Estimation of Dynamic Characteristics of Gageocho Ocean Research Station Using Long-term Measurement Data

Abstract

In order to study ocean and meteorological changes related to the global climate change and global warming, Korea is operating several ocean research stations (ORS) including Ieodo ORS, Gageocho ORS and Sochengcho ORS in remote ocean area. In 2011, the Gageocho ORS was attacked by Typhoon Muifa and was damaged to its structural members and various observation equipments. After that, the Gageocho ORS was reconstructed with increased height by 5m and then dynamic response measurement system has been built to assess the structural integrity of Gageocho ORS whether it is healthy or not. Using the measured dynamic response data including acceleration and tilt, the structural dynamic characteristics of the Gageocho ORS were investigated. As a result, three natural frequencies of the first two bending modes and the first torsional mode were estimated as 1.79 Hz, 1.82 Hz and 2.65 Hz, respectively, and the difference between natural frequencies for two bending modes is not significant because is almost symmetrical shape. It is also found that, when the acceleration response is larger, the damping ratios in first mode can be obtained more consistently with lower irregular fluctuations. The averaged damping ratio was about 0.7%. The present results and those obtained from long term monitoring can be used to identify and to assess the structural integrity of the Gageocho ORS, and can be useful in preliminary design of offshore structures.