FLUID STRUCTURE INTERACTION OF NON-NEWTONIAN FLUIDS AND CIRCULAR CYLINDRICAL SHELL

Fluid-Structure Interaction (FSI) is a field of engineering science across different sectors such as Mechanics, Aeronautics, Civil and Nuclear Engineering. It is known that the interaction between vibrating structures and fluids such as air/water (Newtonians) can give rise to catastrophic phenomena of instability. The interaction with fluids involves additional effects such as: the variation of own frequencies or the reduction of the ability to withstand dynamic compressive loads. However, there is a vast class of fluids whose behaviour is substantially different from Newtonian fluids such as air and water, generically classified with non-Newtonian fluids, a classification that hides complex and sometimes opposite behaviours (Bingham fluids, dilatant fluids). Although classified as fluids, some of them show fluid-solid or solid-fluid state transitions depending on the states of stress and deformation, causing sometimes catastrophic phenomena such as soil liquefaction during earthquakes. When mechanical structures or systems are in contact with non-Newtonian fluids, the scenarios can become surprisingly complex. The field is still substantially unexplored scientifically, even if FSI problems with non-Newtonian fluids are present in many sectors: Biomedical, Food-packaging, Petroleum. The present study aims to investigate new dynamic phenomena resulting from the interaction between vibrating structures and non-Newtonian fluids, between oobleck (dilatant non-Newtonian-fluid) and circular cylindrical shell with top mass subjected to harmonic seismic forcing load. An extensive experimental investigation has been carried out with different types of seismic forcing loads: stationary sinusoidal, sine sweep and random; and with different levels of vibration, up to 100g peak, and different frequency bands. The presented work has been carried out with an experimental approach, the experimental measured time series have been analyzed with ad-hoc Matlab scripts to obtain: bifurcation and phase diagrams and Poincarè maps; the results are novel and can be used as a benchmark for further studies.