• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.8-14
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• 2003

The particle dispersion in the turbulent mixing layer has been numerically investigated to clarify the effect of the velocity ratio in the large-scale vortical structures. In this study the LES with subgrid-scale model is employed. The Lagrangian method to predict the particle motion is applied. The particles of 10, 50, 150, 200${\mu}m$ in mean diameter were loaded into the origin of the mixing layer. It is shown that the characteristics of flow and growth rate are strongly dependent on the variation of the velocity ratio. It is also shown the relationship between the Stokes number and the particle dispersion. As a result, in the case of St~1 the particle dispersion is faster than the diffustion of the flow field while in the cases of both St<<1 and St>>1 it is shown that the particle dispersion in lower than the diffusion of the flow filed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.818-825
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• 2004

In this paper, the study of effects of flow parameters on flame structure and NOx emission concentration was performed in co-axial. laminar partially premixed methane/air flames. Such (low parameters as equivalence ratio(${\Phi}$), fuel split percentage($\sigma$), and mixing distance(x/D$\_$i/) were defined as a premixing degree and varied within ${\Phi}$=1.36∼9.52, $\sigma$=50∼100, and x/D$\_$i/=5∼20. The image of OH$\^$*/ and NOx concentration were obtained with an ICCD camera and a NOx analyzer. The flame structure observations show a categorization of partially premixed flames into three distinct flame regimes corresponding to ${\Phi}$<1.7(premixed flame structure), 1.7<${\Phi}$<3.3(hybrid structure), and ${\Phi}$>3.3(diffusion flame structure existing a luminous sooting region) at $\sigma$=75%, and x/D$\_$i/=10. As o decreases from 100% to 50%, and x/D$\_$i/ decreases, nonpremixed flame structure appear at low equivalence ratio relatively. In addition, the measured emissions for NOx rise steeply from ${\Phi}$=1.7, to ${\Phi}$=3.3, then constants ${\Phi}$>4.76. NOx emissions decrease with increase the level of premixing level. In conclusion, the main effect on flame structure and NOx production was at first equivalence ratio(${\Phi}$), and next fuel split percentage($\sigma$), and finally mixing distance(x/D$\_$i/).

• Journal of Welding and Joining
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• v.23 no.6
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• pp.99-105
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• 2005

The mixing ratio effect of the GTD-111(base metal) powder and the GNI-3 (Ni-l4Cr-9.5Co-3.5Al-2.5B) powder on TLP(Transient Liquid Phase) bonding phenomena and mechanism was investigated. At the mixing ratio of the base metal powder under $50wt\%$, the base metal powders fully melted at the initial time and a large amount of the base metal near the bonded interlayer was dissolved by liquid inter metal. Liquid insert metal was eliminated by isothermal solidification which was controlled by the diffusion of B into the base metal. The solid phases in the bonded interlayer grew epitaxially from the base metal near the bonded interlayer inward the insert metal during the isothermal solidification. The number of grain boundaries farmed at the bonded interlayer corresponded with those of base metal. At the mixing ratio above $60wt\%$, the base metal powder melted only at the surface of the powder and the amount of the base metal dissolution was also less at the initial time. Nuclear of solids firmed not only from the base metal near the bonded interlayer but also from the remained base metal powder in the bonded interlayer. Finally, the polycrystal in the bonded interlayer was formed when the isothermal solidification finished. When the isothermal solidification was finished, the contents of the elements in the boned interlayer were approximately equal to those of the base metal. Cr-W borides and Cr-W-Ta-Ti borides formed in the base metal near the bonded interlayer. And these borides decreased with the increasing of holding time.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.7
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• pp.3275-3284
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• 2012

This study analyzed a 3D hydrodynamic advection diffusion using the EFDC model (Environmental Fluid Dynamics Code) in the agriculture lake to prevent stratification when we install a water circulator. EFDC model was predicted the range of the water circulator and various operational parameters ware derived for minimize the impact of the internal lake. Through EFDC simulation, water circulation is started overall circulation after 30days and a lake overall circulation showed that it was possible operated the water circulator after about 100days. Also, advection diffusion concentration was low in a lake when water circulator operate intermittent condition than continuous condition. And the entire circulation was stable in this condition. The S/B (Surface/Bottom) ratio can reduce the impact of lake as the surface water mixing a lot of. When the same condition (S/B ratio(3:1)), Case 8 (50days operation: 50days stop) of condition were able to minimize the impact of lake.

• Journal of Korea Water Resources Association
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• v.34 no.5
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• pp.499-509
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• 2001

2-D transport model based on a discrete probability distribution for a particle displacement was developed too solve advection-diffusion problems in natural stream. In this proposed model, the probabilities expressed as an average and variance function were used to predict the mass transfer between cells in one time step. The proposed model produces solutions without numerical dispersion for constant velocity, diffusion coefficient, and cross-sectional area. When the stability and positivity restrictions were satisfied, the model produced excellent results compared to analytical solutions and other finite difference methods. The proposed model is tested against the dispersion data collected in the Grand River, Canada. The simulation results show that the proposed model can properly describe the two-dimensional mixing phenomena in the natural stream.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.3
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• pp.41-48
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• 2017

The combustion characteristics of gaseous methane-gaseous oxygen, an eco-friendly bipropellant injected by shear coaxial injector, were investigated. Flame was photographed under various combustion conditions using a DSLR camera, and the characteristics of the flame shape was quantified by image post-processing. From the view point of stabilization, the diffusion flame could be divided into anchored flame regime and blow-off regime. As the oxidizer Reynolds number ($Re_o$) increased, a probability of the formation of anchored flame increased with the length of flame. The shear coaxial injector used in this experiment was found to require a large length-to-diameter ratio of combustion chamber because it formed a relatively long flame in the injection direction due to a poor mixing depending only on the momentum diffusion of two propellant jets.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.65-73
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• 2003

An experimental study on flame lift-off characteristics of propane jet flame highly diluted with nitrogen has been conducted introducing acoustic forcing with a tube resonant frequency. A flame stability curve is attained according to forcing strength and nozzle exit velocity for $N_2$ diluted flames. Flame lift-off behavior with forcing strength and nozzle exit velocity is globally categorized into three; a well premixed behavior caused by a collapsible mixing for large forcing strength, a coexistent behavior of well-premixed and edge flames interacting with well-organized inner fuel vortices for moderate forcing strengths, and edge flame behavior for small forcing strengths. Special focus is concentrated on the coexistent behavior of the flame base in lifted flame since this may give a hint to a possibility which the flame base behaves like a well-mixed premixed flame in highly turbulent lifted flames. It is also shown that the acoustic forcing to self-pulsating laminar lifted flame affects flame lift-off behavior considerably which is closely related to downstream flow velocity, mixture strength, effective fuel Lewis number, and flame stretch.

• Journal of Korean Society on Water Environment
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• v.28 no.1
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• pp.26-37
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• 2012

Multi-dimensional hydrodynamic and water quality models are widely used to simulate the physical and biogeochemical processes in the surface water systems such as reservoirs and estuaries. Most of the models have adopted the Eulerian grid modeling framework, mainly because it can reasonably simulate physical dynamics and chemical species concentrations throughout the entire model domain. Determining the optimum grid cell size is important when using the Eulerian grid-based three-dimensional water quality models because the characteristics of species are assumed uniform in each of the grid cells and chemical species are represented by concentration (mass per volume). The objective of this study was to examine the effect of grid-size of a three dimensional hydrodynamic and water quality model (EFDC) on hydrodynamics and mass transport in the Saemangeum Reservoir. Three grid resolutions, respectively representing coarse (CG), medium (MG), and fine (FG) grid cell sizes, were used for a sensitivity analysis. The simulation results of numerical tracer showed that the grid resolution affects on the flow path, mass transport, and mixing zone of upstream inflow, and results in a bias of temporal and spatial distribution of the tracer. With the CG, in particular, the model overestimates diffusion in the mixing zone, and fails to identify the gradient of concentrations between the inflow and the ambient water.

• Water for future
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• v.28 no.6
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• pp.107-118
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• 1995

Mathematical models have been developed in which storage-relaease processes of pollutants are modeled to explain storage effect of variations of flow and channel geometry on mixing and transport of polluted releases in natural channels including low flow conditions. The models were tested by using the laboratory dispersion data. Comparisons between concentration-time curves predicted by using the proposed model incorporating two different submodels show that Storage-Diffusion Model seems to be superior in explaining physical processes inside the storage zone to the Storage-Exchange Model even though accuracies of simulation results by two models are about the same. The proposed model shows significant improvement over the conventional one-dimensional dispersion model in predicting natural mixing processes in open channels.

• Convergence Security Journal
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• v.6 no.4
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• pp.49-57
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• 2006

Firewall to block a network access of unauthorized IP system and IDS (Intrusion Detection System) to detect malicious code pattern to be known consisted the main current of the information security system at the past. But, with rapid growth the diffusion speed and damage of malicious code like the worm, study of the unknown attack traffic is processed actively. One of such method is detection technique using traffic statistics information on the network viewpoint not to be an individual system. But, it is very difficult but to reserve traffic raw data or statistics information. Therefore, we present extraction technique of a network traffic Raw data and a statistics information like the time series. Also, We confirm the validity of a mixing traffic and show the evidence which is suitable to the experiment.