Design and application of an active vibration control system for a marine engine mount

The mounting points of engines and aggregates are the primary path for coupling vibrations to the ship fuselage or to the vehicle chassis. Passive vibration reduction methods like elastomer dampers or tuned vibration absorbers are limited in their overall reduction performance or the variability of the operating frequency. Therefore an additional active vibration control system is designed to further decrease the vibrations which are induced to the surrounding at different rotational speeds of the engine. The setup used for the design flow of the exemplary control system of a marine engine mount consists of an experimental rig with a partition of the fuselage of the ship and the full-scale engine loaded by an electric output machine. The four mounts are modified by using piezoelectric stack actuators. Accelerometers at the mount points are installed as sensors for the disturbance signal and an inductive sensor at the crank shaft serves as sensor for the rotational speed measurement. The control system is implemented and tested on a Rapid Control Prototyping system as a Multiple-Input-Multiple-Output (MIMO) Filtered-Reference-Least-Mean-Squares (FxLMS) algorithm which uses the rotational speed signal as reference for the generation of the actuator signal. By the use of an adjustable oscillator the control of several harmonics of the engine speed frequency is possible. The design flow starts with the acquisition of the disturbance and rotation signals and the identification of the sixteen control paths between the sensors and the actuators. The transfer functions of the control paths provide a first insight to the structural dynamics of the system. Based on these data a simulation of the control system is set up. Thus, the performance of the FxLMS algorithm, its suitable parameters and the actuator voltages can be estimated in advance of the experiment. Test runs of the experimental rig with varying engine speed are conducted. After the tests in the laboratory, the active vibration control system is mounted to the vessel and final measurements during operation of the ship are carried out.