Application of Control Rods for Passively Suppressing Cross-Flow VIV of an Inclined Flexible Cylinder

Laboratory experiments were conducted to investigate the cross-flow (CF) vortex-induced vibration (VIV) suppression effectiveness of an inclined flexible cylinder by using control rods. 4 control rods with a diameter of 0.25D (where D is the diameter of the main cylinder) and outer wall distance between the control rod and the main cylinder of 0.50D were attached to the main cylinder. The uniform flow was simulated by towing the cylinder models along a water tank. The corresponding flow velocity ranged from 0.05 to 1.00 m/s with an interval of 0.05 m/s. Two inclination angle cases (a = 0° and 45°) were selected in the experiment. The inclination angle a referred to the angle between the main cylinder axis and the plane orthogonal to the oncoming flow. The experimental results indicate that the control rods can effectively mitigate the CF VIV responses, such as the bending strain, displacement amplitude, dominant frequency, and dominant mode, of both the vertical (a = 0°) and inclined (a = 45°) flexible cylinders. The suppression effectiveness of the control rods on the 45° inclined cylinder is as good as that on the vertical cylinder, and the average suppressing efficiency of the control rods is even better on the 45° inclined cylinder.