Coupled three-dimensional dynamics model of multi-component mooring line for motion analysis of floating offshore structure

A coupled dynamics model of multi-component mooring line is proposed to analyze the motion of a floating offshore structure. The model is developed by extending three-dimensional lumped mass method allowing the motion of segment connection points and including an anchor and clump weights. It offers analysis on simultaneous interlocking-segment line motions to solve three-dimensional dynamic responses of a multi-component mooring line. The model integrates hydrodynamic loads, line-seabed interaction, elasticity, current effect, and dragging anchor motions. It is then coupled with a ship-type floating offshore structure and validated by comparing with equivalent model based on a conventional numerical method. Comparison against two-dimensional model is also established. Finally, coupled motion analysis of the floating structure moored by multi-leg with multi-component mooring lines in realistic operations are conducted by considering actual environmental loads. The impact of the presented dynamics model on the evaluation of the response of the floating structure and mooring line tension are investigated. The results conclude that the model can successfully provide the realistic prediction of the motion of the floating structure. Farther, this paper found out that three-dimensional mooring line treatment needs to be considered since lateral mooring line motion has considerable impact on mooring line tension.