• Journal of Biosystems Engineering
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• 제37권4호
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• pp.215-224
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• 2012

Purpose: This study was conducted to classify the energy efficiency of 131 tractor models tested during from 2006 to 2010 in Korea. Methods: Four sub-indexes were developed using the fuel consumptions at 60% and 90% of rated speed with partial loads and at pull speeds of 3.0 km/h and 7.5 km/h with maximum drawbar pull. Weighting factors of the sub-indexes were also considered to reflect the characteristics of tractor's actual working hours in Korea. Four sub-indexes were integrated into a classification index. Using the developed classification index, a five-classification system was made on the basis of normal distribution of tractors over the classification range. Percentage of $1^{st}$ grade interval was expected to be close to 15%, $2^{nd}$ grade 20%, $3^{rd}$ grade 30%, $4^{th}$ grade 20%, $5^{th}$ grade 15%. Results: Number of $1^{st}$ grade was 21, $2^{nd}$ grade 23, $3^{rd}$ grade 39, $4^{th}$ grade 33, $5^{th}$ grade 15 among 131 models. Conclusions: Classification index was developed by integrating four sub-indexes. By the classification method using developed index, distribution of classified tractors was acceptable for practical application.

• ETRI Journal
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• 제22권4호
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• pp.32-39
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• 2000

In low earth orbit (LEO) satellite communication systems, more severe phase distortion due to Doppler shift is frequently detected in the received signal than in cases of geostationary earth orbit (GEO) satellite systems or terrestrial mobile systems. Therefore, an estimation of Doppler shift would be one of the most important factors to enhance performance of LEO satellite communication system. In this paper, a new adaptive Doppler compensation scheme using location information of a user terminal and satellite, as well as a weighting factor for the reduction of prediction error is proposed. The prediction performance of the proposed scheme is simulated in terms of the prediction accuracy and the cumulative density function of the prediction error, with considering the offset variation range of the initial input parameters in LEO satellite system. The simulation results showed that the proposed adaptive compensation algorithm has the better performance accuracy than Ali's method. From the simulation results, it is concluded the adaptive compensation algorithm is the most applicable method that can be applied to LEO satellite systems of a range of altitude between 1,000 km and 2,000 km for the general error tolerance level, M = 250 Hz.

• 대한기계학회논문집 C: 기술과 교육
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• 제2권2호
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• pp.105-111
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• 2014

지구를 둘러싸고 있는 대기의 하층 부분을 구성하는 기체를 보통 공기라 말한다. 지상 20km 이하에서는 그 성분이 거의 일정한 비율로 존재하며, 질소, 산소, 기타 혼합기체로 구성된다. 공기밀도란 단위 부피 중에 포함된 공기의 질량을 말한다. 공기는 거의 일정한 성분으로 조성된 혼합기체이지만, 수증기는 변동이 큰 성분의 하나이다. 같은 온도, 같은 압력에서는 습공기의 밀도가 건공기의 밀도보다 작다. 보통 밀도는 압력이나 온도 변화에 따라 변화된다. 따라서 풍량 계산에 사용되는 중요 인자인 공기 상태량에 따른 밀도 계산과정과 actual air flow 와 standard air flow 의 관계를 살펴 보고자 한다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.3-6
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• 2002

In this study, we investigate the atmospheric environment changes in the aspect of optical remote sensing using surface observation data from 1971 to 2000 of Korea Meteorological Administration. Visibility, spatially averaged over Korean peninsula, is systematically reduced from about 28km to 18km during the last 30 years. It means that atmospheric conditions for the optical remote sensing over Korean peninsula are growing worse and worse due to the degradation of air quality. The 30-year average of cloud amount shows a strong seasonal variation, maximum(75%) in summer and minimum (35%) in autumn. Precipitation also shows a very similar variation pattern with cloud. The temperature and sea level pressure show a opposite seasonal change pattern, maximum(minimum in SLP) in summer and minimum(maximum in SLP) in winter, respectively. Relative humidiy(RH) is one of the variables mostly affected by urbanization or urban heat island. As a results, annual mean RH is decreased from 73% to 68% during last 30 years. When we take into account the favorable and unfavorable factors all together, summer and autumn are the worst and the best season for optical remote sensing in Korea.

• 한국도로학회논문집
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• 제15권3호
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• pp.127-135
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• 2013

PURPOSES : The purpose of this study is development of automatic equipment to measure the road water-reservoir which can be one of factors for road traffic safety inspection and its application to safety analysis. METHODS : The scopes of this study are the examination of the riskiness and location of road water-reservoir through literature review, development of appropriate sensor and automatic equipment to survey the road water-reservoir and evaluation of field application. RESULTS: The laser lighting and IR camera were selected to develop the equipment. It was found from the field calibration that there is a high correlation between rutting and road water-reservoir and road water-reservoir caused by rutting can be correctly calculated. About 20.2km of national highway were inspected for case study and field application. It was found from correlation of traffic incident that 2.08km of the latent length for water-reservoir which is related to 12 traffic incidents were analyzed. CONCLUSIONS : This technique can be utilized evaluation method for road condition such as road water-reservoir for conventional evaluation system such as road traffic safety assessment and safety analysis and it can be use to new evaluation system to apply various road condition and traffic condition.

• 한국지반신소재학회논문집
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• 제15권1호
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• pp.71-81
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• 2016

준설토 이송 시 윤활층에 전자기장을 인가하여 이송 동력을 절감하고, 송토량을 증가시키는 연구의 일환으로, 이런 전자기장 장치의 실제 적용성을 검증하고자 실현장 8.5km의 이송거리의 준설현장에 전자기장 장치를 설치하여 그 효과를 검증하였다. 이송 유속에 관계되는 운전 조건 및 토질상태와 유동상태를 모니터링하고, 획득한 데이터를 송토량과 동력 사이의 관계로 정리하여 전자기장 인가 후 약 30%의 동력대비 이송량 증가가 있음을 확인하였고, 이를 통해 전자기장 인가가 준설토 이송 시 동력절감에 효과가 있음을 확인하였다.

• 전자공학회논문지
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• 제52권9호
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• pp.147-152
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• 2015

지금까지의 전차선 검측 시스템은 검측차량을 이용하여 검사구간을 주행 한 후 결과를 산출하였다. 이것은 아열대기후로의 변화에 인한 자연 환경의 급변과 450Km/h급 고속철도 차량의 등장으로 변화가 요구된다. 이에 고속 주행환경과 노반정보를 반영하는 융합 가변형 전차선 검측시스템의 구조를 연구하였다. 기존의 시스템은 전차선에 한정하여 마모의 정도를 판단하였다. 이에 비해 본 논문에서는 검지를 위하여 참조하는 정보를 검측대상의 영상정보에 추가하여 음향정보를 융합하였고, 지형정보에 따라 검지빈도와 정밀도를 가변적으로 적용함으로써 시설물 검측에 대한 기본적인 모델을 제안하였다.

• 한국도로학회논문집
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• 제19권6호
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• pp.147-153
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• 2017

PURPOSES : This research aims to estimate the occurrence of hydroplaning on roads based on the road alignment types and rainfall intensity in Seoul. METHODS : Three types of data were used for estimation of hydroplaning in this study. The Inner Circulation Road (12.5 km) to the Bukbu Expressway (7.4 km) in Seoul was selected as the test road and data was collected for road information using a probe-vehicle. Precipitation was observed from Automatic Weather System in Seoul. These data were interpolated by applying Inverse Distance Weighted Methodology for hydroplaning estimation. Finally, the water depth information of the roads was observed using an RCM411 device. RESULTS : This study demonstrated that the cross slope with small-angle-tilt or vertical section with large-angle-tilt are the primary factors causing hydroplaning on the roads. The flow velocity on steep slope is high; however, large drainage lengths result in hydroplaning on the roads. CONCLUSIONS : This result can contribute towards the reduction of car accidents on rainy days. Furthermore, information regarding hydroplaning can be delivered to drivers more rapidly and precisely in the future.

• 한국측량학회지
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• 제30권6_2호
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• pp.673-680
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• 2012

Long-term GPS data analysis was performed in order to analyze the seasonal variation of tropospheric delay and the success rate of the ambiguity resolution. For this analysis, a total of 57 stations including 10 IGS stations in East Asia were processed together with double-differenced observables using Bernese GPS Software V5.0. The time span for this study ranges from 2002.0 to 2012.5 (10.5 years). The average baseline length is 339.0 km and the maximum reaches up to 2,000 km. The analysis is focused on two things: the annual variation of the tropospheric delay and the ambiguity resolution rate. The tropospheric delay is closely related to the weather condition, especially relative humidity, therefore it was estimated that the maximum would be in summer, while reaching its minimum in winter with the apparent seasonal variations. On the contrary, however, the success rate of the ambiguity resolution shows the opposite pattern: its maximum was in winter and minimum in summer. The fact seems to be induced by the surrounding conditions; that is, the trees thick with leaves near the GPS antenna interfere with GPS signals in summer. This seems to confirm partly that there is a distinct trend in the decreasing success rate since 2006 because the trees are growing every year. It is necessary to eliminate the factors that degrade the GPS quality and the tropospheric modeling for Korea needs to be studied further.

• Environmental Engineering Research
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• 제25권3호
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• pp.366-373
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• 2020

The autonomous vehicles (AVs) could make a positive or negative impact on reducing mobile emissions. This study investigated the changes of mobile emissions that could be caused by large-scale adoption of AVs. The factors of road capacity increase and speed limit increase impacts were simulated using a conceptual modeling approach that combines a hypothetical speed-emission function and a traffic demand model using a virtual transportation network. The simulation results show that road capacity increase impact is significant in decreasing mobile emissions until the market share of AVs is less than 80%. If the road capacity increases by 100%, the mobile emissions will decrease by about 30%. On the other hand, driving speed limit increase impact is significant in increasing mobile emissions, and the environmentally desirable speed limit was found at around 95 km/h. If the speed limit increases to 140 km/h, the mobile emissions will increase by about 25%. This is because some vehicles begin to bypass the congested routes at high speeds as speed limit increases. Based on the simulation results, it is clear that the vehicle platooning technology implemented at reasonable speed limit is one of the AV technologies that are encouraging from the environmental point of view.