Possibility of Air-Filled Rubber Membrane for Reducing Hull Exciting Pressure Induced by Propeller Cavitation

To mitigate hull excitation induced by propeller cavitation, our previous work proposed a single-nozzle air injection scheme based on the principle of acoustic destructive interference. Although inefficient energy consumption in a conventional air-carpet system with multiple nozzle array could be significantly reduced by the proposed method, its application was still hindered by the continuous usage of an air compressor and maintenance of the nozzle exposed to seawater. We, in this study, take advantage of the acoustic properties of rubber-like materials, which are similar to those of water. That is, a rubber layer existing at the water-to-air interface appears to be transparent in the propagation of acoustic waves. More specifically, a rubber membrane filled with air could be anticipated to act only the role of airpacking without influencing the desired acoustic phenomenon, i.e., destructive interference. Hence, the purpose of this work is to provide analytical evidence to prove that an air-filled rubber membrane is capable of replacing the previous effort of air-injection. A design strategy for tuning the frequency of destructive interference to an exciting frequency is also presented, which can be accomplished by adjusting the rubber membrane size. Finally, two experimental demonstrations conducted in a water tunnel verifies the validity of suggested scheme.