• 천문학회보
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• 제35권1호
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• pp.30.2-30.2
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• 2010

Numerous operational anomalies and satellite failures have been reported since the beginnings of the "space age". Space weather effects on modern spacecraft systems have been emphasized more and more as increasing their complexity and capability. Energetic particles potentially can destroy and degrade electronic components in satellites. We analyzed the geostationary (GEO) satellite anomalies during 1997-2009 to search possible influences of space weather on the satellite anomalies like power problem, control processor problem, attitude control problem, etc. For this we use particle data from GOES and LANL satellites to investigate space weather effects on the GEO satellites' anomalies depending on Kp index, local time, seasonal variation, and high-energy electron contribution. As results, we obtained following results: (1) there is a good correlation between geomagnetic index(Kp) and anomaly occurrences of the GEO satellite; (2) especially during the solar minimum, occurrence of the satellite anomalies are related to electron flux increase due to high speed solar wind; (3) satellite anomalies occurred more preferentially in the midnight and dawn sector than noon and dusk sector; (4) and the anomalies occurred twice more in Spring and Fall than Summer and Winter; (5) the electron with the lowest energy channel (50-75keV) has the highest correlation (cc=0.758) with the anomalies. High association between the anomalies and the low energy electrons could be understand by the facts that electron fluxes in the spring and fall are stronger than those in the summer and winter, and low-energy electron flux is more concentrated in the dawn sector where the GEO satellite anomalies occurred more frequently than high-energy electron flux. While we could not identify what cause such local time dependences, our results shows that low-energy electrons (~100keV) could be main source of the satellite anomaly, which should be carefully taken into account of operating satellites.

• 대기
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• 제27권1호
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• pp.1-16
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• 2017

In this study, trends of upper jet stream characteristics (intensity, altitude, latitude, and longitude) over the Asia-North Pacific region during the recent 30 (1979~2008) years were analyzed by using four reanalysis datasets (CFSR, ERA-Int., JRA-55, MERRA). We defined the characteristics of upper jet stream as the averages of mass weighted wind speed, mass-flux weighted altitude, latitude and longitude between 400 and 100 hPa. Due to the vertical averaging of jet stream characteristics, our results reveal a weaker spatial variabilities and trends than previous studies. In general, the four reanalysis datasets show similar jet stream properties (intensity, altitude, latitude and longitude) although the magnitude and trends are slightly different among the reanalysis datasets. The altitude of MERRA is slightly higher than that of others for all seasons. The domain averaged intensity shows a weakening trend except for winter and the altitude of jet stream shows an increasing trend for all seasons. Also, the meridional trend of jet core shows a poleward trend for all seasons but it shows a contrasting trend, poleward trend in the continental area but equatorward trend in the Western Pacific region during summer. The zonal trend of jet core is very weak but a relatively strong westward trend in jet core except for spring and winter. The trends of jet stream characteristics found in this study are thermodynamically consistent with the global warming trends observed in the Asia-Pacific region.

• 대한원격탐사학회지
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• 제34권1호
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• pp.25-43
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• 2018

The effects of hydro-meteorological and surface variables on the frequency of Asian dust events (FAE) were investigated using ground station and satellite-based data. Present weather codes 7, 8, and 9 derived from surface synoptic observations (SYNOP)were used for counting FAE. Surface wind speed (SWS), air temperature (Ta), relative humidity (RH), and precipitation were analyzed as hydro-meteorological variables for FAE. The Normalized Difference Vegetation Index (NDVI), land surface temperature (LST), and snow cover fraction (SCF) were used to consider the effects of surface variables on FAE. The relationships between FAE and hydro-meteorological variables were analyzed using Z-score and empirical orthogonal function (EOF) analysis. Although all variables expressed the change of FAE, the degrees of expression were different. SWS, LST, and Ta (indices applicable when Z-score was < 0) explained about 63.01, 58.00, and 56.17% of the FAE,respectively. For NDVI, precipitation, and RH, Asian dust events occurred with a frequency of about 55.38, 67.37, and 62.87% when the Z-scores were > 0. EOF analysis for the FAE showed the seasonal cycle, change pattern, and surface influences related to dryness condition for the FAE. The intensity of SWS was the main cause for change of FAE, but surface variables such as LST, SCF, and NDVI also were expressed because wet surface conditions suppress FAE. These results demonstrate that not only SWS and precipitation, but also surface variables, are important and useful precursors for monitoring Asian dust events.

• 한국자동차공학회논문집
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• 제14권3호
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• pp.103-111
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• 2006

The spray behavior of direct-injection spark-ignition(DISI) engines is crucial for obtaining the required mixture distribution for optimal engine combustion. The spray characteristics of DISI engines are affected by many factors such as piston bowl shape, air flow, ambient temperature, injection pressure and fuel temperature. In this study, the effect of fuel temperature on the spray and combustion characteristics was partially investigated for the wall-guided system. The effect of fuel temperature on the fan spray characteristics was investigated in a steady flow rig embodied in a wind tunnel. The shadowgraphy and direct imaging methods were employed to visualize the spray development at different fuel temperatures. The microscopic characteristics of spray were investigated by the particle size measurements using a phase Doppler anemometry(PDA). The effect of injector temperature on the engine combustion characteristics during cold start and warming-up operating conditions was also investigated. Optical single cylinder DISI engine was used for the test, and the successive flame images captured by high speed camera, engine-out emissions and performance data have been analyzed. This could give the way of forming the stable mixture near the spark plug to achieve the stable combustion of DISI engine.

• 한국태양에너지학회 논문집
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• 제30권6호
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• pp.118-124
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• 2010

In order to develop commercial model of 10kW dish-Stirling solar thermal power system, modification for the exiting facility was taken for a year as a Leading Project in KIER. During the project, solar tracking system, control and monitoring system and high durability reflector were developed and long term operation were performed. The solar tracking system was tested for four months to investigate the degree of precision and adapted to the control system for an actual operation from October in 2009. The sun tracking accuracy of ${\pm}4$ mrad using modified control system was obtained and the system operated successfully during the experimental period. The monitoring system displays engine pressure, electric generation amounts, generator RPM, receiver temperatures, and etc. from Stirling engine and weather data of Direct Normal Irradiation, Horizontal Global Insolation, wind speed & direction, and atmosphere temperature from weather station. According to the operating results in a clear sky day, electric power of 6,890 W was generated at the DNI value of 850 W/$m^2$ and the averaged solar-to-electricity efficiency during a whole day reached to 18.99%. From the overall operating results, linear power generation trend could be observed with increasing DNI value. The solar-to-electricity efficiency achieved to 19% around the DNI value of 700 W/$m^2$ and increased to 20% when the DNI value goes up to 900 W/$m^2$.

• 한국환경과학회지
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• 제27권7호
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• pp.489-497
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• 2018

In this study, the ion index characteristics of small and medium urban land use types were investigated in the city of Chungju. The average temperature for each land use type was in the order: general commercial district ($29.59^{\circ}C$) > general residential district ($28.34^{\circ}C$) > productive green district ($28.31^{\circ}C$). The average relative humidity was in the order: productive green district (70.12%) > general residential district (69.93%) > general commercial district (66.48%). The average wind speed was in the order: productive green district (0.95 m/s) > general commercial district (0.87 m/s) > general residential district (0.54 m/s). Positive and negative ions were investigated to determine the ion index by land use type. The average amount of positive ion generated was in the order: general commercial district ($737ea/cm^3$) > general residential district ($492ea/cm^3$) > productive green district ($445ea/cm^3$). The average negative ion production decreased in the order: productive green district ($930ea/cm^3$) > general residential district ($754ea/cm^3$) > general commercial district ($744ea/cm^3$). The ion index calculated from measured data can be arranged in the order: productive green district (2.09) > general residential district (1.53) > general commercial district (1.01). These results confirm the state of positive and negative ion generation in each land use type. Further, the differences in the ion index by land use type were confirmed. However, a limitation of this study is that simple summer measurements were conducted, and seasonal characteristics were not considered. Therefore, any future investigation and research should consider seasonal variation characteristics.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 추계종합학술대회
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• pp.159-163
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• 2005

지난 5년간(1998${\sim}$2002년) 우리나라에서 발생한 해양사고를 살펴보면 100톤 미만의 소형어선이 70.9%를 차지하고 있다. 이것은 소형선박 항해사의 고령화와 선박운항에 관한 전문지식을 결여에 기인한다고 볼 수 있으며, 상선의 경우 연안어선 및 통한선의 증가로 연안항해에 지장을 받고 있는 실정이다. 이러한 상황에서 외부상황을 육안으로 관찰하면서 항해에 필요한 상황을 언어적 표현에 의해 가이딩 받을 수 있다면 항해 안전에 큰 도움이 될 것이다. 현재 선박에서 항해사에게 항로정보를 제공하는 장비는 ECDIS와 GPS 플로터가 많이 사용되고 있으나 자동항로생성 및 항로설명기능이 없어 숙련된 항해사만 사용할 수 있는 문제가 있으며, 특히 종이해도의 대체 시스템인 ECDIS에 사용되는 ENC를 이용한 자동항로생성 및 항로설명에 관한 연구는 없는 실정이다. 본 논문에서는 ENC의 해도데이터와 GPS의 위치데이터, 풍속${\cdot}$풍향계의 풍속${\cdot}$풍향데이터를 이용하여 현 위치에서 목적지까지의 최적항로를 설계하여 안내해주는 항해가이딩시스템을 구축하였고, 시뮬레이션을 통하여 유효성을 확인하였다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2018년도 춘계학술대회
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• pp.318-320
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• 2018

When a ship sails on sea, it may be influenced by the environmental disturbance such as wind, wave, sea surface temperature, etc. These affect on the ship's speed, fuel consumption, safety and operating performance. It is necessary to find the optimal weather route of a ship to avoid adverse weather conditions which can put the crews in serious danger or cause structural damage to the vessel, machinery, and equipment. This study introduced how to apply A* algorithm based on sea trial test data for determining the optimal ship routes. The path cost function was modelled as a function of minimum arrival time or minimum energy depending on the time of various environment conditions. The specially modelled path-cost function and the safety constraints were applied to the A* algorithm in order to find the optimal path of the ship. The comparison of ship performances estimated by real sea trial's path and estimated optimal route during the voyage of the ship was investigated. The result of this study can be used to create a schedule to ensure safe operation of the ship with short passage time or minimum energy. In addition, the result of this study can be integrated into an on-board decision supporting expert system and displayed in Electronic Chart Display and Information System (ECDIS) to provide all the useful information to ship master.

• 농업생명과학연구
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• 제45권4호
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• pp.29-35
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• 2011

본 연구에서는 2005년부터 2009년까지 전라남도 지역의 기상변화와 산불특성과의 관련성을 파악하기 위해 기상요소와 산불 발생자료 (시간, 원인)를 분석한 결과, 최고온도 상승과 상대습도 감소로 인해 산불발생의 위험성이 높은 기후조건이 형성되었으며, 산불은 최고기온 $10{\sim}20^{\circ}C$에서, 상대습도 40~60% 에서, 평균풍속 2 m/s이하에서 주로 발생하였다. 이러한 기상조건은 강우 후에 2~3일이면 산불발생 위험이 높은 기상조건이 형성되었다.

• 한국수자원학회논문집
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• 제51권spc1호
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• pp.1045-1056
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• 2018

지난 수십 년 동안, 변화하는 기후를 이해하기 위해 많은 연구가 있었고, 여러 기후 변량의 변화추세가 발견되었다. 이들 추세를 설명하기는 쉽지 않고, 때로는 서로 모순적으로 보여지기도 한다. 다양한 기후 변량의 변화추세를 일반적으로 설명하기 위한 가설을 제시하기 위해 많은 시도도 있었다. 어느 정도 지식이 축적된 이 시점에서, 우리 시대에 진행되는 기후 변화에 대해 우리가 알고 있는 것을 되돌아보고 신중히 정리해볼 필요가 있다. 여기서는 기온, 일사량, 풍속, 증발, 강수에 초점을 맞추어 변화하는 기후에 대해 우리가 얻은 지식을 종합적으로 살펴보고자 한다. 온난화, 흐려짐, 잔잔하기로 대변되는 주요 변화추세 및 증발의 역설, 강수 변동성의 증가를 서울 지점 자료를 예시로 들어 설명한다. 이러한 변화에 대한 이해를 근거로 수문학자와 공학자들에게 네 가지 함의를 제시하려 한다.