Optimisation of a submarine's resonance changer using the method of moving asymptotes

In order to reduce the sound power radiated by a submarine, the transmission of fluctuating forces from the propeller to the hull can be reduced by implementation of a resonance changer in the propulsion system. A resonance changer acts as a hydraulic vibration absorber and can be modelled as a single degree-of-freedom system with virtual mass, stiffness and damping parameters. However, changing the dynamics of the propeller/shafting system can lead to increased sound radiation from the propeller. A numerical finite element / boundary element model of a submarine has been developed in order to find optimum design parameters for the resonance changer, such that the overall sound power radiated from the hull as well as the propeller is reduced. The global optimum virtual stiffness, damping and mass parameters of the resonance changer have been found by applying the method of moving asymptotes. It is shown that the influence of sound radiation from the propeller is only relevant, if higher harmonics of the blade passing frequency are assumed to have a similar amplitude as the fundamental harmonic of the blade passing frequency.