• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.6
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• pp.38-46
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• 2011

In order to simulate the ignition-gas injection in the interior ballistics, a two-dimensional analytic code for two-phase flows has been developed. The Eulerian-Lagrangian approach and the low-dissipation simple high-resolution upwind scheme(LSHUS) have been adopted in the numerical code for the propellant combustion of the gun propelling charges. The ghost-cell extrapolation method has been used for the moving boundary in the chamber with the projectile movement. The calculation results of the developed code have been compared and verified through those of the dimensionless IBHVG2 code and the previous one-dimensional code. In comparison with the two-phase flows according to the drag models, the numerical analysis of the muzzle velocity has been affected by the drag model.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.38.3-39
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• 2017

The N159 and N160 ionized regions in the Large Magellanic Cloud are an important extragalactic star-forming complex. The physical environments and the star formation stages are different in N159 and N160. We performed near-infrared polarimetry to those star forming regions with IRSF/SIRPOL 1.4-m telescope. Near-infrared polarization enabled us to trace the detailed structure of magnetic fields in star-forming regions. Through the polarimetric data of J, H, and Ks bands, we examined the magnetic field structures in the N159/N160 complex. In this presentation, we show complex distribution of the magnetic fields associated with dust and gas structures. We verify the local magnetic fields in each star-forming region, which appear to be related with local environments, such as interior and boundary of shell structure, star-forming HII regions, and boundaries between HII regions and dense dark clouds. We discuss the formation scenario of the N159/N160 complex suggested from the magnetic field structure.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.67-80
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• 2017

The high-speed bypass effect on the heat exchanger performance has been investigated numerically. The plate-fin type heat exchanger was modeled using two-dimensional porous approximation for the fin region. Governing equations of mass, momentum, and energy equations for compressible turbulent flow were solved using ideal-gas assumption for the air flow. Various bypass-channel height were considered for Mach numbers ranging 0.25-0.65. Due to the existence of the fin in the bypass channel, the main flow tends to turn into the core region of the channel, which results in the distorted velocity profile downstream of the fin region. The boundary layer thickness, displacement thickness, and the momentum thickness showed the variation of mass flow through the fin region. The mass flow variation along the fin region was also shown for various bypass heights and Mach numbers. The volumetric entropy generation was used to assess the loss mechanism inside the bypass duct and the fin region. Finally, the correlations of the friction factor and the Colburn j-factor are summarized.

• Computers and Concrete
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• v.22 no.5
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• pp.493-500
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• 2018

Due to the fact that the ratio of their height to their openings is very large compared to normal beams, there are difficulties in the design and analysis of deep beams, which differ in behavior. In this study, the optimum horizontal and vertical reinforcement diameters of 5 different beams were determined by using genetic algorithms (GA) due to the openness/height ratio (L/h), loading condition and the presence of spaces in the body. In this study, the effect of different mutation operators and improved double times sensitive mutation (DTM) operator on GA's performance was investigated. In the study following random mutation (RM), boundary mutation (BM), non-uniform random mutation (NRM), Makinen, Periaux and Toivanen (MPT) mutation, power mutation (PM), polynomial mutation (PNM), and developed DTM mutation operators were applied to five deep beam problems were used to determine the minimum reinforcement diameter. The fitness values obtained using developed DTM mutation operator was higher than obtained from existing mutation operators. Moreover; obtained reinforcement weight of the deep beams using the developed DTM mutation operator lower than obtained from the existing mutation operators. As a result of the analyzes, the highest fitness value was obtained from the applied double times sensitive mutation (DTM) operator. In addition, it was found that this study, which was carried out using GAs, contributed to the solution of the problems experienced in the design of deep beams.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.12
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• pp.1632-1639
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• 2004

Numerical calculation has been performed to investigate the transport phenomena in the horizontal reactor which has two different gas inlets for MOCVD(metalorganic chemical vapor deposition). The full elliptic governing equations for continuity, momentum, energy and chemical species are solved by using the commercial code FLUENT. It is investigated how thermal characteristics, reactor geometry, and the operating parameters affect flow fields, mass fraction of each reactants. The numerical simulations demonstrate that flow rate of each species, inlet geometry of the reactor, and its distance from the susceptor as well as the inclination of upper wall of reactor can be used effectively to optimize reactor performance. The commonly used idealized boundary conditions are also investigated to predict flow phenomena in the actual deposition system.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.127-132
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• 2003

A study of high-pressure n-heptane droplet vaporization is conducted with emphasis placed on equilibrium at vapor-liquid interface. General frame of previous rigorous model[1] is retained but tailored for flash equilibrium calculation of vapor-liquid interfacial thermodynamics. The model is based on complete time-dependent conservation equations with a full account of variable properties and vapor-liquid interfacial thermodynamics. The influences of high-pressure phenomena, including ambient gas solubility, thermodynamic non-ideality, and property variation on the droplet evaporation are investigated. The governing equations and associated moving interfacial boundary conditions are solved numerically using a implicit scheme with the preconditioning method and the dual time integration technique. And a parametric study of entire droplet vaporization history as a function of ambient pressure, temperature has been conducted. Some computational results are compared with Sato's experimental data for the validation of calculations. For low ambient temperatures, the droplet lifetime first increases with pressures, then decreases for high pressures. For higher ambient temperatures, the droplet lifetime increase with less amplitude than that of low ambient temperatures, which then decreases with more amplitude than that of low temperatures. The solubility of nitrogen can not be neglected in the high pressure and it becomes higher as the pressure goes up.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.205.2-205.2
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• 2014

The effects of ion beam mixing of a SiC film coated on super alloys (hastelloy X substrates) were studied, aiming at developing highly sustainable materials at above $900^{\circ}C$ in decomposed sulfuric acid gas (SO2/SO3/H2O) channels of a process heat exchanger. The bonding between two dissimilar materials is often problematic, particularly in coating metals with a ceramics protective layer. A strong bonding between SiC and hastelloy X was achieved by mixing the atoms at the interface by an ion-beam: The film was not peeled-off at ${\geq}900^{\circ}C$, confirming excellent adhesion, although the thermal expansion coefficient of hastelloy X is about three times higher than that of SiC. Instead, the SiC film was cracked along the grain boundary of the substrate at above $700^{\circ}C$. At ${\geq}900^{\circ}C$, the film was crystallized forming islands on the substrate so that a considerable part of the substrate surface could be exposed to the corrosive environment. To cover the exposed areas and cracks multiple coating/IBM processes have been developed. An immersion corrosion test in 80% sulfuric acid at $300^{\circ}C$ for 100 h showed that the weight retain rate was gradually increased when increasing the processing time.

• Journal of ILASS-Korea
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• v.21 no.1
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• pp.47-52
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• 2016

This paper describes the modeling of CNG direct injection using gaseous sphere injection model. Simulation of CNG direct injection does not need break up and evaporation model compared to that of liquid fuel injection. And very fine mesh is needed near the injector nozzle to resolve the inflow boundary. Therefore it takes long computation time for gaseous fuel injection simulation. However, simulation of CNG direct injection could be performed with the coarse mesh using gaseous sphere injection model. This model was integrated in KIVA-3V code and RNG $k-{\varepsilon}$ turbulence model needs to be modified because this model tends to over-predict gas jet diffusion. Furthermore, we preformed experiments of gaseous fuel injection using PLIF (planar laser induced fluorescence)method. Gaseous fuel injection model was validated against experiment data. The simulation results agreed well with the experiment results. Therefore gaseous sphere injection model has the reliability about gaseous fuel direct injection. And this model was predicted well a general tendency of gaseous fuel injection.

• Journal of Korean Ophthalmic Optics Society
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• v.6 no.1
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• pp.55-58
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• 2001

The rigid gas permeable(RGP) contact lens has nearly side effect on the cornea. So that, this lens has used the clinical reflective correction of the eye. This study have used several methods for research the fine internal structure on the RGP contact lens by scanning electron microscopy. The results have indicated that the postfixation of 1% $OsO_4$ and tannic acid is responsible for a fine structure in the internal plane of RGP contact lens. These internal surface of contact lens appeared the several shape of the hole of the stereo shape form with arrangement of round form. But, on the contact lens with non-postfixation, the stereo shape have not present and the boundary of the vesicle have not clear. Maybe, these results suggest that the fixation methods have effect on the morphological characters of materials on the RGP contact lens.

• Journal of the Korean Society of Combustion
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• v.14 no.2
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• pp.1-9
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• 2009

New way to effectively capture $CO_2$ in coal fired power plant is the combustion of coal using oxy-fuel technology. Combustion characteristics of Minco sub-bituminous coal at oxy-fuel conditions using TGA and drop tube furnace (DTF) were included activation energy about the char burnout, volatile yield and combustion efficiency of raw coal, the porosity of pyrolyzed char and fusion temperature of by-product ash. TGA result shows that the effect of $CO_2$ on combustion kinetics reduces activation energy by approximately 7 kJ/mol at air oxygen level(21% $O_2$) and decreases the burning time by approximately 16%. The results from DTF indicated similar combustion efficiency under $O_2/CO_2$ and $O_2/N_2$ atmospheres for equivalent $O_2$ concentration whereas high combustion efficiency under $O_2/N_2$ than $O_2/CO_2$ was obtained for high temperature of more than $1,100^{\circ}C$. Overall coal burning rate under $O_2/CO_2$ is decreased due to the lower rate of oxygen diffusion into coal surface through the $CO_2$ rich boundary layer. By-product ash produced under $O_2/CO_2$ and $O_2/N_2$ was similar IDT in irrelevant to $O_2$ concentration and atmospheres gas during the coal combustion.