• Journal of ILASS-Korea
• /
• v.8 no.4
• /
• pp.9-16
• /
• 2003

The Purpose of this study is to investigate the relationships between the local heat release rate and CH concentration have been investigated by numerical simulations of methane-air premixed flames. And simultaneous CH and OH PLIF(Planar Laser Induced Fluorescence) measurement has been also conducted for lean premixed flame as well as for laminar flames. Numerical simulations are conducted for laminar premixed flames and turbulent ones by using PREMIX in CHEMKIN and two dimensional DNS code with GRI mechanism version 2.11, respectively. In the case of laminar premixed flame, the distance between the peak of heat release rate and that of CH concentration is under $91{\mu}m$ for all equivalence ratio calculated in present work. Even for the premixed flame in high intensity turbulence, the distribution of the heat release rate coincides with that of CH mole fraction. For CH PLIF measurements in the laminar premixed flame burner, CH fluorescence intensity as a function of equivalence ratio shows a similar trend with CH mole fraction computed by GRI mechanism. Simultaneous CH and OH PLIF measurement gave us useful information of instantaneous reaction zone. In addition, CH fluorescence can be measured even for lean conditions where CH mole fraction significantly decreases compared with that of stoichiometric condition. It was found that CH PLIF measurements can be applicable to the estimation of the spatial fluctuations of heat release rate in the engine combustion.

• Nuclear Engineering and Technology
• /
• v.36 no.3
• /
• pp.248-262
• /
• 2004

Turbulence models are separately assessed for a three dimensional thermal-hydraulic analysis of the integral reactor SMART. Seven models (mixing length, k-l, standard $k-{\epsilon},\;k-{\epsilon}-f{\mu},\;k-{\epsilon}-v2$, RRSM, and ERRSM) are investigated for flat plate channel flow, rotating channel flow, and square sectioned U-bend duct flow. The results of these models are compared to the DNS data and experiment data. The results are assessed in terms of many aspects such as economical efficiency, accuracy, theorization, and applicability. The standard $k-{\epsilon}$ model (high Reynolds model), the $k-{\epsilon}-v2$ model, and the ERRSM (low Reynolds models) are selected from the assessment results. The standard $k-{\epsilon}$ model using small grid numbers predicts the channel flow with higher accuracy in comparison with the other eddy viscosity models in the logarithmic layer. The elliptic-relaxation type models, $k-{\epsilon}-v2$, and ERRSM have the advantage of application to complex geometries and show good prediction for near wall flows.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.3 s.234
• /
• pp.314-321
• /
• 2005

Discrete Wavelet Transform (DWT) has been applied to the Direct Numerical Simulation (DNS) data of turbulent channel flow. DWT splits the turbulent flow into two orthogonal parts, one corresponding to coherent structures and the other to incoherent background flow. The coherent structure is extracted from not vorticity field but velocity's since the channel flow is not isoropic. By comparing DWT's result of channel flow with that of isotropic flow, it is shown that coherent structure maintains the properties of original channel flow. The velocity field of coherent structures can be represented by few wavelet modes and that these modes are sufficient to reproduce the velocity probability density function (PDF) and the energy spectrum over the entire inertial range. The remaining incoherent background flow is homogeneous, has small amplitude, and is uncorrelated. These results are compared with those obtained for the same compression rate using large eddy simulation (LES) filtering. In contrast to the incoherent background flow of DWT, the LES subgrid scales have a much larger amplitude and are correlated, which makes their statistical modeling more difficult.

• Journal of the Society of Naval Architects of Korea
• /
• v.42 no.6 s.144
• /
• pp.608-618
• /
• 2005

A new technique giving significant drag reduction in turbulent shear flows has been proposed by using the buoyancy effect to generate periodic spanwise motion. Such spanwise motion can be obtained by arranging heating and cooling strips periodically aligned in the spanwise direction of a vertical channel, where the streamwise mean flow is perpendicular to the gravity vector The strip size has been changed in order to obtain the optimum size corresponding to the maximum drag reduction. The bulk Reynolds number, $ Re_{m} = U_{m} \delta / \nu \$ is fixed at 2270 while Grashof numbers is changed between $10^{6}$ to $10^{7}$. As Grashof number increases, considerable drag reduction can be obtained, At the highest Grashof number, an optimum strip size of about 250 wail units gives drag reduction of about 35$\%$. The greater the Grashof number, the smaller the strip size attains the maximum drag reduction.

• Proceedings of the Korea Inteligent Information System Society Conference
• /
• 2002.05a
• /
• pp.213-221
• /
• 2002

e-비지니스환경에서의 SCM의 성공적인 추진을 위해서는 우선 e-business 전략과 Supply Chain 관리 전략의 상하 연계, 조직측면에 있어서의 경영자의 변화에 대한 혁신 능력과 리더쉽, 조직 구성원들과의 비전 공유, 저보기술(IT)을 활용한 보다 차별화된 서비스가 제공되어야 한다. 본 연구는 C기업의 사례로 통해, 기존의 SCM 기법에서 정보기술(IT)의 급속한 발달과 인터넷의 급속한 보급, 그리고 e-비지니스의 등장으로 인하여 경영환경의 변화라는 새로운 패러다임 하에서 다수의 경쟁기업, 정보 네트워크시스템 기반에서 보다 효과적으로 기업과 고객에게 대응하기 위한 기업의 구체적이고 실무적인 전략 측면에서 다루어 보았다는 데 그 의의가 있다. 소비재, 생활용품에 있어서 보다 빠른 납기, 보다 전문적이고 다양화되고 있는 고객의 욕구를 충족시키기 위해 제조기업 측면에서 어떻게 기존의 조직구조 및 업무 프로세스를 혁신 할 것인가를 실제 사례를 통하여 연구함으로써 동종 산업체나 또는 기업의 실무자들에게 있어 큰 도움이 될 것이다.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2003.05c
• /
• pp.2089-2092
• /
• 2003

홈 네트워킹 기술을 이용하면 가정내의 각각의 기기를 연결하고, 인터넷에 동시에 접속할 수 있다. 뿐만 아니라 홈 네트워킹 기술로 연결된 가정 기기들은 상호운용이 가능하며 인터넷을 통해 외부에서도 가정내의 기기를 제어할 수 있다. 그러나 이러한 외부로부터의 제어 가능성으로 인하여 홈 네트워크에 대한 접근 및 제어에 대한 인증의 필요성이 대두되었을 뿐만 아니라 전자상거래의 증가 및 VPN을 이용한 자택근무의 증가로 인하여 홈 네트워크의 보안도 중요한 관리요소에 포함되었다. 본 논문에서는 흠 네트워크 보안 및 관리를 위한 홈 네트워크 관제 센터의 구조 및 설계에 대하여 기술한다. 기존의 흠 게이트웨이에 집중되었던 흠 네트워크 관리기능과 방화벽이나 사용자 인증 등의 보안 기능을 홈 네트워크 관제 센터로 이동함으로써 보안관리의 편리성 제공 및 홈 게이트웨이의 부하를 줄일 수 있을 뿐만 아니라 좀 더 완벽한 홈 네트워크 보안을 제공할 수 있다.

• The KIPS Transactions:PartA
• /
• v.14A no.1 s.105
• /
• pp.15-24
• /
• 2007

As a single video server exposes its limitation in scalability, capability, fault-tolerance, and cost-efficiency, solutions of this limitation emerge. However, these solutions have their own problems that will be discussed in this paper. To solve these problems and exploit various video silvers, we designed a parallel multimedia system architecture that supported a content-aware routing to heterogeneous personal computer (PC), operating system (OS), video servers through a HTTP-level redirection. We also developed a prototype, added different video servers into the prototype, and measured its overheads.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.04a
• /
• pp.67-70
• /
• 2004

An investigation was performed to study the impact damage of the laminated composite plates caused by a low- velocity foreign object with multi-scale modeling based on the concepts of Direct Numerical Simulation (DNS)[4]. In the micro-scale part, we discretize the composite plates through separate modeling of fiber and matrix for the local microscopic analysis. A micro-scalemodel was developed for predicting the initiation of the damage and the extent of the final damage as a function of material properties, laminate configuration and the impactor's mass, etc. Anda macro-scale model was developed for description of global dynamic behavior. The connection betweenmicroscopic and macroscopic is implemented by the tied interface constraints of LS-DYNA contact card. A transient dynamic finite element analysis was adopted for calculating the contact force history and the stresses and strains inside the composites during impact resulting from a point-nose impactor. The low-velocity impact events such as contact force, deformation, etc. are simulated in the macroscopic sense and the impact damages, fiber-breakage, matrix cracking and delamination etc. are examined in the microscopic sense.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.1813-1818
• /
• 2004

Discrete Wavelet Transform (DWT) has been applied to the Direct Numerical Simulation (DNS) data of turbulent channel flow. DWT splits the turbulent flow into two orthogonal parts, one corresponding to coherent structures and the other to incoherent background flow. The coherent structure is extracted from not vorticity field but velocity's since the channel flow is not isotropic. By comparing DWT's result of channel flow with that of isotropic flow, it is shown that coherent structure maintains the properties of original channel flow. The velocity field of coherent structures can be represented by few wavelet modes and that these modes are sufficient to reproduce the velocity probability distribution function (PDF) and the energy spectrum over the entire inertial range. The remaining incoherent background flow is homogeneous, has small amplitude, and is uncorrelated. These results are compared with those obtained for the same compression rate using large eddy simulation (LES) filtering. In contrast to the incoherent background flow of DWT, the LES subgrid scales have a much larger amplitude and are correlated, which makes their statistical modeling more difficult.

• Nuclear Engineering and Technology
• /
• v.37 no.6
• /
• pp.511-524
• /
• 2005

Thermalhydraulic reactor simulation of tomorrow will require a new generation of codes combining at least three scales, the CFD scale in open medium, the component scale and the system scale. DNS will be used as a support for modelling more macroscopic models. NEPTUNE is such a new generation multi-scale platform developed jointly by CEA-DEN and EDF-R&D and also supported by IRSN and FRAMATOME-ANP. The major steps towards the next generation lie in new physical models and improved numerical methods. This paper presents the advances obtained so far in physical modelling for each scale. Macroscopic models of system and component scales include multi-field modelling, transport of interfacial area, and turbulence modelling. Two-phase CFD or CMFD was first applied to boiling bubbly flow for departure from nucleate boiling investigations and to stratified flow for pressurised thermal shock investigations. The main challenges of the project are presented, some selected results are shown for each scale, and the perspectives for future are also drawn. Direct Numerical Simulation tools with Interface Tracking Techniques are also developed for even smaller scale investigations leading to a better understanding of basic physical processes and allowing the development of closure relations for macroscopic and CFD models.