Magnetic Bearings for Marine Rotor Systems-Effect of Standard Ship Maneuver

In order to ensure safe motion of ships, the International Maritime Organization has laid down Standards for Ship Maneuverability, and has also specified standard maneuvers for testing of vessels. If an active magnetic bearing (AMB) is used to levitate and support a rotor shaft in a ship, the maneuvering motion of the ship will also be transferred to the AMB. This work analyzes the performance of an AMB used for supporting a marine rotor system under the effect of ship maneuvering. Vibration time response of the rotor shaft and the AMB control current for a standard maneuver, namely, the Zig-Zag-20, is particularly focused upon. A finite element model of the rotor shaft AMB system subject to motion of the base is first presented. The performance of the AMB in compensating for the rotor vibrations with and without the maneuvering of the base is studied. The numerical simulations reveal that the vibration amplitudes caused by the maneuvering of the ship is higher than that caused by mass unbalance in the rotor shaft. Certain design modifications in the AMB is suggested, so as to make it suitable for marine rotor application. Results with two different control laws with optimum control gains are presented.