The pipeline is normally modeled using PIPE31(H) elements.
The shear flexible (Timoshenko) pipe elements are good for finite axial strains, they consist of PIPE21, PIPE22, PIPE31 and PIPE32. The first-order elements of them are good for cases involving contact, such as the laying of a pipeline in a trench or on the seabed. Also used for transient dynamic versions of similar problems (impact) since they use a lumped mass formulation.
The hybrid elements are good for very rigid structures or long flexible structures (riser problems).
PIPE31H elements are first order shear deformable 3D hybrid beam elements based on Timoshenko beam theory, with an additional formulation to distinguish between effective and true wall axial forces.
The hybrid property (indicated by the “H” in the element name) implies that the elements use a formulation in which the axial and transverse shear forces in the elements are included as primary variables, in addition to the nodal displacements and rotations. The hybrid beam element formulation is advantageous in geometrically nonlinear analysis for beams that undergo very large rotations, but are quite rigid in axial and transverse shear deformation (e.g., for long and flexible offshore pipelines and cables). Although hybrid beam elements are computationally more expensive, they generally converge much faster when the beam's rotations are large, thereby being more efficient overall in such cases.
The PIPE-element library in Abaqus is assigned a beam section of type “pipe” by default, implying that the cross-section is modeled as a single-layer hollow cylinder. Thick pipe theory can also be turned on to include section points through the wall thickness.
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