A stochastic analysis approach for marine riser's cross-flow/in-line VIV under heave-induced parametric vibration

This study proposes a theoretical analysis model to analyse the marine riser's coupled cross-flow/in-line vortex induced vibration (VIV) under heave-induced time varying parametric vibration. Combining with the linear-wave theory, the stochastic phase spectrum method is used to simulate the stochastic multi-frequency parametric excitation in the time-domain to reproduce the real sea conditions. The nonlinearities are considered to capture the geometrical coupling of cross-flow/in-line displacements excited by hydrodynamic lift/drag forces and the wake-riser interaction. A generally good agreement between the proposed approach and other analyses can be observed. A parametric study is conducted, it is found that the drag coefficient is of significance for the riser's VIV, and the lift coefficient is affected by vortex shedding. The wave form, in terms of wave height and wave period, need to be considered with caution in design of a riser to avoid the occurrence of resonance under stochastic parametric excitation.