Nonlinear Dynamics of Inextensible Spinning Pipes Conveying Fluid

Fluid–conveying pipe systems appear in many engineering applications where liquids or gases are transported through long, slender pipes that can deform under mechanical and flow induced loads. Typical examples include offshore risers, drill strings, and aerospace refueling lines, and more generally any slender structure that carries moving axial momentum internally. Under operating conditions, this interaction may generate significant vibrations, reduce natural frequencies, and trigger instabilities such as divergence, where the pipe deflects to a new static buckled shape, or flutter, where sustained oscillations grow in time. In this context, the study focuses on a rotating, slender structural member with internal axial transport that can undergo lateral displacements and rotations. The internal flow is represented in the structural model through effective inertia and gyroscopic (Coriolis type) contributions. The imposed spin modifies the effective stiffness and couples axial and transverse motions, giving rise to pronounced nonlinear effects. Within this framework, an inextensible pipe system is examined, meaning that the axial strain of the pipe centreline is constrained to vanish so that the pipe length remains constant during motion. Compared with extensible counterparts, the inextensible configuration exhibits different dynamical characteristics, particularly in the way instabilities develop and saturate under combined spin and internal flow. The resulting nonlinear model is able to capture the post critical dynamic behaviour after instabilities occur, including large amplitude lateral responses beyond the onset of divergence or flutter.