Acoustic Source Characterization of Marine Propulsors

Abstract

Marine propulsors represent one of the most important contributors among anthropogenic sounds radiated into water. Blade based propulsors, e.g., propellers, generate tones at the blade passing frequency and its harmonics, especially in cavitating conditions. In addition to hydrodynamic noise, pressure fluctuations cause vibrations in ship hull leading to mechanical noise. For noise prediction purposes, it is highly beneficial to characterize the noise sources as simplified, complex valued arrays having information on source positions, source strengths and phases. In this paper, procedure to characterize marine propulsors as acoustic sources with inverse method is introduced. First, the numerical model with complete hydro-acoustic sources is investigated. Second, a source model composed of sensible number and distribution of elementary (“equivalent”) compact sources is specified. Then selected responses are used as input in source characterization with inverse method. Finally, the model with equivalent sources is solved and the results are validated by comparison against the results from the complete simulation model. The introduced acoustic source characterization procedure of marine propulsors is applicable also for the responses determined experimentally, e.g., in a cavitation tunnel when the pressure transducer array is determined appropriately.