Numerical Simulation For The On-Bottom Stability Of Offshore Nonmetallic Pipeline And Its Application In Reliability Design

Compared with the steel pipe, nonmetallic pipe has excellent corrosion resistance and flexibility, it can greatly reduce the cost offshore pipeline laying, shorten the pipeline construction period, as well as ensuring the quality of oil and gas products. This makes it to be a new conduits in offshore hydrocarbon developments.Offshore pipelines, considered as lifelines of ocean oil engineering, must be designed to safely operate under harsh environments for economic and environmental reasons. For nonmetallic pipelines laid directly on the seabed, pipeline on-bottom stability is critical for its light-weight. If the self-weight of the pipe is insufficient to ensure the stability requirements, additional weight must be considered for stabilization. An accurate analysis technique has significant influence on the determination of the additional weight.This thesis is concerned with the on-bottom stability analysis of offshore nonmetallic pipeline under the action of hydrodynamic loading. The integrated modeling consist of three parts, which is, hydrodynamic loading modelling, pipe-soil interaction simulation and the coupling effects. The detailed work included are showed as follows:(1) Using the FORTRAN language to develop a program that can simulate the action of JONS WAP spectrum, estimate the water particle kinematics at the pipeline nodes. Formatted into the UWAVE subroutine and connected with the main program ABAQUS, the hydrodynamic loads can be applied through ABAQUS/AQUA module.(2) Based on the empirical formula and plasticity theory of pipe-soil interaction, FRIC subroutine with the definition of frictional behavior between pipe-soil surfaces and UEL subroutine with the definition of load-displacement constitutive relationship between vertical and lateral direction are coded in FORTRAN, respectively.(3) A dynamic non-linear finite element model (FEM) is introduced with taking into account the fluids-pipe-soil interaction. The action of pipe is considered.(4) Taking due account for all the parameters and the uncertainties related to the integrated model, a response surface based reliability design method is developed to determine the optimal weight required under the target level.