Ship Vibration Control Using a Force-Adjustable Mechanical Actuator

Abstract

A mechanical actuator to generate adjustable force and its control algorithm have been developed to reduce ship structural vibration of a single harmonic component of main engine rotating frequency The actuator generates a unidirectional sinusoidal force using the vectorial sum of centrifugal forces of two coun terrotating unbalanced masses. The adjustable-force generation during its operation has been embodied by the mechanism to adjust the eccentric distance of the mass using a link system. The control algorithm using the vibration magnitude and phase signals of both the actuator and main engine has been adopted to reduce ship structural vibration. The algorithm automatically detects the optimal phase and force magnitude. That should be supplied by using the variation of controlled vibratory response according to the phase difference between the main engine and the actuator. This algorithm can be applied without any prior identification of the dynamic characteristics of ship structures. In the control experiments for the superstructure vibration of two large merchant ships, the developed system showed good performance in reducing the vibration levels to 1/6 ~ 1/2 of the uncontrolled levels.