Dynamic Behaviour of Mooring Lines

In designing offshore mooring systems the dynamic behaviour of mooring chains, wires and multi-component lines is of increasing importance. Various authors have reported on experimental results and numerical techniques related to this subject.
An extensive research program has been carried out to gain further insight in the mechanism of the dynamic behaviour of mooring lines, to quantify the effects of important parameters, with special attention to the maximum tension, and to validate a numerical model. For this purpose, results of a developed computer algorithm based on the Lumped Mass Method were compared with results of harmonic oscillation tests for various lines and water depths at different model scales. The ultimate validation was carried out by comparing tension records from irregular wave model tests with those obtained from numerical analysis using the measured fairlead motion as input.
Results from this study clearly show the importance of dynamic analysis for various mooring configurations. Dynamic tension amplification is strongly influenced by nonlinearities due to catenary effects, elasicity and drag. The lumped mass algorithm presented has been proven to be an effective tool to quantify the dynamic behaviour of multi -component mooring configurations. Dynamic tensions in mooring systems may affect the low frequency motions of the moored structure.