Second-order wave drift loads on floating structures with thin perforated shells

The computation of the second-order mean wave drift loads on a body with thin perforated shells is fundamental and relevant to a wide range of applications in marine engineering, marine aquaculture, offshore renewable energy, etc. In this work, formulations involving a control surface at a distance from the body are proposed to compute drift loads on structures composed of an impermeable hull and a perforated surface accurately and efficiently. Applications of mathematical identities and conservation of fluid momentum are proved to yield identical formulations. Due to the presence of perforated shells, an integral caused by the dissipation through perforated surfaces is included in the formulation. The present formulation cannot only give all six components of the mean wave drift force and moment, but also determine the drift loads on each individual body of a multibody system. The developed formulations are applied to a series of structures, including single-body and multibody systems. It is found that the perforated surface integral plays a secondary role in the computation of drift loads. Besides, perforating body surfaces can mitigate the near-trapped wave motion in a multibody system. Compared to a fixed system, the mean wave drift loads can be amplified around the resonance frequencies of body motions. The dissipation through the perforated shell can enhance the damping effect and suppress the excessive motion response, resulting in a reduction in the amplified drift loads.