• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.228-233
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• 2004

The spray and acoustic characteristics by the self-oscillation of a swirl coaxial injector were experimentally studied. The self-oscillation of a swirl coaxial injector is defined as pressure and flowrate oscillations by a time-delayed feedback between liquid and gas phase and has strong influences on atomization and mixing processes. Hence the occurrence and effect of the self-oscillation are measured using shadow photography technique, acoustic test and PDPA. The occurrence of self-oscillation largely depends on the injection conditions, such as pressure drop of liquid phase and relative momentum ratio. From the experimental results, self-oscillation occurs when the momentum of gas phase is enough large and the smaller the pressure drop of liquid phase is, the better self-oscillation occurs at the same momentum ratio. The self-oscillation is also affected by injector geometries, increasing the recess length results in the expansion of self-oscillation region and the increase of sound pressure level. The self-oscillation of a swirl coaxial injector accompanies a high intensity scream and this scream may provide harmful disturbances to combustion processes. Self-oscillation leads to strong changes in the drop size distribution and smoothly varies the slope of radial SMD distribution.

• Journal of ILASS-Korea
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• v.10 no.1
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• pp.35-42
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• 2005

The present study has numerically and experimentally investigated the spray behavior of liquid jet injected in subsonic cross-flow. The corresponding spray characteristics are correlated with jet operating parameters. The spray dynamics are known to be distinctly different in the three regimes: the column, the ligament and the droplet regimes. The behaviors of column, penetration and breakup of liquid jet have been studied. Numerical and physical models are base on a modified KIVA code. The primary atomization is represented by a wave model base on the KH(Kelvin-Helmholtz) instability that is generated by a high interface relative velocity between the liquid and gas flows. In odor to capture the spray trajectory, CCD camera has been utilized. Numerical and experimental results indicate that the breakup point is delayed by increasing gas momentum ratio and the penetration decreases by increasing Weber number.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.1
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• pp.1-12
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• 1996

The fully developed tubulent momentum and heat transfer induced by the square- ribbed roughness elements on both the inner and outer wall surfaces in the concentric annuli are studied analytically based on a modified turbulence model. Heat transfer coefficients for two conditions, i.e, a) inner wall heated as constant heat flux and outer wall insulated b) inner wall insulated and outer wall heated as constant heat flux, are investigated. The analytical results of the fluid flow are verified by experiment. The experiment is done with a pitot tube and a X-type hot wire anemometer to measure the time mean velocity profiles, zero shear stress positions, maximum velocity profiles and friction factors, and etc. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, Nusselt number and Prandtl number.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.5
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• pp.26-36
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• 1996

The fully developed turbulent momentum and heat transfer induced by the square-ribbed roughness elements on both the inner and outer wall surfaces in concentric annuli are studied analytically based on a modified turbulence model. The analytical results of the fuid flow are verified by experiment. The experiment is done with a pitot tube and a X-type hot wire anemometer to measure the time mean velocity profiles, zero shear stress positions, maximum velocity positions and friction factors, and etc. shown in Fig.1. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, Reynolds number, Nusselt bumber and Prand시 number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantage from the overall efficiency point of view by investigating turbulent flows and heat transfer in Fig.1.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.1072-1080
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• 1994

The fully developed turbulent momentum and heat transfer induced by the square-ribed roughness elements on the outer wall surface in concentric annuli are studied analytically based on a modified turbulence model. The analytical results of the fluid flow are verified by experiment. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, Reynolds number, Nusselt number and Prandtl number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantages from the overall efficiency point of view.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.452-457
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• 1993

For the calculation of transonic laminar relative flow fields on the axisymmetric H-S and B-B stream surfaces in turbomachinery, a finite volume method developed in Part (I) is extended. Energy equation is replaced for simplicity by the condition of constant rothalpy throughout the flow fields. For axisymmetric H-S flow the circumferential componets of absolute velocity are given in advance so that this component of momentum equations can be neglected. Some numerical results show good agreement with experimental data.

• Composites Research
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• v.29 no.3
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• pp.91-97
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• 2016

In this paper, impulse-momentum theory was coupled to a constitutive equation both for implementing quasi-static and impact characteristics of EPP (Expanded polypropylene). Also, parameters which have physical meanings were expressed as functions of relative density. Simultaneous nonlinear Newton-Raphson method was applied to find the proper values for parameters in the constitutive equation along with quasi-static test data. Results from the impulse-momentum theory coupled constitutive equation showed good agreement with experimental data and the potential to be applied to different material type polymeric foam.

• The KIPS Transactions:PartB
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• v.9B no.5
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• pp.673-680
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• 2002

This paper proposes a method for detecting edge using an evolutionary programming and a momentum back-propagation algorithm. The evolutionary programming does not perform crossover operation as to consider reduction of capability of algorithm and calculation cost, but uses selection operator and mutation operator. The momentum back-propagation algorithm uses assistant to weight of learning step when weight is changed at learning step. Because learning rate o is settled as less in last back-propagation algorithm the momentum back-propagation algorithm discard the problem that learning is slow as relative reduction because change rate of weight at each learning step. The method using EP-MBP is batter than GA-BP method in both learning time and detection rate and showed the decreasing learning time and effective edge detection, in consequence.

• Journal of Environmental Science International
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• v.16 no.9
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• pp.1051-1061
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• 2007

The impact of midlatitude synoptic system (upper-level trough) on typhoon intensity change was investigated by analyzing the spatial and temporal characteristics of vertical wind shear (VWS), relative eddy momentum flux convergence (REFC), and potential vorticity (PV). These variables were computed over the radial mean $300{\sim}1,000km$ from the typhoon center by using GDAPS (Global Data Assimilation and Prediction System) data provided by the Korea Meteorological Administration (KMA). The selected cases in this study are typhoons Rusa (0215) and Maemi (0314), causing much damage in life and property in Korea. Results show that the threshold value of VWS indicating typhoon intensity change (typhoon to severe tropical storm) is approximately 15 m/s and of REFC ranges 6 to 6.5 $ms^{-1}day^{-1}$ in both cases, respectively. During the period with the intensity of typhoon class, PVs with 3 to 3.5 PVU are present in 360K surface-PV field in the cases. In addition, there is a time-lag of 24 hours between central pressure of typhoon and minimum value of VWS, meaning that the midlatitude upper-level trough interacts with the edge of typhoon with a horizontal distance less than 2,000 km between trough and typhoon. That is, strong midlatitude upper-level divergence above the edge of the typhoon provides a good condition for strengthening the vertical circulation associated with the typhoons. In particular, when the distance between typhoon and midlatitude upper-level trough is less than 1,000 km, the typhoons tend to weaken to STS (Severe Tropical Storm). It might be mentioned that midlatitude synoptic system affects the intensity change of typhoons Rusa (0215) and Maemi (0314) while they moves northward. Thus, these variables are useful for diagnosing the intensity change of typhoon approaching to the Korean peninsula.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.1
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• pp.39-45
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• 2012

In the standard CFD code, Lagrangian-Eulerian method is very popular to simulate the liquid spray penetrating into gaseous phase. Though this method can give a simple solution and low computational cost, it have been reported that the Lagrangian spray models have numerical grid dependency, resulting in serious numerical errors. Many researches have shown the grid dependency arise from two sources. The first is due to unaccurate prediction of the droplet-gas relative velocity, and the second is that the probability of binary droplet collision is dependent on the grid resolution. In order to solve the grid dependency problem, the improved spray models are implemented in the KIVA-3V code in this study. For reducing the errors in predicting the relative velocity, the momentum gain from the gaseous phase to liquid particles were resolved according to the gas-jet theory. In addition, the advanced algorithm of the droplet collision modeling which surmounts the grid dependency problem was applied. Then, in order to validate the improved spray model, the computation is compared to the experimental results. By simultaneously regarding the momentum coupling and the droplet collision modeling, successful reduction of the numerical grid dependency could be accomplished in the simulation of the high-pressure injection diesel spray.