• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.928-933
• /
• 2003

For simulation of three-dimensional turbulent flow with LES and DNS takes much time and expense with current available computing resources. It is nearly impossible to simulate turbulent flow with high Reynolds number. So, the emerging alternative is the Grid computing for needed computation power and working environment. In this study, the CFD code was parallelized to adapt it for the parallel computing under the Grid environment. In the first place, the Grid environment was built to connect the PC-Cluster facilities belong to the different institutions using communication network system. And CFD applications were calculated to check the performance of the parallel code developed for the Grid environment. Although it is a fundamental study, it brings about a important meaning as first step in research of the Grid.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.8
• /
• pp.1060-1067
• /
• 2001

A large-scale bursting event has been analyzed in a turbulent channel flow using a data obtained from a direct numerical simulation (DNS). Large-scale, plume-like structures have been frequently observed in many experimental results, but the origin of those structures is far from being fully understood. It is believed that those large scale events occur occasionally but contribute significantly to the generation of Reynolds shear stress in the outer layer. This paper attempts to give detailed examples of those large-scale motions observed in a turbulent channel flow at relatively low Reynolds number.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
• /
• 2008.04a
• /
• pp.234-237
• /
• 2008

A direct numerical simulation (DNS) code suitable for the prediction of buoyant jet diffusion flames was developed in this study. The thermodynamic and transport properties were evaluated using CHEMKIN package to enhance the prediction performance of the developed DNS code. A two dimensional simulations were performed for the jet diffusion flames in normal and zero-gravity conditions where the Froude numbers are 5 and infinity, respectively. The simulated buoyant jet diffusion flame in normal gravity showed that the unsteady and dynamic motion although the reynolds number is low (400). It was identified that the flame in normal gravity flickered periodically. The periodic motion of the flame disappeared in zero-gravity condition. The dynamic motion of the buoyant jet diffusion flame could be well understood by comparing the flame structures obtained by the simulations of normal and zero-gravity conditions.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2004.05b
• /
• pp.376-380
• /
• 2004

측벽이 존재하는 개수로 난류흐름에 대한 DNS 자료를 이용하여 난류의 비등방성을 해석하였다. 측벽의 2등분선(sidewall bisector)에서 난류강도의 분포를 통해 바닥과 자유수면에서의 비등방성을 분석하고, AIM을 도입하여 흐름장 전반에 걸쳐 세부적인 비등방성 해석을 수행하였다. 측벽의 2등분선에서의 난류강도의 분포를 통해 바닥과 자유수면 근처에서 난류강도가 강한 비등방성을 갖는 것을 볼 수 있었다. 또한 3개의 다른 영역에서 AIM의 도입을 통해 측벽이나 바닥근처에서는 난류의 비등방성이 구형 관수로 흐름과 유사한 것으로 나타났으나, 개수로 난류흐름의 주된 특성이 velocity-dip phenomena가 존재하는 영역에서는 구형 관수로 흐름과는 달리 천이영역이 존재한다는 것을 알 수 있었다.

• Proceedings of the Korean Information Science Society Conference
• /
• 2003.10c
• /
• pp.379-381
• /
• 2003

ENUM은 전세계적으로 유일성이 보장된 ITU­T의 E.164 전화번호를 PSTN과 IP 네트워크를 연결하기 위한 식별자로써 사용하기 위해 정의된 새로운 인터넷 프로토콜이다. ENUM은 일종의 디렉토리 서비스로써 그 기반을 DNS에 두고 있지만, 캐싱의 비효율성과 이중 탐색으로 인한 지연이 발생한다는 단점을 가지고 있다. 본 논문은 CDN 환경과 애니캐스트를 응용하여, ENUM 서비스의 효율적인 제공을 위해 ENUM DNS의 탐색시간을 단축할 수 있는 방안을 제시하고자 한다.

• Proceedings of the IEEK Conference
• /
• 2006.06a
• /
• pp.829-830
• /
• 2006

A distributed web caching system can transmit information to a user quickly and stably, avoiding a congested internet network by storing and later supplying requested content to a cache that is distributed and shared like a proxy server. This paper proposes a client-based distributed web caching system that assigns an object and controls the load using a user's direct connection to shared caches, without the aid of additional domain name system (DNS) requests. The proposed system simplifies information transmission by reducing both DNS queries and delay time.

• Journal of Ocean Engineering and Technology
• /
• v.18 no.2
• /
• pp.1-9
• /
• 2004

As the first step to investigate the nonlinear interactions between turbulence and marine structures inside a viscous NWT, a LES technique was applied to solve the turbulent channel flow for =150. The employed turbulence models included 4 types: the Smagorinsky model, the Dynamic SGS model, the Structure Function model, and the Generalized Normal Stress model. The simulated data in time-series for the LESs were averaged in both time and space, and statistical analyses were performed. The results of the LESs were compared with those of a DNS, developed in the present study and two spectral methods by Yoon et al.(2003) and Kim et a1.(1987). Based on this research, the accuracy of LESs has been found to be still related to the number of grids for fine grid size).

• Korean Institute of Interior Design Journal
• /
• v.15 no.2 s.55
• /
• pp.118-126
• /
• 2006

This study aims at analyzing the characteristics and trends of future workplace in reference to the case for Digital Nomad Space (DNS). For this study, it has been investigated how to converge meanings of the digital environment and physical office space by which surveys to potential digital nomads were fulfilled. As a result, the types and the properties of future workplace in digital environment have been obtained. This study also includes general characteristics and design aspects of the time-based ubiquitous rental workplace followed by investigating future trends of the digital era. Thus, suggestions of spatial requirements of the digitalized office towards the practical level in the architectural interior design is proposed, and DNS has special features such as the cultural complex and ICT-based facilities with free accessibility to existing information and data over the air.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2002.11b
• /
• pp.1181-1184
• /
• 2002

다양한 서비스를 하나의 식별체계를 사용하여 접근하기 위한 프로토콜인 ENUM은 인터넷 도메인 네임 시스템(DNS)을 사용하여 전 세계에서 사용되고 있는 전화번호 체제인 E.164를 인터넷 주소체계로 변환해 줌으로써 인터넷 홈페이지, E-Mail, Fax, 휴대폰, 인스턴트 메시지 등과 같은 다양한 통신 서비스들과 연결할 수 있다. 본 고에서는 IETF ENUM WG에서 논의되고 있는 DNS를 기반으로 한 ENUM 서비스를 실현하기 위하여, 최근 DNSEXT WG에서 표준화 진행중인 DDDS(Dynamic Delegation Discovery) 알고리즘을 기반으로 한 RFC2916bis 표준화 추진 중인 내용에 따라, DNS 기반으로 ENUM 서버를 구축하고, ENUM 가입자 등록대행자인 Registra를 Web 기반으로 구현하고, E.164 번호를 FQDN(Fully Qualified Domain Name)으로 변환하여 DDDS 알고리즘에 따라 URI를 찾아내는 ENUM 클라이언트의 구현 방법을 기술한다.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2759-2764
• /
• 2008

Turbulent mixed convection in heated vertical annulus is investigated using Direct Numerical Simulation (DNS) technique. The objective of this study is to find out the effect of buoyancy on turbulent mixed convection in heated vertical annulus. Downward and upward flows with bulk Reynolds number 8500, based on hydraulic diameter and mean velocity, have been simulated to investigate turbulent mixed convection by gradually increasing the effect of buoyancy. With increased heat flux, heat transfer coefficient first decreases and then increases in the upward flow due to the effect of buoyancy, but it gradually increases in downward flow. The mean velocity and temperature profiles can not be explained by the wall log laws due to the effect of buoyancy, too. All simulation results are in good quantitative agreement with existing numerical results and in good qualitative agreement with existing experimental results.