Static analysis of offshore pipe-lay on flat inelastic seabed

Abstract

Pipeline embedment into a seabed has a great effect on its integrity during its installation and operation. To assess the embedment accurately, inelastic behavior of the seabed should be considered.This paper presents feasible numerical model for the analysis of a pipeline, umbilical or cable configuration in installation on inelastic seabed, capturing irreversible embedment. The model considers the entire pipeline as a single continuous segment, and is valid for S-lay, J-lay and reel-lay techniques. The numerical solution adopts finite difference discretization of the pipeline, and proceeds sequentially following actual pipe-lay process, allowing for an efficient contact detection. At each length increment a new consequent equilibrium configuration is assessed by consistent minimization of a total potential energy, which allows considering non-conservative and path-dependent systems. Representative parametric study is performed to demonstrate the feasibility of the method. The effects of seabed loading and unloading stiffnesses for varying lay tension are considered. The parameter analysis has revealed that accepted static touchdown lay factor should depend on a seabed loading stiffness in a non-monotonic manner.The proposed model provides a less time-consuming alternative to the available special-purpose commercial software that imposes the use of cumbersome Graphical User Interface for model definition and result processing.