General formulation for floating body with elastic mooring in irregular waves: A hybrid linear and nonlinear framework and validation

In the present study, an advanced computational platform has been developed for offshore renewable energy converter systems, considering nonlinear wave input, body dynamics, mooring line dynamics, and kinematic and mechanical constraints. In particular, a hybrid linear and nonlinear hydrodynamic model is formulated through coupling with a numerical wave tank generated by OceanWave3D. A novel nodal position finite element model considering geometrical and material nonlinearities is developed to simulate the nonlinear behaviour of the mooring dynamics. Then, an implicit solver with an iteration process solves the dynamics of the rigid body, the dynamics of the mooring lines, and kinematic and mechanical constraints simultaneously. Therefore, the developed platform is capable of studying the wave body interaction with mooring lines in extreme wave conditions. Wave basin model tests of a single float on a nonlinear mooring line are carried out under a series of irregular waves for comparison. The developed model was also validated against commercial software under identical conditions for idealised cases. In steep wave conditions, the hybrid nonlinear/linear hydrodynamics give improved predictions over the linear hydrodynamic method.