Lateral Buckling Analysis And Optimization Design Of Pipeline With Distributed Buoyancy Sections

The subsea pipeline is an indispensable component of energy resources exploitation and transportation in deep water, which is generally laid on the seabed directly due to the cost and technique difficulty. The global buckling on the seabed plane is the primary failure mode caused by the axial expansion under high temperature and high pressure (HT/HP), and the uncontrolled lateral buckling would threaten the operation safety of the pipeline seriously. As one of the primary lateral buckling control technique, the distributed buoyancy sections has been used in the practical engineering. However, the lack of relevant analytical research restricts the understanding of the behaviour of the distributed buoyancy sections clearly. In addition, the lateral buckling control for the large scale subsea pipeline with distributed buoyancy sections system needs to satisfy different performance requirements, and the adjacent distributed buoyancy sections have interaction effects. The conventional design method could give the feasible design under the performance requirements, but not the optimal design in most cases.Therefore, the research on the analytical solution for lateral buckling of pipeline with distributed buoyancy sections, effective approximate analytical model, the arrangement criteria of lateral buckle trigger and performance requirement-oriented optimization design for lateral buckling control of large scale subsea pipeline with distributed buoyancy sections system, is performed in this dissertation.The main works are given as follows:(1) Analytical solution for lateral buckling of pipeline with distributed buoyancy sections is deduced based on the theoritical model. First, applying the dimensionless method to the design parameters of distributed buoyancy sections, the unbounded physical design region is transformed into the bounded mechanical design region. Second, the buckle equation of lateral buckling of pipeline with distributed buoyancy sections is deduced, and the analytical solution of the displacement function is obtained. The Hobbs's analytical solution for lateral buckling of the ideal and long straight heated pipelines is extended to the pipeline with the special imperfection of distributed buoyancy sections. Compared with the previous analytical research, the reasonability of the analytical solution in this paper is verified. Finally, the engineering significance of analytical solution is discussed, and the internal relation between the mode 1 and mode 3 lateral buckling is explored.(2) The response surface method is adopted to simplify and modify the analytical solution of the lateral buckling of pipeline with distributed buoyancy sections, and the approximate solution is obtained, which overcomes solution which has no engineering significance and improves the computational efficiency considerably. Comparison analysis with the finite element analysis (FEA) of true model of the pipeline verifies the proposed approximate model with the acceptable accuracy in practical engineering. The results show that the error of lateral buckling of mode 3 is acceptable in engineering, and FEA can not excite the lateral buckling of mode 1 of pipeline with distributed buoyancy sections. Based on the approximate model, the influence of design parameters of the distributed buoyancy sections on the lateral buckling behaviour is discussed, which is helpful to the initial design.(3) Failure mode of the lateral buckling control of pipeline with the buckle trigger is studied, and the arrangement criteria is proposed. The criteria of axial force interval for the arrangement of the lateral buckling trigger is presented, whose lower bound and upper bound are studied based on the failure modes. The availability and reasonability of the proposed arrangement criteria is verified by the example. The influence of uncertainty is considered, which shows that the axial force interval for arrangement of lateral buckling trigger is reduced obviously due to the uncertainties.(4)The performance requirement-oriented multiobjective optimization design method for lateral buckling control of the long pipeline system with distributed buoyancy sections is proposed. The safety performance index and the control performance index of lateral buckling control are considered in the optimization design, which is verified by the design example. The influence on the performance requirement by design parameters and location of distributed buoyancy sections is analyzed, which is helpful to the practical engineering.