Analysis of the dynamics of vertical and flexible cylinders subjected to vortex-induced vibrations using the nonlinear normal modes approach

Abstract

Risers are slender cylindrical structures that convey oil and gas from the seabed to the floating unit and their dynamic behavior is the main technological motivation of this research plan.A particular phenomenon of interest in risers's dynamics is named vortex-induced vibration (VIV), a class of flow-induced vibrations problem characterized by oscillation amplitudes close to one structural diameter. Mathematically, the phenomenon can be described in a phenomenological approach(or, equivalently, using a wakeoscillator model), coupling structural oscillators to nonlinear equations that describe the fluid dynamics.This research project focuses on the analytical-numerical investigation of a vertical and flexible cylinder subjected to VIV. The methodology involves two major steps. In the first one, the Galerkin's method will be applied to the nonlinear equations of motion that describe the dynamics of the hydroelastic system composed by the cylinder and the fluid, giving rise to reduced-order models (ROMs). Contrary to the continuum equations, the ROMs consist on a system of ordinary equations. With the ROMs, the nonlinear normal modes (NNMs) will be obtained by using the invariant manifold approach. Numerical and analytical studies of the NNMs will be carried out. The research will be held in Ancona unit of Universita Politecnica delle Marche, Italy, with the collaboration of Professor Stefano Lenci, a recognized expert researcher in nonlinear dynamics. (AU)