Marine propulsor underwater radiated noise emission characterization using sensor arrays

Underwater noise radiation (URN) of ships is a harmful emission and increasingly regulated. Hydrodynamic noise of propulsors is one the most important emission components to be controlled. Low-noise design and associated prediction methods are essential. The equivalent source method (ESM) is a noise radiation prediction tool based on a set of discrete elementary sources, which form an equivalent source model, ES model. The accuracy and reliability of an ESM prediction depends on the complexity of the real source, acoustic environment, as well as
the ES model size, geometry, and quantities to be predicted. In this paper, a model scale propeller in a cavitation tunnel is used as an example. The performance of ES models created is highly dependent on the source-sensor distances, the short distances being better. In addition, exact location of the sources, combined with the acoustic environment plays a role. Concerning sound power, simple models, even consisting of one monopole source, work quite well. Concerning average sound pressures at sensor points, a considerable number of sources and sensors, together with reasonable choice of their locations, is important. However, single point responses predicted using an ES model are subject to considerable uncertainty. The purpose of the model and the target quantities must be carefully considered in advance.