• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.101-104
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• 1995

A acoustic emission (AE) sensor has been used to monitor tool were during milling process. The relation between tool wear and AE RMS (Root mean Square) signal was investigated experimentally. A avaliable monitoring index for monitoring toolwear was newly extracted form AE RMS. And on-line monitoring program was developed. The proposed monitoring system has verified experimentally by roughing end milling titanium alloy with TIN coated HSS tool.

• The Journal of the Acoustical Society of Korea
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• v.35 no.2
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• pp.102-109
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• 2016

This paper proposes a noise suppression method through SNR (Singal-to Noise Ratio) estimation in the two microphone array environment of close spacing. The conventional method uses a noise suppression method for a gain function obtained through the SNR estimation based on coherence function from full band. However, this method cause performance decreased by the noise damage that affects all the feature vector component. So, we propose a noise suppression method that allocates a frequency domain signal into N constant multi frequency band and each frequency band gets a gain function through SNR estimation based on coherence function. Performance evaluation of the proposed method is shown by comparison with PESQ (Perceptual Evaluation of Speech Quality) value which is an objective quality evaluation method provided by the ITU-T (International Telecommunications Union Telecommunication).

• Geophysics and Geophysical Exploration
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• v.22 no.2
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• pp.56-61
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• 2019

In this paper, we studied efficient modeling strategies when we simulate the 3D time-domain acoustic wave propagation using a cell-based finite difference method which can handle the variations of both P-wave velocity and density. The standard finite difference method assigns physical properties such as velocities of elastic waves and density to grid points; on the other hand, the cell-based finite difference method assigns physical properties to cells between grid points. The cell-based finite difference method uses average physical properties of adjacent cells to calculate the finite difference equation centered at a grid point. This feature increases the computational cost of the cell-based finite difference method compared to the standard finite different method. In this study, we used additional memory to mitigate the computational overburden and thus reduced the calculation time by more than 30 %. Furthermore, we were able to enhance the performance of the modeling on several media with limited density variations by using the cell-based and standard finite difference methods together.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.12
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• pp.1346-1351
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• 2014

We propose a novel approach for stereophonic acoustic echo suppression using spectro-temporal filtering based on soft decision. Unlike the conventional approaches estimating the echo pathes directly, the proposed technique can estimate stereo echo spectra without any double-talk detector. In order to improve the estimation of echo spectra, the extended power spectrum density matrix and echo overestimation control matrix are applied on this method. In addition, this echo suppression technique is based on soft decision technique using speech absence probability in STFT domain. Experimental results show that the proposed method improves compared with the conventional approaches.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.2
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• pp.120-126
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• 2019

Recently, there is an increasing need for highly precise processing with the rapid development of precision machinery, electrical and electronics, and semiconductor industries. Cutting machine control relies on the operator's sense and experience in tradition, but it has been greatly enhanced by the adoption of CNC(Computerized Numeric Controller). In addition, cutting dynamics technology has been paid attention to reflect the operating state of machine in real time. This paper presents a method to detect and stabilize tool vibration by attaching an acoustic sensor to a CNC machine. The sensed acoustic data is synchronized with the tool position and the abnormal vibration frequency is separated from the collected acoustic frequency, then analyzed to detect the tool vibration. Also the reliability the tool vibration detection and stabilization is improved by applying the cutting dynamic method. The proposed method is analyzed and evaluated in terms of the surface roughness.

• Journal of the Korea Organic Resources Recycling Association
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• v.12 no.4
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• pp.121-129
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• 2004

Anaerobic digestion is the most common process for sewage sludge stabilization and has benefits of VS reduction and biogas production. Many pretreatment methods have been studied to improve hydrolysis rate because the rate of sewage sludge degradation is slow in anaerobic digestion. This study mainly focused upon the effects on disintegration of sewage sludge by ultrasonic pretreatment according to the variation of acoustic density and duration of sonication time. In this study, acoustic density has been changed as follows : 33W/L, 70W/L, 88W/L, 139W/L in case of 40 kHz with the test time changes of 10min, 20min, 25min, 30min and 40min. In the comparison of $SCOD_{Cr}/TCOD_{Cr}$ variation for excess sludge and mixed sludge disintegration, the rates of $SCOD_{Cr}/TCOD_{Cr}$ have been increased in the condition of denser acoustic density and longer sonication time with acoustic frequency of 40kHz. The pH of the excess sewage sludge and mixed sewage sludge has been decreased in the condition of denser acoustic density and longer sonication time with acoustic frequency of 40kHz.

• The Journal of the Acoustical Society of Korea
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• v.41 no.5
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• pp.589-600
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• 2022

In order to verify the reliability of Dry Test Bench (DTB) used for testing the output energy from ballistic extracorporeal shock wave therapeutic devices, the measurements with DTB were compared with the acoustic energy measured with a Laser Doppler Vibrometer (LDV) for a commercial ballistic ESWT device. It was shown that the mechanical energy detected with DTB had variability maintained within 5 % at the same output power setting and also had a linear correlation (adj. R² = 0.991) with the acoustic energy measured with the LDV for the entire output power settings. Using the correlation between the two methods and the correlation on the acoustic energy measured in between air and water with the LDV, the DTB measurement can be used to estimate the energy flux density in water with an average error of 7.85 % for the entire output power settings of the ballistic shock wave generator considered in the experiment. DTB provides information limited to the output mechanical energy and therefore it is not suitable for testing the various acoustic output parameters required in IEC61846 and IEC63045. However, DTB that is simple in measurement principles and easy to use is expected for manufacturers and clinical users to monitor the performance of ballistic Extracorporeal Shock Wave Therapy (ESWT) devices.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.8
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• pp.1287-1294
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• 2003

The wear process of end mill is so complicated process that a more reliable technique is required for the monitoring and controlling 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 4 cases 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. As the cutter impacts the workpiece surface, a situation of farced vibration arises in which the dominant forcing frequency is equal to the tooth passing frequency of the cutter. The tooth passing frequency appears as a harmonics form, and end mill flank wear is related with the first harmonic. It is possible to detect end . mill flank wear. This paper proposed the new method of the end mill wear detection.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.162-167
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• 2005

Recently, the advanced industries using micro parts are rapidly growing. Micro endmilling is one of the prominent technology that has wide spectrum of application field ranging from macro to micro parts. Also, the method of micro-grooving using micro endmilling is used widely owing to many merit, but has problems of precision and quality of products due to tool wear and tool fracture. This study deals with condition monitoring using acoustic emission(AE) signal in the micro-grooving. First, the feature extraction of AE signal directly related to machining process is executed. Then, the distinctive micro endmill state according to the each tool condition is classified by using the fuzzy C-means algorithm, which is one of the methods to recognize data patterns. These result is effective monitoring method of micro endmill state by the AE sensing techniques which can be expected to be applicable to micro machining processes in the future.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.8
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• pp.742-747
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• 2012

A modified NDIF method using a sub-domain approach is introduced to extract highly accurate eigenvalues of two-dimensional, arbitrarily shaped acoustic cavities. The NDIF method, which was developed by the authors for the eigen-mode analysis of arbitrarily shaped acoustic cavities, has the feature that it yields highly accurate eigenvalues compared with other analytical methods or numerical methods(FEM and BEM). However, the NDIF method has the weak point that it can be applicable for only convex cavities. It was revealed that the solution of the NDIF method is very inaccurate or is not suitable for concave cavities. To overcome the weak point, the paper proposes the sub-domain method of dividing a concave domain into several convex domains. Finally, the validity of the proposed method is verified in two case studies, which indicate that eigenvalues obtained by the proposed method are more accurate compared to the exact method, the NDIF method, or FEM(ANSYS).