• Transactions of the Society of Information Storage Systems
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• v.2 no.3
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• pp.201-207
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• 2006

Information storage devices have been studied to increase the storage capacity and the data transfer rate as well as to decrease the access time and their physical sizes. Optical information storage devices have been achieved high-capacity by reducing optical spot size remarkably due to the development of Blue-ray technology. Optical information storage devices usually use 1.2mm-thick polycarbonate(PC) media to get high enough stiffness. However, it would be better if we can decrease the thickness of a disk for achieving thinner device while keeping the capacity as large as possible. Decreasing the thickness of the storage media makes it difficult to read and write data because it increases the transverse vibration of the rotating disk due to the interaction with surrounding air and the vibration characteristics of thin flexible disk itself, Therefore, a special design based on the fluid mechanics is required to suppress the transverse vibration of the disk in non-contact manner so that the optical pickup can read/write data successfully. In this study, a curved wall is proposed as a stabilizer to suppress the transverse vibration of a $95{\mu}m$-thick PC disk. The characteristics of disk vibration due to a curved wall have been studied through numerical and experimental analysis from the fluid mechanics point of view. The proposed shapes are possible candidates as stabilizers to suppress the transverse vibration of a flexible disk which rotates at high speed.

• Journal of the Korean Geotechnical Society
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• v.37 no.11
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• pp.51-60
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• 2021

River scour erodes the soil around the pier, reducing the lateral bearing capacity of the pier and lowering the stability of the structure. In this study, in order to examine the effect of scouring on the stability of the structure, an experiment was performed to measure the natural frequency of the pier according to the excavation of the surrounding ground. Impact vibration test was conducted on the pier with the caisson foundation of the Mangyeonggang Bridge, which is scheduled to be demolished. Accelerometers were attached to the top, center, and bottom of the pier and the acceleration responses were measured by hitting those three points. The experimental results showed that the top hit showed consistent and reasonable results of the acceleration responses according to the hitting position. The measured accelerations were converted to the frequency domain through Fast Fourier Transform (FFT), and then the natural frequency was determined. In addition, to analyze the scour effect on the natural frequency of the pier, the ground around the pier was excavated and the natural frequency change was analyzed. As a result, the natural frequency showed the decreasing tendency according to the excavation depth, but the decrease was small due to the large stiffness of the caisson foundation.