Axial Stiffness |
 
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Axial Stiffness |
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In the case of the Mooring Line format, the material model is linear elastic. The governing input is axial stiffness (EA), with both bending (EI) and torsional stiffness (GJ) assumed to be negligible. While it is possible to specify very low values of the EI and GJ stiffness terms in the Flexible Riser format, this is not advisable. Recommended practice is to use the dedicated Mooring Line format, for reasons now outlined.
Modelling of mooring lines can be quite challenging, especially in severe dynamic environments, where there is a tendency for the mooring lines to go into compression. As the mooring lines typically have virtually zero structural bending stiffness, the standard beam column elements traditionally employed by Flexcom are not ideally suited for modelling this type of structure.
When you use the Mooring Line format, a slightly different solution procedure is applied internally within the program. Flexcom uses a special type of arrangement which effectively does not consider bending or torsional stiffness terms. Specifically, the mooring line is modelled using a combination of standard beam-column elements interspersed with hinge/articulation elements. This specialised combination means that while the mooring line has a realistic axial stiffness, it has effectively little or no associated bending or torsional resistance. This provides a robust method for modelling mooring lines without any significant loss in accuracy. The approach also results in increased computational efficiency over the standard Flexible Riser format elements.