Force Element Analysis of Vortex-Induced Vibration Mechanism of Three Side-by-Side Cylinders at Low Reynolds Number

This study employs a force element analysis to investigate vortex-induced vibrations (VIV) of three side-by-side circular cylinders at Reynolds number <i>Re</i> = 100, mass ratio <i>m</i>* = 10, spacing ratios <i>S</i>/<i>D</i> = 3–6, and reduced velocities <i>Ur</i> = 2–14. The lift and drag forces are decomposed into three physical components: volume vorticity force, surface vorticity force, and surface acceleration force. The present work systematically examines varying <i>S</i>/<i>D</i> and <i>Ur</i> effects on vibration amplitudes, frequencies, phase relationships, and transitions between distinct vortex-shedding patterns. By quantitative force decomposition, underlying physical mechanisms governing VIV in the triple-cylinder system are elucidated, including vortex dynamics, inter-cylinder interference, and flow structures. Results indicate that when <i>S</i>/<i>D</i> < 4, cylinders exhibit “multi-frequency” vibration responses. When <i>S</i>/<i>D</i> > 4, the “lock-in” region broadens, and the wake structure approaches the patterns of an isolated single cylinder; in addition, the trajectories of cylinders become more regularized. The forces acting on the central cylinder present characteristics of stochastic synchronization, significantly different from those observed in two-cylinder systems. The results can advance the understanding of complex interactions between hydrodynamic and structural dynamic forces under different geometric parameters that govern VIV response characteristics of marine structures.