1.12.3 Slender pipe subject to drag: the “reed in the wind”

Products: ABAQUS/Standard  ABAQUS/Aqua  

Currents flowing past a pipeline result in drag loading, which must be accounted for in designing restraints and moorings for the pipeline. Drag loadings vary approximately as the square of the relative normal velocity (difference between pipe and fluid velocities), and effects can be dramatic, as illustrated in the present example. Numerically drag loading results in an unsymmetric load stiffness contribution, so the resulting finite element equations are also unsymmetric.

The equation of Morison et al. (1950) is used in ABAQUS to account for drag loading. The total drag force is divided into tangential, transverse, inertia, and lift contributions. The first two of these relate the drag force to the square of relative velocity, through the experimentally determined tangential and transverse drag coefficients, respectively. The inertia drag force is an “added mass” contribution based on the relative acceleration. The lift term is relevant when the pipeline lies on the seafloor or near a platform, so that the current velocity varies across the pipe. For details of Morison's drag formulation, see Drag, inertia, and buoyancy loading, Section 6.2.1 of the ABAQUS Theory Manual.

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Figures

Figure 1.12.3–1 Slender pipe subject to drag.

Figure 1.12.3–2 Displaced configuration of pipe subject to drag.