Self-Controlled Vibration of Cylinder in Fluid Stream

A modification of the conventional (forced vibration) approach is suggested to predict the movement of an elastically supported cylinder as a consequence of the von Kármán shedding. Fluidelastic interaction between flow-produced forces and structure deformation is considered; this interaction is essentially ascribed to the variation of the wade width, but, unlike the theory suggested by some authors, the wake is not always widened by an amount equal to the over-all displacement. A comparison with experimental results is provided. It has also been pointed out that, if the damping ratio is less than a critical value, oscillation amplitudes may arise which increase without bound as the velocity increases; in these conditions the vibrational frequency is always very close to the natural frequency of the elastic system.