• 대한기계학회논문집B
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• 제32권2호
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• pp.125-132
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• 2008

The bubble dynamics and heat transfer associated with nucleate boiling in parallel microchannels is studied numerically by solving the equations governing conservation of mass, momentum and energy in the liquid and vapor phases. The liquid-vapor interface is tracked by a level set method which is modified to include the effects of phase change at the interface and contact angle at the wall. Also, the reversible flow observed during flow boiling in parallel microchannels has been investigated. Based on the numerical results, the effects of contact angle, wall superheat and the number of channels on the bubble growth and reversible flow are quantified.

• 보일러설비
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• 통권61호
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• pp.104-105
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• 1999

• 대한기계학회논문집
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• 제18권12호
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• pp.3287-3296
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• 1994

For the numerical computation of three-dimensional compressible flow field within a blade row in a centrifugal compressor, a quasi 3-dimensional solver which combines a reversible B-B flow and an irreversible H-S flow using finite element methods was developed. In a reversible B-B flow, the governing coordinates are modified in order to be applied to any type of turbomachinery, and two kinds of stream functions are introduced in order to make the Kutta condition exactly satisfied. In an irreversible H-S flow, the changes of entropy in the irreversible governing equations are determined not by empirical source but by the theoretical treatment of dissipation forces. The dissipation forces are obtained from the distribution of shear stresses in the flow passage which are given from the wall shear stresses using the exponential functions. A more accurate quasi-3-dimensional solver is established where the effect of body forces is involved in the non-axisymmetric H-S flow. Some numerical results obtained from authors' previous studies for axial flow machines assure that the present method is able to predict well as long as the flow is subsonic and not under strong viscous effect.

• 한국컴퓨터정보학회논문지
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• 제17권11호
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• pp.19-26
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• 2012

교차로에서 가변차선은 이동하는 차량들을 효율적으로 통제하고 교통 혼잡을 줄일 수 있으며 도로의 가용 능력을 증가시키기 위한 도구로 사용되고 있다. 그러나 아직까지 가변차선의 교통통제는 단순하며 수동으로 가변차로를 운용하고 있다. 따라서, 본 연구에서는 가변차로의 이동방향에 대한 변경 여부를 지능적으로 판단하여 교통 흐름을 효율적으로 개선하기 위한 3단계 방법을 제안한다. 첫 번째는 교차로에서 차량이 이동하는 방향으로 효율성을 판단하기 위한 방법으로 퍼지추론 방법, 두 번째는 이동방향으로 가변차로를 변경할 지에 대한 잠정 판단, 세 번째는 이러한 잠정판단을 최종결정하기 위한 판단기준을 제시한다. 이동방향으로의 효율성은 matlab 프로그램을 이용하여 얻는다.

• 대한교통학회지
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• 제22권1호
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• pp.7-18
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• 2004

국내에서는 복잡하고 심각해진 도시교통난을 해소하기 위한 대안으로 1981년부터 교통체계관리 기법 중 가변차로제를 도입하여 현재 서울을 비롯한 주요 도시에서 운용하고 있다. 그러나 가변차로제 시행에 따른 운영 효과에 대한 연구는 미진한 편이고, 적용함에 있어서 일반적인 경험치를 따른 설치기준을 이용하여 가변차로제를 시행하고 있다. 따라서, 본 연구에서는 현재 서울시에서 운영되고 있는 가변차로 구간에 대한 사례조사를 통해 컴퓨터 시뮬레이션을 이용하여 가변차로 수행에 따른 효과를 분석하고, 그 시행의 효율성을 높기 위한 방안으로서, 국내의 교통여건에 부합하는 가변차로제의 설치기준을 재설정 하였다. 가변차로제 시행 효과 분석을 위한 효과측정기준으로 평균지체와 연료소모량을 선정하였다. TRANSYT-7F 컴퓨터 시뮬레이션을 이용하여, 가변차로로 유입 유출되는 v/c별 교통량과 방향별 교통량비율, 그리고 기하구조측면으로 가변차로수와 가변차로 구간 내에서의 좌회전의 허용여부 이 네 가지 영향요소의 변화에 따른 각각의 상황별 가변차로제 시행효과를 분석하였다. 시뮬레이션 결과 왕복 6차로 구간의 경우 현재 가변차로제의 설치기준으로 제시된 방향별 교통량비율보다 더 작은 차이에서도 가변차로제 실시 효과의 의미를 부여 할 수 있는 것으로 나타났다.

• 한국정보통신학회논문지
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• 제14권10호
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• pp.2254-2260
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• 2010

본 논문에서는 H.264/AVC 표준에서 사용되는 정수 변환을 변형하여 무손실 압축에 효율적인 변환 구현 방법을 제안한다. 기존의 가역(reversible) 변환용으로 제시된 정수 변환은 변환 계수의 값의 범위가 상당히 커서 무손실 압축에 효율적이지 못한 면이 있다. 이런 문제점을 해결하기 위해서 효율적인 정수 변환을 제시한다. 기존 정수 변환의 변형은 고속 연산 수행을 위해서 리프팅을 기반으로 설계되고 효율적인 구조를 도출한다. 본 논문의 결과로서 고속 연산 수행을 위한 신호 흐름도를 제시하고, 이에 관련된 실험 결과를 제공한다. 실험 결과는 제안된 변형 정수변환이 기존 구현 방법에 비하여 무손실 압축 성능에서 우수하단 것을 보여준다.

• Asia pacific journal of information systems
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• 제26권3호
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• pp.427-448
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• 2016

The stochastic phenomena of traffic network condition, such as traffic speed and density, are affected not only by exogenous traffic control but also by endogenous changes in service time during congestion. In this paper, we propose a mixed M/G/1 queuing model by introducing a condition-varying parameter of traffic congestion to reflect structural changes in the traffic network. We also develop congestion indices to evaluate network efficiency in terms of traffic flow and economic cost in traffic operating system using structure-changing queuing model, and perform scenario analysis according to various traffic network improvement policies. Empirical analysis using Korean highway traffic operating system shows that our suggested model better captures structural changes in the traffic queue. The scenario analysis also shows that occasional reversible lane operation during peak times can be more efficient and feasible than regular lane extension in Korea.

• 대한교통학회지
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• 제4권1호
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• pp.3-11
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• 1986

One important element of a systematic approach to the management and control of the flow of people over an urban street network is the monitoring and evaluation of system performance. The nature of TSM strategies that, in part, differentiates them from traditional long-range transportation improvement alternatives is that they are less costly, are more quickly implemented and modified, and are often oriented toward sub-area problems which must be addressed at a more microscopic level of analysis. These factors suggest that pre-implementation evaluations of alternative TSM actions will often have to rely on quick-turn around, manual methods of analysis to guide the choice of which management action should be implemented. This paper was prepared to focus on the definition and importance of TSM, specifically associated with monitoring and evaluating traffic performance in the context of TSM startegies. A simple case study of reversible lane technique was presented. The purposes of the case study is to illustrate the methodology of evaluating TSM strategies and demonstrate to identify the benefit from the reversible lane technique, which may otherwise be overlooked in real world. Applying the reversible lane technique to Sam-Il elevate highway, it was found to be a very promising low cost alternative to reduce total travel time(or delay) and fuel consumption.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.247-251
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• 2010

It is very difficult to understand and estimate the heat transfer and flow characteristics in the combustor, which is one of main components in the Auxiliary Power Unit (APU), because its flow filed has very complex structure. In this paper, specified is characteristics of injection and flow through different air goles in the liner, which consist of large circular holes film cooling holes, and tangential air swirl holes. The durability of the liner depends on whether the surface of the liner is exposed to the hot gas over 1000 $^{\circ}C$ of a temperature or net. It is proved that the locations of hot spots estimated from the calculation using CFD are matched well with that from the test. In this study, CFD simulations were performed to examine the heat transfer and temperature distributions in and about a liner wall with film cooling on the wall. This computational study is based on the ensemble average continuity, compressible Navier-Stokes, energy, and PDF combustion equations closed by the standard $k-{\varepsilon}$ turbulence model with standard wall functions for the gas phase and the Fourier equations for conduction in the solid phase.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.674-690
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• 2021

This study proposes a hybrid marine power system combining dual-fuel generators, a fuel cell, and Vanadium Redox Flow Batteries (VRFB). Rigorous verification and validation of the dynamic modelling and integration of the system are conducted. A case study for the application of the hybrid propulsion system to a passenger ship is conducted to examine its time-variant behaviour. A comprehensive model of the reversible and irreversible capacity degradation of the VRFB stack unit is proposed and validated. The capacity retention of the VRFB stack is simulated by being integrated within the hybrid propulsion system. Reversible degradation of the VRFB stack is precisely predicted and rehabilitated based on the predefined operational schedule, while the irreversible portion is retained until the affected components are replaced. Consequently, the advantages of the VRFB system as an on-board ESS are demonstrated through the application of a hybrid propulsion system for liner shipping with fixed routes.