Study on added mass coefficient and oscillation frequency for a Truss Spar subjected to Vortex-Induced Motions

Abstract

Vortex-Induced Motion (VIM) is an important cause of fatigue damage of a Truss Spar. Response frequency is one of the critical components in estimating VIM. Response frequency is related to the natural frequency of the structure, and it is also impacted by the effect of the added mass. In this study, Reynolds numbers of the experiment varied from 8E04 to 2E05. The experiment results indicate that the added mass coefficient decreases with the increasing reduced velocity and the oscillation frequency of the low mass ratio cylinder locks in the natural frequency instead of still water natural frequency. The estimated added mass coefficient from one oscillation cycle to the next varied considerably. The oscillation frequency from one oscillation cycle to the next is associated with the natural frequency which is estimated by the time-variable added mass coefficient.

Keywords:

• Truss Spar
• Vortex-Induced Motions
• added mass coefficient
• oscillation frequency

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (40906049).