A numerical procedure to calculate the VIV response of a catenary riser

In this paper, a numerical procedure to estimate Vortex-Induced Vibration forces for a catenary riser is presented. The VIV numerical procedure for the curved risers is solved in the time domain by applying the independence principle, which considers only the component of the current flow velocity normal to the riser axis. A semi-empirical approach is adopted to calculate the VIV force, which is a function of the lift coefficient (CL) and the phase between the VIV force and the riser movement (φ) determined based on the experimental data. The VIV force frequency is calculated by assessing the change of the riser natural frequency due to the added mass variation with the reduced velocity. Because of the complexity involved in this problem, the procedure is first applied for simpler problems, such as VIV in horizontal and vertical flexible pipes, with the aim of understanding the limitations of the procedure for this type of problem and supporting the analysis of the curved pipes results. Comparisons with experimental results are performed and present good agreement.