Non-linear time domain analysis of cross-flow vortex-induced vibrations

A previously proposed hydrodynamic load model for time domain simulation of cross-flow vortex-induced vibrations (VIV) is modified and combined with Morison's equation. The resulting model includes added mass, drag and a cross-flow vortex shedding force which is able to synchronize with the cylinder motion within a specified range of non-dimensional frequencies. It is demonstrated that the hydrodynamic load model provides a realistic representation of the cross-flow energy transfer and added mass for different values of the non-dimensional frequency and amplitude. Furthermore, it gives a reasonable approximation of the experimentally observed drag amplification. The load model is combined with a non-linear finite element model to predict the cross-flow VIV of a steel catenary riser in two different conditions: VIV due to a stationary uniform flow and VIV caused by periodic oscillation of the riser top end. In the latter case, the prescribed motion leads to an oscillating relative flow around the riser, causing an irregular response. The simulation results are compared to experimental measurements, and it is found that the model provides highly realistic results in terms of r.m.s. values of strains and frequency content, although some discrepancies are seen.