Numerical Modeling of the Configuration of a Long-distance Free-spanning Submarine Pipeline on an Uneven Seabed
- Leige Xu (North China University of Water Resources and Electric Power) | Mian Lin (Chinese Academy of Sciences)
- Document ID
- International Society of Offshore and Polar Engineers
- International Journal of Offshore and Polar Engineering
- Publication Date
- March 2017
- Document Type
- Journal Paper
- 102 - 111
- 2017. The International Society of Offshore and Polar Engineers
- VFIFE method, uneven seabed, free-spanning pipeline, pipe-soil interaction
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- 43 since 2007
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In this paper, a procedure is developed to analyze long-distance free-spanning pipelines on an uneven seabed through the incorporation of the Vector Form Intrinsic Finite Element (VFIFE or V-5) method with the bubble model, which is also called the UWAPIPE model. A dynamic contacting scheme is proposed to model variations of the contact situation between a seabed and a deforming pipeline on it. Specifically, a high-efficiency Message Passing Interface (MPI) parallel scheme is adopted to reduce the computing time of the procedure. Through the use of the procedure, the configuration of a 10 km long-distance pipeline lying on a real irregular seabed in the South China Sea is simulated, and the results are compared with a Remotely Operated Underwater Vehicle (ROV) survey and Det Norske Veritas (DNV) recommendations. The effects of the submerged weight and internal pressure of the pipeline are evaluated. Subsequently, the unevenness ratio is defined, and its relation to the pipeline bending moment is presented. The effects of the seabed undulation and adjacent spans are proved to be significant for the examined case.
Submarine pipelines commonly cross uneven seabed, and free spans could form due to the seabed undulations in practical engineering. In the conventional security assessment for free-spanning pipelines, only the span height and length are considered, while the effects of the seabed configuration and the resulting bending stresses are ignored (Rezazadeh et al., 2010). This would produce errors in the analysis of vortex-induced vibration, global buckling, axial walking, and even the integrity of the pipeline. To consider the effect of the uneven seabed, the pipeline configuration of the static equilibrium, including the free span scenarios, penetration in the soil, and corresponding stress distribution under different work conditions (e.g., as-laid, water-filled, and operational) must be obtained first (DNV, 2006; Larsen et al., 2002; Soreide et al., 2005).
The pipe-soil interaction plays a significant role in the evaluation of the global pipeline stability. In many previous studies, a series of nonlinear springs are used to model the soil resistances in the axial, lateral, and vertical directions, respectively (Gao et al., 2011; Larsen et al., 2002; Pereira et al., 2008; Sun et al., 2009; Wang et al., 2015). While the simplicity of the spring model is acknowledged, it is difficult to predict the actual pipeline embedment and the corresponding vertical soil resistance through the use of the idealized springs because they cannot reflect the actual soil deformation, especially the plastic component. Moreover, the spring model commonly relates the lateral and axial resistances to the pipeline submerged weight instead of to the varying vertical soil resistance (Tian and Cassidy, 2008).
|File Size||3 MB||Number of Pages||10|