A selective coupling scheme for efficient hydrodynamic analysis of large-scale offshore floating photovoltaic arrays

Offshore floating photovoltaic (FPV) systems are typically configured as large-scale arrays of numerous modular floaters, among which pronounced multi-body hydrodynamic interactions arise. Resolving these interactions poses a dilemma: a fully coupled analysis imposes a prohibitive computational burden, whereas completely neglecting the inter-module coupling discards essential near-field information. It is observed, however, that the radiation interaction, the most computationally demanding component of the multi-body coupling, weakens with increasing inter-module spacing and varies systematically with the wave frequency, such that, under certain conditions, the coupling for a portion of the module pairs within an array can be reasonably neglected. Motivated by this observation, the present study develops a selective coupling scheme that retains only the non-negligible interactions. At its core, a non-dimensional threshold K is introduced into the radiation-problem solution to prescribe the maximum tolerable intensity of the radiation interaction between two modules: for any given wave frequency and inter-module spacing, once the quantified interaction intensity falls below K , the interaction is regarded as negligible, and the corresponding off-diagonal terms of the global radiation matrix are set to zero, rendering the originally fully populated matrix sparse without compromising engineering-level accuracy. The scheme is implemented in an in-house program, Multi-Int-Hydro, developed on the basis of three-dimensional potential flow theory and the constant-panel boundary element method; the reliability of the program is first verified against the commercial software HydroD through a side-by-side twin-box benchmark. On this basis, the radiation interaction characteristics of three representative types of FPV platforms, namely the hexagonal semi-submersible, the rectangular semi-submersible, and the multi-floater platform, are systematically investigated, and platform-specific critical curves relating the critical frequency to the inter-module spacing are established. Incorporating these curves into the radiation-problem solution finalizes the selective coupling scheme, which is then verified through multi-module array case studies. Even under the relaxed threshold of K = 10%, the relative errors of the computed response amplitude operators (RAOs) with respect to the fully coupled scheme remain within 5%. In terms of efficiency, approximately 50% of the total analysis time is saved for the two semi-submersible FPV arrays and approximately 20% for the multi-floater FPV array, even under the strict threshold of K = 5%. The proposed methodology provides a feasible and reproducible numerical approach for the rapid hydrodynamic assessment of large-scale offshore FPV arrays at the conceptual-design and configuration-screening stages.