• 한국전산유체공학회지
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• 제2권2호
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• pp.59-72
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• 1997

A numerical model is constructed to simulate the interactions of oblique shock wave / turbulent boundary layer on a strongly heated wall. The heated wall temperature is two times higher than the adiabatic wall temperature and the shock wave is strong enough to induce boundary layer separation. The numerical diffusion in the finite volume method is reduced by the use of a higher order convection scheme(UMIST scheme) which is a TVD version of QUICK scheme. The turbulence model is Chen-Kim two time scale model. The comparison of the wall pressure distribution with the experimental data ensures the validity of this numerical model. The effect of strong wall heating enlarges the separation region upstream and downstream. In order to eliminate the separation, wall suction is applied at the shock foot position. The bleeding slot width is about same as the upstream boundary layer thickness and suction mass flow is 10% of the flow rate in the upstream boundary layer. The final configuration of the shock reflection pattern and the wall pressure distribution approach to the non-viscous value when wall suction is applied.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.99-104
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• 1996

The jet pump is being used in many fields for several purposes because of its simple construction and easy operation. The characteristics of the geometrical variables, pressure gradient and velocity distribution of the jet pump are studied using the CFD technique. The flow calculations through a bended nozzle. a mixing chamber and a venturi are presented and phenomenological aspects are discussed. This study solve 3-D steady incompressible Navier-Stokes equations using the Iterative time marching scheme. The governing equations are differenced with 1st-order accurate backward difference scheme for the time derivatives and 3rd-order accurate QUICK scheme for the convective terms. The Mark-and-cell concept was applied efficiently to solve continuity equation, which is differenced 2nd-order accurate central differenced scheme. The 4th-order artificial damping is added to the continuity equation for numerical stability. A O-type of grid system is generated inside a nozzle and venturi of the jet pump. It has concluded that the results of present study properly agree with physical flow phenomena.

• Smart Structures and Systems
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• 제11권5호
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• pp.497-510
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• 2013

Quick, accurate damage monitoring is strongly required for damage assessment in the aftermath of a large natural disaster. Wireless sensor networks are promising technologies to acquire damage information in a citywide area. The wireless sensor networks, however, would be faced with difficulty to collect data in real-time and to expand the scalability of the networks. This paper discusses a scheme of network architecture to cove a whole city in multi-tier heterogeneous networks, which consist of wireless sensor networks, access networks and a backbone network. We first review previous studies for citywide damage monitoring, and then discuss the feature of multi-tier heterogeneous networks to cover a citywide area.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.86-96
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• 1998

A numerical study has been carried out of three-dimensional turbulent flows around a MIRA reference vehicle model both with and without wheels in computation. Two convective difference schemes with two k-$\varepsilon$ turbulence models are evaluated for the performance such as drag coefficient, velocity and pressure fields. Pressure coefficients along the surfaces of the model are compared with experimental data. The drag coefficient, the velocity and pressure fields are found to change considerably with the adopted finite difference schemes. Drag forces computed in the various regions of the model indicate that design change decisions should not rely just on the total drag and that local flow structures are important. The results also indicate that the RNG model with the QUICK scheme predicts fairly well the tendency of velocity and pressure fields and gives more reliable drag coefficient rather than the other cases.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.685-689
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• 2004

Numerical simulation is conducted to clarify the heat transfer and fluid flow characteristics of HVAC(Heating, Ventilating and Air-Conditioning) for double' deck train. The HVAC system is installed under the roof of carbody. In the lay-out of HVAC system, air duct must be installed to supply air to 1st and 2nd floor respectively. The standard k-$\epsilon$ and LES models for turbulence and SIMPLE algorithm for pressure equation hased on finite volume method are used to solve the physic a] HVAC model. To assure convergence, QUICK scheme for momentum equation and the 2nd order upwind scheme for turbulent equations arc used. From the results of simulation, the temperature and velocity magnitude are also distributed uniformly in the interior of double-deck passenger car.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2015년도 춘계학술대회
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• pp.721-723
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• 2015

최근 클라우드 컴퓨팅 기술에 대한 중요성과 확장성이 급부상하면서 다양한 정보 시스템에 적용하고 있는 추세이다. 현재 모바일 클라우드 환경에서 많은 서비스가 이루어지고 있는데 의료정보 서비스도 빠른 적용이 요구되고 있다. 의료정보는 개인의 중요한 정보가 노출될 경우 심각한 문제가 발생할 수 있으므로 안전한 인증 절차 문제가 해결되어야만 한다. 따라서 본 논문에서는 모바일 클라우드 환경에서 의료정보시스템을 보다 효율적으로 관리 할 수 있는 인증 기법을 제안하려 한다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2000년도 추계학술대회 논문집
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• pp.514-520
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• 2000

Numerical simulation is conducted to clarify the heat transfer and fluid flow characteristics of HVAC(Heating, Ventilating and Air-Conditioning) for Mugunghwa passenger car. The HVAC system is installed under the floor of carbody. This new HVAC system has a lot of merits in respect of the center of gravity of carbody, flow induced noise and reduction of condensation water etc. The standard k-epsilon turbulent model and SIMPLEC algorithm based on finite volume method are used to solve the physical HVAC model. To assure convergence, QUICK scheme for momentum equation and the first order upwind scheme for turbulent equations are used. From the results of simulation, the temperature and velocity magnitude are also distributed uniformly in the interior of car.

• 한국항해학회지
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• 제19권2호
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• pp.13-22
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• 1995

This paper presents the numerical analysis results of the viscous flow for a full ship model. The mass and momentum conservation equations are used for governing equations, and the flow field is discretized by the Finite-Volume Method for the numerical calculation. An algebraic grid and elliptic grid generation techniques are adopted for generation of the body-fitted coordinates system, which is suitable to ship's hull forms. Time-marching procedure is used to solve the three-dimensional unsteady problem, where the convection terms are approximated by the QUICK scheme and the 2nd-order central differencing scheme is used for other spatial derivatives. A Sub-Grid Scale turbulence model is used to approximate the turbulence, and the wall function is used at the body surface. Pressure and velocity fields are calculated by the simultaneous iteration method. Numerical calculations were accomplished for the Crude Oil Tanker(DWT 95,000tons, Cb=0.805) model. Calculation results are compared to the experimental results and show good agreements.

• Journal of electromagnetic engineering and science
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• 제12권3호
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• pp.196-202
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• 2012

Spectrum sensing is one of the most important functions in cognitive radio systems. In this paper, we focus on reducing the sensing time in a cooperative spectrum sensing paradigm. In the proposed scheme, a sequential detection technique is employed to provide a robust and quick detection system. Each of the secondary users measures the log-likelihood probability of the received signals and then sequentially reports to the base station. Here, the maximum ratio combining (MRC) technique is employed to reduce the average sample number (ASN) in order to reduce the sensing time. This proposed scheme is analyzed and simulated to illustrate the performance in comparison with the other given methods. Analysis and simulation are provided to validate the proposed method.

• Journal of Communications and Networks
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• 제13권4호
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• pp.400-407
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• 2011

Various air indexing and data scheduling schemes for wireless broadcast of spatial data have been developed for energy efficient query processing. The existing schemes are not effective when the clients' data access patterns are skewed to some items. It is because the schemes are based on flat broadcast that does not take the popularity of the data items into consideration. In this paper, thus, we propose a data scheduling scheme letting the popular items appear more frequently on the channel, and grid-based distributed index for non-flat broadcast (GDIN) for window query processing. The proposed GDIN allows quick and energy efficient processing of window query, matching the clients' linear channel access pattern and letting the clients access only the queried data items. The simulation results show that the proposed GDIN significantly outperforms the existing schemes in terms of access time, tuning time, and energy efficiency.