Vortex-induced vibrations of a non-linearly supported rigid cylinder

Vortex-Induced Vibrations (VIV) are a complex fluid-structure interaction problem.VIV are particularly strong for low-mass structures subject to a low damping, asencountered in the offshore industry, in which structures experiencing VIV can alsobe subject to strong structural non-linearities.In this project, investigation of the VIV of a low-mass low-damping rigid cylindersubject to structural non-linearities is carried out first experimentally. Non-linearitiesconsidered are the symmetric or asymmetric limitation of the amplitude of thecylinder with soft or stiff stops placed at different offsets from the cylinder andimplying a non-smooth non-linearity of the system. Experimental results show that astrong perturbation of the dynamics of the cylinder occurs when amplitude limitationis strong, and flow visualisations displaying a modification of the vortex wake suggesta change in the fluid-structure interaction affecting the vortex formation process.Attention is also given to the impact velocities in the different cases of amplitudelimitation with stiff stops, as they are an important factor in the design of structures.Two different wake oscillator models are then used to simulate the VIV of the samerigid circular cylinder in the same conditions of non-linear structural restraints.Results show that these simple models exhibit some features observed experimentally,giving in some cases a good estimation of the experimental data