Although twin pipelines in series have been used to transport hydrocarbons in existing engineering practice, previous studies have mostly focused on the dynamic response of the seabed around a single pipeline. In this study, we adopted the two-way coupling algorithm of fluid-structure-seabed interaction to investigate the wave-induced soil response around twin pipelines with different pipe diameters. The present model integrated the wave model and the seabed response model in a two-way coupling algorithm by introducing a boundary condition of velocity continuity in addition to the continuity of pressures at seabed surface, which overcome the contradiction between physical phenomena and existing theoretical models. Numerical results demonstrated the difference between the present two-way coupling model and existing one-way coupling model.
Offshore pipeline is one of the key components in offshore oil and gas industry for the transportation of oil and gas products. The wave–pipeline–seabed interaction has be recognised as one of the important factors in the evaluation of the seabed stability around pipelines. The existence of submarine pipeline will not only change the flow morphology nearby, but also enhance the instability of the seabed around the pipeline, and further causes the destruction of the pipeline (Sumer, 2014).
Based on the field measurements and laboratory experiments, the wave-induced soil response can be divided into two mechanisms. The first is the transient or oscillatory mechanism. It is generally believed that the transient liquefaction occurs due to the interaction between waves and the unsaturated seabed. The pore water pressure, effective stress and soil particle displacement generated in the seabed soil under the action of waves change periodically (Yamamoto et al., 1978). The second mechanism is residual mechanism with the accumulation of excess pore pressure in a saturated seabed caused by soil shrinkage under cyclic loading (Seed and Rahman, 1978; Sumer and Fredsøe, 2002). In this study, we focus on the oscillatory mechanism.
