EFFECTS OF APPENDAGES AND SMALL CURRENTS ON THE HYDRODYNAMIC HEAVE DAMPING OF TLP COLUMNS

A previous paper by the authors reported on the estimation of resonant heave (springing) damping of tension leg platforms (TLPs) and a metho d of scaling for full-scale prototypes. The present paper is a sequel to this work, and examines the effect of adding an appendage in the fo rm of a disk to TLP columns, and the influence of a small uniform curr ent. Model tests conducted on a cylinder + disk in heave show that the heave damping induced by the disk is linear with the amplitude of osc illation. The disk is found to increase tile form drag coefficient two fold, in accordance with published results based on isolated edge theo ry. The effects of a small uniform current were also examined during t he model tests. Results show an increase in heave damping ratio that i s linear with the current velocity. In the presence of a disk, the dam ping induced by the current is doubled as well. Scaling laws are propo sed. in this paper that enable extrapolation of heave damping due to a ppendages and small currents to full scale. An example calculation sho ws that for a full-scale TLP column, the heave damping is increased by about 300 percent due to addition of the disk, and by 87 percent due to a small current. The combination of the disk and the current increa ses the heave damping of the column by a factor of six.