• Journal of the Institute of Convergence Signal Processing
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• v.5 no.4
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• pp.281-286
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• 2004

The wear process of end mill is a so complicated process that a more reliable technique is required for the monitoring and controling the tool life and its performance. This research presents a new tool wear monitoring method based on the sound signal generated on the machining. The experiment carried out continuous-side-milling for using the high-speed steel end mill under wet condition. The sound pressure was measured at 0.5m from the cutting zone by a dynamic microphone, and was analyzed at frequency domain. The tooth passing frequency appears as a harmonics form, and end mill wear is related with the first harmonic. It can be concluded from the result that the tool wear is correlate with the intensity of the measured sound at tooth passing frequency estimation of end mill wear using sound is possible through frequency analysis at tooth passing frequency under the given circumstances.

• The Journal of the Acoustical Society of Korea
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• v.5 no.4
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• pp.16-21
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• 1986

위상이 불규칙적으로 변하는 RZ와 NRZ 신호에 대하여 전력 밀도 스펙트럼을 구하였고 신호의 펄스폭 점유율은 가변으로 하였다. 이때 불규칙 위상의 확률분포는 구간 내에서 일정하다고 가정한다. 단극성 지터없는 신호는 입력된 신호의 기본 주파수의 정수배마다 스펙트럼의 이산성분이 존재하며 이 것은 데이터를 찾기 위한 타이밍 신호로써 이용된다. 그러나 지터가 유입되는 경우에는 이 이산 신호성 분이 점차 감소하게 되며, 균일한 확률 분포를 갖는 지터의 경우는 완전히 소멸하였음을 확인하였다.

• Economic and Environmental Geology
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• v.40 no.6
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• pp.751-759
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• 2007

To better understand the subsurface geological structure of the Kunsan Basin in the Yellow Sea, the mean depths of the density discontinuous layers (DDLs) of the Kunsan Basin were calculated by power spectrum analysis using satellite altimetry gravity data. The calculated mean depths of DDLs were -1.1km, -3.4km, -9.1km and -31.0km. The mean depth of -1.1km DDL was interpreted as regional unconformity shown in about 1 second in two way travel time (TWTT) in the seismic reflection profiles, and the mean depth of -3.4km DDL was also interpreted as top of the acoustic basement in the seismic reflection profiles. Comparing with well data, seismic reflection profiles and regional geology in the study area, the mean depth of -9.1km DDL was interpreted as top of the igneous origin basement. This means that the acoustic basement of the study area is composed mainly of sediments which are disregarded in previous study. The mean depth of -31.0km DDL was interpreted as the Moho discontinuity because this mean depth is similar to one of the normal continental crust thickness. The detection of top of the igneous origin basement suggests that oil gas potential analysis in Kunsan Basin needs to be extended to the deeper part of sediments (acoustic basement).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.272-275
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• 2008

공연장음향성능에 영향을 미치는 중요한 부자재중의 하나인 음향반사판의 면밀도 변화에 따른 흡음특성 변화를 조사하였다. 음향반사판은 목질계반사판으로 밀도 변화는 $11\;㎏/m^2{\sim}41k\;㎏/m^2$으로 총 3개의 시료를 대상으로 측정하였다. 저주파 대역에서의 흡음률을 측정하기 위하여 서브우퍼와 무지향성 스피커를 사용하였으며 측정결과 중고주파수 대역의 흡음률은 면밀도 변화에 따라 큰 차이가 없었으나 저주파수 대역의 흡음률을 면밀도 변화에 따라 차이가 있는 것으로 나타났다. 향후 음악 공연 공간내의 음향반사판의 면밀도 변화에 따른 실내 음향 특성 변화 및 설계지침에 대한 연구가 필요할 것으로 사료된다.

• The Journal of the Acoustical Society of Korea
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• v.29 no.4
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• pp.223-228
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• 2010

High-frequency bottom loss measurements for grazing angle of $82^{\circ}$ in frequency range 17-40 kHz were made in Jinhae bay in the southern part of Korea. Observations of bottom loss showed the strong variation as a function of frequency, which were compared to the predicted values using two-layered sediment reflection model. The geoacoustic parameters including sound speed, density and attenuation coefficient for the second sediment layer were predicted from the empirical relations with the mean grain size obtained from sediment core analysis. The geoacoustic parameters for the surficial sediment layer were inverted using Monte Carlo inversion algorithm. A sensitivity study for the geoacoustic parameters showed that the thickness of surficial sediment layer was most sensitive to the variation of the bottom loss.

• The Journal of the Acoustical Society of Korea
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• v.27 no.7
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• pp.325-332
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• 2008

The prediction method of TS parameters, frequency response, and electrical input impedance is proposed with physical properties of parts and results of electromagnetic FEA(Finite Element Analysis) in a loudspeaker driver design. In design for weight reduction and improvement of flux density asymmetry, the prediction results are well coincided with measurement ones. As the applications, it can be applied in design for improvement of the $2^{nd}$ harmonic distortion with flux density distribution analysis. The proposed method is expected to be utilized for reducing trial-and-error process in electromagnetic parts design. It can also be used for providing guidelines for parts selection in the early stages.

• The Journal of the Acoustical Society of Korea
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• v.22 no.8
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• pp.711-716
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• 2003

This paper proposes the method to select the number of optimal mixtures in each state in Continuous Density HMM (Hidden Markov Models), Previously, researchers used the same number of mixture components in each state of HMM regardless spectral characteristic of speaker, To model each speaker as accurately as possible, we propose to use a different number of mixture components for each state, Selection of mixture components considered the probability value of mixture by each state that affects much parameter estimation of continuous density HMM, Also, we use PCA (principal component analysis) to reduce the correlation and obtain the system' stability when it is reduced the number of mixture components, We experiment it when the proposed method used average 10% small mixture components than the conventional HMM, When experiment result is only applied selection of mixture components, the proposed method could get the similar performance, When we used principal component analysis, the feature vector of the 16 order could get the performance decrease of average 0,35% and the 25 order performance improvement of average 0.65%.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2005.05a
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• pp.3-8
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• 2005

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.1 no.1
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• pp.15-22
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• 2002

This study shows how the change of helix angle of different helix angle end mill affects machining accurracy. It was verified that cutting force are remarkably low when endmill has helix angle of different helix angle 250, 310, 370 and AE signal have less reationshap with the change of helix angle. Moreover, as the number of rotations are increases, the AE signal increased with the proportion to the number but cutting force are inversely proportional to the rotation.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.239-244
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• 2002

This study shows how the change of helix angle for different helix angle end mill affects machining accuracy. It was verified that cutting forces are remarkably low when endmill has helix angle of different helix angle $25^{\circ}\;, \; 31^{\circ}\; , \; 37^{\circ}$and AE signals have less relationship with the chance of helix angle Moreover, as the number of rotations are increased, the AE signals are increased with the proportion to the number but cutting forces are inversely proportional to the rotation.