Vortex-induced vibration super-upper response branch boundaries
The purpose of this study was to experimentally investigate the vortex-induced vibration response of cylindrical structures with low mass ratio. Much of our understanding of vortex-induced vibration has been established through single degree of freedom and/or higher mass ratio experiments. The empirical relationships based on these data capture only the characteristics of the upper vortex-induced vibration response branch. The corresponding super-upper response branch observed in 2 degree of freedom systems at low mass ratio is shown to present significantly larger amplitudes and more regular oscillations. Understanding the boundaries of this super-upper response has implications for offshore structure design. This study revealed that damping in addition to the mass ratio appears to be one of the governing parameters in establishing super-upper response branch vibrations. Based on the experimental evidence available, super-upper response boundaries are suggested, and the potential bearing of these on empirical design formulations not considering the super-upper response are discussed.
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