• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.436-444
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• 2016

Uniformity in transducer performance is a must-have to ensure the reliable acoustic performance of a tile projector, used for active echo reduction. However, practical limitations imposed by variations in material properties and fabrication errors lead to performance variations among unit transducers, which could degrade the radiation characteristics (transmitting voltage response and directivity) of the tile projector and ultimately the echo reduction performance. In this paper we present a method to minimize these adverse effects via an appropriate placement of unit transducers within the tile projector. To this end, we perform a series of coupled acoustic-piezoelectric simulations, assuming a group of 36 unit transducers having 6 dB variations in transmitting voltage response, to analyze and compare the radiation characteristics of tile projectors under different transducer placement schemes.

• The Journal of the Acoustical Society of Korea
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• v.16 no.3
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• pp.45-50
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• 1997

Four different wedge angle absorptive tiles were designed and made, and the magnitudes of the reflected acoustic fields by the wedge shaped underwater sound absorptive tiles were measured. The minimum magnitude was found at the angle of 30$^{\circ}$ and the maximum of it was found at the wedge angle of 120$^{\circ}$ from measured the reflected acoustic fields at the front sides of the tiles. The fact that as wedge angle of the absorptive tile increases, the reflection coefficient is increasing is verified. The measured reflected acoustic fields were not dependent on the frequency in the range of 10kHz~30kHz used in this experiment for the same wedge angle tile. The measured reflected acoustic fields at the back sides of the tiles show that they are independent from both type of the absorptive tiles and the frequencies used in the experiments. The measured values and the computed values by the numerical model for the reflected acoustic fields of the wedge shaped absorptive tiles are fairly well comparable with one another.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.625-629
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• 2014

In this paper, a tile projector for the active control of low-frequency underwater echoes is studied using finite element method. Compared to the existing underwater actuators used for echo reduction, the tile projector is better suited for covering a wide area such as the hull of a submarine. In order to actively match the acoustic impedance at the water-object interface, the projector is driven to radiate a pressure wave that is the inverted replica of the echo at the interface. Finite element simulations demonstrate significant echo reductions due to the active impedance matching by the tile projector.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.198-204
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• 2003

A basic experiment was performed to control tile plant growth using acoustic emission technique considering the environmental conditions for plant. At a dry soil condition, the signals due to the cavitation from xylem of angiosperm and gymnosperm were mainly detected. The strong signal from xylem and the weak signal from plasmodesmata and casparian strip were detected at the same time after distilled water was provided. Two signals after providing tile acid and distilled water were contrary to each other. The wind, number of leaf, music, temperature and humidity affected the acoustic emission count from plants but the frequency ranges of the detected signals were the same.

• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.2058-2061
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• 1997

A main research topic in PWM inverter drive system is to reduce the generated acoustic noise. One method to reduce the acoustic noise is to cause the switching pattern to be random. This RPWM(Random Pulse Width Modulation) technique for voltage controlled inverters is a kind of good solutions for reduction of acoustic noise and suppression of vibration. This paper describes a carrier frequency modulated real-time RPWM inverter. Changing the carrier frequency randomly, the power spectrum of tile acoustic noise was spread over the wide-band area. And experimental results showed that emitted noise is much more comportable and less annoying

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.1
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• pp.43-50
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• 2017

Acoustic tiles are typically installed on the surface of pressure vessels in submarines to minimize echoes based on the ship's own noise and active sonar. In this study, we studied low frequency active echo reduction techniques to reduce underwater target echo signals. Active control algorithms using tile type projectors and FxLMS logic have been developed and the projectors have been installed in the assumed hull structure. The effectiveness of projectors and control algorithms has been evaluated in time and frequency domain analysis through experiments in the tank.

• The KSFM Journal of Fluid Machinery
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• v.3 no.2 s.7
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• pp.15-23
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• 2000

The present work describes the prediction method for the unsteady flow field and the acoustic pressure field of a ducted axial fan. The prediction method is comprised of time-marching free-wake method, acoustic analogy, and the Kirchhoff-Helmholtz BEM. The predicted sound signal of a rotor is similar to the experiment one. We assume that the rotor rotates with a constant angular velocity and the flow field around the rotor is incompressible and inviscid. Then, a time-marching free-wake method is used to model the fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The newly developed Helmholtz-Kirchhoff BEM lot thin body is used to calculate tile sound field of the ducted fan. The ducted fan with 6 blades is analysed and the sound field around the duct is calculated.

• Journal of the Korea Institute of Building Construction
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• v.9 no.3
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• pp.87-94
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• 2009

Recently, in accordance with the interesting on well-being as well as the revitalization of living athletics, it is current tendency that people who use the swimming pools are on increasing. However, because the most of indoor swimming pools have ever used the reflection finishing materials likely as the tile due to the property of its hydrophilic space, the inside of indoor swimming pool is vibrating too much, and some problem which the voice and music do not delivering clearly is occurring when swimming lessons or underwater aerobics(synchronized swimming) and swimming game. Based on such viewpoint, locating the object on actually built indoor swimming pool, this Study has ever grasped its physical acoustic property, and finally designed the indoor swimming pool that contains an optimum acoustic condition, by remodelling it through an acoustic simulation. It is considered that such study result could be utilized as the useful materials when constructing the similar indoor swimming pool, hereafter.

• Journal of KSNVE
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• v.8 no.6
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• pp.1037-1042
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• 1998

This paper discusses the dependence of the convergence rate on the acoustic error path in these popular algorithms and introduces new algorithms which increase the convergence region regardless of the time-delay in the acoustic error path. We also Propose a novel control algorithm (AFC/CAFC) for tonal noise cancellation. The proposed algorithm estimates the magnitude and phase of the tonal noise. The algorithm uses the steepest descent method for the phase/magnitude estimation. Performances of tile CAFC algorithm are presented in comparison with those by the AFC algorithm based on computer simulations and experiments.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.115-119
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• 1996

An estimation of surface roughness value is a very important and difficult issue in grinding process. The definition of the D.A.R.F(Dimensionless Average Roughness Factor) has been made including the absolute average and tile standard deviation that are the parameters of the AE(Acoustic Emission) sign. The theoretical equation of the surface roughness applying the D.A.R.F has been derived from the regressive analysis and specified with respect to the availability through the experimental approach on the machine.