• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.364-370
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable and unstable pitch modes for the lower and higher activation energies, respectively. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of two modes. The maximum pressure history in the stable pitch remained nearly constant, and the single Mach leg existing on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the unstable pitch due to the generation and decay of complex Mach interaction on the shock front shape. The high frequency oscillation was self-induced because the intensity of the transverse wave was changed during propagation in one cycle. The high frequency behavior was not always the same for each cycle, and therefore the low frequency oscillation was also induced in the pressure history.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.457-462
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• 2009

In a high speed train, aluminium extruded panel is widely used in floor, side wall and roof structures for high bending stiffness and weight reduction. However, with some inevitable reasons, aluminium extruded panel shows inferior sound insulation performance compared with the flat panel having same weight. Especially, occurrence of local resonance modes in the particular frequency band, is one of the main reason in the deterioration of the sound insulation performance. Local resonance modes are generated in the structure which consists of periodic unit structure, such as the aluminium extruded panel. The local resonance frequency is determined by the specification of the unit structure. In this study, we predict the local resonance frequency band on the aluminium extruded panel used for the high speed train, and investigate how the design modification in the unit structure influences the local resonance frequency band and panel bending stiffness. The purpose of the study is to provide the design information for the effective unit structure in order to improve the sound insulation performance of the aluminium extruded panel.

• Journal of Hydrospace Technology
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• v.2 no.1
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• pp.18-26
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• 1996

It is normal practice to consider bending wave modes only, when one applies SEA (Statistical Energy Analysis) to ship structures because of complexities in SEA modeling and evaluation of coupling loss factors for inplane modes. According to the result of Tratch[1], the inplane wave modes becomes important for the analysis of a foundation structure as the distance from the source and receiver increases. In this paper, the effect of inplane wave modes on structure-borne noise propagation in ship structures is presented. It is shown that the inplane wave could increase the noise level more than 10 dB compared with the results without inplane wave modes at high frequency bands for compartments far from the source location.

• Journal of Power Electronics
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• v.11 no.1
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• pp.28-36
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• 2011

In this paper, a three phase cycloconverter type high frequency AC link inverter is discussed. The configuration consists of a high frequency full-bridge inverter and a high frequency transformer followed by a three phase cycloconverter whose switch is composed of anti-series connected MOSFETs with a common source. A simple digital control strategy based on space vector modulation (SVM) and repetitive control for the cycloconverter is proposed although its input voltage is a high frequency AC pulse. The operation principle of the proposed control strategy is analyzed and the equivalent working modes during one interval are also presented. The effectiveness of the proposed control strategy is verified through Matlab/Simulink simulations and experiments on a 1.45kW prototype.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1314-1322
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• 2000

The acoustic property of reactive type single expansion chamber can be analyzed by traditional plane wave theory. This theory can be applied in low frequency range and has good performance. But this theory can't include higher order modes, therefore another method is essential to analyze acoustic filter in high frequency range. Many researcher suggested the method that can concern higher order modes, and their methods are using mode matching technique. But there is no method that can be applied to the analysis of single expansion chamber with arbitrary inlet/outlet duct position and numbers of higher order modes of inlet/outlet duct and middle chamber. In this paper, the method which can analyze single expansion chamber with arbitrary inlet/outlet duct position and numbers of higher order modes of inlet/outlet duct and middle chamber using fundamental mode matching technique, was suggested and the predictions by this method was compared with those by the finite element method, and the influence of inlet/outlet location to acoustic performance of single expansion chamber is investigated and explained by higher order mode effects.

• Journal of information and communication convergence engineering
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• v.14 no.4
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• pp.252-257
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• 2016

An edge-located electromagnetic bandgap (EL-EBG) structure using a defected ground structure (DGS) is proposed to suppress resonant modes induced by edge excitation in a two-dimensional planar parallel plate waveguide (PPW). The proposed EL-DGS-EBG PPW significantly mitigates multiple transverse-magnetic (TM) modes in a wideband frequency range corresponding to an EBG stopband. To verify the wideband suppression, test vehicles of a conventional PPW, a PPW with a mushroom-type EBG structure, and an EL-DGS-EBG PPW are fabricated using a commercial process involving printed circuit boards (PCBs). Measurements of the input impedances show that multiple resonant modes of the previous PPWs are significantly excited through an input port located at a PPW edge. In contrast, resonant modes in the EL-DGS-EBG PPW are substantially suppressed over the frequency range of 0.5 GHz to 2 GHz. In addition, we have experimentally demonstrated that the EL-DGS-EBG PPW reduces the radiated emission from -24 dB to -44 dB as compared to the conventional PPW.

• Speech Sciences
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• v.7 no.3
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• pp.263-272
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• 2000

The purpose of this study was to compare receptive language performance and expressive language performance in 13 patients with aphasia by using three stimulus presentation modes: Stimulus mode I (picture), Stimulus mode II (written word), Stimulus m (question using verbal explanation). The stimulus consisted of 10 words. They included 5 functional words and 5 non-functional words. The 13 subjects with aphasia were divided into 2 aphasic types: 5 Broca's aphasics and 8 anomie aphasics. The results were as follows: Firstly, the three stimulus modes didn't affect receptive language performance of aphasia subjects. Secondly; the three stimulus modes were effective on expressive language performance of aphasia subjects. Particularly, stimulus mode II (written words) was effective in naming the aphasia subjects. Thirdly, the functional words with high frequency were better than non-functional words with low frequency on expressive language performance, but not on receptive language performance of aphasia subjects. Finally, the interaction between three stimulus modes and the functional (nonfunctional) words affected expressive language performance only, but not receptive language performance. Particularly, presenting stimulus in written words which are functional words produced the best expressive language performance.

• Journal of the Optical Society of Korea
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• v.13 no.4
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• pp.423-427
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• 2009

The results of the experimental and theoretical studies conducted on terahertz filtering using two parallel-plate waveguides (PPWGs) are presented herein. The first PPWG with 355 ${\mu}m$ plate separation generates 4 THz bandwidth TM modes ($TM_0,\;TM_2,\;and\;TM_4$), whereas the second PPWG with 100 ${\mu}m$ plate separation operated the THz filter for the generated TM modes with 1.5 THz cutoff frequency. The outgoing THz wave of the two PPWGs was truncated until 1.5 THz, and the system was operated using a high-pass THz filter. The absorption and dispersion of the combined TM and TE modes for the filtering system were calculated. The theoretical calculation and measurement results for the cutoff and oscillation frequency in the spectrum domain agreed well.

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.191-197
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• 2006

We analyze the self-pulsation(SP) characteristics due to mode beating of two modes emitted in a multi-section complex-coupled (CC) DFB laser composed of two DFB sections and a phase control section between them. SP frequency due to mode beating of the two modes is determined by the difference of grating periods in the two CC DFB regions. As the difference of grating periods in the two CC DFB regions increases, the SP frequency increases from very low frequency to the THz region. In the case of a mode which is not located in the stop band of the other DFB region, the mode propagates into the other DFB region without a high reflection, so that output powers emitted in a multi-section CC DFB laser have high modulation indexes due to the large interaction between the two modes.

• Journal of the Korean Society of Combustion
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• v.17 no.1
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• pp.30-36
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• 2012

Dynamic characteristics of combustion occurring in various combustion devices have been extensively studied since most of high-performance combustion devices are susceptible to hazardous, unstable combustion that deteriorates combustor's lifetime. One of the most severe unstable combustion phenomena is high-frequency combustion instability in which heat release fluctuations from combustion are coupled to resonant modes of the combustor. Here in this study, characteristics of high-frequency combustion instabilities observed in three different combustion devices have been presented. Lean-premixed combustion instability occurs mainly due to equivalence ratio fluctuations which induce large heat release oscillations at lean conditions. Liquid-fueled combustion also shows high-frequency instability from energy coupling between pressure and heat release oscillations.