Optimisation of a resonance changer to minimise the vibration transmission in marine vessels

Structure-borne noise generated by marine vessels is an area that receives much research attention. Significant noise levels are generated due to onboard machinery such as the diesel engines, gearboxes, generators, and auxiliary machinery. In the case of ships and submarines, a major source of the radiated noise at low frequencies is due to excitation of the hull modes resulting from vibration transmission through the propeller-shafting system. Oscillations occur at the propeller due to small variations in thrust when the propeller blades rotate through the non-uniform wake, resulting in axial excitation of the propeller at the blade pass frequency. This problem can be addressed by the use of a resonance changer (RC) which performs the task of a hydraulic dynamic vibration absorber, thereby reducing the vibration transmission and avoiding excitation of hull axial resonances. This research is concerned with optimisation of both single and dual RC configurations in a submarine. An optimisation scheme involving a genetic and a general nonlinear constrained algorithm is used to minimise two fitness functions associated with the vibration transmission to the hull over a low-frequency range. The dynamic response of the propeller-shafting system is characterised using the transmission matrix approach. This modular description enables greater flexibility for dynamic modelling of the propeller-shafting system, and can be easily manipulated for future design modifications.