Dynamic analysis of deepwater steel lazy wave riser with internal flow and seabed interaction using a nonlinear finite element method

Abstract

Steel lazy wave risers (SLWRs) are regarded as an alternative option of advanced steel catenary risers (SCRs), and their nonlinear dynamic performance is a great challenge as subjected to vessel offsets and wave-current loads. Especially, the mechanical features would be more complicated due to the introduction of the buoyancy module system. This paper presents a numerical model based on three-dimensional (3D) large deformation rod theory. The whole space model is divided into four parts: touchdown segment, decline segment, buoyancy segment and hang-off segment to accurately simulate the favorable motion performance of the SLWR. The governing equations are established in terms of a global coordinate system, which involves the effects of vessel motion, wave-current loads, riser-seabed interaction and internal flow. The finite element method combined with an Adams-Moulton scheme is applied to discretize the governing equation and update the time integration. The numerical model is verified with the published results and numerical simulations are executed to determine the dynamic behavior of the SLWR. The comprehensive parametric analysis is then conducted to investigate the influences of motion amplitude, motion period, length of buoyancy segment, wave-current load, internal flow, seabed friction on the SLWR's dynamic behavior.