The key to suppress vortex-induced vibration: Stability of the structural mode. (August 2022) - Luo, Fuqing
Abstract: The vortex-induced vibration (VIV) problem is common in nature and engineering fields. Current passive or active control methods try to suppress VIV by changing the flow field or improving the flow stability based on the recognition that VIV is caused by resonance. But is VIV really caused by resonance? Tuned mass damper (TMD) has been used in VIV or other vibration control for many years. However, is TMD simply an anti-resonance or energy dissipation device in VIV suppression? With the ARX(Autoregressive with exogenous input)-based reduced-order model (ROM) and the fluid–structure interaction numerical simulation, the physical mechanism of the VIV suppression with TMD in the lock-in region is investigated at a low Reynolds number ( R e = 60 ). According to the root loci, the introduction of TMD does not change the unstable wake mode, but effectively improves the stability of the structural mode. The results obtained by numerical simulation reveal that the violent vibration turns to a micro-amplitude response and the final response frequency is consistent with the vortex shedding frequency. Therefore, VIV is a stability problem rather than a dynamic response problem. Meanwhile, TMD suppresses VIV via structural mode stability enhancement rather than anti-resonance and energy dissipation. In addition, the study also found that when the TMD natural circular frequency is between 0.65 and 1.0, the vibration suppression effect is independent of the initial amplitude. This frequency range happens to be the region where the structural mode is tightly coupled with the wake mode. Graphical abstract: Highlights: The structural modal instability caused by fluid–structure coupling is the crucial reason for the violent VIV rather than vortex shedding induced resonance. The TMD changes the modal coupling of the original FSI system especially improves the stability of the structural mode thus the lock-in has been eliminated. Stability of the structural mode in FSI system is the key for VIV suppression.