On the Self-Recovery Phenomenon for a Cylindrical Rigid Body Rotating in an Incompressible Viscous Fluid

The damping-induced self-recovery phenomenon is well understood for finite-dimensional mechanical systems. In this paper, we discover a self-recovery phenomenon in a composite system that consists of a cylindrical vessel and a surrounding fluid, where the vessel is equipped with an internal rotor and the fluid is incompressible and viscous. In the system dynamics, interactions between the vessel and the ambient fluid are fully taken into account. A combination of the Lyapunov method and the final-value theorem is applied for analysis of the dynamics. It is mathematically shown that after the spin of the rotor comes to a complete stop in finite time or exponentially as time tends to infinity, the vessel, which has deviated from its initial position due to the reaction to rotor spinning, converges back to its initial position as time tends to infinity, and so does every fluid particle. An experimental test is conducted to verify the occurrence of this phenomenon. The simultaneous self-recovery of the vessel and the fluid to the initial configuration is induced by the fluid viscosity as if the viscosity has a memory of the initial configuration. We envision that our discovery may be useful in designing and operating mechatronic systems interacting with fluids such as underwater vehicles.