Numerical study for elastic floating structures coupled with nonlinear mooring system in irregular waves, including a multi-unit floating offshore wind turbine platform

To understand interactions of an elastic floating structure with nonlinear mooring dynamics and multiple wind turbines dynamics especially in irregular waves, the elastic mode expansion of Cummins’ equation for an elastic structure in irregular waves is strongly coupled with nonlinear rod element method for the nonlinear mooring lines through Jacobian matrix formed in a time-domain predictor and corrector solver up to the second order. The multiple wind turbines dynamics is resolved by load mapping of stress resultants at wind turbines into the hosting structure. Three numerical studies are presented to investigate linear elastic mode resonance interacting with both of nonlinear mooring excitation and higher elastic modes with the second order irregular waves, nonlinear elastic mode resonance with higher order harmonic excitation from various mooring lines, and three-dimensional elastic deformation interacting with multiple wind turbines dynamics in combination with nonlinear mooring excitation in irregular wave loads. The numerical study further identifies three-dimensional deformation can have substantial interactions with multiple wind turbine dynamics, influenced by outstanding rigid modes, while analogous symmetry in modes imposes strong coupling between elastic and rigid modes as well. Moreover, the relative configuration between mode shapes, mooring, and wind turbines can determine the coupled hydroelastic responses.