Flow-induced transverse motions of a flexible cable aligned with the flow direction

Experimental studies of the transverse motions induced in a long flexible cable by axial flows have been conducted in a large blowdown water channel. A cable with a diameter of 1.59 cm and a length of 9 m was employed. Experiments were conducted over a fluid velocity range of 4.6-9.1 m/s. Both free and fixed downstream terminations of the cable were utilized, the former simulating a towed cable and the latter a mooring cable. Measurements of the drag coefficient of the cable with the free end were also made. These results were compared with those obtained previously for a flexible cylinder with a smooth exterior surface, and the following conclusions were drawn. 1) The amplitudes of the flow-induced transverse motions in a flexible cable or cylinder with a free downstream end in general decrease with increasing distance from this end, but they exhibit weak dependence on flow velocity and surface roughness near this end. 2) The amplitudes of the flow-induced motions are in general smaller when the cable is fixed at both ends than when the downstream end is free. 3) The drag coefficient of the flexible cylinder or cable increases with increasing surface roughness.