• 한국연소학회지
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• 제6권1호
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• pp.7-13
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• 2001

Propagation characteristics of tribrachial flames have been studied numerically in a two-dimensional fuel/oxidizer mixing layer. A flame is initiated by imposing a high temperature ignition source. Subsequent propagation of a tribrachial flame is traced. The flow redirection effect at the leading edge of a tribrachial flame increases the propagation speed beyond the corresponding stoichiometric laminar burning velocity. The effect of mixture fraction gradient on the propagation speed of a tribrachial flame is analyzed in a mixing layer considering that mixture fraction gradient increases as a tribrachial flame propagates toward upstream. As the flame curvature at the leading edge increases with decreasing mixture fraction gradient, the flow redirection effect becomes more pronounced on the flame propagation speed. As a result, the propagation speed of a tribrachial flame increases with decreasing mixture fraction gradient.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.422-427
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• 2000

Propagation characteristics of tribrachial flames have been investigated experimentally in both two-dimensional and axisymmetric counterflows. Mixture fraction gradient at stoichiometric location is controlled by varying equivalence ratios at the two nozzles, one of which maintains rich while the other lean premixture. Tribrachial flames propagating through these mixtures are investigated. The propagation speed of tribrachial flames in two-dimensional counterflow decreases with fuel concentration gradient and has much higher speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large propagation speed can be attributed to the tribrachial flame propagating with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient is estimated and extrapolated experimental results substantiate this limiting speed. As mixture fraction gradient approaches zero, a transition in propagation characteristics occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar behavior has been obtained for tribrachial flames propagating in axisymmetric counterflow.

• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1710-1718
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• 2002

The effect of fuel concentration gradient on the propagation characteristics of tribrachial (or triple) flames has been investigated experimentally in both two-dimensional and axisymmetric counterflows. The gradient at the stoichiometric location was controlled by the equivalence ratios at the two nozzles; one of which is maintained rich, while the other lean. Results show that the displacement speed of tribrachial flames in the two-dimensional counterflow decreases with fuel concentration gradient and has much larger speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large displacement speed can be attributed to the flame propagation with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient was estimated and the curvefit of the experimental data substantiates this limiting speed. As mixture fraction gradient approaches zero, a transition occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar results have been obtained for tribrachial flames propagating in axisymmetric counterflow.

• 한국자동차공학회논문집
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• 제15권3호
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• pp.166-173
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• 2007

A numerical study was conducted to have the effect of $CO_2$ addition to fuel on the chemical reaction mechanism with the change of the initial concentration of $CO_2$ and the axial velocity gradient. From this study, it was found that there were two serious effects of $CO_2$ addition on a non-premixed flame ; a diluent effect by the reactive species reduction and chemical effect of the breakdown of $CO_2$ by the third-body collision and thermal dissociation. Especially, the chemical effect was serious at the lower velocity gradient of the axial flow. It was certain that the mole fraction profile of $CO_2$ was deflected and CO was increased with the initial concentration of $CO_2$. It was also ascertained that the breakdown of $CO_2$ would cause the increasing of CO mole fraction at the reaction region. It was also found that the addition of $CO_2$ did not alter the basic skeleton of $H_2-O_2$ reaction mechanism, but contributed to the formation and destruction of hydrocarbon products such as HCO. The conversion of CO was also suppressed and $CO_2$ played a role of a dilution in the reaction zone at the higher axial velocity gradient.

• 한국연소학회지
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• 제7권3호
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• pp.47-54
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• 2002

The propagation speed of tribrachial flame in laminar propane jets has been investigated experimentally under normal and micro gravity conditions. The displacement speed was found to vary nonlinearly with axial distance because flow velocity along stoichiometric contour was comparable to the propagation speed of tribrachial flame for the present experiment. Approximate solutions for velocity and concentration accounting density difference and virtual origins have been used in determining the propagation speeds of tribrachial flame. Under micro gravity condition, the results showed that propagation speed of tribrachial flame is largely affected by the mixture fraction gradients, in agreement with previous studies. The limiting maximum value. of propagation speeds under micro gravity conditions are in good agreement with the theoretical prediction, that is, the ratio of maximum propagation speed to the stoichiometric laminar burning velocity is proportional to the square root of the density ratio of unburned to burnt mixture.

• 한국가스학회지
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• 제15권2호
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• pp.47-56
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• 2011

삼지화염의 화염안정화 메커니즘 중 중요한 한 가지는 화염전파속도이다. 화염전파속도의 정량적인 규명을 위해 Bilger는 층류 유동이론에 근거하여 혼합분율 기울기에 비선형적으로 연관된 삼지화염전파속도를 제시하였다. 그러나 지금까지의 연구에서는 화염의 곡률 반경과 스칼라소산율 및 삼지화염의 화염전파속도에 관한 직접적인 관계에 관하여 제시된 바가 없었다. 본 논문은 실험과 수치해석에 따른 수치해석 결과를 검증하고, 수치해석을 통해 스칼라소산율에 따른 화염전파속도를 확인하였다. 그리고 화염스트레치 분석을 통하여 화염전파속도의 곡률반경 및 스칼라소산율에 따른 의존도를 명확히 하였다.

• Ocean and Polar Research
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• 제26권4호
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• pp.647-653
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• 2004

Experimental studies with 4.3m and enlarged 30m in height have been conducted to investigate the flow characteristics of solid-liquid mixture in a lifting pipe and to acquire the design data for sea tests that will be performed in the future. From the results, it was observed that the more the discharged volume fraction and the solid diameter increase, the more the hydraulic gradient increases. Also, the more the diameter of the lifting pipe increases, the smaller the friction loss, and consequently, the less pressure drop and hydraulic gradient. From the enlarged hydraulic pumping experiments, it was shown that the results of the experiments were matched with those of the numerical model previously developed. On the bases of these studies, we plan to conduct further experiments and validate the hydraulic pumping model.

• Steel and Composite Structures
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• 제43권5호
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• pp.639-660
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• 2022

The bending and buckling behaviours of FG-GRNC laminated sandwich plates are investigated by using novel five-variables quasi 3D higher order shear deformation plate theory by considering the modified continuum nonlocal strain gradient theory. To calculate the effective Young's modulus of the GRNC sandwich plate along the thickness direction, and Poisson's ratio and mass density, the modified Halpin-Tsai model and the rule of the mixture are employed. Based on a new field of displacement, governing equilibrium equations of the GRNC sandwich plate are solved using a developed approach of Galerkin method. A detailed parametric analysis is carried out to highlight the influences of length scale and material scale parameters, GPLs distribution pattern, the weight fraction of GPLs, geometry and size of GPLs, the geometry of the sandwich plate and the total number of layers on the stresses, deformation and critical buckling loads. Some details are studied exclusively for the first time, such as stresses and the nonlocality effect.

• 대한의용생체공학회:의공학회지
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• 제16권4호
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• pp.431-438
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• 1995

Tailored RF 경사자계 영상법을 이용하여 혈류효과를 배제한 자화율 효과만의 뇌기능 영상을 얻을수 있었다. 일반적인 RF를 이용한 경사자계 뇌기능 영상법은 빠른 경사자계 영상법으로 인해 정맥뿐만 아니라 동맥에서의 혈류효과와 $T2^{*}$ 효과가 합쳐진 영상을 얻게되는 반면, tailored RF를 이용한 경사자계 영상법은 산소소모와 관계된 자화율 변화에 의한 뇌기능 영상을 얻을 수 있었다. 본 논문에서 tailored RF를 이용하여 뇌기능 영상에서 자화율효과와 혈류효과를 명확히 구분할 수 있음을 보였다. 그리고 실험결과로 얻은 신호는 충분히 크고 산소 소모의 변화를 보다 더 정확히 표현하므로 지금까지 다른 경사자계 영상법으로는 어려웠던 뇌기능 영상에서 정량화된 산소 신진대사 연구의 가능성을 보여주었다.

• Steel and Composite Structures
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• 제26권4호
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• pp.513-531
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• 2018

In this article, static, buckling and free vibration analyses of a sinusoidal micro composite beam reinforced by single-walled carbon nanotubes (SWCNTs) with considering temperature-dependent material properties embedded in an elastic medium in the presence of magnetic field under transverse uniform load are presented. This system is used at micro or sub micro scales to enhance the stiffness of micro composite structures such as bar, beam, plate and shell. In the present work, the size dependent effects based on surface stress effect and modified strain gradient theory (MSGT) are considered. The generalized rule of mixture is employed to predict temperature-dependent mechanical and thermal properties of micro composite beam. Then, the governing equations of motions are derived using Hamilton's principle and energy method. Numerical results are presented to investigate the influences of material length scale parameters, elastic foundation, composite fiber angle, magnetic intensity, temperature changes and carbon nanotubes volume fraction on the bending, buckling and free vibration behaviors of micro composite beam. There is a good agreement between the obtained results by this research and the literature results. The obtained results of this study demonstrate that the magnetic intensity, temperature changes, and two parameters elastic foundations have important effects on micro composite stiffness, while the magnetic field has greater effects on the bending, buckling and free vibration responses of micro composite beams. Moreover, it is shown that the effects of surface layers are important, and observed that the changes of carbon nanotubes volume fraction, beam length-to-thickness ratio and material length scale parameter have noticeable effects on the maximum deflection, critical buckling load and natural frequencies of micro composite beams.