• International Journal of Internet, Broadcasting and Communication
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• 제14권1호
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• pp.152-161
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• 2022

Recently, it is recognized as a high-cost and inefficient logistics system that increases traffic congestion and environmental problems due to an increase in traffic volume due to the activation of the online market. In order to solve inefficient problems such as unavoidable traffic congestion and environmental problems caused by the increase in traffic volume, it is necessary to develop a freight transport system technology using the existing urban railway infrastructure and freight-only urban railway. The urban subway logistics system is a logistics system that requires a combination of various technologies to solve the nationwide demand for urban logistics and road traffic problems. This paper recognized the existing traffic congestion and environmental pollution of road traffic as problems, and supplemented the contact point requirements presented above by identifying the sub-systems constituting the target system and supplementary points for each part-level contact point. In this study, as a complex system operated for one purpose by grafting various technologies, a plan is required to secure the reliability and safety of operation from various viewpoints. The results of this study can contribute to the initial configuration and basic data to solve the interface bottleneck of the urban subway logistics system to be promoted in the future.

• Journal of applied mathematics & informatics
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• 제9권2호
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• pp.561-577
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• 2002

In this paper, a two-dimensional finite volume unstructured mesh method (FVUM) based on a triangular background interpolation mesh is developed for analysing the evolution of the saltwater intrusion into single and multiple coastal aquifer systems. The model formulation consists of a ground-water flow equation and a salt transport equation. These coupled and non-linear partial differential equations are transformed by FVUM into a system of differential/algebraic equations, which is solved using backward differentiation formulas of order one through five. Simulation results are compared with previously published solutions where good agreement is observed.

• 한국자동차공학회논문집
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• 제1권1호
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• pp.1-13
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• 1993

The three-dimensional numerical analysis for in-cylinder flow of four-valve engine without intake port has been successfully computed. These computations have been performed using technique of the general coordinate transformation based on the finite-volume method and body-fitted non-orthogenal grids using staggered control volume and covariant variable as dependent one. Computations are started at intake valve opening and are carried through top-dead-center of compression. A k-$\varepsilon$model is used to represent turbulent transport of momentum. The principal study is the evolution of interaction between mean flow and turbulence and of the role of swirl and tumble in generating near TDC turbulence. Results for three different inlet flow configuration are presented. From these results, complex flow pattern may be effective for promoting combustion in spark-ignition engines and kinetic energy of mean flow near TDC is well converted into turbulent kinetic energy.

• 한국주조공학회지
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• 제22권4호
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• pp.155-159
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• 2002

Magnesium alloys have high strength to weight ratio and are extremely attractive for applications in transport industry. Most of structural magnesium alloys are manufactured by die casting process. The tensile properties of AZ91HP magnesium alloy were investigated after die casting under various die casting conditions. After die casting by using cold chamber machine, the volume porosity of specimens was examined with density method. With the increase of the volume porosity of specimens, both the tensile strength and elongation were significantly decreased, however the 0.2% offset strength was almost independent of the amount of porosity. With the increase of crystal pressure from 500 to 900 bar during die casting, the volume porosity was decreased, which resulted in the increase of the tensile strength. The mould temperature within the range of $150{\sim}250^{\circ}C$ has not influenced the microstructure with the eutectic phase and tensile properties of specimens. The tensile strength was the highest at 90m/sec of gate speed.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4620-4624
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• 2022

Several cadmium zinc telluride (CZT) crystals were fabricated into radiation detectors using methods that included slicing, dicing, lapping, polishing, and chemical etching. A wet passivation with sodium hypochlorite (NaOCl) was then carried out on the Br-etched detectors. The Te-rich layer on the CZT surface was successfully compensated to the Te oxide layer, which was analyzed with X-ray photoelectron spectroscopy data of both a Br-etched crystal and a passivated CZT crystals. We confirmed that passivation with NaOCl improved the transport property by analyzing the mobility-lifetime product and surface recombination velocity. The electrical and spectroscopic properties of large volume detectors were compared before and after passivation, and then the detectors were observed for a month. Both bar and quasi-hemispherical detectors show an enhancement in performance after passivation. Thus, we could identify the effect of NaOCl passivation on large volume CZT detectors.

• 콘크리트학회논문집
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• 제15권2호
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• pp.345-351
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• 2003

The transport characteristics of deleterious ions such as chlorides depend on the pore structures of concrete and are the major factors in the durability of concrete structures in subjected to chloride attack such as in marine environments. In this paper, the effect of the pore structure on compressive strength and chloride diffusivity of concrete was investigated. Six types of concretes were tested. The pore volume of concrete containing mineral admixtures increased in the range of 3∼30nm due to micro filling effect of hydrates of the mineral admixtures. There was a good correlation between the median pore diameter, the pore volume above 50nm and compressive strength of concrete, but there was not a significant correlation between the total pore volume and compressive strength. The relationship between compressive strength and chloride diffusivity were not well correlated, however, pore volume above 50nm were closely related to the chloride diffusion coefficient.

• 한국ITS학회 논문지
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• 제13권5호
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• pp.1-10
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• 2014

본 연구는 미시적 교통류 시뮬레이션 모형을 이용하여 양방향 좌회전차로의 설치기준과 관련된 두 개의 주요한 파라미터를 분석하고 평가하는데 초점을 맞추고 있다. 첫째는 통상적으로 평균 일교통량(ADT)에 기반을 두고 산정되지만 최근 우리나라 도로교통량의 시간변화 특성을 반영한 설계시간 교통량(DHV)의 범위에 대한 분석이며, 다른 하나는 양방향 좌회전차로 내의 구간으로써 양방향 좌회전 수요가 공간점유를 위해 서로 경쟁하면서 상충이 유발되는 부분인 접근로 간격에 관한 것이다. 이에 더해 VISSIM S/W에 VISVAP과 같은 추가 기능 프로그램을 사용하여 TWLTL의 작동을 구현하는 구체적 방법과 절차에 대해 선행 연구들과는 달리 충실히 설명하고자 하였다. 10개의 교통량 수준 시나리오로 수행한 모의실험 결과에 따르면 통과 교통량이 많을수록 좌회전 차량이 경험하는 지체는 예상대로 견조히 증가하였다. 시나리오 대부분에 대한 지체 값이 비신호교차로 서비스수준을 기준으로 LOS C와 D의 범위에 있는 것으로 나타났으며, 교통량 수준 7(중방향으로 3차로 시설 경우 1,116대/시, 5차로 시설은 1,860대/시)까지 양방향 좌회전 차로가 운영가능하다는 것을 알 수 있었다. 이 범위의 교통량은 우리나라 2차로 및 4차로도로 교통량의 상당 부분을 포함하는 것으로 향후 양방향 좌회전차로의 도입 가능성을 한 층 높이는 것이라고 판단하고 있다.

• 대한교통학회지
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• 제31권2호
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• pp.3-10
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• 2013

현재 지방부 도로의 50% 이상을 차지하고 있는 양방향 2차로 도로는 4차로 도로로 확장하기에는 장래 교통량이 부족하지만 양방향 2차로 도로로 계속 운영하기에는 교통량이 많은 문제점이 발생되고 있는 경우가 많다. 또한 양방향 2차로도로의 추월행태에 따른 교통사고 위험과 사고 심각도가 높은 문제 해결을 위하여 2+1차로 도로의 도입을 검토하게 되었는데, 유럽의 여러 국가에서는 양방향 2차로 도로를 2+1차로 도로로 신설 또는 확장함으로써 예산 투자 효율화와 안전성 향상의 효과를 거둔 사례가 있는 것으로 나타났다. 본 연구는 영국, 독일, 스웨덴, 아일랜드, 핀란드 등에서 운영하고 있는 2+1차로 도로 사례를 검토하고 이를 국내 양방향 2차로 도로 개선방안의 하나로 도입하기 위한 가능성을 모색하기 위하여 수행되었다. 본 연구를 통해 국내 도로에 2+1차로 도로를 도입하는 경우 적정 교통량 수준을 산출하고, 이를 이용하여 2+1차로 도로의 계획기준을 개발하였다. 2+1차로 도로가 감당할 수 있는 교통량 수준을 시뮬레이션 프로그램 VISSIM(5.0)을 이용하여 분석하였고, 이를 국내 양방향 2차로 도로의 도로환경 조건을 고려하여 보정한 결과 중차량 비율에 따라 7,300대/일에서 17,000대/일 정도로 분석되었다. 이는 독일 등 유럽의 2+1차로 도로에서 관측된 최대교통량에 비해 약간 작은 값이고, 아일랜드의 관측 최대교통량(17,250대/일)과 유사한 값이다.

• 한국수자원학회논문집
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• 제30권6호
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• pp.597-610
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• 1997

본 연구에서는 하도 내에서의 부정류 유사이송으로 인한 하상변동의 일차원적 수치모델들을 개발하였다. 유사량과 하상변동에 대한 수치해를 얻기 위해 흐름의 방정식은 Preissmann 음해법과 Lax-Wendroff 2단 양해법을 그리고 유사의 연속방정식은 시간 전방차분, 공간 중앙차분 양해법을 사용하여 수치 적분하였고, Lax-Wendroff 기법 내에서 상류와 하류의 추가 경계조건을 구하기 위해 특성곡선법을 적용하였다. 모델의 정확도는 부피보존실험을 통하여 성공적으로 입증되었으며, 모델의 주요 변수들에 대한 민감도 분석결과로부터 보다 큰 최대 홍수위, 하상경사 및 홍수지속기간에 의해 큰 하상세굴이 발생하였고, 하상재료의 평균입경 가운데, $D_{50}=0.4mm$에서 가장 큰 하상변동을 가져왔다. 본 연구에서 개발된 모델들이 각 변수들의 변화에 적절한 반응을 함으로써 모델들이 합리적인 결과를 가져다주는 것으로 결론되어지며, 실제하천에 적용될 수 있는 것으로 판단된다.

• Journal of the korean society of oceanography
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• 제35권3호
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• pp.129-152
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• 2000

The Cheju Current (CC), defined here as a mean eastward flow in the Cheju Strait, mostly carries water of high temperature and salinity originating from the Kuroshio in winter and spring, the Cheju Warm Current Water (CWCW). The strong core of the eastward component of the CC is found close to Cheju Island (Cheju-Do, hereafter) in winter and spring with a peak speed of about 17.0 cm/s. The eastward flow weakens towards the northern Cheju Strait, and a weak westward flow occurs occasionally close to the southern coast of Korea. The volume transport ranges from 0.37 to 0.45 Sv(1 Sv=10$^6$ m$^3$/s) in winter and spring. Seasonal thermocline and harocline are formed in summer and eroded in November. The occurrence of the CWCW is confined in the southern Cheju Strait close to Cheju-Do below the seasonal thermocline in summer and fall, and cold water occupies the lower layer north of the CWCW which is thought to be brought into the area from the area west of Cheju-Do along with the CWCW. Stratification acts to increase both the speed of the CC with a peak speed of greater than 30 cm/s and the vertical shear of the along-strait currents. The strong core of the CC detached from the coast of Cheju-Do and shifted to the north during the stratified seasons. The volume transport in summer and fall ranges 0.510.66 Sv, which is about 1.5 times larger than that in winter and spring. An annual cycle of the cross-strait sea level difference shows its maximum in summer and fall and minimum in winter and spring, whose tendency is consistent with the annual variability of the CC and its transport estimated from the ADCP measurements. Moored current measurements west of Cheju-Do indicate the clockwise turning of the CC, and the moored current measurements in the Cheju Strait for 1530 days show the low-frequency variability of the along-strait flow with a period of about 37 days.