Rod Dynamics With Large Stretch

In the last few decades, the use of synthetic fiber line in mooring systems has become increasingly popular, for instance in composite moors consisting of wire rope, polyester line and chain. Synthetic fiber lines are noted for their large stretch which can under high load be as much as 10 to 20 percent of their unloaded length or more. In developing a consistent model for the motions of a moored offshore platform using composite moors, it is necessary to model the dynamics of the moor recognizing that some elements may exhibit large stretch. The model for the dynamics of a rod without stretch was developed by Garrett (1982). This model has been frequently extended to the case with small stretch by linearizing the stretch term in the compatibility equation, for instance, Paulling & Webster (1986). The research presented here is an extension of Garrett’s theory to include the possibility of large stretch. With the adoption of a simple assumption concerning the character of the stretch, and with the incorporation of visco-elastic behavior of the large-stretch elements given by Kim, Kyoung & Sablok (2010), large stretch can be introduced consistently with few changes in the traditional finite-element scheme. Finally, the effects of large stretch on the physical properties and dynamics of the rod are also discussed.