A formulation using the finite element method is presented in this paper to analyze stresses and displacements of underground pipelines with initial imperfections. The formulation includes both thermal expansion of the pipeline and internal pressure. The method is based on large deformation beam theory with the finite element formulation based on Euler-Bernoulli beam elements of constant cross-section. The pipe-soil interaction is modeled as a nonlinear elastic foundation in the problem formulation. The resulting nonlinear finite element model with appropriate boundary conditions is solved using full Newton-Raphson as the iterative procedure. Numerical examples are provided to show the application of the methodology and to demonstrate the effect of the initial imperfections in the stress distribution of a buried pipe. The results show that initial imperfections have a considerable influence on the stress distribution of buried pipelines, leading in some cases to stress levels above the allowable limit established by the design codes. The results also help to identify the critical temperature at which buckling of the buried pipe might occur.
A new finite element formulation to analyze stresses and displacements in submarine pipelines during laying operations is presented in this paper. The method is based on the corotational formulation using Bernoulli nonlinear beam elements to model the large displacements and rotations of the pipeline. The penalty method is used with spring-contact elements to accurately represent the actual boundary conditions on both the stinger and the sea floor. A comparison with a finite element formulation introduced by the authors in a previous paper is presented in order to verify the accuracy and computational effectiveness of the proposed method. A real laying case of an oil transportation submarine pipeline is also presented at the end of the paper to validate the results obtained with the developed formulation.
A new finite element formulation to analyze stresses and displacements in submarine pipelines during laying operations is presented in this paper. The method is based on the corotational formulation using Bernoulli non-linear beam elements to model the large displacements and rotations of the pipeline. The penalty method is used with spring-contact elements to accurately represent the actual boundary conditions. During the lay barge installation, the pipe rolls over the barge ramp and slides over the stinger before reaching the sea floor. The barge stinger is a ramp over floating supports that holds the pipeline in such a way that the pipe adopts an S-curve during the laying process. Since contact elements allow the pipeline to separate from the stinger at those points where the contact is lost, introducing these elements into the analysis makes it possible to accurately model the actual boundary conditions on the stinger. In addition, the use of contact elements allows the pipe to reach the sea floor at all those points, which naturally require this condition without imposing any displacement boundary condition during the convergence process. A real laying case of an oil transportation submarine pipeline is presented at the end of the paper to validate the results obtained with the developed formulation. A comparison with a finite element formulation introduced by the authors in a previous paper is also presented in order to verify the accuracy and computational effectiveness of the proposed method.
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