Multi-floater-mooring coupled time-domain hydro-elastic analysis in regular and irregular waves

In this study, a time-domain hydro-elastic model is developed to solve the floater-connector-mooring coupled system. The frequency-domain model is first devised with the discrete-modulus-based method in which the deformable floating structure is modeled with multiple rigid bodies connected by high-order beam elements. The corresponding multi-body hydrodynamic coefficients and loads are estimated by 3D potential theory with the coupling stiffness matrix based on the theory of the Euler-Bernoulli beam and Saint-Venant torsion. The time-domain hydro-elastic model with mooring dynamics is then subsequently developed with multi-body Cummins equation with high-order rod-FE (Finite Element) mooring elements connected to relevant floaters. The present frequency- and time-domain models are validated through comparisons with published experimental and frequency-domain results for a VLFS (Very Large Floating Structure) without mooring lines. The present method directly solves the hydro-elastic problem with mooring lines without using the conventional modal superposition method, for which wet modes with mooring need to be obtained in a priori through cumbersome iterations. The developed hydro-elasticity model is also very useful when complex inner structure-connection conditions, such as discontinuity by multiple hinged joints, are involved. Such an example is also numerically tested, and reliable results are obtained. Vertical flexible displacements, bending and torsional moments, shear forces, and mooring tensions in regular and irregular wave conditions are systematically analyzed and compared with rigid-body and without-mooring cases.