• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1238-1243
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• 2002

In this study, the validity of the acoustic impedance model and the estimation model by electro-acoustic analogy suggested by Maa for predicting the absorptive performance of multiple layer perforated plate systems is investigated. From the comparison between the experiment and calculation for the absorption performance of double layer perforated plate system, the calculated results of using Rao and Munjal's impedance model and transfer matrix method are closer to the experimental values than those of using Maa's impedance model and electro-acoustic analogy. Therefore, in order to apply the acoustic impedance model and the estimation model by electro-acoustic analogy suggested by Maa to the multiple layer perforated plate systems, it is necessary that the suggested acoustic impedance and estimation models should be re-examined.

• Journal of Power System Engineering
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• v.12 no.5
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• pp.65-70
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• 2008

The purpose of this study is to verify availability of the acoustic emission in-situ monitoring method to the internal leak and operating conditions of the turbine major valves relating to safety for turbine operating and prevention of turbine trouble at nuclear power plants. In this study, acoustic emission tests are performed when the pressurized electro-hydraulic control oil flowed through turbine electro-hydraulic controller oil check valve and turbine power/trip fluid solenoid valve in the condition of actual turbine operating. The acoustic emission method was applied to the valves at the site, and the background noise was measured far the abnormal plant condition. To judge for the leak existence ell the object valves, voltage analysis and frequency analysis of acoustic signal emitted from infernal leak in the valve operating condition are performed. It was conformed that acoustic emission method could monitor for valve internal leak to high sensitivity.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.333-334
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• 2004

The central aspect of the research into virtual acoustic imaging for multiple listeners involves a detailed study of the relative orientation of both sources and listeners. It is vital in any multiple listener system to first establish the conditioning of the potential geometrical arrangements of transducers and listeners. In this paper, this made clear the important link between the conditioning of the electro-acoustic transfer function matrix between transducers and ears and the design of inverse filters for crosstalk cancellation. This work has been undertaken by using simple free field models of the electro-acoustic transfer functions. Therefore, optimal transducer arrangements have been identified and these have been proved by time domain solutions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1044-1047
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• 2003

An acoustic testing device composed of 2 probe microphones was developed for the electro-acoustic specification testing of the ITE (In-The-Ear) hearing aid (HA). The amplitude ratio and the phase difference between the incident pressure onto the HA microphone and the outward pressure of the HA receiver were measured by the present acoustic system. The microphones were particularly used because of small acoustic cavities where input and output pressures were present. The acoustic wall composed of clay completely blocks the propagation of the sound pressure between the small acoustic cavities. The system has an advantage of structural flexibility for the acoustic testing of different sizes and shapes of ITE-type HAs.

• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.58-61
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• 1993

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.7
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• pp.595-601
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• 2005

A mobile robot system utilizing NDT (Non-Destructive Testing) method is designed and fabricated f3r automatic integrity evaluation of large sized industrial reservoirs and pipelines. The developed mobile robot can crawl over the outer surface of the industrial facilities even though the shape of the structures is various and unsymmetric. The robot detects defects such as pinholes, cracks and thickness reduction at the wall of the facilities using EMAT (Electro-Magnetic Acoustic Transducer). Image processing technology for weld line detection at the surface of the target and host programs including defect detecting algorithms are also developed. Automation of defect detection for these kinds of large facilities using mobile robots is helpful to prevent significant troubles of the structures without danger of human beings under harmful environment.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.06a
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• pp.357-358
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• 2007

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.5
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• pp.522-526
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• 2015

Generally, underwater unmanned vehicle have adopted an inertial navigation system (INS), dead reckoning (DR), acoustic navigation and geophysical navigation techniques as the navigation method because GPS does not work in deep underwater environment. Even if the tactical inertial sensor can provide very detail measurement during long operation time, it is not suitable to use the tactical inertial sensor for small size and low cost UUV because the tactical inertial sensor is expensive and large. One alternative to INS is attitude heading reference system (AHRS) with the micro-machined electro mechanical system (MEMS) inertial sensor because of MEMS inertial sensor's small size and low power requirement. A cost effective and small size attitude heading reference system (AHRS) which incorporates measurements from 3-axis micro-machined electro mechanical system (MEMS) gyroscopes, accelerometers, and 3-axis magnetometers has been developed to provide a complete attitude solution for UUV. The AHRS based MEMS overcome many problems that have inhibited the adoption of inertial system for small UUV such as cost, size and power consumption. Several evaluation experiments were carried out for the validation of the developed AHRS's function and these experiments results are presented. Experiments results prove the fact that the developed MEMS AHRS satisfied the required specification.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.770-774
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• 1994

The volume of an acoustic source is important in determining various acoustic parameters. One of the suggested techniques is the internal pressure method incorporating a loudspeaker attached to a chamber wall and a microphone inserted into the cavity. Although the method is easy to handle with a very simple measurement setup, the coupling effects between the dynamic system of the loudspeaker and acoustic field, and the effects of higher order modes introduced by the discontinuities in the acoustic field, and the effects of higher order modes introduced by the discontinuities in the acoustic field should be considered for precise result. In this study, higher order modes due to the discontinuities of loudspeaker and microphone boundaries are included and the electro-acoustic coupling effects are compensated for by using the results of two cylinders with different lengths. The volume velocity of a loudspeaker thus obtained agrees very with that measured by laser sensor.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.7
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• pp.310-313
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• 2003

The purpose of this paper is to evaluate the effects of pre-formed space charges by DC stress on partial discharge(PD) characteristics in XLPE. We have suggested a modified pulsed electro-acoustic(PEA) method and successfully measured both space charge distribution and current simultaneously. It has been demonstrated that the PD patterns are strongly influenced by the pre-formed space charge distributions, which are hardly disappeared up to AC 8㎸ in electrode configuration including air gap between XLPE layer and electrode. From the results, it could be said that the pre-formed space charges by DC stress can play harmful and dangerous roles in insulating system under AC operating voltages because of the field distortion and localization due to the pre-formed space charge.