Adaptive discretisation and dual-rate time-stepping of mooring cable dynamics

Abstract

Catenary mooring lines experience touchdown and liftoff from the seabed as the applied fairlead tension varies with time. The numerical modelling of touchdown/liftoff effects requires a finer discretisation at the touchdown point to avoid the production of spurious line tension fluctuations. The disparity in element sizes within and outside the local refinement zone gives rise to a stiff dynamical system. As the touchdown point changes with time, the locally refined zone has to shift in tandem to limit the spatial extent of the refined domain. This work introduces an approach for applying adaptive discretisation to a numerical mooring cable model with a non-uniform mesh, and dual-rate time integration for the resultant stiff dynamic system.