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Ignition characteristics of laser-ablated aluminum at shock pressures up to 2 GPa
Lee, Kyung-Cheol,Taira, Tsubasa,Mo Koo, Goon,Young Lee, Jae,Yoh, Jack J. American Institute of Physics 2014 JOURNAL OF APPLIED PHYSICS - Vol.115 No.1
The ignition of aluminum particles under high pressure and temperature conditions is considered. The laser ablation method is used to generate oxide-free aluminum particles exposed to pressures ranging between 0.35 and 2.2GPa. A continuous wave CO2 laser radiation heats the surface of the aluminum target until ignition is observed. We confirm ignition by a spectroscopic analysis of AlO vibronic band of 484 nm wavelength, and the radiant temperature is measured with respect to various pressures for estimating the heating energy for ignition. The ignition characteristics of the oxide-free aluminum particles exposed to extremely high pressures are reported. (C) 2014 AIP Publishing LLC.
Simultaneous optical ignition and spectroscopy of a two-phase spray flame
Lee, Seok Hwan,Do, Hyungrok,Yoh, Jack J. Elsevier 2016 Combustion and Flame Vol.165 No.-
<P><B>Abstract</B></P> <P>Simultaneous laser ignition and spectroscopy is a scheme that enables rapid determination of the local equivalence ratio and condensed fuel concentration during a reaction in a two phase spray flame. In parallel with laser ignition, the equivalence ratio and droplet characteristics such as the concentration, size, and distribution of spray combustion are simultaneously obtained for a feedback control system. The plasma characteristics of fuel droplets are evaluated initially by shadowgraph, and the high-speed imaging of air and spray breakdown provides visualization of the transition from the plasma to a flame kernel. The spectrum in the spray is evaluated according to droplet characteristics such as size and number density. The probability density function is used to analyze the interaction between the fuel droplets and the laser plasma with laser-induced breakdown spectroscopy (LIBS) measurements. In this paper, we have conducted quantitative analysis of the LIBS signals according to the equivalence ratio, droplet size, droplet number density and droplet concentration for development of a control strategy for flame ignition and stabilization with simultaneous in situ combustion flow diagnostics.</P>
Lee, Younghun,Gwak, Min-cheol,Cho, Heaseong,Joo, Hyun Shig,Shin, Sang Joon,Yoh, Jack J.,Shin, Jae-Cheol American Institute of Aeronautics and Astronautics 2018 Journal of spacecraft and rockets Vol.55 No.4
<P>We develop a combined Lagrangian-Eulerian method for transient fluid-structure interaction problems. Based on the ghost fluid framework for improving interface tracking accuracy between a fluid (hot rocket exhaust plume) and a high strain rate deforming solid (rear cover of a vertical launch system), the numerical coupling between the two media ensures an accurate description of the flexible structure. A nine-node quadrilateral element based on total Lagrangian formulation is used, while the hydrodynamic finite difference method is used for the supersonic exhaust plume that forms a complex flow within the plenum. The Lagrangian, Eulerian, and fluid-structure interaction coupling methods are verified by ANSYS results and related theories. A two-dimensional simulation of the full vertical launch system operation mode is conducted. This requires an accurate reproduction of the complex flowfield generated by the rapid rear cover opening under a high-pressure plume during rocket launch. This fluid-structure interaction problem solution may be used for future design upgrades when a vertical launch system is exposed to unusually harsh interactive gas and structure conditions.</P>
Perturbation and Perceptual Analysis of Pathological Sustained Vowels according to Signal Typing
이지연(Lee JiYeoun),최성희(Choi Seong Hee),Jiang Jack J,한민수(Hahn MinSoo),최홍식(Choi Hong-Shik) 한국음성학회 2010 말소리와 음성과학 Vol.2 No.2
In this paper, we investigate a signal typing on the basis of visual impression of distinctive spectrogram. Pathological voices are classified into signal type 1, 2, 3, or 4 to estimate perturbation parameters and to mark perceptual rating based on Consensus Auditory-Perceptual Evaluation of Voice (CAPE-V). The results suggest that perturbation analysis can be applied to only type 1 and 2 signals and the perceptual ratings of overall grade increase with each signal type, overall. A good inter-rater reliability is showed among three raters. We recommend that pathological voices should be marked the signal typing and CAPE-V, together, to definitely describe the characteristics of pathological voices.
Analysis of melt-through process of 1.07 μm continuous wave high power laser irradiation on metal
Kyung-Cheol Lee,Won-Kye Baek,권혁준,신완순,Jack J. Yoh 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.6
Laser-metal interactions are influenced by various parameters, including laser wavelength and laser pulse duration. By proper adjustments of these parameters, one can create states that manifest different phenomena during laser ablation. In this work, we study laser melt-through of metal using 1 kW high power continuous laser with 1.07 μm wave length. A Ytterbium (Yb) doped fiber laser is used on the metal sample of varying thicknesses (0.1 ~ 2 mm). In addition to providing measurements from the melt-through process, numerical study of thermal transport effect of laser heating and thermo-elastic response of metal are reported. The test-based simulation is shown to reproduce the thermal transport characteristics of beam-metal interaction at high power continuous wave irradiation with notable accuracy.