Flow-Induced Vibration Fatigue Damage of A Pair of Flexible Cylinders in A Staggered Array

Flow-induced vibration (FIV) of a group of long, flexible cylinders involves a complex interaction between fluid and structures. Although a substantial number of studies have been devoted to assessing FIV response behaviours, fatigue damage features of staggered flexible cylinders are not fully understood. Moreover, the wake-induced flutter constitutes an intricate hydrodynamic behaviour that frequently occurs when one cylinder is in the vicinity of another one. Unfortunately, existing studies on the fatigue damage caused by wake-induced flutter are incapable of achieving better results. This paper, therefore, estimates the FIV fatigue damage of two staggered flexible cylinders with an aspect ratio of 350 and a mass ratio of 1.90 based on normal S—N curves according to Det Norske Veritas (DNV) regulations. Twelve staggered cases (cross-flow spacing ratios of 2.0, 3.0, 4.0, and 6.0 and in-line spacing ratios of 4.0, 6.0, and 8.0) are discussed for comparison, and fatigue damage caused by wake-induced flutter is thoroughly considered. Fatigue damage results indicate that the variation of the cross-flow (CF) spacing ratio has a greater influence than that of the in-line (IL) spacing ratio on the CF fatigue damage of the upstream cylinder. Lower IL fatigue damages of the upstream cylinder are observed when reduced velocity V r ⩾ 15.03 due to the wake flow patterns with different IL spacing ratios. Moreover, wake interference, especially wake-induced flutter, predominates the fatigue damage characteristics of the downstream cylinder. When V r =8.77−11.27, wake-induced flutter enhances the IL fatigue damage of the downstream cylinder and slightly affects that of the upstream body. Furthermore, wake-induced flutter causes considerable IL fatigue damage disparity between the two staggered cylinders by suppressing the IL fatigue damage of the upstream cylinder when V r ⩾20.04.