Decoupling on the vortex-induced vibration of an underwater cylindrical shell using a fluid force identification and partitioning method

Vortex-induced vibration (VIV) is linked to the exerted fluid force, which is dependent upon the fluid features. However, a few theoretical methods have been proposed to elucidate this physical relationship. Thus, an identification model for the potential force and the vortex-induced force of an underwater cylindrical shell was developed during this study by obtaining insight into the relationships between the vortex pattern, the fluid force, and the VIV response. This model was further used to perform a unidirectional decoupling investigation into the VIV response of the structure for the Reynolds number (Re) range of 8 × 102 < Re < 1.2 × 104. The proposed approaches are verified by comparison with the previous experimental and numerical results. Moreover, the results show that the vortex pattern and its distribution significantly affect the fluid force and its phase, especially for the vortex-induced force. The force that induced by the vortex layer is the primary contributor to the VIV problem of a cylindrical shell. Finally, the proposed methods can be used to predict the fluid force and VIV response for various mass ratios and high Re. In this study, the resonance was more dramatic since the cylindrical shell with a lower mass ratio was sensitive to the vortex feature; however, the fluid force did not obviously vary with the mass ratio. Compared with the amplitude response and the fluid force of low Re, they were higher at high Re; the jumps in the fluid force in the lower branch and the synchronization region were vanished, a jump only occurred in the newly added upper branch.