• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.327-332
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• 2006

In airborne gravimetry, there are two data streams. One is the specific force measured by an air/sea gravimeter or accelerometers, the other is kinematic acceleration measured by DGPS. And the difference of them provides the gravity disturbance information. To satisfy the requirement of most applications, an accuracy of 1mGal $(1mCal=10^{-5}m/s^{2})$ with a spatial resolution of 1km is the aim of current airborne gravimetry. There are two different methods to derive the kinematic acceleration. The generally used method is to differentiate the position twice, and the position can be calculated by commercial DGPS software. The main defect of this method is that integer ambiguities need to be fixed to get the precise position solution, but it's not a trivial thing for long base line. And to fix integer ambiguities, the noisier iono-free measurement is used. When differentiation is applied, noise is amplified and will influence the accuracy of acceleration. The other method is to get carrier phase acceleration by differentiate the carrier phase first, and then using the acceleration of GPS satellite to derive the vehicle acceleration. The main advantages include that fixing integer ambiguities is not needed anymore, position can be relaxed to about 10 meters, and smoother acceleration can be got since iono-free measurement is not needed. In some literatures, it's considered that the dynamic performance of the second method is inferior to that of the first. Through analysis, it is found that the performance degradation in dynamic environment results from the simplification of the GPS carrier phase observable model. And an iterative algorithm is presented to compensate the model error. Using a dynamic GPS data from an aeromagnetic survey, the importance of this compensation is showed at last.

• International Journal of Automotive Technology
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• v.6 no.2
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• pp.149-159
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• 2005

A full nonlinear finite element P185/70Rl4 passenger car radial-ply tire model was developed and run on a 1.7-meter-diameter spinning test drum/cleat model at a constant speed of 50 km/h in order to investigate the tire transient response characteristics, i.e. the tire in-plane free vibration modes transmissibility. The virtual tire/drum finite element model was constructed and tested using the nonlinear finite element analysis software, PAM-SHOCK, a nonlinear finite element analysis code. The tire model was constructed in extreme detail with three-dimensional solid, layered membrane, and beam finite elements, incorporating over 18,000 nodes and 24 different types of materials. The reaction forces of the tire axle in vertical (Z axis) and longitudinal (X axis) directions were recorded when the tire rolled over a cleat on the drum, and then the FFT algorithm was applied to examine the transient response information in the frequency domain. The result showed that this PI 85/70Rl4 tire has clear peaks of 84 and 45 Hz transmissibility in the vertical and longitudinal directions. This result was validated against more than 10 previous studies by either theoretical or experimental approaches and showed excellent agreement. The tire's post-impact response was also investigated to verify the numerical convergence and computational stability of this FEA tire model and simulation strategy, the extraordinarily stable scenario was confirmed. The tire in-plane free vibration modes transmissibility was successfully detected. This approach was never before attempted in investigations of tire in-plane free vibration modes transmission phenomena; this work is believed to be the first of its kind.

• Journal of Korea Water Resources Association
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• v.32 no.6
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• pp.637-647
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• 1999

This study investigated the applicability of generalized TOPMODEL approach which introduces the power law of decreasing transimissivity with depth instead of the traditional exponential decreasing function. The 50m digital elevation model(DEM) of Dongkog subwatershed at Wichon Test Watershed was used to perform runoff simulation. Random number generation algorithm was integrated into the calibration process for the reliable of model performance. General power law version of TOPMODEL with exponent 2 and 3 showed higher simulation efficiency than other the approaches. This results from the fact that the power law models with exponent 2 and 3 can represent the soil characteristics of study area better than other models.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.470-470
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• 2015

본 연구의 목적은 위성영상 기반의 SEBAL(Surface Energy Balance Algorithm for Land) 모형과 SWAT(Soil and Water Assessment Tool) 수문모형을 용담댐 유역($922.3km^2$)에 적용하여 증발산량을 산정하고 모형 간 공간 증발산량의 비교를 통해 각 모형의 적용성을 평가하는데 있다. 이를 위해 SEBAL모형의 입력자료로 Terra MODIS(Moderate Resolution Imaging Spectrometer) Product 중 Normalized Distribution Vegetation Index(NDVI), Albedo 영상을 2012년부터 2013년까지 월단위로 구축하고, 일단위의 Land Surface Temperature(LST) 영상을 구축하였다. 지형자료로는 Digital Elevation Model(DEM)과 Land use를 구축하였으며 SEBAL 모형의 구동을 위한 위성영상 및 지형자료는 500 m의 공간해상도로 재구축하였다. SWAT 모형의 모의를 위해 기상 및 유량 자료를 2000년부터 2013년까지 일단위로 구축하였고, DEM, Land use, 토양도의 지형자료를 30 m의 공간해상도로 구축하였다. SWAT 모형의 유출 검보정 후 수위관측소 지점에서 평균 $R^2$를 산정한 결과 도치(0.80), 동향(0.72), 석정(0.64), 주천(0.80), 천천(0.80), 용담댐(0.72)로 높은 상관성을 나타냈으며, 유출 검보정 후 SWAT 모형의 증발산량 모의 결과를 바탕으로 SEBAL 모형과의 공간 증발산량을 비교하였다. 두 모형의 증발산량은 SEBAL 모형의 경우 지형에 따라 SWAT 모형은 토양 특성에 따라 분포하는 경향이 다르게 나타났다. SEBAL 모형은 주로 저지대에서 증발산량이 높게 산정되며 고지대로 갈수록 감소하여 증발산량이 지형의 고저차에 따라 분포하는 모습을 보였다. SWAT 모형은 토양 특성에 따라 증발산량이 분포하며 유역 내에서 뚜렷한 차이를 나타내지는 않았다. 월별 총 증발산량은 SWAT 모형의 경우 7~8월에 약 90 mm/mon로 가장 높게 나타나고 1~2월은 0 mm/mon로 계절별 변화폭이 컸으나, SEBAL 모형의 경우 5~6월에 증발산량이 약 60 mm/mon로 가장 높게 나타났고 계절별 변화 폭이 SWAT 모형에 비해 적은 모습을 보였다. 이는 위성영상을 기반으로 하는 SEBAL 모형의 특성상 장마 기간에 해당하는 7~8월은 구름으로 인해 일사량이 적게 계산되고, 그 결과 5~6월에 비해 증발산량이 작게 산정되는 것으로 판단된다.

• Journal of Biosystems Engineering
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• v.43 no.4
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• pp.273-284
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• 2018

Purpose: Conventional headland turning typically requires repeated forward and backward movements to move the farming equipment to the next row. This research focuses on developing an upland agricultural robot with an optimized headland turning mechanism that enables a $180^{\circ}$ turning positioning to the next row in one steering motion designed for a two-wheel steering, four-wheel drive agricultural robot named the HADA-bot. The proposed steering mechanism allows for faster turnings at each headland compared to those of the conventional steering system. Methods: The HADA-bot was designed with 1.7-m wide wheel tracks to travel along the furrows of a garlic bed, and a look-ahead path following algorithm was applied using a real-time kinematic global positioning system signal. Pivot turning tests focused primarily on accuracy regarding the turning radius for the next path matching, saving headland turning time, area, and effort. Results: Several test cases were performed by evaluating right and left turns on two different surfaces: concrete and soil, at three speeds: 1, 2, and 3 km/h. From the left and right side pivot turning results, the percentage of lateral deviation is within the acceptable range of 10% even on the soil surface. This U-turn scheme reduces 67% and 54% of the headland turning time, and 36% and 32% of the required headland area compared to a 50 hp tractor (ISEKI, TA5240, Ehime, Japan) and a riding-type cultivator (CFM-1200, Asia Technology, Deagu, Rep. Korea), respectively. Conclusion: The pivot turning trajectory on both soil and concrete surfaces achieved similar results within the typical operating speed range. Overall, these results prove that the pivot turning mechanism is suitable for improving conventional headland turning by reducing both turning radius and turning time.

• Journal of Drive and Control
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• v.19 no.4
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• pp.19-28
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• 2022

This paper introduces an automatic steering system for straight traveling capable of being mounted on drivable agricultural machinery which user can handle it such as a tractor, a transplant, etc. The modular automatic steering device proposed in the paper is composed of RTK GNSS, IMU, HMI, hydraulic valve, and wheel sensor. The path generation method of the automatic steering system is obtained from two location information(latitude and longitude on each point) measured by GNSS in advance. From HMI, a straight path(AB line) can be created by connecting latitude and longitude on each point and the device makes the machine able to follow the path. During traveling along the reference path, it acquires the real time position data every sample time(0.1s), compares the reference with them and calculates the lateral deviation. The values of deviation are used to control the steering angle of the machine using hydraulic valve mounted on the axle of front wheel. In this paper, Pure Pursuit algorithm is applied used in autonomous vehicles frequently. For the analysis of traveling characteristics, field tests were executed about these conditions: velocity of 2, 3, 4km/h which is applied to general agricultural work and ground surface of solid(asphalt) and weak condition(soil) such as farmland. In the case of weak ground state, two experiments were executed about no-load(without work) and load(with work such as plowing). The maximum average deviations were presented 2.44cm, 7.32cm, and 11.34cm during traveling on three ground conditions : asphalt, soil without load and with load(plowing).

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.64-64
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• 2023

황강댐은 임진강 상류 군사분계선으로부터 약 42km떨어진 위치에 존재하며 약 3~4억톤의 규모로 추정된다. 이에 우리나라는 약 7천만톤 규모의 군남홍수조절지를 건설하여 임진강 상류로부터 기인하는 홍수를 방어하고 황강댐의 무단방류에 대비하고 있다. 과거 2009년 9월 6일 임진강 상류 황강댐에서의 대규모 방류로 인해 경기도 연천군 일대에 홍수가 발생하여 이로 인한 인명 및 재산피해가 발생한 바 있으며, 2020년 8월 5일에는 장마전선으로 인한 폭우와 더불어 임진강 필승교 수위관측소의 수위가 급상승하면서 관측 이래 역대 최고수위가 발생하여 홍수경보가 발령되고 인근 주민이 대피하는 사례가 발생하였다. 또한, 2022년 6월 27일부터 발생한 장마전선 및 집중호우로 인해 임진강 필승교 수위관측소의 수위가 급상승하면서 홍수주의보가 발령되고 인근 주민이 대피하는 사례가 발생하였으며, 7월에는 비가 내리지 않는 상황에서 황강댐의 방류로 추정되는 유입량이 필승교 수위관측소와 군남홍수조절지에서 관측되었다. 이에 본 연구에서는 인공위성 영상에서 추출한 황강댐의 수위를 이용하여 수문모형과 저수지 운영 알고리즘을 구축하고 당시 발생한 홍수사례를 분석하여 황강댐의 운영방식을 추정하였다. 분석결과, 2020년 8월 5~7일 사이에 발생한 유입량의 경우 자체 유역 유입량은 전체 유입량대비 약 33%이나 북한 황강댐으로부터 추가로 방류된 양은 약 67%로 군남홍수조절지 유입량의 3/2 가량이 북한 황강댐의 방류량으로부터 발생된 것으로 보이며 2021년 6월에도 유사한 양상을 보였다. 하지만, 북한 황강댐의 운영방식이 용수공급을 위한 고수위 유지 운영방식에서 홍수기에 댐 월류 및 파괴를 방지하기 위한 사전방류를 수행하는 것으로 추정되었다.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.162-162
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• 2020

토양수분은 TDR(Time Domain Reflectometry)이나 Tensiometer 등의 장비를 이용하여 측정을 시행하고 있으나, 이를 위해서는 많은 인력과 경제적 자원이 소비될 뿐만 아니라 시공간적으로 측정할 수 있는 범위에 한계가 있다. 지상 관측의 대안으로 MIRAS(Microwave Imaging Radiometer with Aperture Synthesis)나 SMAP(Soil Moisture Active Passive), AMSR2(Advanced Microwave Scanning Radiometer 2) 등의 수동 마이크로파 위성 센서를 이용한 공간 토양수분 관측이 수행되었으나, 낮은 공간 해상도(9~36km)는 지역 규모의 토양수분 분포를 나타내기 충분하지 않고, 높은 불확실성을 내포하고 있다. 본 연구에서는 금강 상류의 용담댐 유역(930.0㎢)을 대상으로 Sentinel-1 C-band SAR(Synthetic Aperture Radar) 영상을 이용한 토지 피복 및 토양 속성을 고려한 10m 해상도의 토양수분 산출을 수행하였다. 용담댐 유역은 산림 79.7%, 논 9.0%, 밭 5.4%, 주거지 2.9%의 토지 피복 비율을 가지며 토양은 사양토(66.6%)와 양토(20.9%)가 우세하다. Sentinel-1 C-band SAR 영상은 SeNtinel Application Platform(SNAP)을 이용하여 전처리 후, 후방산란계수로 변환하였다. 토양수분 알고리즘은 TU-Wien change detection algorithm과 Regression model을 활용하였고, 검증을 위한 실측 토양수분 자료는 한국수자원공사(K-water)에서 제공하는 5년(2014~2018)간의 토양수분 관측자료를 이용하였다. 산출된 토양수분은 결정계수(Coefficient of determination, R²) 및 평균제곱근오차(Root Mean Square Error, RMSE)를 이용하여 실측 토양수분과 비교하였다. Sentinel-1 C-band SAR 영상을 이용한 고해상도의 토양수분 산출은 토지 피복 및 토양 속성을 고려한 지역 규모의 공간 토양수분 분포 및 시간적 변화를 표현 가능할 것으로 판단된다.

• Herbal Formula Science
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• v.31 no.2
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• pp.81-98
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• 2023

Objectives : This study aimed to analyze the trends in research and development projects related to herbal medicine and natural products in the field of traditional Korean medicine (TKM) over the past 20 years. Methods : Research projects were identified using "Korean medicine" as the subject heading in the National Science and Technology Information Service. The included projects investigated Korean medicine, natural products, or were related to the TKM industry. Data pre-processing and network analysis were performed using Python and Networkx package, and the network was visualized using the ForceAtlas2 visualization algorithm. Results : 1. Over the study period, 4,020 projects were conducted with a research budget of KRW 835.2 billion. Seven institutions performed over 100 projects each, accounting for 2.4% of all participating institutions, and the top 10 institutions accounted for 58.9% of total projects. 2. Obesity was the most frequently mentioned disease-related keyword. Chronic or age-related diseases such as diabetes, osteoporosis, dementia, parkinson's disease, cancer, inflammation, and asthma were also frequent research topics. Clinical research, safety, and standardization were also frequently mentioned. 3. Centrality analysis found that obesity was the only disease-related keyword identified, alongside TKM-related keywords. Standardization, safety, and clinical trials were identified as central keywords. Conclusions : The study found that research projects in TKM have focused on standardizing and ensuring the safety of herbal medicine, as well as on chronic and age-related diseases. Clinical studies aimed at verifying the effectiveness of herbal medicine were also frequent. These findings can guide future research and development in herbal medicine.

• Journal of the Korean Society for Railway
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• v.19 no.6
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• pp.833-843
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• 2016

Recently, in the field of rail freight transportation, the number of trains dedicated for shippers has been increasing. These dedicated trains, which run on the basis of a contract with shippers, had been restricted to the transportation of containers, or so called block trains. Nowadays, such commodities have extended to cement, hard coal, etc. Most full freight cars are transported by dedicated trains. But, for empty car distribution, the efficiency still remains questionable because the distribution plan is manually developed by dispatchers. In this study, we investigated distribution models delineated in the KTOCS system which was developed by KORAIL as well as mathematical models considered in the state-of-the-art. The models are based on optimization models, especially the network flow model. Here we suggest a new optimization model with a framework of the column generation approach. The master problem can be formulated into a transportation problem with additional constraints. The master problem is improved by adding a new edge between the supply node and the demand node; this edge can be found using a simple shorted path in the time-space network. Finally, we applied our algorithm to the Korean freight train network and were able to find the total number of empty car kilometers decreased.