Possibility of air-filled rubber membrane for reducing hull exciting pressure induced by propeller cavitation

• Previous effort of air-injection scheme is made unnecessary by air-filled rubber membrane.
• Analytical acoustic scattering model is established.
• Design strategy for the membrane is also presented.
• Cavitation test in water tunnel demonstrates considerable reduction of hull vibration.

To mitigate hull excitation induced by the propeller cavity, 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 could be reduced significantly, the proposed method was still hindered by the continuous usage of an air compressor and maintenance of the nozzle exposed to sea water.In this study, we take advantage of the acoustic properties of rubber-like materials, which are similar to that of water. Accordingly, 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 air-packing 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 maximum 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 verified the suggested scheme.