Flow-induced vibration and stability transition in a parallel dual-pipe system with series piecewise stiffness clamps

Parallel multipipe systems are common in engineering, where coupled vibration between adjacent pipes is one of the primary instabilities. To explore the nonlinear dynamic mechanism of such vibration, this paper proposes a fluid-conveying parallel dual-pipe system constrained by series piecewise stiffness clamps, and the flow-induced vibration and stability of the system are studied. Two types of nonlinear mechanisms are introduced: geometric and constraint nonlinearities, and the fluid–structure interaction and the elastic coupling between the pipes are considered. Numerical results reveal multiple stability transitions triggered by an internal flow. Within a dimensionless parametric framework, nonlinear analyses further demonstrate that the parallel pipe system experiences limit-cycle oscillation, quasi-periodic motion, and chaotic flutter via Hopf bifurcations. Increasing the piecewise stiffness leads to earlier quasi-periodic bifurcation by disrupting single-frequency energy dissipation, while increasing the clearance suppresses the nonlinear effect and causes the system to return from quasi-periodic to periodic motion. At different flow velocities, the mass ratio induces irregular transitions among periodic, quasi-periodic, chaotic, and stable states via the added mass effect. This study integrates the flow-induced energy input mechanism with piecewise stiffness regulation, providing a mechanistic basis for the dynamic design and vibration control of multipipe systems in engineering.