Added mass variation effect on vortex-induced vibration for flexible risers based on force-decomposition model

Vortex-induced vibration (VIV) due to periodic vortex shedding around the cylindrical structures is a typical and complicated fluid-structure interaction issue. In this paper, an improved time domain numerical simulation model, which can take the variation effect of added mass into account, is proposed to predict VIV for flexible risers. Originated from forced vibration experimental data, a time-varying function of both response frequency and amplitude is used to describe hydrodynamic forces, and added mass coefficient is considered variable with response frequency. Modal analysis serving VIV hydrodynamic forces calculation is implemented at the beginning of each time step, and dominant frequency of every element will be updated based on real-time structural natural frequency. By validating with model tests of two flexible risers, the proposed model is proved to show better performance for VIV prediction than traditional method (assuming C-a = 1). The added mass variation effect on VIV is discussed qualitatively and quantitatively.