Riser Response Analysis by Modal Phase Reconstruction

A methodology is presented to identify the vortex induced vibrational modes of a riser, based on data from computational fluid dynamics coupled to a long beam under tension and placed in cross-flow; two inflow velocity profiles are tested: (a) uniform, and (b) exponential shear. The modes we estimate are in fact nonlinear equilibria between the flow-induced excitation forces and the structural dynamics and are characterized by varying amplitude and phase along the span; these are complex modes, mixtures of traveling and standing waves.