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Nonlinear 3D Finite Element Formulation for the Analysis of Submarine Pipelines during Laying Operations

Abstract:

A new three-dimensional formulation using the finite element method is presented in this paper to analyze stresses and displacements of submarine pipelines during laying operations. The method is based on the Corotational formulation using Bernoulli nonlinear beam elements of constant cross-section. The problem is modeled in such a way that the actual boundary conditions are all taken into account. The pipe rolls over the barge ramp, passes through a tensioner and slides over the stinger before reaching the sea floor. The stinger is modeled introducing gap elements into the analysis, which makes possible to model exactly the actual boundary conditions, since these elements allow the pipeline to separate from the stinger naturally as required. This fact improves noticeably the calculation of the internal forces in the supported length of the pipe as well as in the region close to the lift off point. Additionally, using gap elements allows the pipe to reach the sea floor in all that points that naturally require this condition; therefore it is possible to drive the pipeline to reach the sea floor without imposing any displacement during the convergence process, which can generate instability problems. In addition to the applied tension at the barge, the buoyancy and the weight of the pipe, lateral forces induced by marine currents are also considered in the analysis. Numerical examples are provided in order to verify the accuracy and computational effectiveness of the developed method in comparison with the finite element formulation developed by the authors in previous works.