• 한국인터넷방송통신학회논문지
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• 제14권2호
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• pp.59-64
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• 2014

본 논문은 이동통신 네트워크에서 WiMAX 백홀 구현에 관한 것이다. 최근에 대부분의 ISP들은 T1/E1 및 디지털 가입자 회선(DSL)을 이용하여 Wi-Fi 백홀을 구축하고 있다. WiMAX가 이동통신 백홀의 대안으로 설치된다면, 설치 및 운용비가 대폭 절감될 것이다. 그리고 유선통신 인프라가 구축되어 있지 않은 서비스 지역을 커버하기 위한 비용 효율적인 솔류선중 하나가 될 것이다. WiMAX는 Base Station, Subscriber Station, 그리고 Relay에 사용될 수 있다. 본 논문에서 WiMAX 서버와 WiMAX SS를 구성하여 NAT 및 Port Forwarding 기능을 이용하여 상 하향에서 성능이 측정되었다.

• 대한기계학회논문집
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• 제14권2호
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• pp.470-483
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• 1990

Turbulent jet in a crossflow, issuing from a row of holes on a convex surface of 90 .deg. bend duct, is predicted by a 3-dimensional numerical method. The Cartesian coordinate system in adopted in upstream and downstream tangents and the cylindrical polar coordinate system in curved region. The Reynolds stresses and heat fluxes are obtained from a standard k-e model in the core region and van Driest model in the vicinity of the wall. The governing equations are discretized by a finite volume method and solutions are obtained by a locally elliptic calculation procedure. Pressure and convective terms are treated by SIMPLE algorithm and hybrid scheme respectively. A vortex initially induced by the injected jet has been built up due to the interaction with the secondary flow caused by pressure gradient and centrifugal force. The vortex structure has a strong influence on the wall cooling effectiveness. Another vortex like horseshoe is formed in the vicinity of the injection hole and its strength is getting weak as it moves downward.

• 대한토목학회논문집
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• 제7권3호
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• pp.133-139
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• 1987

한강감조구간(漢江感潮區間)에서 과거(過去)에 발생(發生)했던 세 경우(境遇)의 대홍수(大洪水)를 1차원(次元) 유한차분조석(有限差分潮汐)모형을 이용(利用)하여 수치적(數値的)으로 조사(調査)하였다. 홍수추정기법(洪水推定技法)은 인도교(人道橋)의 홍수위곡선(洪水位曲線)으로부터 유량(流量)을 도출(導出), 입력(入力)시키고 또한 하류경우조건(下流境遇條件)으로는 경계단(境界端)의 조위추정치(潮位推定値)를 규정(規定)하므로서 감조구간(感潮區間)의 홍수위(洪水位) 및 유량(流量)을 산정(算定)하는 것이다. 1925년(年), 1972년(年) 및 1984년(年) 대홍수(大洪水)의 초기산정(初期算定) 결과(結果)가 제시(提示)되고 또한 토의(討議)되었다.

• Journal of Mechanical Science and Technology
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• 제15권8호
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• pp.1165-1173
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• 2001

This paper deals with dynamic analysis of Pipeline Inspection Gauge (PIG) flow control in natural gas pipelines. The dynamic behaviour of PIG depends on the pressure differential generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. To analyze dynamic behaviour characteristics (e.g. gas flow, the PIG position and velocity) mathematical models are derived. Tow types of nonlinear hyperbolic partial differential equations are developed for unsteady flow analysis of the PIG driving and expelled gas. Also, a non-homogeneous differential equation for dynamic analysis of the PIG is given. The nonlinear equations are solved by method of characteristics (MOC) with a regular rectangular grid under appropriate initial and boundary conditions. Runge-Kutta method is used for solving the steady flow equations to get the initial flow values and for solving the dynamic equation of the PIG. The upstream and downstream regions are divided into a number of elements of equal length. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. Simulation is performed with a pipeline segment in the Korea gas corporation (KOGAS) low pressure system. Ueijungboo-Sangye line. The simulation results show that the derived mathematical models and the proposed computational scheme are effective for estimating the position and velocity of the PIG with a given operational condition of pipeline.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권12호
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• pp.5729-5744
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• 2017

Vehicular Ad Hoc Networks (VANET) in the large-scale road section usually have typical characteristics of large number of vehicles and unevenly distribution over geographic spaces. These two inherent characteristics lead to the unsatisfactory performance of VANETs. This poor performance is mainly due to fragile communication link and low dissemination efficiency. We propose a novel routing mechanism to address the issue in the paper, which includes a competition-based routing discovery with priority metrics and a local routing repair strategy. In the routing discovery stage, the algorithm uses adaptive scheme to select a stable route by the priorities of routing metrics, which are the length of each hop, as well as the residual lifetime of each link. Comparisons of different ratios over link length and link stability further show outstanding improvements. In the routing repair process, upstream and downstream nodes also compete for the right to establish repair process and to remain as a member of the active route after repair. Our simulation results confirm the improved performance of the proposed algorithm.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.216-217
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• 2008

In recent years, scientific community has found renewed interest in hypersonic flight research. These hypersonic vehicles undergo severe aero-thermal environment during their flight regimes. During reentry and hypersonic flight of these vehicles through atmosphere real gas effects come into play. The analysis of such hypersonic flows is critical for proper aero-thermal design of these vehicles. The numerical simulation of hypersonic real gas flows is a very challenging task. The present work emphasizes numerical simulation of hypersonic flows with thermal non-equilibrium. Hyperbolic system of equations with stiff relaxation method are identified in recent literature as a novel method of predicting long time behaviour of systems such as gas at high temperature. In present work, Energy Relaxation Method (ERM) has been considered to simulate the real gas flows. Navier-Stokes equations A numerical scheme Advection Upstream Splitting Method (AUSM) has been selected. Navier-Stokes solver along with relaxation method has been used for the simulation of real flow over a circular cylinder. Pressure distribution and heat flux over the surface of cylinder has been compared with experiment results of Hannemann. Present heat flux results over the cylinder compared well with experiment. Thus, real gas effects in hypersonic flows can be modeled through energy relaxation method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.452-455
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• 2008

A new passive control technique of cavity-induced pressure oscillations has been investigated numerically for a supersonic two-dimensional flow over open rectangular cavities at Mach number 1.83 just upstream of a cavity, in which a sub-cavity system is installed on the backward-facing step of the main cavity. A third-order TVD (Total Variation Diminishing) finite difference scheme with MUSCL is used to discretize the spatial derivatives in the unsteady compressible Navier-Stokes equations. The results obtained show that the present sub-cavity system is very effective in reducing cavity-induced pressure oscillations. The results also showed that the resultant amount of attenuation of cavity-induced pressure oscillations was dependent on the length and thickness of the flat plate, and also on the depth of the sub-cavity used as an oscillation suppressor.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 춘계종합학술대회
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• pp.125-128
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• 2001

광대역 액세스 망에서 합류, 분배 지점에서의 효율을 고려한 PON(Passive Optical Network)의 설계는 중요한 관심거리가 되고 있다. PON 구조는 매우 간단하지만, 가입자들에서 발생하는 상향 트래픽 제어를 위해서는 매체 접근 제어 프로토콜이 필요하다. 이러한 매체 접근 제이 프로토콜은 트래픽 클래스별 QoS(Duality of Service) 관리 기능, 효율적인 망 자원 분배 기능, CDV(Cell Delay Variation) 최소화 기능 등이 포함되어야 한다. 본 논문에서는 ATM-PON과 흠 네트워크 환경에 적합한 성능을 제공하고 앞서 기술한 기능을 수행하는 매체 접근 제이 프로토콜 설계에 관한 연구 내용을 기술한다. 설계된 프로토콜은 요구-할당(Request-Permit) 알고리즘을 사용하여 동적인 상향 대역 할당이 가능하게 설계하였다. 이를 위해 ITU-T 권고 G.983:1을 이용하였고, 이에 더하여 새로운 메시지 형식과 동적 대역할당 알고리즘 등을 제시하였다.

• 대한기계학회논문집B
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• 제25권8호
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• pp.1087-1096
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• 2001

The dynamic structures of unsteady CH$_4$/Air jet diffusion flame with a flame-vortex interaction were numerically investigated. A timed-dependent, axisymmetric computational model and a low mach number approximation were employed in the present calculation. A two-step global reaction mechanism which considers 6 species, was used to calculate the reaction rates. The predicted results including the gravitational effect show that the large outer vortices and the small inner vortices can be well simulated without any additional disturbances near nozzle tip. It was found that the temperature and species concentrations have deviated values even for the same mixture fraction in the flame-vortex interaction region. It was also shown that the flame surface is not deformed by the inner vortex in upstream region, while in downstream region, the flame surface is compressed or stretched by the outer vortex roll-up. The present unsteady jet flame configuration accompanying a flame-vortex interaction is expected to give good implications for the unsteady structures of turbulent flames.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.448-448
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• 2000

This paper deals with dynamic behaviour analysis for pipeline inspection gauge (PIG) flow control in natural gas pipeline. The dynamic behaviour of the PIG is depending on the different Pressure between the rear and nose parts, which is generated by injected gas flow behind PIG's tail and expelled gas flow in front of its nose. To analyze the dynamic behaviour characteristics such as gas flow in pipeline, and the PIG's position and velocity, mathematical model is derived as two types of a nonlinear hyperbolic partial differential equation for unsteady flow analysis of the PIG driving and expelled gas, and nonhomogeneous differential equation for dynamic analysis of PIG. The nonlinear equation is solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used when we solve the steady flow equations to get initial flow values and the dynamic equation of PIG. The gas upstream and downstream of PIG are divided into a number of elements of equal length. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. The simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of PIG with different operational conditions of pipeline.