Three-dimensional VIV characteristics of the top-tensioned riser considering platform motion and pipe-soil coupling

The upper and lower boundaries of the riser are often oversimplified as clamped constraints in prior analyses of vortex-induced vibration (VIV), leading to the inaccurate predictions in the VIV responses. A three-dimensional VIV model of the top-tensioned riser is established considering the platform motion and the nonlinear pipe-soil interaction. The VIV hydrodynamic force is calculated by the Van der Pol wake oscillator, while the nonlinear soil resistance is obtained with the p-y curve method. A novel VIV analysis approach for the riser with upper and lower boundary disturbances is proposed based on Newmark-β method and fourth-order Runge-Kutta method. The availability of the methodology is corroborated by multiple cases. The effects of the platform motions and the pipe-soil coupling on the VIV characteristics of the riser are studied. The results show that high-amplitude surge and sway motions cause a deviation of the vibration attitude of the riser from the standard mode shape. The heave motion exerts minimal influence on the VIV characteristics because the majority of the axial displacement of the riser is compensated by the tensioners. The VIV amplitude at the bottom of the riser is heightened, with a slight reduction in VIV frequency attributed to the pipe-soil coupling.