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. When the nonlinear damping is estimated as a function of the vibration amplitude of tubes, vibrations of a tube with the negative damping due to the fluid flow have some limited amplitude if the nonlinear damping trend is strong. It is a limit cycle oscillation. This report shows an approximate solution by using a polynomial function, and compared with time-series simulation results.
