ABSTRACT
The pressure distribution of ship hull can be influenced by a interceptor, which is installed at the stern of ship, to induce a moment for reduing the pitch motion of the ship. However, the phase and amplitude of the moment provided by the interceptor is difficult to determine. This paper aims to design an automatically controlled interceptor to reduce the pitch motion of the ship in wave. Control strategy based on energy reduction is proposed, it uses the pitch angular velocity as feedback to control the interceptor, It increases the damping of pitch motion, thereby reducing the pitch motion of the ship. The model tests in regular head waves are carried out in towing tank, Experimental results indicate that it is effective to use the pitch angular velocity as feedback to control. The amplitude of pitch in waves can be reduced by 20%.
The pitch motion of the ship in the wave will reduce the comfort and safety of the ship. Improving the seakeeping characteristics through optimization of hull form parameters meant that one had to compromise on the calm water resistance performance. For the vertical motions reduction of in head waves, control systems such as trim flaps, T-foils and interceptor were adopted. One of the simplest and effective way to control the pitch motion is to use a controllable interceptors. The interceptor at the stern can change the pressure distribution at the bottom of the ship, forming a moment and changing the longitudinal attitude of the ship. If the interceptor is properly controlled, it can reduce the pitch motion of the ship. However, the phase and amplitude of the moment provided by the interceptor is difficult to determine.
The interceptor produced by Humphree is used in high-speed planing craft, It can adjust the attitude of the planing boat. Model experiments conducted by Wang(1984) demonstrated the reduction in heave and pitch motions of a planing vessel equipped with active transom flaps. The deflection angle of the flaps was controlled proportional to the pitch velocity of the vessel. This control scheme proved to be very effective in reducing the motions of the model sailing in regular head waves. Steen(2007) summarised the experimental results suggesting various approaches to empirical formulas for the coefficients of added lift and drag due to interceptors. Rijkens (2011) conducted the vertical motion modeling based on the model test data, the deflection of the control devices based on a pitch velocity feedback. Karimi (2015) designed a vertical motion controller of planning boats using an optimal control technique. It proved that a feedback of pitch angle and pitch velocity to the interceptors are effective for vertical motion damping of planing boat in calm water and head waves. Choi (2018) designed a differential control algorithm to control attitude of the ship by controllable stern interceptor in calm water. As mentioned above, Most studies mainly explore the control law of the interceptor through experiments, the summarized control strategy is effective but not optimal. This study analyzes the principle of the interceptor, and proposes a control law based on energy reduction to control the interceptor.
