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산소부화된 자유롭게 전파하는 CH<sub>4</sub>/O<sub>2</sub>/N<sub>2</sub>예혼합화염의 화염구조
이기용,남태형,유현석,최동수,Lee, Gi-Yong,Nam, Tae-Hyeong,Yu, Hyeon-Seok,Choe, Dong-Su 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.4
Numerical simulations of freely propagating flames burning stoichiometric CH$_4$/O$_2$/$N_2$mixtures are performed at atmospheric pressure in order to understand the effect of the $O_2$enrichment level on CH$_4$/Air flame. A chemical kinetic mechanism is employed, the adopted scheme involving 54 gas-phase species and 632 forward reactions. The calculated flame speeds are compared with the experiments for the flames established at several $O_2$enrichment level, the results of which is in excellent agreement. As a result of the increased $O_2$enrichment level from 0.21 to 1, the mole fraction of CO in the burred gas is increased. The flame speed and the temperature in the burned gas are also increased, but the thickness of the flame is severely shrunken in the preheat region. The maximum of the calculated EINO is obtained around 0.6 and 0.7 of the $O_2$enrichment level in cases of flames for fuel-lean mixtures.
CH<sub>4</sub>/CHCI<sub>3</sub>/O<sub>2</sub>N<sub>2</sub> 예혼합 화염 구조에서 산소부화의 효과
이기용,Lee, Ki-Yong 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.7
Numerical simulations of freely propagating flames burning stoichiometric C $H_4$/CHC1$_3$/ $O_2$/$N_2$ mixtures are performed at atmospheric pressure in order to understand the effect of the $O_2$ enrichment level and the CHC1$_3$/C $H_4$ molar ratio. A chemical kinetic mechanism is developed, which involves 69 gas-phase species and 379 forward and 364 backward reactions. The calculated flame speeds are compared with the experiments for the flames established at several CHC1$_3$/C $H_4$ molar ratio (R<1), the results of which is in excellent agreement. As a results of the increased $O_2$ enrichment level from 0.21 to 1, the flame speed and the temperature in the burned gas are increased. At high CHC1$_3$/C $H_4$ molar ratio two peak values appear on the $O_2$ consumption rate, which are affected by CC1$_2$+ $O_2$$_{-}$>C1O+CC1O and H+ $O_2$$_{-}$>O+OH.+OH.
개방 종단된 계단형 슬롯을 사용한 UWB용 안테나의 소형화
이기용,이영순,Lee, Ki-yong,Lee, Young-soon 한국항행학회 2017 韓國航行學會論文誌 Vol.21 No.4
In order to reduce the size of the previous stepped slot antenna for UWB applications(3.1 ~ 10.6 GHz) to half, an open ended stepped slot antenna is proposed. The proposed antenna consists of a stepped slot etched on the ground plane as radiation part and a microstrip feed-line with rectangular patch on the top plane for wideband impedance matching. The proposed antenna is designed and fabricated on the FR4 substrate with dielectric constant of 4.3, thickness of 1.6 mm and size of $28.5{\times}32mm^2$. The measured impedance bandwidth (${\mid}S_{11}{\mid}{\leq}-10dB$) of the fabricated antenna is 7.99 GHz(3.01~11 GHz) which is sufficient to cover UWB band (3.1 ~ 10.6 GHz). In particular, it has been observed that antenna has a good omnidirectional radiation patterns and high gain over the entire frequency band of interest even though the size of the proposed antenna is reduced to half when compared with the previous antenna. 기존의 UWB용 계단형 슬롯 안테나의 크기를 절반으로 줄이기 위해 개방 종단된 계단형 슬롯 안테나를 제안하였다. 제안된 안테나는 방사부로써 접지면에 에칭된 계단형 슬롯과 윗면의 광대역 임피던스 정합을 위한 사각형 패치를 가진 마이크로스트립 급전선으로 구성된다. 제안된 안테나는 유전상수(${\epsilon}_r$)가 4.3, 두께가 1.6 mm, 크기가 $28.5{\times}32mm^2$ 인 FR4 기판에 설계 및 제작 되었다. 제안된 안테나의 제작 및 측정 결과, 임피던스 대역폭(${\mid}S_{11}{\mid}{\leq}-10dB$)이 7.99 GHz (3.01~11 GHz)로 UWB 대역(3.1 ~ 10.6 GHz)을 충분히 만족하였다. 특히 제안된 안테나의 크기가 기존의 안테나에 비해 절반으로 줄어들었음에도 불구하고, 사용하고자 하는 전 대역에서 안정되고 우수한 무지향성 방사패턴을 얻을 수 있었으며 2.18 ~ 4.93 dBi의 높은 이득 또한 얻을 수 있었다.
Paper Title : Speech Parameter Estimation and Enhancement Using the EM Algorithm
이기용,강영태,이병국,Lee, Ki-Yong,Kang, Young-Tae,Lee, Byung-Gook The Acoustical Society of Korea 1994 韓國音響學會誌 Vol.13 No.e2
신호처리의 많은 분야에서, 심하게 비가우시안 성질을 가지는 분포, 혹은 분포의 중간은 가우시안 특성을 가지지만 양 끝에서는 편차가 크게 나는 분포를 다루어야 하는 경우가 종종 있다. 이러한 편차에 효과적으로 대처하기 위하여 본 논문에서는 음성 신호의 여기 신호로서 혼합 분포(mixture distribution)을 고려한다. 이것은 음성 분석시 피치 주파수가 미치는 영향을 감소시키며, 배경 잡음을 제거하는 데에도 효과적이다. 음성 신호 파라미터의 추정 및 향상을 위하여 EM 알고리즘을 사용하묘, 향상 과정에서는 강인 칼만 필터링 기법을, 파라미터 추정 관정에서는 검출/추정 기법을 사용한다. 실험 결과, 본 논문에서 제안하는 알고리즘이 입력 신호대잡음비가 열악한 경우에 기존의 것보다 우수한 성능을 보인다. In many applications of signal processing, we have to deal with densities which are highly non-Gaussian or which may have Gaussian shape in the middle but have potent deviations in the tails. To fight against these deviations, we consider a finite mixture distribution for the speech excitation. We utilize the EM algorithm for the estimation of speech parameters and their enhancement. Robust Kalman filtering is used in the enhancement process, and a detection/estimation technique is used for parameter estimation. Experimental results show that the proposed algorithm performs better in adverse SNR input conditions.
CH<sub>4</sub>/CHF<sub>3</sub>/Air 예혼합 화염의 축소 반응 메카니즘 개발
이기용,Lee, Ki Yong 한국연소학회 2014 한국연소학회지 Vol.19 No.1
A short reaction mechanism for premixed $CH_4/CHF_3/Air$ flames was developed with a reduction method of the combined application of simulation error minimization (SEM) which included connectivity method and principal component analysis. It consisted of 43 species and 403 elementary reactions at the condition of less than 5% of maximum error. The calculation time operated with a short mechanism was over 5 times faster than one with a detailed reaction mechanism. Good agreement was found between the flame speeds calculated by the short reaction mechanism and those by the detailed reaction mechanism for the entire range of $CHF_3/CH_4$ mole ratios and equivalence ratios. In addition excellent agreements were determined for the profiles of temperature, species concentration, and the production rates of the various species. So the short reaction mechanism was able to accurately predict the flame structure for premixed $CH_4/CHF_3/Air$ flames.
산소부화된 메탄 예혼합 화염에서 CF<sub>4</sub> 분해에 대한 연구
이기용,Lee, Ki Yong 한국연소학회 2017 한국연소학회지 Vol.22 No.4
The decomposition of tetrafluoromethane has been investigated with the reaction mechanism proposed for freely propagating $CH_4/CF_4/O_2/N_2$ premixed flames on the oxygen enrichment. The factors affecting on the removal efficiency of tetrafluoromethane were analyzed. The increase in flame temperature due to oxygen enrichment has a great influence on the removal efficiency of tetrafluoromethane. At the same oxygen enrichment condition, the removal efficiency in the rich flame is higher than one in the lean flame. The increase of the F/H ratio leads to decrease the flame temperature and the removal efficiency of tetrafluoromethan is decreased at the flame temperature of 2600 K or lower, The elementary reactions that dominate the consumption of tetrafluoromethane are (R1) $CF_4+M=CF_3+F+M$ and (R2) $CF_4+H=CF_3+HF$. (R1) has the greatest effect on the consumption of tetrafluoromethane under the oxygen enhanced flames.