Seacon II Strumming Predictions.

摘要

Seacon II is an ocean-based experimental mooring being used to validate or refute various array motion models. The array essentially consists of three riser cables and a subsurface horizontal delta. The cables comprising the delta are exposed to uniform currents over their lengths and hence are subject to strumming vibrations. As is known, strumming leads to a virtual increase of the drag coefficient of a cable over that value measured for a stationary cable. Since this coefficient is a basic parameter in all array motion models, an accurate knowledge of its value is required to validate or refute the models. In this paper, the strumming behavior of the cables comprising the Seacon II delta is examined. Employing recently-developed strumming modeling techniques, the amplitudes and frequencies of strumming are predicted. These amplitudes and frequencies are, in turn, used to predict the virtual increases of the drag coefficients of the delta cables. It is found that the values of these virtual drag coefficients are frequently 150% to 230% larger than the value of the nominal stationary drag coefficient. (Author)