• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2011년도 전기공동학술대회 논문집
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• pp.233-233
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• 2011

동 연구는 한국 남해안에 시설된 인공어초 주위의 퇴적과 세굴의 특성을 기술한 것이다. 퇴적과 세굴 특성 조사는 2007년 4월에 137개가 시설된 사각형어초의 1단지에서 수행되었다. 사각형어초의 1개의 체적은 8 $m^3$ ($2{\times}2{\times}2$ m)이다. 조사된 사각형어초단지는 1999년 11월에 수심 21.6 m의 사니질에 시설하였다. 연구에 사용된 주요 장비는 Side Scan Sonar, Multi Beam Echo Sounder, Sub-Bottom Profiler, Water Current meter 등 이다. 조사 결과, 인공어초는 중첩된 어초단지 높이의 2-3배인 약 4m 높이로 시설되어 있었고, Side Scan Sonar에 의해 조사된 어초의 형상은 타원형이었다. 인공어초 주위의 최대 유속은 간조시 81.5 cm/sec였으며, 창조시는 72.7 cm/sec 였다. 인공어초 주위의 세굴은 조상(潮上)측에서, 그리고 퇴적은 조하측의 체류역에서 형성되었다. 인공어초 주위의 퇴적은 2.4 - 3.0 m 범위였으며, 퇴적의 가장 높은 봉우리는 어초로부터 10 m의 거리에서 형성되었다. 그리고 경사는 주 흐름에 대한 직각 방향에 있는 어초의 부근에서 가파르게 형성되었으며, 어초로부터 멀어짐에 따라 완만하게 형성되었다. 퇴적은 인공어초의 단지의 높이와 퇴적봉우리의 높이의 차가 적어짐에 따라 감소하였다. 퇴적 봉우리는 어초 높이의 약 1 m까지 퇴적된 후에 서서히 약화되었다. 한편, 세굴은 어초로부터의 용승류, 그리고 퇴적의 옆면에 흐르는 측류에 의해 계속적으로 야기되어 진다. 또한 세굴은 바닥을 파헤친 것이 아니라 퇴적된 부분에서 야기되어지며, 이것은 세굴의 깊이가 변하지 않는다는 것을 의미한다.

• 천문학회지
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• 제44권2호
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• pp.59-65
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• 2011

A small number of active galactic nuclei are known to exhibit prominent double peak emission profiles that are well-fitted by a relativistic accretion disk model. We develop a Monte Carlo code to compute the linear polarization of a double peaked broad emission line arising from Thomson scattering. A Keplerian accretion disk is adopted for the double peak emission line region and the geometry is assumed to be Schwarzschild. Far from the accretion disk where flat Minkowski geometry is appropriate, we place an azimuthally symmetric scattering region in the shape of a spherical shell sliced with ${\Delta}{\mu}=0.1$. Adopting a Monte Carlo method we generate line photons in the accretion disk in arbitrary directions in the local rest frame and follow the geodesic paths of the photons until they hit the scattering region. The profile of the polarized flux is mainly determined by the relative location of the scattering region with respect to the emission source. When the scattering region is in the polar direction, the degree of linear polarization also shows a double peak structure. Under favorable conditions we show that up to 0.6% linear polarization may be obtained. We conclude that spectropolarimetry can be a powerful probe to reveal much information regarding the accretion disk geometry of these active galactic nuclei.

• 한국전산유체공학회지
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• 제17권2호
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• pp.100-106
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• 2012

Ice accretion on the surface of aircraft in flight can adversely affect the safety of aircraft. In particular, it can cause degradation of critical aircraft performances such as maximum lift coefficient and total pressure recovery factor in engine air intake. In this study, computational prediction of ice accretion around a rotorcraft air intake is conducted in order to identify the impingement region with high droplet collection efficiency. Then the amount of ice accretion on the air intake, which is essential in determining the required power of ice protection system, is calculated. Finally, the effect of icing wind tunnel size is investigated in order to check the compatibility with the real in-flight test environment.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.465-468
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• 2011

Ice accretion on aircraft surface can greatly deteriorate the safety of aircraft. In particular, it can be a cause of impediment for aircraft performances such as aerodynamic characteristics, control, and engine. Numerical simulation of icing accretion based on the state-of-art CFD techniques can be alternative to expensive icing wind tunnel test or flight test. In this study, icing conditions are defined in order to predict the ice accretions around the air intake of aircraft. Then the range and amount of ice accretion on the intake in icing wind tunnel were investigated In addition, a study on the size effect of icing wind tunnel was conducted in order to check the compatibility with the real in-flight test environment.

• 한국전산유체공학회지
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• 제18권3호
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• pp.51-59
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• 2013

A significant change in aerodynamic characteristics of wind turbine blade can occur by ice formed on the surface of the blade operated in cold climate. The ice accretion can result in performance loss, overloading due to delayed stall, and excessive vibration associated with mass imbalance. In this study, the impact of ice accretion on the aerodynamic characteristics of NREL 5MW wind turbine blade sections is examined by a CFD-based method. It is shown that the thickness of ice accretion increases from the root to the tip and the effects of icing conditions such as relative wind velocity play a significant role in the shape of ice accretion. In addition, the computational results are used to assess the degradation in the lift and drag coefficients of the blade sections.

• Journal of Astronomy and Space Sciences
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• 제36권3호
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• pp.105-113
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• 2019

Spectroscopic observations of barium star ${\zeta}$ Capricornus (HD204075) obtained at the 8.2 m telescope of the European Southern Observatory, with a spectral resolving power R = 80,000 and signal to noise ratio greater than 300, were used to refine the atmospheric parameters. We found new values for effective temperature ($T_{eff}=5,300{\pm}50K$), surface gravity ($log\;g=1.82{\pm}0.15$), micro-turbulent velocity ($v_{micro}=2.52{\pm}0.10km/s$), and iron abundance ($log\;N(Fe)=7.32{\pm}0.06$). Previously published abundances of chemical elements in the atmosphere of HD204075 were analyzed and no correlations of these abundances with the second ionization potentials of these elements were found. This excludes the possible influence of accretion of hydrogen and helium atoms from the interstellar or circumstellar environment to the atmosphere of this star. The accretion of nuclear processed matter from the evolved binary companion was primary cause of the abundance anomalies. The young age of HD204075 allows an estimation of the time-scale for the creation of the abundance anomalies arising from accretion of interstellar hydrogen and helium as is the case of stars with low magnetic fields; which we estimate should exceed $10^8$ years.

• 천문학논총
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• 제8권1호
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• pp.265-272
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• 1993

Recent X-ray observations of the accretion disks in stellar black hole candidates have revealed rather complex behavior, which cannot be fully described by the simple picture of the standard disk model. In this paper, therefore, we discuss the effects of e+e- pair creation on the structure and the stability of hot accretion disks, aiming at the thorough understanding of emission properties of X-ray binaries containing black holes.

• Journal of Astronomy and Space Sciences
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• 제9권2호
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• pp.171-182
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• 1992

Radiation due to accretion from an accretion disc around the intermediate polars and photoabsorption of this radiation in the accretion funnel have been taken into account as a phenomenological model to study the physics of the magnetic funnel in the magnetic compact star. The first results show that such a model scenario can be used to estimate some parameters in these systems. Some constraints of this model regarding to the observational data of one intermediate polar, EX Hya, are also discussed.

• 천문학회지
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• 제34권4호
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• pp.305-307
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• 2001

Radiation hydrodynamics in high. velocity or high optical-depth flow should be treated under rigorous relativistic formalism. Relativistic radiation hydrodynamic moment equations are summarized, and its application to the near-critical accretion onto neutron star is discussed. The relativistic effects can dominate the dynamics of the flow even when the gravity is weak and the velocity is small. First order equations fail to describe the intricate relativistic effects correctly.

• 천문학회지
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• 제34권4호
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• pp.265-269
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• 2001

We present preliminary numerical simulations of tilted-disk accretion around a rotating black hole. Our goal is to explore whether hydrodynamic instabilities near the Bardeen-Petterson radius could be responsible for generating moderate-frequency quasi-periodic oscillations in X-ray binaries. We review the relevant general relativistic hydrodynamic equations, and discuss preliminary results on the structure and dynamics of a thin, Keplerian disk.