A full three-dimensional vortex-induced vibration prediction model for top-tensioned risers based on vector form intrinsic finite element method

A novel three-dimensional model is proposed to study vortex-induced vibration (VIV) problems of top-tensioned risers. The model is based on the vector form intrinsic finite element (VFIFE) method and applicable to the fullycoupled cross-flow and in-line riser VIV scenarios. The axial time-varying dynamics and movement at the top end boundary of risers are also considered in the model. By using the VFIFE method, the structure is reduced to a set of particles whose motion satisfies Newton's second law and its response is described by the position change of particles in space. The fluctuating fluid force acting on the structure induced by vortex shedding is simulated using the classical van der Pol wake oscillator equation. In order to intuitively describe the time-varying top tension of the real structure, the real-time changes in top tension caused by the array of tensioners simulated by spring is also considered. The results of numerical simulation on top tension, dominant mode numbers, frequencies, and amplitudes are compared with the experiment to prove that the VFIFE method is feasible and effective in predicting the three-dimensional vortex-induced vibration response.