Numeric Analysis And Optimal Control Of Pipeline For Deepwater S-lay Method

As offshore oil and gas exploitation is going forward the deep water,more and more submarine pipelines need to be laid. When the pipelaying by S-lay method in the deepwater,pipelines suffer from the huge environmental load, especially the stinger section, this part of the pipeline deformation curvature is large, which is easy to produce the yield or fracture, so the pipeline safety attracts much attention. Static analysis, multi-parameters optimization of the stinger and dynamic analysis is calculated in this paper based on lumped mass method.The major contents are summarized as follows:(1) Ignoring the damping, friction and torsion, a three-dimension force model for S-lay method in the deepwater is built based on lumped mass method. Axial tension, shear force,fluid drag force, inertial force, the seabed and stinger force is derived in detail.(2) The static calculations are compared with those of Orcaflex to verify the correctness and accuracy of the methods described in this paper. Then the sensitivity analysis mainly involves the influneces of sensitive parameters of the deepwater S-lay method to pipeline configuration, effective tension and bending moment, such as current velocity, water depth,stinger form, stinger curvature radius, stinger length(3) In order to ensure the safety of the pipeline, the discrete stinger rollers position should be adjusted reasonably to decrease the strain and stress of the pipeline, the PSO(Particle Swarm Optimization) algorithm and DE(Differential Evolution) algorithm are used to optimize the stinger parameters. The objective function of optimization is to minimize the maximum bending moment along the pipeline. The constraint condition of optimization is the range of roller height and each stinger angle.(4) The dynamic analysis of pipelay is calculated based on the static calculation results.The advantages and disadvantages of Newmark method and Generalized a method is compared in dynamic analysis. The influneces of heave and surge to pipelay system is studied.The different heave period and amplitude influence on tension of the tensioner is analyzed.