Numerical Investigation on Flow-Induced Vibration Characteristics of Pipe-in-Pipe Auxiliary Pipe System

A pipe-in-pipe structure with a buoyancy damping layer is designed to reduce pipeline weight and suppress vortex-induced vibration. This structure avoids structural pre-stress problems caused by external buoys and mitigates severe local vibration. The four-degree-of-freedom motion equation of the novel pipe-in-pipe system is established, and a corresponding numerical program is compiled. Bidirectional fluid–structure interaction (FSI) simulations are performed to verify the vibration reduction performance of the proposed structure. The auxiliary outer pipe alters surrounding flow field characteristics, generates distinct hydrodynamic forces and modifies structural vibration behaviors. Massive simulation data demonstrate that the buoyancy damping layer of the pipe-in-pipe structure can adapt to hydrodynamic forces with various characteristics and achieves favorable broadband vibration suppression and energy absorption. For all layout parameters, the inner damping layer exhibits an outstanding suppression effect on cross-flow vibration of the cylinder-auxiliary pipe system. The inline vibration amplitude of the pipe-in-pipe-auxiliary pipe system is consistently less than 0.08D and can be neglected. Its vibration frequency is close to that of the cross-flow direction and only half that of the single-layer pipe. The inner damping layer also affects the fluid–structure interaction between the pipeline system and external flow field, resulting in variations of the vorticity field.