Flutter and its application—Flutter mode and ship navigation

摘要

Based on the aerodynamic interaction between the heaving vortex-induced vibration and the torsional flutter, another explanation of the drastic change of the vibrational mode from the 5th symmetrical heaving mode to the 1st asymmetrical torsional mode is introduced. Some fundamental characteristics of the coupled flutter of a thin plate and a plate like structure, such as the flutter modes, the flutter branches, are explained by use of the “Step-by-Step flutter analysis”. The flutter properties obtained by the 3DOF multi-modes-flutter analysis are compared with the ones by the 2DOF 2modes- flutter analysis t. 3DOF multi-modes flutter analysis is recommended to use for more accurate verification of the flutter property as the lessons from the aerodynamic behavior of the full-scale elastic model of Akashi Kaikyo Bridge. The reduction of the key equivalent aerodynamic derivatives, by suitable span-wise arrangement of the girders with different girder-shapes, is significantly effective to stabilize the flutter instability of a long spanned suspension bridge. Furthermore, the significantly similar formula with the Selberg formula can be derived under the simple assumptions. As an application of the coupled flutter, the generation mechanism of the propulsion force by use of coupled flutter motion is introduced. Finally, it is confirmed that the H-90 mode can produce the propulsion force by the test of the ship-navigation with the flapping plate controlled in the particular flutter mode is shown.