Experimental and numerical study of a top tensioned drilling riser subjected to vessel motion

Abstract

Model tests of a top tensioned riser (TTR) model were carried out as a part of a joint industry project, with the purpose of better understanding the dynamic behaviour of drilling riser and verifying the calculations of the riser analysis tools. Sinusoidal motion in one direction was imposed at the top end of the riser model to simulate vessel motion. The tests were carried out in still water, accelerations and bending strains were measured along the riser model. Numerical simulations were performed using RIFLEX and the predicted global responses were compared with the model tests. This paper discusses interesting aspects of this comparison as well as the general dynamic behaviour of the top tensioned riser.

It was found that the dynamic responses of a TTR with vessel motion can consist of not only the in-line (IL) responses due to vessel motion at the riser top end, but also cross-flow (CF) vortex-induced vibrations (VIV) under conditions when Keulegan-Carpenter (KC) number is relatively small. CF VIV response is estimated using a time domain VIV prediction model and compared to the measured response. The main conclusion is that the IL global dynamic responses and CF VIV responses are predicted sufficiently well.