Nonlinear static analysis of flexible offshore pipelines during laying process

SSafety issues during design and installation of flexible offshore pipelines should be addressed. However, existing models neglecting axial-bending coupling or treating bending stiffness locally may over predict the stress of pipeline, leading to overdesign and resource waste. To address these issues, a nonlinear finite element model that accounts for the axial-bending coupling effect is proposed, and is utilized to examine the mechanical behaviors of flexible offshore pipelines during laying process. A systematic comparison is conducted between the proposed model and the classical catenary and boundary layer models to demonstrate the necessity of globally incorporating bending stiffness and axial-bending coupling, and its effectiveness and correctness is further validated against OrcaFlex software. Parametric studies examine the effects of seabed strength, vessel tension, water depth, and current velocity and direction. The results indicate that increasing water depth raises free span and damage risk of pipeline. Higher soil strength increases stress in the touchdown zone. Appropriate vessel tension reduces overall stress of pipeline. Ocean current loads impair pipeline safety more severely under upstream conditions than under downstream conditions. Changes in current direction induce simultaneous axial and lateral forces. This investigation provides a valuable guidance and theoretical basis for offshore pipeline design and installation.