Added mass and oscillation frequency for a circular cylinder subjected to vortex-induced vibrations and external disturbance

This paper reports results from an experiment with a lightly damped elastic ally mounted rigid cylinder subjected to constant flow velocity. The cylind er was allowed to vibrate in the cross-flow direction and was fixed in the flow direction. The Reynolds numbers varied from 10(4) to 6 x 10(4). The ad ded mass for the freely vibrating cylinder agreed well with the results fou nd by others in driven cylinder tests. The predicted natural frequency base d on the measured added mass was approximately equal to the measured mean o scillation frequency. The added mass calculated from one oscillation cycle to the next varied considerably. The oscillation frequency from one oscilla tion to the next corresponded to the natural frequency including the added mass for the same cycle. By movement of the attachment point of the elastic members to the external structure a disturbance could be added to the norm al vortex-induced vibrations (VIV) response. When an external disturbance w as introduced at a frequency other than the VIV frequency, the added mass c oefficient was found to be weakly influenced by the external harmonic distu rbance. (C) 2000 Academic Press.