• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.379.2-379
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• 2002

The support bearing requires high DN to raise specific energy efficiency for the state of the art rotating machine with high speed. Especially for the system has a big rotor(750 kgf) with high speed(about one mi i lion DNs) such as the pulsed generator, tin selection of the bearing and lubrication method are very important. (omitted)

• Nuclear Engineering and Technology
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• v.44 no.8
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• pp.847-854
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• 2012

Despite extensive research efforts, the mechanism of the nucleate boiling phenomena is still not clear. A direct numerical simulation of the boiling phenomena is one of the promising approaches in order to clarify its heat transfer characteristics and discuss their mechanism. Therefore, many DNS procedures have been developed based on recent highly advancing computer technologies. This brief review focuses on the state of the art in direct numerical simulation of the pool boiling phenomena over the past two decades. In this review, the fundamentals of the boiling phenomena and the bubble departure and micro-layer models are briefly introduced, and then the numerical procedures for tracking or capturing interface/surface shape such as the front tracking method, level set method, volume of fluid treatments, and other methods (Lattice Boltzmann method, phase-field method and so on) are briefly reviewed.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.159-168
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• 2005

Noise generated by the blunt trailing edge of lifting surfaces is investigated in this study using fluid structure interaction theory. First, through the eddy modeling, noise generation doe to the flow instability on the rigid trailing edge is surveyed. Then the behavior of elastic cantileverd beam is investigated. Parametric study based on various material properties is employed to analyze the motion of the beam. Moreover, each eigenmode approach of cantilevered beam is used to find when flow induced vibration is resonant. To analyze elastic behavior of cantilever beam efficiently, moving grid generation technique based on non-conservative form of Navier-Stokes equation is used. Equation of the motion associated with the cantilever beam is discretized by the Galerkin procedure with forced vibration. As a consequence, behavior of the elastic cantilevered beam is stable when the first mode natural frequency of the material is relatively higher than that of flow induced pressure fluctuation.

• Journal of the Korea Computer Industry Society
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• v.2 no.6
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• pp.845-852
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• 2001

Electronic commerce and application service is to universal on the internet, and a large quantity information transmitted on the network, It's needs procedure to access only permit objects for the integrity of information. In order to provide regional services is authentication for control resource and client identification. In particular, public key system is to implement in distributed environment, it is able to insurance users convenience and integrity at the same time. In this paper designed mechanism of cross certification between realms in PKI based on X.509 associated with DNS (Domain Name System) that is presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.568-577
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• 2006

Developed in this study is a nonlinear Ekman pumping model to be used in simulating the rotating flows with quasi-three-dimensional Navier-Stokes equations. In this model, the Ekman pumping velocity is given from the solution of the Ekman boundary-layer equations for the region adjacent to the bottom wall of the flow domain; the boundary-layer equations are solved in the momentum-integral form. The developed model is then applied to rotating flows in a rectangular container receiving a time-periodic forcing. By comparing our results with the DNS and experimental data we have validated the developed model. We also compared our results with those given from the classical Ekman pumping model. It was found that our model can predict the rotating flows more precisely than the classical linear model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1327-1334
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• 2003

Flow characteristics of the fluid laden with many particles in the two-dimensional channel are investigated using the Navier-Stokes equations coupled with the equation of motion of particles by direct numerical simulation. A four-step fractional step method with Crank-Nicolson scheme and ALE technique is used for P2P1 mixed finite element method. The motion and distribution of particles in the fluid is virtually described as a result of direct numerical simulation and the increase of viscosity is compared with theoretical equations. The effect of channel height on the relative viscosity and the tubular pinch effect are discussed.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.604-609
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• 2003

Turbulent temperature field in a channel with wall injection has been investigated using dynamic mixed model(DMM). This flow is pertinent to internal flows inside the hybrid rocket motors. In general, the results obtained with DMM are in better agreement with DNS results compared to those of dynamic Smagorinsky model(DSM). Such favorable features of DMM are attributed to the fact that it explicitly calculates the modified Leonard stress term which takes care of the local interaction between resolved and SGS stresses and only models the remaining cross and SGS Reynolds stress terms.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10c
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• pp.238-240
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• 1999

인터넷의 사용자 수는 매년 급격히 증가하고 있으며, 사회 전반에 걸쳐 인터넷에 대한 의존도도 더욱 높아가고 있으나, 현재 인터넷 환경에서는 사용자에 대한 서비스의 지연 및 단절 사태가 빈번하게 발생하고 있다. 이에 대한 원인으로는 네트워크 자체보다는 서버에 의한 지연 현상이 더 심각한 것으로 보고되고 있다. 인터넷의 수요 및 전송량의 폭증에 따라 인터넷 서버의 병목현상이 더욱 심화될 것으로 예상됨에 따라, 인터넷 환경의 신뢰성 증대 및 성능 향상을 위해서는 인터넷 서버성능의 효과적인 관리가 중요하다. 현재 ISP들은 웹, 전자메일, FTP, DNS, Proxy 등 다양한 서비스를 제공하기 위해 다수의 호스트들을 사용하고 있으며, 이러한 다수의 서버 시스템 관리를 위해서 많은 관리비용을 소모하고 있다. 그러나 지금까지의 인터넷 서버 관리 시스템들은 웹 중심의 서비스 관리와 로그 분석 기능만을 지원하고, 서버 시스템 자체의 성능관리 기능은 매우 미약한 형편이다. 본 논문에서는 인터넷 서버의 성능 메트릭을 정의하고, 인터넷 서버 성능 모니터링 시스템을 설계한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.05a
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• pp.1485-1488
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• 2005

현재 인터넷을 구성하고 있는 두가지 중요 이름공간(name space)인 IP(Internet Protocol) 주소와 DNS(Domain Name Service) 이름의 단점을 보완하기 위해 연구되고 있는 HIP(Host Identity Protocol)는 IP와 트랜스포트 계층 사이에 새로운 계층과 프로토콜을 제안함으로써 제한된 형태의 신뢰성을 제공하고 이동(mobility), 멀티홈(multihome), 동적 IP주소변경 등을 지원하며 DoS(Denial of Service) 공격 등을 방어한다. 본 논문에서는 현재까지 IETF에서 진행된 HIP관련 연구 동향을 분석한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.05a
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• pp.1315-1318
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• 2005

본 연구에서는 향후 IPv6로의 주소 체계 전환, 인터넷 서비스의 기술 발전, 개인 정보 보호 추세 등을 감안할 때, 기존 서버 중심의 포털 서비스들이 개인용 포털(personal portal) 중심의 인터넷 서비스로 진화해 것으로 예상되고 있다. 이러한 추세 속에서 활용도가 높은 인터넷 서비스 중의 하나인 인터넷 디스크 서비스의 비중은 점점 더 중요해 질 것이다. 본 연구에서는 향후 IPv6에서 더욱 필요성이 증가하는 동적 DNS 시스템을 기반으로 개인용 포털을 지향하는 인터넷 디스크 시스템의 설계 및 구현에 대해 연구한 것이다.