• Explosives and Blasting
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• v.41 no.4
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• pp.17-28
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• 2023

Recently, the utilization of underground space for research facilities and resource development has been on the rise, expanding development from shallow to deep underground. The establishment of deep underground spaces necessitates a thorough examination of rock stability under conditions of elevated stress and temperature. In instances of greater depth, the stability is influenced not only by the geological structure and discontinuity of rock but also by the propagation of ground vibrations resulting from earthquakes and rock blasting during excavation, causing stress changes in the underground cavity and impacting rock stability. In terms of blasting engineering, empirical regression models and numerical analysis methods are used to predict ground vibration through statistical regression analysis based on measured data. In this study, single-hole blasting was conducted, and the pressure of the blast hole and observation hole and ground vibration were measured. Based on the experimental results, the blast pressure blasting vibration at a distance, and the response characteristics of the tunnel floor, side walls, and ceiling were analyzed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.62-65
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• 2008

Extrusion characteristics of Mg alloys were studied experimentally. The Al-Zn-Mg alloys, AZ31, AZ6l, AZ80, and AZ91 were extruded with hot hydrostatic extrusion process. The hydrostatic process was efficient to reduce surface friction and extend steady state region in extrusion which made it more convenient to examine deformation behavior of the alloys avoiding the disturbance caused by temporary contact state between billet and die, and billet and container. High pressure was cooperative to expand forming limit of the alloys which were applied on the billet during the extrusion process. Extrusion limits were traced in temperature and extrusion speed domain with changing composition of the alloying elements. Effects of process parameters on extrusion load and microstructure evolution were investigated also.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.7-12
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• 2003

The purpose of this work is to investigate the effect of premixing condition on the combustion and exhaust emission characteristics in a HCCI diesel engine. To form homogeneous charge before intake manifold, the premixed fuel is injected into premixed tank by GDI injection system and the premixed fuel is ignited by direct injected diesel fuel. But in the case of high intake air temperature, premixed fuel is auto-ignited before diesel combustion and soot emission is increased. In the case of light load condition, the BSFC is improved by intake air heating because increased air temperature promoted the combustion of premixed mixture. NOx and smoke concentration of exhaust emissions are reduced compared to conventional diesel engine. The combustion characteristics of the HCCI diesel engine such as combustion pressure, rate of heat release, and exhaust emission characteristics are discussed.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2506-2511
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• 2007

The coupled simulation is performed to find out the interaction of arc plasmas with surrounding materials in a thermal puffer plasma chamber. In order to be more realistic, PTFE nozzle ablation and Cu electrode evaporation, which are caused by high temperature of arc plasmas, are considered together. Pressure rise and temperature inside the chamber generated during the whole arcing history are investigated with the applied currents. It is very important to define how thermal flow and mass transfer are processing between the arc plasma and surrounding materials for further understanding complex physics inside the chamber. It is concluded that the result might be very useful to understand the mechanism happened inside and to design thermal puffer plasma chambers, but further experimental studies are required to verify the results for the more practical applications.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.9
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• pp.1226-1233
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• 2002

The purpose of the present study was to examine some basic aspects of laser chemical vapor deposition that will be ultimately utilized for solid freeform fabrication of three dimensional objects. Specifically, deposition of silicon carbide (SiC) using tetramethylsilane (TMS) as precursor was studied for a rod grown by $CO_2$laser-assisted chemical vapor deposition. First, temperature distribution for substrate was analyzed to select proper substrate where temperature was high enough for SiC to be deposited. Then, calculations of chemical equilibrium and heat and mass flow with chemical reactions were performed to predict deposition rates, deposit profiles, and deposit components. Finally, several rods were experimentally grown with varying chamber pressure and compared with the theoretical results.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.23-26
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• 2002

Two modes of shock waves propagating in He II (superfluid helium), this is a compression and a thermal shock waves, were studied experimentally by using superconductive temperature sensors, piezo pressure transducers and Schlieren visualization method with an ultra-high-speed video camera (40,500 pictures/sec). The shock waves are induced by a gas dynamic shock wave impingement upon a He II free surface. It is found that the shock Mach number of a transmitted compression shock wave is up to 1.16, and the shock Mach number of a thermal shock wave coincides well with the second sound velocity under each compressed He II state condition. The temperature rise ratio of an induced thermal shock wave to that of an incident gas dynamic shock wave was found to be very small, as small as 0.003 at 1.80K.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05b
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• pp.47-50
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• 2002

The displacemant current measuring system used for detecting the dynamic behavior of monolayers at the air-water interface is described. It basically consists of a film balance, a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is placed in the water. With Maxwell-displacement-current-measuring method, the phase transitons of $Poly-{\gamma}-benzyl_{L}$ -glutamate (PBLG) and $Poly-{\gamma}-benzyl_{D}$-glutamate(PBDG) on a water surface were detected. Measured surface pressure, displacement current and dipole moment of monolayers of PBLG and PBDG on the water surface. Also, we measured that compression velocity (30, 40, 50[mm/min]) when the sample spread volume was about 370[ul]-400[ul] and displacement current that occur when differed temperature. From the result, it is known that current is generated in the range of high surface pressures as compression velocity become faster and increase of temperature.

• Journal of the Korean Society of Safety
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• v.23 no.3
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• pp.25-29
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• 2008

In automotive disc brake system, friction heat is not uniformly distributed due to various reasons such as thermal expansion and imperfections in geometry. It is well known that thermoelastic distortion due to fictional heating affects the contact pressure distribution and can lead to thermoelastic instability, where the contact load is concentrated in one or more small regions on the brake disc surface. These regions then take very high temperatures and passage of hot spots moving under the brake pads can cause low frequency vibration called brake judder. This paper presents the FEM(finite element method) result for the temperature distribution of ventilated disc brake. A steady state two-dimensional model of disc brake system predicts the surface temperatures during a multi-stop driving schedule.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.507-510
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• 2008

Characteristics of an autothermal reformer at various operating parameters have been studied in this paper. Numerical method has been used, and simulation model has been developed for the analysis. Full Combustion reaction, Steam Reforming(SR) reaction, Water-Gas Shift(WGS) reaction, and Direct Steam Reforming(DSR) reaction are assumed as dominant chemical reactions in the autothermal reformer. Simulation results are compared with experimental results for code validation. Operating parameters of the autothermal reformer are inlet temperature, Oxygen to Carbon Ratio(OCR), Steam to Carbon Ratio(SCR), and Gas Hourly Space Veolcity(GHSV). SR reaction rate decreases with low inlet temperature. If OCR is increased, $H_2$ yield is increased but optimal point is suggested. WGS reaction is activated with high SCR. When GHSV is increased, reforming efficiency is increased but pressure drop may decrease the system efficiency.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.22.1-22.1
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• 2011

In this study, off-axis RF magnetron sputtering was used for the crystallized ITO thin films at a low temperature of about $120^{\circ}C$ instead of the conventional RF sputtering because the off-axis sputtering can avoid the damage for the plasma as well as fabrication of thin films with a high quality. The structural, optical and electrical properties of the obtained films depending on deposition parameters, such as sputtering power, gas flow and working pressure, have been investigated. The ITO thin films grown on PET substrate at $120^{\circ}C$ were crystallized with a (222) preferred orientation. 100-nm thick ITO films showed a resistivity of about $4.2{\times}10^{-4}{\Omega}-cm$ and a transmittance of about 81% at a wavelength of 550nm. The transmittance of the ITO thin films by an insertion of $SiO_2$ thin films on ITO films was improved.