An investigation into the fatigue damage of a long flexible cylinder with multiple control rods in crossflow

摘要

In the field of offshore engineering, the control rod is a common passive device to suppress the vortex-induced vibration (VIV) of cylindrical structures. Some key parameters of control rods (diameter ratio, spacing distance, coverage rate and attack angle) have a great influence on the VIV fatigue life of the cylinder. This paper aims to investigate the fatigue damage of the main flexible cylinder with multiple control rods caused by VIV based on rainflow counting and a standard S N curve, with the final purpose of studying the effectiveness of multiple control rods, in different configurations around the cylinder in improving the structural fatigue life. The results show that control rods can suppress the VIV response of the cylindrical structure and reduce its fatigue damage effectively. The reduction effect of the control rods is very sensitive to the spatial arrangement. The reduction effect of the 3 control rods is the best at the attack angle of 40 degrees, while that of the 4 control rods is the best at the attack angle of 30 degrees. The fatigue damage of the flexible cylinder can be reduced to a lower level with 4 control rods. In addition, "mode transition", a specific feature of VIV in uniform flow, is found in the experiment and has a strong influence on fatigue life.