Vector form intrinsic finite element analysis of deepwater J-laying pipelines on sloping seabed

Abstract

The dynamic responses of offshore pipelines induced by J-laying effects are remarkable and dominate the pipeline design and installation feasibility in practice. Most previous studies have focused on the analysis of pipeline installation on the horizontal seabed. In this paper, an extended J-lay model based on the vector mechanics principle is developed to investigate dynamic behaviors of laying pipelines on the sloping seabed. Two representative seabed slope types are taken into account involving the positive and negative slopes. The laying pipeline is divided into a sequence of mass particles linked by massless elements, and the deformations of the elements and the rotations of the particles are calculated to obtain the internal forces. The explicit central difference technique is applied to solve the movement governing equations of pipeline particles by program coding. Two illustrative cases of a 12-inch pipeline being laid separately from the horizontal seabed to the positive and negative sloping seabed are simulated under a random sea state. The influences of seabed slope type and angle on pipeline responses are estimated quantitatively. Significant differences of pipeline behaviors between the positive and negative sloping seabed are observed, which offer very intuitive evidences of seabed slope effects concerning deepwater J-laying pipelines.