Numerical modelling on dynamic behaviour of deepwater S-lay pipeline

•A model for S-lay systems is developed to investigate the dynamic lay effects.•Surface waves, ocean currents, and pipelay vessel motions are included.•Non-linear hysteretic soil model to identify pipe-seabed interaction mechanism.•Dynamic behaviour of offshore pipeline is estimated in detail.•Significant differences between static and dynamic results are observed.

The dynamic behaviour of offshore pipeline in the process of deepwater S-lay operations, which is of prime importance in the installation design of the pipeline, has drawn extensive research attention. In this paper, a comprehensive finite element model for S-lay systems within the framework of the commercial computer code OrcaFlex is developed to investigate the dynamic lay effects, including surface waves, ocean currents, pipelay vessel motions, and the clashing contact between the pipeline and stinger rollers. Meanwhile, a non-linear hysteretic soil model is applied to identify the vertical pipe-seabed interaction mechanism. The numerical model is then used to conduct a practical engineering analysis of a 6-inch offshore pipeline being laid to a water depth of 1500 m in LW3-1 gas field in the South China Sea using the HYSY 201 pipelay vessel. The dynamic behaviour of offshore pipeline on aspects of deflection, axial tension, bend moment, stress and strain is estimated in detail. Significant differences between static and dynamic results are observed, which offer very intuitive evidences of dynamic effects concerning deepwater S-lay pipeline.