Numerical solutions for nonlinear large deformation behaviour of deepwater steel lazy-wave riser

Abstract

To meet the increasing challenges of simple steel catenary riser on large hang-off tension and fatigue damage of the touchdown point (TDP) in deepwater or ultra deepwater applications, the steel lazy-wave risers (SLWR) have gained a viable solution. This paper is focused on the static equilibrium of SLWR which is of great importance to the basic configuration design of the riser. A more accurate model based on nonlinear large deformation beam theory is proposed to simulate the suspended part of SLWR, having evident advantage over previously applied small deformation beam or catenary theory which ignores the riser's bending stiffness and is hard to simulate the rapid change of the inclination angle. The model also deals with the pipe–soil interaction for simulating the TDP. The finite difference method is applied to obtain the numerical solutions. The results are comparatively in agreement with OrcaFlex. As an application, parametric analysis of the SLWR is carried out to investigate the influences of arc length of buoyancy section, arc length of upper section and soil stiffness on the static performance. The proposed model can be a basic reference for the dynamic analysis of the deepwater SLWR.