This report concerns the oscillation of an elastically supported circular cylinder in a uniform crossflow. Several investigators have observed an unexpected subharmonic-like resonance at fv/fn = 3 in addition to the normal one at fv/fn = 1, where fv is the Ka´rma´n vortex shedding frequency and fn is the natural frequency for the cylinder oscillation. Durgin, et al., proposed an explanation of the mechanism for the abnormal resonance at a higher velocity, which he called the Lower Mode Response. In this work comprehensive experiments on the higher velocity resonance were carried out and two alternative mechanisms are proposed for the phenomenon. It is concluded that, as long as the amplitude of the cylinder oscillation is not too large, the description of Durgin, et al., cannot be applied, and that the end effect at the side wall of the measuring channel or the rotation mode oscillation can be attributed to the local maximum amplitude at a higher velocity.

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