Due to the increasing interest in modelling floating offshore wind turbines, simulation tools need to be adapted from fixed-base applications to surge applications. In this study, an open-source inviscid 3D panel method named Vortexje was adapted for surge motion and its ability to capture the physics of severe surge motion (when the rotor velocity approaches or exceeds the incoming wind velocity) was investigated. A simple test case first found instabilities with direct surface translation, likely a result of attached wake panel placement, justifying the use of equivalent dynamic inflow conditions for subsequent simulations.

It was then found that despite validation for a fixed-base rotor, inaccuracies and numerical instabilities remain when integrating the panel method pressure values directly. Estimating the thrust through the bound circulation provided a more accurate solution, comparable to existing viscous CFD results. It was found that the rotor could, in severe surge cases, briefly operate in propeller mode. Inflow angles were also estimated using existing CFD-related techniques, which provided reasonable results for fixed-base applications but inconsistencies with moderate and severe surge. It was found that the variations in induction factor did not approach those required to induce vortex ring state.