• Journal of Astronomy and Space Sciences
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• 제26권4호
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• pp.439-450
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• 2009

2006년 상반기동안 GOES 10에 의해 관측된 > 2MeV의 전자에너지 채널에서 반복되는 상대론적 전자 증가 이벤트(GREE, Geosynchronous Relativistic Electron Event)가 4회 있었다. 이 현상들은 모두 코로나 구멍(Coronal hole)에서부터 나온 고속 태양풍(HSS, High Speed Solar Wind Stream)과 관련된 것으로 여겨진다. 약 27일 주기를 갖는 이 4회의 전자 증가 현상은 플럭스가 점점 증가하는 형태를 보인다. 현재까지 알려진 상대론적 전자 증가 현상의 주요 원인으로는 다음의 요소들이 언급되어 왔다: (1) 코로나 구멍과 관련된 태양풍 속도, (2) Pc5 ULF 파동, (3) 행성간 자기장(IMF, Interplanetary Magnetic Field) Bz의 남쪽 성 분, (4) 자기 부폭풍(substorm)의 발생, (5) 증가된 휘슬러 모드 코러스 파동(whistler mode chorus wave)과 (6)동압력(dynamic pressure). 따라서 이 논문에서는 2006년 상반기 동안 앞에서 언급한 6가지 현상 들을 분석하여 어느 요소가 상대론적 전자 증가 현상의 플럭스와 가장 가까운 연관성이 있는지 알아보고자 한다.

• Wind and Structures
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• 제38권2호
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• pp.109-118
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• 2024

A solar concentrator is a reflective surface in the shape of a parabola that collects solar rays in a focal area. This concentrator follows the path of the sun during the day with the help of a tracking system. One of the most important issues in the design and construction of these reflectors is the force exerted by the wind. This force can sometimes disrupt the stability of the concentrator and overturn the entire system. One of the ways to estimate the force is to use the numerical solution of the air flow in three dimensions around the dish. Ansys Fluent simulation software has been used for modeling several angles of attack between 0 and 180 with respect to the horizon. From the comparison of the velocity vector lines on the dish at angles of 90 to - 90 degrees, it was found that the flow lines are more concentrated inside the dish and there is a tendency for the flow to escape around in the radial direction, which indicates the presence of more pressure distribution inside the dish. It was observed that the pressure on the concave surface was higher than the convex one. Then, the effect of adding a hole with various diameter of 200, 300, 400, 500, and 600 mm on the dish was investigated. By increasing the diameter up to the optimized size of 400 mm, a decrease in the maximum pressure value in the pressure distribution was shown inside the dish. This pressure drop decreased the drag coefficient. The effect of the hole on the dish was also investigated for the 30-degree angled dish, and it was found that the results of the 90-degree case should be considered as the basis of the design.

• 한국군사과학기술학회지
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• 제11권2호
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• pp.144-151
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• 2008

An experimental study has been conducted to investigate the effects of circular damage hole on the characteristics of airfoil performance. The damage on a wing created from a hit by anti-air artillery was modeled as a circular hole. Force balance measurements and static pressure measurements on the wing surface were carried out for the cases of having damage holes of 10% chord size at quarter chord and/or half chord positions. All experiments were conducted at Reynolds number of $2.85\times10^5$ based on the chord length. The surface pressure data show big pressure alterations near the circular damage holes. This abnormal surface pressure distribution produces shear stress that could lead to the acceleration of the structural degradation of the wing around the circular damage hole. However, in spite of the existence of circular damage holes, the measured force data indicated the only a slight decrease in lift accompanied by increase in drag compared to the results of undamaged one. The influence of damage hole on the aerodynamic performance was increased as the location of damage moved to the leading edge. The effect on the control force was insignificant when the damaged size was not large.

• 천문학논총
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• 제10권1호
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• pp.79-90
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• 1995

The unique compact radio source, Sgr $A^*$, at the Galactic center show many observational signs that it is powered by supermassive black hole. Recent observations also imply that it is surrounded by winds from nearby IR sources. So we explore the model in which multiwavelength spectrum from Sgr $A^*$ is due to the spherical accretion of these winds onto the central supermassive black hole. Improving upon the previous work, we allowed the possibility that ions and electrons have different temperatures, included the Compton effects and pair processes. Electrons radiate via cyclosynchrotron and bresstrahlung with comptoniztion. We find that ion approaches the virial temperature ${\sim}10^{13}K$ while electron temperature saturates at ${\sim}10^{10}K$. However, decoupling between ion and electron does not greatly affect the shape of the emission spectrum. When the mass of the black hole is ${\sim}10^6M_{\odot}$, radio, IR, X-ray, $\gamma$-ray band spectrum is reasonably explained by the model. Yet Compton effect which is neglected in previous works produces significant emission in IR band, which is marginally compatible with observations. Pair production is negligible and annihilation lines cannot be observed.

• 한국위험물학회지
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• 제6권2호
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• pp.62-67
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• 2018

It is very important to classify explosion hazardous area in order to prevent an accident explosion. In order to prevent such a explosion, the Industrial Safety and Health Standards Rules stipulates the establishment and management of explosion hazards in accordance with the criteria set by the Korean Industrial Standards. This study has investigated the range of the explosion hazardous area according to various hole sizes, pressures, vapor densities, and wind velocities in the outdoor flammable liquid tank using KS C IEC-60079-10-1 $2^{nd}$ Ed.(=IEC CODE) and PHAST. The results show that the explosion hazardous areas by IEC CODE have circle shapes. However, the areas by PHAST show ellipse shapes. The different of the explosion hazardous areas increases with the increase of wind velocity.

• 천문학회보
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• 제42권1호
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• pp.41.1-41.1
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• 2017

It is well known that there are good relations of coronal hole (CH) parameters such as the size, location, and magnetic field strength to the solar wind conditions and the geomagnetic storms. Especially in the minimum phase of solar cycle, CHs in mid- or low-latitude are one of major drivers for geomagnetic storms, since they form corotating interaction regions (CIRs). By adopting the method of Vrsnak et al. (2007), the Space Weather Research Center (SWRC) in Korea Astronomy and Space Science Institute (KASI) has done daily forecast of solar wind speed and Dst index from 2010. Through years of experience, we realize that the geomagnetic storms caused by CHs have different characteristics from those by CMEs. Thus, we statistically analyze the characteristics and causality of the geomagnetic storms by the CHs rather than the CMEs with dataset obtained during the solar activity was very low. For this, we examine the CH properties, solar wind parameters as well as geomagnetic storm indices. As the first result, we show the different trends of the solar wind parameters and geomagnetic indices depending on the degree of solar activity represented by CH (quiet) or sunspot number (SSN) in the active region (active) and then we evaluate our forecasts using CH information and suggest several ideas to improve forecasting capability.

• The Korean Journal of Ecology
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• 제17권4호
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• pp.533-545
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• 1994

The bleeding of 39 Acer mono trunks by wounding was investigated at the altitudes of 400m, 500m, 800m, and 1100m on Wangsirobong (1,214m), Mt. Chiri area (127°34'E., 35°14'N.) from February 4 to March 21, 1993 and from February 23 to March 23, 1994. The amount of sap in a day was clodely related to the change of air temperature and wind speed. Especially, the abundant sap was exudated at the ranges of -4~13℃ in the daily range of temperature and it was below 0.14m/s in wind speed. The most abundant bleeding was exudated from Acer mono trunk located south facing slope in 800m altitude. Also the amount of sap increased with incereasing suface area of crown. The maximum bleeding of sap was collected from the hole punctured at 80cm height from the ground surface at southern part of the trunks. And the number of exudation holes had an important effect on bleeding of sap but the number of holes should be controlled by DBH of trunks. These results suggested that the exudation was influenced by the daily range of temperature and wind speed. And the altitude, direction of sloped where the trees occurred, surface area of crown, the number of exudation holes, height form the ground surface and the direction of the hole was 91.6% when germicide (Dimethyl-4,4' -ophenylene bis 3-thio alonate) was treated from April to October after bleeding of sap in the year.

• 한국환경과학회지
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• 제18권9호
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• pp.941-952
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• 2009

The urban microscale wind field around the air quality monitoring station was investigated in order to check how a building complex influences it. For this study as the high density areas Jwa-dong and Yeonsan-dong monitoring sites in Busan were chosen. As the direction of inflow which is perpendicular to the building of the monitoring station was expected to cause the considerable variation of the wind field, that direction was selected. The model Envi-met was used as the diagnostic numerical model for this study. It is suitable for this investigation because Envi-met has the microscale resolution. After simulating it, on the leeward side around a building complex the decrease of flow velocity and some of vortexes or circulation area were discovered. In addition, on the edge of the top at the building and at the back of the building the upward flow was developed. If the sampling hole of monitoring site were located in this upward flow, it would be under the influence of upward flow from the near street.

• 설비공학논문집
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• 제21권7호
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• pp.409-416
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• 2009

On 21st century, global warming is the most serious environmental problem threatening the existence of lives on the earth. One of the serious reasons of this nature phenomena was due to the greenhouse effect by carbon dioxide mainly produced with the combustion process of hydro-carbon fuel. and it is mostly produced. In the high oil prices age, intensification of energy efficiency promotion in the building sector is required. Windows are dominating large percentage whole building loads, and are regarding as the primary target of energy efficiency. The purpose of this research is on the obtaining of the renewable energy source in the skyscrape buildings in the metropolitan area. The air movement is happens due to the atmospheric pressure differences in the air. Due to this simple physical theory, it is easily expected to obtain the useful renewable nature energy through the high -raised vertical air stack installed in a tall building. However, there is one problem that should be resolved which is called air-hole effect in the sky -scrape buildings.

• 조명전기설비학회논문지
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• 제17권4호
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• pp.74-80
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• 2003

직류 고전압이 침 대 평판전극에 인가된 불평등전장에서 코로나방전이 발생하게 되면 하전입자들의 이동에 의한 이온풍이 발생한다. 코로나 방전현상은 오존발생장치, 전기집진장치, 정전 냉각과 도색 등의 응용분야에서 다각도로 연구되어 왔으며, 최근 이온풍은 열전달장치, 공기순환장치 등에 이용되기도 한다. 본 연구에서는 침 대 중공평판전극에 직류 고전압을 인가하였을 때 발생하는 이온풍의 속도와 풍량의 제어 특성을 분석할 목적으로 인가전압, 중공의 크기, 전극간 거리의 변동에 따른 풍속의 변화를 측정하였다. 결과로서 이온풍에 의한 기류가 침전극으로부터 평판전극을 향하는 방향으로 발생하였으며, 중공평판전극의 후면의 100~200 [mm]지점에서 측정한 이온풍의 풍속은 인가전압에 따라 1~3[㎧]의 범위에서 증가하였다.