• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.7
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• pp.275-282
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• 2016

MILD (Moderate and Intense Low-oxygen Dilution) combustion using oxygen as an oxidizer is considered as one of the most promising combustion technologies for high energy efficiency and for reducing nitrogen oxide and carbon dioxide emissions. In order to investigate the effects of nozzle angle and oxygen velocity conditions on the formation of oxygen-MILD combustion, numerical and experimental approaches were performed in this study. The numerical results showed that the recirculation ratio ($K_V$), which is an important parameter for performing MILD combustion, was increased in the main reaction zone when the nozzle angle was changed from 0 degrees to 15 degrees. Also, it was observed that a low and uniform temperature distribution was achieved at an oxygen velocity of 400 m/s. The perfectly invisible oxy-MILD flame was observed experimentally under the condition of a nozzle angle of $10^{\circ}$ and an oxygen velocity of 400 m/s. Moreover, the NOx emission limit was satisfied with NOx regulation of less than 80 ppm.

• Electrical & Electronic Materials
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• v.9 no.6
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• pp.564-571
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• 1996

We calculated the drift-velocities of electrons and holes of I $n_{0.53}$(A $l_{x}$G $a_{1-x}$ )$_{0.47}$As, which is used for semiconductor materials of high performance HBTs, along with the various doping concentrations and Al mole fractions as well as the electric fields by Monte Carlo experiment. Especially, for the valence bands the accuracy of hole-drift-velocity was improved in the consideration of intervalley scattering due to the inelastic scattering of acoustic phonon. From the results the empirical formulas of the low- and high field mobility of electrons and holes were extracted by using nonlinear least square fitting method. The accuracy of the formulas was proved by comparing the formula of low-field electron mobility as well as drift-velocity of I $n_{0.53}$ G $a_{0.47}$As and of low-field hole mobility of GaAs with the measured values, where the error was below 10%. For the high-field mobilities of electron and hole the results calculated by the formulas were very well matched with the MC experimental results except at the narrow field range where the electrons produced the velocity overshoot and the corresponding error was about 30%.0%. 30%.0%.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.9-10
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• 2010

In this study, the static and low velocity impact tests for two-way concrete specimens strengthening with the CFRP sheets were carried out. The specimens that had a dimension of $50{\times}350{\times}350mm$ with 40 MPa plain concrete and steel fiber reinforced concrete which had same mixture to plain concrete and 0.75% steel fibers were fabricated. The specimens reinforced with the CFRP or steel fibers showed mixed failure modes, splitting and punching, also splitting cracks and fragments were much reduced than plain concrete specimens'. Two-way concrete members reinforced with the CFRP and steel fiber simultaneously dissipated 6.8 times larger energy than not-retrofitted members' under the low-velocity impact loading.

• Aerospace Engineering and Technology
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• v.2 no.1
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• pp.213-222
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• 2003

Some analytical methods to analyze low-velocity impact force history of composite laminated structures used in aerospace vehicles are reviewed. A classical method used at initial research of low-velocity impact problem in 1980s was reviewed on its physical meaning, and the approximate method assuming the shape of impact force history as a sinusoidal wave was reviewed. A parametric study on contact constant and exponent in contact law was performed in order to analyze an effect on impact force history, and finally its was understood that impact force history could be analyzed accurately even though the linearized contact law was used. Also, in this paper it was shown that impact problem could be analyzed simply and easily using a commercial finite element code.

• Journal of Mechanical Science and Technology
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• v.19 no.4
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• pp.947-957
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• 2005

In this study a simple model is developed that predicts impact damage in a composite laminate avoiding the need of the time-consuming dynamic finite element method (FEM). The analytical model uses a non-linear approximation method (Rayleigh-Ritz) and the large deflection plate theory to predict the number of failed plies and damage area in a quasi-isotropic composite circular plate (axisymmetric problem) due to a point impact load at its centre. It is assumed that the deformation due to a static transverse load is similar to that oc curred in a low velocity impact. It is found that the model, despite its simplicity, is in good agreement with FEM predictions and experimental data for the deflection of the composite plate and gives a good estimate of the number of failed plies due to fibre breakage. The predicted damage zone could be used with a fracture mechanics model developed by the second investigator and co-workers to calculate the compression after impact strength of such laminates. This approach could save significant running time when compared to FEM solutions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.5
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• pp.368-376
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• 2001

Performance of heat exchanger was evaluated to heat exchanger using oscillating heat pipe for waste heat recovery of low temperature. Oscillating heat pipe used in this study was formed to the closed loop of serpentine shapes using copper tubes. Heat exchanger was formed to shell and tube type and composed of low finned tube. R-22 and R-141b were used to the working fluids of tube side and their charging ratio was 40%. And, water was used to the working fluid of shell side. As the experimental parameters, the inlet temperature difference of heating and cooling part of secondary fluid and the mass velocity of secondary fluid were used. The mass velocity of secondary fluid was changed from 90 kg/$m^2s\; to\;190 kg/m^2$s from the experimental results, heat recovery rate was linearly increased to the increment of the mass velocity of secondary fluid and the inlet temperature difference of secondary fluid. Finally, the performance of heat exchanger was evaluated by using $\varepsilon$-NTU method. It was found that NTU was about 1.5 when effectiveness was decided to 80%.

• Composites Research
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• v.26 no.2
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• pp.116-122
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• 2013

In this study, impact behavior of aluminium and glass-fiber structure is studied under low impact velocity. Compression test is carried out to investigate the compressive strength of the specimens. The degree of damage is observed using microscopy and compared with the experimental analysis data. The maximum load capacity, impact strength and elastic energy of glass-fiber honeycomb sandwich panel are more than the aluminium honeycomb sandwich panel.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.205-212
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• 2006

Atmospheric drag is the most significant factor effecting the low Earth satellites under the altitude of 800 km Although the atmospheric density of the low Earth orbit is very low compared to that of the sea level, the accumulated effect of the atmospheric drag slowly lowers the satellite velocity at the perigee. Decrease in velocity at perigee directly causes decrease in altitude at apogee which changes the eccentricity of the orbit. The orbit finally reaches a circular orbit before reentering the Earth. This paper states the methods of calculating the atmospheric drag and the lifetime of the satellite. The lifetime of the kick motor and the satellites which will be used on KSLV-L are calculated by Satellite Tool Kit.

• Composites Research
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• v.16 no.1
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• pp.50-57
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• 2003

Usually many researchers have used the modified Hertzian contact law or experimental static indentation law to analyze impact response of composite laminates subjected to the low-velocity impact. In this study, physical meaning of the method using the laws was investigated and the difference between the analytical results obtained using the laws was also investigated. Furthermore parametric study on contact constant and exponent in the contact law was performed. Finally it was shown that a linearized contact law can be well applied to low-velocity impact response analysis of composite laminates. If this concept is used, commercial finite element software can be used to solve impact problem without making any auxiliary code.

• Steel and Composite Structures
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• v.18 no.5
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• pp.1291-1303
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• 2015

Damage caused by low velocity impact is so dangerous in composites because although in most cases it is not visible to the eye, it can greatly reduce the strength of the composite material. In this paper, damage development in U-section glass/polyester pultruded beams subjected to low velocity impact was considered. Different failure criteria such as Maximum stress, Maximum strain, Hou, Hashin and the combination of Maximum strain criteria for fiber failure and Hou criteria for matrix failure were programmed and implemented in ABAQUS software via a user subroutine VUMAT. A suitable degradation model was also considered for reducing material constants due to damage. Experimental tests, which performed to validate numerical results, showed that Hashin and Hou failure criteria have better accuracy in predicting force-time history than the other three criteria. However, maximum stress and Hashin failure criteria had the best prediction for damage area, in comparison with the other three criteria. Finally in order to compare numerical model with the experimental results in terms of extent of damage, bending test was performed after impact and the behavior of the beam was considered.