The influence of the yaw angle on the VIV fatigue damage of a yawed cylinder with or without helical strakes

摘要

The structural fatigue damage caused by vortex-induced vibration (VIV) is one of the most important failure reasons for flexible cylinders in offshore engineering applications. Helical strakes are often employed to reduce the VIV of slender marine structures. Based on a previous experimental investigation, this paper further in-vestigates the effects of the yaw angle on the VIV fatigue damage of a yawed flexible cylinder with or without helical strakes in a uniform flow. Four yaw angles (alpha= 0 degrees, 15 degrees, 30 degrees and 45 degrees) are considered. The rain-flow counting (RFC) procedure and the Miner-Palmgren hypothesis are adopted to calculate the fatigue damage of the flexible cylinder. The influence of the yaw angle on the strain response, fatigue damage distribution and max-imum fatigue damage of the flexible cylinder are investigated and discussed. The fatigue damage levels in the cross-flow (CF) and in-line (IL) directions of the flexible cylinder are obviously reduced by helical strakes. The VIV fatigue damage of the smooth cylinder is nearly independent of the yaw angle, while that of the straked cylinder is extremely sensitive to the yaw angle. As the yaw angle increases from 0 degrees to 45 degrees, the fatigue damage of the straked cylinder caused by VIV increases several orders of magnitude.