Abstract: An alternative time domain numerical simulation approach is proposed to predict top-tensioned risers’ dynamic response under combined action of top-end platform heave motion and vortex-induced vibration (VIV). The VIV simulation is based on force-decomposed model, and hydrodynamic force coefficient database originates from forced vibration experimental data. The time-varying axial tension is adopted, and the platform heave motion effect on structural response is taken into account, and structural stiffness matrix is updated at each time step according to the variation of axial tension. A newly published 2.552m riser model test is utilized to validate the proposed numerical approach under constant and time-varying top-end tension situations, and the predicted results based on the numerical model show a good agreement with test observations. For the sub-harmonics response, asymmetrical vibration shape and Mathieu-type resonance phenomena captured in the comparisons between numerical and experimental results, further researches are carried out and the corresponding essential explanations are given as well.

Key words: platform heave motion, time-varying axial tension, top-tensioned risers, vortex-induced vibration, numerical simulation