The heave and pitch motions of a catamaran under severe sea states vary drastically, and the amplitudes of the motions are too large, which seriously affects seaworthiness. To address this problem, this paper proposes a form of vertical stabilization control that combines low-high gain feedback control with high order extended state observer (HOESO) feed-forward compensation.

First, the coupled catamaran vertical motion model is approximately decoupled, and the coupling of the heave and pitch motions, wave disturbances, etc. are regarded as lumped disturbances which are extended into three virtual state quantities. HOESO is designed to improve the accuracy of disturbance estimation, and the estimated values are used for feed-forward compensation. Second, a low-high gain feedback controller is proposed to achieve vertical stabilization and reduce the conservatism of the low gain feedback control while ensuring that the attachment inputs of the T-foil and flaps satisfy the constraints. Finally, MATLAB is used to build the vertical stabilization control system of the catamaran for simulation.

The results show that the proposed control strategy can effectively suppress the amplitudes of the heave and pitch motions and improve the stability of the vertical motion. The heave displacement is reduced by about 49.47%, while the pitch angle is reduced by about 53.83%.

The results of this study have certain practical engineering significance and can provide valuable references for the stabilization control of multihull vessels.