• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.515-516
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• 2009

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.246-247
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• 2014

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.769-770
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• 2011

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.551-556
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• 1997

Based on the experiment for the frequency characteristics and the feedback theory of the impinging-tones, the unstable characteristics of the symmetric mode is analyzed among the various unstable modes of circular impinging jets. There are two different symmetric modes; one is the low-frequency mode S1 due to the vortex at the outside of the jet and the high-frequency mode S2 due to the inside vortex. Each mode has its own characterictics of convection speed decreasing with frequency.

• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.10-20
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• 2014

To study the water-entry impact noise, on-board experiment using a small launcher firing various objects was performed in the Yellow Sea. As the launcher fires a cylindrical object from the ship vertically, generated noise is measured with a hydrophone on the starboard of Chung-hae, Marine surveyor. Three types of cylindrical objects, which have noses of flat-faced, conical, and hemisphere, were used during the experiment. The measured noise exhibits a time-dependency which can be divided into three phases: (1) initial impact phase, (2) open cavity flow phase, (3) cavity collapse and bubble oscillation phase. In most cases, the waveform of bubble oscillation phase is dominant rather than that of initial impact phase. Pinch-off time, where a cavity begins to collapse, occurs at 0.18 ~ 0.2 second and the average lasting time of bubble was 0.9 ~ 1.3 second. The energy of water-entry impact noise is focused in the frequency region lower than 100 Hz, and the generated noise is influenced by the nose shapes, object mass, and launching velocity. As a result, energy spectral density on the bubble frequency is higher in the order of flat-faced, conical, hemisphere nose, and the increase of initial energy raises the energy spectral density on the bubble frequency in the cylinder body of same shape. Finally, we compare the measurements with the simulated signals and spectrum based on the bubble explosion physics, and obtain satisfactory agreements between them.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1276-1279
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• 2007

The main objectives of the Load/Unload are no slider-disk contact and no media damage. But, it remains unsolved technical problems on the unloading process. While the slider climbs up the ramp at the outer edge of the disk, the possibility of the slider-disk contact by lift-off force and rebound of the slider increases. Keeping in mind of these points, to prevent the slider-disk contact, we apply the disk bump on disk outer edge proceeding unload. First, referring to the simulation results, we select the optimal bump shapes to improve unload performance by unload analysis. Second, the disk bump is mechanically manufactured by pressing disk surface using tungsten tips. The bumps are variously processed by changing pressing pressure of tungsten tips. After confirming bump shape by nano-scanner, the optimal bump shape is applied to experimental unload process. Through this experiment, it is conformed that the unload performance was improved by using the optimal disk bump to prevent the slider-disk contact.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.633-640
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• 2007

In this paper, 3-D reciprocating compressor is taken into flow-structure interaction analysis. The full cycle process consisted of cylinder expansion and compression has been modeled without considering flow leakage through cylinder wall. Fully-coupled FSI analysis of this compressor model was iteratively solved and gives sufficient result with the experimental test. The study is emphasized to thoroughly investigate discharge valve motion, opening and closing, in order to determine discharge valve region which is prone to have high effective stress. The cylinder pressure is successfully validated before conducting impact analyses between discharge valve and other susceptible supported structure. Velocity profile has been obtained in FSI analysis is used as initial condition to carry out further impact analyses. Stress result of discharge valve and valve spring gives preliminary estimation of higher stress area due to its impact phenomena.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.975-977
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• 2014

Recently, As portability of storage device has been increased, it is important to analyze the precise anti-shock analysis. For non-operational shock analysis, the accuracy of non-operational shock simulation has been improved. However, because operational shock analysis includes nonlinear process, it is hard to get clear result from operational shock simulation. In this paper, by using Lagrange multiplier method, the FE model including ramp-disk contact of nonlinear process will be analyzed. Through this, we find ramp-disk contact affect the dynamic of slider. Additionally, for the more accurate analysis, we should include ramp-disk contact process at the FE model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1065-1070
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• 2006

The beam structure models with an impactor or contact parts under impact forces have teen applied to the design of mechanical and electronic accessories. Switches, hard-disk pick-ups and sensors are typical structural examples of the structure to be designed to colliding with other parts of structures. In this paper, in order to examine the relationships between the changes of the stiffness and damping of the impactor and vibrations of the dynamic characteristics of the impact model of a cantilevered beam with an impactor, impact force of the impactor and response characteristics of the cantilevered beam were analyzed by both numerical simulation and experiment. Since the stiffness and damping of the impactor have high nonlinear characteristics, the contact model using revised Herz-model was established by experiments. Also, the results of numerical analyses for dynamic response and impact force of a cantilevered beam with an impactor have a good agreement with experimental results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.3
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• pp.55-60
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• 2002

Nebulizer which is on sale in our country has many problems like noise and efficiency In order to solve these problems, we used 0.6[kg/$\textrm{cm}^2$] moter in made of the Diaphragm instead of 2.5[kg/$\textrm{cm}^2$] piston type to reduce noise art output power. Nozzle in the core of the Nebulizer was made of the wild collision cross-section and slope of the fluid in detail. It is found that we could be significantly improve remedial value by doing these efforts.