A numerical model for geometrically nonlinear analysis of a pipe-lay on a rough seafloor

Abstract

Despite a detailed assessment of a potential route for offshore oil and gas transport pipelines, the pipelines are still often being subjected to a pipe-lay on a rough seafloor, which can substantially increase the internal forces within the pipeline.To ensure pipeline integrity during the installation, it is essential to obtain internal force envelope diagrams, which provide the historical maximum and minimum force bounds at every location along the pipeline throughout the entire pipe-lay proceeding.This paper provides a simple numerical technique for calculating the internal force envelope diagrams. The entire pipeline is modeled as a single continuous segment considering geometrical nonlinearity induced by large deformations. The solution technique is based on consistent minimization of the total potential energy of the system discretized as a Riemann sum and the solution of the subsequent algebraic system of nonlinear finite difference equations with a Newton-Raphson technique.The feasibility of the proposed technique is demonstrated through several scenarios of a pipe-lay across the basic types of seafloor irregularity. The results have revealed that, in general, any seafloor irregularity leads to an increase in maximum internal force values at certain locations.The proposed technique provides a time-saving alternative to commercial special-purpose finite element software.