Effects of buoyancy modules geometry on hydro-elastic and hydrodynamic performance of a steep wave riser in steady current

Analysis of the hydrodynamic properties and response of flexible risers in various configurations is paramount to understanding their operative performance. Buoyancy modules play an integral role in providing compliance to flexible riser systems in wave configuration. This study utilised both model testing and numerical simulations to quantify the impact of discretised and smeared buoyancy module sections on the performance of a flexible riser in shallow water steep wave configuration under steady current loading. Model testing was facilitated in the Australian Maritime College’s Circulating Water Channel by a 1:15 scale 8” flexible riser constructed from silicon hose and foam. Variances in the model’s buoyancy module section and system offset were tested at different flow velocities to estimate the effect on in-line drag and top tension, and the change in curvature radius experienced by the riser. The tested systems were also modelled in dynamic analysis software for comparative purposes, where industry recommended practices were employed to specify drag coefficients. Numerical simulations exhibited an appreciably higher in-line drag compared to model testing results at higher flow velocities. Comparison of curvature radius results demonstrated close agreement at lower flow velocities, with numerical simulations exhibiting increased deformations due to the higher in-line drag estimated at higher flow velocities. This discrepancy might be partially attributed to an overestimation of drag coefficients defined within industry recommended practices. The findings from this study have shown the significance of utilising scale model testing to quantify the hydrodynamic responses of a flexible riser, and facilitate a basis for further work which might provide additional insight into the discrepancies between analytical modelling and scale model tests.