An integrated frequency-domain modelling framework for coupled response analysis of pontoon-truss offshore floating photovoltaic systems

Abstract

Pontoon-truss offshore floating photovoltaic (PT-OFPV) systems with higher freeboard have been widely adopted in conceptual designs and prototype tests, effectively reducing the direct wave impact on electrical components. To provide an efficient evaluation of dynamic responses and structural integrity during preliminary design stages, this paper proposes a frequency-domain modelling framework for PT-OFPVs by combining finite element (FE) and discrete module beam (DMB) methods. The structure is divided into two parts and modelled separately according to their exposure to external loads. The superstructures above water are modelled using FE, while the substructures below water are modelled using DMB. Hydrodynamic loads are obtained through multi-body potential theory and applied to lumped mass points in the DMB model. Wind loads are incorporated via a frequency-domain drag formulation and applied to the deck nodes in the FE model. The complete numerical model is then established by coupling these two parts through shared interconnecting points, in combination with a linear mooring system. Then, several cases are simulated to validate the reliability of the potential-theory solution and the proposed coupled modelling framework. Subsequently, the dynamic responses of a PT-OFPV concept under regular and irregular environments are analyzed, including the effects of structural and mooring properties. A structural optimization strategy under the FE-assisted framework is also developed and demonstrated on the PT-OFPV platform. Results show that the proposed modelling framework accurately predicts motion responses compared with model tests. Moreover, stress analysis indicates that vertical trusses and pontoon connections experience the highest loads. The structural optimization reduces the total platform mass by approximately 29.4% and the maximum stress by about 31.8%, demonstrating the feasibility of the proposed optimization strategy.