"CONTROL OF SHIP FIN STABILIZERS BY A PID CONTROLLER: A NUMERICAL ANALYSIS "

The reduction of ship roll motion is important in order to prevent damage to cargo, to allow the crew to work efficiently and to provide comfort for the passengers. There are passive devices like bilge keels or anti – roll tanks and active devices like gyrostabilizer and stabilizing fins which are commonly used to generate an opposed moment to the wave and wind excitation roll moments in response to the command of a control system. The paper presents numerical results of using a Proportional - Integral – Derivative (PID) controller for damping the roll motion of a fishing boat equipped with a fin stabilizer system and sailing in regular waves. The nonlinear roll equation, which includes B1 type damping and quantic restoring, besides the wave excitation moment and moment generated by fins, was linearized for relative small roll angles. The role of PID controller was to generate the corrective roll moment through the controlled fins in order to stabilize the roll motion. The thresholds for the controller’s gains were determined using the Laplace transform and Routh – Hurwitz criterion. A simple but precise iterative scheme was used for the rapid integration of the system equations of motion in three cases: only proportional (P) component, proportional and derivative (PD) components and full PID controller. The numerical simulations have showed that all the analysed variants achieved roll reduction satisfactorily.