Mixed-Modal Self-Excited Oscillation of Fluid-Conveying Cantilevered Pipe with End Mass

An experimental and theoretical investigation was conducted into the spatial motion of the self-excited oscillation of a pipe which is built-in at upper end and has an attached mass at the other. A certain characteristic mode of the pipe vibration is self-excited when the axial flow velocity in the pipe exceeds a certain value. For higher flow velocity, the two distinct eigen modes of the pipe can be simultaneously self-excited with two different natural frequencies, which called mixed-mode flutter. Equations governing amplitudes and the phases were derived and used to clarify nonlinear modal interactions numerically the above specific cases. It is theoretically clarified that the planes, on which second modal oscillation and the third modal oscillation are produced, are perpendicular. Furthermore experiments were conducted with the silicon rubber pipe conveying fluid. As a result, typical features of the mixed-mode flutter were confirmed qualitatively by experiments.