• Proceedings of the KSME Conference
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3209-3214
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• 2007

This study numerically investigates the unsteady flow and acoustic characteristics of a flapping wing using a hydrodynamic/acoustic splitting method. The Reynolds number based on the maximum translation velocity of the wing is Re=8800 and Mach number is M=0.0485. The flow around the flapping wing is predicted by solving the two-dimensional incompressible Navier-Stokes equations (INS) and the acoustic field is calculated by the linearized perturbed compressible equations (LPCE), both solved in moving coordinates. Numerical results show that the hovering sound is largely generated by wing translation (transverse and tangential), which have different dipole sources with different mechanisms. As a distinctive feature of the flapping sound, it is also shown that the dominant frequency varies around the wing.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제13권5호
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• pp.364-374
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• 2003

The performance of an acoustic transducer is determined by the effects of many design variables. and mostly the influences of these design variables are not linearly independent of each other To achieve the optimal performance of an acoustic transducer, we must consider the cross-coupled effects of the design variables. In this study with the FEM. we analyzed the variation of the resonance frequency and sound pressure of a flextensional transducer in relation to Its design variables. Through statistical multiple regression analysis of the results, we derived functional forms of the resonance frequency and sound pressure in terms of the design variables, and with which we determined the optimal structure of the transducer by means of a constrained optimization technique, SQP-PD. The proposed method can reflect all the cross-coupled effects of multiple design variables, and can be utilized to the design of general acoustic transducers.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 한국해양공학회 2004년도 학술대회지
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• pp.386-389
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• 2004

Beamforming for underwater acoustic communication is affected by the broadband feature of underwater acoustic communication signal, which has the low center frequency compared to the signal bandwidth. In this paper, the baseband equivalent array signal model is derived and we present computer simulation results for the broadband finite impulse response (FIR) beamformer performance according to the FIR filter order and the tap spacing. If the FIR filter order is increased above the optimum value, the beamformer performance is degraded. Also the tap spacing is related to the optimum FIR filter order.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.191-192
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• 2002

The scuffing failure is a critical problem in modern machine components, especially for the requirement of high efficiency and small size. In this study. scuffing experiments are conducted using Acoustic Emission(AE) measurement by an indirect sensing approach to detect scuffing failure. Using AE signals we con get and indication about the state of the friction processes, about the quality of solid and liquid layers on the contacting surface in real time. The FFT(Fast Fourier Transform)analyses of the AE signal are used to understand the interfacial interaction and the relationship between the AE signal and the state of contact is presented.

• Proceedings of the KIEE Conference
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• 대한전기학회 2001년도 추계학술대회 논문집 전기물성,응용부문
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• pp.189-191
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• 2001

This paper described the outputs of acoustic sensors due to the vibration of particles in the mock up GIS. We used the two type of acoustic sensors which had 150kHz resonant frequency and 60kHz resonant frequency respectively. In the experiment of the mock up GIS we paid attention to the relationship between applied voltages and sensor outputs due to particles. In this results fall down voltages depended on the material and length of particles but lift off voltages depended on the materials of particles. And the sensors outputs were increased with applied voltages in the same particle.

• Journal of Industrial Technology
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• 제20권A호
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• pp.17-26
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• 2000

To determine the source location of acoustic emission in rock, the least square method has been used until lately but it needs much time and efforts. In this study, neural network system is applied to above model instead of least square method. This system has twenty seven input processing elements and three output processing element. The source locations calculated by above two methods are similarly concordant. The new method using neural network system is relatively simple and easy for calculating source location compared with traditional method.

• Journal of the Korean Society for Nondestructive Testing
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• 제11권1호
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• pp.31-37
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• 1991

Acoustic emission(AE) signals detected during metal cutting were applied as the experimental test to sensing tool wear and chipping on the NC vertical milling machine. The in-process detection of cutting tool wear including chipping, cracking and fracture has been investigated by means of AE in spite of vibration or noise through intermittent metal cutting, then the following results were obtained 1) When the tool wear is increased suddenly, or the amplitude of AE signals changes largely, it indicates chipping or breaking of the insert tip. 2) It was confirmed that AE signal is highly sensitive to the cutting speed and tool wear. 3) At the early period of cutting, the wear were large and RMS value increased highly by the influence of minute chipping and cracking, etc. Therefore, the above situations should be considered for the time when the tool would be changed.

• Journal of KSNVE
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• 제7권6호
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• pp.919-929
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• 1997

Induction motors are used in many areas to transform electrical energy to mechanical energy. In the design of an induction motor, not only energy efficiency but also noise becomes an important factor. To effectively address the noise problem, it will be convenient if one can see where and how noise is generated and propagated. In this study sound radiation by an induction motor is visualized using cylindrical acoustic holography. To minimize the bias error by window effect Minimum Error Window(MEW) is used. Its performance is verified by numerical simulations. Based on these theoretical understanding, sound pressure measurement with an induction motor are performed. Not only sound radiation are visualized but sound pressure level and sound power level are also estimated. Results show that the main source is located at nearly bottom part of the motor and the total sound pressure level is 49dB, which satisfies the guideline value suggested by the KS C 4202.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.248-252
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• 2007

As Waterpower Generation generates electricity using the difference of altitude of water, also let the turbine revolves through water pipe, at this time the revolving turbine causes exceedingly huge noise. Accordingly, not only those workers in the hydraulic turbine dynamo room are suffering the difficulties in mutual communication, but also those workers in the adjacent office are enduring the obstruction to the business due to the noise. Therefore, this Study has analyzed the reduction effect on the noise of hydraulic turbine dynamo room utilizing computer simulation, through the preceding research with the optimized model for architectural acoustic factor of the hydraulic turbine dynamo room. It is considered that such research result could be applied as the useful material for improvement of acoustic performance and noise-reduction effect at other similar hydraulic turbine dynamo room in the future.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.223-225
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• 2008

In this study. we propose a wide bandwidth surface acoustic wave (SAW) motor by design of Inter Digital Transducer (IDT). SAW motor has several benefits compared with preexisted actuator. But it has narrow bandwidth, which causes the lower performance. To widen the bandwidth, the change of IDT structure was proposed, which is slanted IDT and since function apodization. The frequency responses were compared original uniform IDT and changed IDT. And the time responses were compared original uniform IDT and changed IDT. As a result, the feasibility of wide bandwidth SAW motor was certified.