Ship pitch-roll stabilization by active fins using a controller based on onboard hydrodynamic prediction

The reduction of roll and pitch motions is important to improve the safety and operability of a ship. A pitch-roll stabilization (PRS) control approach for a ship with two pairs of active fins is proposed. In this approach, the key part is the onboard forecasting of the ship's hydrodynamic forces. According to the proposed approach, a PRS controller was developed by integrating a short-term predictor, a force estimator and a fin angle allocator. The PRS controller outputs the optimal attack angles for the active fins by inputting the collected ship's motion time series. First, the short-term predictor serves to predict the future motions of the ship. Second, the predicted ship motions are used in the force estimator to estimate the external hydrodynamic forces. Finally, the predicted hydrodynamic forces, regarded as the expected stabilizing forces, are further employed to evaluate the optimal effective attack angles for the fins' actuator. The active fins are actuated based on the specified optimal effective attack angles. To evaluate the performance of the proposed PRS control approach, numerical simulations and experimental tests under various sea states were investigated. Both the numerical and experimental results suggest that the proposed control approach provided a satisfactory reduction of the pitch and roll motions simultaneously.