Abstract
An estimated damping ratio is used to evaluate the occurrence of the fluid-elastic instability. However, many structures contain some nonlinearity, especially in their damping ratios. Then, it is a great problem which value is used for the estimation of the critical flow velocity. As the nonlinear damping usually shows the increasing trend to the vibration amplitude of tubes, vibrations of a tube with the negative damping due to the fluid flow are calculated for some parametric cases, where the structural damping component has a linear relation to the tube-amplitude. The results show the tube plays as a kind of limit cycle in a few seconds, and the final amplitude depends on the nonlinear trend of the structural damping. It is suggested that this nonlinear damping trend is used for the design estimation of the fluid-elastic instability.
