Numerical investigation of second-order Stokes waves impacting a surface vehicle using FSI simulation

Small-sized marine structures such as unmanned surface vehicles (USVs) faces prolonged wave loading throughout its long-term deployment cycle, which requires better fatigue resistance for its float structure. In order to characterize different loading cases, a piston-type numerical wave flume with non-reflecting frontier (NRF) is constructed using the Arbitrary Lagrangian Eulerian (ALE) formulation, and fluid–structure interaction (FSI) simulations are performed. Second-order Stokes waves with 3 different wave heights of 2–4 sea states are generated corresponding to the USV’s usual working conditions. Then, these waves are employed as incident waves to perform impact scenarios on the USV float structure. Related Stokes wave theory, ALE formulation for multi-materials and its computational process, coupling algorithm based on penalty method, as well as the interface tracking technique are presented for those interested in this FSI direction. Simulated wave profiles are measured and compared with analytical solutions, contact pressure data at different positions of the structure are collected. General cyclic wave load and green water load scenes are recorded. Wave generation and impact scenes are presented and analyzed. As a result, the proposed numerical scheme is able to generate second-order Stokes waves with high accuracy, enabling the analysis of wave loading phenomena on a small floating structure under various sea states. Meanwhile, the comparison of wave loads at various structural locations suggests that green water loading represents a more severe safety threat to the deck structure and equipment on it, and therefore needs to be taken into account in the safety design of USVs.