cyclotron maser emission.

• Asian Journal for Public Opinion Research
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• 제8권2호
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• pp.105-125
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• 2020

The purpose of this paper is to analyze 1) who created and distributed fake news, 2) the distribution channels of fake news, 3) who fake news has targeted, and 4) the effects on voting and the impact of fake news on Korean politics. In South Korea, fake news was mainly created by candidates or election campaigns. The reason is that in the wake of the impeachment of President Park Guen Hye, all the political parties in Korea used fake news as a means of mobilizing supporters for each of their candidates or parties to gain an advantage in situations involving political divisions and confrontations between the pro-impeachment, progressive young generation and anti-impeachment, conservative senior generation. Voters' media usage patterns were polarized through social network services (SNS) media and television. Fake news was mostly received through these two media outlets. According to the spreading structure of fake news in Korea, the younger generation generally uses SNS posts intended for unspecified individuals, and the older generation uses closed SNS like KakaoTalk or Naver's BAND. In the end, it is typically characteristic of the older generation to spread fake news through existing offline human networks. In the 2017 presidential election, fake news has been confirmed to have the effect of mobilizing supporters for each political party. In the presidential election, an increase in voter turnout was confirmed among those in their 20s and those in their 60s or older. Evidently, fake news influenced the election of Moon Jae-In. The influence of fake news is expected to grow further as ideological polarization and consequent political polarization continues to intensify in South Korea.

• 한국멀티미디어학회논문지
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• 제18권1호
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• pp.25-34
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• 2015

Recently, in distribution market, demand for electronic shelf label system is increasing gradually to provide the accurate price immediately and detailed product information to consumers and reduce operation costs. Most of electronic shelf label system companies develop the full-graphic display device to display a wide variety of product information as well as the exact price. Our system had introduced Go-Back-N retransmission method in the early. However, we encountered performance problems that it delayed updating of the electronic shelf label system and exhausted the battery life time. Proposed adaptive image retransmission technique based on the selective scheme is that tags of electronic shelf label system recognize idle time of transmission cycle and require partial image retransmission to sever by itself. As a result, it can acquire much more opportunities of partial image retransmission within the same period and increase reception rate of full image for each tags. The experimental result shows that adaptive image retransmission technique's reception rate of full image for each tags is approximately 4% higher than existing previous works. And total battery life time increases 30 hours because tag reduce wake-up time as it receive only lost data instead of whole data.

• 한국항해항만학회지
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• 제32권6호
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• pp.453-458
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• 2008

원형실린더에 크기가 다른 제어봉을 부착하여 2차원 단면 유통특성에 대해서 시간평균유동장을 계측하여 근접후류 제어에 관하여 PIV기법을 적용하여 연구를 수행하였다. 모델시험은 각각 크기가 다른 제어봉을 적용하였으며($d/D=0.1{\sim}d/D=0.5$) 레이놀즈수는 원형실린더의 직경을 기준으로 Re=15,000으로 적용하였다. 유동장의 속도분포론 획득하기 위해 2프레임 상호상관법을 이용하였다. 실험에 적용된 원형실린더(D=50mm)에 제어봉을 부착한 결과를 상호 비교함으로서 시간평균속도분포와 제어봉에 의한 유동제어 효과를 알 수 있었다.

• 한국추진공학회지
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• 제9권2호
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• pp.97-104
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• 2005

많은 장점에도 불구하고 유동함수를 이용한 수치해석용 격자생성 좌표변환기법의 단점은 저속영역에서의 격자간격이 고속영역에 비해 상대적으로 큼에 따라 수치적 처리에 많은 오차를 내포하고 있다는 점이다. 본 연구에서는 이러한 저속영역에서의 단점을 보완하기 위하여 격자간격을 속도크기 및 영역에 따라 적절히 조절할 수 있도록 수학적으로 변형된 압축성 유동함수를 이용한 좌표변환기법을 제안하고 가스터빈엔진에 주로 적용되는 유동모델로서 동심원상 두개 이상의 난류제트혼합유동에 대해 적용하였으며 해당 실험치, 즉 축 방향 평균속도분포, 난류운동에너지, 그리고 난류전단응력분포와 비교하여 난류운동에너지가 약간 과소평가 된 대칭축을 제외한 혼합경계층 내에서 $3.5\%$ 이내의 신뢰성을 확보하였다. 본 기법은 특히 터보팬엔진에 대한 내부흐름들의 혼합유동을 규명하거나 또는 난류전단응력에 의한 제트소음발생 및 저감방법을 도모하는데 유용하게 활용될 것으로 기대된다.

• 대한조선학회논문집
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• 제60권4호
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• pp.231-239
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• 2023

In order to improve the propeller Cavitation Inception Speed (CIS) performance, it needs to modify the propeller geometry and the wake distribution that flows into the propeller. In the previous study, the twisted angles of the V-strut were modified to improve propeller CIS, cavitation behavior and pressure fluctuation performances. Then the propeller behind the modified V-strut (New strut) showed better cavitation characteristics than that behind the existing V-strut (Old strut). However, the CIS of Suction Side Tip Vortex (SSTV) and Pressure Side Tp Vortex (PSTV) showed a big difference at behind each V-strut. In this study, the balance design is conducted to minimize the difference between SSTV CIS and PSTV CIS at behind each V-strut. To improve the propeller CIS performance, 1 propeller is designed at behind the old strut and 3 propellers are designed at behind the new strut. The propeller CIS is increased through the balance design and the stern appendage modification. The final propeller CIS is increased about 5.3 knots higher than that of the existing propeller at behind the old strut. On the basis of the present study, it is thought that the better improvement method for the propeller CIS would be suggested.