• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.378-380
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• 2002

There has been lower the tilt margin by the increase of coma aberration due to the reduction of wave-length and the increase of numerical aperture for high density recording. The RF signal degradation is increased as the decrease of tilt margin. To compensate the tilt margin, the optical pick-up actuator for high-speed CD/DVD re-writable system should be able to drive the radial-tilt motion. We announce that the 3-axis drive actuator for high-speed CD/DVD rewritable system. And what was more, the DC/AC sensitivities of this actuator are suitable fur the low-speed playability, the high-speed readability and the high-speed rewritability.

• 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.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.5 s.110
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• pp.470-478
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• 2006

An efficient method for change of eigenvectors and eigenvalues due to the modifying proportional damping structure using sensitivity coefficients is presented. Sensitivity coefficients are determined by iteration with eigenvalue and eigenvectors before modification of system. The proposed method is applied to examples of 3 degrees of freedom system and plate by modifying mass and stiffness. The predicted change of eigenvectors and eigenvalues are in a good agreement with these from the structural re-analysis after modification of mass and stiffness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.583-586
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• 2012

Wind turbine industry is booming and spending a lot on research for improving the performance of its present machines and increasing their capacity. Wind turbine requires service life of about 20 years and each canponents of wind turbine requires high durability, because installation and maintenance costs are more expensive than generated electricity by wind-turbine. So the design of wind turbine must be verified in various condition before production step. For this work, high reliability model for analysis is required. Drivetrain model is modeled by multibody dynamic modeling method. The model constituted with rotor blades, hub, main shaft, gear box, high speed shaft and generator. Natural frequency and torsional stiffness of drivetrain are calculated and analyzed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.406-410
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• 2005

The wind turbine, Europe and the United States are different with the standards process each other when the manufacturing company which in order to demand the standards process to a construction in the multi country with interested parties of the corresponding nation to, always the re-agreement is difficult. Korean wind turbine also detail there is not a standard, when it produces and establishes of wind turbine, the problem point occurs. It is like that investigation of international standards system it leads and when it prepares the Acoustic noise measurement of the Wind Turbine Systems of Korea, it prepares the base for industrial development wind turbine of Korea.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.924-927
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• 2004

Measurements of fluctuating wall pressures were made with a linear array of 16 piezo-electric transducers beneath a fully-developed turbulent boundary layer. The piezoelectric bimorph actuator applied in this experiment has bonding structures of each polarity to make out-of-plane displacements rather than in-plane ones by using piezoelectric effect To specify the boundary layer characteristics at the location where the actuation was applied, the wall friction coefficients and $Re_\theta$ were measured by using the CPM method. The actuating frequency for the bimorph film was determined according to the priori bursting frequency from boundary layer parameters. The reduction of convecting energies in wave-number space was clearly observed at the specified actuating frequencies.

• International Journal of High-Rise Buildings
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• v.10 no.2
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• pp.117-121
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• 2021

In 2016, an innovative liquid damper system was installed on the roof of a 35-story modular building in Brooklyn, NY to mitigate wind-induced movement of the structure. The new damper presented several advantages over traditional pendulum, liquid column or sloshing dampers, including lower fabrication and maintenance costs, modularity, and the flexibility to be tuned to a wider range of frequencies. The performance of the system was monitored on a regular basis over the past four years and found adequate, with only minor re-tuning and maintenance operations needed. Based on the experience and data gained through this project, a second iteration of the damper was developed. Called Hummingbird, the improved system further mitigates maintenance and tuning concerns, while allowing significant space savings.

• Journal of KSNVE
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• v.9 no.6
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• pp.1152-1156
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• 1999

In this study, a fiber optic air-backed mandrel hydrophone has been constructed and performance of acoustic signal detection has been measured. The hydrophone is based on a Mach-Zehnder interferometer with 35 m of sensing fiber. The sensitivity is measured up to -128 dB re rad/$\mu$ Pa in range from 1.4 kHz to5 kHz. A system with this design of hydrophone may be applied to detect low frequency underwater acoustic signals.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.28 no.4
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• pp.492-502
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• 1995

This paper describes the relationship between the behavior of the snakehead ( Channa arps) of 44cm long and the environmental noise levels due to the piling work. The experiment is conducted in the aquafarm located near Asan lake, Pyongtaek in 1993. The fish trajectory is obtained by a biotelemetry system in which a pulsed ultrasonic pinger attached onto the dorsal is tracked three dimensionally, and the noise and the vibration levels both in air and in water are measured. The results of this study are as follows: 1) The noise levels in water and in air and the vibration level measured at a distance of 90m from the noise source, increased by 36.5dB $(re\;l{\mu}Pa)$, 2308$(re\;0.0002{\mu}bar)$ and $5.9{\mu}m$ repectively compared to the levers before piling. 2) The highest variation of the swimming speed was observed right after the piling works and the width of variation decreased with the elapsed time. The average speeds of the fish before and during the works were measured as 0.8 times and 1.1 times of the body length, respectively. 3) It is found that the fish escapes into the mud of the aquafarm when a heavy shock wave occurred. Consequently, the heavy shock by the piling works could produce a considerably unfavorable effect to the fish.

• Wind and Structures
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• v.12 no.1
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• pp.63-76
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• 2009

The vortex-induced vibration of an ${\sqcap}$-shaped bridge deck sectional model is studied in this paper via the wind tunnel experiment. The vibratory behavior of the model shows that there is a transition of the predominant vibration mode from the vertical to the rotational degree of freedom as the wind speed increases gradually or vice versa as the wind speed decreases gradually. The vertical vibration is, however, much weaker in the latter case than in the former. This is a phenomenon which is difficult to model by existing parametric models for vortex-induced vibrations. In order to characterize the aeroelastic property of the ${\sqcap}$-shaped sectional model, a time domain force identification scheme is proposed to identify the time history of the aeroelastic forces. After the application of the proposed method, the resultant fluid forces are re-sampled in dimensionless time domain so that reduced frequency response function (RFRF) can be obtained to explore the properties of the vortex-induced wind forces in reduced frequency domain. The RFRF model is proven effective to characterize the correlation between the wind forces and bridge deck motions, thus can explain the aeroelastic behavior of the ${\sqcap}$-shaped sectional model.