Experiments on Dynamic Non-Newtonian Fluid Interaction With Shells

In this work the nonlinear vibrations of a fluid-filled circular cylindrical shell under base excitation is investigated. A polymeric (P.E.T.) thin shell with an aluminum top mass is harmonically excited from the base through an electrodynamic shaker in the neighbourhood of the natural frequency of the first axisymmetric mode. Experiments are carried out both in presence and absence of a contained fluid, which is non-Newtonian (dilatant); the dilatant fluid is composed of a cornstarch-water mixture with 60% cornstarch and 40% water of total weight, it is commonly known as oobleck. The results show a strong non-linear response due to the coupling between the fluid and structure and the shaker-structure interaction that leads to a very interesting dynamic scenario. The system has been excited in the axial direction (vertical) through a harmonic load, with a stepped-sine sweep controlled output. Tests have been performed on empty shell, fully or partially filled shell with oobleck quiescent fluid. The dynamic scenario is carefully analyzed by means of time histories, spectra, phase portraits and Poincaré maps. The experiments show the onset of complex dynamics: subharmonic and quasiperiodic responses, Chaos.