• Proceedings of the KSR Conference
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• 2010.06a
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• pp.139-150
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• 2010

Recently, full-scale research about a passenger tube train system is being progressed as a next-generation transportation system in Korea in light of global green technology. The Korea Railroad Research Institute (KRRI) has commenced official research on the construction of a tube train system. In this paper, we studied various parameters of the tube train system such as the internal tube pressure, blockage ratio, and operating speed through computational analysis with a symmetric and elongated vehicle. This study was about the aerodynamic characteristics of a tube train that operated under standard atmospheric pressure (open field system, viz., ground) and in various internal tube environments (varying internal tube pressure, blockage ratio, and operating speed) with the same shape and operating speed. Under these conditions, the internal tube pressure was calculated when the energy efficiency had the same value as that of the open field train depending on various combinations of the operating speed and blockage ratio (the P-D relation). In addition, the dependence of the relation between the internal tube pressure and the blockage ratio (the P-${\beta}$ relation) was shown. Besides, the dependence of the relation between the total drag and the operating speed depending on various combinations of the blockage ratio and internal tube pressure (the D-V relation) was shown. Also, we compared the total (aerodynamic) drag of a train in the open field with the total drag of a train inside a tube. Then, we calculated the limit speed of the tube train, i.e., the maximum speed, for various internal tube pressures (the V-P relation) and the critical speed that leads to shock waves under various blockage ratios, which is related to the efficiency of the tube train (the critical V-${\beta}$ relation). Those results provide guidelines for the initial design and construction of a tube train system.

• Journal of Korean Society for Geospatial Information Science
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• v.23 no.4
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• pp.49-55
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• 2015

This paper explains major considerations for integrated GPS/GLONASS/BDS positioning, and then analyzes integrated GNSS positioning accuracies based on low-cost receivers in open-sky and poor reception environments. In an open-sky environment, horizontal RMSE of the integrated system positioning is about 1.2m. It shows improved result compared with single system positioning, the improvement ratio was 17-55%. In poor reception environments, we sometimes could not do positioning because the number of visible satellites gets below four. In an integrated positioning mode, the number of visible satellites was always higher than four, allowing us to find positions all the time. The horizontal RMSE of the integrated system positioning in poor reception environments is about 6.4m. Compared with single system positioning;the integrated system positioning shows better performance and the improvement ratio was 8-47% for the horizontal directions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.4
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• pp.586-593
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• 2001

본 논문에서는 Cost231-Hata 모델과 Cost231-Walfisch-Ikegami 모델을 비교 분석하고, 두 모델의 전파환경이 서로 근접하게 되는 송신안테나의 높이, 건물군의 높이, 그리고 도로폭의 상관관계를 나타내는 전송손실 곡선들을 제시한다. 이러한 곡선들은 Okumura-Hata 모델의 정성적인 전파환경(도심지, 교외지역, 개활지)을 정량적인 요소(건물군의 높이, 도로폭) 로서 설명하여, Okumura-Hata(Cost231-Hata) 모델을 다른 도시, 나라에 적용시킬 때 하나의 기준으로 활용 될 수 있을 것이다. 또한 최근에 제안된 ITU-R 모델과 Okumura-Hata(Cost231-Hata)모델을 비교 분석한 결과, ITU-R 곡선들은 Okumura-Hata의 교외지역 전파환경에 대한 사용식을 확장한 것으로 사료된다.

• Journal of the Korean Society for Railway
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• v.11 no.6
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• pp.519-523
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• 2008

Inside noise levels of running train is the summation of air borne noise and structure-borne noise. In this paper, structure-borne noise, which is known to dominate inside noise level in open field, is investigated. Structure borne noise is analyzed in terms of vibration sources, transmission path and noise generating part so as to reduce inside noise levels.

• Korean Journal of Environment and Ecology
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• v.21 no.1
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• pp.30-37
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• 2007

Pellets and prey remains were analyzed to compare diets and foraging tactics of Eurasian eagle owls (Bubo bubo) in two different habitat types: forested areas and open fields. Overall 150 prey items of three taxa were identified from 66 pellets and 82 prey remains, and the birds were the most important prey in biomass (78.04%) and in frequency (56.67%). Eurasian eagle owls frequently used rats (Rattus spp.), ring-necked pheasants (Phasianus colchicus), and stripped field mice (Apodemus agrarius), but the ring-necked pheasant was most important in biomass in both habitat types. The owls generally foraged various prey in biomass but the mean mass of vertebrate prey used by the Eurasian eagle owls was 503.3g in central Korea. According to the comparison of diets in the two different habitat types, the owls used bigger and more diverse prey in forested areas than in open fields. In forested areas, the Eurasian eagle owls frequently foraged the pheasants and Mandarin ducks (Aix galericulata), but they preferred prey of particular sizes to prey of particular taxa. In open fields, however, the owls showed opportunistic foraging tactics by selecting many small mammals such as rodents or a few large birds.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.880-887
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• 2020

This study was conducted to investigate the running stability of a high-speed train operated in a tunnel and an open field when external forces such as wind pressure and train crossings were applied to the vehicle. With no external force, the running stability at 400 km/h was examined, and the wheel weight reduction ratio, lateral pressure of the axles, and derailment coefficient satisfied the criteria of the technical standards for a high-speed train. When the distance between the centers of the tracks is 4.6 m, the external force caused by train crossing slightly affects the lateral acceleration of the vehicle but does not significantly affect the wheel weight reduction rate, lateral pressure, and derailment coefficient in a tunnel and open filed. When the distance is 4.6~5.0 m, the wheel weight reduction ratio, lateral pressure, and derailment coefficient satisfy the criteria with 20 m/s wind. When the wind speed was 30 m/s, the derailment coefficient satisfied the criteria, and the other variables exceeded them. It is predicted that a high-speed train can be operated safely at 400 km/h with wind speed of up to 20 m/s, and it should be slowed down at a wind speed of 30 m/s.

• Journal of Satellite, Information and Communications
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• v.10 no.4
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• pp.12-16
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• 2015

Unmanned robot system has become a significant part of network centric warfare. Unnlike the commercial wireless system, however, it is tricky to provide reliable communication in the harsh environment: tactical and military communication. Therefore, it needs to be considered when the base station and mobile has poor communication channel. In this paper, we proposed an efficient operating algorithm for unammned robot system with ensuring communication survivability in the harsh environment. From the simulation, we adopted the SUI channel suitable for domestic mountainous area and open terrain with Rician factor K.

• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.1
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• pp.43-51
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• 2020

In this study, numerical analysis was carried out on a complex pressure field of blast waves caused by the detonation of high explosives in various environments. The generated blast waves propagated in the air, upon the sudden release of high energy induced by the explosion. Reflected waves were created when the pressure waves encountered certain obstacles such as the ground or the walls of structures. The propagation of the blast waves and its interaction with the reflected waves were simulated. An adaptive mesh refinement was applied to improve the efficiency of distribution of computer resource, for the computational calculation of the blast wave propagation in a wide open space. In addition, the integration of the calculation domains for the explosive and air were considered when the maximum density of the explosive region was below critical value. The results were verified by comparison with the pressure time history from blast wave experiments performed under two topographical conditions.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1579-1580
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• 2015

철도차량의 동력원은 화석연료를 사용하던 디젤차량에서 최근 고속전철 및 도시철도차량, 경량전철 등 전기를 주 동력원으로 사용되고 있다. 철도차량에 전기를 공급하는 시스템은 일반적으로 개활지 등 지상구간에 적용되고 있는 가공전차선 방식과 지하구간, 터널 등에 적용되고 있는 강체가선방식 그리고 경량전철 등에 채용되고 있는 제 3궤조방식이 있다. 최근에는 일반적으로 지하구간의 가선시스템에 적용되던 T-Bar방식의 강체가선 방식에서 탈피하여 고속주행이 가능한 R-Bar방식의 강체가선 방식에 대한 연구가 많이 이루어지고 있다. 최근까지 지하구간의 터널구조에서 강체전차선로를 급전시스템으로 채택할 경우 열차의 최고속도는 국내의 경우 90km/h, 국외의 경우 160km/h를 넘지 못하는 실정이었다. 그러나 이를 극복한 제품이 개발되어 열차운행 최고속도를 200~250km/h까지 향상시킬 수 있게 되었다. 본 논문에서는 최근 설계속도 250km/h 급 R-bar방식 강체전차선로 인터페이스를 위한 이선현상 모의 시뮬레이터 개념 설계에 관한 연구를 수행하였다. 이를 위해 집전성능과 관계가 있는 전기철도차량 이선현상 요인 및 영향 분석하였으며 강체전차선로 운행에 따른 이선 등으로 인한 영향을 고찰하기 위해 이선 현상 모의 시뮬레이터 개념 설계에 대한 연구를 수행하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.4
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• pp.207-214
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• 2022

A prediction model is proposed for a blast load acting on a column component because of an external explosion. The model can predict the pressure-time histories acting on a column using the fitting curves established from a database composed of finite-element (FE) analysis results. To this end, 70 numerical simulations using the commercial software AUTODYN were performed by changing the column width. To confirm the performance of the proposed model, pressure-time histories estimated from an existing empirical formula and the proposed model were compared based on the FE analysis results. It was verified that the proposed model can more precisely predict the pressure-time histories compared with the existing model.