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

• Journal of The Korean Society of Integrative Medicine
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• v.12 no.3
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• pp.25-36
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• 2024

Purpose : After coronavirus disease 2019 pandemic, many people around the world became aware of respiratory diseases and developed increased interest in health and exercise. As the elderly population grows larger, the prevalence of brain diseases and respiratory conditions increases. This study aimed to investigate the impact of dynamic neuromuscular stabilization (DNS) exercises on pulmonary function and electroencephalogram (EEG) findings in the elderly population. Methods : In this study, we measured the pulmonary function and performed EEG of 30 elderly individuals. The participants were randomly divided into an experimental group (n=15) and a control group (n=15). The experimental group completed a DNS exercise training protocol, while the control group performed simple exercise training. After the exercise, the pulmonary function and EEG testing were repeated, and the amounts of change within and between groups were determined. Results : In terms of pulmonary function, the experimental group's forced vital capacity (FVC) and forced expiratory volume at 1 second (FEV1) increased significantly after the exercise (p<.05), while the FVC differed significantly between groups (p<.05). In terms of EEG findings, the relative alpha waves significantly decreased in the F3 region (p<.05), while the relative beta waves significantly increased in the F4 region (p<.05). The relative gamma waves increased significantly in the Fp2 and P3 regions (p<.05), while the values in the F3 region differed significantly between groups (p<.05). Conclusion : DNS exercises performed by this elderly population demonstrated significant clinical value by providing fundamental data about both pulmonary function and EEG activity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.628-637
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• 2004

The present study investigates the performance of dynamic mixed model (DMM; Zang et ai.) in a channel with strong wall injection through a Large eddy simulation (LES) technique. The DMM results are compared with those of DNS and the results obtained with popular dynamic Smagorinsky model (DSM). Better agreement is achieved when using the DMM with box filter than DSM and coarse DNS in predicting the first and second order statistics as well as large-scale structures of velocity and temperature fields. Such favorable features of DMM are attributed to the fact that it explicitly calculates the modified Leonard stress term and only models the remaining cross and the SGS Reynolds stress terms and, thus, it reduces the excessive burden put on the model coefficient of DSM. Also it is demonstrated that the DMM can be successfully extended to the prediction of temperature (passive scalar) field where strong streamwise inhomogeneity exists.

• Fire Science and Engineering
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• v.27 no.6
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• pp.64-69
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• 2013

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to simulate an engine nacelle fire and to complement the previous experimental results of the bluff body stabilized flames. Fire Dynamic Simulator (FDS) based on the Direct Numerical Simulation (DNS) was employed to clarify the characteristics of reacting flow around bluff body. The overall reaction was considered and the constant for reaction was determined from flame extinction limits of experimental results. The air used atmosphere and the fuel used methane. For both fuel ejection configurations against an oxidizer stream, the flame stability and flame mode were affected mainly by vortex structure near bluff body. In the coflow configuration, air velocity at the flame extinction limit are increased with fuel velocity, which is comparable to the experiment results. Comparing with the isothermal flow field, the reacting flow produces a weak and small recirculation zone, which is result in the reductions of density and momentum due to temperature increase by reaction in the wake zone.

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

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

• Journal of the Korean Society of Safety
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• v.24 no.1
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• pp.14-20
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• 2009

Direct numerical simulations(DNS) were performed for the prediction of transient buoyant jet diffusion flames where the Froude numbers(Fr) are 5 and 160, respectively. The thermodynamic and transport properties were evaluated using CHEMKIN package to enhance the prediction performance of the DNS code. The simulated buoyant jet diffusion flame of Fr=5 and 160 showed the transient, dynamic motion well. It was identified that the buoyant jet flames were flickered periodically, and the simulated flickering frequency of the jet diffusion flame of Fr=5 was 12.5Hz, which was in good agreement with the experimental results. The flamelet structures of the buoyant jet diffusion flames could be well understood by comparing the scalar dissipation rates(SDR) and the heat release rates(HRR) of the flames. It was found that the SDR was strongly coupled with the HRR in the buoyant jet diffusion flames.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.8
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• pp.849-854
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• 2005

The laminar flame concept in turbulent reacting flow is considered applicable to many practical combustion systems For turbulent premixed combustion under widely used flamelet concept, the flame surface is described as an infinitely thin propagating surface that such a Propagating front can be represented as a level contour of a continuous function G. In this study, for the Purpose of validating the LES of G-equation combustion model. LES of turbulent Premixed combustion with dynamic SGS model of G-equation in turbulent channel flow are carried out A constant density assumption is used. The Predicted flame propagating speed is goof agreement with the DNS result of G. Bruneaux et al.

• 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.

• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1240-1247
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• 2006

Large eddy simulation of turbulent premixed flame in turbulent channel flow is studied by using G-equation. A flamelet model for the premixed flame is combined with a dynamic subgrid combustion model for the filtered propagation flame speed. The objective of this work is to investigate the validity of the dynamic subgrid G-equation model to a complex turbulent premixed flame. The effect of model parameters of the dynamic sub grid G-equation on the turbulent flame speed is investigated. In order to consider quenching of laminar flames on the wall, wall-quenching damping function is employed in this calculation. In the present study, a constant density turbulent channel flow is used. The calculation results are evaluated by comparing with the DNS results of Bruneaux et al.