Theoretical model for the vibro-impact motions of tube bundles under fluidelastic instability

Under fluidelastic forces, tube bundles may become unstable for lower than predicted flow velocities, due to tube-support clearances. Experiments and computer simulations previously reported by the authors and others show that several nonlinear steady tube motion regimes may arise, depending on the system parameters and on the initial conditions of the motion. In the present paper, a theoretical analysis is developed, in order to enlighten some essential aspects of the system nonlinear dynamics. According to this simplified model, of reduced dimension and high impact stiffness, the system may develop a number of possible nonlinear periodic motions, which are essentially controlled by the modal parameters of the first and second unconstrained modes.