Three-dimensional nonlinear statics of pipelaying using condensation in an incremental finite element algorithm

Abstract

The problem of static, nonlinear three-dimensional deformation of pipelaying used in construction and installation of underwater pipelines is studied within the limits of small strain theory. The mathematical model consists of the pipeline model and geometric constraints imposed by the seabed and the lay vessel in stinger or J-type pipelaying. The pipeline is modeled as a thin-walled, slender, extensible or inextensible tubular beam-column. It is subject to gravity, lateral friction from the seabed, nonlinear three-dimensional deformation dependent hydrodynamic loads, torsion and distributed moments, varying axial tension, and internal and external static fluid forces. The problem is solved numerically by developing a nonlinear incremental finite element algorithm which features condensation and principles of contact mechanics. Condensation is used along with the geometric constraints to formulate a condensed problem which produces reaction forces. Strong nonlinearities present in the model are handled by an incremental finite element approach. The developed computer code is used to study stinger pipelaying for various stinger configurations, investigate the effect of water depth, and compare stinger to J-type pipelaying in deep water.