Parametric modelling of radiation forces for hybrid wind-wave energy converters

Mathematical models for design, optimisation, and control of hybrid wind-wave energy conversion systems are of fundamental importance to support their cost-effective development. While numerical solvers can be exploited to compute a characterisation of the hydrodynamical behaviour, these provide non-parametric representations, generating both computational and representational difficulties, manifested through convolution operators linked to radiation effects. Motivated by the necessity of computing parametric models for hybrid wind-wave devices, and the inherent complexity in achieving this task successfully, this paper proposes a radiation parameterisation procedure based on the theory of rational interpolation. Considering a benchmark wind-wave energy conversion system, an approximating state-space model is computed using a Loewner-based approach to replace the radiation convolution operator, using only the raw information available from hydrodynamic codes. The resulting parametric model is analysed extensively, both in the frequency and time domains, including a variety of sea state conditions.