• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.465-468
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• 2009

A frequency in electrical power system changes by the load fluctuation in utility grid, has an influence on a connected generator, and ultimately brings a big trouble in the power system. Therefore, a quick measurement of system frequency and governor control of power system is a very important factor in the reliability and the economic feasibility. In this study, An improve algorithm that measures the power system frequency quickly and accurately is suggested, simulated by using Matlab and programmed using C code through DSP6713 KIT. This algorithm is tested to the arbitrary voltage waveform input. The results show that the suggested algorithm is effective in the accurate and quick frequency measurements.

• The Journal of the Acoustical Society of Korea
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• v.16 no.3
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• pp.73-80
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• 1997

This paper describes structural optimization of optical fiber-wound mandrel hydrophones with Finite Element Method (FEM). The hydrophone is supposed to have operation frequency range of up to 10 kHz and show omni-directional sensitivity pattern at 5 kHz. Studied parameters are mandrel geometry, molding thickness, and material properties of constitutional parts of the hydrophone. Theoretical calculation result shows that pressure sensitivity of the hydrophone increased as either mandrel length or molding thickness gets larger. Also higher pressure sensitivity requires a mandrel or molding material with relatively low Youngs modulus or Poissons ratio. Hydrophone bandwidth increases either as the mandrel length becomes shorter or as the mandrel becomes harder. The omni-directional characteristic is improved as the mandrel length becomes shorter, at 5 kHz. With the above results, we determine the structure of an optical fiber-wound mandrel hydrophone which has the pressure sensitivity of $30 {\times} 10_{-7}$ Rad./Pa, operation frequency range of up to 10 kHz, and shows omni-directional sensitivity pattern at 5 kHz.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.5 s.248
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• pp.576-584
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• 2006

The actuating performance test of plate-type piezoelectric composite actuators having different lay-up sequences was experimentally carried out at simply supported and fixed-free boundary conditions. The actuating displacement of manufactured plate-type piezoelectric composite actuator (PCA) was measured using a non-contact laser displacement measurement system. Our results revealed that the actuating displacement with increasing applied electric field at a drive frequency of 1Hz increased non-linearly at the simply supported boundary condition whereas it almost linearly increased at the fixed-free boundary condition. On the other hand, the actuating displacement of piezoelectric composite actuator depended on the applied electric field in a drive frequency range from 1Hz to 10Hz, but its behavior was different in higher drive frequencies beyond 15Hz due to the occurrence of resonance. On the basis of the above experimental results, the bending characteristics of PCAs revealed different behavior depending on applied electric fields, drive frequencies as well as boundary conditions. Therefore, by investigating drive frequencies together with applied electric fields, actuating performance can be easily controlled and PCAs which were fabricated for this study will be sufficiently applied to pumping devices.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.8
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• pp.870-879
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• 2007

In this study, various damage modes in bending unimorph piezoelectric composite actuators with a thin sandwiched PZT plate during bending fracture tests have been evaluated by monitoring acoustic emission (AE) signals in terms of waveform and peak frequency as well as AE parameters. Three kinds of actuator specimens consisting of woven fabric fiber skin layers and a PZT ceramic core layer are loaded with a roller and an AE activity from the specimen is monitored during the entire loading using an AE transducer mounted on the specimen. AE characteristics from a monolithic PZT ceramic with a thickness of $250{\mu}m$ are examined first in order to distinguish different AE signals from various possible damage modes in piezoelectric composite actuators. Post-failure observations and stress analyses in the respective layers of the specimens are conducted to identify particular features in the acoustic emission signal that correspond to specific types of damage modes. As a result, the signal classification based on waveform and peak frequency analyses successfully describes the failure process of the bending piezoelectric composite actuator exhibiting diverse failure mechanisms. Furthermore, it is elucidated that when the PZT ceramic embedded actuators are loaded mechanical bending loads, the failure process of actuator specimens with different lay-up configurations is almost same irrespective of their lay-up configurations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.492-497
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• 2011

Helicopter uses a rotor system to generate lift, thrust and forces, and its aerodynamic environment is generally complex. Unsteady aerodynamic environment arises such as blade vortex interaction. This unsteady aerodynamic environment induces vibratory aerodynamic loads and high aeroacoustic noise. Those are at N times the rotor blade revolutions (N/rev). But conventional rotor control system composed of pitch links and swash plate is not capable of adjusting such vibratory loads because its control is restricted to 1/rev. Many active control methodologies have been examined to alleviate the problem. The blade using active control device manipulates the blade pitch angle at arbitrary frequencies. In this paper, Active Trailing-edge Flap blade, which is one of the active control methods, is designed to modify the unsteady aerodynamic loads. Active Trailing-edge Flap blade uses a trailing edge flap manipulated by an actuator to change camber of the airfoil. Piezoelectric actuators are installed inside the blade to manipulate the trailing edge flap.

• The Journal of the Acoustical Society of Korea
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• v.33 no.2
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• pp.111-117
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• 2014

In this paper, the structure-borne noise reduction on electrical equipment is discussed by the experimental analysis. The water cooling system in electrical equipment is the only noise source, so the mock-up was made to measure noise characteristics. Effects of power supply, stiffness, isolation of noise source and natural frequency determined by resilient mounts are investigated using the mock-up. The console prototype was made referring to noise reduction technique by the mock-up. The structure-borne noise level of a console prototype was measured and some experiments to reduce the noise was undertaken. The $1^{st}$ and $4^{th}$ harmonics of operating frequency of cooling fans causes highest structure-borne noise levels. The control of operating speeds of several DC cooling fan groups was tried. Also types and installation layouts of resilient mounts were investigated. To reduce structure-borne noise, followings can be applied: increase of stiffness, isolation of source, decrease of natural frequency of mount, combination of operating speed of fans, selection of mounts, and so on.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.9
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• pp.869-874
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• 2010

Recently, a piezo actuator based linear motor has been actively studied because of its higher power density, compactness and quick response. However, the characteristic of small displacement makes the application of a piezo actuator limitative. In order to overcome this limitation, some actuation mechanisms using a piezo actuator are designed by bi-metal composite or more than two piezo actuators. Therefore, it enables to generate large displacement and have high resolution. In the proposed piezo motor, we have designed a bi-directional linear motor that can be operated by only one piezo actuator. In addition, it is activated with low frequency of the applied voltage, since, we utilize first mode shape of structure of motion generator to vibrate. Finally, moving direction can be simply controlled by changing the ratio of input frequency to natural frequency of structure of motion generator.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.169-174
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• 2011

For a double-walled carbon nanotube resonator with a short outer nanotube, the free edge of the short outer wall plays an important role in the vibration of the long inner nanotube. For a double-walled carbon nanotube resonator with a short inner nanotube, the short inner nanotube can be considered as a flexible core, thus, the fundamental frequency is influenced by its length. In this paper, we analysis frequency variation in ultrahigh frequency nanomechanical resonators based on double-walled carbon nanotubes with different wall length. This results will widely apply to the realization of frequency devices controlling the length of the inner or outer nanotube.

• Journal of the Korean Vacuum Society
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• v.20 no.1
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• pp.1-6
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• 2011

A sudden step change is observed in the vertical position readings from beam position monitors (BPMs) mounted at the several sector vacuum chambers of Pohang Light Source. To study the source of this sudden step change, we measured the RF transmission scattering matrix (S21) through the pickup electrodes of BPMs mounted at the both ends of the sector vacuum chamber. The measured $S_{21}$ graph of the sector vacuum chambers suffering sudden step change has a peak in the BPM operation frequency bandwidth. Otherwise that of the other sector vacuum chambers doesn't have a peak. It is shown by the numerical simulation that the peak found in the BPM operation frequency bandwidth corresponds to the longitudinal harmonic of transverse electric resonance mode.

• Journal of the Korean Magnetics Society
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• v.23 no.5
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• pp.173-177
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• 2013

This work describes the experimental investigations on sloshing characteristics of water and ferrofluid as working fluids in the spherical container with the horizontal oscillation motion and compared the results obtained by two working fluids. In order to Investigate the sloshing characteristics of the sphere container with the horizontal oscillation, experiments are performed with the magnetic intensities from 0 mT to 50 mT and horizontal oscillation motions from 5 mm to 15 mm. As results, Ferrofluid without magnetic field in the sphere container showed a similar liquid surface movement with water. The resonance point of the ferrofluid in the sphere container happened at higher value than that of the theoretical resonance frequency with the rise of the magnetic field. In addition, the sloshing characteristics of the ferrofluid in the sphere container can be controlled with the resonance frequency with the magnetic intensity and the liquid surface displacement could be also controlled.