The influence of a plate’s buckling instability on the early onset of large oscillatory motions

We study the onset of large oscillatory motions of a thin elastic plate buckled into a second mode-like deformation created by an applied external net compressive force. We subject the deformed plate to an incompressible flow to induce oscillations, and document three states of motions with the aid of image-based edge detection, acoustic Doppler velocimetry, and particle image velocimetry: a) weak perturbations below a critical flow velocity (Uc), b) large oscillatory motions above Uc, and c) chaotic oscillatory motions above a transitional flow velocity (Ut). We find an early onset of flapping of the deformed plate compared to flag- or inverted-flag type configurations (i.e., lower Uc), where the main physical mechanisms contributing to the reduced Uc are the destabilizing action of the compressive force, a deformed locally-stable plate, and a non-zero pressure drag, all existent prior to structural oscillations. A mathematical model of the structure coupled with the fluid through slender body theory, provides insights on the contribution towards a reduced Uc from the combined destabilizing influence of the net compressive force, and Coriolis and centrifugal forces.