Vertical plane motion control of an S-SWATH vehicle with flapping foil stabilisers sailing in waves

The sailing performance of an S-type small waterplane area twin hull (S-SWATH) vehicle, which has comparable total resistance at low and high speeds, in waves is investigated. A flapping foil stabiliser is proposed to enhance the seakeeping advantages of the vehicle in rough waves. The unsteady hydrodynamic characteristics of the flapping foil stabiliser are investigated, and its working mechanism is modelled based on the data generated using the computational fluid dynamics method with fixed-grid technology. Compared with a conventional fin, the results show the benefits of the flapping foil with relatively higher lift coefficients and lower drag coefficients. The vertical plane motion control model coupled with the mathematical force model of flapping foils is built. A controller combining the model predictive control scheme with input disturbance measurement is designed to compare the performance of the conventional fins and flapping foils in stabilising the heave-pitch motions of the vehicle. For the simulations, the hydrodynamic coefficients of the vehicle and the wave force-moment on S-SWATH are updated based on Salvesen, Tuck and Faltinsen strip theory, which is equivalent to measuring the approaching wave elevation directly. The flapping foil stabilisers show significant improvements in damping the heave-pitch motions of the vehicle in rough seas.