Phase space structure of spinning disks

Using a Hamiltonian formalism and a sequence of canonical transformations, we show that the ordinary differential equations associated with the forced oscillations of rotating circular disks admit the first integral of motion. This reduces the phase space dimension of the governing equations from five to three. The phase space flows of the reduced system are then visualized using Poincaré maps. Our results show that single mode oscillations of rotating disks are subject to chaotic behavior through the emergence of higher-order resonant islands that surround fundamental periodic cycles. We extend our new formalism to imperfect disks and construct adiabatic invariants near to and far from resonances. For low-speed imperfect disks, we find a new kind of bifurcations of the phase space flows as the system parameters vary. We study the effect of structural damping using Hamilton's principle for non-conservative systems and reveal the existence of asymptotically stable limit cycles for the damped system near the 1:1 resonance. We show that a low-speed disk is eventually flattened due to damping effect.