About Pipes
The Pipe Mechanics interface is intended for modeling slender pipes with arbitrary cross sections. It is based on beam theory, and the similarities with the Beam interface are large. The most important features that make the Pipe Mechanics interface different from the Beam interface are:
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In a pipe, the hoop stress caused by the internal pressure gives a significant contribution to the stress state.
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The hoop stress will cause a contraction of the pipe in the axial direction due to Poisson’s ratio effects.
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The mass of the enclosed fluid must be taken into account when computing gravity loads and dynamic properties. This effect is active only in the transverse direction of the pipe, but not in the axial direction.
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When working with thermal expansion, the temperature is assumed to have one value at the inside of the pipe and another value at the outside. There is thus no global bending temperature gradient causing a net moment over the cross section. Rather, there is local thermal stress gradient through the pipe wall.
Most of the theory of the Pipe Mechanics interface is shared with the Beam Interface.
In the documentation for the Beam interface:
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Shape Functions
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Geometric Nonlinearity
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Strain-Displacement/Rotation Relation
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Stress-Strain Relation
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Initial Load and Strain
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Geometric Variables
Only the parts of the theory which is specific to pipes will be covered here. Since the by far most common cross section is a circular pipe, this geometry is on several occasions given a special treatment.