Hydrodynamic interactions of two elastically connected floating bodies using a hybrid field-domain decomposition method

The hydrodynamic interaction and fluid resonance between two elastically connected floating bodies are numerically studied using a hybrid two-way coupled field-domain decomposition method. In the present method, the fluid domain is decomposed into a viscous-flow region and a potential-flow region, and the Navier–Stokes equations and the Laplace equation are solved in the two regions, respectively. The flow field in the potential-flow domain is separated into an incident-wave part and a disturbance part, aiming to enhance computational robustness and efficiency further. The coupling between the two domains is realized by applying the Wheeler stretching method and the relaxation method. The proposed method is implemented in OpenFOAM and validated against model test data. Based on the present solver, simulations are conducted for two connected floating bodies swaying in regular waves with various connecting stiffness values and degree-of-freedom set-ups. From the simulation results, it is found that when the upstream body is fixed and the downstream one is free to sway, resonant frequencies of gap elevation and sway motion align, with softer springs amplifying sway but suppressing gap resonance. Freeing the sway motions of both bodies further complicates the coupling responses, as both resonant and anti-resonant responses are noticed. It is confirmed that the resonant frequency is dominated by the connecting stiffness for soft connecting set-ups, otherwise by the gap resonance, and the anti-resonant frequency is directly related to the gap width.