Line theory: Treatment of compression

A segment is said to experience compression if the effective tension is negative. OrcaFlex has two modes for handling this, depending on the setting of the compression is limited data item on the line types form.

Compression is limited: No

The segment is treated as a strut which can support unlimited elastic compression. This is the preferred model if the bend stiffness is significant.

Compression is limited: Yes

The segment is treated as an elastic Euler strut; the compression is limited to the segment Euler load value for the segment $\pi^2 EI / l_0^2$, where $EI$ is the bending stiffness of the segment and $l_0$ the unstretched length. This correctly models a chain or very flexible rope, which can support little or no compression. In the case of a chain, the bending stiffness is set to zero, and the segment Euler load limit is also zero.

The segment Euler load provides a check on the ability of the model to represent compressive loads and the deformations which result. Compression causes the line to deform laterally, the deformation being controlled by bending. Given adequate segmentation, OrcaFlex will correctly represent this deformation. If compression exceeds the segment Euler load of an individual segment, this indicates that the wavelength of deformation is shorter than can be represented by the chosen segmentation and the results may be unreliable. The model should be re-run with shorter segments in the affected area. The segment Euler load is shown on effective tension range graphs and infringement warnings are given on the results form and in the statistics tables.

For more details see modelling compression in flexibles.