On the Vibration of Cylinders Caused by Karman Vortex

As bridges becomes larger in size, the members become slenderer and a severe vibration sometimes occurs in the cylinder members because of a Karman vortex caused by gentle winds. A lot of studies have already been conducted on this phenomenon, but there are still many unknown factors left about the behaviors of cylinders, qualititatively and quantitatively. In this study we carried out a few wind tunnel tests in the subcritical range and investigated the vibrating characteristics of the cylinder and the aerodynamic force working on the vibrating cylinder. The following facts were made clear. (1) The vibration of cylinders caused by Karman vortex is self-excited and the range of self-excited vibration is effected by the damping factor of the system. (2) Strouhal's number at the resonant condition reduces to 0.17 as vibrating amplitude increases. (3) Life coefficient at the resonant condition is effected by vibrating amplitude. In the case of the large amplitude, it can be arranged from the view-point of the forced vibration to some extent.