• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1366-1370
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• 2007

Predicting the noise radiated from vibrating structures is important in the automotive, aerospace, construction equipment, and defense industries. In this paper, a numerical implementation of the boundary element method in solving the Helmholtz integral equation for radiated noise prediction is presented. To predict the noise emitted by vibrating structure, the developed code can use the results from a structure analysis performed by a multi-purpose structural finite element code like ANSYS and directly measured data by non-contact vibration sensor like Laser Doppler Vibrometer. To verify the accuracy of developed code, two kinds of verification are perfomed. Firstly, the computer code used the harmonic analysis results of ANSYS in simple model and try to match with SYSNOISE. After matching with simulation results, the code compared with the result from SYSNOISE which used the velocity data from the LDV measurement with different number of points. The performance of the developed code for vibro-acoustic noise prediction is presented using the experimental results of the non-contact sensor

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.8
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• pp.628-635
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• 2014

The procedure to estimate the sources of noise and vibrations in a typical drum-type washing machine was presented. The sources should be identified to predict the radiated noise with computational model of structure. Source identification techniques based on singular decomposition were implemented using the measured signals of accelerometers and microphones. The finite element analysis and indirect boundary element analysis were implemented to predict the structural vibrations and the acoustic pressures at the field points. The predicted results by only structural sources were compared with those by both structural and acoustical sources. It was verified that not only the structural-borne source but also air-borne source should be considered to predict the radiated noise with better accuracy. The contribution analysis with respect to the transfer path was also preformed.

• The Journal of the Acoustical Society of Korea
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• v.30 no.1
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• pp.42-48
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• 2011

This preliminary study is about the application of the compound source to the active noise barrier system as control sources. A compound source is composed of two monopole sources but having opposite phase. However, both monopole sources in one compound source are not independently controlled. The source strength of monopole source close to the noise source is proportional to the other one. Therefore, the cost for the hardware system is cheaper than usual system but known to possibly having a similar performance in generating anti-noise acoustic field. In this study, using a simple active noise barrier system model having a non-reflective floor, the effectiveness of the system with compound sources is investigated through computer simulations and shows 30~40 % performance improvement of noise reduction.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.7
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• pp.1487-1494
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• 2011

In this paper, a novel genre classification algorithm is proposed for music recommendation system. Especially, to improve the classification accuracy, the band-pass filter for octave-based spectral contrast (OSC) feature is designed considering the psycho-acoustic model and actual frequency range of musical instruments. The GTZAN database including 10 genres was used for 10-fold cross validation experiments. The proposed multiple-octave based OSC produces better accuracy by 2.26% compared with the conventional OSC. The combined feature vector based on the proposed OSC and mel-frequency cepstral coefficient (MFCC) gives even better accuracy.

• Journal of Broadcast Engineering
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• v.12 no.1 s.34
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• pp.28-40
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• 2007

In this paper, we proposes an idea for improved sound characteristic which decreasing a problem in previous reverberation algorism structure. To later reflection sound, proposed new reverberation structure, using a lopped and nested all-pass delay line, and it is designed to improve an natural concert hall sound. In addition, In order to have best imaginary sound effect, we extracted the factors by controlling each delay line's delay time, and we realized a proposed new algorithm by using general-purpose DSP. Through several experimental cases, we observed better effect on improvement of linear flatten and reverberation density and decreasing about colorlessness and non-linear sound at previous proposed model about impulse input.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.1346-1353
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• 1993

Recently , it has been popular for family use to sell a watermelon by the piece such as a half or a quarter. Therefore, it has been necessary to detect and sort out hollow or overripened watermelons before they are shipped. Previously, inspection and rejection of hollow or overripened watermelons were carried out by skilled inspectors with their experience and intuition based on the traditional slapping method. In recent years many inspectors have became older and are going to retire. Thus automatic quality measuring devices have to be developed. There are many reports on the measurement of internal quality for watermelons with non-destructive methods. However, there is no online device to detect and measure both hollow and ripeness of watermelons until now. We have developed the model MWA-9002 online device to detect hollow and measuring the ripeness of watermelons by acoustic impulse. The developed of this devices has enables accurate distinction and rejection at the same level of the skilled inspectors, and also has saved labor. Nowadays nine automatic watermelon sorting and packing facilities applied this device have installed in Japan.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.996-999
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• 2011

The flow and combustion dynamics in the ignition and ramjet sustainer phase of an integrated rocket-ramjet(IRR) engine are investigated. The physical model includes the entire engine flowpath, from the freestream in front of the inlet to the exit of the exhaust nozzle. The flowfield obtained from a rocket booster study is used as the initial condition for the present analysis, so that the complete operation history of the engine can be obtained. The analysis for the primary factor governing flame propagation during the ignition and the key mechanisms for driving and sustaining the flow oscillations are performed.

• Proceedings of the Acoustical Society of Korea Conference
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• 1997.06a
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• pp.27-34
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• 1997

In this study , we tried to test the classification performance of a neural netow and thereby to examine its applicability to the signals distorted by a shallow water einvironment . We conducted an acoustic experiment iin a shallow sea near Pohang, Korea in which water depth is about 60m. The signals, on which the network has been tested, is ilinear frequency modulated ones centered on one of the frequencies, 200, 400, 600 and 800 Hz, each being swept up or down with bandwidth 100Hz. we considered two transforms, STFT(short-time Fourier transform) and PWVD (pseudo Wigner-Ville distribution), form which power spectra were derived. The training signals were simulated using an acoutic model based on the Fourier synthesis scheme. When the network has been trained on the measured signals of center frequency 600Hz,it gave a little better results than that trained onthe simulated . With the center frequencies varied, the overall performance reached over 90% except one case of center frequency 800Hz. With the feature extraction techniques(STFT and PWVD) varied,the network showed performance comparable to each other . In conclusion , the signals which have been simulated with water depth were successully applied to training a neural network, and the trained network performed well in classifying the signals distorted by a surrounding environment and corrupted by noise.

• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.231-235
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• 2001

Insulation aging diagnosis system provides early warning regarding electrical equipment defect. Early warning is very important in that it can avoid great losses resulting from unexpected shutdown of the production line. Since relations of insulation aging and partial discharge dynamics are non-linear, it is very difficult to provide early warning in an electrical equipment. In this paper, we propose the design method of insulation aging diagnosis system that use a magnetic wave and acoustic signal to diagnoses an electrical equipment. Proposed system measures the partial discharge on-line from DAS(Data Acquisition System) and acquires 2D Patterns from analyzing it. For fettering the noise contained in sensor signals we used ICA algorithms. Using this data design of the neuro-fuzzy model that diagnoses an electrical equipment is investigated. Validity of the new method is asserted by numerical simulation.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.254-257
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• 2004

An electromagnetic acoustic transducers (EMAT) can usually generate or detect an ultrasonic wave into specimens across a small gap. Especially stiffness of composites depends on layup sequence of CFRP(carbon fiber reinforced plastics) laminates because the layup of composite laminates influences there properties. It is very important to evaluate the layup errors in prepreg laminates. A nondestructive technique can therefore serve as a useful measurement for detecting layup errors. It was shown experimentally that this shear waves for detecting the presence of the errors is very sensitive. It is found that high probability shows between tests and the model developed in characterizing cured layups of the laminates. Also a C-scan method was used for detecting layup of the laminates because of extracting fiber orientation information from the ultrasonic reflection caused by structural imperfections in the laminates. Therefore, it was found that interface C-scan images show the fiber orientation information by using two-dimensional fast Fourier transform(2-D FFT).