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 elastically mounted rigid cylinder subjected to constant flow velocity. The cylinder 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 added mass for the freely vibrating cylinder agreed well with the results found by others in driven cylinder tests. The predicted natural frequency based on the measured added mass was approximately equal to the measured mean oscillation frequency. The added mass calculated from one oscillation cycle to the next varied considerably. The oscillation frequency from one oscillation 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 normal vortex-induced vibrations (VIV) response. When an external disturbance was introduced at a frequency other than the VIV frequency, the added mass coefficient was found to be weakly influenced by the external harmonic disturbance. (C) 2000 Academic Press.