As interest in maritime applications of lightweight materials increases, understanding the flow-induced vibration characteristics becomes more important to ensure structural safety and to optimize performance and control. The objective of this paper is to investigate the flow-induced vibration characteristics of lightweight lifting bodies in water. The results show that the in-water to in-air natural frequency ratios decrease rapidly as the structure becomes lighter, and the natural frequencies become mode and speed dependent due to changes in the fluid added mass, damping, and disturbing force terms. The fluid damping and stiffness terms are also modified by viscous fluid-structure interaction effects, including changes in the center of pressure, separation, as well as generation and interaction of vortices with body motions. The results also show that the linear potential theory significantly over-predicts the fluid damping for lightweight lifting bodies in water. Hence, care is needed when designing lightweight lifting bodies in water to avoid hydroelastic instability failures, and to avoid unexpected accelerated fatigue, noise, vibration issues.

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