as a variation of drag coefficient with Keulegan Carpenter number for different β values. The KC range tested was from about 0.003 to 3 and the maximum β was about 60,000. Two methods have been used to correct the results for the effect of tare drag. It is found that end conditions are important at low KC and large diameter end plates were required to give approximately two dimensional flow. Some preliminary results have been presented for a model of a TLP hull.
At low KC all results indicate that the product of CD and KC tends to a constant, as predicted by laminar flow theory. However, the level of CD is higher than that predicted by the theory at all KC values. By considering the drag to be composed of a boundary layer and a vortex component, relationships are proposed for the variation of CD with KC and β. These are shown to give a reasonable fit to the experimental data for the complete KC range examined. It remains for these relationships to be applied to predict the damping of the complete TLP hull. The TLP results show the same inverse relationship between CD and KC at low KC and CD appears to be dominated by the drag of the square section pontoon at higher KC values. The damping levels measured for the TLP at 0 ° and 45° incidence are similar.
This research is sponsored by the Marine Technology Directorate Ltd and is funded by EPSRC and the Offshore Industry. It forms part of a managed programme of research entitled Uncertainties in Loads of Offshore Structures.
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